Earbuds, Equalization and Headphones.

by Michael Hoffman

Editor: This page is updated regularly. Please continue to correspond with Michael Hoffman or send new postings to the HeadWize Webmaster. For questions or comments, please visit the HeadWize Discussion Forums.

Contents

  • The Potential of Earbuds
    • My favorite earbud model
    • Headphone Sites
  • Sony Earbuds
    • Table of Sony Earbuds
    • Sony Low-End Earbuds versus 868
    • Sony Low-End Earbuds (807, 817, 827, 837)
    • Sony 238 Earbuds
    • Sony 868 Earbuds
    • Sony 888 Earbuds
    • Stock Earbuds for Sony R3 MiniDisc Recorder
    • Stock Earbuds for Sony E3 MiniDisc Player
    • Sony MDR-E464 earbuds
    • Sony NC10 Noise Cancelling Headphones
  • Other Brands of Earbuds
    • Etymotics – The Ultimate Earbuds
    • Stax earbud electrostatic in-ear headphones
    • Sennheiser Earbuds
    • Sharp Stock Earbud
    • Headphones for Sharp 311
    • Aiwa
    • Koss
    • Kenwood
    • Radio Shack
  • Headphone Tips and Ideas
    • Breaking-In Earbuds
    • Matching Megabass and Earbud Response
    • Equalizing Headphones, Built-In EQ Compensation
    • Defining Smoothness and Balance in Terms of Frequency Response
    • Cushions Increase Bass
    • Coupling with the Ear Canal
    • Packaging
    • Testing Headphones
    • Headphone Extension Cables
    • Equalized-crossfeed to simulate speakers
  • Non-Earbud Headphones
    • Vertical Headphones
    • JVC HA-D700, 990
    • Grado 60
    • Denon 950
    • Denon AH-D210 Headphones
    • Sennheiser 580
    • AKG 240
    • AKG 270
    • Radio Shack Pro-25
    • Koss KSC/35
    • Koss Porta Pro Jr.
    • Koss Porta Pro
    • Sony MDR-D65
    • Sony StreetSound Headphones
    • Sony R11/33/55/77 portable headphones

The Potential of Earbuds

There is great disagreement about:

  • Whether earbuds could potentially sound good, given their small size.
  • Whether any actual earbuds sound good, or whether the whole idea needs further development.
  • Which earbuds sound good and which sound bad.
  • Which of the expensive ($40-$80) earbuds sound so good that the extra cost is justified.

After testing many headphones and earbuds and applying my extensive experience tweaking equalizers, I think that earbuds actually have the potential to sound even *better* than standard headphones. In any case, all headphones and earbuds need a new approach: a calibrated equalization curve built into the player, to yield flat response. Megabass is a step toward such a compensation curve.

Like the Etymotics, earbuds have the potential to have smoother response than even the best popular standard headphones, such as the Sennheiser 580’s. I’ve dialed in some truly vibrant, open sound using equalization together with $10 earbuds. It is easy and straightforward to equalize earbuds; just do anti-rolloff to a greater or lesser degree, and leave the rest flat; there aren’t mysterious jags hidden along the entire spectrum that need unique shapes of compensation. I’d rather trust my ears than the common assumption that earbuds are inferior. If the conditions are right and the appropriate, ordinary EQ compensations are made, earbuds can be superior, rather than inferior, to good standard headphones. It’s simply a matter of starting with a decent earbud driver, and providing the inverse of the earbud driver’s frequency response.

If someone shows me a measured response curve of an earbud and it’s rough and jagged, I will change my view somewhat, but in any case, I think that eq-compensated earbuds at least *can sound* unusually smooth and natural. Players need more fancy curves to compensate for specific earbud models.

“Though I like the R3 stock earbuds even better than the 888’s, I can’t stop seeking for even better sound, as I believe it can be a lot better. If I press against an earbud I get very powerful bass, so it is possible. I will keep on looking, and if I find something interesting I will let you know. Please let me know your findings on this matter.” (from a private email to me)

Some people haven’t been lucky and haven’t heard the one or two models that are really good. No wonder they think earbuds are a poor packaging and sound poor. I was starting to suspect that *some* Sony stock earbuds (included with the player) sound great, and some sound lousy.

My favorite earbud model

Of the earbuds I’ve tested, I recommend the low-end Sony models such as the 821 (MDR-E821LP): very inexpensive, wide-response, no humps, good coupling, case included. Their only flaw: a little too much high-treble, so that cymbals tend to overshadow the rest of the treble. People have complained about certain earbuds having too much treble; they might be referring to this. If you want less high-treble, choose from the higher-end units (8n8 such as 848). Some people claim that the high-end such as 888 have a lot of “treble”, but I know that my 868 has extra mid-treble with less high-treble, compared to my 817 [821] or 807V, and the other high-end units I demo’d in a store had the same overall treble sound as the 868: that is, less high-treble than the 817 [821]. The high-end have too much sibilant mid-treble at first; several people reported that this “smoothes out” after break-in. After a reasonable time, my 868’s still sound like they have a lot of mid-treble with much less high-treble than the 817s [821’s].

I don’t listen to my 238L’s — not enough mid-treble, not enough high-treble. I tend to alternate between 817 (now redesigned as the MDR-E821LP) and 868.

Headphone manufacturers should stop shooting for the impossible goal of flat headphone response, and think instead in terms of *systems*, combining calibrated eq, good drivers, and cross-channel delay.

Headphone Sites

Headwize.com – Headphones resource site

Headphone.com – lots of info about headphones

Official Sony headphones product pages

  • Earbuds
  • Lightweight
  • Digital Reference
  • Noise cancelling
  • Sport
  • Street style
  • Vertical

Sony site map

Sony phone numbers

(800) 222-7669 – Sony parts and product info

Sony Earbuds

Table of Sony Earbuds

Detailed Table of Sony Earbuds (Word 2.0)

There are many Sony earbud models, but there are only 4 or 5 unique drivers/housings.

_____________________________________________________________

MDR-E811LP:

hoff1.gif

MDR-E821LP: [I have these]

hoff2.gif

MDR-E821V: [I have the predecessor, 817V]

hoff3.gif

_____________________________________________________________

MDR-E848LP:

hoff4.gif

[Where is the MDR-E868LP?] [I have these]

MDR-E888LP:

hoff5.gif

_____________________________________________________________

MDR-E228LP:

hoff6.gif

MDR-E238LP: [I have these]

hoff7.gif

MDR-E268LP:

hoff8.gif

_____________________________________________________________

Sony Low-End Earbuds versus the 8n8 models

These two sound different, but it’s pretty arbitrary which one you pick. Overall, they sound equally good or equally flawed, as far as frequency response; the humps and dips are merely in different places in the spectrum. Neither of them has a major hump or dip, aside from bass rolloff. They both have a fairly good coupling with the ear canal. Given that their flaws are equivalent, just shifted to different places, I’d have to recommend Sony’s low-end earbuds, based on price.

I did a demo of the ~$10 817 [821] (same driver and housing as the other 8n7’s) against the 868 ($40, almost the most expensive). The 868’s have been broken in for several days, 24 hours (in case it makes any difference). I wish I had a simple response curve for these instead of trying to hear the curve. But I’m sure of the following major differences, analyzed in terms of 9 divisions of the frequency response curve (I wish eq’s had 9 bands, not 10 — easier to label, such as “low-midrange”). (See Michael Schuster’s note in the Aiwa section below – he dislikes the low-end Sony’s.)

The low-end models overemphasize high-treble, and have a lot of mid-bass, and a fair amount of low-bass:
low-bass: less
mid-bass: more
mid-treble: less
upper-treble: more

The 8n8 models have more mid-treble, but less high-treble; and has a little less mid-bass with a little more low-bass:
low-bass: more
mid-bass: less
mid-treble: more
upper-treble: less

Neither curve is better; they are equally imperfect — at least they are both smooth; no really jagged response peaks or dips. I really need to draw the two curves on a sheet of paper and scan and upload it.

The dream earbuds I am looking for would be an average of the Sony low-end earbuds and the 868: these wouldn’t have so much high-treble as the 817 [821], and would have more mid-treble (thus sounding less cold than the 817 [821], while still having more upper presence than the 868). The ideal earbud would have the same amount of low-bass and mid-bass — it should have more mid-bass than the 868.

I compared the mid-bass and low-bass using _No Sleep til Hammersmith_, a live album by Motorhead, with prominent bass guitar as well as kick bass drum. With the 868, the bass leads sounded thin, like a guitar, rather than full and meaty — and the bass drum (low-bass) drew too much attention away from the central region of the bass spectrum, which is occupied by the bass guitar. On the other hand, with the 817 [821], the cymbals were overly present, and distracted from the lead guitar. Although wide frequency response is important, you don’t want extreme bass (low-bass) overshadowing the mid-bass. And you don’t want the extreme, high-treble so loud that it weakens the presence of the mid-treble. (I assume that you always have a good amount of upper-bass and lower-treble; these are easier to reproduce.)

Sony Low-End Earbuds (807, 817, 827, 837 in 1997/98) (in 1998/99: 811, 821, which are “reduced leakage”)

The low-end Sony earbuds are light, small, durable, fit well for most ears, are comfortable for most ears, and have a lot of bass (including low-bass) and treble (especially upper-treble), and are inexpensive ($9-$30).

My 807V and 817 [821] have the symmetrical wires; the left earbud does not have a much shorter wire than the right earbud.

A good thing about studying the Sony line is that you can find them most everywhere – particularly the 807, 807V, and 817 [821]. Some hi-fi stores don’t carry the 817’s [now 821’s], but they carry the [old] 837’s [now no low-end ones with gold plug?] with the same drivers but a gold plug, to make a secure connection.

Sony 238 Earbuds

>My MDR30 came with an ad for MDR-ED238L Fontopia Ear Buds. Any opinion on these?

>Paul Buckley

These sacrifice too much treble, in my opinion, to earn a little more mid-bass.

Some owners recommend these, but I think they have too little mid-treble and upper-treble, and too much upper-mids and lower-treble, resulting in a moderate “can-like” sound. They have the most bass, at least the most mid-bass. This model is not recommended by me, though most everyone is happy with the quantity of general bass. The chamber shape and mouth of the 238 seems to introduce resonance problems, similar to closed-back headphones. The bass sounds quite good on mine, *if* they are inserted into my ears. (The mid-bass dominates over the low-bass, unlike with the low-end earbuds, which have a balanced amount of low-bass and mid-bass. I think the low-end Sonys have the best balance of mid-bass versus low-bass.)

238 has the highest ratio of mid-bass to low-bass. Then the low-end buds, then finally the 868 has the least mid-bass, with the most low-bass — meaning that the bass isn’t quite full-bodied in the heart of the bass spectrum. (This all assumes a typical megabass compensation setting.) I own these 3 models and have focused on comparing these ratios — but most people just think in terms of “how much bass is there”. You might not want to be so detail-oriented, but I think you will hear the difference, even if you can’t specify it in terms of frequency response. Bass differences are important, but treble differences are greater than bass differences in Sony earbuds.

The coupling factor: you can rotate the shaped part. They have more mid-bass fullness than my 817’s [821’s]; the 817’s have the powerful low-bass but not so much mid-bass. The 238’s have a hill-shaped response, with the peak centered around the mid-bass. See also: Coupling.

The driver housing and stem is one-piece. Instead of a front grill and a cushion, there is a tapered horn with 7 holes that goes into the beginning of the ear canal. These collect ear wax and you have to clean your ears vigorously every few hours.

The plastic hurts (irritates) my ears badly. Another owner reported them feeling very comfortable later. I am used to cushions on earbuds; these don’t come with any.

Sony 868 Earbuds

At first, these have less low-bass than the low-end Sony earbuds (unless pressed against the ear) – but they might loosen up in 2 weeks. They also (at least initially) have less upper-treble than the low-end earbuds; instead, they have have sibilance-spasms: when the music hits an “s” or “t” sound, there is a sharp peak in the mid-treble, caused by the headphones. This is the well-known “roughness” that is supposed to go away and “smooth out” after the break-in period; supposedly this spasm turns into smooth high-treble. Something similar is supposed to happen with the low-bass too.

A little *big* and heavy, coupling not quite as good as the low-end models, thus bass is practically weaker. I’m continuing to test and live with these, comparing them to my 238 and 817’s. [now “821’s”]

>I’ve been using the 868 for quite a while, and I recently bought the MZ-R30. The earbuds that came with it were surprisingly good and I find myself constantly comparing between the two. When I first bought the 868’s, I hated them. I immediately noticed their lack of deep bass, and I found the design to be very uncomfortable. Since then I’ve really gotten use to them. The R30’s (i don’t know the actual model #, they’re silver on the sides with a remote and a gold plug) are the complete opposite. Very strong bass, but the overall sound quality isn’t as good. I’ve got this one song with a very deep bassline that the 868 just can’t handle (unless at a very low volume,) the left one, especially, starts cracking at every beat, but the R30 has no problem with it. With other tracks, however, the fuller sound of the 868 clearly outshines that of the R30’s. I find myself having to switch back and forth on a regular basis depending on the nature of the song that i’m listening to. Are the 888 the solution to my problem? Are they really worth the extra 40$ that they cost over the 868?

>I bought the 868’s and felt that the sound was good but that they were also very umcomfortable. About a month after I bought them they broke where the wire enters the device and then it happened with the other ear.

I own many sets of earbuds including Sony high-end. But I like the $10 Sony earbuds best of all. And they are comfortable except for *long* sessions. The bigger Sony’s irritate my ears almost immediately.

Let me put it this way: everyone who is looking for earbuds should own a cheap pair of Sony earbuds, for only $10. I haven’t heard their new “reduced sound leakage” design though.

Date: Fri, 20 Feb 1998 16:22:39 -0800
From: Ken Savage
Subject: Sony earbuds

>I have a pair of MDR-E565’s that I’ve owned for about a year and a half now. I don’t think they’re made any more, but prior to them, I had a pair of 868’s. The 868’s (bless their souls) were nice earbuds, but they started to buzz in one ear, so I put them out of their misery. The 565’s were more expensive, between the 868’s and the 888’s, and I’m quite impressed with the sound quality. Like most earbuds, they’re not as powerful in the bass end, but if you push down on them, bass goes up a *lot*. I use them in my MD player (E30) and I’m sure the day THEY die, a few tears (of frustration at finding and breaking in an expensive pair of buds) will be shed.

>Ken

Sony 888 Earbuds

Some owners say that the 888’s sound terrible, and some say they sound great; some claim they sound terrible for two weeks and then they sound great. If my $40 868’s sound much better after break-in period, then I might gamble $80 and buy (and break in) a pair of 888’s; I’ll update this page as my tests progress.

“At first the sound was terrible, no bass, harsh treble. Really dissappointing. I knew earplugs like these aren’t exactly high end, but this was bad! With bass boost on the MZ-E30, it was worse – more bass all right, but also more treble spasms. The more bass boost the more terrible sound, thin and ugly. Well, after a few weeks things started to change! They ‘loosened up’. Now the bass is there, deep and realistic, treble is right, I’m impressed! (it is important to push them into your ears). Extreme ‘s’ and ‘t’-sounds are only there when the material says so.”

From my in-store testing of a pair that might not have been broken in: these $80 earbuds had less midbass, less low-bass, and less upper-treble than the low-end earbuds. People give very conflicting reviews of these.

The shiny pearl-blue metal accent calls too much attention to itself; it looks like earrings.

>I have an MZ-E30, and had an MZ-R3. Upgrading the R3 stock headphones to a pair of Sony’s top of the line E888 headphones yielded excellent sound. However, when the E30 stock earbuds were replaced by 888’s, the sound was much poorer, treble was really rolled off, and the sound was sort of on the soft side. Some people might like it, but it is FAR from being representative of the music.

>The E30 and R3 both had the same factory headphones (E838), and I’ve also tried swapping them…. Same results.

>Either there is some sort of impedance mismatch, or it could be the megabass settings that are different on both. I’ve tried different settings too.

>Try Sony MDR-E888, with biocelluloid membrane. Do -not- try them in the store before you buy, if you are not sure they are allready well used – they sound terrible the first couple of weeks. Now I enjoy these so much that I even use them at home. I prefer them to Koss Porta Pro (which is ‘warmer’, but a bit muddy in bass and midrange, and not so huge and spacious), Sony MDR-D65 (has thin tinny treble and tiny bass because connection to the head (my head anyway) is not good). They even come really close to my AKG 270 (which is not intended for portable use at all (and cost twice as much)). I never believed tiny earbuds could sound so huge, dynamic and weighty. If I should pick on something, the treble is perhaps still a little bit sharp (on the MZ-E30) [sibilance spasms?], but this may just as well be because most studio recordings are a sonic mess anyway.

“Don’t buy Sony’s 888 top model, since they sound lousy. There is hardly any bass, even if you max your bass boost. They costed me $75 and are now in a drawer, with the rest of the earbuds I’ve tried. I currently still use the ones that came with my first Sony portable, the MZ-R3, rather than the 888’s. I find the earbuds included with this model (there’s no number on them, just the word MiniDisk) very good, rich bass and exellent mid and high. No other earbud has topped the R3’s stock earbuds so far. For now, I can only say: don’t buy the expensive Sony 888’s!”

I have spoken with sincere, experienced salespeople who consider the 888’s the world’s best earbuds, and the 888’s have gotten some favorable remarks in the mailing list. Some owners say buy them, some say don’t.

From: “Toby & Kan Lai” Subject: Earbuds for R50 Date: Fri, 13 Mar 1998 19:46:23 -0500

>I want to replace my Sony MZ-R50 stock E838 earbuds. Not that I don’t like them, in fact, I do, but the phones wire is damn to short (designed to use with the remote control). Now I want to find another pair that would sound close, if not the same, to the E838s. What’s your suggestions? I’m considering the E848s because 1) they are in the same 8×8 class, and 2) according to your Sony earbuds table, the sound characteristics “fair bass, fair treble” suits my needs.

>Any suggestions/pointers are greatly appreciated.

>Toby Lai

Stock Earbuds for Sony R3 MiniDisc Recorder

“I currently still use the earbuds that came with my first Sony MiniDisc portable, the MZ-R3, rather than the 888’s. I find the earbuds included with this model (there’s no number on them, just the word MiniDisk) very good, rich bass and exellent mid and high. No other earbud has topped the R3’s stock earbuds so far.”

Stock Earbuds for Sony E3 MiniDisc Player

“Last summer I bought a MZ-E3, with horrible earbuds included with it. I also bought the 888’s. I also bought the 238 (“Groove”) model, which should have enhanced bass sound because of the new cap design. Well, bass sucked [! I question this -mh], as did mid [too much??] and high [too little??][sucked in what way?] sound. After all these comparisons, I’m back to the MZ-R3 MiniDisc player’s stock earbuds, because they sound better than the 238 earbuds, the 888 earbuds, and the E3 MiniDisc player’s stock earbuds.”

