![]() R x 1, x 2 ( τ ) = ∑ n = − ∞ ∞ x 1 ( n ) x 2 ( n + τ ) is the angle between the baseline of the sensors (ears) and the incident sound, in degrees. The cross-correlation function between two microphones is defined as With a sensor array (for instance a microphone array) consisting of at least two probes it is possible to obtain the source direction using the cross-correlation function between each probes' signal. This method can be used with pressure microphones as well as with particle velocity probes. The traditional method to obtain the source direction is using the time difference of arrival (TDOA) method. There is a wide variety of measuring systems and solutions that employ this type of probe to localize acoustic sources in a wide range of applications, including identifying and resolving noise issues, evaluating the acoustic performance of different products, and providing objective data to support subjective sound assessments. The particle velocity is a vector and thus also contains directional information. The simplest but still a relatively new method is to measure the acoustic particle velocity using a particle velocity probe. ![]() Particle velocity or intensity vector ģD sound localization of a large compressor Some have termed acoustic source localization an " inverse problem" in that the measured sound field is translated to the position of the sound source.ĭifferent methods for obtaining either source direction or source location are possible. Many of these methods use the time difference of arrival (TDOA) technique. Other more complicated methods using multiple sensors are also possible. By measuring particle velocity one obtains a source direction directly. ![]() The particle velocity is another quantity related to acoustic waves however, unlike sound pressure, particle velocity is a vector. Besides considering microphones that measure sound pressure, it is also possible to use a particle velocity probe to measure the acoustic particle velocity directly. This however is still no solution for the sound localization problem as one tries to determine either an exact direction, or a point of origin. Microphones with other polar patterns exist that are more sensitive in a certain direction. Many microphones have an omnidirectional polar pattern which means their sensitivity is independent of the direction of the incident sound. Microphones have a polar pattern describing their sensitivity as a function of the direction of the incident sound. Traditionally sound pressure is measured using microphones. By measuring these properties it is (indirectly) possible to obtain a source direction. The sound field can be described using physical quantities like sound pressure and particle velocity. Overview Īcoustic source localization is the task of locating a sound source given measurements of the sound field. The civilian uses include locating wildlife and locating the shooting position of a firearm. Acoustic techniques had the advantage that they could 'see' around corners and over hills, due to sound diffraction. It was rendered obsolete before and during World War II by the introduction of radar, which was far more effective (but interceptable). Typically, more than one device is used, and the location is then triangulated between the several devices.Īs 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. 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.īoth of these techniques, when used in water, are known as sonar passive sonar and active sonar are both widely used.Īcoustic mirrors and dishes, when using microphones, are a means of passive acoustic localization, but when using speakers are a means of active localization.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.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). Swedish soldiers operating an acoustic locator in 1940Īcoustic location is the use of sound to determine the distance and direction of its source or reflector.
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