Reverberation Chamber Study of the Sound Power Output of Subsonic Air Jets

Abstract

The reverberation chamber technique was used to determine the sound spectra and acoustic power radiated by air jets over a range of subsonic velocities. Different air jets were used with round and square velocity profiles; nozzles of circular cross section, and nozzles with saw-tooth and corrugated ends were also used. Of these nozzles only the latter type gave a significant (9 db) reduction in sound power output for a given exit-pressure ratio. A study was made of the limitations of the reverberation chamber technique caused by the absorption in the chamber. When this absorption became considerable, the measurement of sound pressure level in a circle around the sound source revealed a directional pattern, and the assumption of uniform energy distribution in the chamber became invalid. This situation was noticeable at frequencies above 5 kc in the National Bureau of Standards chamber, owing to air absorption.