Sony MDR-E464 earbuds

Date: Thu, 19 Feb 1998 13:03:38 -0500
From: Kevin Brower

>Are you familiar with Sony’s MDR-E464 earbuds? I purchased them about 8 years ago and they were high end at the time. I continue to use them today instead of the earphones that came with my R3 unit. They still sound great. Do you know what model Sony currently has that compair to the MDR-E464? What earplug do you beleive is the best?

>Kage

Sony NC10 Noise Cancelling Headphones

Date: Thu, 19 Feb 1998 03:16:52 EST
From: Ellissan at aol.com

>Have you ever compared Sony’s MDR-NC10 Noise Cancelling headphones? I use them when I travel with my MZ-R30 and MZ-E30. They are a little more expensive than the others Suggested retail is around $199. But I am convinced that I can’t find anything better in the size category.

>Anyone who travels alot by plane or who is consistently communting by rail will appreciate the amount of outside noise reductions these puppies provide. You don’t even have to have them connected to a source to appreciate the cancellation effect. I get a kick when the flight attendants come around asking people to turn off their portable electronic devices (because I’m still wearing the headphones at this point) and they’ll ask me to put my MD away….then I show them the miniplug which isn’t plugged into anything. Anyway, if you have the means…I highly recommend them.

>Pete Date: Thu, 19 Feb 1998 05:34:15 PST
From: E Davantes

>I am a military resident of Japan. Your page is great and well-needed, considering the mass of awful sounding earphones out there. I’ve wasted lots of cash on crappy earphones and have gone through a countless number of earbuds and headphones. These earphones I’m about to explain are the best I have heard. I even almost purchased the Sony StreetSounds hours before seeing your page, they look too cool to sound so bad. [search this page for “street”]

>I almost died not reading anything about my favorite earbuds on your page. I bought them overseas, the Sony MDR-NC10. They are noise-canceling earbuds that are optionally powered by a single AAA battery. They have one large button on a “remote” that allows you to hear your surroundings as you press the button. The buds are the size of hearing aids but the sound on this model surpass even the best full-sized headphones. The sound can be compared to listening to a boomin’ car system and with few instances of distortion. I cannot begin to explain the bass on these things! Without power, the bass is deep and clear. When powered, they really *kick*. The treble is average-to-good without the AAA battery, but when powered, they have strong mid-treble and have the sweetest high’s. These are the best sounding earbuds I have heard-hands down. [are they earbuds, or headphones?] I use a Aiwa AM-F5 MD recorder that has about the same bass as a MZ-R50. I can send pictures in case you haven’t seen them before.

Other Brands of Earbuds

Etymotics – The Ultimate Earbuds

Etymotics page at Headphone.com

>Date: Sun, 21 Jun 1998 22:12:12 +0800
>From: “Mark Jones”
>To: hoff at cybtrans.com
>Subject: Earbuds and the Etymotics in-ear phones

>I am, what I consider to be a (“serious”) portable audio listener. Your comments on earbuds was fascinating to me. Until a week ago all I used was either the MDR-E827 or the MDR-E888. I picked the 888’s up in Hong Kong a few months ago, and was, and still am disappointed in their bass response. The 827’s I have had for over a year, and until a week ago there was nothing on the market which came close to their bass response.

>Now a week ago I made a significant investment and purchased the Etymotics Ear Canal Phones. I say significant investment, because a laid out $270.00 for these things! These phones fit in your ear canal, and provide 25db isolation. Everytime I pout them on, it takes me a few minutes to crawl back up from the floor! The sound is just amazing! The bass you don’t feel pounding at your chest, you actually hear it! These things are just amazing!

>The problem with them though is that you need a good amp to push them. In addition to this purchase I bought a headphone amp from HeadRoom (“Supreme”), and with my Sony MZ-R50 coupled to the Supreme Headphone Amp and the Etymotics, well I have true portable hi-fi audio! The investment was $850.00 total, but if you are serious about portable audio, then this is a good investment.

>I spend allot of time on the road, international travel, and not having quality audio for months on end is just not exceptable to me. My portable system includes the Sony MZ-R50 MD Recorder / Player, a Sony D-E805 Portable CD (“I love it!”), a pair of Bose Room Mate II Self Powered Speakers (“the bass is awesome”), the HeadRoom Traveler System, and the Etymotic Ear Canal Phones.

>Now, I still use the MDR-E827’s quite often. They are moisture proof, and have excellent bass, and fit my ears nicely. When I am riding my bike through southeast China, I have a problem using my Etymotics and having them fill with sweat! The MDR-827’s are just as amazing to me as the Etymotics. And the sound seems to just get better and better the more I listen to them. And with the 827’s coupled directly to my MZ-R50 MD, their is no need for an amp, you got all the volume you would need.

>The 888’s just don’t have any bass, even after a 2 week break in period they did not improve! I have even tried cushions over cushions, and this did not help. I would not recommend them to anyone, though no one individual hears the same, so you be the judge. I also got some Senn’s and Grado headphones, though don’t listen to them very often, especially since I got the Etymotics. Seriously, there is nothing on the market which can compete with the Etymotics! These things are simply amazing in every sense of the word!

Stax earbud electrostatic in-ear headphones

>Just saw your page linked from the minidisc page. I’ve got some 888’s bought in the hope they’d sound good – they seem OK, but so far I’ve only used them on the CD player output of my SGI 02 CD-ROM drive at work – not the best quality of sound! I must take them home some time. I had a pair of 575’s (?) which used to sound nice, but then they stopped working.

>There are a pair of Stax earbud electrostatic ‘phones. Actually they may be in the ear with headband (?) If you want to know more, let me know, I have some literature at home, and a scanner at work.

>Amardeep Bhattal

Sennheiser Earbuds

Magnolia Hi-Fi said Sennheiser earbuds sounded disappointing; they said Sony’s high-end earbuds sound much better (with cushions, after break-in, as usual).

Sharp Stock Earbud

Someone said the Sharp earbud was really good, that came with a particular model of Sharp player.

Headphones for Sharp 311

Date: Wed, 5 Aug 1998 17:47:53 +0100
From: Mark.Howard at wdr.com

>I had a look at your earphone page – very interesting and good news as I much prefer to stay with earbuds.

>I’m looking to order Sharp’s 311 from Japan but concerned that its headphone amp is only 5mW. I’m worried that the volume will be too low like Sony’s EP11.

>Are you aware of any earphones that I could get that would ensure volume is adequate? Nothing excessive – just up to the level of the Sony R30 for instance.

>Mark

Aiwa

I bought some cheap Aiwa earbuds. They have peaky low-treble or upper-midrange (fatiguing). The wire doesn’t enter each driver housing in a secure way; the resulting rubbing creates a terrible noise — poor design; avoid. However, note another opinion, below. We need to track model numbers. I’ve only heard one Aiwa model.

Date: Sun, 19 Jul 1998 18:01:51 -0400 (EDT)
From: Michael Schuster
Subject: Sony earbuds

>I differ with your opinions about the cheap Sony earbuds. I was surprised to see you recommend $9 Sony phones as your top choice. I went earbud shopping in Chinatown NYC after reading your article, and on the shelf the 817’s looked like the crappy stuff they package in with $49 tape players – things that sound so bad I don’t even bother unwrapping them as a matter of principle.

>Anyway I invested $10 and listened to them using a known pocket radio on the way home. Bleeeraaachhhhh!!!!!!

>These sound harsh, shrill, tinny, and have almost NO bass compared to what I’m used to (see below). Turning on the bass boost improved the situation somewhat, but only marginally. And yes, I was wearing the earpads which I always use – not so much to boost bass but to keep them from falling out of my ears!

>Anyway, I was surprised to see you dismiss my favorites – Aiwa – without a second thought. My favorites have always been the mid-priced Aiwa phones (about $25-$30) represented by the last ones I bought, the HP-56. I’m sure they’ve been replaced by a couple of generations of newer models with similar numbers. Actually my favorites have been the expensive HP-V88 (long discontinued) which sound the closest to my favorite over-ear standard phones, the Sony MDR-V6.

>I find the AIWAs to have smooth high end without sounding shrill, excellent high and mid-bass, and at least some response in the low bass. And I hear no artifacts related to movement of the wire attachment point as you note. Perhaps you might want to give this line a second look.

>Regards
>– Mike

From: DOX

>I have a pair of $15 Aiwa buds that I absolutely love! They don’t have the unsecure wire problem you listed. Their biggest advantage is the smooth rounded exterior design (with the bass-boost pipe design) that allows you to insert them in your ear “backwards” (pipe out above ear lobe rather than vertically down your sideburn). This seals the ear, boosting bass response, and places the driver at the outside facing into the ear flap dramatically smoothing treble response.

>Now the bad news… I blew one driver when I plugged it into an over-driven jack! Big bummer because when I went to the local Best Buy (where I bought the original) they only had the HP-V155 model which I assumed was the same… needless to say it is not. The mechanical design makes it very uncomfortable and I’m sure the driver won’t get any better after a “break-in”. Still looking for a comparable model to my old ones. If they still make that model I would highly recommend it! If all of there models are like the V155 I’d say AIWA truly sucks.

Koss

I’d like to try Koss earbuds. The cheap Koss ones have a secure entry-point for the wire to enter the driver housing of each earpiece, eliminating that loud rubbing noise.

Kenwood

I bought the $10 earbuds by Kenwood. They have the letters “Kenwood” and a little gold strip on the side. They come with a fairly large bag/case. These have a wide frequency response but a major, narrow hump around 250 Hz (upper bass). When I cut this band by 12 dB using a 10-band equalizer, then the boxy sound was eliminated and they sounded normal. Avoid – very boxy sound.

Date: Thu, 19 Feb 1998 02:58:00 -0800
From: Lithium
Subject: Earbuds

>You said that you wanted to try the Kenwood earbuds, well I recently bought the Kenwood DMC-J7R MD portable, and I really love the earbuds that came with it. They sound great, but you are right, you need to boost the bass a bit. I have stopped using my studio monitor headphones and have started using the earbuds. 🙂 Mostly because the headphones are big and hot… The Kenwood earbuds don’t come with cushions, but I went out and got some and it did help the bass.

>You complained that the Sony megabass was too much and they needed a new level 1 setting, well I have listening to the Sony and I think the Kenwood/Sharp (Kenwood just clones the Sharp MDs) bass boost is FAR better. It is clearer and the level 1 is much less than Sony’s, it has levels 1-3 and I usually prefer level 2. I have heard other people say the same thing about the Sony megaboost, that the Sharp’s is much better.

>Matt Staver

Date: Thu, 19 Feb 1998 05:34:15 PST
From: E Davantes

>The stock Kenwood earbuds that come with DMC-G7R (an MS200 clone) sound pretty darn good. Deep/mid bass is amazingly clear and treble is strong. They don’t hit (bass) very hard, but that makes the lows very clear and prevent distortion. However, on a new DMC-J7R (MS701 clone) the stock earbuds sounded awful. Same company, and the earbuds look the same, but the sound was very tinny and distorted easily.

Radio Shack

Their $30 high-end earbuds look interesting. Has anyone heard these? They are next on my list to demo, but I am done with research for now.

Headphone Tips and Ideas

Breaking-In Earbuds

Like a violin, or speakers, earbuds supposedly need to be broken in and loosened up, before they sound good. I’m burning in my $40 868’s by leaving them playing an FM station all day long, at a fairly high power level.

The standard driver has much more high-treble than the high-end models. Some people say the high-end models have more than the regular models, after a couple weeks.

My new 868’s currently have less low-bass than the low-end Sony earbuds (unless pressed against the ear) – but they might loosen up in 2 weeks. They also (at least initially) have less upper-treble than the low-end earbuds; instead, they have have sibilance-spasms: when the music hits an “s” or “t” sound, there is a sharp peak in the mid-treble, caused by the headphones. This is the well-known “roughness” that is supposed to go away and “smooth out” after the break-in period; supposedly this spasm turns into smooth high-treble. Something similar is supposed to happen with the low-bass too.

Due to break-in considerations, you can’t do a meaningful demo of the high-end earbuds in the store. You have to have faith, buy them, play them a lot, then listen to them. This complicates A/B testing efforts.

Matching Megabass and Earbud Response

Megabass parameters differ among players. You have to factor in megabass together with headphones, there’s no way around it for portables. Finding the right combination of settings and headphones is important. The Sony earbud packages say “designed for megabass” — but the opposite might be more historically accurate; the eq parameters for megabass were designed to produce the inverse response curve of earbuds, to complement earbuds. The E40 player has massive boost (*much* more than my Sony CD diskman player’s “megabass”) that fits like a glove with bass-challenged earbuds. The E40 has a good first-position boost, but the second position is far too much. It needs to move position 1 to position 2, and insert a new position 1 setting that’s half the level of the current position 1 curve.

Equalizing Headphones, Built-In EQ Compensation

I did some more critical eq’ing and listening to my $10 817’s on my home hi-fi. These sound amazingly smooth; they just need a lot of low-bass boost and a little upper-treble boost to sound unusually smooth and flat all across the spectrum. So I am familiar with the full voice and potential of these. They certainly do respond musically to the lowest bass and highest treble, without sounding jagged from one frequency to the next, though they do need some electronic boosting. Then when I listen to these without the help of tone controls, I have a better, ideal reference point. Really bad headphones or speakers are impossible to fix with a 10-band eq; their curve is just too jagged and rough from one frequency to the next.

Skillful use of a 10-band eq can fix any decent headphones, or even lousy headphones. For home listening, then, an issue is *how easy* is it to eq a particular headphone? I’ve found all the earbuds very easy to equalize: simply progressively alter the highest and lowest bands. Some full-sized headphones have weird jags (peaks and valleys at unpredictable frequencies) that make it tricky to iron out the curve with an eq. In other words, I find earbuds to be *smooth* and straightforward in their frequency response.

How I use the $10 817 earbuds as hi-fidelity home headphones:

On 10-band eq:
31.5 Hz at +12db
63 Hz at about +6 db
16 KHz at about +5 db
optional: cut 2 mid-bass bands on the eq by 2 db.

On receiver:
Bass set at 3 o’clock
Treble at 1 o’clock

With serious equalization, I can get very, very good sound through my $10 headphones — I suspect that they are actually as smooth as Sennheisers or Etymotics, but just bass-challenged. These earbuds do have smooth bass from one frequency to the next and they do have musical response in the 31.5 Hz band of a 10-band eq, it’s just that the overall level of the bass (20 Hz-120 Hz) needs a lot of amplification — which is what some of the more intense megabass controls are designed to do, with the mathematical smoothness and precision of R-C curves. The result is an exceptionally flat, smooth, and controllable response curve. Thus I now think that equalization is what needs attention these days, rather than particular models of earbuds or ATRAC versions.

The bass and mid and treble should be present and should be at the same levels. Mid is not evil, it’s just that there is usually too much of it relative to bass and treble. Mid’s can be warm and rich.

I haven’t found any headphones that sound flat without eq. All headphones need eq, to sound flat. I’m still in the market for full-sized headphones that are comfortable. Maybe the 580’s, though they do need bass boost.

Defining Smoothness and Balance in Terms of Frequency Response

hoff9.gif
hoff10.gif

(The earbud curves above assume using a standard bass-boost compensation curve.)

Smoothness is fine-level response from one frequency to the next (such as 16,000 Hz vs. 16,100 Hz). Balance is broad-level response of the entire bass region, mid region, and treble region. By “smoothness” I mean breaking the spectrum into many narrow bands and comparing volume levels of adjacent bands. By “balance” I mean breaking the spectrum into 3 or 9 bands, and comparing the volume levels in each of these broad bands, whether adjacent or distant.

The bass drum should be about as prominent as the cymbals, and all the frequencies in between should get their fair share of prominence too. Cymbals shouldn’t steal attention from the bass drum, and vice versa, and the guitar needs to sound warm too. Equal opportunity for all waves, long, short, and in-between.

From: Sergey Belonozhko
Subject: Equalization

>I have read your article about ear-buds and I like it. You have taken a really important question about equalization. You are right that all portable players have to have equalization (preset or manual). And now the best way is to buy portable amplifier from Headphone, but it’s “a little bit” expensive for most of the listeners. I found something very cheap (in comparison to Headphone amplifier), but may be helpful (I didn’t try it yet). It’s Koss portable equalizer (not amplifier!) which allows 3-band stereo equalization. Koss’s crummy headphone equalizer

This is the worst piece of equipment I have ever tried. I tried all combinations of volume pot settings, but the bottom line is, this has no headroom at all — there is no space between its noise level and the point at which it distorts. Do not buy the Koss! — hoff

>If it doesn’t work just try http://www.koss.com and find eq/30 equalizer there in Portable Accessories. Please, write what do you think about. Probably, I’m gonna use it with Koss ksc/35 sportclips or with Sony 817.

>Thanks,
>Sergey

Cushions Increase Bass

Use the cushions; they make the bass much louder. One earbud enthusiast has a collection of earbuds and uses cushions over the cushions, claiming significantly more bass than one layer of cushions — definitely worth an experiment, given that there is an amazing, total difference between no cushions and one layer of cushions.

The 238’s don’t have cushions… Adding (customized) cushions to the 238s *might* make them have even more bass, but I don’t know if they would have enough low-bass to match their mid-bass.

Use cushions (felt/foam) with earbuds. This gives much better bass! Bass also depends on your ear shape.

Earbuds have no bass when I take the cushions off, but relatively awesome bass when the cushions are used. Does anyone have a hypothesis for this? It’s striking – night and day. Now when I say “earbuds can sound excellent” I make sure to say *with the cushions on* as well as “with some bass boost”.

This is a *huge* bass boost effect, so take note and be sure to do a comparison test of with/without cushions! Note that the contoured Sony 238 earbuds have no cushions.

The Sony packages say “if the size is too small to fit right, then use the cushions”. But that’s bad advice. The cushions are mandatory, to get loud bass. The smaller 817’s are the right size, if the cushions are used. The 868’s are perhaps too big, if the cushions are used; they are heavy and big; I imagine they flop away from my ears, especially with the asymetrical cable, that pulls down on the left earbud. The Sony low-end earbuds are so light and small, they can be placed right up against the ear canal, and they stay there. I don’t know about other people’s ears, though; ear shape variation (and psychoacoustic variation) could explain why people give conflicting advice about earbuds. (See also Coupling.)

Coupling with the Ear Canal

Bigger drivers and better stated response do not necessarily mean louder resulting bass. Tight coupling with the ear is the dominant factor, and small size can couple better with some ears. The high-end Sony earbuds are big, which seems like it would be better, but at least initially, these seem to effectively have *less* bass than the low-end earbuds. With earbuds, the coupling with the ear canal is 90% of the bass problem. Making the driver bigger actually can make for poorer coupling with the ear, and thus, *less* bass. We Americans have trouble with the concept “small performs better than big”.

See also Sony 238 Earbuds.

Packaging

Sony low-end earbuds: each channel’s unit is one-piece, no joint or narrow spot to break – indestructible. The low-end models are *solid*, literally, with no joint to break, between the driver and stem; it’s one smooth curve of tough plastic with no narrowing.

