I decided to do an in-depth analysis of the MDR-7506 headphone this evening, since you mentioned this headphone. I analysed the left and right channels, looking for common minor anomolies that can be easily corrected and enhance sound quality in the process.
My objective was not to change the response or signature of the headphone -- only to remove seemingly obvious minor problems.
Note that this analysis is based on one sample of the headphone. I do not have additional sets of this model, in order to draw a statistically valid conclusion of typical behaviour. Execution of the transfer fuctions I am about to specify may or may not be applicable, because of this detail.
The headphone was measured on a jig, and the area that is usually occupied by the ear was filled with a cutout of acoustic foam in order to prevent/reduce interference from reflections from within this cavity. The point here is to analyse and find corrections due to transducer non-linear response.
I recommend three filters(For (A) and (B) Refer to
[1] for measured effect(s); for (C) refer to
[2] for measured effect(s). ):
(A)
F= 4407 Hz
Q= 4.5
G= -3.0 dB
(B)
F= 10300 Hz
Q= 10
G= -3.5 dB
(C)
F= 205 Hz
Q= 5
G= +5.0 dB
Note: (A) and (B) may be utilized with passive line level notch filter circuits. (C) requires an active circuit to utilize. Application of all 3 filters is recommended. If you have available, a 3 or more band, fully adjustable parametric equalizer, the filters should be easy to implement. If you can not select the specific frequencies above, you should be able to choose neighboring frequencies, within 3-5%, and still have sufficient precision.
My subjective impression of the transfer functions applied vs. not applied: In stock response, the 7506 seems to be a little bit more detailed at first impression. This is an artifact of the midrange and treble resonances. With the transfer functions applied, the sound is less fatiguing and more natural by a subtle, but very noticable(after DBTing) amount.
I recommend you do your own ABX testing with the ABX comparator in Foobar or similar before actually applying the functions. I prepared two short sound clips of a jazz vocalist piece. One has been compensated(clearly labeled as such) with the filter specifications I gave above, the other has not. Play these files with all effects or tone adjustements in your hardware or software disabled. The transfer function(s) applied to the compensated file will accurately simulate the effect of a parametric equalizer.
http://www.linaeum.com/downloads/misc/dk_1.mp3
http://www.linaeum.com/downloads/misc/dk_1_compensated.mp3
-Chris
[1]
[2]