I edited the post. I've heard multiple units of the M50. One in a SamAsh, and some from friends who own them. I'm not relying on descriptions, I'm relying on what I heard from them in person. My take on them has always been:
slight 2k coloration
bright-ish very upper treble octave
slightly scooped mids
moderately boosted, maybe 3-6 dB mid-bass
good sub-bass extension but not as much of a boost as the mid-bass.
whereas the DT770/80s are bass cannons, they sound like they have at least 8 dB boost between sub and mid-bass. This causes the mids to sound like they are in the background. My unit doesn't have overly shrill treble, but it is a little forward. I also hear a pretty prominent dip in the low treble, somewhere around 5k. It's a strange FR.
It's worth nothing that I have the newer design 770s, not the old one.
Basically to sum it up, where the M50s are considered dark-leaning and bassy cans, I consider the DT770/80 to be so bass heavy that no one should ever need to boost it. It's really a little out of control.
Edited by metal571 - 11/25/14 at 2:49pm