Ok, picked these up just last week. Now let me say I own the HD600 and the HD800... also the MX985 for portable devices. I was looking at these are a replacement for the MX985 (not that those aren't great but wanted something with a little fuller sound).
Also note that I am NOT a bass head, in fact I like a little extra treble if anything.
So I unpack these things (and after admiring the looks and solid construction)... I plug them into my computer running Foobar and....
My first impression was WTF... is Sennheiser serious? CRAZY BASS... RIDICULOUS AMOUNTS OF CRAZY BASS. There was NO CHANCE IN HELL that I could listen to these as is, no way no how. Don't get me wrong here, they aren't at the level of Beats or Bose as far as stupid bass is concerned, but this was, coming from Sennheiser a real surprise, a shock even.
So... I listened and listened and realized everything about this headphone was great except for the booming bass. I loved the mids, the treble was fantastic but the bass really took away from the overall sound... seriously.
I decided to see what I could do to resolve this. I wasn't going to physically mod these things so I figured lets see if an EQ works here. I downloaded the graphic EQ for Foobar. After much fiddling I managed to dial out the boomy bass and still keep the rest of the sound signature pretty much intact.
Now while I'm not a fan of running an EQ I must say these things are GREAT when the bass is dialed down a notch or two...and in my case several notches. Now if they could just make a pair exactly like this with the bass dialed way down I'd say they would be the perfect portable headphone, and while the bass issue annoys me (as if you haven't figured that out already) I haven't found anything close to these as far as a portable set is concerned, no matter how much EQ I used on other offerings.