Stellar build quality and very deep, powerful (yet somehow not boomy) bass, but I departed with mine after realizing I couldn't really listen to them for more than 20 minutes at a time without listening fatigue. The HFI 580s are the headphones I've owned that come closest to the sound signature of an SPL car audio system and Beyer is probably the only other brand occupying the same price levels with such solid construction.
Like MalVeauX said, very love it/hate it sound signature. He compared to Sennheiser.
I'll compare to Grado, which I can appreciate, but not really listen to for any length of time.
Edited by machoboy - 11/23/12 at 5:48am