Audio Lab // Stereo Polarity
SPEAKER PHASE & POLARITY TEST
Compare a matched stereo signal with the right channel digitally inverted. Use the difference in center image, bass and mono cancellation to troubleshoot stereo speaker wiring and signal-path polarity without downloading audio files.
Start with your physical volume low. The browser generator is deliberately capped at a low app level, but your operating-system, amplifier and powered-speaker volume still determine the actual acoustic output.
How to check speaker polarity
- Confirm left and right routing first with the dedicated channel test.
- Sit roughly centered between two speakers and keep all spatial audio or virtual surround effects off for the comparison.
- Press Play In Phase. The tone should normally form a more stable center image and can sound fuller.
- Press Play Out of Phase at the same volume. The image commonly becomes wider, hollow or difficult to localize, with more cancellation around the listening position.
- If the comparison seems reversed, inspect polarity/wiring on one speaker and repeat before changing anything else.
What this tool actually generates
One Web Audio oscillator feeds both stereo channels, so the digital source is identical on the left and right. In Phase uses a gain of +1 on both channels. Out of Phase keeps the left at +1 and changes the right to -1, which inverts its waveform by 180 degrees.
Because the same oscillator feeds both channels, the comparison does not depend on two separate oscillators starting at exactly the same instant.
What “out of phase” can sound like
With stereo speakers, opposite polarity can weaken the center image and cause partial acoustic cancellation, especially where both speakers contribute similar energy. The exact result depends on room reflections, listening position, speaker spacing and frequency.
Do not expect complete silence. Two real speakers in a room do not reach your ears with perfectly identical level and timing.
Headphones are different
Headphones isolate the left and right transducers much more strongly than speakers in a room. You may hear an unusual diffuse or inside/outside-head image when one channel is inverted, but that is not the same physical cancellation mechanism used to diagnose reversed speaker wiring.
Use headphones mainly to confirm that the playback path preserves a clear digital phase contrast.
Mono cancellation clue
If a playback device or accessibility setting sums stereo to mono, the out-of-phase signal can become dramatically quieter because opposite channels cancel in the mono sum. That is useful evidence about the signal path, but it does not by itself identify a reversed speaker cable.
Limitations
- The browser does not know how your physical speaker terminals are wired.
- Room acoustics and listening position strongly affect perceived cancellation.
- DSP, surround virtualization, crossfeed and EQ can change the result.
- The test is not a calibrated acoustic phase measurement.
- It does not identify absolute acoustic polarity of an individual loudspeaker driver.
Speaker phase test FAQ
Why use a lower-frequency tone?
Moderately low frequencies often make speaker-pair cancellation and loss of center solidity easier to notice than very high tones. The control is limited to 100–500 Hz to keep the comparison focused.
Does “out of phase” mean my speakers are broken?
No. This page intentionally generates an out-of-phase reference. A wiring problem is only one possible reason your real system might resemble that reference.
Can I test Bluetooth speakers?
Yes if the device exposes a true stereo playback path, but some Bluetooth products internally process or mono-sum their input, which can change the comparison.
Can this damage my speakers?
Polarity inversion itself is not a damage mechanism. Excessive volume is the risk, which is why the app starts at a low level and caps its own generator gain. Keep the physical playback volume comfortable.
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