Sony high-end earbuds have separate disk-and-stem, which can break — I saw a broken one in the store; can’t happen with low-end models.

For portable MD, good earbuds are the best way to go, I think. Walkmans etc. are a little out of style in the U.S., it seems to me, so I really want my portable system to be small and invisible, low-key. Over-the-head or behind-the-head are too visible. Near-invisible systems such as miniaturized MiniDisc players with earbuds are stylish, insofar as any system of equipment and wires can make you look stylish.

If earbuds don’t fit your ears, try different shapes of earbuds. Or hook-over ears, or vertical. (Unfortunately, “try” usually means “spend $100+ buying several”).

Testing Headphones

Your testing results may differ, depending on the unit, cushion, ear shape, eardrum, tastes, song mastering, and psychoacoustics. Many people are happy with each Sony earbud (low-end, 238, 888). Other people think earbuds are all sonic junk. All do need appropriate low-bass boosting, but megabass when properly designed, could perfectly compensate. E40’s first megabass position is great except for the terrible fact of bridging the bass to mono.

When listening for bass response, don’t be fooled by mid-bass. Listen to the *tone* of the bass, not just the quantity. Listen for the ratio of mid-bass to low-bass. Same for treble. Don’t be fooled by loud mid-treble. A tinny (tin-like) sound often means loud mid-treble with a sharp drop. At both ends of the spectrum, beware of the hump-then-dropoff effect, which gives the illusion of wide frequency response, but stops short.

Headphone Extension Cables

Radio Shack’s 1/8″ headphone extension cable is 20 feet long, and kind of thick. Sony has a nice extension: for $10, you get a 10-foot cable of nice, *thin* cable, and a 1/8″ to 1/4″ adapter — better for earbuds. In fact, I recommend plugging the thick, long Radio Shack cable into your home stereo, then connect the thin short Sony extension, then your earbuds – it’s most ergonomic as far as cable weight distribution. The extension’s jack and the earbud’s plug together are too heavy though; I’d love a lightweight microplug and microjack here, if they are secure and sturdy enough to walk on or yank.

Equalized-crossfeed to simulate speakers

Date: Fri, 20 Feb 1998 12:27:41 +0100
From: Peter Clijsters

>Hello from another MD freak,

>On your pages I read something about an eq’d crossfeed circuit, and information about it could be found at www.headspace.com. I din’t find anything about it, could you please give me the exact URL of this page. BTW great job on the earbud thing. I myself use them to (when I have to that is, like walking in the streets), but most of the time a use the Sony MDR-D77 headphones. Have you tried these, what do you think of them?

>Thank you,
>Peter

Delayed eq’d crossfeed circuit, psychoacoustics of speaker placement

Their cheapest speaker-simulating headphone processor/amp

This delayed, eq’d crossfeed circuit that should be added to walkmans and all stereos’ headphone jacks. It makes the ears think the speakers are placed away from the head, which should then sound a lot better.

I haven’t heard the D77’s.

Non-Earbud Headphones

Vertical Headphones

See also the Sony so-called “vertical headphones” (over-the-head headband, with earbuds turned sideways). Note: no cushions here. What if you put cushions around them – wouldn’t they have more bass, like earbuds? I saw another brand that had cushions on vertical micro-headphones.

JVC HA-D700, 990

I have had the $65-80 700’s for several years. They have the best combination of balance and smoothness of any headphones. They are my favorite headphone for flat-eq listening, such as the headphone jack of a home CD deck. They have the most balanced bass vs. mid vs. treble, and sound smooth from each frequency to the next. I don’t see them on the JVC web site; only the 990’s are there.

The 700’s are snug and comfortable. The 990’s appear to be the 700’s, with packaging that’s supposed to be a little nicer. I don’t know if the drivers are different.

The 990’s, which I have not heard, are $120 (see Jvc.com). They need a slight boost around 13kHz. They are warm and very tube-like without being muddy; they seem to have a medium-width emphasis through the lower mids. The bass is extremely good, strong but not boomy; closed-back but not boxy sounding. I really lucked out when I found these. I still think the Sennheiser 580’s and the new high-end super-open Sony’s are interesting and I would like a pair, but those are open-back and *must* have treble cut and bass boost.

Grado 60

Very clunky packaging. Earpieces spin (takes effort to put the phones onto your head). Far too thick cables. Thick, sharp y-connector at your upper chest or back. Need bass boost and treble cut. Too much treble; in rock, cymbals are so loud, they block the rest of the spectrum. These don’t sit securely on the head. Very weak where wire enters driver; can break in the store.

I think, “I would enjoy this music if you would stop banging that great-sounding cymbal right in my ear, drowning out the rest of the band.” The treble in the Grado’s sounds great, open, and smooth (a hard achievement) – there’s just too much of it. Here I should clear up my statement about Sennheiser 580’s and Grado 60’s having “no bass” — I mean, when you plug into the CD player’s headphone jack, the treble is certainly too loud compared to the bass, though they both are smooth curves. The Grado’s sound more balanced with bass at 3 o’clock and treble at 10 o’clock.

Denon 950

Thin peaky high treble (a sharp single-frequency hiss, not smooth/uniform across frequencies).

Denon AH-D210 Headphones

Date: Fri, 20 Feb 1998 16:49:52 -0500
From: John Hoffman

>I use a pair of earbuds that came with RCA’s old MD player; they’re very good, though bass response is a little on the low side… I’ll have to try some cushions, they didn’t come with any…

>I *STRONGLY* recommend Denon AH-D210 headphones. They have an incredibly deep, clear bass response. The only thing I don’t like about them is they’re a bit larger than I’d like for portable use; otherwise they’re ideal.

>The Denon 950’s are cozy, tons of bass. But the treble is fizzy, thin, 1-dimensional, not smoothe. I had to make a jagged eq curve to smooth out the results. They seem to have a sharp peak around 16kHz – sandy sound. Good packaging, blows away the Grado’s. But I’m going to buy the $120 JVC 990’s – very comparable to the Denon 950’s in packaging. I haven’t heard the 990’s yet though. I will listen to the other Denon’s in the store. — hoff

>I haven’t tried the Denon 950, they’re somewhat out of my price range, but I haven’t noticed any problems with the treble.

Low bass response is to be expected with all earbuds. The part I’m critical of is, how smooth is the treble and mid’s? — hoff

>I’m afraid I’m not a musical gourmet, more of a gourmand; the sounds I listen to tend to wipe out any subtleties in the playback medium, aside from white noise, and increasing the range is the way to improve it.

>John Hoffman.

Sennheiser 580

I like these. Nice packaging, though not so snug and cozy as the Denon 950’s or JVC 990’s. Open-air. Inefficient; too quiet for walkmans. Breakable where wires enter drivers; often broken here in the stores. Sound similar to Grado’s: need bass boost and treble cut for balanced rock sound. Smooth, but not balanced; tilted toward treble like a flat up-ramp across the spectrum.

AKG 240

Steve wrote:

>The choice of many recording engineers are the AKG 240 or 240M’s. I know several very good freelance and staff engineers who alway carry a pair because they are not sure what the montitors will be like in any particular studio. I’ve seen them mainly used for referencing while tracking or checking mixes, but also watched a very good engineer use them as the basic monitors in a project studio that had a poor control room listening evvironment. He mixed the project on them then ‘referenced ‘ through the studio’s speakers, small aurotones, a boombox and a car cassette player.

>Since they are closed ear they can also be used for tracking if the there is no control room and the console is in the same room (or nearby) as the players.

>They are very comfortable to wear and extremely flat. I have a pair for my modest studio, but really enjoy them for other uses like plugging into a preamp or hifi VCR. The list for about $100 but can be had for $89 on sale. They are worth the extra money.

>Steve

AKG 270

“The 888 earbuds come really close to my AKG 270 (which is not intended for portable use at all (and cost twice as much)).”

Radio Shack Pro-25

Very good bass, fairly good treble. Recommended by many people. $40; on sale every other month for only $20. Not the same as Koss Porta Pro Jr; it’s a myth that these are the same. They are indeed made by Koss, says “Koss” on the plug casing. Cover ears mostly. Very nice fit, more secure than Grado’s; comfortable. Porta Pro users say the Pro 25s are less comfortable for extended listening.

These are bass monsters — perhaps too much bass, relative to the treble. I’d like to A/B them against the Porta Pro Jr, which supposedly are slanted toward the treble (too much?).

Koss KSC/35

Clip-over ears, no headband. Cover ears mostly. Same driver as Porta Pro Jr. Recommended by many.

Koss Porta Pro Jr.

Foldable. Recommended by many. Compare RS Pro-25. Headband. Supraaural. Above-ear temple pressure pads relieve ear pressure.

Koss Porta Pro

Recommended by many. Bigger version of P.P.Jr.

“Koss Porta Pro is ‘warmer’ than the 888 earbuds, but a bit muddy in bass and midrange, and not so huge and spacious.”

Sony MDR-D65

“The Sony MDR-D65 has thin tinny treble and tiny bass because the connection to my head is not good.”

Sony StreetSound Headphones

>Recently I tried Sony’s StreetSound (there are two models here, I bought the most expensive one, $30) model that covers the ear completely. This design could actually be excellent, but they were disappointing, yet the concept is very promising. If they would make a high end model of this concept, it could be a winner.

Sony R11/33/55/77 portable headphones

From: Peter Clijsters
Subject: Re: headspace.com

>I own the R77 and I think they are the best “portable” headphones on the market. I use them with my MZ-R30 and they make a very good combination. They come with a microplug connection cable and an ingenious folding headband that lets you fold them together (when folded, they are not much larger than my fist). There is a cheaper version (the R11) for about $50.

>Best regards,
>Peter

c. 1998, 1999, Michael Hoffman.
From Hoff’s Audio Site. Republished with permission.

 

Seven Darn Fine Reasons to Own a Headphone System Too!

by Doug Schneider (SoundStage!)

Note that in the title I said too. Although some people use headphones exclusively, I’m addressing this to those people who, like me, have a full home system. Why? Because a supplementary headphone system can add enjoyment to the music-listening experience and take you places your home system won’t allow.

Now first let me get something straight: My home headphone system is nothing grand. We’re simply talking about a Denon DCP- 70 portable CD player (can’t handle any bump and grinds whatsoever, but it is one of the rare players that sports a digital output) and some Grado SR-60 headphones. That’s it, that’s all, and for now that’s just what I need. But it’s now a valuable part of my life, and here are some of the reasons why.

 

  • First and foremost, we all don’t keep the same hours. I’m not talking about you and me. I’m talking about the person sleeping in the next room at this very moment. And no, this isn’t some sick fantasy about a neighbor-it’s her, the person sharing my rent, food, and life! Although I rise (and am expected to rise) when my unofficial spousal unit does, late-night hours reading and browsing the ‘net, as well as writing stuff such as this usually mean I’m awake much later than she is (or most other people are). My neighbors don’t care if I play my stereo after 10, but SHE certainly does. Without my ‘phones, I’d be screwed. I’d never get to listen to half the discs I have. Well, “up yours,” I say! With ‘phones you’ve got your own hours and can at least reclaim and live out a valuable part of your life.
  • Apartments, or other such small dwellings, usually equal a cramped life. My listening room also serves duty as a living room, TV room, computer room, beer room, hanging-out room, etc. I can certainly see the purpose of a 15-room mansion since single-room multi-tasking just isn’t all that practical. So when someone else calls room dibs and is watching the tube, reading, drinking, sleeping, or whatever, music is usually out for the Douger…until…now yer gettin’ the picture.
  • Movies sound better through your headphones than through crappy TV speakers. You guys with home theaters can ignore this, but for others like me-well, this discovery happened quite by accident when Doug’s Other pulled the usual “call it quits early” again. It looked as though I just wasn’t going to be able to watch Leaving Las Vegas with any appreciable volume. But I plugged the Grados into my VCR’s headphone jack and presto, wayyyy better full-stereo sound than the Sony box can crank out on its own.
  • Long-distance traveling becomes a breeze. Endless hours jiggling in a car or airplane seat and being forced to listen to someone else’s choice of tunes becomes a thing of the past. Just stock up on batteries and get ahold of Headroom so you can get yourself a full-fledged, full-function traveling pack to haul your portable music center around the world with the least frustration possible.
  • Sometimes you just need your own space. Nothing can piss off avid audiophiles more than someone talking to them while they’re trying to enjoy some music. Headphones give you an excuse to ignore such people. They don’t know whether you can hear them or not, and they can’t tell. If you can hear, who cares? Just pretend you don’t and smile whenever they talk. After a bit, they’ll get the subtlety of your hints and you’ll have all the time you need.
  • A headphone system doesn’t cost that much. I did it for less than $250 bucks. It could even be a lot cheaper, or certainly a lot more. I say start cheap but keep expansion in mind. I can’t think of better reasonably priced ‘phones than the Grado SR- 60s. Other people dig some of the low-price Shack models. Your expansion will come through your player-if you need one. Heck, if you have a headphone jack on some of the gear, you’re off to the races (although the portability factor is gone). But remember, in time you may want to add an external headphone amp like those from Headroom. If you don’t know why you would want one, just give one a listen to and you’ll understand. Almost all Headroom models absolutely kill a portable player’s headphone output, or even the jack on your CD player or preamp. And if you’re lucky to have a digital output, you can add an Audio Alchemy DAC-MAN or something similar to improve your player’s sound significantly. Ahhh, separates for headphone listening….
  • And finally, headphones can sound darn good. That’s right, sometimes music is better served through headphones. And you need something on hand just in case music like that comes along.

 

If you do go ahead and do something along the headphone route, don’t forget to drop me a line to tell me how you made out.

c. 1998, Doug Schneider.
From SoundStage!. (Republished with permission.)

Headsets help tune in to productivity.

cagle1
by Karl Leif Bates
The Detroit News (12/15/95)

Office workers should tune in and turn on, according to a University of Illinois researcher.
Employees who are allowed to wear personal stereo headsets show higher productivity, better attitudes and greater satisfaction with the workplace, says Greg Oldham, a professor of organizational behavior.
And they don’t have to fight over which radio station to play on the public address system.
Oldham gave 75 out of 256 workers at a large retail company the personal stereos to wear at work for four weeks and then measured the results.
Headphone-wearers exhibited a 10-percent jump in productivity and were “less nervous, less fatigued, more enthusiastic and more relaxed at work than the people in the control group,” Oldham said.
“They do seem to be more comfortable and relaxed,” said Paul Wilson, a safety specialist for the U.S. Postal Service in Detroit, where headsets are allowed for some workers.
Of course, not everyone can wear stereo headphones at work, Wilson cautions. “They can wear headsets as long as they’re not around moving equipment,” he said. “And we tell them not to turn them up too loud. We don’t want them to go deaf.”
Employees who talk on a phone frequently or work in teams also should ditch the diversion. “Most of our people have headsets on already, but they’re not listening to music,” noted Ameritech spokesman Jonathan James.
Workers in Oldham’s study reported listening to their tunes for an average of 20 hours in a 36-hour workweek and favored oldies and country.

Article c. 1995, from The Detroit News (republished with permission).
Cartoon c. 1998, Daryl Cagle, from Daryl Cagle’s Professional Cartoonists Index. (Republished with permission.)

Binaural In-Depth.

by John Sunier

SO WHAT IS BINAURAL?

The binaural experience places the listener sonically where the sounds on the recording or broadcast originated, and requires no special equipment of any sort other than the binaural source and a pair of stereo headphones. The listener experiences sounds quite accurately localized in a complete 360-degree sphere- a true virtual audio environment. It does this via two tiny omnidirectional mikes placed at the entrance of the ear canals on a replica of a human head (“dummy head”). The two signals are kept entirely separate all the way from this artificial head mike system to the corresponding left and right drivers of the headphones worn by listeners.Though all modern binaural recordings are perfectly compatible for loudspeaker playback, in a normal stereo speaker setup you will lose the “you are there” binaural effect due to leakage of the sound cues intended for one ear into the other ear and vice versa.

Even sophisticated audiophiles are often confused about binaural due to the wrongful use of the term back in the l950’s by many who used Binaural and Stereo as synonyms for one another. Recording pioneer Emory Cook (if you were around then you’ll remember his twin-tracked early stereo LPs) was one of these. Yet in the notes provided with all RCA Victor two-track stereo open-reel tapes starting around 1956 was the following:

Stereophonic recording differs from Binaural (a term sometimes incorrectly applied to stereophonic records) in that the microphone placements are selected for loudspeaker reproduction. Binaural properly applies to a two-channel system designed for headphone reproduction. It thus requires the use of two channels fed by microphones spaced about seven inches apart (normal ear separation).

That definition just about tells the tale. All of us have noticed the tremendous difference between hearing a stereo recording on speakers and hearing it on headphones. Headphones seem to put a giant sonic magnifying glass on all aspects of the recording, including stereo separation. Many recordings sound like half the band or orchestra is in one studio with its signal feeding your left ear, and the other half in another studio with its signal feeding your right ear. The sounds seems to be localized at your two ears and totally inside your skull rather than happening outside your head. Some persons also image a central area of sounds in their skull, so that it feels like three little separated groups of musicians inside your head. The HeadRoom circuit was developed to minimize this effect when listening to standard stereo recordings.

The truth is that over 200 million stereo headphones having been sold in the past decade (way over 600 million if you include all the throw-away headphones bought by those airlines no longer giving passengers primitive plastic tubing). But the source material that nearly everyone is listening to on their headphones was never designed for listening on headphones, but for playing via loudspeakers! With speaker playback, the left channel sounds are meant to reach the right ear and visa versa. Producers of commercial recordings almost always monitor with speakers rather than headphones. Binaural keeps the left and right channels absolutely separated from the original dummy head (or your actual head) all the way to the listener’s headphones without mixing. This applies whether the medium is a recording, live, or a radio broadcast.

PROFESSIONAL MIKE SYSTEMS FOR BINAURAL

Commercial binaural recordings generally use one of two different expensive professional “dummy heads” (“Kunstkopf” in German). In fact, both come from Germany. The Neumann KU-81 or KU-100 head was probably used — often in conjunction with other mikes — on a CD or two in your collection. (Cost: about $6500.) The Aachen Head Acoustics system is more complex, with special equalization to achieve the most natural reproduction on both speakers and headphones. (Their current model is also used for precise acoustic measurement and runs about $29,000.) Some recording engineers feel either of these mikes is capable of making more natural and well-balanced ordinary stereo recordings for speaker playback than the best purist mike techniques. Of course, the full binaural effect is not present in speaker playback except with expensive specialized cross-cancellation electronics; which also force you to sit in a narrow “sweet spot” without the freedom of movement that headphones allow. However, any matrix surround processor using “ambience recovery” rather than “ambience synthesis” will give a better surround sound effect with binaural recordings than with most specially-encoded Dolby Surround CDs. Most Dolby Pro Logic decoders will suffice, though processes such as Circle Surround, Six Axes and EARS are even better. Just stay away from what colleague Dan Kumin calls “boingerizers” – those Hall/Stadium/Jazz Club processors that artificially generate reverberation (echo) to add to the original ambient signal on the recording.

