Revisiting Koss “The Plug” Headphones.

by Chu Moy


[The original modification for the Koss Plugs was a substitution of the cushions only. This revision describes a second modification to mitigate the “tinny” sound quality that manifests itself even after the cushions are replaced. The latest version of The Plugs comes with a variety of ear cushion styles, including cylindrical types. Recent reports indicate that the new cushions may still not provide an adequate seal for some ears.

In addition to the more cushion types, the new version of the Plugs has removable, soft plastic acoustic tubes. This article refers to the original version of the Koss Plugs with the fixed/hard plastic acoustic tubes. The mod can be applied to the new version of the Plugs, but see the project addendum for suggestions and mods specific to the new version.]

When I purchased Koss’ “The Plug” canal-type headphones, I was filled with great expectations. Its cousin, the famous Etymotic Canalphones, retailed for over $300 and were prized by many headphone devotees for their acoustic isolation and clarity of reproduction. Here, for less than $20, the Koss Plugs promised many of the same advantages of the illustrious Etymotic headphones. The Koss packaging loudly proclaimed “isolation to the max,” “custom fit,” “deep bass” and “sounds great.” I could not wait to try them.


Unfortunately, from the moment I first put them on, the disappointment began building. The Plugs fit so loosely that they fell out of my ears with the slightest tug. I tried reversing the funnel-shaped cushions as the instructions suggested, but then they were uncomfortable, and I could feel the hard plastic acoustic tubes pressing against my ear canals. Nor was the acoustic isolation anything to marvel at. I could hear noises around me as clearly as when I had nothing in my ears. And to top it all off, the sound was tinny and there was no deep bass to speak of. I put them away and did not think about them again, until a posting in the HeadWize forums complaining about the poor design of The Plugs led me to think about how to improve their performance.

The poor bass response was at least partially due to the inadequate seal provided by the ear cushions. The original Plugs had only the conical cushions, which were supposed to help “focus” sound directly into the ear. The size of the cushions was too small and the density of the foam too low to be a good match with my ears. The tinniness, though, was most likely a reflection of the irregularities in the treble response of the transducers. The first modification is to create new cushions for The Plugs that have superior sealing characteristics. To smooth out irregularities in the treble response, the second mod adds acoustic damping to the Plug enclosures.

Neither of these mods is permanent. If you don’t like the sound of a particular mod, you can remove it. Each mod can be installed independently of the other. If the Koss cushions fit your ears, then try mod #2 by itself. Although the mods can be done in any order, I recommend that mod #1 is done first, so that the effects of the second mod can be judged with the new cushions installed. These mods may also work for other canal-type headphones that suffer from similar fit and frequency response characteristics. The cushions will work best on canal-type phones that have an acoustic tube about the same length as The Plugs. With shorter length tubes, the cushions will have trouble maintaining the seal.

Modification #1
New Cushions for The Plugs

I based the new cushions on foam ear plugs, and cylindrical-shaped plugs generally have a more effective seal than the conical types when the foam expands after insertion. The shape and the material composition of the ear plugs could affect the sound. It is a good idea to test several brands of ear plugs for the best sound quality, as well as the best individual fit and noise reduction. For example, if The Plugs with ear cushions made from the Flent’s turn out to be bass-heavy, another set of ear plugs with a different shape or composition might result in a more balanced frequency response.

I have not tried the cotton-wax and silicone putty-type ear plugs. Since these types are moldable, they might serve as replacement cushions by wrapping the material around the transducer tubes. Putty-type plugs may last longer than the foam ear plugs, which will lose their ability to recover their shape after about a week or two of constant wear. However, they usually do not attenuate noise as well as foam ear plugs. Pre-molded ear plugs (the rubbery kind) may require additional preparation (such as drilling or shaping) to work in this application.

Figure 1

For maximum acoustic isolation, it is important to get foam ear plugs that fit snuggly and have a high noise reduction rating. The noise reduction figure is usually prominently displayed on package. I chose Flents ear plugs (figure 1) that reduce ambient noise by 29dB. A Flent’s box containing 10 pairs of ear plugs costs about $4.00 and is sold in drugstores. The ear plugs should be long enough to cover the length of the acoustic tube, although they may have to be shortened later during testing.

