| Abstrakt: |
The geometric nearfield of a finite acoustic radiator is the area around the radiator where the sound pressure level does not follow spherical or cylindrical spreading. The geometric nearfield has been studied extensively for circular and rectangular piston radiators. The Rayleigh distance D = ka2/2, where k = 2πf/c, f is the frequency, c is the sound speed, and a is half the largest dimension, has been used to approximate the size of the geometric nearfield of plane radiators. We found that, for variously shaped radiators, the Rayleigh distance is useful in approximating the geometric nearfield size. As with plane radiators, we found large SPL changes with radial distance in the geometric nearfield. One implication is that in noisy environments, where the SPL aroung a large machine may, necessarily, be measured in the nearfield, the sound power contribution to the sound field can be grossly underestimated. Knowledge of the nearfield size may be useful in industrial situations for determining the validity of sound power estimates. [Work supported by the U.S. Coast Guard.] [ABSTRACT FROM AUTHOR] |
