Audio-Technica ATH-AD700 Correction Circuit

These are mid-priced (~$150) "Open-Air" headphones which have strong following among head-fi enthusiasts. Among the general consensus are high-resolution, airy and transparent sound. I heard them first when JP Howard  brought them to my house a few years ago and was immediately impressed.

I guess being open-aired they do not have to deal with back pressure from the typical cups, and for me the appeal is dipole-like neutrality. There is less fatique because the ears would not be pressurised by the bass too much. The disadvantage is, of course, other people will hear the songs you are playing!

Upon hearing the headphones after their arrival, I noticed they sound too bright for my liking. Hence I measured them as per above photo.

From the impulse response we can see that the headphones exhibit strong resonances at 5khz and 10khz with a rising trend to the frequency response. This explains the bright sound of the headphones.

Raw nearfield measurement of ATH-AD700

Although looking non-flat, these are actually typical response for headphones. They are basically 2" fullrange transducers and would experience breakup at some point. Compare with Stereophile's measurements of AKG K530, Audio-Technica ATH-AD700, Beyerdynamic DT440, and Grado SR80 here.

The response can be improved by utilising passive EQ consisting of 1.56mH inductor. Effectively a 1st order lowpass filter with corner frequency of ~5khz.

Schematic diagram of ATH-AD700 Passive EQ.
The parts can be obtained from Jaycar in Australia, or any other electronics shops.
note: you can also use single 1.5mH inductor from SoundLabsGroup.

Finished Passive EQ

Measured acoustic output of ATH-AD700 when equalised with Passive EQ.
There is very little noticeable loss as higher gauge inductors (0.8mm/20AWG) are used.

Perceptually the headphones now sounds very natural. 

Of course as with all headphones they still exhibit high spatial distortion. That is ... the sound seems to emanate from inside the head. So they are not a true replacement for proper loudspeakers.

Discussions on this EQ are in HeadFi and SNA.

Other measurements of interests:

2nd, 3rd, and 4th Harmonic distortions

Burst response


Below DSP eq was Archived on 29/5/12.
Passive EQ above is preferred due to its simplicity.

These can be improved by applying two notch filters. I do not have separate headphone amplifier on-hand so the equalization process utilised external pink noise. Not ideal, but close. I would revisit this later on.

EQ1: fo = 47780hz, Q = 1.86, Gain = -2.2dB
EQ2: fo = 11,669hz, Q = 1.10, Gain = -8.2dB

Pink noise measurement of ATH-AD700
Blue = Before EQ, Black = After EQ

I use Foobar2000 VST Plugin and TDAe EQ2004P parametric equalizer to prototype the notches.