Hearing Direction and Distance
by Ron Kurtus (revised 22 August 2002)
A reason humans and animals have two ears is to allow them to determine the direction of the sound they hear. Processing the time lag and difference in volume provides the perception of direction.
Volume and sound quality also help to determine the distance a sound is coming from. Some animals use a sonar effect to determine the distance of their prey.
Awareness and practice can enhance your ability to sense direction and distance with sound.
Questions you may have include:
- How is direction determined?
- How is distance determined?
- How can I enhance these abilities?
This lesson will answer those questions.
You can readily detect whether a sound is coming from the left or right, you can tell to a degree if the sound is coming from above, and some people can tell if the sound is in front or behind them.
Left or right
Having an ear on each side of your head allows you to distinguish whether a sound is coming from the left or the right. The direction is determined by perception of the difference of arrival time or difference in phase of sounds at each ear. The wavelength of the sound and its tone are also important factors for the brain to determine the direction of the sound source.
Sound coming from one direction will reach the ear furthest away approximately 1/500 second later than the closer ear. The brain can discern this time lag.
A difference in volume between the two ears depends on the frequency of the sounds. You can tell the direction of high frequency sounds better than low frequency sounds.
High frequency sounds are blocked by the head and will not easily reach the far ear. This results in a slightly higher volume in the near ear. But if the frequency is low, the wavelength is long enough that the head does not block the sound as readily.
Indications are that it is more difficult to tell direction with low frequencies. This is probably due to the fact that the ear is less sensitive to volume variations with low frequencies and the fact that at low frequencies the wavelength is greater than the distance between the ears. This could also muddle the sound heard.
Another factor may be that the ear furthest from the sound gets some sound reflected off objects.
From above, below or in front
You can determine when a sound comes from above, below or in front of the face. This is especially true with high frequency sounds. Height information is provided by a small amount of reflection off the back edge of the ear lobe. This reflection is out of phase for one specific sound frequency, and the elongated shape of the lobe causes the frequency to vary with angle of the source of sound. You can then tell the direction. Height detection does not work well for sounds originating to the side or back, or those lacking high frequency content.
You can detect distance from the sounds you hear, because the loudness is less and the sound is often muffled. It takes experience to be able to judge how far away sounds are coming from.
Some animals such as bats and dolphins use sound to measure distance, as well as direction.
Similar to sonar
Bats and dolphins create very short chirps and are able to estimate the distance of an object, as well as to get other information about the object from the reflected sound they hear. This is very similar to sonar which fishermen use to find fish or that is used by submarines.
Bats get much information from sound
The bat can tell the direction of the object by comparing the sound detected from its two ears. It can tell the distance from the time it takes for the reflected sound to be heard, after being emitted. The bat can also tell if the object is hard or softlike a tasty mothby the frequencies that are received, as compared to what was emitted.
Different objects reflect sound frequencies selectively, just like different objects reflect different colors or frequencies of light.
Dolphins and porpoises use sonar the same way as batsexcept they use it underwater. It is a shame that humans dont have this capability, because it might be real handy to have.
By being more aware of where sounds are coming from, you can enhance your ability to tell direction. Likewise, practicing guessing how far away a sound is and then verifying your guess, you can improve your ability to approximate distance through listening to the sounds.
You detect direction by comparing the sound coming into each ear. By listening carefully, you can sometimes determine the distance a sound comes from. Bats and dolphins can find objects through making noises and listening to the reflection.
Be careful, thoughtful and listen
Resources and references
The Direction of Sound - Explanation from Hear-It, a site dedicated to preventing hearing loss
Hearing and Perception - From USCS Electronic Music Studios
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Hearing Direction and Distance with Sound