The Sumptuous and Sonorous Bowers & Wilkins P7 Measurements
I experienced quite a bit of difficulty getting these headphones to seal on my Head Acoustics measurement head, as a result I got quite a bit of low frequency variation in the raw measurements. I measured these headphones a few times (due to some unrelated problems in my system during distortion measurements) and on other occasions I found the drivers to be better matched. I suspect the difference in bass response between channes is more a function of headphone seal than actual driver missmatch. My sense in listening testes was that they readily achieved a good seal on my head.
Compensated frequency response shows a wide bass hump centered at around 60Hz, followed by a mid-range dip centered at about 500Hz, followed by a presence hump from about 900Hz to 2.2kHz. The mid-bass hump and mid-range suckout were both moderately audible in listening.
Usually, headphones will head downward from 2kHz to roughly 7kHz quite rapidly followed by a peak at 10kHz. What I see in the P7 response in this region is a leveling of the usual features in this area, filling in the valley from 3-7kHz and mellowing of the peak at 10kHz. My takeaway from dialog with with Stuart Nevill at B&W is that it is the second cavity in the ear-pad plate that is controlling the 3-7kHz region. Subsequent treble fall-off in the highest octave above 10kHz is very mild. Many headphones will drop-off 10dB to 20dB more than that shown by the P7. I'd like to see the P7 5dB down from where it is, but the treble resolution is so good it doesn't bother me much with its current voicing. Bottom line: the line from 2kHz to 20kHz is surprisingly clean and straight.
The initial spike of the 30Hz square wave is markedly higher than the following waveform indicating too much treble to me, and the latter half of the waveform is a bit swayback from the mild bass roll-off.
300Hz shows a very fast and elevated initial transient spike, which rapidly returns to the baseline waveform. There is some following noise, but very little ringing. Similarly the Impulse response is quick, nicely shaped, and without much ringing. Though it does show some noise which lasts for about 1 mSec (about average) the noise level is fairly low.
Above 100Hz the distortion measurements are fairly good with the 100dBspl markedly below the 90dBspl lines indicating good power handling abilities. Under 100Hz the 90dB plot shows a modest rise, but the 100dBspl curve rises more rapidly. This is actually a fairly good resultthe Sennheiser Momentum, for example, shows a similar shape but at higher distortion levels. I would say this plot shows a small amount of bass distortion in loud passages, which would resonate with my listening experience that while the bass might have some issues, it's fairly minor in terms of distorted sound.
Impedance plot shows a nominally 25 Ohm impedance headphone, with a primary driver resonance at 50Hz.
Isolation is about average for a circumaural, sealed headphone, and clocks in at -15dB broadband attenuation. 44mVrms to achieve 90dBspl is about average for a good portable headset; P7 will play fairly loud from portable sources.