Speaker Polarity Test: Check Phase and Wiring Online
Click Play In-Phase and Play Out-of-Phase on this speaker polarity test to hear reversed wiring instantly. Nothing you do in the speaker test ever leaves your device — the whole test runs locally in your browser tab.
Cross two wires behind one speaker and nothing looks wrong, yet the music loses its punch. This speaker polarity and phase test is a free online speaker polarity test that runs in your browser: it plays the same signal through your stereo speakers twice, once normal and once with one side reversed, so you can hear which version is right. Matching phase polarity on both speakers gives you full bass and a solid center.
How the Speaker Polarity and Phase Test Works
The speaker test sends one identical signal to the left and right speakers. In the first version both cones move outward together. In the second, the right side is inverted, so the cones move in opposite directions and the pair is out of phase. Unlike a general sound test, only the sign of one side changes, so whichever clip sounds bigger tells you how your polarity & phase stand.
Test Signal Choices: Sine Tone, Rumble and Music
Bass makes the difference easiest to hear, so most test tones sit below 150 Hz. A steady sine tone at 75 Hz or 110 Hz shows the clearest jump in loudness, and some tools use 100Hz. A low frequency rumble adds texture, while a short guitar recording shows whether an instrument sounds solid. Each audio test pair is mono, so any difference comes from polarity alone.
Why Relative Polarity Shapes Stereo Imaging
Absolute polarity, whether a cone first moves out or in, is close to inaudible on one speaker, and blind tests of absolute phase are notoriously hard to pass. Relative polarity between two loudspeakers is different. When one speaker cone moves forward to push air while the other pulls back, the displaced air from one fills the gap left by the other at your listening position, and stereo imaging falls apart. Nothing you do in the test your subwoofer bass response ever leaves your device — the whole test runs locally in your browser tab.
Out of Phase Speakers and Bass Cancellation
Cancellation depends on wavelengths, and a wavelength is the speed of sound divided by frequency:
$$\lambda = \frac{c}{f} = \frac{343\ \text{m/s}}{f}$$
Take a seat where the two paths differ by 10 cm. At 45 Hz a wave is 7.62 m long, so that 10 cm barely matters: the reversed pair reaches only −21.7 dB against one speaker alone, while the correctly wired pair reaches +6.0 dB, a 27.7 dB gap. At 400 Hz (0.86 m) the gap shrinks to 8.3 dB, and at 1,200 Hz (0.29 m) the reversed pair is 5.0 dB louder. That is why loss of bass is the main symptom: long waves cancel across the room, the bass weight you expect is cancelled, and treble survives. A visualizer that sums both channels shows a flat line, yet you still hear sound, because the low end only cancels fully where both paths match.
Center Image and Phantom Image
Correctly wired, a mono voice forms a phantom image exactly between the speakers. Out of phase, the center image smears into a diffuse cloud, and the soundstage feels wide but empty.
Reading In Phase vs Out of Phase Results
Play both versions at the same volume. Your speakers are connected correctly when the version labelled in phase sounds fuller and more focused. If the out of phase version sounds better, one speaker is reversed.
| What you listen for | Correct phase | One speaker reversed |
|---|---|---|
| Bass | Strong, full body | Thin, weak low notes |
| Center | Voice centered between the speakers | Hollow, hard to locate |
| Width | Natural spread | Wide and vague |
| Earphone check | Sound in front of you | Sound inside your head |
Fixing Reversed Polarity in Your Speaker Wiring
Reversed wiring is behind almost every failed speaker polarity test. To fix swapped polarity, flip the two wires on one speaker only, at the amp or at the speaker, never both. Then re-run the check.
Speaker Terminals: Positive and Negative
The positive amplifier terminal must reach the positive speaker terminal on both sides. Speaker terminals are usually red for positive and black for negative, and speaker wires mark one conductor with a stripe or printed text. On an audio interface, a miswired XLR or TRS cable can reverse one side too.
Left / Right Stereo Test Before You Swap
Before you swap anything, run a quick left / right stereo test: each channel should play only from its own side, and red plugs carry the right channel by convention. Stereophonic playback needs both, and a stereo balance or stereo separation problem can sound like a phase fault. This wiring check takes seconds.
Finding Swapped Polarity on a Freshly Wired Desk Setup
I've just moved a pair of bookshelf speakers onto a desk shelf, 1.37 m apart, and rewired them to a small stereo amplifier with unmarked bell wire. The question is simple: did I keep polarity matched, or does one speaker need its leads reversed? The answer comes back fast: the flipped clip sounds bigger, so the left speaker is wired backwards.
My ears sit 1.12 m from the line between the speakers, and a tape measure puts my head 8.3 cm left of center, because the monitor isn't quite in the middle of the shelf. I pick a 58 Hz tone and keep the level modest. The normal clip is weak; the flipped one has a solid low note in the middle. At the terminals, the left lead with the ridged insulation lands on positive at the back panel but negative at the speaker.
