A short dissertation:
There may be several aspects to consider when sound proofing.
Considering how light acts helps. There are several methods
used.
1) Changing the direction of the sound.
2) Sound entrapment.
3) Sound attenuation.
Changing the direction is used to reduce echoes. I.E. the egg
crate surface.
Absorption of sound as used in pockets or cavities in brick walls
until which doesn't allow the sound to reflect back into the open
space. It eventual ceases due to this constant bouncing around
loosing energy each time it relects.
Sound attenuation by increasing the vibrating components mass. A
larger mass vibrates at a lower frequency which is less
irritable. Also a larger mass takes more energy to put in
motion. E=M(V*V).
Remember the more solid (dense) the medium, the better sound
travels in it. Ever listen to a set of railroad tracks?
So, you would need material with mass, irregular surfaces, and
interior cavities to reduce sound. Many cars use a combination.
On my 240Z, the first layer on the floor is hard dense rubber 1/8
inch mat glued to the floor. (Increases the mass). The second
layer is felt. (irregular surfaces and interior cavities). The
third layer is the carpet which also has a thin layer of jute.
Heat is transferred by conduction, convection, and radiation.
For radiation, you need a reflective surface.
For conduction, you need a material that doesn't absorb heat: the
space shuttles tiles, asbestos, or some other modern material.
For convection, you need a material which stops the heated air
from circulating: insulation.
So, I believe the best medium for both sound absorption and heat
reduction would be a modern reflective material, with low heat
absorption, and with large mass (heavy), but not dense (soft).
The preferable installation would be to place this barrier
between the heat source and the floor or firewall. This would
keep these objects from heating up. Heat shields between the
exhaust system and the cars body would also help on heat buildup
and use heat resistance mountings between the pipes and the cars
body. For example, on my TD I have a layer of asbestos gasket
material between the circular clamp and the exhaust pipe where
the pipe attaches to the transmission bracket.
Blake
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