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Re: Sound Deadening

To: "David Councill" <>, <>
Subject: Re: Sound Deadening
From: "Rick Lindsay" <>
Date: Thu, 21 Feb 2002 10:38:39 -0600
   David, what is your exact goal?
   The DynaMat solution is pretty high end.  I see that as
the stuff you use in your 750iL restoration project so you
can hear the nuances of each of the violins in the section
from your zillion-dollar car stereo.
   The stuff inside doors is sometimes called 'anti-drum', in
that it's goal is not to insulate but rather to stop the larger
panels from resonating.
   Old BMWs uses what amounts to thick layers of tar paper
attached to the floor and inside doors.  I have seen actual
tar paper used in restorations -- and used well!  Carefully
cut a number of layers (3 or 4) and cement them in place with
roofing tar (cement)!  That will anti-drum about anything.
Newer BMWs negate the problem by eliminating many flat
surfaces.  The floor is 'crenulated' so it won't drum; stronger
   Foam rubber could be used but as leaky as LBCs can be,
I have always thought of any 'open cell' material as a good way
to guarantee rust by holding water against metal.  Read: sponge.
Closed cell foam like the stuff they use in swimming pool mats
and 'noodles' will work.
   Remember, in any acoustic insullation, the goal is to hold
air trapped.  If I was trying to really quiten, say a B-GT, I
would put anti-drum in the doors and on the inside of any
panel larger than 6" square; 1/2" or so closed cell foam custom
fit to the inside of the firewall THEN install the under-dash
finishing trim, thereby creating yet another air cell between
the engine and the cockpit; and 1/2" or better carpet pad
below all carpets -- including the transmission tunnel.
   Extreme?  Yes, but if the goal is quiet, that is how to get it.
Open up any later model BMW and you will find most of
these tricks.
  Does any of this help?


> I was pondering the relatively expensive sound deadening material that
> sells for my bare floor boards. Any experiernce on this stuff? Is Dynamat
> better choice? And where could I find this stuff? We don't have Pep Boys
> here in Montana that I know of.

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