It's kinda triangular shaped, maybe 8-10" at the bottom and like 4" at the top. It fits perfect and still gives me trunk space. My system is an Alpine stereo, 6x9 Alpines in the rear deck and the sub is a Kicker Bass Station. I get great sound and it is definitely loud enough. My next step is putting 2 5" speakers in the kick panels.....
This is very clean setup! Bar none. Not mine, but another members (forget) Speakers on the doors/front