An Empirical Method To Improve Accuracy Of In-situ Sound Power Measurements Of Industrial Equipment

摘要

Standards prescribe accurate methods to measure the sound power level (Lw) of sources orequipment in a free field. When measurements must be made indoors, these standards are notapplicable, and if used anyway, give unrealistically low values for Lw due to room effects. ISO3744, and other standards, describe a method to determine the in-situ Lw of the equipment bysubtracting an 'environmental correction' factor for room effects from the sound pressure level(Lp) measured on a conformal surface. This measurement procedure is also used in reverse, i.e.,to predict the Lp on the equipment's conformal surface by adjusting the equipment’s Lw usingthis calculated environmental correction factor. These corrections are based on the Sabinereverberation theory. Observations and data presented here indicate that the environmentalcorrections determined using ISO 3744 are unrealistically high. Because a reverberant fieldrarely exists in an indoor industrial space, this is not surprising. An empirical correction to theenvironmental correction from 3744 is suggested. Measured sound pressure levels and theenvironmental correction factors from 3744 and the one suggested here for gas-turbine generatorpackages located in seven different turbine halls are compared. The accuracy of theenvironmental corrections is discussed. This work is intended to improve the accuracy of theapproximate method described in 3744.