Check that left and right come out where they should, based on what you actually hear
The speaker and headphone left-right test plays a sound on the left, in the center, and on the right, one after another, and asks where you actually heard it. From your answers it works out whether left and right are swapped, whether the sound has been merged into mono, whether one side is silent, and whether the center sound leans to one side, then tells you what to check first for headphones or for speakers.
You can go two steps further than left and right. The phase comparison plays version A, with the same sound sent identically to both sides, and version B, with only the right side flipped, and asks which one is clearer. It is a way to catch speakers where the + and − wires of one side were swapped. The bass sweep plays a tone that rises from 20 Hz to 320 Hz over 16 seconds and compares the first frequency you heard with the lowest notes of a piano, a bass, and a guitar. Every sound is generated in your browser on the spot. The test never turns on your microphone or downloads an audio file.
When it pays to check left and right first
Swapped channels or a weak side are easy to miss when you only listen to music, because your ears adapt as long as sound comes out. When direction and balance matter, a minute of checking up front saves a lot of guessing later.
- You just bought new earphones or headphones: check that both sides play and that left and right are correct when worn as marked. Finding a defect inside the return window is much easier.
- You connected speakers or moved them: plugging the left speaker into the R terminal, or swapping + and − on one side, is a common mistake. The left-right verdict and the phase comparison cover both.
- Before a game: in games where footsteps and gunfire tell you where opponents are, swapped channels send you the wrong way.
- Before a video meeting or online class: a Bluetooth headset drops into mono call mode the moment the microphone turns on. Knowing why only one side plays, or why the sound suddenly narrows, saves you from panicking. You can continue with the Microphone Test for the microphone.
- One side seems quieter: checking whether the center sound leans to one side helps you decide where to look first: how the earphones sit, the balance setting, or a hardware fault.
- Video editing and broadcast monitoring: if you balance sound on a swapped setup, the finished work is swapped too. Check your listening device before you edit.
How to run the test
- Choose your listening device. Pick headphones or speakers, whichever you are using, and the diagram and next-step advice adapt to it. Start at "Medium" volume and set the device volume to about the middle.
- Press the Left button and choose where you heard it. A three-note signal plays twice. Below, pick what you actually heard: "Left", "Center/both", "Right", or "Not heard".
- Listen to Right and Center the same way. Once you have answered for left and right, the overall verdict appears, and answering for the center adds a balance verdict.
- If you like, play "Pan left-right". Over 8 seconds the sound travels from the far left to the far right and back. If it cuts out in the middle or suddenly gets louder on one side, suspect the connection or the balance setting on that side.
- Compare A and B in ② Phase. "A·B alternate" switches between them four times, 2 seconds each. Choose the one that sounds more centered and clearer.
- Listen to ③ Bass sweep. Press Start sweep and press "I hear it" the moment you first hear the tone. While it keeps rising, press "Buzz / rattle" whenever you hear rattling or buzzing.
- Read the summary. Each finished step adds a verdict and a next step. "Copy results" copies the verdict as text that you can paste into a repair request or a note.
How the verdict follows from where you heard each sound
The tool pairs where you heard the left sound with where you heard the right sound. The Left button sends sound only to the left channel, and the Right button only to the right channel, and the opposite channel is exactly zero. So if the left sound is audible on both sides, your device or settings are mixing the two channels.
| Where you heard the left sound | Where you heard the right sound | Verdict | Check first |
|---|---|---|---|
| Left | Right | OK | Listen to the center as well to check balance |
| Right | Left | Swapped | How the earphones are worn (L and R), the speaker L and R terminals |
| Center/both | Center/both | Mono | Mono audio setting, Bluetooth call mode, devices with a single speaker |
| Not heard | Right | Left silent | Left earbud connection or power, left speaker cable, balance |
| Left | Not heard | Right silent | Right earbud connection or power, right speaker cable, balance |
| Left | Left | One side only (left) | Mono audio is combining both channels while the right side is off (check the right connection and whether the balance is all the way left) |
| Not heard | Not heard | No sound | Volume and mute, output device |
When left and right are fine but the center sounds like it comes from the "Left" or "Right", the verdict is off-center. A combination that is not in the table (for example, the left sound on both sides and the right sound on the right) is marked "Recheck", and you are asked to press the same button once more. You can change an answer once you press that button again.
