On the in situ impedance measurement with pu-probes--simulation of the measurement setup

High-quality numerical simulations in room acoustics require a detailed knowledge of the acoustic reflection characteristics of the materials in the room, in order to realistically model the interferences between multiple sound reflections at the room boundaries. While different standardized measurement methods exist for the determination of the absorption coefficient and reflection factor these methods can generally not be applied in situ. Thus time-consuming laboratory measurements and the supply of material samples are required. Driven by the obvious demand for a reliable in situ measurement technique, a pu-probe based method has emerged during the last years, which derives the reflection factor based on the simultaneous measurement of sound pressure and velocity. However, previous investigations of the setup and publications by other authors have shown that the measurement results are affected by various uncertainty factors. The present study aims at the identification, separation, and quantitative assessment of the uncertainty factors related to reflection and diffraction effects at the loudspeaker, sensor, and the absorber geometry. Therefore, a purely simulative approach will be used that replicates the actual measurement situation in every detail, including the geometries of sensor, loudspeaker, and absorber. The simulation setup is validated by measurements and is used to systematically separate the different uncertainty factors.