now I've started something
it makes a huge difference. camera isnt here but I'll show you a 33 door (beofre and after) when I find my camera.
the whole idea is to make the door as acoustically dead as possible (there is a LOT of tech to this but that is the gist of it,.) so you have almost zero refelctions and cancelation.
the foam stops the reflections the sound deadening stops the panels from moving by adding weight. the result is better sound and a quieter car when the music is off.