An Equalization Circuit for the beyerdynamic DT990 Pro Headphones.

by LXH2

In my quest for the perfect headphones, I searched far and wide to hear every pair of headphones that I could get my hands on. I heard the Stax electrostatic headphones. I listened to the Sennheiser HD580. Although I auditioned many headphones from a wide variety of manufacturers, I had yet to find a pair of headphones that I thought sounded completely natural and accurate. Here are some of my impressions:

Sony…..sounded like there was some ringing in the high end….different models, different ringing

Sennheiser….not bad at all, but did not quite sound completely natural

AKG……I heard colorations that annoyed me

Stax….. great transient response, but sounded pinched in the high end, and not that comfortable

Grado…..not at all bad, a little too forward for me, not at all comfortable

There were many others such as Koss, Radio Shack, etc…

I was almost resigned to get a pair of Sennheiser HD580’s, but one store had a pair of beyerdynamic DT990 Pro’s. I slipped them on and found them to be the most comfortable headphones I had yet tried, but they had a ridiculous rising characteristic in the high frequencies that made them sound somewhat like they installed an equalizer in the headphones and turned the 16khz control way up. There was no ringing. Just a simple rise in the high frequencies.

After some thought, I bought the DT990 Pros and started tinkering with a passive equalization circuit to correct the frequency response and make it sound completely natural. I finally settled on the exact design and offer it here for those who want a set of headphones that they will find remarkably natural sounding. It is my opinion that with this passive equalization circuit, the beyerdynamic DT990 Pros exceed any other headphone in comfort and natural and accurate sound.

I offer 2 versions of the equalization circuit, the first having 6 db less insertion loss than the other. However, some may not be able to find a .68 microfarad capacitor. The second version uses a more common .22 microfarad capacitor. Both of these circuits operate to reduce the frequencies above 2 kHz with a 6db/oct slope until 15 kHz, where they turn flat once again.

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The source impedance will have a significant effect on the properties of the passive networks and should be less than 50 ohms. These circuits are only for the beyerdynamic DT990 Pro headphones.

I do the final mix for my CD’s on the beyer DT990 Pros, and my mixes sound correct on every boombox, car stereo, minisystem, audiophile system, and puny TV speaker that I have played them on. In fact, I never use speakers to mix; they are quite disorienting. I tried out all the headphones that I could get my hands on, and with this EQ circuit, the DT990 Pros sound more accurate than any others, regardless of price.

Addendum

11/24/2002: Capt. Z modified LXH2’s filter for less treble attenuation. He writes:

beyer_captz

I have bought my DT 990 (600 Ohm version) properly in 1986 or so, after reading a review in the German stereoplay magazine stating, that these were the best dynamic headphones. Well, I can’t remember what they sounded back than, but I do remember than someone noted that these headphones were pretty strong in the bass. Actually, I do remember them sounding pretty heavy in the bass.

After using them for some time, they ended up somewhere in a moving box and did not get pulled out until the mid 90’s, when I replaced the deteriorated ear pads with some artificial leather ear pads made by Beyerdynamic. At that time the DT 990 still sounded pretty heavy in the bass, so heavy that I thought that I needed an equalizer for these headphones, to turn down the bass and up the treble. That was also the time I asked on AudioAsylum and HeadWize.com for some help.

I was advised to buy the new gray velvet ear pads from Beyerdynamic, which I did. Well, I could not believe my ears after I changed the ear pads. The whole sound changed completely. Suddenly the bass was “almost” on the lean side, the mids where very airy and the highs very extended. So far so good. Except I started to realize, that the highs were too aggressive and too much and that this airiness was due to the access treble. Another post on AudioAsylum and HeadWize got me into the right direction. I was directed to LXH2 article on HeadWize.

After reading that, I build myself the equalization circuit version 1. Listening revealed right away, that the attenuation in the highs were way too much for my taste. So I decided to build another circuit, but this time I played around with different values in resistor and caps. I ended up changing C1 from 0.69 uf to 0.10 uF; and R1 stayed the same; R2 was eliminated and R3 remains 22 ohms.

Now I find that the DT 990 sound very balanced to my ears and I believe that they will give me many more hours of pleasure. After the mod I asked my wife to compare the DT 990’s with my old Stax SR-X headphones. Well, after switching back and forth she said: “The Beyerdynamic sound louder. Well, not in volume.” After listening for myself again, I saw what she was hearing. There was a lot more “commotion” going on with the DT 990’s. The old Stax do sound more refined and cleaner.

BTW, the DT 990 are powered by an Amity HPA2 headphone amp.

c. 1999 LXH2.
The author’s website: The Official LXH2 Website.

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