Yeah, it's weird right? I'm thinking the same thing. I think the problem with my HD-600 is that it's mid-bass isn't really as well controlled. This crazy HD-650 has some of the most accurate and well controlled bass i've heard. Makes no sense. No mid-bass emphasis at all! My HD-650 actually sounds exactly like a clearer and more refined HD-580. I know that's hard to believe. About the same amount of bass and treble!! Soundstage is also better compared to the HD-600. That'll be hard for almost anyone to believe.
Actually what surprised me is that this HD-650 clearly has more low bass presence than my HD-600/580. Not that much more, but it's nice.
If you've only heard an HD-650 that has a mid-bass emphasis that sticks out like a sore thumb (like my last 2 pairs), then you'd be surprised what this pair sounds like. It also not VERY warm, but just about perfect. Can't even call it dark but pretty close. Not sure what Sennheiser did and all my gear is mostly the same.
I swear i've seen some graphs that shows the HD-600 having more mid-bass than the HD-650, but not sure where I saw that. I know my HD-580 has less bass than my HD-600 too. Just very slightly!
Check out this graph:
Probably not accurate, but who knows..
(comparison to HD-650)
Have to say after having two HD-650s previously, I'm surprised how much I like this HD-650 purchased in late 2012 (NEW).
This is not hard to believe at all. Mostly because mine sound EXACTLY the same way. We bought ours at about the same time and I think that we've talked about this before. I suspect some unannounced driver change but who knows. I have NO veil, NO mid bass hump and a surprising amount of sub bass punch.
That adds up to make this one sweet hp. And one that I would never sell.