Originally Posted by bigshot
Flat is within the range of human hearing, which means +/- 1 to 3 dB (depending on the frequency).
Yeah, I got that, I was just saying for the sake of discussion, say we had a perfect transducer. But even with what you're describing, I'm leaning on it sounding bright and gnarly.
I read somewhere there is an EQ adjustment you have to make with headphones to make them sound flat to the ear... Something to do with the drivers being pressed up against the ear. Measuring flat doesn't turn out flat once they're clamped on your head. Someone around here may know what that exact correction is.
There are actually a few different corrections that can be made, Diffuse-Field and Free-Field are the most common and have some degree of standardization. Regarding why it doesn't work out "perfectly" - it's because the acoustic coupling between the driver and the sensory parts of the ear has the outer ear, the seal of the earcup, and the ear canal getting in the way. I know that Ultrasone has researched this problem fairly extensively, and their conclusion is basically that different folks will respond to the same headphone (no matter how well it measures) differently. In their testing of their own headphones, they found that "non-ideal" earshapes more often than not (as in, with statistic confidence) mean users complaining of an over-bright or over-harsh sound, than anything else.
Tyll's "ideal FR" has a roll-off on the top-end, you can see it here: http://www.innerfidelity.com/content/headphone-measurements-explained-square-wave-response-page-2
But perceived flat eliminates problems with masking and listening fatigue, and gives the most natural sound.
Perceived flat is closer to a v-curve if you're trying to compensate for Fletcher-Munson *and* ear acoustics, and it won't be "flat" to all listeners. It may be flat in your model, and for your dummy head, but that's an approximation - not reality.
There are some headphones that are pretty flat overall, but I wouldn't consider any of them absolutely non-fatiguing compared to models that you'd likely say are very fatiguing.
Found this ancient post on the topic: http://www.head-fi.org/t/19259/what-is-diffuse-field-equalization#post_215696
If you go find the K1000 thread in Headphones (Full-Size), where one of the principal engineers popped in about a week ago (yeah!), he talks about DF being AKG's goal, at least back in the day.
Also, thanks to DuckDuck:
(scroll down to "Localization").Edited by obobskivich - 10/16/12 at 5:30pm