I have those on mine. They definitely add a cushion between the speaker and the door. But as far as hearing a difference no. It also protects the speakers from moisture which is a plus. But they are cheap so go for it.

 

for >$9 plus s&h? why not?

 

Simple answer, no.

Real answer, modern good car audio speakers are made of materials that are designed to last in the automotive environment, polypropolene cones, butyl rubber surrounds, and coated baskets. Also they are generally designed to use the air space of your door as an enclosure. Adding the baffle will give you more protection againt water getting in the door and on the speaker but that is not a major concern with a newer car. What they will do is create a much smaller enclosure around the speaker reducing it's ability to play low bass notes as well.

 

I use them, but I cut out the bottom half of the foam, where they act like a rain shield. The car audio shop I used to work at (why back when) used them primarily as rain shields. While new speaker materials in the cone and surrounds are water proof, the spider is water permeable. Also, the speaker frame is normally steel and does rust.

When the baffles are used, they do act like a small enclosure, restricting the speaker's bass response. Use them, but just cut out the lower section.

 

It's a rain shield. If you want more sound quality damplify your door.