If you can go 16 inches high, you should really look at a DIY sub if you can do the building. You could use the Stryke AV12 or the Adire Shiva (which I use). I built a sonotube using the Shive. Since you can go long, you could build a tube and make it long using 16 inch tube and sit it on it's side. Check out the DIY forum at www.hometheaterforum.com. They've go the best DIY info around.

Frank