I measured the Amiron Homes 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.
The Amiron Homes’ frequency response is a little unusual. Typically we see a strong peak in the region of 2.5kHz, then one or two weaker peaks at higher frequencies. In the Amiron Homes, the peak centered at 7.5kHz is by far the strongest. I can’t recall seeing a response quite like this before, so I can’t speculate as to what its subjective effects might be.
Adding 70 ohms output impedance to the V-Can’s 5 ohms, to simulate the effects of using a typical low-quality headphone amp, boosts the Amiron Homes’ bass by about 1dB.
This chart shows the Amiron Homes’ measured frequency response compared with those of the HiFiMan HE560s (a similarly priced planar-magnetic open-back model) and the NAD Viso HP50s, my comparison standard for midpriced closed-back headphones. Except for that strong peak at 7.5kHz, the Amirons seem within the norm for headphone frequency response.
The spectral-decay (waterfall) chart indicates that the Amiron Homes have almost no resonances. What few there are are well damped and die out within a few milliseconds.
The total harmonic distortion (THD) of the Amiron Homes is negligible at 90dBA, almost nonexistent above 60Hz, and rises to just 3% at 20Hz. At the extremely loud level of 100dBA, the THD is comparably low above 60Hz but rises to 9% at 20Hz.
In this chart, the external noise level is 75dB SPL, and the numbers below that indicate the degree of attenuation of outside sounds. For comparison, I’ve included the isolation plots of the open-back HiFiMan HE560s, the closed-back NAD Viso HP50s, and the noise-canceling Bose QC25s. The Amiron Homes provide above-average isolation for open-back headphones -- nothing below 1kHz, but they decrease environmental noise by 11 to 17dB at frequencies above 2kHz.
Through most of the audioband, the Amiron Homes’ impedance is closer to 300 ohms than the specified 250 ohms, and rises to a peak of 690 ohms at 95Hz. There’s some mild phase shift on either side of that peak, but the impedance phase is relatively flat overall.
The Amiron Homes’ sensitivity, measured between 300Hz and 3kHz with a 1mW signal calculated for the specified 250 ohms impedance, is 102.4dB -- high enough for a typical smartphone to be able to drive the Amiron Homes to loud levels.
. . . Brent Butterworth
brentb@soundstagenetwork.com
