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Speaker Polarity Checker

This speaker polarity checker plays a correlated low-frequency signal to both channels and lets you flip the right channel in-phase vs out-of-phase, so you can check matched polarity by ear. With correctly wired speakers, out-of-phase bass sounds noticeably thinner, weaker and vaguer in the centre — if the two settings sound the same, one speaker 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

Test signal

Volume

25%

Phase between left & right

Press Play, then toggle In-phase / Out-of-phase and listen for the bass to drop out on out-of-phase. Start quiet.

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. Reversed speaker wiring of this kind is the most common cause of a mismatched stereo phase — the result is a degraded soundstage even when every other part of the system is working correctly. It most often happens through a simple wiring error — a cable connected back-to-front at the amplifier binding post or at the speaker terminal, a pre-terminated cable with the conductors swapped at one end, or a driver replaced without noting the original lead orientation.

This tool turns that physics into a listening test — a quick speaker phase test you can run with any stereo speaker pair. 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. A tone generator set to any frequency in this range will show the same physics; this tool uses a dedicated, matched stereo signal so both channels are always identical and phase-locked.

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. Absolute polarity — whether the complete signal chain from source to driver is non-inverting or inverting — requires a reference click or impulse of known sign; many listeners cannot hear absolute polarity differences at all. For a relative wiring fix, follow the battery pop test described below, or use the stereo channel tester alongside this check to confirm correct left/right routing before rewiring.

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.

Frequently Asked Questions

What does it mean if in-phase and out-of-phase sound the same?

It strongly suggests your two speakers are wired with opposite polarity to each other — one has its + and − leads swapped. With matched wiring the out-of-phase setting clearly thins and de-centres the bass; if you can’t hear that difference, the cancelling case is probably your “normal” listening, which means a reversed speaker. Note that placement, mono content, and room modes can also mask the effect, so confirm with the battery pop test before rewiring.

Can this tell me which speaker is wired backwards?

No. This is a relative test between the two speakers — it can reveal that they disagree, but not which one is at fault, and it can’t test a single speaker’s absolute polarity at all. To find the specific reversed speaker, do the 1.5 V AA battery pop test on each driver (+ battery to + terminal should push the cone outward) or use a dedicated polarity tester.

Why does the test use bass instead of a high tone or a click?

Low frequencies have long wavelengths that are nearly omnidirectional and combine in the room rather than beaming straight at each ear, so in-phase reinforcement and out-of-phase cancellation are far easier to hear as a change in bass weight and centre focus. High tones are directional and the cancellation pattern becomes a fragile, position-dependent comb that moves with the smallest head shift — unreliable for a quick by-ear check.

Does out-of-phase or reversed polarity damage my speakers?

No — reversed polarity is an electrical inconvenience, not a hazard; the speaker just moves the wrong way and the stereo image suffers. What can stress small speakers is volume: this tool plays sustained low frequencies, which demand a lot of excursion. Keep the level low, especially with small bookshelf speakers or laptop/phone drivers, and stop if you hear any buzzing or distortion.

Can I check polarity on headphones, a soundbar, or a phone?

Headphones can show the effect — out-of-phase bass sounds oddly “inside-out” and de-localised — but it’s a phase/wiring sanity check, not a true acoustic cancellation since the two drivers don’t share air. Soundbars, single-speaker phones, and any mono/summed-to-one-driver output can’t demonstrate it at all, because there’s no separate left and right acoustic source to cancel. The test needs two genuinely separate, spaced speakers playing into the same room.

Does reversed speaker polarity affect stereo imaging and soundstage?

Yes, noticeably. Correctly wired speakers produce a solid phantom centre image and instruments spread convincingly between the speakers. A reversed speaker disrupts the inter-channel summing that creates that image: the centre image smears or vanishes, bass feels diffuse, and the soundstage can sound “wide but empty” rather than focused. Many listeners diagnose the problem as “my speakers lack bass” or “the stereo image is poor” without realising a simple wiring swap would fix both symptoms at once.

Can a streaming service, DAC, or amplifier invert polarity in the signal chain?

Yes. Some amplifiers (especially older designs using many inverting stages) invert the signal electrically, and a handful of mastering engineers have recorded or processed tracks with an inverted waveform. A DAC, DSP processor, or digital crossover can also introduce a polarity inversion. These are all forms of absolute polarity inversion — the whole chain is flipped, so both speakers are equally inverted and the bass cancellation check here will show no problem. This tool detects only a relative mismatch between the two channels; absolute chain inversions are harder to detect by ear and are generally considered inaudible to most listeners.

My subwoofer has a 0°/180° polarity switch — how does that relate to this test?

A subwoofer’s 0°/180° switch addresses a different problem: acoustic timing. Because a sub sits at a different distance and is fed through a crossover, the low-frequency wavefronts from the sub and the main speakers can arrive slightly out of step at your seat. The switch lets you choose whichever setting gives the fullest bass at the crossover frequency — it is not about correcting wiring errors. This polarity checker tests the two main speakers against each other and should be run with the sub switched off or at very low level to avoid its bass output masking the cancellation effect you are listening for.

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