Measurement of the flanking sound reduction in normal test facilities

Most laboratories don't possess special test facilities for the measurement of the flanking sound reduction. Those laboratories, as a remedy, install the test object into normal test facilities. PTB examined this procedure.

The prediction of the sound insulation in buildings according to DIN 4109 requires the knowledge of the flanking sound reduction of flanking components of buildings. Only a few laboratories possess the necessary test facilities for the measurement of the flanking sound reduction. Instead, flanking test objects are usually installed into normal test facilities thereby producing a flanking cavity.

Figure 1: diagram of the layout of a test facility with a flanking test object installed alongside the test facility wall

It was the task of a research programme funded by the Deutsches Institut für Bautechnik to examine the influence of these flanking cavities. It was to be clarified under which conditions the flanking sound reduction can be measured using normal test facilities.

The examination was conducted experimentally using models of real test facilities scaled down by a factor of 10 as well as computationally using the method of finite elements.

Figure 2: view from the front on a model test facility having a width of 1m

Great attention was payed to the examination of the paths of sound propagation by incremental changes in the construction of the model test facilities. Thereby the influence of the test object emerged significantly.

Further changes in the construction were undertaken to vary the thickness of the test object, the width of the flanking cavity and the damping within that cavity by mineral absorbers. Thereby the sound transmission through the flanking cavity could be examined.

Especially with lightweight test objects installed, a significant influence on the flanking sound reduction was observed by special airborne modes arising inside the flanking cavity. Insertion of absorbing material into that cavity allows the damping of these airborne sound modes and the sound transmission accompanied by them.

The comparability of measurements of interior building elements therefore requires the exact specification of the geometry of the flanking cavity as well as kind and position of damping material within that cavity. For facade elements a test facility has to avoid any flanking cavity and is to be settled within an anechoic sound field.

Contact person:

Martin Schmelzer, FB 1.7, AG 1.71, E-mail: martin.schmelzer@ptb.de