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Sound Wavefronts
Sound WavefrontsPlane wavesPlane waves are the form of wave propagation in one dimension. The wavefronts of plane waves are planes perpendicular to the propagation direction. Plane waves are generated by a plane source. The surface area of wavefront does not vary with the distance away from the sound source. Since there is no geometrical divergence along the propagation path, both the sound intensity and sound pressure remain unchanged. and where
A_{x} is the surface area at distance x and is a constant Therefore, both the sound intensity level and the sound pressure level remains constant with distance away from the source. Plane waves propagation can be found in musical pipe instrument, e.g. flutes, clarinets, or noise in ducts. Cylindrical WavesCylindrical waves are the form of wave propagation in two dimension. The wavefronts of cylindrical waves are coaxial cylinders with axis of symmetry normal to the propagation direction. Cylindrical waves are generated by a line source. The surface area of wavefront increases with the distance away from the sound source. Since there is geometrical divergence along the propagaton path, both the sound intensity and sound pressure decreases with distance away from the source. and where
2πrh is the surface area at distance r Therefore, both the sound intensity level in term of I and sound pressure level in term of p^{2} decrease by 3dB as the distance of receiver away from the source is increased by double.
and
where
L_{Ir} is the sound intensity level at distance r Cylindrical waves propagation can be found in sound radiation from a circular pipes or duct, or noise field in an open space radiated by a lane of closely spaced vehicles. Spherical WavesSpherical waves are the form of wave propagation in three dimension. The wavefronts of spherical waves are concentric spheres with center at the center of propagation in all directions. Spherical waves are generated by a point source. The surface area of wavefront increases with the distance away from the sound source. Since there is geometrical divergence along the propagation path, both the sound intensity and sound pressure level decreases with distance away from the source. and where
4πr^{2} is the surface area at distance r Therefore, both the sound intensity level in term of I and sound pressure level in term of p^{2} decrease by 6dB as the distance of receiver away from the source is increased by double.
and
where
L_{Ir} is the sound intensity level at distance r Spherical waves propagation in practical can be found by approximating a sound source with source dimension and radiated wavelength much smaller than the distance away from the receiver. ©sideway ID: 100900010 Last Updated: 9/8/2010 Revision: 0 Ref: References
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