I used xtc baffles in a few systems. I have had a pretty crappy experience with them once.
In my 2011 Silverado I used them in my kick panels. Took trimming so you didn't see them
and to make it look like it wasn't done by an inexperienced rookie. Anyway, on decent volume
the baffles were actually slapping the carpet floor below them. I removed one and left the
other, and to be quite honest, it sounded better without it. I removed the other side and the
entire sound changed. I then decided to try the sound change from removing them from the
rear doors...got worse. Not nearly as noticeable as the change up front, but still a noticeable
change. So, I put them back in. Amazing little creatures to use.
The sound of them slapping the carpet sounded like a paper speaker fluttering. Which to my
ears...sounds dreadful, like a blown speaker.
In my G8 I didnt use any, but the change from stock speakers to the JBL GXs....good enough!