A note to the style conscious: most ear plugs are white or beige. There are colorful alternatives, although flashy foam ear plugs are not easy to find. In addition to colored foam plugs, pre-molded ear plugs that are sold in a variety of colors and shapes. However, non-cylindrical ear plugs may not be physically suitable as ear cushions for the Koss Plugs, and the sound quality, fit and noise reduction of the ear plugs should not take a back seat to style.

My original method for making the holes in the foam ear plugs was to use a large sewing needle to pierce the length of the ear plugs and ream a hole. However, this method was both tedious and messy, and resulted in a rough finish. Some DIYers have reported that an electric hobbyist drill (such as the Dremel) does the job nicely. I don’t have a hobbyist drill, and my Fiskar’s hand-drill would compress and get stuck in the foam material.

Trevor Walton emailed me with the idea of using a hot nail (held with pliers and heated with a torch) to melt a hole in the ear plugs (see the addendum). Mark Calder followed up with an email saying that the hot-nail method worked beautifully. The nail does not need to be red hot. He held the nail with pliers and heated it with a match instead of a torch. I didn’t have any nails handy (at least none that were thin enough for this application), so I adapted this idea for use with a soldering iron as a heating element. I call it the “heated needle” method.

Figure 2

First, make a “needle” from a 4″ length of solid 22ga. wire. Strip off the insulation from about 2 inches and wrap the insulated length around one jaw of a mini needlenose plier. Bend the exposed wire so that it is straight and perpendicular to the pliers (figure 2). This is the type of needle that I first used. If it seems too flimsy, try a thicker gauge wire or twist two lengths of 22 ga. solid wire together. Twist the wires together just enough to form a sturdy needle.

Figure 3

A book cover can serve as a work surface for positioning the ear plug. Center a piece of double sided tape on the book cover, and gently put the ear plug on tape. Apply only enough pressure to anchor the ear plug on the tape – or the plug may become permanently attached to the tape. Choose ear plugs that are as close to perfect cylinders as possible. Squished or mis-shaped plugs may be corrected by tugging and pulling at them.

Figure 4

The goal is to make a single hole for the Plug’s acoustic tube that is centered all the way through the ear plug. The same hole is formed twice to ensure that the opening has not closed back up and to correct any mistakes. Make the hole by holding the needle perpendicular on top of the earplug, and centering it. Apply a hot soldering iron to the needle and slowly push the needle through the earplug until the it hits bottom, keeping the needle straight and perpendicular all the way down. The soldering iron must NOT touch the foam. Pull the needle out. Carefully lift the ear plug off the tape, turn it over and put it back on the tape. If the first hole is correctly centered, then repeat the process by inserting the needle through the same hole. If the first hole is not centered correctly, form the second hole to compensate.

Figure 5

With a 22 ga. needle, the hole will still be too small. Enlarge it with a 3/16″ drill bit, gently pushing it through the ear plug while twisting it forwards and backwards between your fingers. As a safety precaution, it is a good idea to put the heated needle back into the hole one more time to “cauterize” any loose bits of foam. The hole should be just large enough for the acoustic tube to go through, but not allow the cushion to fall off.

Adjusting the New Cushions

Figure 6

When installing the new cushions, the shiny end should face out and be flat with the opening of the acoustic tube, but not extend beyond it. Examine each end of the ear plug – one side is shinier than the other. Stephen Lafferty says that the shinier side inserts into the ear canal more easily. Apply a utility knife to the other side of the ear plug and cut off about 1/8″ so that the cushion installs flush with the acoustic tube.


