Howdy all. I've been modding My HD800's for several years now, and Have spent a lot of time getting to the current mod stage... It's gonna be a bit of a longer post, so bear with me. Why I mod the HD800's: I got my HD800's in a trade for $20 and a handful of thriftshop records. It's a funny story, ask me about it if you see me in person some time. the Tl;DR is amazon shipping mistakes are hilarious and rich hipsters don't know anything. But basically, being a recent, underemployed college grad, I have limited funds, so the option of buying flagship cans isn't really on the table. I do a lot of mixing and mastering projects though and I live with others so a good pair of headphones is a must. What I'm looking for in a pair of headphones: Linearity. I need the headphones to be neutral, but slight deviations from this aren't a problem (I use EQ in my daw to hit a target curve) However the headphone can't have wacky peaks or valleys or be super fatiguing. Plus I'd like to also be able to use it as a daily driver with minimal EQ if possible. So here's what I currently have: Internally: I'm using the SDR mod, a variation of the SBAF rug mod, except instead of the thick rug liner I have a thinner, more rubbery shelf-liner material which soaks up less high-mid/treble energy, and evens out the low mids more, I also use the trapezoid mod on the black plastic, my chosen material is a kind of closed-cell double-sided foam tape. It's a little thicker than cork and I prefer the absorption characteristics and CSD results. I also have used some medical tape to make the pad opening a little smaller than the ZMF pads already do. Driver: I have done Serious' driver dynamat mods, re-using the foam from the underside of the metal ring as baffle damping stuck on top of the dynamat. I've also more extensively dynamatted the back of the driver spider. Accidentally broke the teeny wires on one of the drivers and it was a massive pain to get it soldered cuz it was so small. Not recommended. Externally: I had a really complicated damping scheme previously on the back, involving closed and open cell foams covering the center hole and ports, a bizarre taped-up cotton rear-chamber that looked like Princess Leia's hair had grown infested boils. Kinda the reason I named if the fugly mod. Fashion potential was up there with audiophile fanny packs. Now I just have dynamat on the silver outside part of the cup. In investigating the behavior of the HD800 enclosure, there's been a wealth of great mods involving the inside of the cup, but I found the spun aluminum stuff to be relatively transparent to sound... The cheap silver plastic however, is a nasty and awful material to use in audio. So once we SDR, SBAF and pad swap, we have a basically much improved 'room' or cup environment. A backwave damping scheme can help to linearize the bass more, but often at the cost of imaging and soundstage, and the HD800 driver really will never have tight punchy bass like a Focal can for example. Doing more internal cup modding can either overdamp or horn load the driver which causes terrible bass and usually shouty middrange issues. On doing some poking and prodding of the enclosure after removing the fugly backwave damper thingy I noticed that applying a little bit of dynamat to the silver outside of the cup helped smooth out the treble and bring up subbass... so I basically covered the entire back/outside of the headphone in dynamat. The results were some funky treble dips and crappy, overdamped bass. So I removed dynamat until I got the balance you see here. Just the silver outside and the back of the driver. This seemed to produce the best combination of bass while smoothing out but not killing treble. Oh, I also use a ZMF protein leather headband pad. It's really nice and soft, and I have kind of a big noggin so the smaller openings of the ZMF and the increased weight of the pads mean the thicker headband is more comfortable for me. YMMV. So how does it sound? Here are some miniDSP EARs measurements. I removed the calibration file (basically just a scoop at 4Khz) My EARs seems to have a bump at 5khz, and then a weird spike at 9khz which moves around a lot depending on position. Ignore those two areas for now. I haven't got around to calibrating it precisely because positioning changes the exact locations. I'm fairly certain they are measurement rig deficiencies however. My setup is a bit noisy, so distortion and CSD measurements aren't as good as they could be, but still very clean. The worst offender is actually in the bass now - you can see that the treble and midrange is almost entirely cleaned up with practically no ringing or junk. Subjective impressions: For how easy this mod is to do, I'd have to say it's yielded the most peace of mind in a while. I don't recommend Serious' dynamat driver frame mods unless you're willing to void the warranty. The screws are so small and absurdly tightly torqued and the plastic threads fragile enough that breakages are nearly guaranteed unless you have a featherlight touch. However, with all these mods in place (the ZMF pad swap is huge) the HD800 retains an above average soundstage, very linear, neutral sound with just a touch of sweetness and darkness in the lower mids. I think this is an inherent characteristic of the sennheiser drivers, resolving with a touch of low mid/mid bass a la HD650. The lower bass is still kinda soft sounding even though the level is better. Treble is clear but not harsh at all, the only thing I'd want would be tighter bass and a tad more subbass, but otherwise the headphone is wonderfully smooth and even more highly detailed than the stock HD800.