Speaker Polarity Checker
Check whether your two speakers are wired with matched polarity by ear. This tool plays a correlated low-frequency signal to both channels and lets you flip the right channel in-phase vs out-of-phase. With matched speakers, out-of-phase bass should sound noticeably thinner, weaker and vaguer in the centre — if the two settings sound the same, one of your speakers is probably wired backwards.
ℹ This is a relative, by-ear check of polarity between your two speakers using bass cancellation. How obvious the effect is depends entirely on your speakers, placement and room — close-spaced or mono/summed setups, subwoofer crossovers and strong room modes can blur or even hide it. It is not an absolute, per-driver polarity test and cannot tell you which speaker is reversed. For a definitive per-speaker answer use the classic 1.5 V AA battery pop test (cone jumps out = + to +) or a dedicated polarity/phase tester. Start at a low volume: this plays sustained bass that can stress small drivers if pushed loud.
Play the polarity test
Illustration of the two channels. In-phase, the waves add (louder bass); out-of-phase the right channel is inverted, so the bass largely cancels and the centre image collapses. This is a schematic of the signal, not a measurement of your speakers.
Speaker wiring (+ / −)
Correct wiring (left): amplifier + goes to speaker + and − to −. Reversed wiring (right, dashed): the + and − are swapped, so that speaker pushes when the other pulls.
How It Works
Stereo speakers should be wired so that a positive electrical signal pushes both cones outward at the same instant. If one speaker has its + and − leads swapped, its cone moves opposite to the other. For most music you barely notice on the surface, but the centre image and the bass suffer: low frequencies from the two speakers, which normally reinforce one another, instead partly cancel.
This tool turns that physics into a listening test. It generates a single correlated low-frequency signal — either a steady tone (50–250 Hz) or band-limited noise around 60–250 Hz — and feeds the identical signal to the left and right channels. In the in-phase setting both channels carry the same waveform. In the out-of-phase setting the right channel is multiplied by −1 (a gain of −1, an inverting path), exactly mimicking a reversed speaker. Bass is used because its long wavelengths are roughly omnidirectional and meet in the room rather than beaming at your ears, so the in-phase summing and out-of-phase cancellation are easiest to hear.
Listen for the difference: with two matched, correctly wired speakers, in-phase sounds full and solidly centred, while flipping to out-of-phase makes the bass go thin and the sound feel vague, hollow or “outside the speakers”. If the two settings sound essentially the same, your speakers are most likely already wired with opposite polarity to each other (one is reversed), because then your “in-phase” setting is the cancelling one. The crucial honesty: this only compares the two speakers against each other. It tells you they disagree, not which one is wrong, and it cannot test a single speaker’s absolute polarity. For that you need a physical test — touch a 1.5 V AA battery briefly across one driver’s terminals and watch which way the cone jumps (+ battery to + terminal pushes the cone out) — or a dedicated polarity tester.
How to fix reversed polarity
- Confirm it by ear first. Sit centred, play this test at a low level, and toggle In-phase / Out-of-phase a few times. If out-of-phase clearly loses bass and focus, your polarity is already matched — no fix needed. If the two sound the same (or in-phase is the weak one), suspect a reversed speaker.
- Power down. Switch off and unplug the amplifier or receiver before touching any speaker wiring.
- Inspect both ends of each cable. Trace each speaker’s pair of wires. The colour-coded or marked conductor (stripe, ridge, copper-vs-silver, or red insulation) should land on the + terminal at both the amplifier and the speaker. Make sure both speakers follow the same convention.
- Swap the leads on ONE speaker only. Reversed polarity is fixed by moving that single speaker’s two wires to the opposite terminals (+ to −, − to +) — at either end of the cable. Never swap both speakers; that just brings you back to the same mismatch.
- For a definitive per-speaker check, do the battery pop test. With the speaker disconnected, briefly tap a 1.5 V AA across its terminals: + battery to + terminal makes the cone jump outward. A jump inward means that terminal pair is reversed. (Tap briefly — do not hold the battery on.)
- Re-test. Reconnect, power up, and run this tool again. Out-of-phase should now clearly cancel the bass.
Subwoofers add a wrinkle: a sub usually has its own phase or polarity (0°/180°) switch, and crossover delay can make “correct” polarity the one that sounds fuller. Set sub polarity by whichever switch position gives the most bass at your seat, not by this stereo test.