I disagree with between the HD 650 and the AD2000. There is certainly a very appreciable difference between the two. Whether you like it or not is a different matter, but the difference is very noticeable. I wouldn't mind either as my main pair of headphones, but to say there's a subtle difference between the two is lying.
I have found that most people never hear the potential of their headphones, because they never find the source and amp that properly matches the electrical characteristics of each phone - sounds like you are one of those. And... they fail to implement the "tweaks" needed to bring their phones to their potential.
Perhaps... you just need more experience with both phones and matching set ups. When each is properly matched to their respective set ups, they sound very similar. Though the AD2000's do have a wee bit more attack, and a wee bit brighter highs - though my AD2000's have the "phat pad" mod and have been fully burnt in - which makes a huge difference in the sound of the AD2000's. These are somewhat subtle differences between the "new version" Senns and modified AD2000's.
But... then... I also have the "new version" of the Senns, a RAL Cryo-silver cable, and have deveiled them. These "tweaks" make a pretty significant improvement in their sound - more like the AD2000's, or Grados. And... of course... the WA6 SEm, or the Millett MiniMax, and the Monarchy M24 match both phones extremely well.
Of course, the "old version" of the Senns were a "night and day" difference from the AD2000's, or RS-1's - not so much with the "new version."
I should also note... that the drivers in my "new version" HD580s and my "new version" HD650's are / were identical... resulting in IDENTICAL sound between the two - which is very similar to my AD2000's and RS-1s.
But... that wasn't really my point. My point was... there is very little difference between the "new version" HD580/600/650's, when properly matched to their set up, and LCD2's, HE-6 / HE-500's, SR-507's, SR-007's, etc. There are just not dramatic improvements in the sound as you move up to these "higher-end" phones - only subtle improvements, unless you're one who tends to focus on / overemphasize such "nuances" in the sound. Certainly, the differences are not anywhere near proportionate to the substantial increase in their cost. You must focus very closely on A:B comparisons to discern the differences in many of these phones compared to the Senns, or AD2000's. That's just way to "compulsive" for me.
Though, I admit, I focus on the "nuances" enough, that I have a very difficult time deciding which of my phones I prefer - so much so, that I haven't been able to decide which one's to keep and which to sell.
Many other's have noted this same point in their reviews and comments. Specifically, that the HD600's or HD650s sound as good, or better, than these other "high-end" phones, when properly matched with a source and amp.
That has been my experience with all.
Edited by Gradofan2 - 7/10/11 at 7:58am