I measured the Sonorous IIIs 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, a Musical Fidelity V-Can headphone amplifier, and an Audio-gd NFB-1AMP amplifier for distortion measurements. This is a “flat” measurement; no diffuse-field or free-field compensation curve was employed.

Frequency response

The Sonorous IIIs’ frequency response is flatter than I’m used to seeing from headphones of this type. Instead of the usual response peak around 3kHz, which is generally thought to make headphones sound more like speakers in an actual room, there’s a broad, shallow peak between 1.5 and 6kHz. I can’t recall seeing a measurement like this before, so I hesitate to speculate as to what effect it might have on the sound. I wonder if the lack of a 3kHz peak is why the Sonorous IIIs sounded a bit less spacious than some competing models.

Frequency response

Adding 70 ohms output impedance to the V-Can’s 5 ohms, to simulate the effects of using a typical low-quality headphone amplifier, has no significant effect on the Sonorous IIIs’ tonal balance.

Frequency response

This chart shows the Sonorous IIIs’ response compared with two well-regarded, midpriced closed-back models: the NAD Viso HP50s ($299) and the Oppo Digital PM-3s ($399). It’s easy to see that the Sonorous IIIs are something different, with less treble response than either competitor. But that’s not necessarily a bad thing -- the Sonorous IIIs’ somewhat rolled-off bass could counteract it, to give the headphones a perceived flat response.


Their spectral-decay (waterfall) plot indicates that the Sonorous IIIs seem to have a bit stronger initial resonance below 700Hz than I’m used to seeing, but it’s well damped, and drops to very low levels (-40dB and below) within 5 milliseconds.


The total harmonic distortion (THD) of the Sonorous IIIs is very low. Even at the extremely loud level of 100dBA, it rises to just 3% at 20Hz.


In this chart, the level of external noise is 75dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. For reference, I’ve included another set of passive closed-back headphones, the NAD Viso HP50s, as well as that of a set of headphones with active noise canceling: the Bose QC25s ($299). The Sonorous IIIs’ isolation is not quite as good as the Viso HP50s’, probably because the Finals’ large earpads made it tough to get a good seal on the ear/cheek simulator (and on my actual, unsimulated ear and cheek). As always with this measurement, your results may vary; the better the fit, the better the isolation.


The Sonorous IIIs’ impedance is essentially flat, averaging 19 ohms, with negligible phase shift.

The sensitivity of the Sonorous IIIs, measured between 300Hz and 3kHz with a 1mW signal calculated for the specified impedance of 16 ohms, is 105.8dB. That’s excellent for headphones of this type; there should be no problem getting loud volumes from any source device.

. . . Brent Butterworth