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#redirect[[auditory perception]]
==Perception of sound==
[[Image:Processing-of-sound.svg|thumb|right|300px|A schematic representation of hearing. (Blue: sound waves. Red: [[eardrum]]. Yellow: [[cochlea]]. Green: [[stereocilia|auditory receptor cells]]. Purple: [[frequency spectrum]] of hearing response. Orange: [[nerve impulse]])]]
Sound is perceived through the [[sense]] of [[hearing (sense)|hearing]]. Humans and many animals use their [[ear]]s to hear sound, but loud sounds and low-frequency sounds can be perceived by other parts of the body through the [[tactition|sense of touch]] as vibrations. Sounds are used in several ways, notably for communication through [[speech]] and [[music]]. They can also be used to acquire information about properties of the surrounding environment such as spatial characteristics and presence of other animals or objects. For example, [[bat]]s use [[animal echolocation|echolocation]], ships and submarines use [[sonar]] and humans can determine spatial information by the way in which they perceive sounds.
Humans can generally hear sounds with frequencies between 20 [[Hertz|Hz]] and 20 [[kHz]] (the audio range) although this range varies significantly with age, occupational hearing damage, and gender; the majority of people can no longer hear 20,000 Hz by the time they are teenagers, and progressively lose the ability to hear higher frequencies as they get older. Most human speech communication takes place between 200 and 8,000 Hz and the human ear is most sensitive to frequencies around 1000-3,500 Hz. Sound above the hearing range is known as [[ultrasound]], and that below the hearing range as [[infrasound]].
The amplitude of a sound wave is specified in terms of its [[pressure]]. The human ear can detect sounds with a very wide range of amplitudes and so a [[logarithm]]ic [[decibel]] amplitude scale is used. The quietest sounds that humans can hear have an amplitude of approximately 20 µPa ([[micropascal]]s) or a sound pressure level (SPL) of 0 dB re 20 µPa (often incorrectly abbreviated as 0 dB SPL). Prolonged exposure to a sound pressure level exceeding 85 dB can permanently damage the ear, resulting in [[tinnitus]] and [[hearing impairment]]. Sound levels in excess of 130 dB are more than the human ear can safely withstand and can result in serious pain and permanent damage.
At very high amplitudes, sound waves exhibit [[nonlinear]] effects, including [[shock wave|shock]].
The way in which sound travels or propagates is difficult to imagine, as sound appears to humans as invisible. Imagine a long tube exposed to air whereby sound travels longitudinally through it. The air acts like a Slinky spring in this tube. As sound is generated at one end, the wave will begin to travel down through the air in the tube, (watching an earth worm move by pulsating its long body on the top of the ground helps to visualize this same phenomenon). The length of pulse cycle will determine the sound wave length. Low bass sounds will have large pulse lengths, in the order of 10-50 feet long, where high treble sounds will have pulse lengths as small as 1/2 an inch.
[[Category:Auditory perception]]

Latest revision as of 16:03, May 20, 2013

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