A visible dropping of the jaw is the most frequent indication that someone who has put on headphones is hearing effective binaural for the very first time. Followed by exclamations of surprise, wonder and unbelievability. Binaural, rather than trying to bring the sounds into your listening room, takes you where the sounds originally occurred. You are aware of sounds 360 degrees around you ­ not just right & left but forward & back and up & down! Someone whispering in one ear can make you jump, and a good rainstorm in binaural will have you opening your eyes (if they’re shut – which helps the impression) to make certain you’re not actually getting soaked!

In Binaural, the pinna or outer ears of the dummy head or head of the original recordist set up subtle interference patterns that locate the sounds around the head quite specifically in space. These are known technically as HRTFs – Head Related Transfer Functions – and have become central to current audio research directed toward achieving virtual audio effects with two or more loudspeakers that approach the realism of binaural with headphones. Computer gaming and virtual reality software are fertile fields for this sort of enveloping sound. Sounds coming from directly in front of us bounce off the rear part of the outer ear; sounds from below bounce off the top part of the ear. When a sound is directly in line with the left or right ear there is a straight shot into the ear canal, and this provides different directional information from the other approaches. The ear/brain combination works together closely in binaural hearing. Take for example “the cocktail party effect” – in which we “steer” our binaural hearing around a noisy room and focus it on the one person we want to hear, while minimizing the distraction of other voices.

EARLY BINAURAL

The first experiment with binaural, way back in 1881, compared the effect to the popular stereoscopic views of the period. The inventor said of his binaural patent, “This double listening to sound produces the same effects on the ear that the stereoscope produces on the eye.” He set up a series of carbon telephone mikes in pairs (about 7 inches apart) along the edge of the stage of the Paris Opera. As the singers performed on stage, their voices were carried on twin pairs of telephone lines to a few subscribers homes who had two lines installed. They put the earpiece from one line to their left ear and the earpiece from the other to their right ear. Fortunately, a wide frequency response is not a requirement to convey the binaural effect, because the phone system of the time was surely quite primitive.

MORE RECENT BINAURAL ACTIVITY

There has been sporadic interest and activity in binaural since those early days late in the 19th century. In the middle 1920’s some radio stations in Connecticut and elsewhere broadcast experimentally on two different frequencies — feeding each transmitter separately from a left-ear and right-ear mike in a dummy head in the studio. Listeners were already listening on headsets for the most part, since primitive speakers were just coming into fashion. So this worked out well — they merely put one mono headset, tuned to the left-ear station, to one ear and put the other mono headset tuned to the second station, to their right ear. Some of the West German radio stations have devoted time to special binaural transmissions — often of radio dramas which they call “horspiel.” There has also been interest in Japan. “The Cabinet of Dr. Fritz” series of binaural radio dramas from ZBS Productions was carried for some years on public radio stations here in the U.S. Many of those same stations also carried my own weekly program, AUDIOPHILE AUDITION, on which I presented All Binaural Special broadcasts once per quarter for over 13 years.

In 1970 Stereo Review offered a binaural demonstration LP of music and sound effects which used a homemade dummy head known as the Blue Max. There have been many binaural recordings available in Germany, mainly of classical material and on LP. The disadvantage of employing either analog LP or cassette for binaural material is the noise problem. The surface noise or hiss that we have become accustomed to when listening via loudspeakers can become intolerable with headphones. The greater clarity via headphones makes extraneous noises in the source stand out and detracts from the total sonic experience of binaural. Add to that a peaky high end in some headphones that further points up surface noise and hiss compared to speaker reproduction.

As a result of this, the compact disc and other digital media such as MiniDisc and DAT have proven the perfect medium for binaural. The excellent signal-to-noise lets the listener concentrate on the sounds and begin to forget that he or she is actually listening to a recording – one just starts to take part in the original music or sound-making!

YOU CAN DO IT YOURSELF

Their introduction to binaural makes a great impact on some listeners. Then when they learn how basically simple the recording process can be they are energised to make their very own binaural recordings. Some years ago consumer-level binaural mike systems were offered by Sennheiser, Sony and JVC, but have been long discontinued. Today several suppliers provide a variety of in-ear mike systems at a $70-$300 price range. They are usually paired with a DAT or MiniDisc portable recorder, though a good quality cassette recorder may also be used. [Editor: See the Commercial Links page for binaural resources.]

For such recording efforts, sounds in motion are especially effective in binaural, as well as sounds that are spatially separated. I have some binaural tapes of a symphony orchestral rehearsal, and for demo purposes, it must be admitted that feeling like you are sitting right on stage with the orchestra during the rehearsal, with music stands clanking, chairs squeaking, the conductor walking around to help some of the players with small problems, can sometimes be more exciting than hearing the final performance of the music. Sound effects such as a motorcycle or train passing by, take on a quantum step in “you are there” realism with binaural vs. the old-fashioned stereo demos of trains passing between your loudspeakers. Keep some of these tricks in mind when doing your own recording with binaural mike systems. For example, if you have a quartet of instruments or singers, have them perform in a circle around you instead of in a line in front of you! (I’m a nut on sax quartets and do they ever sound great recorded in this way!) Instead of sitting out in the front row of the audience to tape an early music ensemble, one recordist set up his dummy head with mics in a chair right in the middle of the group onstage – creating an effect as though the listener is one of the musicians performing! – most exciting early music recording I’ve every heard. The surrounding spatiality adds great interest to the music. Another recordist taped his taking an elevator, walking into the concert hall and settling in his seat at the beginning of a concert and then the reverse at the end to make it a more complete binaural experience for listeners. (Unfortunately, the elevator was totally silent, so he edited out that part.)

HEADPHONES FOR BINAURAL

While binaural can be heard with any stereo headphones down to the simplest $5 “ear-buds,” the better the phones, the more amazing the experience. I have found some of the Sony phones around the $100 price point to be good. (The Grado SR-80 at the same price is excellent.) I can’t vouch for current Sony models, but do stay away from the MDR-V6 (once recommended by Consumer Reports) because it destroys much of the binaural effect. Among the best under-$600 phones I have heard for binaural are the Sennheiser HD 600, SONY MDR-CD3000, AKG K-501, Beyer 990 Pro, Etymotic ER-4S, and Grado RS-1. (No special order intended in that list.) The K-500 has many of the qualities of AKG’s flagship K-1000 ($895) which I find the best all-around binaural phone due especially to its ability to help image the sounds outside one’s head. The Jecklin and Ergo headphones from Switzerland, at about the same price point, also offer this advantage. The Etymotic are basically test probes inserted deeply into the ear canals – just the opposite of the off-ear-driver phones. However, their fans rave about them for binaural, and with the tight seal to the eardrum bass reproduction equals the most monster subwoofer you could fit in a room! Extra-cost custom ear molds make the Etymotic more comfortable for extended wear.

The Grado RS-1 Reference phones and the Sennheiser HD 600 are also excellent and of interest to those who find the AKGs too bizarre with their little earspeakers suspended on either side of your head. Both the Grado and Sennheiser provide more deep bass than any other on or off -ear headphones I have heard. The Stax electrostatic earspeakers have been the standard for binaural for years. Their top-of-line Omega has a dedicated tubed amp and goes for over $4000 but is probably the best-sounding headphone ever. Don’t worry about the suitability to binaural of feature differences such as circumaural vs. on-ear, free field vs. diffuse field or electrostatic vs. dynamic. Even extended frequency response is not a prerequisite for successfully transmitting the full binaural effect. Phase accuracy and flat response within the frequency spectrum are the most important parameters. A trend showing the increased interest in headphones and binaural is dedicated high end headphone amps — HeadRoom, Melos, Grado, Music Hall, Musical Fidelity and others have them. AKG will introduce a new model soon. Some of the high end phones practically demand a good dedicated amp, and even a modest amp can upgrade the sonics of a more modest headphone.

c. 1999, John Sunier.
From The Binaural Source. (Republished with permission.)

Depth Perception in Headphones.

(The value of headphones in relation to loudspeakers)

by Ron Soh

head

In a Stax Omega 1 versus Stax Omega 2 headphone discussion that I was involved in several weeks ago, responses from a number of headphone hobbyists revolved around the issue of the value of expensive high-end headphones. I made an appeal for the value of headphones to be judged not just against other headphones, but also against speakers that cost far more. In this essay, I want to share with you what I mean by headphones having a better value than speakers, and also to delve into the subject of how headphones, like loudspeakers, portray soundstage when playing conventional two-channel recordings.

The psychoacoustics of sound localisation need not be brought into this discussion. This essay is NOT about a magic trick of shifting the soundstage from inside the head to a plane between the speakers! Instead, it outlines a simple experiment to illustrate these main two points: (1) headphones sound better than speakers costing more, and (2) headphones do portray a soundstage. If depth clues are portrayed in speakers, then why not in headphones? After all, it is the same signal we are feeding to both of them. In the last section is a tutorial for training one’s ears to identify depth cues in headphones. The tutorial lists specific recordings and passages which have captured these cues clearly and are good training examples.

EXPERIMENT: play some music on your speakers, and make sure you sit (or stand) at the ‘sweet spot’. The ‘sweet spot’ is the position where you are equidistant from the left and right speaker, and not too far and not too near the speakers. Make sure that you have switched off any ‘loudness’ buttons and set all bass/treble control knobs to neutral (if your amplifier has these knobs). Listen to the music via the speakers for a few minutes. Then listen to the same piece of music via your headphones, but sit (or stand) at the same ‘sweet spot’, facing the speakers. Of course, turn off the speakers. Make sure you position yourself at the ‘sweet spot’, face and look at the speakers. Listen to your headphone, and be surprised.

(This experiment assumes that your speakers do not cost more than five times your headphone, as a guideline. For instance, don’t compare a $100 headphone with $2000 speakers! Also this experiment assumes that you are not using cheap $15 headphones. And finally, don’t expect the headstage of your headphone to suddenly shift towards the speakers just because you are looking at the speakers.)

The differences you will notice can be quite entertaining/ educational. Generally, what you will find is that:

  1. the headphone sounds clearer, and it is easier to distinguish between various instruments, as compared to the speaker.
  2. the loudspeaker will likely have a ‘veil’ covering the sound of voices/instruments, and this ‘veil’ is located somewhere around the upper bass/ lower midrange region. This upper bass / lower midrange ‘veil’ is typical of loudspeaker ‘box colorations’, which is the effect of resonances of the speaker cabinet. Your headphone is not perfect either, but it is more likely that your headphone has less ‘box colorations’ than your speakers.
  3. the purpose of facing the speakers while you listen to the headphone is to give you visual clues while you listen to the headphones, so that you can appreciate that headphones DO convey ‘depth clues’. (I will delve into this intricate matter in detail later.)

The purpose of the little experiment above is to demonstrate two key points, which are:

  1. Headphones can be better transducers than speakers
  2. Of course a headphone conveys depth clues

Headphones Can Be Better Transducers Than Speakers

Speakers face more difficulties in painting a sonic picture, because speakers need to move a lot more air compared to headphones. When a speaker has to move more air, its cone (or dome or diaphragm or whatever) has to move back and forth through greater distances, and these greater driver excursions create peculiar problems such as non-linear excursions, cone break-ups, ringing (which is the problem caused when the cone moves forward and then instead of moving back immediately its momentum carries it forward a little bit more), and other problems I might know only if I were a speaker designer.

A headphone has a far easier life. Most headphones do not have woofers, midranges and tweeters — they usually full-range transducers. Therefore a headphone needs no electronic crossover circuits to split up the frequency spectrum into low-frequency, mid-frequency and high-frequency signals that will be subsequently fed to woofers, midranges and tweeters. Crossover circuits present a longer signal path that tend to degrade signal quality. Also, sometimes the crossover is not handled properly and you have problems at the crossover frequency region where the two drivers try to overlap but not successfully.

A headphone also does not have big cabinets that tend to resonate. A speaker, in having to move more air, has to generate a lot of pistonic movement, and that results in huge backlash forces being transferred to the cabinet. A headphone does not need to generate huge pistonic movements, so less backlash energy is transferred to its chasis.

A headphone does not have to contend with room reflections. Of course, headphones have a cavity environment to deal with (a cavity environment is the space enclosed between the headset and your ears). In fact, most of the time, a headphone’s frequency response is not just due to the frequency response of its cone/diaphragm, but also due to this cavity environment. Headphone makers know how to ‘tune’ this cavity envoronment so as to compensate and counter-compensate for the frequency (im)balances of the cone/diaphragm. This cavity environment is far easier to predict, compared to the room environment where a pair of loudspeakers are found. Different rooms create different reflection characteristics, not to mention problems such as standing waves, and cause unpredictable colorations to the sound of speakers.

A headphone’s diaphragm is smaller and far lighter than a speaker’s. This single lone factor gives headphones a better start towards the goal of superior accuracy in the translation of electrical impulses to mechanical movement. Due to the lower inertia, a headphone’s diaphragm starts and stops more quickly than a speaker’s drivers can—therefore a well designed headphone can exhibit more transient attack speed.

A Headphone Can Convey Depth Clues

I hope that little experiment demonstrated for you that headphones give spatial clues, the same way loudspeakers do. In switching to and from your headphone and your speakers, you should be able to hear these depth clues. (If you cannot hear these depth clues, read on – especially the section and tutorial on how to perceive depth clues, then re-conduct the experiment.)

It is such a common misconception that headphones do not have a soundstage. Just because you wear the soundstage on your head does not mean that your headphone has no soundstage. To appreciate the differences between a headphone’s headstage and speakers’ soundstage, we first have to establish how speakers construct their soundstages.

When you position yourself in the ‘sweet spot’ in front of a pair of loudspeakers, a triangle is formed between you and the two speakers. The two speakers form a ‘picture plane’, which is the vertical plane that contains both speakers. This ‘picture plane’ faces you front-on, and depending on whether the speaker’s sonic character is forward or laid-back, images are formed in front of, or within, or behind this ‘picture plane’. Depending on the type of recording, some of the images appear to be positioned further behind this picture plane than other images, and this creates a sense of layering or depth of space. This combination of lateral (left-right) spread and front-to-back depth create what we call a 3-dimensional ‘soundstage’.

People say that although headphones portray lateral left-right spread, headphones do not have a soundstage because headphones do not portray depth — that missing third dimension. Which is the point you can disprove for yourself by conducting that little experiment. Listen to your speakers and notice which images appear to be positioned further back than others. Then listen to your headphones (and while still looking at your speakers). Do you hear the depth clues?

You may hear four ‘layers’ of depth:

  • 1st layer: very near (apparently only inches from the recording microphone)
  • 2nd layer: near (apparently 1 or 2 meters away from the recording microphone)
  • 3rd layer: not near, not far (apparently 5 to 10 meters away from the mike)
  • 4th layer: far (apparently 30 meters or more away from the mike).

Do not be too fixated on the actual numerical value of these distances – do not focus on an image and rack your brains out trying to figure out whether it is 2 meters or 5 meters from you. You are enjoying music, not taking a stressful high-school examination. Moreover, you are not a bat. It is difficult to actually assign a numerical value to the distance of an instrument from the microphone just by hearing it. The numerical figures I mention above are simply to help you picture what I am trying to say—don’t take the numerical digits too seriously.

Close-miked, heavily-mixed recordings tend to have almost all their images in the 1st layer, with the odd image sometimes suddenly appearing in the 4th layer — for example, the sound of a synthesizer that has been given an excessive reverberation treatment. Classical symphonic recordings portray images mainly in the 2nd, 3rd and 4th layers (the occasional solo instrument in the 2nd layer, massed strings in the 3rd, the occasional timpani/cymbals in the 4th, for example). However, please note that even if all the images appear to be in the 3rd layer only, that‘s depth perception already. Most recordings with a lot of depth clues contain images that reside mainly within a single layer, with occasional images making their guest-star appearances in a different layer.

(The reason why I don’t listen to pop CDs exclusively is because most pop recordings contain images that are exclusively positioned in the 1st layer. After listening to one pop CD I like to change to a different recording type which portray images in the 2nd or 3rd layer. It gets rather tiring to keep listening to CD after CD of exclusively 1st layer images.)

Now we come to the most important point I am making in this essay. How does a headphone give you depth clues? Imagine that a school band is performing a musical number and marching along a road steadily AWAY from you. If you were to close your eyes you could hear them receding slowly away from you. How is that so? When playing conventional stereo recordings, you perceive depth clues in three ways: (1) loudness, (2) texture clarity and (3) reverberation. Take these 3 clues one by one:

  1. LOUDNESS: When an instrument is near to you it tends to sound louder. Conversely, the softer an instrument sounds, the further away you infer it to be.
  2. TEXTURE CLARITY: But what happens when an instrument is very near to you, but is played softly? Would you perceive it as being very far away? No, you would not, because the second way you perceive distance is through texture. When your ears hear that the texture of an instrument is very well defined, you infer that it is near to you. The further an instrument is from you, the less specific its texture appears to be. When a guiter string is plucked near you, you can hear its steely nature, its lower and upper harmonics, even though the guitar is plucked softly. But when the guitar string is plucked far from you, you may no longer appreciate its steely nature nor its lower and upper harmonics—you may only hear the principal harmonic. When the texture of an instrument sounds less rich you infer it to be farther away from you. When a drum-sound image has a specific texture of a stretched dry skin being hit, along with a loud sound of a steely rattle, you perceive it to be near; however when its texture is more ‘washed-out’, i.e. less specific, you perceive it to be far away. When a saxophone-sound image has a raspy texture you infer that it is near; when it doesn’t have this strong raspy texture you infer that it is far away.
  3. REVERBERATION: Reverberation is sum total effect of sound reflecting off the wall, floor and ceiling surfaces of the recorded environment. The further an instrument is positioned from the microphone, the more reverberation is captured by the microphone. Consequently, the more an image is surrounded by a reverberative halo, the further away you perceive this image to be. Reverberation causes an image to sound more laid-back, enveloped in a softer, cushier halo. It is always pleasant to listen to recordings with reverberation when listening to headphones, because such images are robbed of any jarring directness, seemingly buffered from you by air cushion. (This is not to say that close-up images are always irritating—not at all. Close-up images in the 1st layer can be very enjoyable via headphones when they have a sense of ‘liquid-ness’ about them. The three states of matter—air, liquid and solid—are very apt metaphors to describe and appreciate the quality of sound.)

The above three ways of perceiving depth clues are the reasons why I say headphones portray soundstages. The reason for me asking you to look at your speakers whilst listening to your headphone is simply to give your some visual references to latch on to while you mentally assign the images to their respective layers (1st, 2nd, 3rd or 4th layer) through the perception of the above three depth clues (loudness, texture clarity and reverberation).

