What does the stereo test check?
Three things: (1) whether your left and right channels both work, (2) whether they are correctly wired (left audio comes out the left earpiece, not the right), and (3) the relative balance between them (one side noticeably quieter usually means a hardware fault). The frequency sweep also catches dead frequency ranges where a speaker driver has failed.
How do I know if my AirPods are balanced correctly?
Run the Left-Only test, then the Right-Only test. If both sound at roughly the same loudness when worn the same distance from each ear, your AirPods are balanced. iPhone has an additional balance fix: Settings > Accessibility > Audio/Visual > Balance slider. If one AirPod sounds quieter, try cleaning the mesh with a soft brush (earwax buildup) before suspecting hardware failure.
Why do both my earbuds play the same audio? It is not stereo.
Your audio source might be set to mono (one of: Settings > Accessibility > Mono Audio on iOS or Android; Windows Sound > Properties > Enhancements > Mono on PC). Stereo audio playing in mono sounds full but you cannot tell left from right. Disable Mono Audio in your accessibility settings, then re-run the Left and Right tests - you should hear them in different ears.
Why does only one earbud work, even though the test plays both?
Common causes: (1) one earbud is paired but its battery is dead (Bluetooth earbuds), (2) the earbud is dirty / clogged with earwax, (3) the audio source (your phone) has stereo balance shifted all the way to one side - check Settings > Accessibility > Audio Balance. (4) Hardware failure of one driver. Try the test with wired headphones to isolate Bluetooth from speaker issues.
What frequencies are good for testing?
Music covers roughly 20 Hz to 20 kHz. Most headphone drivers reproduce 50 Hz to 16 kHz well. The frequency sweep on this tool covers 50 Hz (deep bass) up to 16 kHz (cymbals/sibilance). Dead spots in this range indicate a damaged driver. People over 40 typically cannot hear above 13-14 kHz - this is normal age-related hearing loss, not a headphone fault.
Is this safe? Will it damage my hearing?
The tool defaults to 50% volume to limit volume to safe levels. If your system volume is already maxed out, you may want to lower it first. The frequency sweep includes both bass and treble - sustained high-volume bass can damage low-cost drivers, and sustained high-frequency tones above 12 kHz can be uncomfortable. Do not run the sweep at 100% volume for extended periods.
Does the test work on speakers or only headphones?
It works on any stereo output - headphones, earbuds, laptop speakers, external speakers, monitor speakers, soundbars, car stereos (if you can play web audio in your car). Stereo positioning is most obvious with headphones because each driver is dedicated to one ear; with speakers, the left/right distinction is muddier because both ears hear both speakers (just at different volumes).
What is mono vs stereo vs surround?
Mono: one channel - same audio comes from both speakers (or just one). Stereo: two channels - left and right are recorded separately, music is panned across the soundstage. Surround (5.1, 7.1, Dolby Atmos): multiple channels - center, front L/R, rear L/R, plus subwoofer. This tool tests STEREO. Surround test requires specific surround-formatted audio files and is out of scope for a browser tool.
Why is my left ear quieter than my right?
Possible causes in order of likelihood: (1) accessibility balance is off - check Settings > Accessibility > Audio Balance and recenter; (2) earwax buildup in one ear (real, not headphone issue) - try a different headphone, see if it persists; (3) earwax buildup in the headphone driver itself - gently clean with a soft brush; (4) age-related hearing loss is often asymmetric, especially if you favor one ear for phone calls; (5) hardware failure - usually wired into a warranty replacement.
Does this work on Bluetooth headphones?
Yes. The browser sends stereo audio to your default output device, including Bluetooth. Note: Bluetooth codec quality varies (SBC is the worst, AAC/aptX/LDAC are better) - lossy codecs may slightly compress the frequency sweep, but the left/right channel test is unaffected by codec choice.