Use a battery. On a subwoofer I'll use a 9v, but start with a AA. Plug the + end to one terminal and the - end to the other. If the woofer moves out, then that's in phase, if the woofer moves in, it's out of phase (reverse polarity)
A forum community dedicated to home theater owners and enthusiasts. Come join the discussion about home audio/video, TVs, projectors, screens, receivers, speakers, projects, DIY’s, product reviews, accessories, classifieds, and more!