This SAE Recommended Practice presents a test procedure for determining the airborne sound insulation performance of materials and composite layers of materials commonly found in mobility@ industrial and commercial products under conditions of representative size and sound incidence so as to allow better correlation with in-use sound insulator performance. The frequency range of interest is typically 125 to 8000 Hz 1/3 octave band center frequencies. This test method is designed for testing flat samples@ although in some applications the methodology can be extended to evaluate formed parts@ pass-throughs@ or other assemblies to determine their acoustical properties. For non-flat parts or assemblies where transmitted sound varies strongly across the test sample surface@ a more appropriate methodology would be ASTM E90 (with a reverberant receiving chamber) or ASTM E 2249 (intensity method with an anechoic or hemianechoic receiving chamber).