Dynamat/sound deadending help?

Okay, so first question. Now when using dynamat or some sort of sound deadener all throught the interior of my car, is it just making the interior sound better, or when the subs hit, will it hit harder outside of the car also? Secondly how many SQ ft of dynamat/sound deadening material does one generally need for a 2 dr car (91 eclipse). I was looking at 20 foot, but dunno? 50 ft? thnx in advanced

well first off I would go with second skin....it's the best. What the sound deadening does is a few things...... Eliminates rattles.....Improves midbass in doors... can make subs slightly louder..... eliminaes road noises

sound deadener helps "absorb" rattles, but mostly it adds mass to objects so that the objects will not shake/vibrate as much

if you want to know what i mean, find a thin bare sheet of metal, and tap it, what happens? it feels hollow, resonant, but now hold onto it with your hand, and hit it, what happend now? there is less of a "hollow" sound which will effectively make ur sound system better