Put on The Plugs one at a time. First, squeeze the cushion all around the acoustic tube to flatten it. Then insert The Plug into the ear canal and hold it there for a few seconds until the foam expands. Test the new ear cushions by listening to a variety of music. Be prepared for the near lack of ambient noise and the “dead quiet” background of these headphones. If The Plugs sound muffled, it may be because the expanded foam is partially covering the transducer tube inside the ears. First, try pushing the cushions back until the transducer tubes protrude slightly. If the sound is still muffled, bevel cushions by trimming a small amount of foam off the top along the outer perimeter of the cushions. If the sound is still wanting, then trim back the length of the cushions by a millimeter or so. Do not to trim too much.

Modification #2
Adding Acoustic Damping to The Plugs

The Koss Plugs with and without the new cushions have been the subject of some discussion in the HeadWize forums. One frequently raised complaint about the sound quality was a peak in the lower treble that made listening to The Plugs for long periods very fatiguing. I wondered if I could change that as well. My first thought was to replace the original Koss Plug transducers with better sounding ones (as suggested by “Strap” in the forums). Unfortunately, the transducers have to be 13mm or they will not fit the Plug enclosure. Strap used transducers from Sony E837 earbuds, which at 13.5mm are too large. He somehow managed to cram them in. In general, earbuds with 13mm transducers are not common except in the budget models. The only ones I could find were in the EarHugger A1000; the A1000 sounded terrible. Even if I could find earbuds with 13mm transducers, I did not want to spend too much money on replacement transducers.

Since I would not be able to substitute transducers, I thought about altering the frequency response of The Plugs themselves. One common cause of frequency response irregularities in headphones is underdamped transducers and/or a resonant enclosure. Several mods had been posted in the forum to address this issue. For example, Bob Horn suggested adding mass to the enclosure by drilling a hole in a penny coin and putting the coin on the acoustic tube before installing the cushions. Since The Plugs have a vented enclosure, I could dampen the transducer’s response by acoustically loading the vent holes with some earbud cushion foam or polyester batting. This method has the advantage of not increasing the weight of the Koss Plugs and dampens both the Plug housing and transducer.

figure 8

The acoustic foam for my mod came from the EarHugger A1000 cushions. Other foam cushions should work equally well. Select a thin cushion material – it is not necessary or advisable to spend money on thick, “high quality” cushions. A tiny amount of polyester batting (from a pillow or comforter) works as well. To disassemble a Koss Plug enclosure, gently slide the edge of a pocket knife along the enclosure’s blue/yellow seam line where the front and back parts meet until it “slips” in. Then rock the knife edge slightly to open the enclosure. Be careful not to damage the transducers!

figure 9

Cut a 3/8-inch foam square from the earbud cushion or polyester batting. [If using batting, it should be teased out a bit – pull it with fingers – first to reduce the density a bit. Then cut out a thin 3/8-inch square of the batting.] Insert the foam square behind the transducer over the enclosure’s vent holes. Reassemble The Plug enclosure by snapping the front and back parts together. Leave the other Plug enclosure unmodified for now and audition The Plug headphones with a music source. The size of the foam square will affect the degree of damping. It will smooth out the upper frequency response, but it will also augment the bass response. If the foam square is too large, The Plugs will sound muffled. If necessary, reduce the size of the foam square to achieve the best balance between the bass response and treble damping. Once the sound of the modified Plug is optimized, apply the same mod to the other Plug enclosure.

figure 10

Even when optimized, the bass response of The Plugs may very strong and have a slightly loose or “tubby” character. If you like the sound of The Plugs at this point, then you need not go further. The next step of this mod is to restore some balance and control to the bass frequencies and is based on a mod for the Sony MDR-EX70 headphones described by “Neruda” in the forums. Cut a strip of the foam 1/8-inch wide by 1-inch long (polyester batting may also work, but I have not tried it). Cover the opening of the acoustic tube with it and secure the foam against the acoustic tube with a piece of adhesive tape or some superglue applied near the tip of the tube. Trim any excess foam strip. The superglue is the best method (thanks to Tom Rons for this suggestion – see the addendum) because the tape can come off. Add this modification to the other Koss Plug and audition the headphones. If the treble is too muted, try pulling the foam tighter over the acoustic tube or reduce the width of the foam strip so that a small bit of the acoustic tube’s opening is exposed.

