I measured the AF1120s using a G.R.A.S. Model RA0045 ear simulator (plus a Model 43AG ear/cheek simulator for isolation measurements), 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 a medium-size Comply foam tip because it fit the RA0045 best. This is a “flat” measurement; no diffuse-field or free-field compensation curve was employed.
The AF1120s’ frequency response is unusually flat for earphones. Most earphones have more boost in the bass, and a fairly large response peak around 3kHz. In this case, however, flatter isn’t necessarily better. It’s generally considered best for earphones to have a somewhat stronger bass response and a stronger peak in the lower treble, which is thought to make them sound more like actual speakers in a room.
Adding 70 ohms output impedance to the V-Can’s 5 ohms, to simulate the effects of using a typical low-quality headphone amp, does affect the AF1120s’ tonal balance. This suggests that it would be unwise to use the AF1120s with a low-quality, high-output-impedance headphone amp, such as those built into typical laptop computers. With a high-impedance source (i.e., greater than 40 ohms or so), the AF1120s will likely sound too trebly. This relatively large difference in frequency response with high-impedance sources is typical for earphones using balanced-armature drivers.
This chart shows the AF1120s’ frequency response compared with two similar models, the PSB M4U 4s and the Optoma NuForce HEM8s. Notice how unusually flat the AF1120s’ response is. My subjective impressions were that the M4U 4s sound slightly trebly, while the HEM8s have a somewhat soft-sounding treble.
Despite the AF1120s’ no-frills plastic housings, their spectral decay (waterfall) chart is extremely clean, indicating no noteworthy resonances.
The total harmonic distortion (THD) of the AF1120s is insignificant at 90dBA, which is a pretty loud listening level. At the extremely loud level of 100dBA, the distortion rises to about 3% below 2kHz; that’s slightly on the high side, but if you listen long at this level you won’t have much hearing left anyway.
In this chart, the external noise level is 75dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. For comparison with the AF1120s, I’ve included the isolation plots of two similarly designed passive earphones, the PSB M4U 4s and the Optoma NuForce HEM8s, as well as the Bose QC20s, the last offering the best isolation of any earphones I’ve measured. The AF1120s deliver an average level of isolation for earphones with over-ear cable routing, which is to say an above-average level of isolation compared with other earphones and most over- and on-ear headphones.
Like most earphones using balanced-armature drivers, the AF1120s exhibit a large impedance swing in the treble. It rises from the specified 10 ohms at 100Hz to a peak of 42 ohms at 8.9kHz. The impedance phase also shows large swings throughout most of the audioband.
The sensitivity of the AF1120s, measured between 300Hz and 3kHz with a 1mW signal calculated for the rated 10 ohms impedance, is 109.8dB. That’s above average, which means that any source device should be able to drive these earphones to loud levels.
. . . Brent Butterworth
brentb@soundstagenetwork.com
