Really? man, the speaker specs said 1.25 so that is what I did. I could fit a 2 maybe even a 2.5 (with no trunk space), and I could have gotten the same box, but bigger, for like $3 more. It does sound night and day different than the box I did have. I'm just trying to compete with my door speakers at max volume which when listening to rock and metal, it sound fantastic, even kick the bass down a lil, but hip-hop and rap is underwhelming. It vibrates everything pretty good, I barely use my rear view mirror because I always have to adjust it. My side mirrors are hard to see out of, and it make my arm hair stick up. I got a lot of head hair, so it just kinda moves that.
It was also a lot louder when I had it facing away from the windshield, but I didn't like it for Rock and Metal.