Crutchfield Customer Review (What's this?)
I bought these for water protection, not to try to improve sound quality. I thought mine were too large at first, but they actually fit just fine for my 6.75" speakers. They form a nice gasket between the back of the speaker and the mounting surface, and it's easy to cut out the 1/4 of the foam that faces the bottom of the door. The result is a well-protected speaker that sounds great.
Pros: Protection from water leaking through the door/window seam. Fits Serves as a foam gasket between the speaker and the mounting surface