I've had like 30min of A/B testing with the hd650 and i thought they were pretty similar without comparing them side to side but they aren't that much similar.
First i'm not sure if this is normal but the px100-II bass on my unit really has arkward problem
It bleed alot in the lower midrange, similar to the klipsch image one. The main difference between the hd650 and the portable px100 is that the px100-II has its mids pretty congested upfront, pretty much like a closed headphone like the klipsch image one ( Image one mids are pretty much destroy by bass bleed px100-II aren't as much!!!)
hd650 are just in another league in the lower end area. It might have less 'gratifying' impact than the px100-II but they have alot more precision, extension and overall texture to it. Even if the hd650 are well known to be a little boosted in the upper bass range it just add a fun feeling to it while i think the px100-II kinda degrade the lower mids. Honestly from what i'm reading here i think they might be defective, but sinewave tests just didn't show any problems....
The voice is ALOT more forward on the px100-II than the hd650. The hd650 honestly kill the 50$ sennheiser version in every aspect of soundstage. I'd say it's pretty deceiving for an open headphone, especially compared to the good and cheap ksc75, which are really impressive in that regard. The hd650 aren't sounstage king by any mean but they do have a huge edge over the px100-II.
High are more recessed on the px100-II than on the hd-650 but otherwise this is were the two headphone sound the most similar. The hd650 once again extend a little more and they sound kinda more relax and laid back.
If breaking time help the px100-II bass noise and bleeding it will turn into a REAL good deal, otherwise it's just another fun cheap headphone with its flaws....
sorry for my english... not my native language ;)
They both are really confortable, which is a great thing
Edited by Xprime4 - 9/20/13 at 8:47pm