And the reason why I asked you to listen to your speakers FIRST before listening to your headphones is also to convince you that the way a speaker gives depth clues is exactly similar to the way a headphone gives depth clues. By listening to your speakers first you hear the three depth clues (loudness, texture and reverberation), and then when you switch to your headphones next you would be able hear that these very same depth clues are also present via your headphones. Speakers are not televisions, and if it seems that a speaker positions its images in 3-dimensional space it is only because your ears hear these depth clues, not because your eyes are seeing actual objects. If you can hear depth clues via speakers, then why can’t you hear depth clues via headphones? The purpose of looking at your speakers while listening to your headphones is to ‘compare apples to apples’, i.e., to create a level playing field, where the visual asistance normally given by speakers in image positioning is also extended to your headphones.

Having said that headphones have soundstages, it is quite appropriate for me to qualify here that the soundstage thrown by speakers is ‘easier to visualise’ than that portrayed by headphones. When listening to speakers there is something quite literal about the way an image that is perceived BY THE EARS to have more depth actually seems TO THE EYE to be positioned further behind the ‘picture plane’. This visual assistance in image positioning is why people say speakers create a soundstage whilst headphones don’t. But the truth is headphones do give ample depth clues, if not more so. (Note: listening to speakers with the lights off and in a completely dark room still lends this visual assistance to image positioning, because you have a visual memory of where the speakers are placed.)

I hope that if you initially did not perceive your headphone’s ‘depth clues’ when you first conducted the experiment, you will now re-conduct the experiment. You may need to try it out over a few CDs, before your ability to discern these ‘depth clues’ catches on 1.

The psychoacoustics of sound localisation are EXTRINSIC factors that are not the focus of my essay. These extrinsic factors of sound localisation are caused by the position of the transducers (be it speaker or headphone) in relation to our ears. If the transducers are placed in front of us, we perceive the images to be located in front of us. If the transducers are placed directly on our ears, we perceive the images to be located inside or around our heads.

The focus of my essay is the perception of depth clues that are already INTRINSICALLY present in the recordings that we play. These 3 depth clues (comparative loudness, comparative textural specificity, and comparative reverberation) are already part of the signal that we feed to our speakers and headphone. If these depth clues are portrayed by one transducer, then why not the other? After all, it is the same signal we are feeding to both of them.

If you have one of those audiophile test CDs you can demonstrate for yourself the truth of what I say. Listen to the track where the demonstrater hits a percussive instrument, while he slowly walks further and further from the pick-up microphone. The image that you hear over your headphone will CONSTANTLY RESIDE INSIDE YOUR HEAD, but you can tell that the demonstrator is walking progressively away from the microphone. How so? Via the perception of the 3 depth clues I outlined, i.e., the percussive instrument progressively gets (i) softer in volume, (ii) less specific in texture, and (iii) more and more diffused by a reverberative halo.

The psychoacoustics of sound localisation need not be mixed-up with the perception of depth clues via headphones. How far or how near you perceive an image to be is related to extrinsic factors of where the transducers are located in relation to your ears. Whether that image is located in front of you (in the case of speakers) or inside your head (in the case of headphones) does not change the historical fact that instrument A was placed 5 meters from the pick-up mike and instrument B was placed 30 meters from the pick-up mike. These ‘historical facts’ are INTRINSIC to the recordings we play, and are perceivable via headphones.

The purpose of asking the reader to look at his speakers while listening to his headphone was to extend a visual assistance in perceiving these 3 depth clues. I am already accustomed to perceiving depth clues present in recordings, and therefore do not need visual assistance in perceiving that certain instruments are placed further from the recording microphone than others. But for a reader who is new to this perception, this visual assistance is a helpful, but temporary, crutch.

Ear-Training For Depth Perception in Headphones

An audiophile test CD can give a simple demonstration of depth perception in headphones. Listen to the track where the demonstrater hits a percussive instrument, while slowly walking further and further from the pick-up microphone. The image that you hear over your headphone will CONSTANTLY RESIDE INSIDE YOUR HEAD, but you can tell that the demonstrator is walking progressively away from the microphone. How so? Via the perception of the 3 depth clues I outlined, i.e., the percussive instrument progressively gets (i) softer in volume, (ii) less specific in texture, and (iii) more and more diffused by a reverberative halo.

Thus, there are three mechanics of perceiving distances of voices/instruments from the pick-up mikes: (i)comparative loudness, (ii)comparative textural specificity, and (iii)comparative reverberation. These three mechanics are perceivable over any CD, and below is just a sampling:

(1) The Three Tenors In Concert (Teldec 4509-96200-2)
Track 5 Granada- Placido Domingo’s voice is Layer 2. He is not a pop singer who needs to stand so close to the mike!!! So it is not a Layer 1 voice. The tambourine is Layer 3. When only a few people clap, it appears that these people are at Layer 4, but the moment all of them start clapping, it appears they are closer to the mike; they appear to be at Layer 3. This must be the comparative loudness mechanism at work: the louder a sound is, the closer it appears to be.

(2) Planet Drum by Mickey Hart (Rykodisc RCD 80206)
All the images in this CD seem to be layer 2 images. The instruments appear all to be close-miked. However, because my headphone has a laid-back presentation style, I suspect this causes the images to become layer 2 images. A more forward-sounding headphone might portray these them as layer 1 images. I do not know; I don’t have a forward-sounding headphone at hand to verify.

(3) The Emissary by Chico Freeman (Clarity Recordings CCD-1015)
Track 2 Mandela- The saxophone is Layer 1 image (even on my laid-back phones), but the drum kit is Layer 2 in the sense that it is definitely a little further away from the mike than the lead saxophone is. The rest of the accompanying instruments like tambourine, electric guitar and background voices are likewise Layer 2. This style of layering is obviously to highlight the lead saxophone, who is Chico Freeman, the rightful star of this CD.

It is also interesting to note that Clarity Recordings employs a minimally-miked approach here, but the musicians, especially the lead sax, are positioned so close to these mikes that the recording seems a little reverberatively dry, at least where minimally-miked recordings go. I would characterise this CD as a forward-sounding minimally-miked recording. I am used to the idea that minimally-miked recordings are not forward-sounding.

(4) Toolbox by Toolbox (Vaccum Tube Logic Of America VTL 008)
This entire jazz CD is unbelievably reverberatively lush. The lead flute is Layer 2, the piano is Layer 3. The drum kit, oh the drum kit, how do I describe this one? The drum kit itself is Layer 3, but the faint echo/reverberation of that drum kit is Layer 4!!! Heavenly! At the end of each cymbal hit or drum hit the hall is suddenly ‘lit up’ for a very brief moment, and the that Layer 4 designation of the drum kit’s echo is also a sonic description of the acoustic within which this recording was made. Recordings by VTL (which employ a complete line-up of Manley equipment) are so incredible for headphone listening because of the way the layering of apparent distances are achieved by means of reverberation.

The other two mechanisms, i.e., comparative loudness and comparative textural specificity, are not so important in VTL recordings. VTL recordings are must-haves for headphone-freakos! Unfortunately, they do not release new recordings anymore. The alternative to hear the effect of reveberation on the perception of distances is to listen to binaural CDs, which also capture a lot of hall reverb, as a secondary by-product of the recording method.

(5) Music For Strings, Percussion & Celesta by Bartok (Decca 430 352-2)
This classical recording definitely employs a lot of accent mikes placed close to the musicians. Most of the images here are Layer 2 images, with that wierd piano-like percussive instrument being placed somewhere between Layer 1 and Layer 2, in the sense that it is more forward than the rest of the orchestra, but not so forward like the way Madonna would like to eat a mike. Strangely, even the timpani is a Layer 2 image. Timpanis are usually placed way way back at the rear of the orchestra, but this particular timpani does not sound that far away. Must be those accent mikes making the timpani sound nearer than it actually is.

(6) Fireworks by Stravinsky (Delos D/CD 3504)
Delos definitely does not use many accent mikes. The sense of layering in Delos CDs is definitely top-notch. The marvellous bloom of the lush violin section is Layer 3. The brass instruments appear closer, at Layer 2. And that gong-like/drum-like sound (cannot think of the name of that instrument) is way, way at the back of the orchestra, a Layer 4 image. I think the impulse reverberation of the gong-like/drum-like sound contributes to ts sense of being a Layer 4 image. There’s a sense of immense majesty when a timpani/gong/drum becomes a Layer 4 image – like the sound of a distant thunder, growling with authority from afar. No Layer 1 images here.

(7) Stereophile Test CD3 (STPH 006-2) Track 10.

CAUTION! THIS RECORDING IS HEAVY-GOING!

Index 1: 2nos Omni-mikes – John Atkinson talks and hits a cowbell (a percussive thing) in a church interior, and walks from far-stage-left towards the mikes placed in the centre and then away from the mikes towards far-stage-right. His movement nearer and further from the mikes are obvious over headphones. Then he stands at the very back of the church, and walks along the centre aisle towards the mike. This last movement pattern (from back to front of church) is really obvious: his voice/cowbell is decreasingly diffused by church reveberation as he walks towards the front of the church where the mikes are. This is a smooth transition from Layer 4, through Layers 3 and 2, then finally Layer 1. There is no better proof than this track that the distance of a voice/instrument from the pick-up mike is perceivable via headphones!

Index 2: 3nos Omni-mikes – same pattern of movements, except with a different microphone array: a center mike was added. The sense of depth or movement to and from the mikes is likewise the same as Index 1, but due to the center mike, images far-left do not seem as far-left and the images far-right do not seem as far-right, compared to Index 1.

Index 3: ORTF cardiod mikes – same pattern of movements, except with a different microphone type. The sense of depth or movement to and from the mikes is likewise the same as Index 1 and 2, but due to the ORTFs picking up less hall reverb, the image of Mr. Atkinson’s voice/cowbell is less diffused by reverberation. Strangely, it is also very easy to tell when he is standing at the back of the church. This is due to (i)his voice being softer in volume, and (ii)the textural specificity of his voice being reduced, i.e., vocal pronounciations of vowels/consonants are less clear, and the cowbell is less sharp in transient attack when he stands at the back of the church. This experiment clearly shows that reverberation is not the sole mechanics of distance-perception.

Index 4: ORTF cardiod mikes with post-processing. Same as Index 3, but with Blumlein processing to add low-frequency bloom. Same observations as Index 3. I really cannot appreciate the so-called increased-LF-bloom. I do not hear it. But the LF bloom is not relevant to the issue at hand, which is distance perception.

Index 5: Schoeps sphere microphone (binaural) – same pattern of movements, but illusion of sound localisation is partially realised, unlike with the other 4 indexes above, due to the usage of a Schoeps microphone. Image size is smaller and more precisely located in relation to the headphone-wearer. The mechanics of perception of distance here is different from the above 4 indexes, because here the psychoacoustics of sound localisation is called into play. However, because my head is different from the plastic head used, the binaural illusion is only partially realised for me. Index 5 is not a good example to demonstrate the 3 mechanisms listed above, because a fourth mechanism, i.e., the mechanism of sound localisation, is involved here. This mechanism of sound localisation is the basis of binaural recordings.

Note: I am aware that recordings, even minimally-miked ones, are usually not just 2-mike affairs. In conjunction with the main microphones, there are accent microphones which pick up the clarity of the instruments’ musical lines, and there are also hall mikes that are placed further from the musicians to pick up hall reverberation. And the gain applied to each of these mikes is different, depending on the recording engineer’s sonic intentions.

But my contention is this: for every microphone array and mixing configuration, there is such a thing as the centre-of-gravity of that array. This centre-of-gravity is the location where our ears appear to be located, when we listen to a recording. This is an unavoidable fact, I guess due to the egocentric nature of perception: we will always perceive the world, the sonic world even, in relation to ourselves. One will always locate oneself as the centre of the perceived world. When one listens to a particular recording with a particular microphone array, there will always be that one spot where one thinks the musicians and the room/hall are located in relation to oneself. That spot is the centre-of-gravity of the microphone array.

Notes: 1: All these notes about depth clues should not mislead anyone into thinking that listening to a headphone is a very demanding effort. It sure is a cerebral effort for me to try to explain the construction of a headphone’s soundstage to you, but it should not be a cerebral affair for you to discern depth clues via headphones. Like I mentioned earlier, this isn’t a high-school examination — it is music you are enjoying. Remember: an appreciation of depth clues is only one-third of the appreciation of a headphone. There are three ways to enjoy your headphone: its sense of air (this is the category where depth clues fall into), its sense of liquid-ness, and its sense of solidity.

c. 2000, Ron Soh.

Blue Hawaii Hybrid Electrostatic Amplifier for Stax Omega II Headphones.

by Kevin Gilmore
(Project Editor: Chris Young)

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The Blue Hawaii amp is my latest design in my search for the perfect amp to pair with my Stax Omega II headphones. The genesis for this hybrid electrostatic headphone amplifier occurred when I was in Hawaii on vacation, at a fancy hotel on Maui. Sitting at the bar on the beach, drinking “Blue Hawaiis,” I drew the schematic for the amp on a placemat. The design is my conception of the mysterious and rare Stax T2 amp, which I have never been able to find at anything resembling a rational price.

I searched out any information I could find on the T2 in an attempt to create my own version. I was able to determine that it used EL34s as output tubes in a grounded grid configuration, which is the lowest distortion tube output circuit known. It also used 6DJ8s as input tubes with some solid state in the second and third stages. My design uses the first and second stages from my solid state electrostatic amplifier coupled with a third FET stage and then the final grounded grid stage.

My design ended up with a fairly large amplifier pulling significant amounts of power which results in a very smooth and extended frequency range from DC to over 200khz (-3dB at 400khz). Of all my electrostatic amps, this one has the largest output voltage swing. This is not an amplifier for the timid, nor is it a good idea to build this as your first project, though some, however, have actually done so.

The Circuit

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Figure 1
(Click here to see single-image schematic of amplifier.)

Figure 1 is the amplifier schematic. The entire amplifier has a differential topology from input to output to get a balanced input and for lower noise, less ground loop problems. The first stage is a differential amplifier with feedback directly from the output stage. It works equally well with both balanced and unbalanced audio input sources. The step attenuators from Goldpoint make good volume controls for this stage. The JFET device (Q1) is a dual JFET all on one wafer. It is known for extremely low noise and excellent matching, and is used in a number of expensive designs, such as the Nelson Pass amplifiers. Q17 is a current source that sinks 3mA.

Because the amp is totally DC coupled from input to output, drift in the input stage is a bad idea. Since the first two stages run in current mode, the JFET input is more linear than a pair of bipolar transistors. Dual transistors all on one wafer suitable for audio use are hard to find these days. The FETs steer current away from the current sources Q2 and Q3. Together Q2 and Q3 each supply 2mA or a total of 4mA. The Q17 current source takes away 3mA leaving 0.5mA in each of Q4 and Q5, but some of the sink current is coming from the output feedback, so each FET is actually using somewhere between 0.5mA and 1mA.

The approximate voltage gain of this stage is 5; this stage really runs in current mode. The unit was designed to work equally well in both balanced and unbalanced mode. For single-ended signals, ground either the + or – input and apply signal to the other. The much higher impedance of the JFET works better when one side is grounded for unbalanced inputs.

The second stage starts with a constant current source (Q2 and Q3). The current source feeds a common base amplifier (Q4 and Q5). The common base amplifier feeds a modified Vbe multiplier. I believe a famous designer is now calling this circuit a current tunnel. It’s the most linear way of translating the voltage down to the bottom rail. The voltage gain of this section is about 4. The basic idea of the first two stages is to supply the third stage with a very fast low impedance drive signal that is referenced to the bottom rail.

The currents flowing into the common base amplifier (Q4 and Q5) are the difference between what Q2 and Q3 are supplying and what the FET is taking away. The rest of the current goes down the tunnel to the vbe multipliers (Q6 and Q7) that convert the current back to voltage. The current sources in the second stage supply 2 mA each. With no signal, the FETs take 1 mA, leaving 1 mA going through the common base amplifier into the bottom transistors, which are wired as Vbe multipliers (like a zener diode in series with a resistor, except a lot less noisy). This generates the 13 volts (referenced to – rail) necessary to properly bias the third stage.

The third stage is another differential amplifier (Q13 and Q14) being driven via another constant current source (Q10 and Q16). The voltage gain is about 200. Q11 is the power supply for this stage and makes a 100 volt power supply with -400V as the reference. The power supply voltage for this stage is kept down to 100 volts to reduce the Miller effect and keep the frequency response up. The higher output impedance of this stage is lowered by the use of 2SJ79 transistors, which are used as zero voltage gain emitter followers. The use of FETs in this stage coupled with the current source further reduces the distortion and provides for a solid low impedance drive signal for the output stage.

The 4th and final stage is a tube in grounded grid configuration (V1/Q8 and V2/Q15), similar to the common base amplifier in the 3rd section of my solid-state current-domain electrostatic amp. Q9 and Q12 are high compliance current sources and supply 25mA of bias current. Think of them as linear pull-up resistors for current (in fact, one builder has replaced the current sources with large resistors). The use of a current source here instead of load resistors acts to further linearize the output stage and reduce output distortion. V1 and V2 are the equivalent of common base amplifiers and do the entire rail-to-rail output voltage swings.

With feedback, the overall voltage gain of the amp is exactly 1000. The frequency response is kept high due to the low impedance cathode drive. The EL34s are biased at 10 watts and have an 800V voltage swing (by comparison, the output tubes of my original DC-coupled electrostatic amp are biased at 2 watts with a 600V swing), resulting in a frequency response well in excess of 100kHz into a 150pF load. (+0/-0.1dB).

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Figure 2

A regulated power supply design is shown above. The ±15V supply is made with the standard 7815/7915 regulators. The high voltage supply is a pair of 400 VDC supplies, glued together at the output (P-channel MOSFETs are a lot more money than the equivalent N-channel MOSFET). In each section, beginning with a 460V raw supply, a PNP transistor (2SA1968) is used as a current source to feed the 400V zener reference. Then a N-channel FET is used as a high impedance, input voltage follower and outputs 400VDC. By the way, the same exact supply with a 350V zener reference string instead and a slightly smaller transformer (without filament windings) is what I use now for the solid state current domain headphone amp.

The bias supply is a voltage doubler with an adjustable reference. It has a range of about 350VDC to 650VDC. For low bias Stax headphones, put a 10M resistor to ground at the end of the 4.7M. to make the output voltage .66 times the voltage before the 4.7M, which puts it in the range for low bias.

Construction

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(Click here to download pc board patterns in pdf format. 1)
(Click here to download pc board patterns in pdf format. 2)
(Click here to download pc board patterns in pdf format. 3)

Caution: This project involves working with high voltages, so be extremely careful! Keep one hand behind your back at all times. 800VDC across both arms might possibly stop your heart.

This amp was assembled on three printed circuit boards (two for each channel of the amp and one for the power supply) and housed in separate enclosures. A complete set of pc board patterns (pdf format) can be found above. They could be sent to just about any circuit board manufacturer to have boards made. The top of the board is almost all groundplane. All the parts, including the tubes, are mounted on these boards – the tubes are installed in pc-mounted ceramic tube sockets from Parts Express. The tubes must be exposed through the chassis. They dissipate 20W each (actually 10 to 12 watts of plate dissipation plus another 6.3V * 1.6A = 10 Watts of filament power).

