People that have used these or done design for them, I have guy locally that already has 4 of these 15's in a scion xa, subs up, port forward and it sounds like crap. He wants me to take all out, build new box, and rewire everything. The powerbass site says 5 cubes per sub, but the few builds I can find say they used about 7-7.5 cubes per pair. He is running 2 powerbass 2250's to these. I dont mind paying for design after I get his car friday, im just trying to see what kind of cubic feet I need so when I get to measuring I can see how Im gonna build.