Before you clap
- Use a phone if you canA phone's microphone hears the echo as it is. Laptops and earbuds often clean up the sound, which makes a room seem quieter than it is. No headphones or AirPods.
- An empty roomNo learners, with the furniture in place. Doors and windows closed, fans and air conditioners off if you can.
- Stand near the middleAway from the walls and the board.
- Put the phone about a metre awayRest it on a desk near the middle of the room, screen up, or ask a colleague to hold it, about an arm's length from where you clap. On a laptop, stand about two metres back.
- One sharp clap, flat palmsThen stay still and quiet for two seconds while the echo fades. We ask for three claps and use the middle result.
The test takes about a minute. If a clap goes wrong, we say why and you do that one again.
Your browser will ask to use the microphone.
Your phone measures the echo. Nothing is sent to us unless you choose to send your claps at the end.
What it measures, and why it matters.
What it measures
How long a sharp sound takes to die away: the time it takes to become 60 decibels quieter, roughly until it fades into the room's background sound. Acousticians call this the reverberation time, or RT60.
How it works, for the technical
The test listens to your clap and the echo that follows. It splits the sound into four bands of pitch, from 500 Hz to 4 kHz, the range that matters most for speech, and works out how fast each one fades with Schroeder backward integration, the method behind our case study measurements.
Why it matters
South Africa's regulations for public school buildings ask for clear speech between teacher and learners, and for background noise and echo to be kept as low as reasonably practicable, but give no figure. The targets on this page come from the guidelines and standards below.
DBE school infrastructure regulations, 2013The World Health Organization's guidelines say a classroom's reverberation time should be about 0.6 seconds, and lower for children with hearing loss.
WHO Guidelines for Community Noise, 1999The American classroom standard allows no more than 0.6 seconds in a typical classroom, furnished but empty.
ANSI/ASA S12.60The UK's school standard asks for 0.6 seconds or less in a new primary classroom, and 0.8 seconds in a refurbished one.
Building Bulletin 93, 2015Noise, reverberation and the distance from the teacher all affect how well children hear speech in class.
Crandell and Smaldino, 2000Noise makes listening harder for children than for adults, and noise and reverberation in classrooms have been linked to poorer results in verbal tasks.
Klatte, Bergström and Lachmann, 2013
How accurate is it?
A phone gives an estimate, not a certified measurement. On recordings of two rooms at a school in Johannesburg, before and after treatment, the clap test came within 0.04 seconds of the averages our installation partner measured. Your phone, your clap and where you stand can all move the number a little, which is why it asks for three claps.
| Room | Installation partner | Clap test |
|---|---|---|
| Classroom 1, before | 0.92 s | 0.96 s |
| Classroom 1, after | 0.63 s | 0.62 s |
| Meeting room, before | 0.97 s | 0.98 s |
| Meeting room, after | 0.60 s | 0.62 s |
Good questions
While the test runs, your phone keeps the last few seconds of sound in its memory and works out the echo. Nothing is saved or sent unless you choose, at the end, to send us your claps so our team can listen: then we receive only the claps and their echoes (about 9 seconds of sound), with your name and email so we can reply. The microphone switches off when the test ends or you leave the page.
One clap can be thrown by a cough or a closing door. Three claps, with the middle result used, give a steadier number. If one clap is very different from the others, you can redo it.
Voices, footsteps and fans fill the room with sound that hides the echo as it fades. Furniture is fine: the American classroom standard measures classrooms furnished but empty.
It is built for recent versions of Chrome, Safari, Edge and Firefox on phones, tablets and computers. Phone microphones differ, so treat the result as an estimate.
The clap test is a quick first look at one room. On a site visit we measure each room, listen to how it's used and talk to the people who use it, then recommend what fits your budget.
Want a quieter classroom?
Tell us about the rooms you tested and what the numbers were.
What happens next
- We reply within one working day.
- If it helps, we set up a free 20-minute call about your school.
- Anything with a cost, we price in writing before it is booked.
Prefer to pick a time? See the calendar →