TB303 said:
So yousuggest the HD600 actually sounds more natural (better) than the HD650? Is it posisble to drive them off an iphone (without an amp?) Thanks!
I'm not suggesting it - Sennheiser designed them that way. In fact, I had both when both of them sounded the same (circa 2000-2001), then Sennheiser re-released the "new" HD650 that had the darker bassier sound. The forums are full of info on that development.
You can use a phone, but many tracks will run out of volume.