Sound Dampening Info
I have NO affiliation and have purchased nothing from it. The info is great and I wanted to share it so we could all benefit. You don't see very many places telling you to buy less and minimize your expenses because the rest is overkill or to buy it local or somewhere else.
Ed
http://www.sounddeadenershowdown.com/
I now link the old version, when it was just about information, and not selling products.By the way, as I have said many a time and will continue to say, foam is MUCH better than mat as a general purpose sound insulator. Mat is only good for vibrations. I do NOT recommend mat to be applied to an entire car, because it will not help as much as you think, and it will add way too much weight. I recommend strategically placed mat plus a layer of Secondskin Luxury Liner. Or you can use a couple layers of whatever foam - I first used Ensolite from RAAMAudio.

