Pros: never harsh sounding, no sibilance, easy to listen to, detailed yet not harsh
Cons: too much midbass, dark sounding, warm sounding, veiled sounding
I don't like this headphone. Or rather I don't enjoy this headphone. But I can't deny it's impressive.
Plagued with the typical Sennheiser problems of being built cheaply and being overpriced, yet it's really the only in its class, the audiophile's favorite.
That warm and dark sound, that you can never get tired of. That impedance curve that makes it scalable. This is the audiophile's dream, it may not be relevant today with all the FOTMs but it still remains a classic. Grab one used from the classifieds if you're into this kind of sound.
As someone who is into accuracy, it was natural that I prefer the HD600... the HD650 was too thick in the mid-bass and lower midrange and the highs was rolled off, but the roll off wasn't really bad as the clarity is there, but the veiled like sound comes from the mid-bass and lower midrange.
Some complain that it's slow, I disagree, it's pretty clean and fast, but not harsh. Technically impressive, very low distortion.