Effect of airborne sound on installation noise. Pt.1: Basic investigations

The noise excitation of buildings by service equipment takes place by both structure-borne and airborne sound. Mostly sound transmission is determined by the structure-borne portion. For some sources, however, the contribution of airborne sound can't be neglected. A typical example is the EMPA-hammer, defined in the swiss standard SIA 181 as a standardized source for the simulation of user noise. If airborne sound contributes substantially, conventional measures for noise reduction based on elastic isolation between source and building won't work properly. In order to develop efficient measures for that kind of excitation, structureborne and airborne sound must be separated and investigated in context with each other. The separation of structure-borne and airborne sound was performed by means of a simplified experimental set-up consisting of two parallel plates acoustically connected by an adjustable structure- borne sound bridge and by the air gap between the plates. Since the receiving plate was bedded on an elastic support the transmitted sound power could be determined directly from the mean velocity level on the surface of the plate. For investigation of sound transport the experimental conditions such as distance of the plates or damping and division of the air gap were varied systematically.