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Originally Posted by Kabeer
So it turns out the Yamaha YHD-2 has two layers of some fairly thin barely useful tissue felt behind the driver.
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I believe it's a dust protector disc. Nonwoven but porous and acoustically close enough to transparent as makes no odds. Probably reflects a little treble, which is all to the good, but obviously something a bit stronger in effect was called for.
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Originally Posted by Kabeer
Comparatively the Yamaha YHD-1 had an even more useless layer of thin reticulated foam behind the driver and then one layer of that tissue. (thats the foam that turns into sticky goop).
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Maybe they had a rattle problem. Who knows. That's why I'd love to sit one of the designers down for some jasmine tea and a little chat. It's sad that no one from that era has come forth.
As for materials and resonance, keep in mind that the problem is complex. Sound can travel through materials and along materials, and can be reflected from materials. If you have any doubt about the suitability of a plastic or wood, form it into a cup, hang it by a string and tap it with something. Ideally you'd hear nothing more than the click of the impact.
Mostly what you want is a compound that is
self-damping or lossy and a structure that acts as a "vibration sink"-- in other words, a step input applied to one part is transmitted to the entire structure, which converts the energy into heat and dissipates it. A monocoque. Two nested shells separated by a thin viscoelastic layer would be the ideal, but perhaps overkill.
