JL Audio

I use two JL f110's for my stereo where they play in the background to fill in the sound. I had one f113 in my room, but for better imaging and the small roll they play in my 11x25 foot room the f110 (for the price) is all I need.
For home theater where a sub plays a larger part you need the f113 for better impact and to shake the walls.

Music get one 112
Movies do the 113
Depends what you listen to.

The 110 doesn't have enough punch.
That is just my 2c ymmv.

I use two F113's. The point is not to shake the walls but to even out the frequency response in the room (always easier with two subs). I would buy one F113 now and when funds become available buy the second one later. You can run them in stereo (master/master) or as master/slave (which I do).

By the way, if the walls are shaking and you are not watching the pod scene in War of the Worlds you are running them way too hot and/or you have room mode issues to fix.