Sound Deadening

Assuming that butyl and asphalt products perform exactly the same (I don't know that I'd agree with this assumption, but will concede for the sake of this argument), I think it's fair to say that the only advantage of asphalt products is the lower price. I could not be more sympathetic! Who doesn't want to save $$$ ?

For those not looking to break the bank for sound-deadening, one of the things to consider is how you use the product - asphalt, butyl, whatever it may be. The 'mat' products (the sticky stuff with aluminum backing that slices your fingers to bits) are mostly effective at controlling panel resonance. Putting the 'mat' at the edges of panels, support ribs/braces, etc, will have limited benefits when it comes to sound. Or rather, it's not making the most of what they do best. By focusing a smaller amount of the product in the center of panels (floorpans, door panels) you are getting more bang-for-your-buck by making the best use of their intended purpose: controlling resonance (vibration) by lowering the resonant frequency of the panel. Also valuable for those worried about weight.

Once you've taken care of the resonating panels, you can then cover everything else with mass-loaded vinyl or closed cell foam (this is important! open-cell foam will collect moisture and rot) to lower overall sound levels. This stuff is generally cheaper per SF than the 'mat' product. Getting the mass-backing option on replacement carpets can help significantly as well.

I'm not a client or user of his products, but Don over at www.sounddeadenershowdown.com has a long history of studying this stuff and there's some good info to be found there.

Just some more stuff to ponder. Turn that sh*t up! :D