Numerical prediction of the quality of an anechoic chamber in the low frequency range

The present work focuses on the numerical prediction of the quality of an anechoic chamber in the planning stage. The quality of any numerical prediction is determined by the quality of the modeling procedure used to account for the wall treatment in the numerical simulation. Based on experimental data, this study shows that the use of a local admittance condition to account for the wall treatment is not suitable in the low-frequency range. A new type of boundary condition is described, in which the scalar admittance is replaced by a frequency-dependent admittance matrix. This matrix is calculated from the parameters of the absorbing material, the geometry of the acoustic lining and its mounting conditions. An error estimator is also presented, which makes it possible to check the accuracy of the boundary condition developed. With the boundary condition developed and applied here, the quality of an anechoic chamber was accurately predicted.