The Results


The final assessment: quite listenable! These mods together demonstrate the great potential of the Koss Plugs. I don’t claim that the modded Plugs will trounce the Etymotic canalphones, but they do a very credible job. I imagine that they are an unbeatable value for travel headphones and for listening in any environment where acoustic isolation is important. Because of cord noise (a problem with all canal-type headphones), I do not recommend The Plugs for jogging or other activity which causes the cord to thrash about, unless it can be immobilized (such as by pinning it to clothing). The modded Plugs are slightly less efficient than the stock version, and seem to be missing the highest octave of treble and transparency.

Nevertheless, I think that the modded Koss Plugs will please very much – especially when compared to the originals. Where The Plugs before were loose-fitting, they are now molded to the ear canals for a true custom fit. Where The Plugs before had poor acoustic isolation, external noise is now substantially attenuated. Where The Plugs before had a bright fatiguing sound with no low end, they now sound balanced with a clear and strong bass response. And despite the slight drop in efficiency, they still run plenty loud from portables. I particularly recommend these mods for current Plug owners. Anyone who is dissatisfied with the sound of The Plugs should try these modifications. Since the investment in materials and effort is so minimal, modding the Koss Plugs is like getting a new pair of quality headphones for the price of a bus ride.

c. 1999, 2000, 2001, 2002, 2004 Chu Moy.


12/13/99: Added figure 4 and section on adjusting the new ear cushions.

12/15/99: From Sebast on the MiniDiscussion board: My improved plugs work much better!!! You can also try to cut off about 2 mm of the yellow acoustic tube if you have shallow ear tunnel like I do…

12/20/99: From John B on the MiniDiscussion board: Top idea. Just modified my “plug”, and it is way better. Better fit, stronger bass and better isolation.

1/7/00: From Jerry Johnson: I couldn’t wait to try your suggested mod for the The Plug headphones. I had sought out these phones for 2 months, looking for a headphone that would sound good and not “sound leak” while listening in bed late at night – don’t want to disturb the wife. I thought the Plugs would be the answer but out of the box they were clearly lacking due to the poor fit of the pads. Now, with your suggested mod, they are finally listenable…. Thanks for the tip!

1/14/00: JKaiser in the HeadWize DIY forum recommends using a round toothpick to make the hole in the ear plugs and then use a drill bit (not a drill) to enlarge the hole. Complete instructions are in his forum posting.

5/1/00: JonR in the HeadWize DIY forum suggested this idea for making the ear plug holes: Although reversing the Koss foam pieces worked well for my ears, I still wanted to make custom plugs, so I followed these instructions. But with the brand I use (my favorite for sleeping and on the bus) the hole wouldn’t stay open. So I inserted a piece of electrical wire insulation and now there is a rigid “hole” and it stays open; the Koss tube is an exact fit inside the insulation.

7/7/00: Trevor Walton writes: Ran across your page today, didn’t realize there was a page describing that mod. Doing that was the first thing that occurred to me after buying them, not surprised the same idea has occurred to others… Anyway, to get to the point, have you tried using a red hot nail heated with a torch to simply melt a hole in the plug? That’s how I did mine and it works quite well – smooth, clean hole. It is nearly effortlessly. Just gotta be careful not to burn yourself…

10/9/00: Leon Werenka had these suggestions for punching holes in the ear plugs:

– a leather hole punching tool – it typically looks like a handheld paper hole punch that has a wheel with 4 or 6 various hole sizes that can be rotated and punched.

– hardware stores sell the two pieces needed for putting snaps in clothing (like the front snap on blue jeans). Before they are compressed with a tool, one piece looks like a little funnel with a tiny hole. The edge is actually needed to punch through the cloth in the installation process. One of these could be purchased for a few cents and easily be pushed through the ear plug against a hard surface.

