I got to try these at the last day at thr festival of sound, with acorn audio just behind me with his stock of zmf and his personal iha1 (my favourite amp so far). Headphone section at a British speaker show where the "biggest" companies are focal, naim, b&w, chord and all other brit-fi stuff which sounded dreary. So it was really quiet for a show. Sennheisser subverted my expectations a lot with this. Starting from the bass, it's immediately lost the control and resolve that was a significant part of the original hd800. The bass comes across as one note compared to the eikon and hd800S. It was definitely a lot warmer than the hd800S and it felt flabbier, to the extent that I would say that the eikon has a lot more bass control. The transition from bass to mids is basically a dip, upper bass is missing, the lower middle are missing. While I would say that the eikon has a mid honk, the hd820 seems to be much worse in this regard. What it does aside from the honk is contribute more to the thickness of the mids that the hd800 variants have. Rather than just having dipped upper mids, the lower mids are dipped too. This makes it really congested, which is worse on this than the hd800 because it doesn't have the same openness f. This seems to have a significant effect on the timbre, I already found that the original hd800 decayed slightly too quick. This seemed to decay a lot faster and lost a lot of the texture resolution that the hd800 has, it made the timbre really plasticy. This smoothed over plasticy texture described how I heard the general timbre and resolution of this headphone. It just seemed like every subtle nuance was just smoothed over, compared to an hd800 or an eikon. Sure I could hear effects like doubled vocals or reverb and tell them apart, but the same happens with balanced armature iems. I can hear the macro detail, but I can't hear the body around these things, the decay, it's texture or any of the small details which bring life to music like I can with other competitors. I'd say the resolution beats out my trusted hd580, but falls short of something like the eikon, while I didn't compare them directly at the time, it's probably around where the Atticus sits. The treble was quite interesting for me, since it wasn't as extended or as bright as the hd800. But for some reason it sounded really harsh. I'm usually fine with treble, the hd800 and the brighter adx5000 don't bother me. Stuff like the emu teaks, b&w speakers and now the hd820 do, there is this harsh brittleness to them which is fatiguing. It isn't fatiguing in the same way the edge from a violin or the sizzle of a drum kit is, these seem more like mid treble issues. The dynamics and staging of these headphones weren't my cup of tea. The original hd800 has that upper octave extension and because of that the stage expands quite far to the point of being somewhat diffuse. This doesn't have that, the mix of the mid congestion and the lack of air makes this headphone closed in soubding. Even if the stage is a bit further back than the eikon it doesn't sound as open. The dyanmics don't sound as clean and there is a general fuzziness to them, I'd consider the eikon superior in this sense as dynamic range is rendered a bit more naturally and matters because there isn't an overwhelming sense of congestion. While the hd820 shares the hd800S it doesn't share the same imaging quality, it images fine without any major issues, but that sense of fuzziness gets in the way. Considering the hype around these and my own sennheisser fanboyism, it's kind of dissapointing to hear these. My main issue with these is that they take the original issues I had with the hd800, made them worse whilst adding a couple of other issues, whilst also taking away what makes you deal with the issues the hd800 has. Technical capabilities aside, I feel that the tonal issues with these headphones are enough to take many cheaper alternatives over these, because the tone doesn't sound normal by any stretch of the imagination. I would rather have the eikon with it's warmth, midrange honk and laid backish presentation because despite these colourations, it's not as far off normal. For those people who stick with their hd6x0 instead of utopias and hd800s, I can see why you would have an emu teak instead of these.