you can get a cheap set up that'll boom ... mainly u want to get a large amp, and big woofers. to me, 12's sound better all around, but 15's thump harder... altho the 15's had little to no mid-range. make sure u have a cross-over, so ur not sending ur tweeter sounds to the thumping speakers, and ur not thumping ur tweeters(blow them out real quick) ... u have any problem with the speakers rattling ur trunk, make sure to put weather stripping around it. nothing bugs me more than to see a thumping car, rattling hard on the outside. if u can afford a setup, then finish the job.