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Measurement based equalization of HD650, HD700

post #1 of 8
Thread Starter 

There's been some recent discussion over in the Sound Science forum about new research on the measured and subjective response of headphones, including a revelatory paper (summarized here) on the subjective impressions of equalized frequency responses.


I've been doing a bit of measurements and experimentation with various frequency response curves myself, and wanted to share the results because they have resulted in significant improvements to my Sennheiser HD650 and HD700 headphones. The improvements are so drastic that I could not listen to these headphones anymore without equalization.


The measurements were taken using a MS-TFB-2 in-ear microphone on a dummy head (mine). I've compared the free response of this microphone against calibrated microphones, and it compares very well.


First, here's a graph of the natural and equalized response of the HD700, mounted on the dummy head. The equalized response was predicted using Room EQ Wizard's "Generic" EQ.




The unequalized response matches well with measurements from purrin, as well as InnerFidelity's post-HRTF curves. The equalization target was motivated by the cited paper's findings, and adjusted based on my own subjective impressions. Subjective listening was done using jRiver's parametric eq. The exact settings were:


38hz +4db Q=2

50hz +5db Q=1

2500hz +5db Q=1

5900hz -8db Q=5


Based on the measured response matching the other published curves, my subjective preference matching well with a flat equalized response, and my previous measurement of my own HRTF using this microphone, my conclusion is that measurements taken this way (at entrance of ear canal) matches well with perceived response. Further compensation with HRTF does not seem necessary.


Second, here's the same for the HD650:



The settings were:


38hz +4db Q=2

50hz +5db Q=1

2500hz +1db Q=1


So, the difference in settings is less of a boost at 2.5khz for the HD650, and no removal of the peak at 5.9khz. The equalized curves match well up to 10khz.


After equalization, both headphones have about the same, neutral spectral balance, comparable to my hi-end, room-corrected speaker system. They are both significantly improved by the equalization, the HD700 more so than the HD650. However, that's not to say they now sound the same The HD700 still sounds a significant margin better to me.


Both before and after equalization, the HD700's bass takes the HD650's to school, with more authority while remaining tight. From the curves, we can see the HD650 rolls off earlier. Despite the EQ, I suspect its drivers simply could not respond to the bass boost. In the treble, the HD650 still has a sort of haziness that makes violins sound smoother, less detailed than they should be. I feel that the HD700's after-equalization sound is top notch, perhaps besting the unequalized sound of some of the other top headphones I've heard, like the T1, Q701, PSB M4U2, LCD-3, and perhaps even my former favorite, the HD800, although I don't have those headphones handy for a re-comparison.


As for why there remains a subjective difference besides the bass, my only guess is the remaining slight differences in response, and differences above 10khz, whose measurement are known to be "BS" due to sensitivity to positional effects.


I'd welcome your thoughts and comments.

post #2 of 8

I like the objectivism seen here.  I have been playing around with some Graphical EQ in Foobar with my Denon AH-D2000.  It is hard to tell, but the digital EQ is ever so slightly coloring the sound beyond what I am setting for EQ.


I am starting to enjoy some slight EQ tweaks as it lends itself to reducing fatigue, brightness or darkness, and even sibilance in a headphone.

post #3 of 8
Thread Starter 

What I learned from this experience is that both measurements and listening are required for a proper equalization. The measurements were telling me where the issues are and what to try to correct, but the listening told me how much correction to apply. I wouldn't have arrived at the same settings by listening alone, nor by measuring alone.

post #4 of 8

I still cannot adequately EQ with the Graphical EQ in Foobar without noticing a hint of distortion.  This is with only lowering EQ relative to 0dB.  Sometimes it is subtly, but with tracks from James Brown I can hear the slight distortion.  This lead me to not utilize any digital EQ any further.

post #5 of 8

I hope you're not using the default graphic eq, Blur.

post #6 of 8

I am using the updated Graphical EQ, but if you listen carefully you can still here it color the distort the sound.

post #7 of 8

I tried out your settings for the Parametric EQ in JRiver with my own set of HD700s and HD650s. Loved both settings, and I do agree that the difference in much more pronounced in the HD700 than in the HD650.


It took a while for my ears to 'break-in' to the sound signature of the HD700, but once it did, I definitely thought the HD700 was the better headphone, with a couple of faults.


My two chief complaints about the 700 was the lack of bass impact (though I grew to love the tightness and detail of the bass), and the sharp treble peak at around 6-8KHz. I sorta fixed the treble issue with JRivers Graphic equalizer by setting the 6Khz bar down about 2dbs, but I still had occasional nasty peaks, and setting the EQ at this frequency any lower impacted the sound of music too much. These Parametric EQ settings have soundly fixed both problems, and now the bass has more impact, is still just as controlled and tight, and the overall sound is more rich with only the slightest hint of the treble peak.


Although I did adjust both the 38Hz and 50Hz settings to +3.2db and +4.0db respectively as I noticed that on certain recordings, the bass tended to pop the headphones a bit.

post #8 of 8

Thanks alot JNS. I am very happy with HD700 but the siblance was really penetrating and even painful sometimes. The bass was always good but i just noticed that with your EQ settings the bass sounds so much better. It has much more impact and my HD700 are alot more enoyable now. I created this account just to thank you though i guess i will use it again someday.


EDIT: Haven't had the bass problems yet which BruinAnteater has. But maybe i am listenting to music more silently. I am also using APO Equlizer with my Xonar Essence STX. Works like a charm.

Edited by menuki - 5/26/15 at 8:09am
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