I measured the NightHawks using a G.R.A.S. Model 43AG ear/cheek simulator, a Clio 10 FW audio analyzer, a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface, and a Musical Fidelity V-Can headphone amplifier. I moved the NightHawk earpiece around to several different locations on the ear/cheek simulator to find the position that gave the most bass and the best average of midrange and treble responses. This is a “flat” measurement; no diffuse-field or free-field compensation curve was employed.
This chart shows the NightHawks’ frequency response, which is most notable for being fairly flat, with little to none of the usual peak between 2 and 4kHz. There’s a dip centered at 1.2kHz, and a gradual bass rolloff.
Adding 70 ohms of output impedance to the V-Can’s 5 ohms to simulate the effects of using a typical low-quality headphone amp has no audible effect on the NightHawks’ frequency response.
This chart compares the NightHawks (blue trace) with the Oppo Digital PM-3s (red trace) and the NAD Viso HP50s (green trace); both of the latter have received generally positive reviews. The NightHawks are clearly very different, with a more resonant (less flat) bass response and about 10dB less treble energy on average.
The NightHawks’ waterfall plot looks clean, with no major resonances, and very low resonance in the bass frequencies compared with most over-ear headphones I’ve measured.
The total harmonic distortion (THD) of the NightHawks is, as claimed by AQ, very low, even at the extremely high level of 100dBA, measured with pink noise. Even at 10Hz/100dB, there is only 1% THD. Note that because of the AQs’ semi-open-back design and the fact that I measure distortion in a very quiet room but not in an anechoic chamber, even the slight distortion seen in this chart may be mostly noise leaking in. (To improve the signal/noise ratio of this measurement, I use denim insulation on the back of open-back and semi-open-back headphones, but it’s not perfect.)
In this chart, the external noise level is 75dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. The NightHawks’ isolation is roughly what I’ve measured from typical closed-back designs -- remarkable for a semi-open-back model. Consider AudioQuest’s claims for their diffuser confirmed.
The impedance magnitude of the NightHawks is basically flat, but my test gear measured it as 13 ohms -- much less than the specified 25 ohms. (I checked the test setup with a couple of other headphones; it was working properly.) The impedance phase, too, is basically flat.
The NightHawks’ sensitivity, measured between 300Hz and 3kHz with a 1mW signal calculated for the claimed 25-ohm impedance, averages 100.4dB -- enough to get plenty of volume from almost any source device.
. . . Brent Butterworth
brentb@soundstagenetwork.com