Specification of Realistic Boundary Conditions for the FE Simulation of Low Frequency Sound Fields in Recording Studios

Abstract

The room acoustic design of the low frequency characteristics of control and recording rooms in studio facilities still poses a challenging task to acoustic designers and consultants. Due to the low density of eigenmodes at frequencies below the Schroeder frequency, the statistical assumptions underlying geometrical acoustics theory do not hold for this frequency range. Consequently simulation methods such as 'raytracing' or the 'mirror-image-method' cannot supply reliable results here. On the other hand analytical solutions for the wave equation of the sound field in enclosed spaces are generally restrained to rather simple room geometries and boundary conditions. Therefore numerical methods such as the finite element method (FEM) are promising contenders for the simulation of low frequency sound fields in arbitrarily shaped rooms with complex boundary conditions. In the course of this study the FEM was used to simulate the low frequency sound field in the control room of a recording studio in Munich, Germany. The results are compared to measurements in the real room in order to evaluate the performance of the simulation. Special attention is paid to a realistic representation of the acoustic characteristics of the room boundaries in the model and the limitations of an impedance approach are discussed. It is made clear, that the Achilles' heel of room acoustic FEM simulations appears to be the realistic boundary specification and that further work has to focus on the identification or development of robust and reliable measurement or modelling techniques to determine the acoustic characteristics of the various materials on the room boundaries.