Bass shaker question: +/- wires

Hook them up either way to the speaker out of any amp, It's better to find one that plays down to <20hz ..
at moderate volume, just switch the + - back and forth to see which give more response.(hold the shaker in your hands)....then you'll know which is in/out of phase.

You won't damage them, they are not a paper woofer.. tuff buggers to damage.
You'll need to play a test CD/DVD with plent of low bass.

To clarify what stevegamble said, the easiest way is to hook two of them up (probably in series if you're dealing with a standard receiver output), put one in each hand playing a very low frequency tone, then bring them together until they touch back to back, and again front to back. In one direction, the vibrations will completely cancel out, and in the other, they won't. You can make note of which one is which way, and ensure you have them all working in tandem. Wire all the ones that vibrate one way the opposite of the ones that vibrate the other way.

The reason you need to do this is because even though they appear to have designated + & - leads (one has a small connector on a silver wire, while the other has a wider connector on a copper colored wire), the reality is, they aren't always wired consistently. I can tell you after installing 25 of these things in my furniture, about 1/3of them come from the factory wired "backwards" compared to the other 2/3. It SEEMED to me that ones that came in the same package were typically wired identical, but I acquired mine in several batches, so it seems the manufacture of these wasn't consistent.