Pros: pleasant sound, quite comfortable, easily exchangable parts
Cons: lacks clarity and transparency, overblown bass, quality issues (paint flaking, one of the drivers broke after three years)
As much as I cannot understand the overwhalming positive reviews of these headplones I admit that I actually can understand that people can get in love with their pleasant and forgiving sound. If you wish to get close to the soul of a recording however, you should go somewhere else because HD650 are neither natural or neutral sounding headphones. Compared to some other cans (AKG k70x or Beyerdynamic DT880 namely) these Senns are muddy to say the least and lack sparkle, transparency and sheer excitement. The bass is more prominent than with k701's but the definition of the same is not as good. Listening to the HD650 I really miss the sparkle and the excitement that should be there. When listening to accoustic music and classical there is no air at all. A huge amount of information, upper harmonics are simply absent. It is important to say that I have had some issues with my pair. One of the drivers broke after three years of use. The paint on the headband started chipping after 2 years.
However I can understand that many people get in love with their sound. They sound "relaxing" in their own way and are very forgiving on the quality of the recording. The problem is that you can get all that and more at half their price.
Amplifiers used: Lehmann Black Cube Linear, Musical Fidelity X-Can v3, Matrix M-Stage