摘要：A new concept for easy reduction of the sound reflection coefficient at an open duct end is proposed in this paper. If the duct side wall next to the open end is made of an appropriate perforated plate or porous material which can prevent abrupt change of the wall acoustic impedance to the free field condition, it is expected that sound reflection at that open end will be markedly reduced. This phenomenon is analyzed theoretically and proved experimentally. Some parameter studies clarify the optimum wall impedance of the porous side wall. Moreover a model test result shows that this technique is effective for reducing low-frequency sound radiated from a stack, as predicted by the analysis. This technique is useful and applicable to reducing the acoustic resonant factor in ducts, such as plant stacks and engine mufflers. As the result, the resonant sound radiation from an open duct end can be reduced.
关键词：Duct;Sound Reflection at Open End;Porous Side Wall;Acoustic Damping
