### 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
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*Lab. for Advanced Indust. Concepts, Clarence W. Mitchell School of Eng.,
Morgan State Univ., Baltimore, MD 21239
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**J. T. Kalb
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G. Garinther
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*U.S. Army Human Eng. Lab., Aberdeen Proving Ground, MD 21005
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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.]