Sound transmission at low frequencies through the walls of distorted circular ducts |
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Authors: | A Cummings I-J Chang RJ Astley |
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Institution: | Department of Mechanical and Aerospace Engineering, University of Missouri-Rolla, Rolla, Missouri 65401, U.S.A.;Department of Mechanical Engineering, University of Canterbury, Christchurch, New Zealand |
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Abstract: | A theoretical treatment of sound transmission through the walls of distorted circular ducts is given, for plane mode transmission within the duct. The transmission mechanism is essentially that of “mode coupling”, whereby higher structural modes in the duct walls are excited, because of the wall distortion, by the internal sound field. The theory is in two parts: an approximate analytical model for the structural response of the walls to the internal sound field, and a structural radiation model. Computed results, based on the theory, are compared to measurements on “long-seam” air conditioning ducts. Where the duct geometry can be reliably specified, reasonably good agreement is obtained between theoretical and experimental data. It is concluded that mode coupling effects serve to account for the discrepancies between ideal and observed behaviour in sound transmission through duct walls. |
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