Where to find mono audio and balance settings
If the verdict is "Mono" or "One side", check your operating system settings first. Mono audio is an accessibility feature that sends the same sound to the left and right, and the balance control lowers the volume on one side. If the balance sits at one extreme, the other side can seem to be silent.
| Device | Mono audio | Left-right balance |
|---|---|---|
| iPhone | Settings > Accessibility > Audio & Visual > Mono Audio | Balance slider on the same screen |
| Mac | System Settings > Accessibility > Audio > "Play stereo audio as mono" | System Settings > Sound > Balance slider |
| Windows 11 | Settings > Accessibility > Audio > Mono audio | Settings > System > Sound, choose the output device, then the left and right channel volumes |
| Android | Settings > Accessibility > Audio adjustment > Mono audio (the name differs by manufacturer) | Audio balance on the same screen |
On Android, menu names and locations differ by manufacturer. If you cannot find the menu, type "mono" or "balance" into the search box at the top of Settings. When only a Bluetooth device plays from one side on Windows, Microsoft's support article also tells you to check that the left and right channel volumes of the output device are equal.
Why a Bluetooth headset turns mono during meetings
Bluetooth audio uses different profiles for different uses. For music and video it uses A2DP, a high-quality stereo playback profile, and for calls it uses HFP, which carries the microphone and speaker together. According to Microsoft's documentation, HFP plays and records in mono at a sample rate of 16 kHz (wideband) or 8 kHz (narrowband), and if an app opens the microphone while you listen over A2DP, the device switches to HFP.
That is why running this test with a meeting app open can produce a "Mono" verdict, with both the left and right sounds heard in the middle. It is not a fault but a property of the call profile. To check the earphones themselves, close the meeting app and every other tab that uses the microphone, then listen again. If you want stereo during meetings, use a separate microphone or a wired headset.
Where to sit when you test speakers
With speakers, your seat affects the verdict. If you sit closer to one speaker, the center sound leans toward it. ITU-R BS.775, the layout standard for multichannel broadcast audio, puts the front left and right speakers 30° to each side of the center as seen from the listening position (60° between them). The center image is sharpest when the two speakers and your seat form a near-equilateral triangle. On a device such as a laptop, whose speakers sit within a hand's width of each other, a small left-right difference is normal.
What the phase (polarity) comparison tells you
Version A sends the same sound to the left and right. Version B flips only the sign of the right sound, so when the left side pushes, the right side pulls. This is called polarity inversion, and it is equivalent to a 180° phase shift at every frequency. The tool uses pink noise filtered below 1,200 Hz, so you hear the low range where the difference stands out.
| Device | A (same phase) | B (one side flipped) | If B is clearer |
|---|---|---|---|
| Speakers | Focused midway between the speakers, with full bass | Vague position, thinner bass | The + and − wires of one speaker may be swapped |
| Headphones | Focused clearly in the middle of the head | Vague position, or oddly spread out inside the head | An unusual result: listen again and check on another device |
With speakers, the two sounds meet in the room and the low frequencies cancel each other, so the bass gets thinner. A support article from the speaker maker Lithe Audio explains that if the + and − of one side are swapped, you get weak or hollow bass and a vague stereo image, while if both sides are swapped there is no major problem. With headphones the two sounds reach your ears separately, with your head in between, so the bass does not cancel. The difference shows up instead as a vaguer sense of position.
On an output that combines left and right into one (mono audio, Bluetooth call mode, a device with a single speaker), the two halves of B are added together and cancel each other out, so B becomes nearly silent. In that case choose "B nearly silent" and the tool reports mono. If A and B sound identical, only one side may be playing, so read the result together with ① Left/Center.
