[size=small]Let me add some more explanation as to what I'm trying to accomplish, which I really should have done in the initial post.[/size]
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[size=small] The motivation is to establish an ideal frequency response for headphones, in terms of subjective preference. For loudspeakers, we already have good research on what this response should be: when measured in-room, it's a flat line sloped downwards (see Floyd Toole's book on loudspeakers). Now, is there an equivalent statement that we can make for a headphone's frequency response?[/size]
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[size=small] Given the loudspeaker research, we might guess that the ideal headphone response should also be a downwards sloping line like the in-room loudspeaker response. However, we need to account for modifications to the in-room response by the listener's HRTF. To measure the listener's HRTF, we place a dummy head (mine) in the listening seat, and measure how the in-room response with the microphones mounted in-ear differs from the response with the microphones free standing. These were my measurements (a) and (b). Our candidate for the ideal headphone response would be a flat line sloped downwards but modified by this difference. This is why I said the original loudspeakers' and room's frequency response are largely irrelevant: we are only interested in the difference between two measurements.[/size]
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[size=small] Then we measure our headphones using the same in-ear microphones. These were my measurements (c). The ideal headphone should have a measurement (c) such that:[/size]
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[size=small] (c) = "flat line sloped downwards" + ((b) - (a))[/size]
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[size=small] Note that if the room and speakers were ideal, then (a) = "flat line sloped downwards", so we'd want (c) = (b).[/size]
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[size=small] Hope this clarifies the motivation behind these measurements.[/size]