Sound transmission acrosss a plenum window with an active noise cancellation system

A series of experiments was conducted in the present study in an attempt to understand how the implementation of active noise control would affect the sound transmission across a plenum window. A simple squared pressure control scheme with three error sensors equi-spaced on the vertical centerline of the indoor window opening was adopted. The secondary control loudspeakers were fixed close to the outdoor window opening. The effects of secondary control loudspeaker orientation relative to the plenum cavity and their locations on the performance of the active control were investigated. Results show that the active control system with two loudspeakers located symmetrically about the plenum cavity horizontal centerline facing directly the incoming noise gives the best performance. However, the effective frequency range is restricted to that below the first asymmetric mode cut-off frequency in the window gap direction. The active control performance is improved when the reverberation strength of the receiver chamber is reduced in general.