5/24/01: Mark Calder suggests that DIYers who have constructed the Koss Plug replacement cushions with a drill bit may want to “cauterize” the interior wall of the hole to prevent any foam bits from coming loose and lodging in the ear canal. Since the acoustic tube of the Plug presses against the interior wall of the cushions, I don’t think it is easy for foam bits to come loose, but cauterizing the hole is a good safety precaution. The cauterization can be done with a hot nail (see Trevor Walton’s suggestion) or with the simple heated needle method described above.

5/27/01: Major revision of article. Added description of heated needle method for making holes in the ear plugs. Also, added section on damping the Koss Plug transducers (modification #2).

5/27/01: “Duncan” in the forums reports on the latest mod (which was posted in the forums prior to this article update): I’ve just done this mod (not as yet done the first one) and you are right, it does seem to equalise the sound. Admittedly I wasn’t very scientific about it (ripped an earpad in half and placed it underneath the wire by the vent) but what you get out, as you say is quite listenable… not fatiguing (imo) at all anymore.

8/7/01: Richard Petrilla made replacement cushions for the Koss Plugs from Smith & Wesson “Quick-Fit” ear plugs, which cost about $5.00 per set at Walmart. He writes: The plastic cord between the two sides easily slides off and this leaves a guide for you to bore a hole. You can use a drill, but I would suggest using a hot piece of straight coat hanger. My holes ended being very straight with this method. There is very little melted plastic mess if you do it quickly. I also cut the base just a tad to get the plug at its fatest part.

My plugs have a removable acoustic tube and no mute button. It took me a while at first but now I could do a pair of replacement cushions in five minutes. The cushions are installed on the acoustic tubes up through the middle.

Now for the sound. I like the isolation that the plugs provide. I used mine a few times on the plane and it blocks out a good portion of the outside noise. As typical with other in-ear plugs, the sound can change quite a bit by the way they are worn. If you leave them out a bit, they sound lean. If you push them in farther, they get bass heavy. I did eventually find a good balance and they sound respectable for the $20 that they ended up costing me. I find these to be more comfortable than the foam cushion pads but others may not.


8/7/01: Forum member Mail4U tried the mods on the new version of the Koss Plugs (removable acoustic tube, no mute switch) with these comments: I did the complete cmoy mod – this needs to be done or it sounds very tinny. With the cmoy modification the treble smooths right out, though accurate bass is still a problem with the foam ear plugs. The midrange and treble to me are very liquid and non-fatiguing with the mod.

I replaced the foam mod with the Etymotic ER20 ear pieces ($10 + $5 shipping). Bass much clearer and isolation is excellent. Generally very smooth non-fatiguing sound. For total $30 cost can’t be beat. Think it gives a lot of the under $100 phones a run for the money – the cheapskates Etymotic ER4P!”

12/9/2002: Jason Carr freezes his earplugs before drilling them. He writes: For getting a perfect hole into foam earplugs, I compressed my foam plugs as flat as possible (end to end), and held them underwater while allowing to expand to them with water. I froze them, which allowed for a very clean drilling. Allow to thaw/dry, then mount as usual. Yippee! Perfect hole, straight, lovely.

The main advantage of this method is that the earplug is hardened (for greatest accuracy and ease of handling), and does not pick up soot from heated metal objects. The perfect and potentially larger gauge hole allows the plug to be kept at normal length for comfort and secure fit while not getting crimped as can happen with smaller-diameter holes.

12/7/2002: Tom Rons writes: I bought a pair of Koss The Plug earbuds, because I have been wanting earbuds that went straight into my ear for a loooong time. I’m simple not satisfied with the sound level regular earbuds direct into my ear.. and everyone else on my bus ride. Immediately after I had placed an online order (the earbuds aren’t available anywhere near me), I started looking around for sites with some more pictures and information on the sound quality, as I usually do (I always get obsessed with things like this for a while). Excited as I was, I stumbled upon your page (thanks Google!), and read about your mods.

I must say, at first I was very sceptical. I’m 17, and I have a mentality that goes either you do it right or you don’t do it at all, so I wasn’t planning on doing these mods at first. Also, because you stated the earbuds would be slightly less efficient after the modification. I also didn’t think it would be necessary for me to mod them, as I usually don’t hear any differences.

