Experimental investigation of modal power distribution in a duct at high frequency

Abstract

Sound attenuation in a lined duct depends on the distribution of acoustic power among the propagating modes. This paper describes the application of a new data analysis technique for investigating in-duct modal power distributions. The technique is designed for high frequencies, with many more propagating modes present than available data points, so that mode-by-mode analysis techniques are impractical. The technique involves fitting continuous parametric models of the modal distribution to experimental data. Using data from a twelvepoint microphone traverse experiment, information has been obtained about the structure of a duct field at frequencies high enough to allow as many as 500 modes to propagate.