L. F. Peretti Experimental Verification of the Asymptotic Modal Analysis Method as Applied to a Rectangular Acoustic Cavity Excited by Structural Vibration

An experiment was performed on a rigid wall rectangular acoustic cavity driven by a flexible plate mounted in a quarter of one end wall and excited by white noise. The experiment was designed so that the assumptions of Asymptotic Modal Introduction Enclosed spaces such as the interiors of airplanes or automobiles, in which the enclosure itself or portions of a wall vibrate, are most often subject to interior noise problems. This structural vibration induces an acoustic field in the interior space, and the wall flexibility allows external sound fields to be transmitted to the interior. Two methods which are traditionally used to predict the interior noise levels are Classical Modal Analysis (CMA) and Statistical Energy Analysis (SEA). Another method, Asymptotic Modal Analysis (AMA) which contains aspects of both CMA and SEA, has recently been developed for structural-acoustic applications. Classical Modal Analysis involves consideration of each individual mode of the system: the structural modes of the enclosure, the acoustic modes of the cavity, as well as the coupled structural-acoustic modes. Recent work by A new method, Asymptotic Modal Analysis (AMA), which was developed by Peretti and Dowell (1992a) analyzed the acoustic field inside a rectangular cavity where five walls were rigid and the sixth wall, or a portion of that wall, was vibrating. In their work, the interior noise levels were studied through a comparison of the results obtained by Asymptotic Modal Analysis (AMA) and those obtained by Classical Modal Analysis (CMA). It was found that AMA, which in theory is valid in the limit when there is an infinite number of modes responding, gave 546 / Vol. 114, OCTOBER 1992 Transactions of the ASME Copyright © 1992 by ASME surprisingly good results when the number of modes was infinite and only moderately large. The purpose of this work is to compare these previous analytical results with experimental data and to test the practical limitations of the theory. To this end, an experiment was performed in which a portion of one wall of an otherwise rigid rectangular cavity was excited structurally with a white noise time history. The experimental design was chosen to best match the assumptions which were made in the theoretical study o