You want two. Most subs have to cover a range from low bass, which is 'locatable' by a listener, to very low bass which isn't and the power needed to produce a given spl is only 1/4 as much with a pair than it is with one.
Best test is to play a CD of organ music with low notes with no sub, then with one, and finally with two - makes a big difference and moves you, the room walls and anything in between.
You need pretty decent quality subs to integrate well with hi fi audio. The best bang for the buck I could find was the VTF-15H MK2 DualDrive
http://www.hsuresearch.com/products/vtf-15hmk2Dual.html
110 lbs each, 600 watt on board amps and they look pretty decent, not like something that got drop kicked off the back of the band's bus.
Best test is to play a CD of organ music with low notes with no sub, then with one, and finally with two - makes a big difference and moves you, the room walls and anything in between.
You need pretty decent quality subs to integrate well with hi fi audio. The best bang for the buck I could find was the VTF-15H MK2 DualDrive
http://www.hsuresearch.com/products/vtf-15hmk2Dual.html
110 lbs each, 600 watt on board amps and they look pretty decent, not like something that got drop kicked off the back of the band's bus.