[AceX]

Tons of work for minimal results.

18's do nothing but move air. They are generally not useable for music. If you want to get seriously loud and stay somewhat in the realm of audible reproduction, then four 15's and four 8's do the job nicely.

You could also go with just four 12's. This is by far one of my favorite combos thus far. I've listend to ALOT of different stereos using alot of different equipment and approaches and so far 4 sealed 12's is my favorite mix of power and quality.

One system that also stands out in my mind is one that is in a candy orange 2000 Chevy 2500 up in Yuba City. Guy's name is Larry and he knows his stuff. He's rockin' four 15's in a blow-through and it sounds increadible and I'm told can hit mid 160's when burped.