Determination of sound power of coupled machines

Abstract

Several procedures are available for the determination of the sound power level of machines in normal environments. Most of these give adequate results for single medium-sized equipment, but difficulties arise in extending the concepts to large coupled machines. [“Evaluation of Proposed ASME PTC 36 Code for Sound Power Level Determination of Large Steam Turbine Generators,” S.E. Grabkowski, J. MacDonald, and T. Van Schaick (General Electric Company), to be presented at Fall 1975 ASME meeting.] Much of the problem is because the direct acoustic field of a component machine may not extend to as much as one foot from its surface due to reverberation from other components. A procedure is suggested in which all acoustic measurements are confined to surfaces near each component machine. Correction is made for the reverberant acoustic field of the entire environment. The correction procedure utilizes reverberation time determinations from impulsive noise tests; and applies a Monte Carlo approach to the problem of correcting for nearfield effects in the evaluation of sound power. An iterative computation is employed. Comparisons with free-field sound power determinations are shown.