Enhancing Muffler or Silencer Performance by Adding Bypass Ducts

摘要

A bypass duct similar to a Herschel-Quincke tube can be used to increase the transmission loss ofmufflers and insertion loss of enclosures at selected frequencies. In many cases, the duct can beshort and thought of as a leak. It is shown that the optimal length and cross-sectional area can bedetermined by using a simple optimization technique known as the Vincent Circle. To prove theconcept, a muffler was designed and optimized using transfer matrix theory. Then, the optimizedmuffler was constructed and the transmission loss was measured using the two-load method. Themeasured results compared well with predictions from transfer matrix theory for the muffler. Asimilar study was performed for a partial enclosure. A small bypass duct was introduced on aninterior panel. It was demonstrated using boundary element analysis that a bypass duct can shiftthe trough of the insertion loss curve to another frequency avoiding the need to change the shapeand size of the enclosure.