earthquake SLAPS system

www.earthquakesound.com/slaps.htm what exactly do these do??? will they work with any sub? the website wasnt really clear on this. has anyone used these before???

They're "passive radiators", and they've been around for a long time.  You see them more in home audio than in car audio, but the theory is the same.  Think of it like a subwoofer cone with nothing attached to it - no voice coil, no motor, no magnet.  You mount the radiator in a sealed box, along with a subwoofer.  As your subwoofer cone moves out, the passive radiator "cone" moves in, and vice versa.  They allow you to pick up a little bit lower frequency extension because they mimic the effects of a slightly larger box.  The net effect is somewhere between a sealed box and a ported box.