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It was so much easier to do a pc board for this amp, but if I were to make a prototype, I would again use the 0.1mm perf board; the layout look much like the circuit board. (Note: For a layout in a single chassis, see the interior view of Headamp.com’s Blue Hawaii amp below.) 99% of the wiring would be on the bottom, and it would be, therefore, rather flat. Mounting the tubes would be trouble though, and would cause mechanical problems. The tubes are fairly heavy and get stinking hot. Each chassis measures 12″ x 10″ x 3.5″. (Note: Headamp.com is selling the Blue Hawaii design in a single chassis measuring about 16.5″ W x 16.0″ D x 3.5″ H and may sell the Blue Hawaii pc boards. Please contact Headamp for more information.)

I have Mullard EL34 tubes, but keep them put away due to what I could sell them for if I wanted. I actually used the National Union tubes from Richardson Electronics which cost $11.50 US each.

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All of the parts except the 2SA1968 have lots and lots of sources such as Digi-Key, MCM Electronics and Mouser Electornics. Only B&D; Enterprises has the 2SA1968 in the United States. In Japan and Canada, they can be ordered from Sanyo direct – the minimum order is 100 at a time, but then they are $1.25 each or so.

Q9 and Q12 are each made of six 2SA1968 transistors in parallel with one 2SA1968 as the driver. Matching the transistors is not required – unless one of the 2SA1968s is way off compared to the rest in which case it might get way too hot.

All resistors are 0.25W except where labeled. It is important to have all the pnp current source transistors correctly mounted to a large heatsink with silicon impregnated washers. If any one pnp transistor gets too hot it can short out the whole current source.

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Standard tab heat sinks will do for the 2SK216 and 2SJ79 transistors, but the 2SA1968 and 2SC3675 transistors must be mounted a big heatsink (one for each channel), capable of dissipating 20 Watts of heat. I obviously fabricated them, but otherwise they can be obtained from Conrad Heatsinks cut to length. The IRFBC30 MOSFETs in the power supply must be heatsinked too: Mouser part number 532-529902b25.

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The Stax SRC-5 headphone jack came from AudioCubes.com. Since the price has gone up to $19 each (I paid $10), it may be more cost effective to use the Allied jacks (see the current domain amp project article). Allied has a $25 minimum order, the cost of three pieces. Then they must be filed down on a lathe. Actually I am buying the male connectors from Allied, because no one else sells them. The male connectors are much easier to convert to standard Stax plugs. The power supply-to-amplifier connectors are the Amphenol military 12-pin connectors. The 4 connectors (two male and two female) were $130.

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The custom Victoria Magnetics power transformer has these specs: 2 x 330VAC/150mA, 36VCT/100mA, 2 x 6.3V/5A (filament supplies). Everything with Victoria Magnetics is custom. I paid $110 for the transformer with shipping. They know about the Blue Hawaii design and will supply the correct transformer on request. For safety, I recommend a 2A/110Vac fuse located in the input line to the power supply.

Setup and Results

Test voltages (with the amp at idle) are shown in red on the schematic and are with respect to ground. To set up the amp, adjust the two pots in each channel of the amp. P1 controls the differential output voltage. Put a voltmeter between the 2 stators of one channel of the headphone and set this pot for zero. P2 controls the voltage with respect to ground. Put a voltmeter between any stator and ground and set for zero. Then repeat both adjustments a few times. The plates of both tubes should measure 0 volts with respect to ground when the pots correctly adjusted. Once the pots are adjusted, that’s it – there’s no change from headphone to headphone.

Setting the bias voltage depends on the headphones. For Stax headphones that can accept a high bias voltage, adjust the pot for 560V. I do not think that the Omega II headphones can be damaged by this amp unless the bias is set way too high. If the bias is set right, the outputs are close to 0V at idle, and all the LEDs are lit, then the amp pretty much has to be working correctly. Now if one or more of the outputs is stuck at +400V or -400V, then something is seriously wrong and needs to be fixed. An oscilloscope really helps.

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Adjust the pot to 580 volts for Sennheiser HE-90 and HE-70 headphones or leave it at 560V. For Koss headphones, adjust the bias for 600V. To use the Sennheiser HE60 headphones with this amp, I made the adapter shown above. Those are RS-232 female connector pins that fit the HE60 pins perfectly. By hand I cut a circuit board with lands exactly 3.5mm apart put the pins on the HE60 connector, lay them down on the circuit board and solder. Then attach wires and a standard stax plug.

The amp can output 1500 V p-p measured stator to stator. At 800Vp-p, THD is less than 0.004% from 20Hz to 20kHz. The actual frequency response is 0 to 100kHz (-3dB at 150kHz) into an Omega II load. Compared to the sound of my previous tube amplifier, the bass is no longer tubby; it’s very sharp and tight. The high end is no longer rolled off, so female voices sound much more real. If the bias supply is reduced to 280V, the amplifier will drive all electrostatic headphones. I tried it last night on a pair of SRX’s. I never ever heard them sound so good.

Previously with a standard dummy head, I measured the SPL in Omega 2 headphones driven by this amplifier. With a drive signal of 800Vp-p per side, the resulting spl is 106dB. THAT’S LOUD! The amp can put out 1500 volts peak-to-peak, and thats louder! I just ordered a pair of Stax SR-001 MkIIs, which can reach up to 120dB. My ears distort before the amplifer/headphones do. It is quite loud at clipping, but the clipping is a hard clip with no oscillation or ringing. To use the amplifier with electret headphones, delete the bias voltage. And probably keep the output swing under 200V. Electrets phones when driven with this amplifier can probably get very very loud.

Several of my previous electrostatic designs are available in the Headwize Projects section. Comparing the Blue Hawaii to my all solid-state current domain amplifier, they really are more the same than they are different, but in general, the differences are the differences between tubes and solid state, such as a much smoother high frequency response, which in the case of the Blue Hawaii goes well beyond 500kHz. Additionally, the four times power consumption of the Blue Hawaii means a much stiffer and tighter bass response. Even though both are flat to zero and test similar, the BH bass is much more apparent and tighter.

c. 2004 Kevin Gilmore.

Build These Noise-Canceling Headphones (plus: Binaural Mike Headset, Audio Probe and Parabolic Mike).

by Jules Ryckebusch

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In today’s hectic and noisy world, we are all searching for a little peace and quiet. Well, you might not be able to slip off to a tranquil forest for an hour or two, but you can block out background noise with the Noise-Canceling Headphones. The theory behind this project is that by picking up ambient sound with a microphone and reproducing it out of phase, we can actively cancel or “null” out background noise. In fact, several commercially available devices perform the same function. However, by building your own headset, you can add features not otherwise available and have fun while doing it!

Along with noise-features, the Active Noise-Canceling Headphones let you mix in an auxiliary line-level signal from a CD or tape player. That allows you to minimize background noise while quietly listening to music. The project also has a phase switch that will let you keep the microphone signals in phase, thus amplifying background sound. In addition, the design of the Noise-Canceling Headphones lends itself to several other interesting functions, which we will look at later.

How It Works.

The electronics consist of three op-amp circuits; each built around one half of an NE5532 dual op-amp. Each circuit uses that op-amp in a different configuration. The first circuit is a non-inverting pre-amp, the second is a unity-gain phase-inverter, and the third is an inverting headphone amplifier. Since the Noise-Canceling Headphones is a stereo device, the circuit is actually two identical circuits side-by-side. Only one channel will be described; the second channel works in exactly the same way.

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Fig. 1. The Noise-Canceling Headphones is a simple phase-inverting amplifier. All inverted sounds played back through the headphones cancel out the original sounds, leaving nothing but silence. The amount of canceling can be adjusted for different situations. A CD player or cassette tape can be listened to if you want to “fill the quiet.”

The schematic diagram in Fig. 1 shows the design of the electronics portion of the project. A headset-mounted microphone is connected to J1, a 1/8-inch stereo jack. Electret-condenser microphones need a 2- to 10-volt bias voltage for their internal FET pre-amps. That is supplied by R2. A voltage-dividing network, which also decouples the bias volt-age from the power supply, is provided by Rl and Cl. That is necessary due to the high gain of the entire signal chain.

The signals from the microphone then go to ICl-a. an NE5532 set up as a standard non-inverting pre-amp. The gain is set to one plus the ratio of R8/R6 in the feedback path. The total gain for that stage is about 31 dB. Resistor R4 provides a ground reference for the pre-amp. A pair of high-pass filters is formed by C2/R4 and C4/R6. Those filters block any DC that tries to slip through the pre-amp.

From the output of the pre-amp, the microphone signal is sent down two different paths. It feeds both one pole of Sl-a and the phase-inverter. The phase inverter is nothing more than a second NE5532 configured as a unity-gain inverting op-amp (IC2-a). The output of IC2-a is connected to the other pole of Sl-a. That way, Sl-a can select either the inverted or the non-inverted signal. The selected signal on Sl-a’s common pole goes to potentiometer R14-a. That potentiometer sets the level of the microphone signal feeding the headphone amplifier.

The headphone amplifier is built around IC3-a, a third NE5532 wired as an inverting op-amp stage. The gain here is set by the ratio of R19/R15. That type of op-amp configuration can be easily modified to add a summing feature by the inclusion of R17. The second input comes from an auxiliary line-level input that is attenuated by potentiometer R23-a.

There is a reason why 10K-ohms was chosen for the value of R15 and R17. Besides keeping the values of R19 manageable, the 10K-ohms resistors interact with the 100K-ohm linear potentiometers. The potentiometers then behave in a logarithmic fashion.

This is how that feature works: One end of the potentiometer is tied to ground because we are using it as a voltage divider. Because the sum-ming junction of an op-amp is at a virtual ground, the 10K ohm resistor is also essentially tied to ground. That affects the response of the potentiometer, As the potentiometer is rotated, there is a more pronounced increase in the output as the end of the potentiometer’s travel is reached. That causes a smooth increase in perceived loudness of the signal. Potentiometers with an audio taper are, of course, available, but a linear-taper unit is easier to obtain and costs less.

The output of the headphone amplifiers is coupled to output jack J3 through R21. That resistor provides overload protection to IC3-a in case the output is shorted. If you have never used an op-amp for driving headphones before, you are in for a nice surprise. The NE5532 will supply a 10-volt rms signal into a 600-ohm load with very little distortion. That works out to 166 mW of power. Most personal stereos only supply 20 to 30 mW of power to headphones.

A final note on using operational amplifiers as headphone amps: Most generic ones will not supply enough current to function properly. Some substitutes for the NE5532 that are known to work include the 0P275 from Analog Devices, the OPA2604 from Burr Brown, and the LM833 from National Semiconductor. Those components are available from several sources, including Digi-Key, Allied Electronics, and Jameco.

Construction.

There are two parts to this project: building the electronics and modifying a pair of headphones. The circuit is relatively simple and can easily be assembled on a perfboard. One style of perfboard that simplifies construction is one having a pre-etched copper pattern on its solder side that connects groups of holes together. One example of that type of perfboard is Radio Shack #276-150.

The etched pattern on that board has a pair of buses that run the length of the board. Those buses are very convenient for power distribution. If you use that type of board for the Noise-Canceling Headphones, it is best to start by spacing out the three ICs on the board so that they straddle the buses. Then attach the power supply leads from each chip to the buses. It is then a simple matter of point-to-point wiring the rest of the circuit.

Check your work often while building the circuit. A common mistake many hobbyists make is not checking their work thoroughly enough. Often a few components are accidentally wired in backwards. The usual result is that the circuit will probably not work, the ICs could be damaged, and the electrolytic capacitors might explode!

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Fig. 2. The circuit board and batteries fit neatly into a simple project box. Keeping the wiring neat and following the layout shown here makes assembling the unit and changing the batteries easier.

When wiring the jacks, it is a good idea to follow the audio industry standards as to which jack connection is for which stereo channel. Normal standards for stereo connections are to connect the right channel to the ring and the left channel to the tip. The board and batteries are mounted in a suitable enclosure. A suggested layout for the components and control panel is shown in Fig. 2.

When selecting a case for the project, be sure that it is large enough to hold the circuit board and the two 9-volt batteries comfortably. After the front panel is laid out and drilled, check to make sure all the controls and jacks will fit. One method for labeling the front panel is to spray the entire panel with a flat color such as white or yellow. After applying transfer let-ters, seal the panel. Use several thin coats of a clear coating such as Crystal Clear by Krylon. The results are worth the effort. While the front panel is drying, we can start on the headphones.

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Fig. 3. The microphones are mounted on the earpieces of the headphones with a dab of silicone sealant. Tie both wires together in order to make the headphones more comfortable to wear (A). Follow the diagram in (B) when wiring the microphones. The left mic is connected to the plug’s tip and the right is connected to the ring. The ground connection on an electret microphone cartridge is easily identified by the solder connection between the terminal and the mic’s case (C).

Headphones with Ears.

The headphones are a standard pair of aftermarket Walkman-type units. They sell for about $20 at most record or electronics stores. The headphones are modified by mounting two small electret-condenser microphones on the head-phones, one on each earpiece. That modification is shown in Fig. 3.

The key to making the headphones wearable is to use thin wires running to the microphones. An excellent source of thin audio cable is to buy another set of cheap headphones – the cheapest you can find. Cutting the wire off them will yield a shielded stereo cable that is thin and flexible. As an added bonus, the wire will have a l/8-inch stereo plug molded on to it already!

The best way to strip that type of wire is to roll a razor blade very carefully over the insulation without cutting the wire underneath. Once the insulation is cut, carefully pull it away from the wire. That method works especially well on Teflon-insulated wire. After you have prepped the wire, mark the wire that is connected to the ring and the one that goes to the tip of the jack. An ohmmeter makes that task easy.

Carefully solder the wires to the microphone elements. The easiest way to do that is to pre-tin the wires and melt the little dab of solder on the microphone element with the tinned wire beneath the soldering iron tip. Look carefully at the microphone. As shown in Fig. 3C, the terminal that is connected to the case of the microphone is the ground connection. The other terminal is the actual microphone output. Holding the microphone element in an alligator-clip holder will make the job much easier. After soldering on the microphone elements, it is good idea to test them prior to gluing them to the headphones. The wiring should follow Fig. 3B.

Mount the microphones on the headphones as shown in Fig. 3A. One way to attach the microphones to the headphones is to use a dab of silicone sealant. Using a toothpick or other suitable substitute, mold the silicone around the edges of the microphone element to smooth everything off. Be careful not to get any on the black felt surface – that is where the sound enters. Obviously, the left and right microphones should be attached to the left and right sides of the headphones, respectively. Trying to cancel out a sound on the right with a sound from the left will not work.

After the glue is dry, gather and bundle the wires together with several nylon tie wraps along the length of the wires. With the headphones complete, it is time to experiment with the Noise-Canceling Headphones.

Creating A Quiet Zone.

For testing purposes, you should be in a quiet room with just a little background sound, such as a heater or air-conditioner fan. Plug in the microphone jack and the headphone jack, and put on the headphones. Turn both controls all the way down and turn the power switch on. Slowly turn up the microphone level. You should either hear the background sound increase or start to fade. If it increases, change the position of the phase switch. At some point, you should reach a “null” point where the background sound is at a minimum. If you adjust beyond the null, background sound will become louder as the out-of-phase signal exceeds the ambient sound level. Try talking aloud. If it sounds like you have a massive head cold and can barely hear yourself, the circuit is functioning properly.

Note that it is impossible to eliminate all incoming sound. Many things affect the ability to cancel out noise. The loudness of the incoming sound, the specific frequencies involved, and the position of the sound source all play a part in how well the headphones do their job. Feel free to experiment.

If everything is working fine, try connecting a CD player to J2. You will need a 1/8-inch -to- 1/8-inch patch cord similar to the ones used to connect portable CD players into a car stereo. After connecting the CD player, slowly turn up R23. It should sound clear with no distortion. Experiment with combining low levels on the CD player and canceling out room noise. The Noise-Canceling Headphones is the perfect device for environments that have a loud ambient sound level, such as rooms with loud ventilation systems.

Beyond Peace and Quiet.

This project lends itself to many other uses. Several interesting applications will suggest themselves that do not require any additional hardware. For example, by switching the microphones to “in-phase,” the unit can be used to assist hearing or improve hearing. Areas that can benefit include outdoor activities such as hunting or just observing nature.

Another unusual application for the Noise-Canceling Headphones is in binaural recording. Since we already have two microphones mounted in essentially the same place human ears are, all we have to do is send the headphone output to a tape recorder input. Binaural recordings put the listener directly in the sound field. The two microphones capture the exact phase and timing relationships of sound as we hear it. Those are the clues our ears use to determine the location of a sound.

Try this little experiment: record a person talking to you while you are wearing the headphones and have them walk around you in a circle. Then listen to the recording on the headphones. You will hear the person walk around you! The microphone elements used in this project feature full 20-Hz to 20-kHz frequency response. They provide a signal with surprisingly high fidelity.

rychke5.jpg

Fig. 4. Mounting both microphones angled apart at the end of a long stick makes an audio probe. It is very useful when you need to listen at a location that you can’ t reach.

Other interesting tools can be created by building different types of housings for the microphones. If two microphones are mounted on the end of a length of 1/2-inch dowel, an audio probe is the result (Fig. 4). It is wired similarly to Fig. 3B. That device lets you listen to things up close that you wouldn’t normally hear. It can be used to “sniff” out problems in mechanical equipment or to record things like hamsters chewing on cardboard. With the microphones mounted at an angle between 90 degrees and 120 degrees, you will have a stereo image of the sound source too!

rychke6.jpg
Fig. 5. A parabolic dish or lamp reflector makes a usable “Big Ear” microphone. The microphone is mounted at the focal point facing in towards the dish. Either one or two microphones can be mounted in the dish. If you build two, you can pick up stereo sounds.

An extension of the shotgun-style microphone is a “Big Ear.” The general arrangement is shown in Fig. 5. The main component is a small parabolic dish. Place one or both microphones at the focal point of the dish and experiment away. Sources for parabolic dishes can be as close as a local hardware store. A simple reflector for a light bulb can be found at a very reasonable price. Another source of true parabolic dishes is Edmund Scientific, 101 East Glouchester Pike, Barrington, NJ 08007. For some advanced experimenting, use two dishes (one for the left microphone, one for the right) and experiment with stereo reception of a distant sound.

