If you're going to wimp out and not follow any of my above advice and just want to add a subwoofer to an existing system, the NHT 1259 has a good reputation for medium output DIY subwoofer projects. See the NHT 1259 FAQ. A "Do-It-Yourself" Speaker Project is a good article on how to build one. A good supplier is Madisound. See Speaker City U.S.A or Meniscus for a integrated power amp/x-over.
Mother Nature's a bitch. In short. Most any powered subwoofer under $1,200, or so, should be classified as a woofer, not a subwoofer. (With the possible exception of Bob Carver's Sunfire "True Subwoofer". More info on this later on.) They are designed to mate with a tiny satellite speaker and end up giving you roughly the 40 Hz bass extension that you used to get with your old "monkey coffin" Advent, KLH, etc. bookshelf speaker. Real subwoofers should go down to 20 (or at least 30) Hz and move a LOT of air. They also should have 2 inch thick heavily braced cabinet walls, in order to not mush up when they are containing those force-of-nature rumbles. Whereas there are techniques to trade-off sensitivity for low frequency extension, you know that this deal with the devil won't work. (See above discussion on dynamic range.) These boxes are very large and heavy, and commercial speaker makers don't want to pay to freight them around the country. Much easier to just call a woofer a subwoofer. (Is it smaller than a washing machine? Uh, oh.)
On your end, the situation is different. The drivers aren't that expensive, and YOU can take a pickup to the lumberyard and get however much baltic birch plywood (not particle board!) that is needed to build a real box without too much trouble. (Your brother-in-law probably owes you a favor anyway, right.)
This page was written after being frustrated by the dynamic range limitations of the speakers that are conventionally used for home use. Please read The Ancient Audiophile's Quest for the Ultimate Home System for some more thoughts on this subject. Apparently, this was written several years ago, (not by me!) with all references stripped out of the file. I have found this reference to JBL Professional, but they don't seem to list individual drivers on-line. I guess you have to badger an individual distributer for this information.
Um, no, my system isn't quite up to those standards yet, but it is a 4 way electronically crossed over system that uses the Audax PR170X0 high efficiency "pro" driver as described in my electronic crossover page.
Even though I haven't got the rest of my system to those standards yet, I did do some additional research on drivers that would be suitable. I am really intrigued by the McCauley pro sound drivers. All information is downloadable. These are VERY heavy duty woofers, designed for arena-type PA sound systems. Whereas a lot of the drivers are optimized for high efficiency/high frequency roll off (80 Hz at 95-100 db efficiency), like a lot of pro sound "bass" boxes, they have a few drivers that are designed to go down real low, be real efficient, BUT by using a big (6-15 cubic foot) box. (Check out the 6174 Ultra-Performence Sub Bass Driver. Wow! "Capable of delivering 132 db at 20 Hz." Run the parameters through your box plotting software and your eyes will pop.) I believe the target audience for those drivers is discos and dance clubs.
You also might want to check out the Horn Speaker Home Page. It has links to other "pro" driver sites. Personally, I don't believe in horns and try to avoid them, but your milage may vary.
I think that the only way to make a real monster sub is to use carefully chosen pro sound drivers. But you have to watch out, because a lot of pro sound bass systems are only designed to go down to 80-40 HZ, or so, to keep the efficiency up. (Got to be around 100 db for any pro sound work. Or living room use, in my opinion, and that is what eliminates 99% of conventional home stereo drivers.)
I've read a lot cautionary stories about fabled, but obscure, drivers that end up having a lot of drawbacks. (Yeah, it does go down to 20 HZ, but has a 50 db peak at 500 HZ, etc.) Better to stay somewhat with well known brands.
Umm, the other alternative is the Bob Carver Sunfire "True Subwoofer." (http://www.sunfire.com, I think, but web site doesn't work right now. Sunfire, P.O. Box 1589, Snohomish, WA 98290 (425)335-4748 Reviewed in Audio, Nov 97.) This powered subwoofer seems real hard to beat for the price. 2,500 watt amp, box only 11 inches square, $1,299. Uses an optimized very heavy duty driver interfaced with a specialized amp in a way that amateurs can't duplicate. Makes it hard to be a hobbiest anymore. It would be real embarrassing to build a home-brew subwoofer and have a smart-aleck friend carry one of these in under his arm and blow your system away. (Well, not if you go the McCauley route.)
Now do some cookbooking and box plotting and build a real speaker.
Wayne Larmon can be reached at email@example.com
Back to Wayne's Speaker Building Page.