Hello Dave and all,
Very interesting post, even if it approaches several aspects which would require several developments.
I wish to contribute only about the surrounding and cone/dome treatments:
It's true that if a membrane has to be damped, the wave energy must be converted into heat by friction or viscosity. The real problem here is that the wave MUST be propagated from one environment (the membrane) to the other (the treatment layer or the surrounding). Now, if these two environments have not the same or closest specific mechanical impedance, the wave is obligatory reflected and will return to its source. In such a case, we have to place some materials having progressive impedances to allow the wave to be propagated from one to the other. In a driver, it's impossible because of the lack of place and because it would weigh down the membrane too much.
Damping materials (surrounding or treatment layer) must have feable specific impedance (non-isopropic, great absorbsionQ _k_on the good fr-range) to be efficiant, it's why i.e. foam is better than caoutchoug or latex in this matter.
Metal cones have high impedance, paper and fabric have less impedance, at least closer to that of the damping materials.
So, in fact, it's a lot easier to damp a paper cone or fabric dome than a metal cone. Believe that we can damp a metal cone resonance with damping layer or surrounding is utopian.
Also, another little explanation: the accuton membranes (ceramic) are more damped than seas membranes (magnesium) because in (this) ceramic are a lot of very small air bubbles; the wave propagates in the ceramic, then in the air-bubble (different impedances) and on and on; the wave is partly absorbed by the air, parly reflected at the frontier between air and ceramic. Here it is not a friction or viscosity which damp the wave but the multiplicity of the reflexions which allow the wave to lose its energy; result: more dampening than in the more isotropic metal.
I hope my bad english was good enough to allow you to understand what I said. Hi, rez
