Just use a couple wires and a battery(ie: AA, C, D, or 9V), briefly touching the woofer terminals. You can do the same test with a multimeter, set to "ohms". The speaker should either push out, or pull in, depending on the polarity of the hook up. If it speaker has ever been stored in an area with high humidity: there could be rust in the voicecoil gap. If it's ever been dropped: the polepiece or magnet could have shifted. Either would hold the voicecoil captive, and eliminate it's excursion. If the voicecoil is burned: you'll get limited excursion, and a lot of rattle(with music).