Acoustical Environment Due to Equipment Vibration

Abstract

A rotating or reciprocating equipment acts as a source of vibration and thereby of radiated noise. For noise-control considerations, the sound pressure level (SPL) is needed as a function of the vibration. When the equipment is in an occupied enclosure, the problem can be treated in the framework of the reverberant field, with a constant reverberant SPL that is related directly to source power. Rotation at steady speed produces a pure-tone noise component; a rotating acoustic dipole is created by symmetric rotation of an unbalanced cylindrical unit. This source is omnidirectional in the plane perpendicular to its axis. Treatment of the pure tone as a source of energy in the reverberant field presents some difficulties because of interference patterns, which, however, can be minimized at high frequencies where the room modal density is high. Other factors that facilitate the application of the reverberant field relations include room irregularity and nondirectional character of the source. Relations between source vibration (acceleration and velocity), sound-power output, and reverberant SPL are obtained—sound power being a function of source velocity amplitude, frequency, radius, and length.