When I received the earbuds, I was very excited. I ripped the package apart and put The Plugs into my ears, ‘Plugged’ them into my sony NW-MS9 and hit the play button. After being deafened for about 3 seconds (the volume is always at max, which was pretty silent in my opinion, using all kinds of regular earbuds from whatever brand: Sony, Sennheiser, you name it!), I turned down the volume to about 60% and noticed the sound was just horrible. I usually kick on loads of bass, but not in this case. It was as if every bass kept echoing into my ear canal for a few seconds.. I figured if I wasn’t going to try and mod these earbuds, I wasn’t going to use them at all, like you did at first.

I printed out your project page and started gathering what I needed, aside for the foam ear plugs, the conical ones that came in the package fit me great for now! I used circular cut foam from my old Sony earbuds (the cheapest model with Twin Turbo circuitry) to balance out the bass and further dampen the sound that could escape through the vent holes. Then I used a drop of super glue to attach a string of foam over the canal on each side, to equalize the treble and act as a filter against ear wax (my primary concern ;). Not expecting much, I plugged in the earbuds (again, into the Sony NW-MS9) and hit play again, only to find out this was the best output any earbud had ever provided me with. Clear bass responses, hardly any interference for my direct environment, and at 100% volume on the NW-MS9 it gave me more output than I ever expected from a portable audio player (before, I was very displeased with the low volume the NW-MS9 provided). Thanks for a great mod, I’m sure it will continue to please many people in the future!

2/4/2003: The new version of the Koss Plugs has a soft, removable acoustic tube and no mute button. Stephen Runa (a.k.a. “Moonwalker” in the forums) sent in this version of the mod with special instructions for the new Plugs: I posted few times about the Koss Plugs in the past, but now I think I found a way how to mod them so they sound their best. This post will help anybody who tried the mods from Chu Moy’s project article and is still unsatisfied with the Plugs. The new procedures will be explained in detail, the ones included in the projects will be only mentioned shortly.


Step 1: Buy some ear plugs and burn hole through them – the supplied ones are very poor quality (as explained in Plugs mod article).

Step 2: Open enclosure using knife (as explained in the Plugs mod article).


Step 3: Use sticker of cca. 5 mm square size and place it inside the small bowl part where cable enters enclosure. The purpose is to close the rear venting (6 small holes). I tested the Plugs have better sound balance when rear holes are closed. After the rear vents are closed, the Plugs no longer produce the annoying squelching sound of the air-crushed diaphragm, when air is trying to equalize pressure on inserting into one’s ear.


Step 4: Look at transducer – there’s small hole in the middle of it. It’s because the magnet is hollow, but for some reason, in the Plugs the manufacturer decided to block the rear hole with some glue. This make waves of some frequencies assymetrical and worsens the sound. I used pure alcohol and small tweezer to remove the softened glue and free the magnet hole.


Step 5: If you have the new version, there’s soft removable acoustic tube that can be prone to loss. Remove the tube and apply drop of glue to the outer side of the short solid tube. Wait few minutes, then reinsert the soft tube. Don’t use fast drying glue – it’s too strong and you may not be able to detach the tube if needed in the future without damaging whole phones.

Step 6: There’s also small piece of foam on outer diameter on the back side of the driver. Remove it, since there will be of no use because of the much larger foam inserted in the next step.


Step 7: Now complete the enclosures and listen to some full-specrum sounds/music: the drivers are often very poorly matched, so there’s usually more bass on one channel. The side with more bass will need larger piece of foam. Open the Plugs again. Cut a cylindrical piece of some soft foam (diameter=13mm, height=4mm) and put it in the rear enclosure to the channel with more bass emitted. The foam will fit in nicely, expanding to cover entire inner space. Be sure the cable node is under the foam, not touching the driver. This may affect sound quality. Close the modded plug and compare with the other channel.

