On the in situ measurement of acoustic impedance of the surfaces of a real room by an inverse optimization acoustical approach.

Abstract

As numerical simulations of large‐scale complex‐shape sound fields have become affordable by powerful computers and algorithms, there is an increasing interest on new methods of in situ assessment of acoustic impedance and absorption coefficients to yield accurate sound predictions. Among the existent approaches, those based on inverse boundary frameworks offer the advantage of dealing with surfaces of arbitrary shapes. Moreover, estimation of the acoustic impedance of not one but all the surfaces in an interior using one microphone has been demonstrated. A drawback of these frameworks is a high sensitivity to noise due to a rank deficient inverse model. The authors have previously introduced an iterative optimization method that avoids the direct solution of such ill‐conditioned model by exploiting prior knowledge of the surface geometry. Numerical simulations suggest that the proposed approach improves the signal‐to‐noise ratio, which motivated preliminary experiments in a reverberation chamber. This report presents experimental data of a new attempt to estimate the acoustic impedance on the (interchangeable) surfaces of a real room. The results were further investigated by creating a novel surface configuration and contrasting both sound fields, that of the real room and the predicted one (using the estimated impedance values).