going to vary for every vehicle of course, but my explorer is a LOT quieter outside the vehicle after i did the sound deadening. granted i went overboard and did over 200 sq. feet, but i'd say at full tilt you can only hear bass 15-20 feet away. thats kind of the point of deadening is to keep the sound in your car, and dampening the metal to lower resonation.
i've had the deadening in for about a year, so i can't compare with the setup i have now. at the time i had 2 fi bl 15's on 3.5kw, before i did it i parked and walked away from it to see how far you could hear, and i got tired of walking and came back after about 1500 feet. that was with all the windows down and the sunroof open. same test after the deadening, and i think it was about half that distance.
if you're talking about a trunk car with the trunk sealed off from the cabin, you probably wont accomplish your goals (which are pretty childish goals, but thats been stated several times already) with sound deadener unless you have it port through your rear decklid or something like that.
heres a video of my explorer, i put the windows up about halfway through the video so you can see the difference.
//content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif wow why do people really want everyone else to hear their music. build the system until it sounds good inside it's for you fuk everyone else.
I want my car to look like its morphing rolling down the road from the flex, but i could care less if other people heard it. Besides i think it would be fun to drive around wearing some blaze orange ear muffs like the guys at the airport wear.