Investigating “parasitic noise” in laboratory impact noise testing

The standardized tapping machine (STM) is a structure-borne noise excitation device, designed to simulate footfall for evaluation of the impact insulation performance of a floor–ceiling assembly, and the resulting Impact Insulation Class (IIC) rating. IIC is used to determine the assembly’s suitability for construction in accordance with the minimum acoustic performance requirements of the International Building Code (IBC), requiring a minimum IIC rating of 50 for floor–ceiling assemblies separating dwelling units. The STM generates structure-borne sound via impacts standardized nominally with effective mass of 500 g, impacting the surface at 0.886 m/s, as specified in ASTM E3458-24. This paper examines if “parasitic noise,” defined as airborne sound generated by the hammers of the STM impacting the surface being tested can affect the IIC rating in an ASTM E492 laboratory test environment. Two enclosures are constructed to contain the radiated noise. ASTM E492 testing is performed on the assembly, followed by tests with enclosures surrounding the tapping machine. To assess proximity and loading effects, tests were repeated with shims under the enclosure and with the enclosure suspended by a crane. Sound pressure levels are measured in both the source and receiver rooms for each configuration.