Old enough to know better
Join Date: Dec 2006
Location: Beacon, NY
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Re: Acoustic Insulation for engine room?
Recent episode of Holmes on Homes emphasized the need for a dead air space between sound absorbing sheets. They got 50dB of attenuation that way, especially effective for lower frequencies (like engine noise).
A friend in a sound lab, told me that when using lead on foam, the foam makes no difference whatever. It's the lead doing the sound deadening.
Carpet is just as effective as fibreglass, just a lot tougher, and easier to deal with.
I think the foam acts as an air space, so it in it's self does not stop much sound, but it creates an airspace.
By the way Dynamat is really just asphalt, so there are adhesive roofing materials that work the same, again really just the mass of the heavy coating. The stuff does smell pretty bad though. I have used it successfully in car installations.