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Journal of the Acoustical Society of America

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Oct 2003

Volume 114, Issue 4, pp. 1695-2468

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An angle-by-angle approach to predicting broadband high-frequency sound fields in rectangular enclosures with experimental comparison

Linda P. Franzoni and Christopher M. Elliott

J. Acoust. Soc. Am. Volume 114, Issue 4, pp. 1968-1979 (2003); (12 pages)

Online Publication Date: 08 Oct 2003

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Experiments were performed on an elongated rectangular acoustic enclosure with different levels of absorptive material placed on side walls and an end wall. The acoustic source was a broadband high-frequency sound from a loudspeaker flush-mounted to an end wall of the enclosure. Measurements of sound-pressure levels were averaged in cross sections of the enclosure and then compared to theoretical results. Discrepancies between the experimental results and theoretical predictions that treated all incidence angles as equally probable led to the development of an angle-by-angle approach. The new approach agrees well with the experimentally obtained values. In addition, treating the absorptive material as bulk reacting rather than point reacting was found to significantly change the theoretical value for the absorption coefficient and to improve agreement with experiment. The new theory refines an earlier theory based on power conservation and locally diffuse assumptions. Furthermore, the new theory includes both the angle of incidence effects on the resistive and reactive properties of the absorptive material, and the effects of angle filtering, i.e., that reflecting waves associated with shallow angles become relatively stronger than those associated with steep angles as a function of distance from the source. © 2003 Acoustical Society of America.
Show PACS
43.55.Br Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.55.Ka Computer simulation of acoustics in enclosures, modeling

Behavioral criterion quantifying the edge-constrained effects on foams in the standing wave tube

Dominic Pilon, Raymond Panneton, and Franck Sgard

J. Acoust. Soc. Am. Volume 114, Issue 4, pp. 1980-1987 (2003); (8 pages) | Cited 10 times

Online Publication Date: 08 Oct 2003

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The influence of mounting conditions on the measurement of the sound absorption coefficient is investigated. More specifically, the effects of a circumferential edge constraint applied on elastic foams in a standing wave tube are studied. The objective is to identify the foams for which it is possible to measure the theoretical absorption coefficient using the tube. This identification relies on the evaluation of a new parameter, the Frame Acoustical Excitability (FAE), based on the foams’ physical properties. In order to quantify the difference between the measured and theoretical absorptions, a linear correlation coefficient is evaluated for a wide range of foams with various sample sizes. The calculated correlation coefficients are then sorted in terms of the FAE. It is shown that as the value of FAE increases, the difference between the measured and theoretical absorption coefficients becomes more significant. A critical value of FAE, below which the theoretical absorption can be efficiently measured using the tube, is established. Through the use of this elasto-acoustic criterion, an experimenter can make an educated guess as to which absorption is measured with the tube: the theoretical absorption or one that is affected by either the edge constraint or the sample’s dimensions. © 2003 Acoustical Society of America.
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43.55.Ev Sound absorption properties of materials: theory and measurement of sound absorption coefficients; acoustic impedance and admittance
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.20.Jr Velocity and attenuation of elastic and poroelastic waves
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