Controlling sound radiation through openings with an active noise control system at the edge

According to Huygens’ principle, sound radiation through a cavity opening can be reduced by secondary sources over the entire opening if the sound outside is solely that transmitted through the opening. However, secondary sources in the middle of an 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 an opening. Double-layer secondary sources at the edge achieve better performance than a single-layer system with the same number of secondary sources. The modal decomposition method is used to explain the mechanisms. Similarly, a double-layer error microphone arrangement at the edge is proposed and is found to outperform single-layer error microphones. With nothing in the middle of the opening, such a system can reduce sound radiated through the opening while maintaining the functionalities of the opening.