On the relevance of impact source impedance at low frequencies

Abstract

Many researchers have posed the question of whether the standard tapping machine simulates the impedance of real sources well enough to properly judge the impact sound insulation performance of a floor. Proposed solutions such as the modified tapping machine, the bang machine, and ball were results of these investigations. Recent data collected on bare (wood and concrete) floors, suggest that in the low frequency range, the impedance of the source has no influence on the power injected into the floor. This is presumably due to the fact that the bare floors have much higher impedances than most common sources, meaning only the blocked force of the source influences the injected power. This furthermore suggests that modifying or redeveloping the source is not necessary, and that through use of an appropriate weighting curve a single number rating that correlates well with subjective measurements can be defined. Supporting objective and subjective results are presented. © 2013 Acoustical Society of America.