Sunday, February 18, 2018

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I measured the Focal Clears using a G.R.A.S. Model 43AG ear/cheek simulator (including the RA040X high-resolution ear simulator), a Clio 10 FW audio analyzer, a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface, and Musical Fidelity V-CAN and Audio-gd NFB1-AMP amplifiers. On the Model 43AG I used the original KB0065 simulated pinna for most measurements, as well as the new KB5000 pinna for certain measurements, as noted. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed.

Frequency response

The Clears’ frequency response is not far outside the norm for open-back headphones, with a few anomalies worth noting. First, these headphones have a strong response peak centered at about 1.5kHz; with most headphones, this peak is somewhere between 2 and 3kHz, and is generally thought to make headphones sound more like loudspeakers in a room. Second, some small wrinkles in the response curves between 1.3 and 3.3kHz correspond with the resonances I note below. (This is an unsmoothed measurement; smoothing to 1/12 octave, which many technicians do when measuring headphones, conceals these tiny anomalies.) Third, the left and right earpieces don’t match very well between 1.7 and 4kHz. Channel mismatches are common due to the differences between the left and right simulated pinnae, and because it’s practically impossible to get precisely the same fit every time you place a headphone on the ear/cheek simulator, but this was a larger mismatch than I usually see -- and a more consistent one, as I confirmed by measuring each earpiece six times.

Frequency response

This chart shows the Clears’ measured right-channel frequency response measured with the old KB0065 pinna (which I’ve used for years) and G.R.A.S.’s new KB5000 pinna, which I’ll be switching to because it more accurately reflects the structure and pliability of the human ear. (I include this more for future reference than as something you should draw conclusions from; I intend to show both measurements until I completely switch to the new pinna, probably sometime this spring.)

Frequency response

This chart shows the results of 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. Obviously, there’s a large difference, due to the big impedance swing in the bass (see below) -- the Clears will sound a lot bassier, and probably duller, if plugged into a headphone amp with high output impedance, such as some of those built into laptop computers as well as some professional amps. I recommend using a good-quality amp with a low output impedance, preferably under 5 ohms.

Frequency response

This chart shows the Clears’ measured right-channel frequency response compared with the responses of the Audeze LCD-X and Oppo Digital PM-1 open-back planar-magnetic headphones and Sennheiser’s HD 800 S dynamic open-back model. The Clears had somewhat less response above 4kHz than the other three, and stronger response between 800Hz and 2kHz, which perhaps explains my perception of hearing more midrange detail with the Clears.

Waterfall

The spectral decay (waterfall) chart shows many very high-Q (narrow), low-magnitude resonances between 1.3 and 7kHz. This is something I often see with open-back models, even some of the most highly regarded headphones on the market. (When I do this measurement, I cover the back of the headphone with 4” of denim insulation so that the measurement doesn’t include environmental noise, or echoes of the sound leaking from the earpiece’s open back.)

THD

The Clears’ total harmonic distortion (THD) was generally low, rising to 1.3% at 20Hz at 90dBA, a very loud listening level. At 100dBA, the THD did rise below 30Hz, to 8.8% at 20Hz, but considering that 100dBA is extremely loud and that music has almost no content below 30Hz, this shouldn’t be significant.

Isolation

In this chart, the external noise level is 85dB SPL; the numbers below that indicate the level of attenuation of exterior sounds. (Note that I recently switched to measuring at a level of 85dB instead of 75dB; this doesn’t change the way the isolation curves look, but 85dB lets me get more accurate measurements of noise-canceling headphones, which demand a lower noise floor.) Like other open-back models, the Clears offer negligible isolation; I include the closed-back Audeze LCD-XC ’phones to illustrate the isolation of a similarly constructed closed-back model.

Impedance

The Clears’ impedance magnitude ran higher than its specified 55 ohms, averaging about 70 ohms above 200Hz and rising to a peak of 420 ohms (the driver’s resonance) at 42Hz. Phase shift is a little on the high side, running +/-25% from 250Hz to 20kHz, with a bigger swing in the bass that corresponds with the driver resonance.

The sensitivity of the Clears, measured between 300Hz and 3kHz with a 1mW signal at the specified 55 ohms impedance, was 101.6dB. You should be able to get adequate listening volume from practically any portable device, although, as my other measurements show, the tonal balance may tilt in a way that doesn’t sound great.

. . . Brent Butterworth
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