Uncertainty analysis of acoustic and non-acoustic parameters derived from four-microphone impedance tube measurements

The uncertainty related to measurements is fundamental for qualifying the method applied to the estimation of the quantities derived from an experimental test. In this paper an uncertainty analysis is given for the estimation of the intrinsic properties of fibrous porous materials, i.e. the characteristic impedance and the characteristic wavenumber, from measurement data obtained by a four-microphone impedance tube. In addition, an uncertainty analysis is given for some other derived material properties, amongst which the flow resistivity. The uncertainty analysis is based on the principles contained in the Guide to the Expression of Uncertainty in Measurements (GUM) and on its supplement 1, concerning the propagation of distributions using a Monte Carlo (MC) method. The GUM and the MC frameworks are compared with each other in terms of accuracy and in terms of flexibility of use. The uncertainty arising from the process of sampling is also evaluated by testing several samples cut from the same material batch.