Allan - you asked:
>Does anyone out there have any ideas on sound deadening materials to reduce
>interior noise levels? ... What we need to know is what has maximum
>attenuation for lowest weight, and best place to put it.
I fear that the depressing answer is LEAD! To achieve real sound
attenuation at low frequencies (and those are the ones that engines tend to
make lots of) you need mass, and preferably mass that doesn't 'ring'.
Higher frequencies can be easily attenuated by fibrous/foam materials.
These can also help make things quieter by reducing reflected energy within
the treated compartment as well as energy transmitted through whatever
bulkhead/skin they're attached to. This means they can be used with some
effect inside the cockpit as well as beyond the firewall.
I don't know what materials are suitable for the unpleasant environment in
the engine compartment - I think fire safety, etc, should take precendence
over ultimate sound deadening ability.
One thing to consider is that a certain amount of noise will enter the
cockpit from the engine via its mounts and the solid structure of the
aircraft - it would be a lot quieter if the engine was not actually
connected to the rest of the aeroplane, but that's difficult to arrange
....
Sorry to sound so unhelpful, but I don't think there's any quick fix.
Naturally I'm open to correction from anyone more versed in the science of
acoustics as it relates to aeroplanes.
cheers
Rowland
... that's Rowland with a 'w' ...
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