A person seen from behind on a park bench in evening light, head turned slightly to one side as if listening
AI-generated image, not a photograph of a real person or place.
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HOW HEARING FINDS DIRECTION

Two ears,
one direction.

0.68 MS the widest gap

  • First ear wins on timing
  • Head casts a sound shadow
  • Ear folds hint at height
  • Three cues, one map

Close your eyes and you can still point at a sound.

Your brain compares what reaches each ear: which one hears it first, which one hears it louder. The folds of the outer ear add clues about height. University teaching texts call these the binaural and monaural cues.

Updated

Place a sound

THE SHORT ANSWER

The brain compares
your two ears.

Timing works best for low sounds,
loudness differences for high ones.

TIMING

Which ear hears it first

A sound from the left reaches the left ear first. The biggest gap, for a sound directly to one side, is only a little over half a millisecond, and the brain reads it.

See the numbers

LOUDNESS

The head casts a shadow

High sounds, with short wavelengths, are blocked by the head, so the far ear hears them quieter. Below about 1,000 Hz the sound sweeps round the head and this cue fades.

Place a sound

THE EAR FLAP

Folds that sense height

The shape of the outer ear filters sound differently depending on its angle. That is how we tell above from below, and everyone's ears do it slightly differently.

Try it yourself

PLACE A SOUND

Where is it
coming from?

Pick a sound to see which cue does the work. The bar shows how easily the cues let us place it.

Sound check

Choose a sound
A voice to your leftTiming and loudness

It reaches your left ear first, so the timing cue works, and the head shadows its higher-pitched parts from your right ear, so the loudness cue helps too.

A high chirp to your rightLoudness

High sounds are shadowed by the head, so the left ear hears them quieter. Level differences can be as big as 20 dB, depending on frequency and direction.

A sound above youEar folds

Timing and loudness say little about height. The outer ear's folds filter pitches differently by angle, giving the brain an elevation cue.

Straight ahead or behindTurn your head

A sound in front and one behind can reach both ears with the same timing and level, the cone of confusion. Moving your head helps sort it out.

A deep hum or bassHard to place

Below about 200 Hz the cues become ineffective, which is why a subwoofer can sit out of the way in a surround sound set-up.

Sources: University of Minnesota, Introduction to Sensation and Perception (interaural time and level differences, head-related transfer function); Indiana University, An Acoustics Primer: Localization.

Based on University of Minnesota and Indiana University teaching texts on sound localisation. General information about hearing, not a hearing test.

TWO NUMBERS WORTH KNOWING

Tiny gaps,
read precisely.

The largest timing gap your head allows,
and the smallest one you can notice.

≈ 0.68 ms

Arrival difference, sound directly to one side

With about 23 cm of extra path to the far ear and sound at 340 m/s, the gap is at most about 0.676 milliseconds, a little over half a millisecond.

LARGEST GAP · UMN

10 µs

Timing difference people can detect

With some practice, people can learn to detect a timing difference of 10 to 20 millionths of a second between the ears, a 1956 finding cited by the University of Minnesota text.

SMALLEST GAP · UMN

The two timing signals first meet in the brainstem, in the superior olivary complex. Timing differences stop being useful at about 1,500 Hz, where level differences take over: together this is known as the duplex theory.

FOUR THINGS TO NOTICE

Your hearing,
at work.

A small songbird singing on a bare branch, beak open, against a soft blurred woodland background
AI-generated image, not a photograph of a real person or place.

You use these cues all day without thinking. A few everyday moments show them in action.

  1. Turn your head

    When a sound is hard to place, a small head turn changes the timing and loudness at each ear and breaks the front-back confusion.

  2. Fold your ear flap

    The Indiana primer suggests folding your ear flap over and noticing how much harder it becomes to place sounds.

  3. Notice the bass

    Deep bass seems to come from everywhere. Below about 200 Hz the cues stop working, so a subwoofer's position matters little.

  4. Sit in the middle

    If the same sound comes from two speakers, you hear it at the nearer one unless the arrivals are within about 35 to 50 ms.

HEARING WITH ONE EAR

When one side
goes quiet.

A close-up of an adult's outer ear in soft daylight, showing the curves and folds of the ear flap
AI-generated image, not a photograph of a real person or place.

RNID says that with single-sided deafness it can be harder to tell where sounds come from, because the brain uses timing and loudness information from both ears. Crossing the road and following speech in noisy places can become harder.

An audiologist can work through options such as CROS hearing aids or remote microphones, and many people develop their own tactics, like sitting with their hearing ear towards the person speaking.

Questions

Questions people ask

How do we know which direction a sound comes from?

The brain compares the two ears: the difference in arrival time and the difference in loudness. The shape of the outer ear adds cues about height.

How big is the time difference between the ears?

At most a little over half a millisecond, about 0.68 ms by the University of Minnesota's worked example, for a sound directly to one side.

Why is deep bass hard to locate?

Low sounds have long wavelengths that pass around the head, so the loudness cue disappears. The Indiana University primer says the cues become ineffective below about 200 Hz.

What is the cone of confusion?

A set of positions where timing and loudness are the same at both ears, such as directly in front and directly behind. Head movements and the outer ear help resolve it.

Is it harder to locate sounds with hearing in only one ear?

Yes. RNID says single-sided deafness can make it harder to tell where sounds come from, because direction relies on information from both ears.

Sources

Where the facts come from

  1. University of Minnesota, Introduction to Sensation and Perception: Interaural time difference
  2. University of Minnesota, Introduction to Sensation and Perception: Interaural level difference
  3. University of Minnesota, Introduction to Sensation and Perception: Head-related transfer function
  4. Indiana University Jacobs School of Music, An Acoustics Primer: Localization
  5. RNID: Single-sided deafness

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