A quantitative analysis of uncertainties within transfer function based impedance tube methods

Abstract

Measuring the acoustical properties of materials including the surface impedance, the propagation coefficient and the characteristic impedance within a controlled, testable environment is essential to understanding and shaping acoustical environments. In recent years, a three-microphone impedance tube measurement technique has been explored. This project pursues a quantitative analysis of uncertainties within this normal incident in-duct testing method. Investigations are conducted on both the methodical difficulties that produce ambiguous data and the statistical degrees to which uncertain results are affected. As a possible solution, a method of determining acoustic distances between microphones using Bayesian inference is introduced and compared to existing methods.