Sound deadening mat installation Q's

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I'm ordering some acoustical mat to install in a couple cars. I see on several brands' websites that they say to make sure and cover everything and overlap the edges. Is that really true, or are they just trying to sell me more product?

I guess my question is this: In my wife's Tercel I want to get some panels to be a little more dead around the speakers, and I want to cut out a little noise, but I don't want to do things like pull out carpet and seats. If I do things like the back deck, trunk floor, some in the doors behind the speakers, etc, will it be worth my time, or does it have to be all or nothing?
 
There's 2 ways to sound damp things;

Mass damping, where you simply make the panels heavier, so it takes more sound energy to flex them, and also lowers the resonant frequency of the panel.

Stiffness damping, where you use braces and other structural materials to physically prevent the panel from flexing, this typically raises the resonant frequency, but the required sound energy to "excite" the panel treated in this way is increased dramatically.

Idealy you want both

Now we apply these principles to the car, sheet metal is very strong in curves and bends, and weak in large flat or gently curving areas.

There for most of the panel flex will occur in the large flat areas.

bah I'm rambling again, in short, attack the areas that need damping the most, or look like needing it the most, you get most of the improvement in the first 80% of coverage with diminishing returns after that.

100% coverage and overlapping edges are nice but don't stress over it:smash:
 
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