# How an Acoustic Imaging Camera Works

How a handheld acoustic imaging camera turns tiny arrival\-time differences across 64 microphones into a colour sound map on its live picture\.

By greenlig

Topic: Physics & Chemistry

[Open the interactive Jig](https://ask.jig.com/j/JNtZACrw1Qfe)

## Transcript

### 1. A camera that can see sound

This handheld acoustic camera finds sounds you cannot see, like the hiss of a leaking air pipe\. Its screen shows an ordinary picture with a glowing colour patch right where the sound comes from\. Let's find out how it knows where to paint it\.

Drag empty space to turn the scene and look around\.

### 2. Inside: 64 tiny ears

Let's take the camera apart\. The front plate has 64 tiny holes, and right behind each one a microphone smaller than a grain of rice sits on a circuit board\. A small ordinary camera peeks through the big middle hole\. Further in, the main circuit board does the maths, a battery in the grip powers it, and the screen shows the result\.

The holes are scattered in a spiral on purpose: an irregular pattern stops false ghost spots\. The inside is a typical layout, simplified\.

### 3. A ripple of sound

The leak sends sound out in every direction, like ripples spreading on a pond\. Here the waves are slowed down about a million times\. Watch each microphone light up the moment the wave reaches it, while the card records six of them\.

Sound travels about 343 metres per second, so a real wave crosses the plate in less than half a thousandth of a second\.

### 4. Tiny differences in time

Microphones nearer the leak hear the hiss first and farther ones a moment later\. The plate shows that order: bright blue first, deep violet last\. On the card, each recording starts at its own blue tick\.

Two extra centimetres of travel delays the sound by about 58 millionths of a second\.

### 5. Beamforming: line them up

To test one direction, the camera works out the delay each microphone would hear from there and slides every recording back by that much\. If the guess is right, the waves line up and add into one strong signal\. A wrong guess leaves them out of step, so they cancel\.

This trick is called delay\-and\-sum beamforming\.

### 6. Checking every direction

The camera repeats that test for a whole grid of directions\. Each square keeps how loud the lined\-up sound was there\. The loudest squares point straight at the leak\.

Real imagers redo the whole map about 25 times every second\.

### 7. Painting sound on the picture

The microphones and the camera look out across the same view, so each square matches a spot in the picture\. Loudness becomes colour, from cyan for quiet to red for loudest, laid see\-through over the live image\. These colours show sound, not heat\.

Many leaks hiss in ultrasound, pitches above what people can hear\. This imager listens from 2 to 100 kHz\.

### 8. Find the leak yourself

Drag the brass joint along the pipe and watch the colour spot follow it on the screen\. Then try a lower pitch: longer waves make a wider, blurrier spot\. High\-pitched hiss gives the sharpest picture\.

Bigger microphone arrays also make sharper spots\.