well, think of it in math terms. 3 10" is 30" of surface moving air. The 2 12" are only moving 24" of air. 3 10's might sound louder, but quality 12's can do the same as 3 10's. Obviously 4 15's will sound much louder. Try Memphis 12's. They're pretty loud and decently priced. Otherwise, i've always been a fan of JBL GTO's (I have a single 12 in my X, and it's plenty loud powered by a single 400w monoblock)