Decibel Shield
Left and right audio test › Speaker polarity test
Speaker polarity test: is one speaker wired backwards?
Sit centred between your two speakers and play A, then B. Both are the same low noise, but B flips one side. With correctly wired speakers, A sounds fuller in the bass and solidly in the middle. If B sounds fuller instead, one speaker is wired out of phase: swap the two wires on that speaker only.
Sit centred between the two speakers. Play A, then B, then answer: which one sounded fuller in the bass and more solidly in the middle?
Low noise plays through your speakers; there is no microphone and nothing is recorded. On headphones the same test works, and a reversed result there means a wiring fault in the cable or an adapter.
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What reversed polarity sounds like
Each speaker makes sound by pushing its cone out and pulling it back. When both are wired the same way, they push together, the bass from the two adds up, and a voice in the mix sounds as if it comes from a point between them. Swap the wires on one, and that speaker pulls while the other pushes. The low frequencies, which reach your seat from both speakers at almost the same moment, partly cancel, so the sound goes thin; the middle blurs into a wide, hard-to-place image. That difference is what A and B let you hear side by side.
How to fix it
Turn the amplifier off first. At the back of one speaker, and only one, swap the two wires: positive to the red or + terminal and negative to the black or - terminal, matching the amplifier end. Speaker wire marks one of its two conductors with a stripe, a ridge or text so you can follow it from the amplifier to the speaker. Then run A and B again: A should now be the fuller one.
Headphones and other channels
On headphones the same test works, and a reversed result there means a wiring fault in the cable or an adapter. For a full check of left and right, balance and both sweeps, use the left and right audio test; for a 5.1 or 7.1 system, the surround sound test plays each speaker on its own.
How do I know if my speakers are out of phase?
Play A and B from the centre of the room. With both speakers wired the same way, A sounds fuller in the bass and solidly in the middle, and B sounds thin and spread out. If B is the fuller one, one speaker is wired backwards.
How do I fix a speaker that is out of phase?
Swap the two wires at the back of one speaker only, so that positive goes to positive and negative to negative at both ends: usually red to red and black to black. On speaker wire, one conductor is marked with a stripe, a ridge or printing so you can follow it from end to end.
Is polarity the same as phase?
Not quite. Polarity is a flip: the speaker pushes when it should pull. Phase is a delay, which shifts different frequencies by different amounts. A reversed wire is a polarity problem, and it is the one this test finds and the one a wire swap fixes.
Does polarity matter with a subwoofer?
It matters where the subwoofer and the main speakers both play the same low notes. Many subwoofers have a phase switch or dial; set it to whichever position gives the fuller bass from your listening seat.
Sources: Sound On Sound, common studio problems; AudioCheck, polarity check.