I had a friend who knows a lot about car audio build a box (sealed enclosure) for my sub (JL 12W0) about 2 years ago. I opened the box just now (removed the speaker) b/c I am planning on using the same box for my new sub, but I noticed he put like big sheet of 1" thick cotton in there.
Is this normal? Does this not effect the overall volume? Why did he do that? Any response would help..