In regards to the bass response variation we are getting on this thread. I did do a little subjective listening myself as well as looked at some interesting data that Tyll has on his own objective measurements of the P7. I'll go over the objective data that Tyll has first, then go to the subjective experience. This should clear up, or at least give some reason why, the bass response is subjectively variating on this thread. The objective measurements show it too!
Tyll made a statement on Innerfidelity in November in a comment made on his November update. He stated that he received the Bowers & Wilkins P7 (as well as a few other headphones), but just wasn't able to get a good measurement of them for some reason.
His statement is made here. I have a feeling it has to do with the placement of the headphones in relation to the ear. Tyll also goes on to make statements in his final review of the P7 that he had trouble getting good measurements with the P7 because of the bass. He suspected it was due to the seal it had with his dummy head that he uses to measure with.
Tyll's Bowers & Wilkins P7 Review (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.
I would actually agree with him on this as well. Depending on placement on your own head, you can get stronger and weaker seals due to the way the pads are with the P7. His measurements that he has provided of the P7 also show that the seal can cause a difference of 6 dB (possibly more) in the bass. So while his measurement's left headphone had relatively neutral bass (in reference to the 1k), his right measurement showed a 6 dB bump in the bass. This could easily account for the differences everyone is hearing in the sound. Additionally, the 30 Hz square sine waves show that the time domain characteristics of the right headphone seems to look a little more bloated and big in contrast to the left (there is a
possibility that I'm reading the sine wave wrong). I personally feel that those measurements can account for the differences in subjective analysis we are seeing on this thread.
Excerpt from Tyll's Bowers & Wilkins P7 Measurement (PDF)
Personally, I do feel that the seal has a lot to do with how we perceive the bass response of these headphones, I will agree fully with Tyll on this, his measurements kind of show it. I'll also go further to state that the positioning of the headphones, in reference to the ears, will make a large difference as well. This will also affect the seal the headphones have on the ears. As Tyll states in the review, the headphones aren't utilizing memory foam and the pads constantly try to get back to their original position. That said, without the proper positioning on your ears, you will get a different seal.
I've found that it's quite easy to break the seal while the P7 are on my head. Jaw movements tend to break the acoustic seal quite easily. Playing around with placement on my ears, I found that the further back the headphones are on your head, the tamer the bass becomes (I felt the same way with the P3 as well). Additionally, the pads may not be memory foam, but they will soften up with use. Just like any material, if you exert enough force on it for a long time, it will deform. The pads are the same way with the P7. They aren't memory foam, so it'll take much longer for this to occur. That said, you might get sound change with time simply because the pads are changing themselves. I've also found the pressure that the headphones create to lessen with time. This leads to the comfort issues I had when I used them straight out of the box to really suppress themselves (I've got no issues with comfort any longer).
Hopefully this information makes at least a little sense, but Tyll's measurements do show variation in measurements (those drivers are not as mismatched, he states that in his review).
