ASA 124th Meeting New Orleans 1992 October

4pPA5. Indirect acoustic impedance computations involving fixed free-space attenuation or fixed boundary loss factors: Experimental model validation studies.

A. A. Oni

Lab. for Advanced Indust. Concepts, Clarence W. Mitchell School of Eng., Morgan State Univ., Baltimore, MD 21239

J. T. Kalb

G. Garinther

U.S. Army Human Eng. Lab., Aberdeen Proving Ground, MD 21005

An experimental verification of a surface acoustic impedance estimation theory and method is hereby presented. Two distinct estimation methods are evaluated. Each method utilizes a search algorithm to estimate the impedance that will validate analytical expressions for ground attenuation of sound, using experimental measurements of continuous-wave sound attenuation changes between two above-ground sound source locations with respect to a single microphone close to the ground. With each of the two methods evaluated, reliable ground impedance estimates were computed with considerable reduction in computation and experimental complexity: The first method requires an experimental arrangement that allowed spherical spreading components of the excess attenuation terms to essentially cancel out. With the second method, the arrangement allowed the boundary loss factor to remain constant while the source sound location changes. Variations in meteorological parameters between the two sound source locations were assumed negligible in each case. These successfully verified analytical and experimental arrangements display the potential to provide a means of obtaining speedy and efficient estimates of acoustic impedance for various surfaces. [Work was supported by the US Army Research Office and the Human Engineering Laboratory, Aberdeen Proving Ground, MD.]