Here is my take on the Nighthawk. Quick version: The recessed mids and over emphasized bass make them almost unlistenable - they sound like somebody put a wool blanket over everything. This together with the semi-closed nature of the headphones lead to a cramped/dark tonality with a lot of oomph. So why am i keeping them? First, they are supremely comfortable - the new suspension mechanism is a fantastic innovation. In fact they are the most comfortable HP in their weight class and even more comfortable than a lot of HPs weighing a lot less. Second, i suspect that the driver - without any proof - is OEMed by Fostex and is identical/nearly identical to the TH600, TH-X00, Teac etc.This means low-distortion (see innerfidelities measurements), great sub-bass extention (negliable less than the fostex cans due less pressure from the suspension mechanism for sealing the ears) and possibility for insane SPL levels. This makes them very good for equalisation. And low-and-behold once you raise the presence range to more conventional (HK curve or Sennheisers House Curve) levels and reduce the bass a little - they sound great. They are still semi-closed, so a little (10%) crossfeed takes the edge of studio recordings where instruments are placed in exactly one channel. One could also equalise the Fostex Family of HP but i found the Audioquest much more comfortable to wear. I have measures a number of rooms (including the AIX studios) with the realiser A8. This allows me to compare tonality of a virtualised room with the pure headphone sound, both over headphones. I find that the classical tunings (HK, Senn) sound much more than real loudspeakers (decent ones) in real rooms than audioquests nighthawk. This was consistent over a number of PRIRs i testet. On a plus side they make music from the 70s and also some of the dreaded 80s CDs listenable without any fatigue.
Bottom line - the bad:
very dark, bass heavy headphones with extremely recessed mids (to much for almost any taste i would dare to say),
Bottom line - the good:
supremely comfortable with innovative suspension mechanism,
low distortion, good sub-bass -> very good for equalizing
I kept them, because after equalization they are fantastic, comfortable headphones and i prefer them to the Fostex TH-XXX (which are likely based on the same driver). For people who do not want to equalize i would say AVOID, except if you want to posess a real differently tuned headphone that gives you that muffled, small jazz club from the 60s kind of sound.