On low-profile subwoofers

I finally noticed earlier this week that the placement of my subwoofer leads the vast majority of its sound energy to wind up outside the livingroom and instead be in the kitchen and dining room. (Which kinda explains a few things, but anyway...)

There are only two other places I could put the subwoofer in that room, but both places put it so close to an outside wall that I'd worry about bothering the neighbors. (Yeah, yeah, I know, you risk that with subwoofers. That doesn't mean I won't take precautions...)

Ideally, you want a subwoofer in the center of the room, so that the sound gets spread fairly equally among the people listening, but that position is taken by a very large rug and a low wooden table.

It occurred to me that what I really wanted was a low-profile subwoofer. Preferably something disguised as a rug, or even a floor.

The first option that came to mind was attaching a weight to a solenoid, and the whole thing to the center of the foor of the room from underneath. Much like those turn-your-window-into-a-tweeter devices you can find on ThinkGeek, I'd then have turned my floor into a subwoofer.

The second option that came to mind was to take one of those powerful magnets I'm so fond of, ditch the solenoid, and use the magnet itself as the free weight with a high-power voice coil vibrating it. For that approach, I'd probably use one of these, and put on a good additional mass of plain old steel to protect the magnet and give it some actual heft. Suspending the magnet+steel mass is left as an exercise for the mechanically inclined. (Hint: A simple spring or elastic band would probably be enough; It's the voice coil that actually moves the floor.)

The third option that came to mind doesn't use any permanent magnets. Instead, you take two voice coils, and power them such that they're like polarized on a signal high and opposite-polarized (or less-like polarized, depending on if there are any external stresses on the system) on a signal low.

Take that a step farther and give each each coil a core such as silicon steel to concentrate the field lines, and your cores will attract and repel each other.

Now you've got a nice, giant degausser in your living room; You're losing concentration of your field liines, and they're spreading out. Need to add some shielding, some material to pretty much complete the magnetic circuit. Instead of wrapping around your discs for your metal cores, cut a wire route groove somewhere within the disc. If you sandwich the two discs together, they should look like one disc. Now, of course, you'll need to drill holes in each disc to let your coil feeds in. At this point, it's worth mentioning you've created a good old-fashioned toroidal transformer, except you're powering both windings.

You'll want some sort of tough, spongy material in between the two halves, to keep them from banging together. And then something decorative so that it can be walked on. I'd be careful about setting things on it; They might start walking around like a wine glass on magic fingers.

Of course, now you've got to power the coils.