I love how smooth sounding they are. They remind me of my old HD-600, but more clear and detailed, less forgiving, and a little thinner sounding (which is what I want, but not too thin). Feel like I could listen to these all night without fatigue and even maybe fall asleep with them on my head.
Even the treble on them is smoother than the K601, yet it's more extended. The K601 feels almost dark in comparison! Definitely less treble than the K702 though.
One thing I love the most is that it's soundstage is massive, but someone manages to sound accurate unlike the K702. Never does anything sound too distant and it still often feels like I get a front row or 2nd row experience, which of course varies depending on the recording.
Somehow this pair seems to have more much bass than my K601 and K702. It's V.1 which is said to be the one with the lightest bass?!
I connected them up to an old Playstation 1 with the RCA jacks to my amp and I was shocked at how much bass they had!! K501 loves this old PS1 for whatever reason. Now you may think I'm crazy, but you just have to try it.
K501 is definitely one of the best headphones I ever heard. Just wish I had heard it sooner. K601 fans just have to try it!