I found this article on subs which was very interesting.
http://www.soundoctor.com/whitepapers/subs.htm#2SUBS
check it out, goes into great detail about correct set-up, placement, crossover etc. well worth a read.
http://www.soundoctor.com/whitepapers/subs.htm#2SUBS
check it out, goes into great detail about correct set-up, placement, crossover etc. well worth a read.