I took some Klipsch proto-type cabinets and modded them for 18" McCauley 6174 utra-subs.

You can check the whole thing out here: http://wardsweb.org/audio/beast.html

For a sonotube sub:

http://www.io.com/~patman/sunosub.html

Gives great instructions. There are numerous sonotube sub projects, search Google, for example.

That's a very nice piece of work, Wardsweb.

Pete

Here is a great, if not the best, DIY sub site:
DIY Subwoofer Site (http://www.diysubwoofers.org/)

Neat stuff. Deserves a wider audience.

Just a project on the cheap, that seemed to have favorable results.

Details (http://www.hometheaterforum.com/htforum/showthread.php?s=&threadid=20551&highlight=%2481)

Finished Product (http://www.mindspring.com/~jine/Index.html)

Cheers,
Russ