A study of the effect of floor mobility on structure-borne sound power transmission

Force transmissibility is usually employed by engineers to select suitable vibration isolators for building services equipment. In the derivation of this usual engineering force transmissibility, floor structure is assumed to be unmovable and the effect of floor mobility is neglected. Based on this assumption, the use of spring isolators will certainly reduce sound power transmitted to the floor for all values of the ratio of forcing frequency and natural frequency greater than 1.414. However, floor structure is flexible and movable in reality. This paper will therefore discuss the effect of floor mobility on structure-borne sound power transmission from which it is shown that spring isolators do not help in vibration isolation at disturbing frequencies near the resonant frequency of the floor and may even worsen the problem at those particular frequencies.