POWER OUTPUT OF NOISE SOURCES OPERATING NEAR ELASTIC SCATTERERS OF FINITE DIMENSIONS

The problem of variation of the sound power output of noise sources due to reflecting boundaries and elastic scatterers is considered experimentally and numerically. In the laboratory experiment with a source of loudspeakers operating near a resonant scatterer, the increase in the radiated power obtained is about one hundred. An important role of the source near field in the power enhancement is shown. In computer simulation, a two-dimensional radiation problem for a circle vibrating near a finite elastic beam is studied. Most attention is paid to revealing physical mechanisms of the power output variations. It is shown that, for the source and elastic scatterer of finite dimensions, the radiated power can reach orders of magnitude of the free-field value. Especially, high-power amplification can be obtained at low frequencies for the sources that are poor radiators in free space, i.e., behave as multipoles of high order: presence of a scatterer or reflector makes such a source to be of monopole or dipole type. The results presented can be useful in better understanding sound generation mechanisms in complicated industrial noise sources.