Acoustics

Acoustics is a branch of physics and is the study of sound, mechanical waves in gases, liquids, and solids. A scientist who works in the field of acoustics is an acoustician. The application of acoustics in technology is called acoustical engineering. There is often much overlap and interaction between the interests of acousticians and acoustical engineers.

Helmholtz resonator

A Helmholtz resonator is a container with an open hole or neck.

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It is sometimes used as a passive noise control device.

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It behaves essentially as a mass-spring-damper system, and its resonant frequency can be calculated as follows:

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• f = resonant frequency
• s = speed of sound in air
• r = radius of neck
• a = area of neck
• l = length of neck
• L′ = effective length of neck

:L′ = l + 1.7r (outer end flanged)

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:L′ = l + 1.4r (outer end unflanged)

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• v = volume

:f = (s/2 pi)(sqrt{a/(L' cdot v)})

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(A container with a hole, rather than a neck, behaves as being flanged, with a neck length of 0.)

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The Helmholtz resonator is an example of the lumped component model of acoustic systems which is useful when the wavelength of interest is significantly larger than the physical dimensions of the system.

Related Topics:
Lumped component - Wavelength

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Familiar examples of Helmholtz resonators include blowing across the top of a bottle, whistling, and the ocarina.

Related Topics:
Whistling - Ocarina

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