I finally figured out my cheap car speakers sounded bad for 2 years because of the door panel, not the speakers
Bought a pair of $35 6.5 inch speakers for my 2004 Civic about two years ago and they always sounded hollow and rattly, so I figured cheap speakers just sound like that. Last Saturday I pulled the door panel off to fix a window regulator and noticed I had mounted them straight to the flimsy plastic door card with no baffle or backing at all, just screwed into plastic. The sound was basically bouncing around the inside of a hollow door. I cut two circles out of an old plastic cutting board I had in the garage, screwed those to the door metal first, then mounted the speakers to that, and the difference was night and day for zero dollars. Same cheap speakers, way more bass and no more rattle at volume. Has anyone else done the cutting board trick or is there something even better I could grab from the dollar store?