Measurement of flanking sound transmission at low frequencies with a laser doppler vibrometer

Invited paper

Stefan Schoenwald

Empa, Swiss Federal Laboratory for Materials Science&Technology

Monday 1 june, 2015, 16:00 - 16:20

Auditorium 2 (592)

In a recent research project one new and two existing approaches for the measurement of flanking sound transmission by a particular path were applied at a wall-floor junction mock-up and the measurement results were analyzed. With the common indirect method of ISO 10848 the sound pressure level difference between two rooms is measured, when transmission occurs by a single flanking path. This is realized by shielding certain surfaces of the separating and flanking elements in the source and receiving room to suppress their excitation and radiation. However, the method lacks in the low frequency range, as there, usually only very conservative estimates can be obtained for flanking sound insulation, because the direct sound insulation of shielded separating element is still less due to the resonances of the applied shielding. With the second existing approach flanking sound transmission is predicted with the EN 12354-methods using measured input data of the element performance and of the vibration reduction index K<sub>ij</sub> for the junction. Hereby, no shielding is necessary as the source element is excited structurally and velocity level differences are measured on the coupled elements. The third new method is more related to the first approach. The specimen is excited in the source room with airborne sound and here the sound pressure level is measured. In the receiving room the sound power radiated by an element is determined numerically with the so-called Discrete-Calculation-Method from its surface velocity distribution that is measured in a grid with a scanning laser Doppler vibrometer. In this paper the applied methods are outlined and their benefits and disadvantages are highlighted regarding to the obtained low frequency flanking sound insulation estimates.

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