At 10:46 AM 4/8/2010, Alistair Bell wrote:
>Supposedly the best thing, after applying the panel dampener is a,
>(oh shoot, I forget the term), a "de-coupling sheet"  - heavy vinyl
>sheet that absorbs the vibrations, then some foam type insulation
>(closed cell foam best in the van, for obvious corrosion reasons).

You can get multilayer lead or lead-substitute silencing material
from marine suppliers, intended for lining engine boxes/rooms.  It's
pretty spendy IIRC.

When I was a lad the Navy was using a composite substance for
submarine quieting -- they called it RAL, or rubber-air-lead.  I
found a piece of it once and asked my dad about it.  It was maybe 3/4
or an inch thick, bendable but not stretchy, black rubber-stoffe
impregnated with little flattened voids and similar-sized flakes of
lead.  A bit dirty to handle; I probably took five years off my life
playing with it.  I'm guessing it was cast in some way and then
rolled to thickness.  No idea whether they still use it.

Ah ha.  Here's a milspec for the version that superceded what I'm
talking about.
<http://www.tpub.com/content/MIL-SPEC/MIL-R/MIL-R-23074C/index.htm>.
This type is made with molded grooves filled with #8 lead shot,
weighs about 5 psf.  It was "inactivated" in 1998 -- obsoleted?  I
don't want to pay USD24 to read one page of bumf.

Yours,
David