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 or equipment in a free field. When measurements must be made indoors, these standards are not applicable, and if used anyway, give unrealistically low values for Lw due to room effects. ISO 3744, and other standards, describe a method to determine the in-situ Lw of the equipment by subtracting 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 using this calculated environmental correction factor. These corrections are based on the Sabine reverberation theory. Observations and data presented here indicate that the environmental corrections determined using ISO 3744 are unrealistically high. Because a reverberant field rarely exists in an indoor industrial space, this is not surprising. An empirical correction to the environmental correction from 3744 is suggested. Measured sound pressure levels and the environmental correction factors from 3744 and the one suggested here for gas-turbine generator packages located in seven different turbine halls are compared. The accuracy of the environmental corrections is discussed. This work is intended to improve the accuracy of the approximate method described in 3744.