[Sound Quest]

I was comparing some high-end full sized headphones on the frequency response chart and couldn't help but notice a trend where theres a major dip around the 12khz region.

I'm not all that clued up on high end audio. But is there a scientific explaination for this?

 

[Delirious Lab]

In a nutshell: if you listen to loudspeakers with a "flat" frequency response, you will perceive a dip in high frequencies because they don't travel as well as the low ones.
 
To reproduce this experience, headphones need to roll off the treble or the ear will perceive too much of it.

 

[rhythm is life]

Yeah, all headphones roll off the highs to some extent because of the headphone drivers' proximity to the ear. When I performed a frequency test on my audio-technica M50s, the signal sounded progressively louder from 10 to 12khz, even though the M50 has the typical ~12khz dip. This is because the human ear is more sensitive to ~12khz than 10khz, as illustrated by this graph.

 
So if there was no dip, the 12khz range would be too loud, resulting in squeaky highs.

 

[Sound Quest]

If that's true, then won't the HD800's sound squeeky, because they don't seem to have the 12khz roll off like other headphones?

 

[TMRaven]

Equal loudness contour got nothing to do with the headphone frequency graphs.
 
In short measurements after 10khz on most frequency response graphs are hard to get right, so I wouldn't put too much stock in them.  I'm assuming you used inner fidelity or headroom graphs?  Their >10khz data will always be different compared to say-- Purrin's graphs, which mostly show a big rise post 10khz.  It all boils down to the compensation and method of measuring. 
 
Lesson of the day, don't put too much stock in the FR graphs that high up.

 

[Delirious Lab]

Quote:

Lesson of the day, don't put too much stock in the FR graphs that high up.

 
Also, keep in mind that our perception of sound frequency is logarithmic.  To move up one octave, one has to double the frequency.  Therefore, the 10kHz - 20kHz range is only the one last octave audible to humans.  Whereas 20Hz - 10kHz is nine octaves.