Great for eliminating bass
Crutchfield Customer Review (What's this?)
Contrary to all acoustic principles, these will cause any speaker to deaden all bass. After installing in 2012 Escape, I tried with one cappy factory speaker and one Rockfield Fosgate P1683 6 x 8 with a boom mat. The factory junk speaker had far more bass than the Rockfield Fosgate. There is no room once the speaker is enclosed inside the boom mat to allow any speaker to reproduce bass. The larger the enclosure, the more bass.It's an acoustic principal. In fact, the product info makes no claims about increasing bass. I cannot recommend.
Pros: May protect from water or rattles.
Cons: Deadens all bass from any speaker.