[FC] Interior Panel insulation

[corvanatics@corvair.org]

I've used the modified tar/rubber construction waterproofer strips (usually 
found near the windows in Home Depot) as a low cost substitute for Dynamat. I 
can't tell you it works as well, but it does work, and I think it comes out to 
less that a $1 per sqft. I've come across two kinds; one only has removable 
plastic film on one side, the other you can peel it off both sides. If you get 
the second kind, you can then attach thin closed cell foam rubber or other 
material to the already sticky tar-like material. The way the modified rubber 
stuff works to stop sound is to keep the sheet metal panel from reverberating. I 
don't think it does much to stop sound waves that are already in the air (i.e.; 
road and engine noise would be reduced, but someone honking at you wouldn't 
be deadened as much). That's where you add the foam rubber.
   I've done some sound insulation in buildings for music rehearsal space, 
and I'm sure that the principle is the same; use sound absorbing material 
between the source of the sound and the wall, and don't let anything "hard" (wood, 
metal, etc.) touch anything "hard" between the sound absorber and the wall. 
That would let the sound waves travel through the sound absorber and the wall. 
You can use rubber washers to isolate metal from metal if possible. I went to 
great lengths to isolate my engine cover from the body in My Greenbrier, as well 
as the Tranny cover. I also used that foil covered insulation material (like 
for hot water heaters) underneath covers with excellent results. It's nice to 
have a waterproof insulation that you can hose off if you like (make sure to 
seal all the edges with stainless steel tape).