Parts List

Resistors (1/4W, 1% metal film):

R1 – 4.7Kohm
R2, R3 – 2.2Kohm
R4, R5 – 1M
R6, R7 – 1Kohm
R8, R9 – 33Kohm
R10-13, R15-18 – 10Kohm
R14, R23 – 100Kohm pot, dual-gang, linear taper
R19, R20 – 100Kohm
R21, R22 – 47 ohm

Additional Parts and Materials:

IC1-3 – NE5532 dual audio op-amp
C1 – 33uF, 25WVDC, electrolytic capacitor
C2, C3 – 0.01uF Mylar capacitor
C4, C5 – 10uF, 25 WVDC, electrolytic capacitor
J1-3 – Audio jacks, 1/8-inch, stereo
S1, S2 – Dpdt toggle switch
B1, B2 – Battery, 9 volt
Microphones (Digik-Key P9967-ND or similar), headphones, PC board, case, wire, hardware, etc.

Addendum

10/5/1998: The following sentence: “The signals from the microphone then go to ICl-a. an NE5532 set up as a standard non-inverting pre-amp” originally identified an NE5522. Corrected.

7/8/2000: Marc Goodman built a noise-cancelling headphone amplifier for his Sennheiser HD580 headphones based on the circuit in this article. He writes: Just thought I’d report some results on building a noise cancelling headphone amp for my Sennheiser HD580’s. I started with the Ryckebusch project from this site, but I ended up making a fair number of changes. My goals were, in order of importance, 1). get the best audio quality possible driving my HD580’s from my Pioneer portable DVD player (PDV-LC10), 2). cancel enough noise, on demand, to make airplane listening/movie watching possible, 3). maximize listening times between battery recharging, 4). make the resulting project with enclosure small enough to fit into a camcorder bag along with the DVD player, headphones, and a selection of DVDs (i.e., not too big but no need to make it as small as, say, a CMOY amp).

1. Optimizing Audio
The Ryckebush NC project uses a single NE5532 inverting op amp stage for line-in amplification. I didn’t like the fact that the audio signal gets inverted, so I first tried changing the circuit to use a non-inverting amplifier. It sounded OK to me, but when I went to a unity-gain inverting op-amp as a first stage with an inverting amplifier as a second stage, it sounded cleaner, so that’s what I went with. I also used LM6172’s for both stages. As other people have noted, the LM6172 requires a fair amount of voltage. More about this in section three.

2. Noise Cancellation
Ryckebush feeds the output of electret condenser microphones through a non-inverting preamp and allows switching of this output through a unity-gain inverting op-amp to select between cancelling the noise or amplifying the noise. The inverted or non-inverted signal is then summed with the line-in signal through the final inverting amplifier. I was more concerned with conserving power than I was with being able to amplify external sounds, and feedback was a real problem with the Senns in any event, so I opted to drop the inverter from the circuit and to separately switch the power on/off for the entire mic/preamp stage. Since the preamp is non-inverting and the final audio stage is an inverting amplifier, the output of the preamp can be fed directly (via a potentiometer) to the input of the final stage. I would call the result “noise reducing” rather than “noise cancelling,” but the effect is quite noticable especially for lower frequency sounds. There is also a faint but noticable hiss when the noise cancelling circuit is enabled, so I wouldn’t want to use this stage unless the environment was pretty noisy to start with.

I wasn’t thrilled with the notion of gluing microphones to the outside of my Senns, both because it would look ugly and also because I carry them around with me everywhere and they’d be bound to get snagged/knocked off. Fortunately, the Senns have removable covers over the speakers with plenty of space between the speaker and the cover. In order to both reduce higher frequency noise and to provide a secure mounting for the microphones, I cut and shaped pieces of low-density foam (squishy) to fit the inside of the cover and give the speaker a little room. Though this closed the speakers off a little, the effect was not significant enough to be noticable (to me, anyway). It also teneded to acoustically isolate the microphones from the speaker elements which reduced the likelihood of feedback. I found the best results to be when the mics were placed to one side of the foam cover, directly in front of my ear canals.

3. Batteries
My first implementation of the circuit used dual 9V batteries as in the original Ryckebush circuit. However, I was completely bummed by how short a charge lasted. So, I tried using 6 C rechargeable batteries instead with a ground tap in the middle. These batteries held around 1200mAh as opposed to around 140mAh for the 9V’s, so they lasted a long time. But, I was driving the circuit with only around +/-4V instead of +/-9V, and while this turned out to be enough for the LM6172’s to power up, there was a huge amount of clipping at higher volumes with my HD580’s.

My solution was to build a separate DC voltage doubler using the ICL7662. The 7662 is a higher-voltage version of the 7660 that avoids latch-up on startup. It operates at 10KHz, which is smack in the middle of the audible range so ripple is a big issue. I found that by using 22uF low-ESR tantalum caps for the reservoir capacitor and by carefully routing all wires away from this capacitor to minimize inductive coupling, the ripple was beneath the threshold of my hearing. Note that getting the wires positioned just right was extremely important, as was putting the voltage doubler on a separate circuit board. Also, I had to shorten the wire lengths to all of my input/output jacks. It was kind of a pain, but not as bad as listening to a barely audible high-pitched whine ;).

4. Enclosure
It’s about the size of a paperback novel with roughly half the space taken up by the 6 C batteries in three rows of 2 lying in a Z and the other half taken up by the PCBs and controls (two DPDT switches, two pots, three 1/8th” jacks and a power on/off LED).

Conclusion
All in all, kind of fun and only around three times as expensive as if I had bought something from a store ;).

7/15/2000: Laura Balzano, Anna Huang, Eric Rombokas and Yasushi Yamazaki at Rice University built noise-cancelling headphones based on the Ryckebusch design for their project: “Sound Cancellation by Signal Inversion.”
As you know, we were using low-quality headphones, and when we mounted the mics on the outside of the headphones, we got little beneficial effect. We found that we could get better results using nice headphones, but they still were not very effective. We moved mics inside headphones to decrease sound delay effects. This greatly improved performance, but introduced feedback until we rigidly pointed the mics away from the headphones’ speakers and covered the mics with headphone foam (from the pair of headphones that we had to sacrifice)…. We found that due to sound propogation delay, non-inverted output (in our case) produced better effect than inverted output. We also observed that headphones were ineffectual for high frequencies, so to reduce noise produced by the circuit, the input was put through a simple RC lowpass filter with Wo=1K.

Results: The apparatus heavily attenuates sounds of very low frequencies, and somewhat attenuates all frequencies <= 1Khz. The headphones also get rid of the part of your voice that “echoes” in your inner ear– the extra echo that you typically hear when your ears are covered and you speak.

2/10/2002: Value of C3 in figure 1 corrected to 0.01uF. Also posted larger version of images and cleaned up figure 1.

c. 1997, Gernsback Publications (Popular Electronics and Electronics Now).
From Electronics Now, September 1997. (Republished with permission.)

Poor Man’s Surround Headphones.

by Steve Connors

Disclaimer: Try this project with a pair of inexpensive or disposable headphones first. Otherwise, purchase one or two additional sets of ear cushions for experimenting, so that the headphones can be restored to original condition if desired. Neither the author nor HeadWize is responsible for any damage to headphones or earbuds that results from building this project.

I came up with an idea to make surround sound headphones from a pair of old but nice stereo headphones to use with a SB Live soundcard. I have a surround sound system with 5 speakers, but there are a huge number of gamers that just can’t blast the neighbors and family late at night. Quad headphones ? … a blast from the past but they seem to have disappeared. My main problem was finding a good reasonable set for my SB Live.

connors1.gif
Figure 1

These surround headphones use three sets of earbuds to supplement the stereo headphones for front/back sound – 2 rear channel earbuds and 1 front channel earbud per side. My main headphone is a Sony Digital Reference MDR-CD60. I got them at WalMart a couple years ago for 10 bucks. For the back speaker effect, I’m using Sony Walkman earphones MDR – E821Lp with Mega Bass. I use Koss earbuds for the front speaker effect. Someone said you couldn’t get front/back effect. Well, I beg to differ. As long as you can tell where sound is coming from, the brain will figure it out, and the surround immersion is complete.

[Editor: Adding an acoustic simulator.to the front channels may enhance the realism of the soundfield.]

Having two earbuds for the rear channel does help compared to just one to help resolve the characteristics of behind vs front. In my setup, the back is a tad louder and bass is pumped up. To power the rear channels, I have an old Labtec PC stereo speaker set that has a headphone jack (I’m sure there are endless ways to get the signals to the back earbuds). The front channel headphone/earbud combo is just plugged into the headphone jack of the SB Live.

Here are step-by-step instructions for making the surround headphones:

1. Make buttonholes in each ear cushion – 1 front, 2 back. Earbuds along the back of the ear ended up being the best location for me.

2. Use two sony earbuds with mega bass as buttons in back; these need the bass turned up just a tad and the volume cranked up.

Note: they are to be used in a way they really weren’t made to be, i.e., kept loud as possible just to point before they distort. Yes it will take two earbud, but hey! I had a couple of them sitting around.

3. I’m using Koss earbuds in the front ear cushion buttonhole.

Note: all earbuds face toward ear. [Editor: for ideas on how to position the earbuds, see the section on multichannel headphones in Technologies for Surround Sound Presentation in Headphones.]

4. Two stereo splitters hooked to 20ft extension chord. I bought my stuff at Radio Shack. Get the gold-plated versions.

5. The back earbuds go into one splitter/20ft extension.

6. The front earbud and main headphone speaker go into the other 20ft splitter extension.

7. Make it neat and put connection mess in a little sack. Tie top of sack. This will protect connections, allow easy access and keep them from being pulled apart.

8. Fix up the wires now … group neatly. Earbuds at top taped neatly to the Y of headphones. Headphone and front earbud all neat and secure.

9. The rear channel earbud extension goes to the headphone jack of the Labtec speakers.

Note: I just happend to have a Labtec CS900 in the closet with stereo headphone jack and bass, treble, and volume controls. I’m thinking up ways now to get a graphic equalizer into the fray. Why ?… because it’s there. The nice thing is to have some control of bass and treble, not to mention volume. Getting the rear channel earbuds to work means they have to be pushed. They have to reproduce back whispers, low rumblings, etc. and still sound clean.

10. The headphone/front earbud extension goes to the front headphone jack of your SB Live.

11. Set up your SB Live up to headphones … read the docs … they won’t be much help with the surround headphone setup, but you basically have a quadrophonic surround with 4 speakers.

12. Make all neat. Secure and protect lines to achieve max range of wires. I ended up with good 15 feet.

The headphones look fairly good now that I have wires organized down the cord. I’ll end here but would like to say that the front-back and right-left directions can be tweaked with the SB Live mixer and SB Live value experience positioning toys. You will have to go to Audio HQ – mixer – view -> check the box to show balance sliders on mixer.

They work pretty good, but as you can imagine, getting the depth front and back is the promise land of directional sound. For me what this does is creating an obvious difference when sound is coming from the back. I can really pinpoint where someone shoots at me now.

One drawback thus far. I’m all headphones. I’m going to use a toggle switch from Radio Shack to send SB Live signals to the surround sound receiver. That way I can just change my SB Live settings from the 4-speaker quadrophonic surround to 5 speaker surround… flip a switch and presto, I’m using speakers.

c. 1998 Steve Connors.

How To Remagnetize Old Headphones.

by Tom Provost and Gary D’Amico

Presented by Tom Provost and Gary D’Amico (John Dilks, Ed.)
at the November 1996 NJARC Meeting
Last updated Nov. 21, 1996

First, evaluate your headphones.

provost1.gif

  1. Check your phones for continuity. Most high impedance phones are about 1000 ohms per phone. Since the phones are connected in series the resistance measured from wire to wire of the phone cord and should be around 2000 ohms. If the cord is bad you can make up something from modern materials or obtain an authentic replacement (See supplier list at the end.) Make sure that you wire the phones in series and observe the proper polarity relationship. If your phones don’t have continuity – check for corroded joints, a bad cord or open coil windings. [Open coil windings are big trouble, as the wire is very fine and hard to replace, but not impossible. It is assumed that you have basic trouble-shooting skills. If not, get a friend to help. Ed.]
  2. The strength of the magnets. Remove the earpiece. Take the metal diaphragm and hold it over one the poles and attempt to lift it up and away from the magnet. A strong attraction is a sign of healthy magnets. Strength is relative, but a ballpark test of passable magnet strength is to suspend the metal diaphragm edgewise from the pole of the magnet. If it can hold up the diaphragm it’s probably good enough to use. If it displays weak characteristics you’ll have to remagnetize the magnet(s).
  3. Check the diaphragms for flatness, replace if not flat. (see vendor list)

Re-magnetizing your phones

Two ways are being described:

provost2.gif

  1. Rubbing the magnets with another strong magnet
    and
  2. Placing the weak coil magnets within a homemade electromagnet to renergize them.

First, using a magnetic compass identify the magnetic orientation of the earphone. You want to retain and enhance this magnetic identity. Using the compass find the pole that attracts the north indicating pointer (the arrow end is actually the south pole of the compass needle), mark the phone with a pencil, indicating that this is the north pole of the earphone. (Remember like poles repel, unlike poles attract.) Also mark the magnets themselves, inside the earphone with a permanent marker.

Method 1: Using permanent magnets (without disassembly of phones)

provost3.gif

Remove the covers and diaphragm from the earphone. Identify the pole. of the earphones and mark them. Identify and mark the poles of the two strong magnets with permanent marker. Radio Shack sells ceramic magnets, 64-1877 @ $.99 each, that are fine for this job. Orient the magnets side by side so that you have a North and a South facing as shown. Think of them together as a horseshoe magnet. Place the North and South of the ceramic magnet against the opposite polarity of the phone pole piece. Slide the ceramic magnet pair across the earphone 10 or more times, in the manner shown.

Method 2: Using a electromagnet and a 6 volt gel cell battery (this produces stronger magnets)

provost4.gif

Identify the poles of the earphone and mark them. Wind about 20 turns of #18 (or thereabouts) insulated wire in a shape such that the phone (without the screw on cover and diaphragm) can be placed inside the winding. Using your compass momentarily connect the winding; (just a “tap” is what’s needed) to the gel cell battery and observe the magnetic polarity of the electromagnet. Mark the leads and the winding showing the electrical and magnetic polarity so you can reproduce it. Now remove the cover and diaphragm from the weak earphone and place it inside the electromagnet winding with the poles of the electromagnet and the earphone matching (both north poles to the left etc.) Connect the winding to the cell, in the same manner, tap, tap, tap. Do it about 6 times. Check the earphone polarity. It should be the same as you marked it. Check it with the diaphragm for hanging strength. It should be much stronger.

The headphones used for this example were Brandes, a common type. With the ideas shown here you should be able to adapt the techniques to other types.

Suppliers of headphone parts

Playthings of the Past

9511 Sunrise Blvd. #J23
Cleveland, Ohio 44133

Modern Radio Labs

P 0 Box 14902
Minneapolis, MN. 55414-0902

[Of course, the live talk and demonstration was much better. Plan to attend the next meeting. Visitors are always welcome. Ed.]

c. 1996, Tom Provost, Gary D’Amico, John Dilks.
From the New Jersey Antique Radio Club site. Republished with permission.

Notes on DIY Electrostatic Headphones.

by Chu Moy

Electrostatic headphones continue to capture the imaginations of audiophiles, although dynamic types comprise by far the largest portion of headphones sold. The sound of electrostatic headphones is often characterized as detailed, low distortion and spacious, owing to their large area, lightweight diaphragms driven over the entire surface. For all the mystique that surrounds them, electrostatic transducers are in many respects easier for the DIYer to make than dynamic ones. Although commercial electrostatic headphones are the product of sophisticated manufacturing processes, homemade versions are also capable of high performance.

From 1968 to 1979, the U.K. magazine Wireless World published three projects for DIY electrostatic headphones by J.P. WilsonPhilip D. Harvey and Neil Pollock. This article reviews the concepts of electrostatic headphone design with attention to the contributions of each of the above authors. Warning: the high voltages involved in these projects do pose a serious danger. Only advanced DIYers familiar with high voltage construction techniques should attempt to build electrostatic headphones. As the projects are over twenty years old, some of the materials and parts described may be obsolete. However, the resourceful DIYer may find some inspiration herein to use modern materials and parts.

PRINCIPLES OF ELECTROSTATIC HEADPHONE DESIGN

electro1.gif
Figure 1

For linear operation, an electrostatic transducer should be push-pull, and operate with a constant charge on its diaphragm. Figure 1 shows a cross-section of the basic assembly of a push-pull electrostatic transducer. It consists of two plates, two sets of spacers and a diaphragm. In a push-pull configuration, the diaphragm is suspended between two conducting, acoustically transparent plates which are fed high voltage audio signals that are 180 degrees out of phase. The diaphragm, which maintains a constant charge from a DC bias voltage, moves as the electrostatic differential between it and the plates varies with the audio signal.

In general, the requirements of a high performance electrostatic transducer are:

  • The diaphragm should be light and flexible. A lighter diaphragm will result in a transducer with a wider frequency response. Also, the thinner the diaphragm is, the easier it will be to damp.
  • A large transducer area that covers the ear will produce a more planar wavefront with more accurate localization cues. It will also provide a low diaphragm resonance frequency without requiring accurate control of the diaphragm tension. If the resonance frequency is too low, the transducer may become sensitive to subsonic signals or suffer a loss in sensitivity, because the bias voltage may have to be reduced.
  • The transducer area should not be so large that the interplate capacitance makes the unit difficult to drive.
  • In order for the diaphragm to hold a constant charge at low frequencies (when parts of the diaphragm can become unstable), it should have a very high resistance coating.
  • The rear of the transducer should be open to radiate the backwave from the diaphragm.
  • The spacers should be flat, insulating and of uniform thickness.
  • For maximum acoustic output, the spacer thickness should be as small as possible, but not restrict low-frequency movement.
  • The plates must be rigid, at least 20% open with a perforation spacing much smaller than the shortest wavelength to be reproduced. If the plates flex or are uneven, there could be variations in the signal field strength.
  • The transducer should have adequate acoustic damping to damp the diaphragm resonance and to prevent ringing on transients. The acoustic loading from the perforations in the plates provides some damping, but additional damping is usually necessary to even out irregularities in the frequency response.

Diaphragm Resistivity

The motion of the diaphragm is affected as follows: by the diaphragm tension at low frequencies, by the acoustic resistance of air at mid frequencies, and by the mass-per-unit area of the diaphragm at high frequencies. The resonance frequency of the transducer determines the lower frequency limit. If the resonance frequency is too low, it could limit the apparent sensitivity of the transducer.

To ensure that the diaphragm maintains a constant charge at low frequencies, no significant current should flow in less than half the time period of the lowest frequency to be reproduced. Given a diaphragm with perfect conductivity and a transducer having capacitance C farads, and low frequency response to 27Hz, then the diaphragm must be fed via a resistance R ohms, such that:

RC > 1/(2 x 27) (approx.)
If C = 150pF (C= eA/d)
then R > 1 x 108 ohms.

 

 

However, R cannot be so high as to prevent the diaphragm from charging.

The Transducer Frequency Response

electro2.gif
Figure 2

Figure 2a shows the mechanical-equivalent circuit of the transducer. m is the mass-per-unit area of the diaphragm, S is the suspension of the diaphragm in the transverse direction, and 2Rm is the damping in the mid frequencies from the impedance of the air. Fo is the peak force-per-unit area on the diaphragm.

