Infinite baffle subs are popular when you have access to the required space. This four driver manifold delivers the bass to the room above it. Of course it is equally loud in the basement! Using multiple drivers, the design has very good transient response

If you like the idea of this arrangement, you can find out all about it at The Cult of the Infinitely Baffled

I've recently built a larger version of this, and I love it!