Ok, since the M2's showed up on my doorstep in good time, I'm going to answer my previous post in comparing these to the Plantronics Backbeat Pro. This is no easy take but here goes.
This is the first pair of Sennheiser's I've heard, so no previous bias here other than knowing the good name. Obviously, what others have said about the design of the M2's is true...they are the best fitting, most comfortable phones I've tried. And against the bulky Plantronics, there is no contest. The ANC on the M2's performed noticeably better, both with lower frequencies and random sounds. I do prefer the ease of control of the Plantronics, as well as the ability to auto pause the music when you remove them.
In regard to sound performance (wireless only), the Plantronics focus more on the ends of the spectrum. The lows are broader providing a fuller sound, whereas the M2's seem to do a better job isolating instruments in that range. Using Rush's Moving Pictures as a test, I was able to "follow" the bass a little better with the M2's, but the Plantronics provided more breadth and overall fullness. Probably the biggest difference I heard was the stretch at the higher frequencies with the Plantronics -- classical strings, horns, and vocals certainly have a brighter flavor. The M2's do have a nudge in the mids, but with some rock and jazz, I felt it was somewhat too concentrated, and in some songs, overshadowed the highs. I also did some limited testing with electronic music and both phones did very well -- the M2's having a tighter punch in the low range and the Plantronics creating more separation at the high end.
Bottom line, very tough call here, and certainly choosing one over the other is going to be based on one's listening preference. If I had to lean, it would be with the Plantronics, but in fairness to the Senn's, they need much more listening time.
