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Differences in the sound reduction in test facilities and in buildings

Categories:
  • Metrology for Society
15.03.2007

It was shown by scaled model measurements that in test facilities, homogeneous building elements have a larger sound reduction than in real buildings. This is a broadband effect which decreases with increasing frequencies and amounts up to 5 dB at low frequencies.

A central task of building acoustics is the prediction of the sound reduction of building elements in buildings. Starting point for this are sound reductions which were measured in test facilities. A particularity is hereby that the neighbouring rooms in such test facilities always have unequal volumes, whereas in real buildings rooms of equal volumes are often adjacent to each other, e.g. in multi-storey buildings, where rooms are on top of each other. To find out whether the measurement results from the test facilities can be transferred to real building situations, scaled model measurements have been carried out within the scope of a cooperation with the Deutsches Institut für Bautechnik (DIBt). By means of a movable back wall, 6 different test facility geometries (two rooms of unequal volumes each) and 6 different real building geometries (some of them with two rooms of equal volumes) were investigated. The test objects were made of 3 mm hardboard and 18 mm gypsum fibre board. This corresponds to a 24 mm fibre board and a 140 mm lime brick wall, respectively. The mean sound reduction index in the real building situations turned out to be smaller than in the test facilities (Figure 1) for both objects. This effect is of broadband nature and vanishes towards higher frequencies. The work will be continued, whereby the influence of diffusing elements, additional absorption and further geometric parameters will be investigated.

Mean sound reduction indices in test facilities and in real buildings and corresponding standard deviations for a thin homogeneous building element

Figure 1: Mean sound reduction indices in test facilities and in real buildings and corresponding standard deviations for a thin homogeneous building element

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V. Wittstock, FB 1.7, AG 1.71, volker.wittstock@ptb.de

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