Determining acoustical directionality in an impedance tube using multiple fixed microphones

Abstract

Acoustic impedance of a port or object is a valuable piece of knowledge describing how well sound is transmitted or reflected. The commonly used slotted-line method is labourious and time consuming, requiring manual movement to find the maxima and minima at each frequency. This paper outlines a technique to computationally determine the magnitude and phase of the constituent travelling waves from the standing plane sound wave measurements in an impedance tube. Measured magnitude and phase data from multiple fixed microphones carefully spaced along the length of the impedance tube is numerically fitted to incident and reflected wave models, which can then be used to calculate the complex acoustic impedance at each frequency of interest.