ON SOUND POWER DETERMINATION IN FLOW DUCTS

The following problems associated with sound power determination in circular ducts carrying mean flow are discussed: axial standing waves due to sound reflections from the duct end; acoustic loading of the source; turbulent flow pressures superimposed on the sound field; discrimination between sound pressures and turbulent flow pressures; radial measurement position in the duct in view of higher order mode sound propagation and directional characteristic of the microphone probe used; modal distribution of sound power. Early and recent work on the above topics is reviewed. Brief descriptions of the standardized in-duct method ISO 5136:1990 (International Organization for Standardization, Geneva, Switzerland, International Standard) [1] and the revised measurement procedure ISO/DIS 5136:1999 (International Organization for Standardization, Geneva Switzerland, Layout for a Draft International Standard) [2] are given.