A theoretical analysis of the field of a random noise source above an infinite plane

Author / Creator

Franken, Peter A., author

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Online

Summary

A theoretical study of the sound field from a random noise source above ground as measured by a receiver with finite band width is presented herein. This study represents one phase of a general pro...

A theoretical study of the sound field from a random noise source above ground as measured by a receiver with finite band width is presented herein. This study represents one phase of a general program of research in atmospheric acoustics. For simplicity, only the far field has been considered. The special case of a perfectly reflecting plane is discussed first, and nondimensional curves are given of sound pressure level versus distance for two different receiver band widths. The analysis is then extended to the case of a plane of arbitrary impedance, and curves of pressure level versus distance are given for typical field operating conditions. The sound field consists of two major regions. In the first sound pressure level fluctuates about an average curve sloping approximately 6 decibels per doubling of the distance. Beyond a certain distance from the source the level decreases monotonically 12 decibels per doubling of distance. The fluctuations depend on the band width of the receiver and on the ground impedance. With, for example, an octive band of 1,000 to 2,000 cycles and the receiver 10 feet above a ground of normal impedance, the maximum pressure-level fluctuation is about 2 decibels and occurs around 300 feet from the source, and the transition between the 6-decibel-slope region and the 12-decibel-slope region occurs around 700 feet from the source.

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