Saturday, November 18, 2017

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I measured the Viso HP30s 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 used the clamping mechanism on the ear/cheek simulator to ensure a good seal (as I always do with on-ear models), and moved the headphone around to several different locations on the simulator plate to find the one with 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.

Frequency response

This chart shows the HP30s’ frequency response, which is fairly flat. There’s a mild dip in the midrange, which I believe has something to do with the RoomFeel voicing (and anyway isn’t uncommon in headphones), plus a broad, relatively mild peak centered at 3.5kHz. In most of the headphones I measure, this peak -- which is intended to make headphones sound more like speakers in a room -- is narrower, higher in magnitude, and a little lower in frequency.

Frequency response

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 shows a broad boost below 80Hz that maxes out at +1.5dB. It might barely be audible, but certainly wouldn’t be objectionable.

Frequency response

This chart compares the HP30s (blue trace) with NAD’s Viso HP50 over-ear (red) and Beyerdyamic’s T 51 p (green) and Bowers & Wilkins’ P3 (orange) on-ear models. These curves are normalized to 500Hz, which is near where the HP30s’ response is weakest; while it looks as if the HP30s have a lot more bass and treble than the others, they’re actually fairly close to what I measured from the HP50s.

Waterfall

The HP30s’ waterfall plot shows less bass resonance than usual (not so surprising, considering there’s not much enclosure to resonate), and only a few extremely narrow and almost certainly inaudible resonances at a few higher frequencies.

THD

The measured total harmonic distortion (THD) of the HP30s is a little on the high side in the bass, although I didn’t notice it in my listening tests. (I could, however, hear the distortion when I cranked up Mötley Crüe’s “Kickstart My Heart” to a level louder than I’d ordinarily listen.) The THD is about 2% at 100Hz, measured at the high listening level of 90dBA measured with pink noise. At the extremely high level of 100dBA, which I use only for measurement purposes, it hits 3% at 100Hz, rising to 11% at 20kHz.

Isolation

In this chart, the external noise level is 75dB SPL; the numbers below that indicate the level of attenuation of outside sounds. The HP30s don’t offer much isolation, but few passive on-ear models do. There’s little or no attenuation below 600Hz, and attenuation of only 5 to 7dB from 600Hz to 2kHz. The HP30s wouldn’t be a good choice for air travel.

Impedance

The HP30s’ impedance magnitude is fairly flat, running at or near the specified 32 ohms, except for a peak at 37 ohms right around 50Hz. The impedance phase is also mostly flat.

The sensitivity of the HP30s, measured between 300Hz and 3kHz with a 1mW signal calculated for the specified 32-ohm impedance, averages 109.2dB, which means they’ll play loud from any source device.

. . . Brent Butterworth
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