Best sound dampener?? foam or cork??

[rahvin]

That is spray foam insulation, not car undercoating (asphalt based). Two completely different products.

 

[hfx]

Asphalt coatings work to damp sound largely because they are so heavy. The extra weight on your case panels increases their inertia and thus the amount of energy required to make them vibrate. The energy of course must go somewhere, so it either ends up as heat or it vibrates the panels so slowly that the noise is out of the range of human hearing. The more weight you add the better the damping.

The denser and heavier a material is the better it will damp sound. Sound it primarily transmitted out of your computer in two manners. the first is by vibrations of components traveling through each other, into the case, and out into the environment. The best ways to fix this are to mount all fans on rubber dampers (as suggested above), to add weight to body panels, and to add rubber gaskets between body seams (where the case meets the frame).

The second way sound exits your case is by the air in the case carrying it to body panels or out through direct exhaust. The best ways to stop this method of transmission are to add weight to body panels, to use trapped air to damp the vibrations, and to close all intake and exhaust ports on your case (not practical). Here the amount of air that can travel through the material affects things significantly. An open cell foam will allow air transmitted vibrations to travel through its depth. A solid body with few cavities (asphalt) will not transmit air, so air transmitted vibrations transmit their energy to it and then to your case. Again, the heavier your case panels are the better this will work. A closed cell foam or closed body will absorb vibrations and reduce them because the air trapped within the cell(s) will tranfer the energy to the cell walls and generate heat. A standard closed cell foam will transmit some energy to the material, but the material lacks elasticity and will still allow most sound through. A urethane foam or foam rubber will damp sound better because the walls of each cell are elastic and absorb more energy. A large butyl rubber bladder will absorb quite a bit of sound as well, because the walls are both elastic and heavy and the cavity is large enough that smaller, higher pitch vibrations are not transmitted well.

Since urethane foam, foam rubber, and butyl bladders (WW2 surplus water bladders) are expensive and still not very heavy your best bet is to get a number of rubber washers - hardware store, some thin rubber weather stripping for case seams - hardware store, and grill filters for your fans to break up turbulence (mesh work best - http://www.2cooltek.com). If you feel like adding weight to your case panels then get a few asphalt shingles (you can tar paper, but it's not as heavy) from the harware store or building supply and a can of 3M Super 77 apray adhesive from the hardware store. Bond the shingles to the case panels to add weight. They're cheap so you can add several layers if you want. The spray adhesive peels away easier than the adhesive on Dynamat, but you'll still need some solvent to get the residual off.