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Concept
Acoustic location
Summary
Acoustic location is the use of sound to determine the distance and direction of its source or reflector. Location can be done actively or passively, and can take place in gases (such as the atmosphere), liquids (such as water), and in solids (such as in the earth).
Active acoustic location involves the creation of sound in order to produce an echo, which is then analyzed to determine the location of the object in question.
Passive acoustic location involves the detection of sound or vibration created by the object being detected, which is then analyzed to determine the location of the object in question.
Both of these techniques, when used in water, are known as sonar; passive sonar and active sonar are both widely used.
Acoustic mirrors and dishes, when using microphones, are a means of passive acoustic localization, but when using speakers are a means of active localization. Typically, more than one device is used, and the location is then triangulated between the several devices.
As a military air defense tool, passive acoustic location was used from mid-World War I to the early years of World War II to detect enemy aircraft by picking up the noise of their engines. It was rendered obsolete before and during World War II by the introduction of radar, which was far more effective (but interceptable). Acoustic techniques had the advantage that they could 'see' around corners and over hills, due to sound diffraction.
The civilian uses include locating wildlife and locating the shooting position of a firearm.
Acoustic source localization is the task of locating a sound source given measurements of the sound field. The sound field can be described using physical quantities like sound pressure and particle velocity. By measuring these properties it is (indirectly) possible to obtain a source direction.
Traditionally sound pressure is measured using microphones. Microphones have a polar pattern describing their sensitivity as a function of the direction of the incident sound.
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Sound
In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the reception of such waves and their perception by the brain. Only acoustic waves that have frequencies lying between about 20 Hz and 20 kHz, the audio frequency range, elicit an auditory percept in humans. In air at atmospheric pressure, these represent sound waves with wavelengths of to . Sound waves above 20 kHz are known as ultrasound and are not audible to humans.
Acoustics
Acoustics is a branch of physics that deals with the study of mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical engineer. The application of acoustics is present in almost all aspects of modern society with the most obvious being the audio and noise control industries.