How do our ears know sounds are coming from a specific direction?

Question

I have a right and left ear, so I get how I can tell if a sound comes from my right or left. How can my 2 ears tell me if a sound is coming from in front of me, behind me, above me or below me?

In: 2

Answer 1

The other answers are correct but incomplete.

For sounds with wavelengths smaller than your head, the left/right position is located simply by paying attention to the relative loudness. Your head blocks some of the sound so that it will be *slightly* quieter on the side away from the source.

For a bit of context, your ears can hear sounds that move your eardrum less than the width of an atom. Your ears are *very* sensitive to small differences in volume.

Sounds with wavelengths larger than your head can wrap or bend around your head. Lower-pitched sounds do not *attenuate* as fast as high sounds – that is, they don’t lose volume over distance as quickly – and your head can’t block some of the sound because it goes around.

To locate these sounds, your brain looks at the relative *phase* of the sound. That is, sound is made of waves of high pressure and low pressure, and if you graph the waves it creates a sine wave with peaks and troughs. Going around your head changes the distance ever so slightly, which changes where the peaks and troughs line up on either side of your head. Your brain is sensitive to the timing of these differences in phase, and uses that to determine which side it came from.

For forward/backwards, the shape of your ear changes the sound. Partly it’s that sounds in front tend to be louder because your pinna (the fleshy outer part of your ear) funnels sound from the front and partially blocks sound from the back. Your pinna also resonates with different frequencies depending on where they come from, so that they sound *barely* different, which your brain can recognize.

Also, don’t discount your eyes. If there is ambiguity about the source of the sound, your brain will look for potential sources in what you can see. If something in your field of vision looks like it should be the source, your brain will try to use it as the source. Even if you can’t see something, if you know that there is something around you that should be the source, you will use that as the source if there is enough ambiguity.