I've had a T1.1 here for a few months now and spent far too much time playing with bits of foam trying to change the sound (read: fix the ridiculous treble peak). Ultimately I wasn't able to get these to where I wanted them, but before I sell them off I thought I would share a few measurements and thoughts just in case someone finds this useful down the track... I make no claims as to the accuracy of my measurement rig, but I get pretty consistent results so I make use of it for mod comparisons. Stock measurement: The first thing I tried was the EDT770 pads in an attempt to increase the bass response. I remember a while back someone was selling T1s with these pads and said they preferred it over stock. Yeah, no. These don't sound as crazy as they measure but the v-shape and the mid suckout is still pretty horrible. Just no. If I can provide any sort of service with this thread, it will hopefully be to stop some poor sap putting 770 pads on their T1. Especially if they have to pay through the nose for brand new ones from overseas, like I did. Next I experimented with material in front of the driver/baffle. This isn't particularly easy due to the angled driver, but all in all it wasn't too bad. Unfortunately despite trying every material I could lay my hands on I couldn't get them behave. Shelf liner fucked up the treble, thick foam reduced the measured treble response nicely but still sounded fucked to me. The only thing I found to have any positive (subjective) effect was putting on the front of the baffle (not on top of the driver itself): The only thing I can think of is that the slightly increased midrange response somehow forgave the treble peaks a little. Anyway, I liked it. The final attempts involved stuff behind the driver. Beyer has put NO damping back here and for some reason decided that it was a good idea to stick a thick plastic ring right behind the driver for everything to bounce off. If you listen to some of Tyll's talks about headphone measurements at shows he mentions the treble response of the T1 and postulates that the peaks and troughs could be the result of comb filter effects from sound bleeding back into the ear chamber from the back of the driver. So my theory was that rear damping would help this problem (ignore the rough measurement, it was raining pretty hard when I took it): This is with a single ball of cotton teased out in the chamber behind the driver. Lower bass response (as expected with rear damping) but the treble looks a bit smoother. I tried more cotton and other materials but it reduced the bass too much without affecting the treble. I also tried placing felt over the plastic ring (as suggested on some old HF thread) but it didn't do anything. I think that this type of mod has the most potential, and if I had more patience I'd like to play with more rear damping schemes. However the T1 is not the easiest thing to disassemble and to be honest I'd rather listen to my HD650 than fool around with this any more. If I ever have another go at this I'll post an update, but for now I'm done. For the record, I think these are great headphones that just have fatally flawed treble response. The soundstage and imaging are superb. Bass texture too. I would love to see what someone competent (paging @Bill-P) could do with these, I really do think they could be amazing if modded right.