Speaker Polarity Test

In short A speaker wired backwards moves outward when it should move inward, and on its own that is inaudible. Against its correctly-wired partner it is not: the two cones push and pull against each other, and the shared content between the channels cancels. Bass suffers most because low frequencies are largely mono, so the first symptom is a system that sounds thin and lacks weight despite the drivers being fine. The centre image goes with it — vocals, which normally appear to come from a point between the two speakers, become wide, hollow and impossible to locate. That is what the two test signals demonstrate. In phase, the noise appears as one solid point between the speakers. Out of phase, it spreads out and seems to come from everywhere and nowhere, and once you have heard the difference you cannot unhear it. The fix is simply swapping the positive and negative leads on ONE speaker, which is why the fault appears at all: it is a wiring mistake that leaves everything looking correct. On headphones the effect is different and stranger — the sound seems to sit inside your head rather than in front of it, because there is no acoustic space for the cancellation to happen in.