So I got my pair of HD 650's and they sound nothing like I've been reading all these years. They do, however, sound how people are describing the "upgraded" version of the phones that supposedly came in around end of 2007.
I'm comparing the phones to my K701's. I'm running both phones through the Asus Xonar Essence STX soundcard with FLAC files. Amping is done by a Heed Canamp.
The 650's are much brighter than my K701's. The K701's focal point in the treble was around 8k, while with the Senns it seems to be around 15k. There isn't a sign of the Sennheiser Veil that was very present in my old HD570's. They've hardly got more bass than the K701's, quantity-wise, though there seems to be more impact and lower extension. The bass isn't sloppy at all, it's just as tight as my K701's to me. The lower mids are warmer and more present on the HD650's, and the upper mids are less in-your-face. I prefer the 650's for everything except the treble, which I find somewhat hissy or shizzly, on the 650's. Cymbals seem to have more body on the K701's.
The 650's have only had a few hours of burn-in, though. I'm not a big believer, but I won't rule out the chance something might change.
Good observations. I wouldn't say the HD650 is brighter than K701, but you are indeed correct in saying that the HD650 treble extension is greater than the K701 but not in overal volume level or presence. Both cans are virtually identical in technical merits, with the HD650 taking the lead in bass transients and the K701 edging out the HD650 in treble transients. The K701 is the only treble orientated can that exhibits no sibilance - possibly due to lesser transients than HD800 for instance and the fact that the upper treble is more rolled off than HD650.
These cans, on a technical level, are more similar than different IMO.
Edited by SP Wild - 9/13/10 at 6:13pm