Development of an insertion loss for vibration isolation of building services equipment

Force transmissibility is commonly used in building services engineering in assessing the performance of vibration isolation. However, it neglects the effect of floor mobility on structure-borne sound power transmission and the interactions among contact points between a vibratory machine and the floor. The problem that motivated this study is the occasional unsatisfactory performance of vibration isolators. This my be due to the over-simplification of the vibratory problem in the usual definition of the un-damped force transmissibility commonly used in practice. Dynamic characteristics of receiving floor structures can be determined from mobility measurements which is of importance in the prediction of the response of connected and supporting structures when subject to machine excitation. Mak and Su have recently proposed an “insertion loss” which includes the effect of floor mobility and the interaction of dynamic forces transmitted to the floor. Based on the preliminary measurement of the floor structural dynamics characteristics, the insertion loss used to assess the performance of vibration isolation is discussed.