- This article is about compression waves. You may be looking for the geographical term, sound, a large ocean
inlet, or a narrow ocean channel between two bodies of land, the geographic location called the Sound, or a urethral sound, which is a medical
instrument used for dilating the urethra.
Sound is defined as a mechanical compression and rarefaction or longitudinal displacement waves that propagate through a medium (solid, liquid or gas). Most sounds are combinations of signals, but a
theoretical pure sound can be described as having a given speed of oscillation or frequency measured in hertz (Hz) and amplitude or sound pressure with measures such as decibel level. The
range of sound audible to the human ear falls roughly between 20 Hz and 20 kHz at typical
amplitudes with wide variations in response curves. Above and below this range are ultrasound and infrasound, respectively. The propagation speed
of sound in air depends on temperature. Sound travels at the speed of 332 m/s at 273 K in air.
Humans and several animals perceive sounds with the sense of hearing with their ears, but low
frequency sounds can also be felt by other parts of the body. Sounds are used in several ways, most notably for communication
through speech or, for example, music. Sound
perception can also be used for acquiring information about the surrounding environment in properties such as spatial
characterics and presence of other animals or objects. For example, bats use one sort of
echo-location for flying. Ships and submarines use sonar. Humans acquire and use spatial
information perceived in sounds.
The perceived "amount" of sound (pressure wave) is defined as loudness and measured in
sones. The human ear is most sensitive to sound in the middle of the audible frequency
range. The amplitude of a sound wave (sound pressure) is measured in pascals, and the strength
(amplitude) of a sound is measured in decibels relative to a stated reference sound
pressure. The minimum audible sound pressure level
(SPL) across all audible frequencies is defined as the Absolute Threshold of Hearing (ATH).
Scientific studies of sound are generally classified under the field of acoustics. Perception of sounds, i.e. hearing, are studied in psychoacoustics, which also implies the close relation between perception and psychology. Modelling the sounds that can be heard (and leaving out the inaudible sounds) is discussed in
the psychoacoustic model. Further, the class of techniques
and methods involving sound processing are usually called audio signal processing methods.
The hearing range varies between different animals: Bats have an unsually large one, while
frogs have a narrow one. Typical frequencies (in hertz) are listed below:
See Also
Sound Measurement
External Links
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