To be sure the difference isn't just my seat, I work the geometry. The two paths differ by 8.6 cm. Correctly wired, the pair sits +6.0 dB above one speaker at 58 Hz; reversed, it falls to −20.7 dB, a 26.7 dB gap. Then I rerun the numbers for a seat 27 cm off center:
| Seat offset | Path difference | Gap at 58 Hz | Gap at 150 Hz | Both clips equal at |
|---|---|---|---|---|
| 8.3 cm | 8.6 cm | 26.7 dB | 18.5 dB | 991 Hz |
| 27 cm | 27.7 cm | 16.6 dB | 7.9 dB | 309 Hz |
Even well off to the side, a reversed pair loses more than 10 dB at 58 Hz, so a low tone is the right pick; at 150 Hz the 27 cm seat leaves only 7.9 dB, which room reflections could blur. The last column is \(c \div (4 \times \text{path difference})\): above that frequency, the phase comparison stops being fair from that seat, because the wrongly wired pair becomes the louder one anyway.
I reverse the two leads at the left speaker only, re-run both clips, and the normal clip now carries the bass. My hand calculation and the 343 m/s speed of sound used above agree with what I hear.
The caveat I'd flag is bass management. Most receivers send everything below an 80 Hz crossover (the THX recommendation) to the subwoofer as a mono sum of left and right, and a waveform plus its inverse sums to zero. A 58 Hz tone then vanishes from the flipped clip in the electronics, whatever the cables do, so the result says nothing about the mains. With a sub in the chain, I'd switch it off or test above the crossover, around 150 Hz, and sit nearer the center so the gap stays readable.
Inverted Phase in Headphones
Headphones are wired at the factory, but a damaged cable, a cracked solder joint or a cheap adapter can flip one earcup. Stereo polarity errors cost little bass here, because your head separates the drivers. Instead the out of phase sample sounds diffuse and stuck inside your head. If it sounds more natural than the in phase one, the headphones or their lead are at fault.
Speaker Placement and Listening Position Before a Polarity Check
Equal paths from each speaker make the gap between the two clips loudest:
- Start at low volume and raise it until the tone is clear.
- Sit centered, equally far from each speaker; an equilateral triangle works well.
- Set the tweeters at ear height.
- Clear rattling objects that could mask the bass difference.
Beyond the Polarity Test: Other Speaker Checks
Once phase is settled, a few other audio checks catch problems polarity can't, from damaged drivers to the limits of your own hearing.
Frequency Sweep and Subwoofer Checks
A subwoofer set to the wrong phase can cancel the mains around its crossover, so give it its own audio test: a frequency sweep from 20Hz to 20kHz shows a dip there if it does. The same sweep reveals your frequency response, where treble disappears, and sub-bass rattles from a cabinet or a struggling driver.
Pink Noise and Home Theater Setups
In a home theater or surround system, check phase & polarity on every speaker pair, not just the front two; pink noise works well as the source for that check.
When Speaker Phase Is Fine but Something Still Sounds Wrong
A passed test means your speakers are wired correctly and the browser audio path works. If the low end still seems weak, check the subwoofer's phase switch. If music still sounds off, a frequency response dip from the room or a hearing issue is more likely than polarity.
Frequently Asked Questions
- What does it mean when speakers are out of phase?
- One speaker cone moves forward while the other moves back, because the positive and negative leads are reversed on one speaker. The two speakers then cancel each other, mostly in the bass, and the center image turns vague.
- How does the speaker polarity and phase test work?
- It plays the same signal through both speakers twice: once with both channels normal, and once with the right channel inverted. With correct wiring, the in phase version sounds fuller and centered and the out of phase version thin and diffuse. If it is the other way round, one speaker is reversed.
- How do I fix speakers that are out of phase?
- Check that the positive amplifier terminal (usually red) reaches the positive speaker terminal on both sides. Swap the two wires on one speaker only, at either end, then run both versions again.
- Why does the bass disappear when speakers are out of phase?
- Bass wavelengths are several metres long, so the waves from the two speakers stay lined up across the room and cancel. Treble wavelengths are only centimetres long, so small differences in distance break the cancellation and the treble survives.
- Does polarity matter for headphones?
- Headphones are wired at the factory, so faults are rare, but a damaged cable, a bad solder joint or a faulty adapter can invert one side. The out of phase sample then sounds as if it is inside your head; if it sounds more natural than the in phase sample, the wiring is at fault.
- Which test signal should I use?
- Use a low tone or the rumble to judge bass, since that is where cancellation is strongest. Use the mid tone, guitar recording or pink noise to judge whether the sound sits in a fixed spot between the speakers.
- Can I run the test on a laptop or phone?
- The page plays on any modern browser, but built-in laptop and phone speakers are too close together and too small to show much difference. Use a pair of separate stereo speakers for a clear result.