Classroom Noise Meter & Timer
Put the class sound level on the smart board. The meter turns red when the room gets too loud, the activity timer counts down beside it, and a quiet class earns stars. Nothing is ever recorded or uploaded.
A classroom noise meter shows the room's sound level on screen and turns red when the class gets too loud. This one uses your microphone, works out loudness as dB = 20 × log₁₀(RMS) relative to your own room, flashes a warning after a few seconds above your limit, and never records, saves or uploads any audio.
Class sound level
Measured by your microphone, in your browser only.
The microphone is off
Press Turn on microphone and allow access. The meter only measures how loud the room is — no audio is recorded, saved or sent anywhere, and the sound never leaves this page. Everything below the meter, including the timer, works without it.
Waiting for the room…
Activity timer
Works with or without the microphone.
Space start / pauseM microphone on / off
Quiet class stars
One star per 20 quiet seconds.
Turn the microphone on to start earning stars.
Last 60 seconds
Show the class how they did — the line is the sound level, the dashed line is your limit.
This session
Time spent at each level since the meter was switched on.
Settings
Every room is different — calibrate once and the meter fits your classroom.
A calm class, without raising your voice
Children control noise far better when they can see it. Put the meter on the board, agree a level together, and let the class watch their own stars grow.
Switch the microphone on
Allow access once. The browser shows a small recording icon — that is the meter listening, nothing more.
Calibrate the room
With the class silent, press Calibrate. Three seconds later the meter knows what “quiet” means in your room.
Agree the limit
Set the red line together — 50 for silent reading, 65 for pair work, 80 for an activity period.
Go full screen
Classroom mode makes the gauge and the timer readable from the last bench.
What the meter measures
Sound is a wave of pressure. The microphone gives the page thousands of samples a second; the page squares them, averages, and takes the square root — the RMS, or typical size of the wave.
RMS = √( (s₁² + s₂² + … + sₙ²) ÷ n )
Why decibels, not plain numbers
Our ears hear ratios, not differences. Loudness is therefore measured on a logarithmic scale:
dB = 20 × log₁₀(RMS)
Ten times the wave height is only +20 dB. That is why the meter uses this scale — it matches how loud the room feels. Levels here are relative to your own room, not an official decibel reading.
Why the needle is smooth
A raw level jumps dozens of times a second. The meter uses a smoothing filter: each new reading only pulls the needle part of the way.
shown = shown + (new − shown) × k
k is large when the sound rises (so a bang shows instantly) and small when it falls (so the needle glides back) — exactly how a studio sound meter behaves.
Classroom ideas
- Silent reading: limit 45, 10-minute timer, aim for five stars.
- Group work: limit 70 — the class learns what a “working buzz” looks like.
- Make a class record for the longest quiet streak and beat it each week.
- Science lesson: clap, whisper and talk, and read the level each time.
Classroom Noise Meter & Timer — your questions
How does a classroom noise meter work?
The microphone sends the page thousands of samples a second. The page squares them, averages, and takes the square root to get the RMS, the typical size of the sound wave. That is converted to a decibel-style number and used to move the needle. Readings are relative to your own room, not an official decibel measurement.
Does the noise meter record my class?
No. The page asks the microphone only for the loudness of each moment, uses it to move the needle, and throws it away. No audio is stored on your device and nothing is sent over the internet. The microphone stops the instant you switch the meter off or close the tab.
Why is loudness measured in decibels?
Because our ears hear ratios rather than differences, loudness is measured on a logarithmic scale: dB = 20 × log₁₀(RMS). Ten times the wave height is only about +20 dB. That matches how much louder a room actually feels, which is why a sound meter uses this scale instead of plain numbers.
What noise level should I set for my class?
Set it with the class rather than for them. Around 45 suits silent reading, 65 suits pair and group work where a working buzz is expected, and 80 suits an activity or craft period. Because every room is different, calibrate once in silence first so the limit means the same thing each day.
How do the quiet class stars work?
Every time the class stays below your limit for a set number of seconds — 20 by default, adjustable from 5 to 60 — they earn one star. Going over the limit stops the stars growing. Many teachers make a class record for the longest quiet streak and try to beat it each week.
Can I use the timer without the microphone?
Yes. The activity timer, the presets from 1 to 15 minutes, the custom minutes box and the end-of-timer chime all work with the microphone switched off. The space bar starts and pauses it, so you can run a timed activity on the smart board without using the meter at all.
Why does the needle move smoothly instead of jumping?
A raw sound level jumps dozens of times a second. The meter uses a smoothing filter — shown = shown + (new − shown) × k — where k is large when the sound rises, so a bang shows instantly, and small when it falls, so the needle glides back. That is how a studio sound meter behaves.