Predicted Noise Reduction Research Articles

Predicting Noise Reduction from Absorptive Treatments in Industrial Spaces: Alternatives to the “Sabine” Method

Absorptive treatments for noise control have an important place in an overall engineering control strategy. However, predictions based on the easiest to use method, the Sabine equation, often understate the amount of existing absorption. This is because the method does not adequately account for the absorptive effect of room contents, specifically machines, in industrial settings. This underestimation of existing absorption can result in false optimism toward the potential benefits of architectural absorption. This paper reviews three alternate methods which may be better suited to predict the amount of absorption present in an industrial space. The alternate methods are the reverberation time method, the sound power method and the loss due to distance (LDD) method. The last method, put forth by the authors, is often well suited for use by those in the general practice of industrial hygiene because it does not require a great deal of user familiarity or specialized measuring equipment.

Predicting Noise Reduction from Absorptive Treatments in Industrial Spaces: Alternatives to the “Sabine” Method

Absorptive treatments for noise control have an important place in an overall engineering control strategy. However, predictions based on the easiest to use method, the Sabine equation, often understate the amount of existing absorption. This is because the method does not adequately account for the absorptive effect of room contents, specifically machines, in industrial settings. This underestimation of existing absorption can result in false optimism toward the potential benefits of architectural absorption. This paper reviews three alternate methods which may be better suited to predict the amount of absorption present in an industrial space. The alternate methods are the reverberation time method, the sound power method and the loss due to distance (LDD) method. The last method, put forth by the authors, is often well suited for use by those in the general practice of industrial hygiene because it does not require a great deal of user familiarity or specialized measuring equipment.

Computation of acoustical impedance of Helmholtz resonator in aircraft engine environments

The nonlinear impedance of a Helmholtz resonator is an important parameter when predicting noise reduction in the environment of high sound-pressure level and grazing flow in fan ducts of aircraft engines. In recent experiments [G. D. Garrison, A. C. Schnell, C. D. Baldwin, and P. R. Russell, “Suppression of Combustion Oscillations with Mechanical Damping Devices,” Pratt & Whitney Aircraft Rep. PWA-FR-3299 (1969)], the impedance was found to be affected by the exciting sound spectrum distribution. An integration method was presented by Rice [E. J. Rice, “A Model for the Acoustic Impedance of a Perforated Plate Liner with Multiple Frequency Excitation,” NASA TMX-67950 (1971)[ to compute the impedance under such an environment. However, the integration requires substantial computation time. Since the impedance is determined by solving the multiple-frequency velocity components of the nonlinear resonator, a direct method to compute the velocity components of the resonator is desirable. A simple iteration method to determine the impedance is presented by the author. In this method, the lengthy integration is not used; instead, an algebraic equation converted from the nonlinear differential equation has to be solved. The physical modeling includes both the effects of multiple-frequency excitation and grazing flow, using similar relationships to those presented in Rice's paper. The impedance computation of this approach requires much less computer time and the results are in good agreement with those from the integration method.