Structure-Borne Sound in Buildings: Application of Vibro-Acoustic Methods for Measurement and Prediction

The methods required for prediction of structure-borne sound (i.e. the radiated sound due to vibration transmission between machines and supporting/connected structures) are more complicated than for airborne sound. However, practitioners of building acoustics require methods for the former, which are as straightforward as for the latter. The source-path-receiver model for airborne sound is replaced by a vibro-acoustic model, i.e. a source-transmission-path-receiver model, for structure-borne sound. The transmission provides input data for numerical or empirical building sound propagation models. To obtain the transmission, for all or a wide range of installation conditions, three quantities are required in some form: source activity (either the free velocity or the blocked force of the operating machine), source mobility (or the inverse, impedance) and the receiver mobility (or impedance) of the supporting and connected structural element. In a form of sub-structuring, the three quantities are measured separately and then combined numerically for the transmission. However, the precise method is time consuming and involves extensive measurement and calculation. Alternative methods are less precise but provide practical data as frequency band-averaged values, e.g. in one-third octave bands, and the source and receiver data are expressed as equivalent single values. The source quantities are measured in the laboratory using the reception plate method, which is gaining general acceptance in international Standards. A database is proposed, based on the reception plate measurements and on simple calculations, which offers consultants and design engineers a practical approach to predicting structure-borne sound.