Application of Quincke tubes to flow ducts as a sound attenuation device

Reduction of the noise propagating in a duct with how is an important pract ical problem. In this paper an application of the Quincke tube to how ducts as a sound attenuation device is studied theoretically and experimentally. First, joint conditions and relevant governing equations for sound propaga ting in a flow duct are developed, and the transmission loss in different h ow cases is then computed numerically and discussed. Second, the transmissi on loss computed for a Quincke tube with flow but without end reflection is compared with that measured in experiments. The computational predictions and measured results are in good agreement. In order to widen the band of a ttenuation and to consider the effect of end reflection, the transmission l oss of a flow duct system with a double-stage Quincke tube including the ef fect of end reflections is analyzed. Finally, a prototype experiment involv ing a flow duct system with double-stage Quincke tube and with end reflecti on is carried out to demonstrate application of the Quincke tube as a sound attenuation device in practice. It is demonstrated by the experiment that a noise reduction in A-weighted sound pressure level of 6.4 dB can be obtai ned even though the parameters of the double-stage Quincke tube are not opt imized. (C) 1998 Institute of Noise Control Engineering. [S0736-2501(98) 00 206-9].