A discussion on impedance boundary conditions for room acoustics simulations measured by ensemble averaging method

With the continuous progress of digital computers, it has come to be possible for wave-based methods like finite element method (FEM) to solve sound fields of rooms with certain large volumes. Herein, at first, the frequency upper limitation of FEM sound field analysis is discussed in relation to the recent computational environment, room's volume and accuracy achieved. The accuracy of computed results strongly depends on the modeling of the boundary conditions and absorption modeling is a crucial problem in these decades because of insufficient amount of reliable impedance database. In our previous paper, we proposed a novel method for measuring materials' surface normal impedance using ensemble averaging technique (EA method). Herein, the outline of EA method is summarized briefly and advantages of applying EA method to construct boundary conditions of FEM sound field analyses are discussed. In the discussion, uncertainties of EA method measurements are investigated from the view point of pressure-velocity-sensor (PU-sensor) calibration. Example results of EA method measurements with appropriate calibrations are given to show the basic potential of EA method as a measurement method with less uncertainty that is required for room acoustics simulations. Finally, several applicational simulations of practical rooms' sound fields are presented to show the validity of the impedance boundary conditions measured by EA method.