While not strictly a brew project, there is nothing I like better after a hard day to sit with a home brew and watch a movie with a kicka$$ surround system. I built these "Butt Kickers" mostly out of stuff I had laying around (No Honey, I am not a packrat, and please don't open that closet door. Just had to buy a Sub Amp. It was extremely simple to do:
I took a set of 10" woofers and put a thin coat of 5 minute epoxy over the dust cone (the convex piece in the middle of the speaker) and let it dry. It helps to use a heat gun on the epoxy as it will make it flow more easily and dry quicker, just have to keep moving the speaker around until the liquid starts to harden so that you get an even layer. Added a 2nd thin coat & let it dry. (These coats are just to reinforce the cone. You may be able to get away with 1 layer, but I didn't want to chance it) I then laid a 2" iron flat across the speaker frame and measured from it to the cone and cut a small plastic drinking cup to that dimension. At this time, it helps to drill the flat so that you can use the existing speaker mount holes to attach it. You want this to just fit the area. If it is too long, it will pre-load the speaker driver and limit its' performance. Once you have the cup ready, mix up the 3rd batch of epoxy and glue the cup in open end toward the cone so that pressure is spread around the cone and not just in the center. Once this dries, mix up the 4th and final batch of epoxy. Use it to create a fillet around the cup/cone interface and also put a liberal amount on the cup bottom. Lay the flat in the epoxy and use screws with Nylock nuts to attach it to the speaker frame before the epoxy dries.
Once dry, you can then use a fine X-Acto knife to cut the paper portion of the speaker cone (BE VERY CAREFUL not to cut the wires that are attached there). The reason for waiting to cut the paper until after the flat is glued to the cup is to keep the speaker driver from cocking. If it does not travel in a linear fashion, you will get all sorts of weird sounds from it and it will most likely overdrive your amp.
When that was done, I took a couple of diving weights and ty-wrapped them to the flat to give it a bit more mass to move. I originally had 4 wieghts on each one, but with the cheap amp that I bought, the response was not crisp enough.
All that's left is to attach them to the chair or couch of your choice (I have even attached them to the floor joists in my friends theater room) and then hook them up to a suitable Sub-Driver, turn down the frequency to 40Hz or below and branch in to your surround sound "Sub-Out". I tested it with the movie Jurassic Park and the first time T-Rex starts trashing the place, you can really feel it. The best part is that unsuspecting friends will sit there and the first time there is a surprise loud noise, they normally jump out of their skin. You can get reasonably priced parts, for this project, from here http://www.partsexpress.com/