Actually, since you brought this up here, I guess it might be easier to discuss it here.
The Z7 has some design "problems" from my standpoint that goes beyond just "intended" engineering design philosophy. Perhaps my approach to a proper headphone design would be different from how those at Sony see it, but here are some of the pain points I saw from my perspective:
1) The structure indeed acts like a massive box of air to create the "subwoofer" boomy feel. But only if that is the case in practice. In reality, the Z7 doesn't sound anything like a subwoofer, and it's far from that.
2) The cross structure in the middle is indeed a reflecting chamber intended to boost the upper midrange and lower treble to give the Z7 a bit of "clarity", per se, but all it really accomplishes is resonance at those frequencies. Measurements (not made by me) have shown that the Z7 has resonance around 3KHz, and then extra resonance at 7-8KHz.
3) The plastic enclosure is far too light to reduce excess vibrations caused by the super strong drivers. As a result, the Z7 would have a bit of extra lower midrange or upper bass resonance that can "mask" clarity. This is not shown on a frequency response graph since these graphs are obtained using an impulse sent at a specific frequency, but play back any other frequency, and the lower midrange actually would peak up a little in an RTA analyzer, suggesting enclosure resonance.
4) Having the enclosure that way would create reflections in the inner chamber that can effectively drown out any high frequency content. This is evident in actual listening.
So instead of sounding like a high-end headphone with subwoofer bass, as intended, the Z7 actually sounds like a muddy, thick, blurry, and super indistinct mess of a headphone.
As for my choice of materials, if you'd read the links you provided, you'd know a bit more:
1) The "thick rubber material" is actually a shelf-liner with essentially the same properties as sound-absorbent foam. Here's what your link has to say about sound-absorbent foam:
Generally available in two shapes / profiles, flat and egg box, the foam family are usually opaque in colour and have a closed cell construction, The foam cells are chosen to be a specific size / diameter in order to provide a bulk material characteristic suitable for acoustic damping, i.e. the cells are mostly airtight and provide resistance to the passage of air if you try to blow through the material. This closed cell structure absorbs energy when the cell content, air, is compressed and rarefied due to the sound pressure wave. This type of damping is used to alter the high frequency response of cabinets and transmission lines. It does not work well for low frequencies as the amount of damping / energy absorption which the foam can support is relatively small.
This is what I did intend for the foam to be. The foam is there to reduce extra reflections caused by the aluminum surfaces of the dynamat pieces underneath. Also, they lay relatively flat against the surface, so the reduction in volume is minimal. The reduced 80-250Hz content is actually due to the effect of blocking the top port of the Z7 rather than as an effect of the foam. The foam by themselves are only there to smooth out midrange and high frequency peaks.
Here are graphs (I didn't measure these, but you can probably look up the rest on Google) of the effects of covering the top and bottom vents on the Z7:
Covering top vent:
Covering bottom vent:
2) As mentioned, using dynamat as a dampening and mass-loading material would work well for reducing excess vibrations and resonance at lower frequencies, but they would cause reflections, so proper care has to be taken while applying these things. I did intentionally use the shelf-liner to tune the upper midrange and lower treble peak of the Z7, though, as I found those peaks to be too much contrast out of the recessed feel of the frequencies around them.
3) Using acoustic fiber or some sort of wool felt in order to "effectively increase internal volume" would work well, but then that only works for sound waves. It limits air flow inside the enclosure, and again, proper care has to be taken in order to make sure pressure difference between both sides of the diaphragm is minimal. I realized later on that the Z7 already has a fairly clever way to achieve this, and so... the ports really are just there to tune frequency response. Since I enjoy a more "flat" frequency response than what the stock headphone had to offer, I nudged the frequency response in the direction that I saw fit.
4) Since that post, I did poke around a bit more and learned more about the design of the Z7 to apply a more advanced scheme of the dampening mod in order to achieve a completely different sound. But the frequency response would look almost exactly the same, because at some point, I'd bump into the stock tuning of the frequency response of the drivers. That's a hardware limitation that would require more... invasive methods to alter.
Needless to say, I didn't quite like the way the Z7 sound at stock, but I loved its technicality.
I have not heard the CD3000, so I have no idea how it would sound like... but like you said, if someone already loves the way the CD3000 sound like at stock, then I would say... don't bother messing with it.
). I was inspired by the R10 ear pads, which I understand are angled (yes, I know the CD3k is already angled itself). The ear pads are a bit angled themselves and bear a pretty striking resemblance to the R10's pads, which is just neat! Isolation is amazing, soundstage is wonderful. :3 Memory foam and uber soft leather means wearing never gets tiring. Oh yeah, and I previously refitted an elastic strap in the headband so it would fit more tightly, which means no more loose CD3ks.