Can someone comment on the appropriate uses of sound deadening products? Is it all marketing hype? Where do you put them? Under what circumstances? Thanks
Sound deadening products work! They should be used in areas of your car which rattle when the bass hits. Most people use them on the trunk, roof, reardeck, and interior panels which normally rattle.
the purpose of damping materials (and they do work) is to absorb metal resonance and vibrations, which means less lost energy. this translates to more SPL, and cleaner sound, and usually, a better resonant frequency for the vehicle cabin. dynamat, or other similar matting materials (they're all about the same excepting price) should be laid in strips on all metal surfaces, about 2" wise, diagonally, about 4 to 6" apart. you can cover the entire surface, but this uses more matting and doesn't really make any improvement in absorbing the vibrations. for areas you can't reach with matting materials, expanding spray foam works well. good for plastics liek the dash, too.