Experimental study of duct noise reflection by a side-branch plate supported by a cavity

摘要

Low frequency duct noise is difficult to deal with by traditional methods, such as duct lining. In a recent study, the second author developed a broadband wave reflector to tackle this problem, which consisting of a plate backed by a hard-walled cavity. In this study, the theoretical prediction is validated experimentally. The test rig was built with a small square duct of 100 mm in dimension, and the cavity is 100 mm deep and 500 mm long. The plate was made of balsawood. It is 2 mm thick and 102 mm wide. As an important parameter, the Young’s modulus of the plate was measured as 2600 MPa. Transmission loss was measured using a four-microphone, two-load measurement system. Experimental results were compared with the analytical prediction. The spectral peaks and the range of the range of the stopband were in good agreement with each other, which validated the theoretical model. In addition, the experiment suggests that plate damping can cause significant sound energy dissipation, and must be modelled properly in the theoretical prediction.