Here's a bit of a weird thing. Though I love my DT880 Pro the treble does get a bit tiring on certain recordings, and though I've tried various amps (yes, including one tube) none has really addressed the problem. So I thought I might try what I've tried with a couple of other headphones: cut a couple of circles of light cloth (in this case a cleaning rag) and place one in each ear cup. I expected a slight reduction in treble, as you would. What I got was a whole new headphone.
As I say, this is weird. I'm not sure the treble is even reduced, but the whole sound is like I've moved up a full notch to one of the flagship phones. Everything is better. There's still plenty of treble, but somehow it's no longer bothersome. There's noticeably more bass and lower midrange, but above all everything just sounds more realistic (I listen to mostly classical/orchestral). I've been listening to several recordings whose sound I normally can't stand (wiry treble, muddled soundstage etc) and suddenly they sounds perfectly acceptable, if not great. As I say, this is the sort of improvement I'd have expected moving up to the T90 or evenT1, and I can't explain it. Any effect of putting damping in the ear cups should only be on the treble--yes? This is an overall improvement, and not subtle. I've owned headphones since 1970, and done a lot of experiments, but this one has me bamboozled.
You might be wondering about the composition of this magic rag. In a previous incarnation it was just a flannalette sheet; that's all I can tell you. And no, this isn't a leg-pull. The improvement is startling and real. I'm convinced that if Beyer were to cut up a few hundred flannalette sheets they could make a fortune marketing a 'vastly improved' Mk 2 DT880.