How to read the bass sweep
The bass sweep is a sine wave that rises from 20 Hz to 320 Hz over 16 seconds. It doubles in frequency (one octave) every 4 seconds, so the scale on screen is a logarithmic scale with the same spacing. The tool records the frequency your device was outputting at the moment you pressed "I hear it" (part of any Bluetooth delay may not be included), and uses the whole-number Hz value shown on screen for the verdict.
| Time since start | Frequency | Reference marked on the scale |
|---|---|---|
| 0 s | 20 Hz | Start of the sweep |
| 4 s | 40 Hz | Just below the lowest note of a 4-string bass (41.2 Hz) |
| 8 s | 80 Hz | Just below the lowest guitar note (82.4 Hz) |
| 12 s | 160 Hz | Just above the fundamental range of male voices (90–155 Hz) |
| 16 s | 320 Hz | End of the sweep |
Read the first frequency you heard as follows. The instrument notes are equal-temperament values at standard pitch (A4 = 440 Hz).
| First frequency heard | Interpretation |
|---|---|
| 27 Hz or below | Deep bass that reaches the lowest piano note, A0 (27.5 Hz) |
| 28–41 Hz | You can hear down to the lowest note of a 4-string bass, E1 (41.2 Hz) |
| 42–82 Hz | You hear the lowest guitar note, E2 (82.4 Hz), but the lowest bass note is weak or inaudible |
| 83 Hz or above | Weak bass for music. Speech is understandable within the telephone band (300–3,400 Hz) alone, so calls and meetings are hardly affected |
| Not pressed up to 320 Hz | Raise the volume or check the output device, then try again |
The time it takes you to press the button raises the recorded value a little above the real one. Pressing 0.3 seconds late means the frequency has already climbed about 5%, so a tone you started hearing at 40 Hz is logged as 42 Hz. Repeating the sweep two or three times and taking the lowest value is more accurate. With earphones, the ear tips must seal your ears for the bass to come through properly. Apple notes that a good ear tip fit enriches the bass in music.
Why low sounds are heard late
The bass sweep result reflects the sensitivity of your ears as well as the performance of your device. Human hearing is duller for low sounds, so the level at which a sound barely becomes audible (the hearing threshold) varies greatly with frequency. The values from the international standard ISO 226:2023 are below (sound from the front, young listeners with normal hearing).
| Frequency | Hearing threshold (dB SPL) | How much louder than 1,000 Hz it must be |
|---|---|---|
| 20 Hz | 78.1 | 75.7 dB |
| 31.5 Hz | 59.5 | 57.1 dB |
| 40 Hz | 51.1 | 48.7 dB |
| 63 Hz | 37.5 | 35.1 dB |
| 80 Hz | 31.5 | 29.1 dB |
| 125 Hz | 22.1 | 19.7 dB |
| 200 Hz | 14.4 | 12.0 dB |
| 315 Hz | 8.6 | 6.2 dB |
| 1,000 Hz | 2.4 | 0 dB |
For example, 20 Hz must be about 76 dB louder than 1,000 Hz before it is barely audible. That is why the same earphones give a higher first frequency at "Low" volume and a lower one at "High". When you compare devices, keep the volume step and the device volume the same.
Marking buzzes and rattles
When the bass reaches a certain frequency, objects next to the speaker, the desk, the monitor, or the speaker cabinet itself can start to resonate, producing rattling or buzzing. Press "Buzz / rattle" at that moment to leave a mark on the scale. If the sound repeats at the marked frequency, move nearby objects away or change what the speaker sits on. If it still buzzes at the same place after you tidy up, the driver (diaphragm unit) may be torn or loose. If you hear buzzing from earphones, lower the volume one step and listen again, because even a healthy pair distorts when it is too loud.
