To measure the X7i's performance, I used a G.R.A.S. Type RA0045 ear simulator, a Clio 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 silicon tips in the medium size because these fit the ear simulator best. I inserted and reinserted each earpiece several times, and settled on a position for each that gave the most representative result.
The X7i’s measured frequency response is flatter than we usually measure with IEMs, largely because it doesn’t have the big boost in the bass that most of them have. It’s about -3 to -5 dB lower at 100 Hz, relative to the treble, than most IEMs we’ve tested. Otherwise, the response looks pretty textbook, although the little peak at 10 kHz makes the high treble a bit stronger than average. 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 tilted the tonal balance substantially, with about -2 dB less bass and +2 to +3 dB more treble. Thus, I’d recommend the X7i only for use with devices that have relatively low output impedance, such as iPhones. It’ll probably sound too thin if you connect it to one of the junky soundcards found in most laptops, and to some cheaper, non-Apple smartphones.
Total harmonic distortion (THD) at 100 dBA is relatively low, maxing out at 2.5% at 900 Hz, and just 1.5% at 20 Hz—an above-average result in the bass frequencies, where headphone distortion is often high. Isolation is fantastic, ranging from a minimum of -15 dB in the deep bass to -45 dB at 2 kHz. That’s probably because the small ceramic body allowed the silicone tip to fit deep inside the G.R.A.S. coupler (and, I assume, into your ear canal).
As with almost all balanced armature drivers, impedance changes considerably with frequency: from a low of 38 ohms in the bass to 230 ohms at 20 kHz. That’s why frequency response is so strongly affected by the output impedance of the source device. Average sensitivity with a 1 mW signal at 50 ohms rated impedance is 110.3 dB from 300 Hz to 6 kHz.
The Image X7i is a pretty extraordinary little IEM, but it's not for everybody. Audiophiles will applaud its detail and love its neutral, precise sound, but we think the average listener will find it a little light in the bass. And hey, you know which group you fall into....
Brent Butterworth and Geoff Morrison combine their years of gear testing and knowledge in one überblog of irreverence and techiness.
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