I just bought a subwoofer from a thrift store for 60 bucks....its a MTX audio thunder 6000 with a q-logic box....the only thing wrong is I dunno if its 4ohm or 8ohm....how can you tell?....I went to their site to find out but the same model comes with both so is there a way to tell? Also what would be the best amp to get with a low budget?