Low-frequency assessment of the in situ acoustic absorption of materials in rooms: an inverse problem approach using evolutionary optimization

The in situ assessment of the acoustic absorption of materials is often a necessity. The need to cover the whole frequency range of interest for the building engineer has led the authors to an approach involving two frequency-complementary measurement methods. This paper deals with the part dedicated to low frequencies. The measurement is de=ned here as a boundary inverse interior problem. A numerical model of the room under investigation, allowing for the computation of the pressure =eld in the volume, given impedance boundary conditions and a point source, is combined to a global optimization algorithm. The algorithm explores the set of possible boundary conditions in order to minimize the di>erence between the computed pressure values and the one observed at a few measurement points, leading to the determination of all the boundary conditions at a time. In practice, the =nite element method (FEM) or the =nite di>erence method (FDM) is used here to model the room and an Evolution Strategy as the optimization tool. After describing the ES operators, a numerical study is carried out on simulated measurements, both on problem- and algorithm-speci=c parameters, in the case of an academic twodimensional room geometry. The method is then applied to a three-dimensional room with promising results.