OK, spent more time with the Z7 (I'm assuming still modded) today from a variety of DAC/amps that I have on hand. The first night I tried them, I thought they sounded OK from my phone, but I didn't listen too long or closely. After some dedicated time with them, I've decided I really don't care for them. I must have been in a more forgiving mood the first night I listened, hehe.

I've heard quite a few describe these as a bit laid-back, but I do not hear that at all. Even from a warm, mushy NOS DAC and a couple different nothing-super-special amps, the Z7 sounds somewhat shrill, metallic, and even a bit bright to my ears. There's some sort of upper-mid and/or treble peak, if not a slight bit of resonance (sometimes my ears mix up peaks and resonance).

Bass seems OK. Extends well but despite the measured emphasis has less kick than I expected. Gets a bit indistinct the lower it goes. Otherwise seems fairly balanced.

Upper treble response seems pretty good. Fairly clean and fairly good at detail retrieval, probably the main area of potential here. I liked what the headphone did for cymbals, though the tone issues I mentioned above did hinder this.

Sound can be a bit nasally at times, or, at least, that's how I want to describe it. Soundstage and imaging seem pretty decent, probably another area of potential.

Looks, finish, feel, comfort...all top notch, of course. I like the cables and cup connectors. This sort of stuff makes me want to like the Z7 more, but they just hurt my ears pretty quickly due to how they sound to me. I would like to hear these from a nicer, more powerful amp than what I had to use it with, but I suspect that won't change my mind much. I think with some additional tuning, these might make for a good mid-fi headphone. As they are now, though, they're not for me. Maybe I'd be a loaner in preferring them without the current mods in them? Haha.

I've got quite a few things on my plate this weekend, so I only had time to take a few quick measurements from the left channel. They all looked pretty consistent, so I just picked one. I think it's the weirdness from roughly 700Hz to 3 or 4KHz that bothers my ears most. CSDs don't look bad but might indicate some extra resonance around 1KHz.

but will also most likely leave the back hollow since I think the drivers need that breathing room in order to reproduce bass.

Acoustic fiber (not cotton or random fluffy materials) effectively expands the volume inside the cups.

I used toilet paper for front damping. Front damping is always tricky because you don't want to kill the sound like how those big felt discs did on the dog training kits for the Alpha Dog.

Did you try applying strips of dynamat extreme like materials (mass-loading / absorption) on the baffle on back of the driver (being careful not to cover the back vent)? That helped a little bit in terms of speed.

Yeah, I tried dynamat. It seems to do the trick, but the reflections off of the aluminum surface causes some extra spike or resonance that I can detect (somehow the measurements don't really show it, so I'm guessing more resonance than spike). So for now, I'm only putting dynamat in specific spots.

I think the dry vocal can be traced to the hump around 2-4KHz... because my ATH-ES10 also had a hump around 1-2KHz (slightly lower) that causes a bit of harshness, but not as "dry" as the Z7.

Tried felt, foam, shelf liner, microfiber cloth of different thickness, etc... on top of the driver opening in various sizes and no dice. I think it's best to leave at least that opening, and probably reduce reflections around it with the plastic enclosure, the ridge, and the ear pads...

Well, going to keep experimenting. The Z7 really sounds very close to being perfect to me. The lack of blackground has been somewhat addressed now, so I'm happy. Initially, it does sound really grey, and that grey-ness actually persisted for a while until I learned that damping this headphone won't be the same as damping other headphones. Perhaps that's why Sony left the back completely open.