Measurement of sound insulation in laboratory - comparison of different methods

For measuring the sound insulation of building elements in laboratory three standardized methods based on different acoustic principles are available. According to ISO 140-3 the element under test is installed between two reverberant rooms. The measurements acc. to ISO 140-5 combine free field excitation with a reverberant receiving room and ISO 15186-1 uses sound intensity for determination of transmission loss. All methods assume idealized acoustic conditions that differ more or less from the situation found in practice. In addition to the inherent statistic variation of the measuring results this gives rise to systematic deviations between the different measuring methods. Since the deviations are so far only partly understood, they were investigated by means of an extensive series of tests. The tests comprised three different types of building elements (a chipboard, a lightweight double-leaf construction and a membrane partition) and were performed under well-defined conditions in the test facilities of the Fraunhofer-Institute for Building Physics. Apart from comparing the different measuring methods additional investigations on the influence of the most important measuring parameters (reverberation time, number and position of microphones, etc.) are presented. The results of the investigations contribute to a better understanding of accuracy and reliability in measuring sound insulation.