first off i know an ohm is a unit of measurement but what exactly is it measuring? and if ive got an amp that can be 2 or 4 ohm why is the wattage different depending on the ohms? also what exactly is "bridged"? i apologize if these are noob questions but i like to be knowledgable about things im buying. especially when it comes to things with limitless combinations like subs and amps. thanks in advance.