I know relatively little about electricity so this might sound kind of elementary. Say you have a public address system installed in a building, and someone is trying to do a prank that involves playing audio over the loudspeakers. Each loudspeaker has a signal (positive) wire and a ground (negative) wire. If you disconnected one of the speakers and attached the stripped ends of the two wires to the plug of an aux cord connected to a phone or other device, would you be able to use the device to play audio over the whole PA system? From what I understand, a PA system usually has to have an amplifier on the input end to boost the signal from the input; if you were to use just a phone/iPod on a large system, would the signal not be strong enough? I guess what I'm asking is whether you could hypothetically use one of the outputs of an audio system as an input.