IMPEDANCE DEDUCTION FROM BROAD-BAND, POINT-SOURCE MEASUREMENTS AT GRAZING-INCIDENCE

A new method has been developed which derives surface impedance from m easurements of excess attenuation at grazing angles over locally react ing surfaces. The technique uses classical sound propagation theory to fit complex surface impedance to acoustic measurements. Short range e xcess attenuation measurements have been made over dry sand, glass bea ds and felt. Two versions of the impedance deduction technique and two non-invasive measurement methods are presented. The results obtained using both procedures are shown to be consistent with each other and w ith standing wave tube data.