Active sound transmission reduction across acoustic window

Abstract

In this study, the experimental method of transfer functions is employed to investigate the possibility of improving the sound transmission loss of acoustic windows using an active control technique. Twenty-five microphones, 20 of them located evenly over the acoustic window's indoor exit (provide error signals) and 5 fixed in the receiver room (capture the transmitted sound), and 19 small loudspeakers were used in the experiments. The loudspeakers acted as the canceling sources, and they were located along the window's interior perimeter (except the bottom part). The receiver room was made relatively “dead” using fiberglass linings. A loudspeaker array located in the source room acted as the primary sound source. The active control is implemented by minimizing the squared sound pressures at selected error microphones. Results show that the active noise control method can improve the sound transmission loss across acoustic window. The performance depends on the arrangement of the cancelling sources and the error microphone locations. It is found that an average of between 6 and 8 dB reduction of sound transmission within the frequency range from 100 to 1000 Hz can be achieved by an active control system with 4 or 6 error microphones and only three cancelling loudspeakers.