2012 Volume 7 Issue 1 Pages 76-91
Active acoustic shielding (AAS) is the system that can attenuate a sound passing through an open window. AAS is constructed from a number of AAS cells set in an array with having an approximately collocated microphone and speaker. Each AAS cell is individually controlled by a single-channel feedforward method. The concept of AAS was proposed by the authors and its feasibility was demonstrated in the previous report by performing some simple simulations and experiments. In this study, an AAS window with four AAS cells in a small open window was manufactured and installed in the door of a test room. Its noise-reducing performances were measured for noise from outside. The effects of multiple noise sources, moving noise sources and reflected sound in the room were also examined. As the results, the AAS window is demonstrated to be able to attenuate not only normal incident sound but also oblique incident sound in the frequency range from 500Hz to 1.5 or 2kHz. Moreover, noise reduction is obtained over a wide area in the room. Additionally the AAS window is also effective for multiple sound sources and moving sound sources.
