There are different types of carpet there, cool guy. Acoustic carpet is the theatre stuff and it absorbs sound. Acoustically transparent carpet lets sound pass through it. Its used where a grill or trim panel is going to be covered with carpet to match the surrounding panels and also needs to allow the speaker behind it to play through. Very useful in stealth installs and was used fairly readily in the 80's and 90's. Most unbacked automotive carpet is fairly transparent to sound.
