Decibel Shield
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Classroom noise meter
A noise level monitor for the classroom that shows one colour and one number the whole room can read: green when the room is under your quiet threshold, amber as it rises, red when it is too loud. Set the thresholds, press Big display for the projector, and nothing is recorded.
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Suggested thresholds by activity
| Activity | Green up to | Red from |
|---|---|---|
| Silent reading, tests | 45 dB | 60 dB |
| Independent work, quiet talk allowed | 55 dB | 70 dB |
| Group work, discussion | 65 dB | 78 dB |
| Practical, art, workshop | 70 dB | 85 dB |
For scale, normal conversation is 60 to 70 dB and a vacuum cleaner about 70 to 75 dB on the decibel chart. Above 85 dB sustained, NIOSH begins counting exposure time; a classroom should not get there.
What the colours mean
- Green: under the quiet threshold. The room is where you asked it to be.
- Amber: between the two thresholds. Rising; a glance at the screen is usually enough.
- Red: at or above the loud threshold. The seconds-in-red counter keeps a tally for the session.
What decibel level should a classroom be?
Quiet independent work sits around 40 to 50 dB, normal group work around 60 to 65 dB, and a room that has reached 70 to 75 dB is loud enough that people are raising their voices to be heard. The defaults here turn amber at 60 dB and red at 75 dB; move the sliders to fit your room and your activity.
Is this accurate enough for a classroom?
For a traffic light, yes. Phone and laptop microphones are calibrated here against a reference and read within a few decibels of a sound level meter in the range a classroom lives in. Treat the number as a guide and the colour as the signal; do not use it to certify anything.
Does it record the class?
No. The microphone feeds a level calculation that runs in your browser and is thrown away every fifth of a second. Nothing is stored, nothing leaves the device, and there is no account.
Can I put it on the projector or interactive board?
Yes. Press Big display for a full-width light and number, and use your browser's full-screen key (F11 on Windows, Control-Command-F on a Mac) to remove the browser frame. The thresholds you set are remembered on that device.
How is this different from the decibel meter?
Same microphone pipeline and calibration, different display. The decibel meter shows the live curve, the average and the peak for a measurement. This page shows one colour and one number the whole room can read from the back.
Measure a level properly
Need the actual reading, the average and the peak? The online decibel meter uses the same microphone pipeline with A-weighting, a calibration trim and a saved report.