Speaker and headphone test
Sound in one ear only is the most common audio complaint there is, and it has four completely different causes. Playing each channel on its own, with the side clearly marked on screen, separates them in about ten seconds.
Put your headphones on the right way round first — L is left.
Did each side play from the side it said?
What each result means
| What happened | What it is | What to do |
|---|---|---|
| One side silent | Plug, balance, cable or driver | Work the list below in order |
| Both play on a single-side test | Audio downmixed to mono | Turn off the mono setting |
| Sides swapped | Headphones on backwards, or wrong socket | Check physically first |
| One side quieter | Balance offset, or a worn driver | Centre balance, then compare |
| Crackling on one side | Cable near the plug, or a loose socket | Move the cable while it plays |
The order to check in
- Push the plug all the way in. A 3.5 mm connector carries left, right and ground on separate contacts along its length. One step short and a channel is simply not connected. Phone cases and thick socket surrounds cause this constantly.
- Centre the balance. It is a system-wide setting that survives reboots and applies to everything, and it is easy to move by accident.
- Flex the cable near the plug while a channel plays. If the sound cuts in and out, the cable has failed there — which is where they nearly always fail.
- Try another socket or another device. This is what separates the headphones from the computer, and it takes ten seconds.
Windows 11
- Balance. Settings → System → Sound → your output device → Volume, where left and right have separate sliders.
- Mono audio. Settings → Accessibility → Audio → Mono audio. If this is on, every one-sided test will play on both sides, which looks like a fault in the test rather than a setting.
- Front and rear sockets are different devices on most desktops, each with its own volume and balance. A working rear socket and a silent front one is a jack detection setting, not a broken speaker.
- Bluetooth headsets switch to a low quality hands-free mode when an application opens the microphone, and some collapse to mono in the process.
macOS
- Balance. System Settings → Sound → Output, with a balance slider under the device list. It is per-device, so fixing it for headphones does not fix it for speakers.
- Play stereo audio as mono lives in System Settings → Accessibility → Audio, and does the same thing as the Windows setting.
- On a Mac with an external interface, check that the correct output is selected — macOS switches automatically when a device appears, and the balance of the newly selected device may be different.
If both channels are fine and it still sounds wrong
Then the fault is not level but phase. Two speakers wired in opposite polarity each measure perfectly, play on the correct sides, and still produce a hollow sound with almost no bass. That is the next test in this run.
Common questions
Only one side plays. Is the headphone broken?
Not necessarily, and it is worth ruling out three cheaper things first. A partly inserted plug is the most common cause of all: the connector has several contacts along its length, and stopping one step short leaves a channel unconnected. Then the balance control, which can be pushed fully to one side in the system settings and affects everything. Then the cable near the plug, which is where they fail. Only after those is the driver itself likely.
Both sides play when I only asked for one. Why?
The audio is being downmixed to mono somewhere. On Windows this is usually the mono audio accessibility setting; on macOS, "Play stereo audio as mono". Some Bluetooth headsets also collapse to mono when the microphone is active, which is why a headset can be stereo for music and mono on a call.
The sides are swapped. Can I fix it in software?
Usually you should not have to. Check first that the headphones are on the right way round and that the cable is in the correct socket, because a swapped result is almost always physical. Where it is genuinely a wiring fault in a fixed installation, both Windows and macOS can swap channels, but treat that as a workaround rather than a repair.
One side is quieter rather than silent.
Check the balance control first — it is a slider, not a switch, and a small offset is easy to make by accident. If balance is centred, an unevenly worn driver or a partly broken cable core will do it, and both get worse over time.
Why noise instead of a tone?
Because broadband noise contains every frequency at once, so it reveals a channel that works but is dull or thin. A single tone can fall into a dip in a speaker response and sound wrong on a perfectly good driver.