Headphone Test

Three quick checks for headphones and stereo speakers. First, polarity: play the same low tone twice, once normally and once with one side flipped. If everything's wired correctly, the flipped one sounds hollow, with no centre.

Polarity check

Channel swap check

Stereo image check

What out of phase sounds like

The polarity check plays the same tone twice: once normally, and once with one side's waveform flipped upside down. In phase, the two sides add up and the sound sits in one solid spot. Out of phase, they partly cancel each other out. It doesn't just get quieter; it sounds hollow and spread out, as if it's coming from nowhere in particular. The centre goes first: instead of sitting between the two sides, it smears across the space or drops out of the middle while the sides stay. The bass thins out too, because low notes cancel the most. On headphones it's even stranger: the sound seems to be inside your head instead of in front of you. That inside-your-head feeling, more than any drop in volume, is the giveaway. For why it happens, and why one speaker on its own can never show it, see our guide to out of phase and reversed polarity.

Reversed polarity is one of the easiest fixes in audio

On wired speakers, reversed polarity nearly always means one thing: a cable is connected the right way round at one end and swapped at the other. Speaker wire only has a plus and a minus, and it's easy to connect red to black at one end and red to red at the other without noticing, especially on bare-wire terminals. That makes it one of the few audio problems with a guaranteed fix: find the swapped pair, switch it back, and the problem is completely gone. Compare that with a buzzing cabinet or a worn-out driver, where you can only improve things. Headphones and most consumer gear are wired correctly at the factory and can't be reversed by you, so if headphones fail this check, the cause is more likely the device they're plugged into, or a third-party cable.

Why the centre disappears

Play the same signal from two speakers set apart, in phase and at the same level, and your ears don't hear two sources. They merge them into one imaginary source in the middle, where there's no speaker at all. That's the phantom centre, and it's how stereo recordings put a singer or a kick drum in the middle without a centre speaker. It only works when both sides are in step. Flip one side and they fight in the middle instead of adding up, and the centre collapses into that hollow, placeless sound. If the centre won't form, or only forms when you switch which side is flipped, you've found a wiring fault by ear, no equipment needed.

A left-right swap can go unnoticed for years

A plain left-right swap doesn't sound broken. Both sides work, they're in phase and the levels match; the only problem is which side each one comes out of. Most music is balanced enough, and most seats forgiving enough, that a swap can go unnoticed for years. What you lose is precision. The person who mixed the song put the guitar on the right and the harmony on the left for a reason, and a swap quietly undoes all of it. It also throws off anything that relies on real stereo, like a game placing footsteps behind you on the left, or a film panning a car across the screen. The channel swap check above is there because nobody goes looking for a problem this quiet.

When the device makes both sides the same

Some Bluetooth speakers, soundbars and USB audio devices tell your computer or phone they're stereo, but mix both sides into one before the sound reaches a speaker. Test one of those and every check on this page says "both sides the same", including a centre that never moves. Nothing is wired backwards; there's simply only one signal left by the time the sound comes out. It's a limit of the hardware, not a fault this page can find or fix. Before blaming a cable, try a different device, or wired headphones with a separate speaker in each ear, and see whether the result changes.

What these checks can't tell you

These checks test the whole path from this browser tab, through your computer, over the cable or wireless link, to the speakers that make the sound. That's a useful path to check, and it's all a web page can reach. They can't tell whether a fault is inside your headphones or in an amplifier, DAC or mixer before them: a reversed pair of wires in a headphone cable and a reversed output in an amplifier sound exactly the same here. They also can't measure real loudness, distortion or frequency response, because a browser has nothing calibrated to compare against at the other end of your headphone jack. What you do get is a clear, repeatable answer to three questions: is the phase right, are left and right the right way round, and does the centre hold together.

Using a headset? The headset test checks left and right and the microphone together, on one page.

Not sure where the problem is? Run the full sound check. It's six quick questions, and at the end it tells you which tool to use next.