Controlling Sound Radiation through Openings with the Active Noise Control System at the Edge

According to the Huygens' Principle, sound radiation through a cavity opening can be reduced with secondary sources over the entire opening if the sound outside is solely that transmitted through the opening; however, secondary sources in the middle of the opening affect the lighting, natural ventilation and the access through it. This paper investigates the possibility of applying an active noise control system at the edge of the opening. It is found that double-layer secondary sources at the edge achieve better performance than a single-layer system with the same number of secondary sources and the modal decomposition method is used to explain the reason. Similarly, double-layer error microphones at the edge outperform single-layer error microphones. It is demonstrated with experiments that satisfactory noise reduction can be achieved with double-layer secondary sources and error microphones at the edge of the opening. With nothing in the middle of the opening, such a system helps keep the functionalities of the opening.