Bought my d2000 some 9 months ago, not sure how many hours of burn in. I haven't been quite satisfied with these phones due to the ripping highs and obviously loose bass. A few weeks ago received a HRT Headstreamer DAC/headphone amp to use between my laptop and my headphones. It brought out even more of the jagged sort of shrills or sibilance.
I've been interested in this mod since i first read about it, but very suspicious, trying to understand the different viewpoints and preferences of the people writing here. I've been sceptic since a lot of this is so hard to define objectively when it comes to sound. But I'm very curious and also very much a DIY person. So i ordered some locally available dampening mat which looked very similar to the dynamat with the foil and all. I't was a brand called Mohawk, not much of it can be found searching in the internet. sticky gooey stuff about maybe 4 mm thick and an aluminium on top. I used the template (thanks. Don't have printer so i traced it out on a transparent paper from my screen. Worked out well after I zoomed it so the 1" marker was in scale. I did the partial mod with the ear cups around the grey disk and the inner circle for the drivers backside. Not any stuffing of ear pads yet. To avoid any unwanted reflections (and this is my own theory) punched the surface of the foil full of dents with a sharp knife. just to make the surface very ripply. (read about peolpe using some cloth to cover it). Then i put these now slightly heavier headphones on my head and voilá, it was a noticeable difference. I'm not an experienced Hi-Fi freak, but still very glad it did this mod. Now i know what you guys mean with the bass having more resolution and tightness. And maybe it's the burn in or getting familiar with the sound signiture too but the highs are sounding smoother as well. Maybe i'll try the stuffing/taper mod to improve the soundstage, but I enjoy these as they are for now. Just wanted to write my experience as a thank you to Markl and all others who contributed.
Cheers from Finland,