The sounds this tool plays
| Step | Sound | Length | Sent to |
|---|---|---|---|
| Left, center, right | A three-note signal of E5 (659.3 Hz), G5 (784.0 Hz), and C6 (1,046.5 Hz), played twice | About 1.7 s | Left channel only, both channels, right channel only |
| Pan left-right | Pink noise | 8 s | Far left → far right → far left (equal-power panning) |
| Phase A·B | Pink noise filtered below 1,200 Hz | 3 s, or 2 s each four times when alternating | A is the same wave on both channels, B has the right sign flipped |
| Bass sweep | Sine wave, 20 → 320 Hz | 16 s | The same wave on both channels |
The volume button has three steps, 6 dB apart. The peak level of the bass sweep sine wave is −20.0 dBFS at "Low", −14.0 dBFS at "Medium", and −8.0 dBFS at "High". dBFS sets the maximum a digital signal can hold to 0, so the loudness you actually hear depends on your device volume and on your earphones or speakers. The left and right signals go to a single channel through the Web Audio ChannelMerger, and the left-right pan uses equal-power panning (StereoPanner).
Volume and ear protection
The test sounds are short, but if the device volume is at maximum while earphones are in your ears, they can suddenly be very loud. Set the device volume to about the middle, start at "Medium", and raise it to "High" only if you cannot hear well. The World Health Organization (WHO) says adults can listen to 80 dB sound for up to 40 hours a week. The louder the sound, the shorter the time that is safe, so set the device volume back to your usual level after the test.
Common misjudgments
- Treating a single-speaker device as broken: many phones and Bluetooth speakers have one speaker, or two speakers so close together that left and right barely differ. A "Mono" verdict on such a device is normal.
- Testing with a meeting app open: a Bluetooth headset switches to call mode (HFP) and the verdict is mono. Close the meeting app and listen again.
- Judging with one ear: if you wear only one earbud, you naturally cannot hear the other side. Wear both while you judge.
- Blaming the device alone for the bass result: the first audible frequency depends on volume, ear tip seal, and the sensitivity of your ears. To compare devices, the same person should listen at the same volume.
- Deciding from a single phase comparison: the difference between A and B can be subtle. Play "A·B alternate" two or three times, and treat the result as reliable when you give the same answer each time.
Limits
- The device that plays the sound (built-in speakers, earphones, monitor speakers, and so on) follows the output settings of your operating system or browser. This tool does not change the output device.
- It checks only the two channels, left and right. The center, rear, and subwoofer channels of 5.1 and 7.1 surround do not get a sound of their own.
- The verdict is based on the answers you choose. It is not an instrument measurement that records frequency response with a measurement microphone, and the bass result depends on the sensitivity of your ears and your reaction time.
- The number of output channels is the maximum channel count of the default output device that the browser reports. Even if it shows 2 channels, that does not guarantee the actual state of your earphone or speaker connection.
- Bluetooth devices add delay, so the sound may arrive a moment after you press a button.
Reference date The source documents and menu names were checked on 2026-10-27. Menu names may change when your operating system updates.
Sources
- 01Microsoft Learn: Bluetooth Classic AudioA2DP is high-quality stereo playback, HFP is mono playback and recording (16 kHz wideband, 8 kHz narrowband), and opening the microphone during A2DP playback switches to HFP
- 02Apple iPhone User Guide: Adjust the audio settingsMono Audio and the Balance slider under Accessibility > Audio & Visual
- 03Mac User Guide: Accessibility audio settingsThe "Play stereo audio as mono" option
- 04Mac User Guide: Change the sound output settingsThe Balance slider under System Settings > Sound
- 05Microsoft Support: Make Windows easier to hearThe Mono audio toggle under Settings > Accessibility > Audio
- 06Microsoft Support: Fix Bluetooth audio only playing in one channelSetting the left and right channel volumes of the output device to the same level
- 07AbilityNet: How to adjust the left/right sound balance in Android 15The audio balance slider under Settings > Accessibility > Audio adjustment (Motorola's help pages describe mono audio on the same screen)
- 08ITU-R BS.775: Multichannel stereophonic sound systemFront left and right speakers placed at ±30° (60° apart) from the listening position
