Tuesday, September 26, 2017

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I measured the performance of the Audeze LCD-X headphones using a G.R.A.S. 43AG ear/cheek 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. Measurements were calibrated for ear reference point (ERP), which is roughly the point in space where your palm intersects with the axis of your ear canal when you press your hand against your ear, and the place where the front of a driver grille sits when you wear the headphones. This is a “flat” measurement; no diffuse-field or free-field compensation curve was used. I experimented with the positions of the earpads by moving them around slightly on the ear/cheek simulator, and settled on the positions that gave the best bass response and the most characteristic result overall.

Frequency response

The LCD-X’s frequency response is about what I’m used to seeing from planar-magnetic headphones: dead flat from about 50Hz to 1.2kHz, with a peak at around 2.5kHz, which is typical. The only anomaly is that the treble response is a little less than I’m used to seeing from planar magnetics. Note the difference in bass response between the right and left channels: Each represents the best measurement I was able to get in more than a half-dozen tries; however, because slight differences in the seal of the earpads against the ear/cheek simulator can have huge effects on the measured response, I have no way of knowing if this represents an actual imbalance or a measurement artifact. Regardless, I didn’t notice any difference in the sounds of the left and right channels in my listening to the Audezes.

Frequency response

Because planar-magnetic drivers have an almost purely resistive (i.e., flat) impedance curve, their tonal balance rarely changes with different source devices. I simulated a change in source device by adding 70 ohms output impedance to the V-Can’s 5-ohm output impedance, for a total of 75 ohms, which is typical of the low-quality headphone amps built into laptops and cheap MP3 players. As you can see, there’s no significant difference in the Audezes’ response.

Frequency response

This chart compares the LCD-X with Audeze’s top model, the LCD-3, and with Oppo Digital’s new PM-1 planar-magnetic headphones. You can see that the LCD-X and LCD-3 headphones are practically identical up to 7kHz, but that the LCD-3s have 4 to 6dB more output between 7 and 9kHz. This should, at least in theory, give the LCD-3s a slightly brighter sound, and probably an enhanced sense of “air” and spaciousness. The Oppo PM-1s have a flatter response, but less energy in the lower treble.

Waterfall

The spectral-decay (waterfall) plot shows a couple of mild resonances in the vicinities of 800Hz and 1.4kHz, but their duration and bandwidth are so low that you probably wouldn’t notice them.

THD

This plot of the LCD-Xs’ total harmonic distortion vs. frequency is one of the cleanest I’ve seen. The orange trace is taken at 100dBA, a higher level than most people could stand to listen to for more than a few seconds; even so, distortion is practically nonexistent.

THD

This spectrum plot of the distortion harmonics, again taken at very loud levels, provides still more evidence that these are super-clean-sounding headphones.

Isolation

Open-back planar-magnetic headphones provide little or no isolation from outside sounds, and the LCD-Xs almost none at all -- along with your music, you’ll hear everything going on around you.

Impedance

The LCD-Xs’ impedance magnitude is essentially flat at 22 ohms (which matches the specification), and the impedance phase shift is near zero.

The LCD-Xs’ average sensitivity from 300Hz to 3kHz, at the rated 22 ohms, measured 101.5dB, which is very high for planar-magnetic headphones.

. . . Brent Butterworth
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