When I was driving an 04 coupe I could crank up the volume and the door speakers never sounded distorted, it sounded great. But when I got the SRT6 it sounded like crap cranked up, go figure they were the same systems . I done this mod on the door speakers and it sounded like a totally different system. I don't recall what size cap's I used, but I ordered them from Crutchfields and they were called bass-blockers they had three different size's.