GOTCHA,Thanks alot!!
The reason why I'm asking is because today at a shop I go to they were finishing up a install and they were explaining to me that along with a set of 15's they had also installed 2 12in and some tweeters in a custom box to add more voice.
When he turned it on for me,not only did it have crazy bass, it also sounded CRYSTAL and LOUD (I'm talking REALLY CRYSTAL).He explained that they installed mids/highs in the door as well but the ones in the back added more projection.