The electrical-equivalent circuit in figure 2b converts m to an inductance of M = jwm henries, the suspension S to a capacitance of S-1 farads, the damping to 2Rm ohms, and the force to a voltage Fosin(wt)V. The high frequency response of this circuit is constrained by the inductance M, which is directly proportional to the diaphragm’s mass-per-unit area. Therefore, the lighter the diaphragm, the smaller the inductance and the wider the frequency response.

The transducer acoustic output

The acoustic output of an electrostatic transducer is limited by the breakdown of air and diaphragm stability, but can be improved by coating the plates with insulation. At low frequencies, the output is constrained by the diaphragm touching the plates, and so is affected by the spacing between the diaphragm and the plates. The force acting on a diaphragm in a push-pull transducer is calculated as:

electro3.gif

where e is the differential plate voltage, E is the polarizing potential on the diaphragm, A is the diaphragm area, and d is the spacer thickness. This equation suggests that output can be maximized by increasing e or E. However, the maximum value of E for diaphragm stability is

electro4.gif

where T is the diaphragm tension. The maximum bias voltage, then, is limited by the plate spacing. The maximum voltage between the diaphragm and plate is limited by arcing in the airgap, which is also a function of d. Thus, the construction criteria for a high output electrostatic transducer are: a high diaphragm tension, a small diaphragm area with the highest acceptable diaphragm resonance frequency, the smallest plate spacing with good low frequency response.

CONSTRUCTION OF ELECTROSTATIC TRANSDUCERS

The following sections describe the electrostatic headphones built by J.P. Wilson, Philip D. Harvey and Neil Pollock. All three designs are similar and construction techniques for one can often be used with the others. When assembling the transducers, all drilled holes should be deburred, and all dirt or lint between the diaphragm and the plates should be carefully removed; otherwise, there might be arcing or a loss of sensitivity. All exposed high voltage areas on the transducers must be insulated to avoid shock.

Because the diaphragm bias supplies for all of the headphones have a high impedance (see the section on Electrostatic Headphone Amplifiers below), there is no danger of lethal shock – although DIY electrostatic headphones should be inspected periodically to ensure proper and safe operation. As a further precaution, Mark Rehorst recommends that bias supplies be built from low voltage DC step-up converters (available to 5000VDC or more), instead of using high-voltage AC transformers. These converters are sold in IC packages by companies such as Emco High Voltage Co.

The Wilson Electrostatic Headphone

electro5.gif

J.P. Wilson built a pair of electrostatic headphones as an experiment to eliminate the “in-head” characteristic of headphone sound fields. He reasoned that normal hearing of sound involves the processing of head motion cues and the acoustic diffracting properties of the outer ear. The wavefront of a sound source arriving at the ear is nearly planar and could be simulated with large-area headphone transducers that covered the ears. The transducers had to be poor acoustic reflectors to prevent sound reflection between the transducer and the head and ears, and to be free-air mounted so as not to form a semi-enclosed resonant cavity with the ears.

electro6.gif
Figure 3

The Plates

Figure 3 is a detailed illustration of the Wilson transducer. The size of the plates was chosen to be large enough to overlap the ears and give the desired bass resonance frequency to the diaphragm. Wilson used paxolin boards (4.75″ x 4″) with holes that comprised at least 20% of the total area and spaced closer than the shortest wavelength to be reproduced. .

The smoother side of each plate was made conductive by first applying a stripe of high conductivity paint over the surface to the edge of the plate to be the connection point for the brass shims that carry the signal source (the shims could also contact the graphite directly, without the paint). Wilson then covered the perforated area of the plates with a thick coat of colloidal graphite (Aquadag), being careful that none of the paint or Aquadag would spill into the holes. Once dry, the surface was polished with a dry cloth and blown clean. A flame was applied to the surface just before assembly to remove any remaining dust or lint.

The Spacers

The spacer material should have uniform thickness and be an excellent insulator. Wilson used acetate sheeting with a 0.04″ thickness, which produced 90dB SPL (free field – the level is about 10dB higher in an artificial ear) from 30Hz onward. The output increased to nearly 100dB by reducing the thickness to 0.025″, but only above 60Hz due to restrictions on the diaphragm excursion. For each plate, Wilson cut four rectangular pieces of acetate that formed a frame with the same outer dimensions as the plate. After gluing the spacers to the plates (Evostick adhesive), he drilled the assembly holes around the spacers and applied a stripe of high conductivity paint to the inner edge of the spacers for connecting the bias supply.

The Diaphragm

The factors affecting the resonance frequency of the diaphragm are size, shape, mass and tension. Wilson’s diaphragm was formed from a sheet of 0.0005″ thick plastic foodwrap (Vitafilm), which gave the assembled transducer a free-air resonance of 50Hz (damped to about 30Hz). When the transducer was placed against the ear, the resonance frequency was further reduced due to the increased effective mass of the trapped air.

Wilson put a conductive coat of colloidal graphite to both sides of the diaphragm, so that it would hold a charge. The resistance of the coating had to be in the range of 100M to 10G ohms (as measured between two parallel electrodes 1″ long and separated by 1″). Too low a resistance would result in charge migration during signal movements and a loss of linearity.

To apply the graphite, Wilson first pressed the plastic sheet onto moistened glass with a rubber roller. When the top of the plastic surface was dry, he used a piece of cotton to rub on colloidal graphite, rubbing until nearly all of the graphite was removed. When the coating reached the proper resistance, he turned over the plastic sheet and coated the other side (rubbing carefully to avoid damage to the first coat).

The diaphragm was then glued to the spacers (Evostick adhesive) on one of the plates and was pressed between two flat surfaces to dry (the glue should not touch the connection between the diaphragm and the conducting stripes on the spacers). Wilson put the diaphragm assembly under a hot grill for a few seconds to tension the plastic (a fan heater with restricted air flow would also work). The Vitafilm tensioned in a consistent manner, so Wilson concluded that the resonance frequency was constant for same size diaphragms.

The two halves of the transducer were joined together with 6BA nylon nuts and bolts and brass shims inserted to make contact with the conducting stripes. Note: both sides of the diaphragm are charged by the bias voltage. Wilson used a single brass shim for bias supply by “nicking” the edge of each diaphragm so that the conducting stripes on both sides were in contact.

Acoustic Damping and Final Assembly

electro7.gif
Figure 4

Without foam acoustic damping, the frequency response of the Wilson transducer was not very flat (figure 4). Wilson sandwiched the transducers between two layers of 4mm foam, which served as acoustic damping and were held in place with rubber bands. Adding additional layers of foam did not improve the response. He fashioned a 12″ x 0.5″ strip of 16-gauge aluminum into the headband with a slight twist at each end to hold the transducers flat against the ears.

Wilson set the bias voltage for each transducer, so that when he blew the diaphragm in the direction of one of the plates, it returned to the central position. The source of the bias voltage was from the high voltage power supply of a 15W tube amplifier (375V), which had been converted to drive the electrostatic headphones directly (see below more details about the amplifier connections). Note: to avoid excessive capacitance, Wilson bundled the transducer wires neatly in parallel, not twisted. The capacitance of each transducer is about 80pF.

The Harvey Electrostatic Headphone

electro8.gif
Figure 5

Philip D. Harvey designed an electrostatic headphone that featured a small frame around the transducer to extend the low frequency response (figure 5). He called the frame a “transmission tunnel,” which was bolted to the transducer with plastic screws. The tunnel was molded from polystyrene plastic and lined with latex rubber foam for acoustic damping.

The Plates

electro9.gif
Figure 6

The plates are made from singled-sided copper-plated fiberglass board. Harvey drilled 3mm holes, spaced 5mm apart, in the plates, such that the holes comprised 30% of the total plate area (figure 6). He removed a 2mm copper border around the edge of each plate and the bolt holes to prevent charge leakage if the diaphragm tore.

electro10.gif
Figure 7

To form tags on the plates for making safer high voltage connections, Harvey clipped a corner on each plate (an alternate corner on the second plate) and both corresponding corners on the spacers (figure 7). When the spacers and plates were stacked, each plate had an exposed corner for soldering a connection. The connections were insulated with Plasticine.

The Spacers

The spacers are cut in a single piece from a sheet of 0.37mm thick polyvinyl acetate (see figure 7). Harvey experimented with different spacer thicknesses. With thinner spacers (0.18mm and 0.25mm), the acoustic output increased, but the airgap tended to ionize on humid days (the ionization manifested itself as low frequency clicks).

The Transmission Tunnel

electro11.gif
Figure 8

The transmission tunnel is a type of earcup for mounting the transducer assembly (figure 8). Harvey cast the tunnel from polystyrene with a two-part wooden mold that was overwaxed for easy removal. Tunnels made from colored polystyrene turned out to be more sturdy than the clear polystyrene versions. He did not specify the depth of the tunnel, but denoted it as “short.”

The Diaphragm

For the diaphragm, Harvey selected a thin, light film made by the Borden Chemical Co. (15u thick p.v.c. sheeting with a resistivity of 109 ohms). To prepare the diaphragm, he constructed a wood frame (200mm x 250mm) over which he stretched and taped the plastic film (smoothing any creases). The frame was placed over a slightly thicker piece of glass (240mm x 190mm) to support the film. Harvey rubbed colloidal graphite (Aquadag) over the plastic surface until it had a resistivity of 108 ohms – (he used the same method as Wilson for measuring resistivity). Unlike the Wilson diaphragm, the Harvey diaphragm appears to be coated with graphite only on one side.

Acoustic Damping and Final Assembly

electro12.gif
Figure 9

To connect the bias supply to the diaphragm, he enlarged a bolt hole in one of the plates and the corresponding hole in one spacer (the lower plate and spacer) to accommodate a brass bush, which when inserted into the plate-spacer, made electrical contact with the diaphragm (figure 9). Harvey assembled the transducer by first taping the diaphragm (graphite side up) over the the upper spacer with double-sided tape. The lower spacer and plate with the brass bush went over the diaphragm. Then, he positioned the transmission tunnel over the lower plate, clamping the bias supply wire in between and in contact with the brass bush.

Nylon nuts and bolts completed the assembly. The diaphragm was tensioned with warm air and the tunnel’s inside walls lined were with latex foam rubber (polyurethane foam) to dampen cavity resonances and insulate the ear. Harvey constructed two amplifiers (tube and solid state versions – see the section on electrostatic headphone amplifiers) for driving his headphones. Harvey tried bias voltages from 200V to 600V, which gave increasing acoustic output, leveling off above 600V. The finished units had a bias voltage of 300-350V.

electro13.gif
Figure 10

The Pollock Electrostatic Headphone

Neil Pollock sought to make an electrostatic headphone that could produce more realistic sound pressure levels. Most electrostatic headphones of that time (1979) had a bias voltage of 400V or less and a minimum spacer thickness of 0.5mm. These could generate a maximum free field r.m.s. sound pressure of about 93dB, whereas some musical recordings sounded best when the headphones could reach 100dB or more. Pollock designed a transducer with a bias voltage of 800V to 1300V (as well as a matching amplifier, discussed below) that could output over 100dB SPL.

The Plates

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Figure 11

The four plates (figure 11) are cut from a sheet of 3mm thick Perspex acrylic. Pollock stacked the plates and drilled a matrix of 3mm holes through all four plates. He drilled a countersunk hole in one corner of each plate so that a M2.5 or M2 brass screw would lie slightly below the surface. All of the holes were deburred and the plates were masked before applying the Aquadag. The brass screws were attached with connecting tags and then the resistance between the tag and any point on the plate measured. If the resistance was more than 10K ohms, he applied additional coats of Aquadag. Finally, he covered the Aquadag with a coat of clear polyurethane varnish to prevent ionization in the airgap during periods of high humidity. The dry varnish was sanded slightly to reduce the surface gloss, which tended to stick to the diaphragm.

The Spacers

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Figure 12

The spacers (figure 12) were built by layering sheets of drafting film, laminated to a 0.8mm thickness with rubber cement. After cementing the spacers to the Aquadag side of the plates, Pollock drilled countersunk holes for the diaphragm. Each pair of plate-spacers was positioned face-to-face, and the assembly holes drilled. He painted the spacers with Aquadag to the inner edge of the spacer and into the countersunk hole to provide electrical contact with the diaphragm (taking care that no Aquadag should spill into the assembly holes). After installing the diaphragm contact screws, Pollock checked that there was a resistance from the connecting tags to all points on the Aquadag.

The Diaphragm

Unlike the other diaphragm designs, the Pollock diaphragm is not coated with graphite, but is used without any coating. The diaphragm material is 0.0127mm thick food wrap film, similar to Vitafilm. So long as the diaphragm contacts are made as shown, the film’s own high surface resistance is adequate to hold a charge.

Pollock began assembling the transducer by stretching and taping the plastic film (smoothing out any wrinkles) over a piece of rigid cardboard that had a cutout larger than the plates. Then he pressed the diaphragm between the two plate-spacer assemblies and bolted the plates together with nylon nuts and bolts. The excess film around the plates was trimmed with a razor blade.

Acoustic Damping and Final Assembly

electro15a.gif
Figure 13

To test the transducers, Pollock connected the bias supply (set to the minimum of 800V) to the diaphragms, and checked them for centering. If a diaphragm moved to one side or oscillated, he heated it with a light bulb to tension it. The transducers were then wired into headphones, and silicone rubber applied to insulate the exposed contacts. He made acoustic dampers from 6mm foam plastic, glued (or sewn) into pouches that enclosed the transducers. With the dampers, the frequency response of the transducer is 30Hz to 40kHz ± 5dB and down to 20Hz when measured in an artificial ear (figure 13).

electro.gif

The headband came from an old pair of headphones. Pollock attached an acrylic bridge between two of the assembly screws that protruded from the foam damper of each transducer to mount the headband. Each transducer has an approximate capacitance of 100pF. To minimize capacitance, he loosely bundled the wires between the headphone and amplifier (as opposed to twisting them together) and kept the resulting cable less than 1.5m in length.

Once the headphones are assembled and connected to the amplifer, the bias voltage is increased to the point just before the diaphragm collapses or the airgap ionizes. Pollock was able to set a maximum bias voltage of 1,300V on his units.

ELECTROSTATIC HEADPHONE AMPLIFIERS

The impedance of an electrostatic headphone is primarily capacitive. Step-up transformers that can provide sufficient voltage to a capacitive load are difficult to manufacture to manufacture and to find. Direct-drive amplifiers may be a more practical solution, if they can handle capacitive loads and have high voltage gain. Although the following electrostatic amplifier designs are more complex than those for dynamic headphone amplifiers, they are not exceedingly so – the requirement of high voltage power supplies notwithstanding.

electro16
Figure 14

Wilson drove his headphone with a commercial 15W push-pull tube amplifier (a Radford STA 15) that had been converted for electrostatic headphones (figure 14). The audio signals for the plates were taken from the anodes of the amplifier output stage. The Radford had a power supply of 375V, which Wilson tapped with a 10M resistor for the bias supply. It ran without a load connected to the output transformer for maximum voltage swing, but adding an output load may be preferable in some cases for amplifier stability. Further, some tube amps may balk at providing maximum output continuously to an electrostatic load in this manner. Harvey tried the circuit with his electrostatic headphone and could not eliminate the intermodulation distortion, which was audible even at low levels.

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Figure 15

Instead, Harvey built two dedicated amplifiers to drive his headphones, one tube-based and the other solid state. The spacer thickness used in his transducers was 0.37mm, which limited the voltage between the diaphragm and either plate to about 1000V. With a diaphragm bias voltage of 300V, the plate voltage could go as high as 500V and still have a safety margin against ionization on humid days or from signal surges.

electro18.gif
Figure 16

The amps are designed to output between 300V to 400V peak and have a similar topology: a differential input stage feeding a push-pull output stage. The tube version (figure 15) can generate a 400V peak signal; the transistor version (figure 16) a 300V peak signal. The transistors in the differential stage (Q1/Q2) are matched (they can be any NPN silicon unit with an hfe > 50 at 1 ma. and a VCE > 35V). P1 is adjusted to match the base voltages of Q1/Q2. The collector voltages of Q3/Q4 are set to an average of 115V using P3. Then the collector voltages are balanced with P2 and the process repeated until the collector voltages of Q3/Q4 are at 155V.

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Figure 17

Pollock devised two electrostatic headphone amplifiers based on the National Semiconductor LM3900N current-input opamp. The standard bias version (figure 17) is for an earlier electrostatic headphone that he built based on the Wilson transducer and can be driven to full power from the standard headphone outputs of a stereo receiver or preamp. It produces a 300V peak-to-peak signal with 1.0% harmonic distortion at 1kHz. The amp has a frequency response of 10Hz-40kHz (-3dB) and a power bandwidth of 10Hz-15kHz.

The output stages are class A. IC1a is an inverting stage to produce an opposite phase output. R1 compensates for the small signal resistance of a diode in the non-inverting input of IC1b. If the headphone capacitance is greater than 150pF, R2 and R3 should be reduced to maintain the power bandwidth and the transistors should be heatsinked. The value of Rx is missing in the original schematic, but is estimated to be about 2.4K ohms from the similar topology of the high-bias version of the amplifier. P1 and P2 are adjusted so V1 and V2 are at one-half the supply voltage.

electro19.gif
Figure 18

The high-bias version of the Pollock amplifier (figure 18) can generate 1400V peak-to-peak at 5kHz with an input sensitivity of 2.8Vrms for maximum output. The circuit topology is virtually identical to the standard-bias amplifier. Of special note are the output transistors, which must have VCE ratings in excess of 1000V. Pollock chose transistors that are used in television horizontal deflection circuits. These have peak VCEs in the range of 1.5kV. The specified device is a Matsushita 2SD200. Substitutes include the BU206, BU209A, MJ105, PTC146-RT and SK3115-RT.

electro20.gif
Figure 19

Pollock built the high and low voltage sections on separate circuit boards to reduce the risk of instability and damage from building errors. Q1 and Q2 were heatsinked. The signal ground was taken from the source to avoid ground loops. If the amplifier shows instability, C1 can be increased to compensate. The power supply was installed in a ventilated, grounded, metal case. The high voltage section employes a half-wave voltage doubler (figure 19). The low voltage supply is decoupled at the amplifier with 0.1uF ceramic capacitors next to each opamp.

Addendum

9/10/99: Added new figure 17. Also made various corrections and additions to text.

References
Harvey, Philip D., “Electrostatic Headphone Design,” Wireless World, Nov. 1971, p. 527.
Pollock, Neil, “Electrostatic Headphone Amplifier,” Wireless World, July 1976, p. 35.
Pollock, Neil, “Electrostatic Headphones,” Wireless World, Nov. 1979, p. 51.
Wilson, J.P., “High Quality Electrostatic Headphones,” Wireless World, Dec. 1968, p. 440.

c. 1999, Chu Moy.