If he drops the subwoofer into the bathtub plugged in there are three things that could happen: The first is the GFCI outlets will kill the power before anything happens, this is the most likely case. If there aren't GFCI outlets, or they don't work, and he drops it in and there is any water connecting him to the bathtub he could get electrocuted. Third, and extremely unlikely because of the first scenario, the subwoofer blows.