Kletschkowski T., Sachau D., Sommer J.

The pollution of rest rooms with noise, especially during the nights, results in an un-wanted limitation of comfort and causes indispositions. In order to prevent serious dis-eases caused by continuous noise pollution and to guarantee a restorative sleep, the con-cept of active noise control has been applied to daybeds. A transmission test system ¡V consisting of an anechoic chamber and a reverberation room ¡V has been used to simulate an apartment with an open window. The primary noise field has been generated inside the anechoic chamber. Tonal as well as broadband noise (f ƒñ 1 kHz) has been applied to excite the reverberation room. A conventional daybed with a dummy head microphone has been used to model the sleeping person. In addition an array ¡V consisting of 16 microphones ¡V has been in-stalled to measure the sound field around the dummy head. Two microphones that have been placed close to the dummy head ears have been used as error sensors for the active control system. An FxLMS-Algorithm ¡V implemented on a real time hardware ¡V has been applied to generate the secondary sound field. For this purpose two small loud-speakers have been mounted 25 cm above the dummy head. The results of the experiments show that the sound pressure level around the dummy head has been significantly reduced by the application of active noise cancelling. For tonal noise a minimum reduction of 10 dB has been achieved for every tested fre-quency. In case of broadband noise the sound pressure level has been lowered by 8 dB. The resulting zone of quiet around the error sensors depends on the excitation frequency or the frequency band of the broadband noise.