Exploration of proposed improvements for low-frequency impedance tube measurements

Low-frequency dissipation exhibits distinct behavior which affects the accuracy of impedance tube measurements. The complex-valued propagation coefficient can be estimated by measuring the acoustic conditions inside an empty impedance tube with a rigid termination involving the resulting transfer function between two microphone positions of a hypothetical ideal-condition scenario given the experimentally measured one. Parameter estimation is performed on measured data using Bayesian inference, and the outcome is analyzed on the basis of impedance, reflectance, and absorption coefficient. This talk will cover the viability of proposed improvements to the transfer function model, including multiple-order polynomial models of the dissipation, transfer function crossover utilizing additional microphone positions, and an extended frequency range via modal decomposition.