Proceedings of the 26th Conference on Noise and Vibration Engineering (ISMA2014) vol:26 pages:279-288
Conference on Noise and Vibration Engineering (ISMA2014) edition:26 location:Leuven, Belgium date:15-17 September 2014
Linear acoustic network models are commonly used to characterize the acoustic behaviour of flow duct systems. In such a model, each element is represented, independent of the elements up- and downstream, by a so-called acoustic two-port. The behaviour of the complete system can be retrieved by simple matrix multiplications from the two-port representations of the individual components. Although this characterization approach is limited to low frequencies, below the traversal cut-on frequency of the inlet and outlet ducts, it allows making an in-depth analysis of the acoustic transmission properties of a duct system and its components. The accuracy of the two-port characterization of an acoustic element depends solely on a plane wave decomposition in its in- and outlet duct. The established linear multiple microphone technique computes the wave amplitudes from measured pressure fluctuations at two or more axial positions in the in- and outlet ducts. However, its accuracy depends largely on the accuracy of a number of environmental and geometrical parameters. To reduce the influence of uncertainties on these parameters and to increase the accuracy of the result, this paper proposes an iterative procedure that optimizes these parameters directly from the measured pressure fluctuations.