- 09Lithe Audio Support: What happens if you mix up the positive and negative wires of a speaker cableWith only one side reversed, bass weakens and the stereo image blurs; with both sides reversed there is no major problem
- 10audiocheck.net: Polarity checkOn headphones the two sounds are split by the head, so bass does not cancel, and reversed polarity sounds twisted inside the head
- 11ISO 226:2023 equal-loudness-level contours (sample PDF)Hearing threshold Tf by frequency: 20 Hz 78.1 dB, 40 Hz 51.1 dB, 1,000 Hz 2.4 dB
- 12Wikipedia: Piano key frequenciesA0 27.5 Hz, E1 41.2 Hz (open string of a bass), E2 82.4 Hz (lowest guitar note), A4 440 Hz
- 13Wikipedia: Voice frequencyFundamental frequency of adult voices (men about 90–155 Hz, women about 165–255 Hz)
- 14WHO: Deafness and hearing loss, safe listening80 dB is safe for up to 40 hours a week
- 15Apple Support: AirPods Pro ear tip fit testA good ear tip fit improves noise blocking and enriches the bass in music
- 16MDN: StereoPannerNodeEqual-power panning, pan −1 = far left, 1 = far right
- 17MDN: ChannelMergerNodeCombines several mono inputs into one multichannel output (one input per channel)
Frequently asked questions
The left sound plays on the right. What is wrong?
With earphones, first check that you are not wearing them the wrong way around relative to the L and R marks. With speakers, the left speaker is probably connected to the R terminal of the amplifier or computer. If it is swapped even though everything is connected as marked, run the same test on another phone or computer. If it is swapped there too, the earphones or speakers are at fault; if only one device swaps, the problem is that device's settings or connection.
The left and right sounds both play identically on both sides.
The sound is being merged into one channel (mono). Check whether Mono Audio is turned on in the accessibility settings of your phone and computer. A Bluetooth headset plays in mono in call mode (HFP), which uses the microphone, so close any meeting app and listen again. Phones and Bluetooth speakers with only one speaker sound like this by design.
Sound comes from only one side and nothing from the other.
For wireless earbuds, put both in the charging case and take them out again to reconnect; for wired ones, check that the plug is fully inserted. If the operating system's balance is pushed all the way to one side, the other side switches off as well. For speakers, check the power, the cables, and the amplifier terminals. If the same side stays silent on other devices, the earphones or speakers are most likely faulty.
The center sound leans to one side.
First check that the operating system's balance is centered. For earphones, check that both sit at the same depth and that the ear tips or mesh are not blocked; for speakers, check that you sit the same distance from both. If the sound always leans the same way even with different earphones, one ear may hear less well, and a hearing test is worth considering.
What should I do if B is clearer in the phase comparison?
With speakers, the + and − wires of one speaker may be swapped relative to the amplifier terminals. With only one side reversed, bass weakens and the image blurs, while with both sides reversed there is little difference. Look at the wire colors or stripes and connect both speakers the same way. On headphones this is an unusual result, so listen two or three more times.
From what frequency should the bass sweep be audible?
There is no fixed normal value. It varies with volume and ear tip seal, and human hearing is duller at low frequencies: 20 Hz must be about 76 dB louder than 1,000 Hz to be barely audible (ISO 226:2023). Compare your result with the lowest piano note at 27.5 Hz, bass at 41.2 Hz, and guitar at 82.4 Hz. Comparing devices at the same volume shows differences best.
Sound suddenly gets worse when I start a meeting with Bluetooth earphones.
For music, Bluetooth audio uses the stereo playback profile (A2DP), but when an app opens the microphone it switches to the call profile (HFP). HFP is mono and its sample rate drops to 16 kHz or 8 kHz, so the sound gets narrow and muffled. To keep stereo during meetings, use a separate microphone or a wired headset.
I press the buttons but hear nothing.
First check the device volume and mute, and the mute on the browser tab. The sound may be going to another device (a Bluetooth device that is still connected, monitor speakers), so check the operating system's output device too. If you still hear nothing, set the volume to "High" and try another browser. This tool does not use the microphone, so you do not need to grant any permission.