Study of the active sound field control in building acoustics

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This research project has been planned to investigate the principle of active noise control technology and its applicabilities in building acoustics and the following results have been obtained.(1) Active sound absorption : As a basic application of active control to sound absorption, the way of producing an 1-dimensional sound field terminated with an absorptive boundary by using a loudspeaker, two reference microphones and the "Filtered-X" LMS algorithm has been studied.(2) Active sound insulation : To investigate the effectiveness of the active control technology for increasing the sound insulation of building walls, basic experiments using the adaptive feedforward control have been conducted. As a result, it has been found that sound insulation deficiencies of double walls can be recovered and the sound transmission from the openings can be reduced.(3) Active noise reduction in duct systems : As a method of reducing noises in HVAC duct systems, the adaptive feedforward control was … More applied to a multi-chamber duct. The effect obtained by the experiment was compared with the FEM calculation results, and a fairly good accordance was found between them.(4) Active control using sound intensity : The method using sound intensity as the reference quantity in active noise control was investigated theoretically and experimentally.(5) Application of active control to air-ventilation system : The application of the active noise control technology to air-ventilation system in a electric power station was examined by a scale model experiment.(6) Active mode control : To reduce the sound pressure caused by low dimensional modes in closed enclosures, the application of active control was examined by BEM calculation and scale model experiment.(7) Production of quiet zone : To produce a localized quiet zone in noisy rooms, the effectiveness of the active control was examined experimentally.(8) Active vibration control in pipe system : Regarding the structural vibration problems, an experiment was conducted using a pipe system containing water. As a result, it has been found that the vibration propagation in pipe system and resulting noise radiation can be reduced by the active control technology. Less