I'll throw in on this one...SVS makes a whole line of subs that rattle the rafters. They come with very thorough software application to help integrate into your system and if you choose correctly you'll find they offer very low distortion and enough headroom to satisfy anyone, especially if you intend to do multiple subs. They have a just recently released model in the 17" size that looks very impressive and according to what I have read about it sports the lowest distortion of any sub currently available that I am aware of. They are not cheap but I can say with confidence they are sure worth taking a listen to. They are readily available thru Crutchfield and other places too as well as direct from SVS. I have a couple of their smaller subs in my music room and they do a fine job of filling in that bottom octave.