Now listen and you will notice there’s less bass, more mids and trebles and more balance to the sounds. The other channel was initially less bassy, so it will need smaller foam damping. Use the same diameter (13mm), but cut it so it’s height is only 2mm, or roughly one half of the first piece. Now listen for bass balance of both channels and enlarge or reduce the smaller piece of the foam as necessary to obtain the best balance. Remember: leave the larger foam untouched – the larger, the better (less peaks and muddy, loose bass).

Step 8: Open phones last time, remove drivers, fix them on the table in diaphragm upside position. Use hair dryer on minimal flow setting from close distance (2-5 cm) for no more than 4 minutes. I watched the temperature using contact thermometer, the safe temp is about 93-98 degrees Centigrade. This will loosen any stresses in the diaphragm material, and tighten the voice coil. You can also use the pliers too to hold the drivers in diaphragm upside position for the hair dryer “de-stress” process. Just secure the magnet section (now upside) between the jaws and apply hot air on the driver.

Remember using this procedure only on cheap phones, not on Senn HD-600! Do not use higher flow settings, the hot and soft diaphragm dome may collapse! When this happens, use small, weak sticker to re-form original shape of the diaphragm. After this ‘cure’ the sound of the drivers is much!!! less peaky, less bassy and much more close to each other – easy proof of different stresses in individual diaphragms from the factory.


Step 9: Let the drivers cool down, put together the canalphones and let the bass-heavy music flow through them at their max. allowable rated volume for at least 3 hours. If you hear diaphragm clipping or hitting the enclosure, reduce immediately volume a bit. I used short skewer shallow inserted into the soft tubes to reduce noise coming from these phones on the burn-in phase. (This doesn’t work for old hard tubes – the holes are too small.)


Now you have near perfectly matched drivers in cheap canalphones. Sound is relaxed now, less bassy, more mid present, not fatiguing at all! I wish I did it first day I purchased my Plugs. I hope all of you will be pleased as much as I am!

PS: I’m not responsible for any damage you can do to your equipment/phones/health or any other damage/injury beacuse of proceeding with my guide and making the suggested mods. Happy listening!

2/4/2003: Richard Chacon (a.k.a. orl2222 in the forums) has a mod for the new version of the Plugs: I recently bought the new version of the koss plug. I tried Chu Moy’s modifications. However, on the new models with the removable transducer tubes, they still sounded too “bassy” for my tastes, also the “rubber” transducer tubes didn’t seem to allow a tight fit with my ears, not like my Etymotic ER-4Ps. I then decided to try something.I proceeded to cut off the “tube” of a ball point pen,(making sure it was thoroughly cleaned with alcohol)enlarged one end, and inserted it over the small transducer tubes, cutting it to fit snuggly with the foam ear plugs as suggested by Chu Moy. I was also able to use a couple of Ety “rubber” tips also over my makeshift transducer tubes. The difference was night and day. The boominess of the bass was gone, midrange and treble were smoothed out. If you have the new model of the plug, try this you will be amazed at the difference.


The modified Koss Plugs are hooked up to my Sony D25-S. pcdp. I mainly listen to classical, and jazz. With the Ety 4 rubber earpieces attached, i get more of a well balanced sound. With the foamies, they sound more bass orientated. Isolation is good, blocking out 90% of outside noise. I’ve found that positioning the modified Koss Plugs with wires coming from the top of the ears, rather than the bottom like my Etys, provides better sound and more isolation. I’ve also found that I can listen to them at night, without discomfort while sleeping.

What I’ve done is completely remove the rubber tubes, and enlarge the plastic Pen tube using some small Phillips jeweler’s screwdrivers by heating them up with a lighter, then enlarging the hole so that it fits on the end of the Koss Plugs. Once you take off the rubber tubes from the Plugs, you’ll see what I mean. The replacement “pen” transducer tubes are approx. 1 millimeter in length. I used some super glue to “glue” the pen tube transducers to the Koss Plugs. I’ve found that using the Ety 4 “rubber” ear pieces to provide the best sound to me. The foamies tend to accentuate more bass.

