Marc Aretz

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.

Balancing Sound Strength and Reverberation Time in Small Concert Halls by Means of Variable Acoustics

Sound strength G is a measure of the physical sound level in a concert hall and is closely related to the subjective sensation of loudness. It has been measured in six small concert halls in Cambridge, UK, in combination with measurements of reverberation time. The aim is to investigate the relationship between sound strength and reverberation time in small halls and to study the effect of variable acoustics in these halls. Large ensembles in small halls are often too loud and it is desirable to reduce the sound level. This can be done by introducing acoustically absorbent material but the reverberation time is also decreased. Reverberation time cannot be decreased by an arbitrary amount as it is closely related to sound quality. Therefore, reverberation time and strength have to be carefully balanced in order to maintain sufficient reverberance whilst at the same time avoiding excessive loudness. The study also compares measured strength levels with values derived from traditional and revised theories for strength calculations [1]. Measured strength levels were consistently lower than theoretical predictions and possible reasons for this are discussed with reference to design features of the halls and objective acoustics parameters.

Different approaches for efficient finite element modelling of absorbers in small rooms

The FEM is a powerful tool for the numerical simulation of sound fields in enclosures. It accounts for the modal characteristics of the sound field, which are dominant at frequencies below the Schroeder frequency and it is also possible to model the mutual coupling between airborne and structure borne sound fields, when an appropriate structure model is implemented. When applying the FEM to complex room acoustics applications, like e.g. a control room in a recording studio, it is a challenging task to specify realistic boundary conditions. Different kinds of acoustical absorbers like Helmholtz resonators, plate absorbers and complex layered porous absorbers are found in these environments. While it is possible in principle to use complex and exhaustive models for these acoustical absorbers, it is often computationally much more efficient to use acoustic impedances or two‐port network FEM elements to represent the fluid structure interactions. In the course of this study we compare different approaches for...