I measured the Acoustic Research AR-H1s 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 amp. On the Model 43AG, I used the original KB0065 simulated pinna for most measurements as well as the new KB5000 pinna for certain measurements, as noted. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed.
The AR-H1s’ frequency response runs close to the norm for open-back planar-magnetic headphones, with a couple of exceptions. First, the response is flatter than normal, with a less prominent peak in the 2.5-3kHz range than I’m used to seeing. Second, the response in the midrange is slightly jagged, with a peak/dip in the region between 600 and 700Hz and another between 1.6 and 2kHz. However, these sorts of low-magnitude, high-Q anomalies typically aren’t very audible, if at all.
This chart shows the AR-H1s’ measured right-channel frequency response measured with the old KB0065 pinna (which I’ve used for years) and G.R.A.S.’s new KB5000 pinna, which I’ll be switching to because it more accurately reflects the structure and pliability of the human ear. I include this mostly for future reference rather than as something you should draw conclusions from; I intend to show both measurements in every review for at least the next year before I begin using only the new pinna.
This chart shows the results of adding 70 ohms output impedance to the V-CAN’s 5-ohm output impedance, to simulate the effects of using a typical low-quality headphone amp. The difference is practically zero, with an inaudible bass boost (about 1dB at 10Hz) visible with the higher output impedance.
This chart shows the AR-H1s’ measured right-channel frequency response compared with those of the similar Oppo Digital PM-2s, the HiFiMan HE400i’s (a well-regarded but less costly planar-magnetic headphone), and the Beyerdynamic Amiron Homes (dynamic-driver, open-back headphones). As you can see, the AR-H1s’ response is the flattest, though it’s very similar to that of the PM-2s. The other headphones have stronger treble response above 4kHz.
The spectral decay (waterfall) chart shows a lot of resonance, even for a planar-magnetic headphone, with very strong but narrow resonances between 600 and 700Hz and between 1.6 and 2kHz -- which correspond precisely with the peak/dip series I noted in the frequency response.
The AR-H1s’ total harmonic distortion (THD) is practically nonexistent even at extremely loud listening levels, as is common with large planar-magnetic models.
In this chart, the external noise level is 85dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. (Note that I recently switched to measuring at a level of 85dB instead of 75dB; this doesn’t change the way the isolation curves look, but an 85dB level lets me get better measurements of noise-canceling headphones, which demand a lower noise floor.) As expected, the AR-H1s offer negligible isolation -- even less than the Oppo Digital PM-2s, and far less than sealed and noise-canceling models.
The AR-H1s’ impedance magnitude and phase are extremely flat, with the impedance at almost precisely 31 ohms throughout the audioband, and negligible phase shift.
The sensitivity of the AR-H1s, measured between 300Hz and 3kHz with a 1mW signal at the rated 33 ohms impedance, is 96.5dB. That’s a little on the low side; to get the best results with the AR-H1s, you’ll want to use a headphone amp, a good portable player, or an Apple iOS device.
. . . Brent Butterworth
brentb@soundstagenetwork.com