Overall the modified Koss Plugs sound a heck of a lot better than my sony MDR-EX70s. As compared to the Etys, the isolation is just as good. Sound wise, I’d say they are a notch below my Etys, but not by much – a heck of a lot better than any other ear-plug headphones out on the market currently, except of course, my Etys. Put it this way, my sony EX70s cost me about $70. These modified Plugs sound a whole lot better than those. Don’t forget to put in the pieces of old ear foamies behind the transducers. Instead of a pocket knife, I used a single edged razor to open up the koss ear plugs. Also, I’ve found that positioning the Plugs with the wires coming from the top of your ears works best.

I suggest ordering some Ety 4 replacement ear pieces (not the foamies) from HeadRoom for people who don’t have Etys. They are priced at $15 for five sets. Hope this helps. Attached is a picture of the modded Plugs. They do say “Radio Shack” on them, but they are the Koss new style Plugs. I just found them a couple of bucks cheaper at Radio Shack.

6/7/2004: An anonymous submission: Thank you so much for your article on modifying the Koss “The Plug” in-ear headphones. It allowed me to get a relatively inexpensive replacement for my Shure E2c while I send them in for repair. While I’ve found the modified phones to not be quite as good as the E2c, they’re close enough for being a quarter of the price, and I find them much better than the phones that shipped with my iPod.

While modifying my own pair, I found out a couple of things you might be interested in:


1) Shure’s foam sleeves for their E2c fit exactly right on the Koss (or the equivalent Radio Shack earphones, which are the ones I worked with). The sleeves can be had at Shure’s online store, they cost $12 + shipping for 5 pair, and they can be used with the Koss without any need for drilling (see the pictures below). In fact, these sleeves have a reinforced tube around their middle which makes them great for use with the Koss.


2) With the newer model of the Koss, which have a removable acoustic tubes, it’s easy to add foam to cover the opening of the acoustic tube: Just remove the removable part of the tube, put a square of foam over the opening to the fixed part, and squeeze the removable part back onto that. That will hold the foam in place across the opening of the fixed part of the tube without any tape of glue (you might want to use glue at the base of the removable tube if you’re afraid it will fall off). The pictures below give an idea of the process.




6/7/2004: From “soulgirl” in the forums: The old fashioned earplugs that come with mp3 players are far from acceptable as far as comfort is concerned. So I went and bought some ‘in ear’ earphones. I had done my homework and plumped for The Plug.

The insertable canal plug is cone shaped… it is made from a material that you can screw up and it will expand again. Now, the idea is that you squash it to a thin cylindracal shape, quickly plug it in your ear and let it gently expand to the shape of your ear canal. Sounds simple right? Wrong. Ferverently squashing the plugs and trying to insert them before expanding is a feat in itself.

I came across this web page dedicated to the mod of the Plugs. They explained in minute detail, but it still appeared that they were relying on inferior ‘in canal’ plugs. I wanted a true in ear experience that didn’t necessitate the squishing and squashing of spongy objects. I wanted something more akin to the needs of my own personal ear canal.

I looked around the net for something I could mod myself! I found these Mack’s Ear Seals. Yes, I know, they are for swimming, but the shape was right and it was a push straight in affair as opposed to a squish in affair. Of course, they are not supplied with a straight through hole so this needed to be attained before I would be able to hear any music through them.

I looked at the material and it was fairly pliable. I thought the use of a drill would be too heavy and prone to accidental damage. Having a small set of mini screwdrivers I heated up a cross-head over my gas hob and inserted the red hot tip throught the end of the plug. It bore a nice clean round hole that created a through-fare from top to bottom.

They are exactly the correct size on the yellow end to push tightly over the Koss fitment. Now for the real test… to try them on for size! Fiddly to get in if your ears are dry… a little spit did the trick. Slipped right in like long time lovers. The bass was superior to the original plugs – they had a tinny end sound that was unbearable.

Here are a couple of photos of my finished product. Happy earphone modding 😀 – oh, total cost of mod! £6.00. You can buy similar in ear phones for around £200 I think 😀



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