i am a car audio installer and when trying to find out which loudspeaker wire belongs to which loudspeaker, we use a 1.5v battery with a red and a black wire soldered to the positive and the negative terminals of the battery respectively. when touching a pair of speaker wires for a short period (tap) it makes the speaker crackle and therefore you can identify which channel of the amplifiers output you need to use. when you can see the loudspeaker you can also determine polarity because when speaker moves outward the positive lead of the battery is connected to the positive terminal of the speaker, and if cone moves inward the wires are out of phase. the problem is when you cannot see the loudspeaker and need to remove lots of panels to do so, the job becomes complicated and the only way to find out correct phase is to hook up all the speakers and fade to each one and listen for loss of bass and a stereo wide effect. what i need to know is, would it be possible to build a circuit that can generate an audible tone and also light up an led corresponding to the phase in which the speaker has just travelled when injected with the tone? is there any way in which the voicecoils direction of travel can do this? pehaps the circuit can make a 800hz tone and light up a green led when in phase and a red led when out of phase. any help would be greatly appreciated.