Reflected sound field over microperforated panel systems

In this paper the reflected sound field over micro-perforated systems (MPPS) is investigated by using experimental, numerical and theoretical approaches. Two types of MPPS configurations are considered: one with an air cavity termination and the other with a honeycomb layer termination. A theoretical model to assess the reflected sound pressure and particles velocity fields by a microperforated panel backed by a honeycomb layer or by a simple air layer, as well as the angle of reflection, is reported. The theoretical method has been validated by means of experimental measurements in free field and numerical finite element simulations. Results highlight significant differences between MPPS in the case of honeycomb layer or when a simple air cavity is considered. Measurements performed in reverberation chamber and standing wave tube for the same micro-perforated panel have been carried out as well, allowing a further validation of the theoretical model. The latter measurements make possible, at the same time, experimentally appreciate the differences of the absorption coefficient values with and without honeycomb layer, in the case of normal, oblique and diffuse sound incidence. • Honeycomb layers alter the reflected sound field and modify the sound absorption. • Due to honeycomb layer the Reflection angle exceeds specular one. • A new model to predict the reflected sound for a MPPS is presented and validated.