It has an auto-EQ function that uses a calibrated mic in conjunction with the real-time analyzer to adjust the 61-band equalizer to flatten the frequency response in a room. I use it to good effect with my speakers in a smallish listening room.
I thought it would be fun to stick the RTA mic (it's about the diameter of a pencil) inside the earcup of the Stax sr202 and let it attempt to auto-equalize. It plays pink noise through one channel at a time as it adjusts the equalizer to get the desired response curve. In my case I went for a flat curve between 100 Hz and 16 kHz. It will ignore below 100 and above 16k if I set it this way. The manual recommends not EQing below 100 Hz so I took their advice although it worked fine with my room EQ down to 30 Hz.
I looked at the resulting two EQ curves and threw out dis-similar points at the high and low frequency ends, and just retained the mid-range part of the curve that looked nearly identical between the L and R channels. This I figured was the most significant part of the correction and the fact that it looked similar in both channels led me to believe it was a good measurement.
See the resulting EQ curves below. I stored this curve in memory under the name of "Stax EQ". I also have a "Stax Flat" setting stored which does nothing (EQ is 0 for all frequencies). I can switch back and forth between the 2 rapidly. In fact the DEQ2496 stores around 100 such settings in memory - the complete state of the device is stored each time.
So what difference did it make on the sound? When I listen to the EQ setting and go to the Flat setting it sounds like I hear a "cupped hands" sort of resonance in the non-EQd version. Switching back to the EQd setting removes this resonance and it indeed sounds flatter. Of course it is easy to fool the ear into hearing what you think you should hear. Perhaps the flat setting is really flat after all and I am introducing an anti-resonance (suck out) with the EQ. I will do more listening and see if I still think the EQd version sounds better. It also may be that introducing the mic into the earcup modified the frequency response since it is such a small chamber and the mic takes up a not insignificant portion of the total volume. Surely Stax has much better techniques and equipment than this - I am just playing around with what I have and should probably trust that the engineers at Stax got it right!
I can bring the EQ and phones to the Houston meet in October to demonstrate. I can even auto-EQ anyone else's phones should they want to try it, although you need to be in a QUIET environment (I had to shut the A/C off) or the auto-EQ says there's too much ambient noise to do the measurement.
The DEQ2496 costs $300 new, I got mine for $200 since it was a returned unit.