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I measured the P9 Signatures using a G.R.A.S. Model 43AG ear/cheek simulator, a Clio 10 FW audio analyzer, a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface, a Musical Fidelity V-Can headphone amplifier, and an Audio-gd NFB-1AMP amplifier for distortion measurements. This is a “flat” measurement; no diffuse-field or free-field compensation curve was employed.

Frequency response

The elephant in the measuring room is the P9s’ wide, deep dip centered at 550Hz. If that dip were about 6dB less deep, it would be pretty close to what I’d call a textbook headphone frequency response. What does that mean in terms of sound? I hate to predict headphones’ sound based only on their measured frequency response, but that big dip sure won’t make voices sound more prominent.

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 amplifier. Using the higher-impedance source boosts the bass by a maximum 1.5dB, which will result in only a subtle difference in the sound.

Frequency response

This chart compares the P9s’ measured right-channel frequency response with those of two other high-quality closed-back headphones (Oppo’s PM-3s and B&W’s own P7s) as well as Audeze’s LCD-X open-back headphones, the last used as the comparison standard in the review. The fact that the P9s’ big midrange dip is centered very close to 500Hz -- the reference frequency for this measurement -- makes the P9s look more different than they really are from the others. Still, the P9s will likely sound the most different of the four.

Waterfall

The spectral-decay (waterfall) chart shows a narrow but strong resonance at 1kHz that might occasionally be audible, depending on what you’re listening to. There are also resonances at 2.8 and 3.6kHz, but they’re so narrow and low in magnitude that it’s hard to imagine they’d be audible.

THD

The P9s’ total harmonic distortion (THD) is low for dynamic over-ear headphones, maxing out at 1% at 20Hz at 90dBA and 3% at 100dBA -- and 100dBA is extremely loud.

Isolation

In this chart, the external noise level is 75dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. For comparison, I’ve included the isolation plots of other closed-back over-ear headphones: B&W’s P7s and Oppo’s PM-3s, plus Bose’s noise-canceling QC25s. The P9s’ isolation is about average, or maybe slightly above average, for this type of headphone.

Impedance

Except at their impedance peak at 55Hz, the P9s average about 30 ohms impedance. Electrical phase is nearly flat.

The P9s’ sensitivity, measured between 300Hz and 3kHz with a 1mW signal, is 100.1dB, calculated for the specified 22 ohms impedance -- about average for closed-back headphones. In practical terms, this means that they’ll play at satisfyingly loud volumes with a Samsung Galaxy smartphone, and at very loud volumes with an iPhone.

. . . Brent Butterworth
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