I have a felt-type ring around my tweeters. I like the sound with it on.
Also have another set of speaker with the baffle covered with leather - slight differences before and after the leather.

In speaker building the baffle design is one of the most important aspects. This includes driver placement, depth of each unit and even the material the baffle is covered with. All this impact on the final sound and can give measurable results.
Also, you can try with something less dense similar to velvet with double sided tape - choose one that comes off easy