for you who are sweating noise control stuff:
Here is an article (HTML Document format) from Boeing on light weight ACTIVE noise control
material. It is very interesting but the material is probably not really available.

My experience with PASSIVE noise absorption material is that weight is the
first order gauge of  effectiveness.  That is, a pound of lead, a pound
of bricks or a pound of chicken feathers has the same sound reduction
effectiveness within 10 percent.  Noise is also perceived logarithmically,
which means a 10% change is completely trivial. Therefore it makes no
difference what material  is used.  Chose the material  for convenience of
installation and cost.  Exotic high cost "miracle" stuff does not really
perform.

But the biggest item is to close all the cracks and holes between you and
the noise source and it also makes no difference what you use to close the
holes and cracks.  This is the biggest control.

There can also be resonant vibrations of panels but usually these are not a
factor for compound curved epoxy reinforced panels. It is more of a problem
on RVs and spam cans.

Ross W. Colebrook 235 N7828