Technical Sound Deadening - What are the options?

[turbo500]

I believe from the factory, the 500 came with felt cutouts that went behind the rear seats top & bottom.

I've noticed that several online stores sell different materials for sound deadening in the 500s.

Here are the options I've seen:

Felt roll (popular on classic cars)

Bitumen coated sheets for sale

bitumen+felt (slightly thicker)

aluminium rolls with different properties (heat/noise/etc)

I did some research as well, and there are some other interesting materials that people recommend, one of which is Closed Cell PE Foam. Some suggested that higher end cars are lined with copious amounts of this stuff, adding large amounts of weight, getting in return a very quiet drive.

Example of Closed Cell PE with adhesive backing

Now, obviously, the 500 will never be a silent car, it was not designed with this in mind. But I know several people on here have used various types of insulation.

I was looking to get some feedback on anyone who has put in new sound deadening, to see what their results are and if anyone has anything to say about the various materials available.

I'm considering using this Closed Cell PE, since it's thicker than aluminium sheets, but haven't seen many classic car owners use it. Jute seems to be outdated as it has the downside of being thick, and absorbing moisture. So with all these newer materials, I'm sure there's something that can help.

Ciao

 

[kennyrayandersen]

I'm not sure how much room is there, but the real truck to sound deadening is two fold. First dampen, second isolate. There are several such as dynamat which have a bitumenous layer with a heavy aluminium foil outer layer. The bitumen layer has high internal damping so the panel it is placed on won't 'ring'.


The second method would be to isolate the panel so that it doesn't pass the vibration on. This is done by having multiple layers with different densities i.e. the first layer might be, 1/4" of foam followed by a heavy metallic layer followed by another acoustic foam layer. What happens is the panel vibrates but the heavy metallic layer doesn't respond.
The frequency of the panel would generally be higher and the first layer of foam just jiggles underneath the metal layer.

It's always about striking a balance between sound deadening and weight. The sheet metal on a 500 is actually thicker than many of the modern cars albeit there are no crumple zones or reinforcing beams etc. So I say that because the inner wheel wells are pretty stiff. My guess is if you put the damping material on the firewall and back seat you'd get a fair amount of it knocked out and then if you put some on the floor as well you get most of the available benefit.