Originally Posted by applaudio
I think that if a headphone extends all the way to 110kHz, then there's a pretty good chance that it doesn't have trouble reproducing the highest audible frequencies (as a general rule, that means up to 20kHz, usually lower, but depending on the person, maybe slightly higher), so one would expect the treble response to be very audible and sharp... hence the bright sound. Similarly, if a headphone extends all the way down to 3Hz, it would be no surprise to find that it does an excellent job of reproducing the very lowest tones you can hear. When they engineer a headphone in such a way that it has incredible extension either high or low, chances are it's going to sound slanted toward the high or low frequencies, respectively. A pair of headphones isn't going to sound bright just because it is physically capable of reproducing frequencies that lie far beyond the range audible to humans, and thus, far beyond the range present in any recording you might feed to the headphones anyway. But it might sound bright if it extends very high, very cleanly, without the treble roll-off that almost always occurs even in ultra high-end headphones.
My two cents.
In the case of Grado headphone, when a bunch of 'similar sounding' models are all rated 20-20 and the 'bassier' Grado is rated 18-24 surely one would say thats because it extends lower than the others. In the case of the Sony XB series XB700 is the deepest of the bunch and coincidentally is 3Hz, the XB500 is 4Hz and the XB300 5Hz; they all seem to represent there own low frequency range.
On another note they made a rotary sub woofer which is reportedly 1Hz, if we can't hear below 20Hz that wouldn't explain the need for a 1Hz sub woofer nor explain why it is the deepest sounding 'speaker' to date.