I just got mine (from my forwarder, Massdrop actually delivered this to my US Address like lightning) and I'm just getting used to the sound. I didn't want to join the original drop and got the HD6XX instead, but when I saw the leaked graphs of preproduction I wanted to smash my head on the wall, so when Massdrop announced there will be some leftover units to dispatch immediately, I was sure to be one of the first to join when the drop was lived again. My unit actually was the 4846.
I already have HD600, HD6XX, Momentums V1 (My favorite, so far) and ATHM50. Also, all my impressions are just from laptop audio without a dedicated DAC/AMP (Still waiting my Aune X1S)
So, THIS ONES ARE AMAZING, Bass it's not so overwhelming like in the HD6XX, but hits harder, while retaining some of the treble clarity of the HD600 (maybe too much some times).
This is a FUN headphone, but certainly not V-Shaped, the glorious mids of the HD6 family are there like the star of the show, it's just that this time the bass it's really punchy, and the highs doesn't feel recessed, it sounds correct, or at least it's the one that, to my ears, sounds closer to the Momentums V1, which is why I actually was looking as a headphone upgrade.
Comfort wise, it's the least comfortable of all my headphones, clamping force it's the stronger of my HD6's, but tolerable.
Soundstage it's also the narrower of the HD6's, almost like a closed back headphone, with the HD6XX being the widest and the HD600 falling mid way between those 2.
Cons: Maybe it's the extended treble, but I can perceive some little bits of harshness that weren't there before, and just in the right side, don't know if it's the recording or a defect in the driver. On this same note, some recordings can be a bit of fatiguing, though nothing compared like in the M50's.
For $ 150, this is maybe the best overall value headphone that exists right now, it certainly gives a fair fight to it's older siblings, I wouldn't go that far as to say this is the best of the HD6 family, though that is my feeling right now (leaving aside the HD660S which I haven't listen yet), but maybe it's new toy syndrome, so I'll be cautious and will give it time to fully assimilate their sound.
However, if you're wondering which one to buy, between the HD600 and HD650/6XX, and you'd ask me, I'd say THIS ONE, forget everything else, get THIS.