Calculation of the mean and maximum mobility for concrete floors

Abstract When calculating the structure-borne sound power of a vibration source, such as machines or footfall, it is necessary to know the point mobility of the supporting floor. The frequency-averaged mobility is easily calculated, but the height of the resonant peaks is also important for power flow at low frequencies. This paper describes how the complicated mobility curve for rods, beams and plates can be reduced to a skeleton plot consisting of a mean line, and an envelope of the resonant peaks. Skudrzyk's 'mean value method' 1 is used to provide a simple expression for the peak envelope which is independent of the resonance frequencies. The formula is exact for rods and beams when coupling losses are correctly included. For plates a good approximation is obtained and the predicted skeleton plot shows good agreement with measured mobilities of concrete floors.