I just got a infinity 12 inch sub. After installing it into my box I noticed there was some black foam with adhesive backing in a bag that same along with the sub. Its thin and looks like it should go around the speaker trim. Whats it for exactly? Does it go around the subs circumference, in the middle between the box and sub. Some kind of padding? Or is it something to cover the screws? What is it for? Thanks.