Boundary control of sound transmission into a cavity through its opening

Recently, a wavenumber approach was proposed to analyse the active control of plane waves with arrays of secondary sources (J. Sound Vib. 419, 405-419, 2018) for improving the sound transmission loss of open windows by distributing an array of loudspeakers evenly on the opening. This paper investigates the feasibility of the boundary control for sound transmission through an opening, which only installs the secondary sources on its frame and thus has advantages of better ventilation and easier access. An analytical model is developed first to obtain the sound field transmitted into a cavity with a baffled opening by using the modal expansion method, and then the performances of the boundary control systems are investigated for different primary source and secondary source configurations numerically based on the model. The wavelength corresponding to the upper limit effective frequency of the proposed boundary control system with more than 10 dB noise reduction is found to be equal to the length of the short sides of the opening. Finally, experimental results are presented to verify the discoveries. (C) 2018 Elsevier Ltd. All rights reserved.