Speaker phase test
Two speakers are in phase when their cones move the same way at the same time. Here is how to hear it.
Press left, right or both to start. Space stops everything.
Sound
Phase
Run the test
The page is set to pink noise. Press both, sit in the middle between the speakers and flip the phase switch below (the switch is orange when the speakers are in phase). With the switch grey, the right speaker is inverted on purpose.
What you should hear
In phase, the noise sounds full and seems to come from a point between the speakers, with solid bass. Out of phase, it sounds thinner, vaguer and wider than the speaker distance, and the bass gets weak. The scope shows the same: when the switch is grey, the right wave is the mirror image of the left.
If the out-of-phase version sounds better
Then one speaker is probably wired the wrong way round: its plus and minus wires are swapped. Check the markings on the terminals and the cable, and compare both speakers. The test compares the two speakers with each other, so it cannot tell you which wire is the positive one.
Questions
How do I test my speakers with this page?
Turn the volume down low, then press Left. You should hear a steady tone from the left speaker only, and the left half of the scope should move while the right half stays flat. Do the same with Right, then Both.
The tone is a plain sine wave, so a buzz, a rattle or a missing side points to the speaker, the cable or a setting. The keys A, S and D start Left, Both and Right, and Space stops everything.
Left and right are swapped. How do I fix it?
Press Left. If the sound comes from the right side, the channels are reversed. Check the output settings of your system or audio interface, and how the speaker cables are connected.
With headphones, check that you are wearing them the right way round: the small L and R marks are easy to miss.
How do I check if my speakers are out of phase?
Two speakers are in phase when their cones move the same way at the same time. Wired out of phase, one pushes while the other pulls: the bass thins out and the sound seems to come from nowhere in particular.
Choose Both and Noise (pink is the usual choice), sit in the middle between the speakers and flip the Phase switch (key P). Orange is In phase, grey is Out of phase, which inverts the right speaker. In phase should sound solid and centred between the speakers, out of phase thinner and vague, especially in the bass. If the out-of-phase version sounds better, one speaker's plus and minus wires are probably reversed.
The test compares your two speakers with each other; it cannot tell you which wire is the positive one.