Kletschkowski T., Sachau D., Böhme S., Breitbach H.

In many situations global pollution of interiors with noise is caused by a local transmis-sion of sound through a limited number of transmission paths. In order to reduce un-wanted noise globally, global sound reduction techniques have been applied in the past. But this is not necessary, if a local hot spot – responsible for the transmission or radia-tion of sound – can be identified. If a local hot spot, like an open window has been located, the sound transmission into the interior can be blocked successfully by a new local approach of anti noise generation – the acoustic window. The main idea of this concept is presented by the example of a reverberation room that is polluted with tonal noise – transmitted trough a window. The primary noise that re-sults in sound pressure levels of 100 dB in the reverberation room is generated in an as-sociated anechoic chamber. In order to eliminate this primary disturbance, a secondary sound field is created by secondary sound sources that have been placed next to the window. The amplification of these secondary sound sources has been determined by the application of the LSQR-Algorithm. This example has been studied numerically. Therefore, the Finite-Element-Method has been applied. The results of the investigation show that a significant global reduction of the sound pressure level can be expected by the application of the new local concept. Furthermore, it has been found out that the amount of global sound pressure level reduction depends not only on the number of sensors but also on their placement. In order to choose the optimal position, the sound pressure distribution of the primary noise field has to be analyzed.