Tuesday, January 17, 2017
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To measure the Focal Spirit Classic headphones, I used my usual rig: 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): 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, roughly, the place where the front of the driver grille will sit when you wear the headphones. This is a “flat” measurement; no diffuse-field or free-field compensation curve was employed. 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

Although there’s still no broad agreement on what measurement of headphone frequency response would correspond to a perceived flat response, the Spirit Classics’ measured response pretty much squares with what I’ve found most people to perceive as flat. There’s a typical response bump at 3.1kHz, to accommodate the natural resonance of the human ear canal, and a strong measured response out to 9kHz. Only the bass looks a bit deficient, but this curve is actually quite similar to measurements I’ve taken of several respected audiophile models.

Frequency response

Adding 70 ohms to the V-Can’s output impedance of 5 ohms, to simulate the effects of using a typical low-quality headphone amp, produces no significant difference in response. Considering that the Spirit Classics’ sensitivity is fairly high, you should be able to get plenty of output and decent sound from anything with a headphone jack.

Frequency response

Compared to the ADL H118 and Bowers & Wilkins P7 headphones (both shown in the accompanying chart), the Spirit Classics have a little more bass and a little less treble, but their tonal balance looks flatter than either competitor’s.

Waterfall

The Focals’ spectral decay (waterfall) plot shows a very strong resonance at 800Hz -- which happens to correspond with a dip in the measured frequency response right at that frequency. However, this is a fairly narrow resonance, so I suspect it would be only occasionally audible.

THD

Total harmonic distortion (THD) is practically nonexistent, even at 100dBA.

THD

The spectrum of a 500Hz sinewave shows that the most audible distortion artifact at 100dB is the third harmonic (1500Hz), at about -56dB (about 0.16%).

Isolation

The Spirit Classics attenuate external sounds pretty well for passive, closed-back headphones, reducing outside noise by -14dB at 1kHz and by as much as -32dB at higher frequencies. There’s no reduction in the “jet-engine band” below 200Hz, though.

Impedance

The Focals’ impedance is mostly flat, averaging 33 ohms below 10kHz.

The average sensitivity from 300Hz to 3kHz at the specified impedance of 32 ohms measures 104.8dB with a 1mW signal.

. . . Brent Butterworth
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