Equalization Circuit

Posted on Jan 12, 2013

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. 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.

Equalization Circuit
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Equalization Circuit - image 1
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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...

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