I am only doing front speakers right now, and do not see myself ever doing a sub. I am putting off rears for now. I have bought a
Dynamat Extreme door kit which is 4 pieces of 12" x 36" [12 sqft @ 0.45 lbs/sqft = 5.4 lbs]. I plan to put this on the front doors only, and maybe double up behind the speakers.
You'll note that their inexpensive
Speaker kits (only $18 for the extreme kit at
onlinecarstereo.com) just put it behind the speakers. Obviously that is putting just a tiny amount and is nowhere near doing the whole car.
Now I am no expert in this, by all means. However, I have read a number of reports that it does work and really improves the sound, especially the bass and mid-bass. Without a sub I am concerned about the bass from my main speakers, so I'm thinking I'll spend the money / weight. I won't be doing a before/after comparison (will put it in at the same time the speakers go in), so I won't be able to give you my opinion on the effectiveness. After all, a lot of people believed in green markers on CDs, so who really knows. But it makes at least some logical sense, so I'll give it a try.
Since the STi is a performance car, I won't be putting more in. With no sub and the volume I listen to music, I won't worry about resonating (there is not much I hate more than hearing
thump,
thump from any car -- impressed is rather the opposite of my reaction). For a minivan or a highway cruiser, I could see coating as much of the car as possible with this stuff (or
Brown Bread), then using some of the
foam absorber in door panels to really give a solid feel and block a lot of noise. Sounds great, but it would add a lot of weight. I'm already getting people suggesting that I'm stupid for putting a stereo in the STi at all.