Decibel Shield
Left and right audio test › Surround sound test
Surround sound test (5.1 and 7.1)
Press Start and the page plays a short burst through each speaker of a 5.1 or 7.1 system on its own: front left, centre, front right, the surrounds, the rears and the subwoofer. Check each burst comes from the speaker named on the button. It works when your browser exposes six or more output channels; if it reports two, the page says so and explains how to open the rest.
Each speaker gets a two-second burst of noise (the subwoofer a 50 Hz tone). No microphone, nothing recorded, and the level is capped; start with the volume low.
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Where each speaker goes, and what it plays
| Speaker | Where it goes | What it carries |
|---|---|---|
| Front left and right | Either side of the screen, angled at the listener | Music, effects and the width of the picture |
| Centre | Above or below the screen, in the middle | Most of the dialogue, so it carries the most important sound |
| Surround left and right (5.1) | Beside and slightly behind the listener | Ambience and effects that move around the room |
| Side and rear pairs (7.1) | The side pair beside you, the rear pair behind you | The same, split so sound can move from side to back |
| Subwoofer (LFE) | Anywhere on the floor that sounds even; corners boost it | Only deep bass, the ".1" in 5.1 |
The international layout for 5.1, ITU-R BS.775, puts the front pair 30 degrees either side of the centre and the surrounds between 100 and 120 degrees round from the front, all at the same distance from the listener. Rooms rarely allow that exactly; a receiver's distance and level settings make up most of the difference.
If the browser only reports two channels
A web page can only reach as many channels as the operating system gives the browser, and the default for most devices is two. Set the output device's speaker configuration to 5.1 or 7.1 (on Windows under the device's "Configure speakers"; on a Mac in Audio MIDI Setup), make sure the receiver or interface is connected by HDMI or a multichannel USB or optical link rather than Bluetooth, reload the page and press Start again. Headphones, Bluetooth speakers and most soundbars report two channels whatever they decode internally. In that case the left and right audio test is the useful check.
What the test can and cannot tell you
It settles routing: whether each channel reaches the speaker it should, which catches swapped cables, a dead speaker and a receiver mode that spreads one channel across several. It does not measure levels or timing; for that, use the receiver's own calibration or a sound level meter. The decibel meter gives a rough reading from where you sit, and the bass test shows how low the subwoofer really goes.
Why does the test say my browser only has two channels?
Because that is what the operating system is offering it. A browser can only address as many channels as the output device is configured for, so a receiver connected over HDMI but set up as stereo, a Bluetooth speaker or soundbar, or headphones all report two. Set the speaker configuration to 5.1 or 7.1 in your system sound settings (Windows: Sound, then the device, then Configure speakers; Mac: Audio MIDI Setup, then Configure Speakers), reload the page and press Start again. If it still reports two, try a different browser.
Can this test Dolby Atmos?
Not the height speakers, and no web page can. Atmos height channels are sound objects that a receiver or soundbar decodes from a Dolby bitstream; a browser can only send plain channels. What this page can check is the 5.1 or 7.1 bed underneath Atmos, which is where most wiring and placement mistakes are. For the height speakers, use the test tones built into your receiver or soundbar.
The centre speaker plays when I press front left. What is wrong?
Usually nothing is wired wrong: a receiver set to a mode such as Pro Logic or a "multichannel stereo" mode spreads every input across several speakers. Switch the receiver to a direct or straight decoding mode for the test. If the wrong speaker plays on its own, the speaker cables are on the wrong terminals.
Why do I hear the subwoofer test only faintly, or not at all?
The subwoofer channel carries only deep bass, so a 50 Hz tone through a small speaker is barely audible, and some receivers send it nowhere unless a subwoofer is enabled in their speaker setup. Check the subwoofer is switched on, its own volume is up, and the receiver lists it as present. The bass test runs a ladder down to 20 Hz if you want to see how low it really goes.
What is the difference between 5.1 and 7.1?
5.1 has front left, centre, front right, two surround speakers and a subwoofer. 7.1 splits the surrounds into a side pair and a rear pair, for eight channels in all. The test offers 7.1 only when your browser reports at least eight output channels.