Where's That Noise?

Our ears, like those of all other mammals, have evolved over billions of years to help us detect noises from all directions.

Usually we can tell where they came from quite accurately… but not always. Check how good your sound location skills for yourself with this simple activity….

You will need:

* an empty photographic film canister and lid
* some grains of uncooked rice
* a volunteer


What to do:

1. Place the grains of rice in the film canister and put the lid on firmly.

2. Make sure the room is quiet.

3. Ask your volunteer to sit facing away from you with their eyes closed (or you could blindfold them, so long as the blindfold doesn’t cover their ears).

4. Tell them you’re going to make a sound and you would like them to point to where they think the sound is coming from.

5. Shake the film canister near your volunteer’s left ear. Did they guess right? Now try at other positions around their head. What about over the top – or round the back. Do they always point at the right place?


What's going on?

Your brain can tell whether a sound is coming from the right or the left by calculating what scientists call the ‘time of arrival difference’ – the time difference between the sound hitting one ear and the other. It will similarly be slightly louder in one ear than the other depending on its location. If it reaches both ears at the same time, at the same volume, then it must be coming from somewhere in the middle, whether that’s in front of your head, behind it, or up above it.

That’s not the only information your brain has to go on though. The outsides of your ears have a role to play. These are the ‘pinnae’, and the reason we have these – and people like Andrew Marr and Gary Lineker have particularly prominent ones – is to catch the sound waves as they come in, and to give the brain information about where they came from. The brain can do this because the way the sound bounces back and forth as it enters the ear canal differs depending on where it started out.

If you were a dog or a kangaroo, you’d be able to swivel your ears to home in on noises coming from behind you, whereas we humans don’t have such agile ears and are really best at detecting noises in front of us. However, there’s one thing we can do that dogs and kangroos can’t – and that is cupping our hands round our ears to imitate the ears of a bat. Have a go, it works!