A quick followup on the AQ Nighthawk review: I've been measuring the relative response of headphones using an equalizer and several sets of test tones - not as an absolute against what sounds "flat" to me, but in comparison to numerous other headphones including some flagship models. I've found that in most cases, the lower tier headphones (especially portable types) have a lot of treble recess, whereas the so-called flagships are generally bright and peaky in the upper treble.
I've mostly been using the Audioforge iOS app for estimating those responses, because it has a WYSIWYG interface with immediate results, and a simple frequency response shouldn't vary between devices that output the digital data directly to audiophile-quality amplifiers.
However, whereas I measured the Nighthawk (using Audioforge and the Oppo HA-2 DAC/amp) as having a 4-5 db emphasis between ~150-400 hz and a 4-5 db recess through most of the treble, I measured only plus/minus 2 db using Foobar2000 on a WinXP computer with the Microstreamer and Dragonfly-1.2 DACs, to get the same balance as with the iOS devices and the Oppo DAC/amp.
I wonder then how many users are not getting the better sound that's provided by computers playing through USB mini-DACs such as those I mentioned, or even better, using dedicated desktop headphone amps. Could it be that the high efficiency of the Nighthawk is encouraging a lot of use with portable devices? I don't know. I also don't know why the Apple music players would sound worse when used with DACs such as the Oppo, the v-moda Verza, or the Beyerdynamic A200p, but my results are pretty consistent.
