Comparisons of predicted steady-state levels in rooms with extended- and local-reaction bounding surfaces

Defining accurate acoustical boundary conditions is of crucial importance for room acoustic simulations. In predicting sound fields using phased geometrical acoustics methods, both absorption coefficients and surface impedances of the boundary surfaces can be used, but no guideline has been developed on which boundary condition produces accurate results. In this study, various boundary conditions in terms of normal, random, and field incidence absorption coefficients and normal incidence surface impedance are used in a phased beam tracing model, and the simulated results are validated with boundary element solutions. Two rectangular rooms with uniform and non-uniform absorption distributions are tested. Effects of the neglect of reflection phase shift are also investigated. It is concluded that the impedance, random incidence, and field incidence absorption boundary conditions produce reasonable results with some exceptions at low frequencies for acoustically soft materials.

“…Hodgson and Wareing also found large differences in predicted sound pressure levels based on local and non-local reaction at low frequencies. 18 …”

Section: F Remarks On Local Reactionmentioning

confidence: 99%

Absorption and impedance boundary conditions for phased geometrical-acoustics methods

Jeong

2012

“…If the room boundaries are acoustically absorptive, there are substantial attenuations of the reflections from the boundaries, producing a high D-R energy ratio. All in all, in moderately damped large rooms, the direct sound and early reflections are dominant contributers to the steady-state pressure, 4,5 resulting in more accurate results because PBTM results are accurate particularly in the early parts of impulse responses. 3,4 Such a D-R energy ratio is also related to one of the important underlying assumptions of the statistical energy analysis, that is, high modal overlap.…”

Section: Introductionmentioning

confidence: 99%

Effects of source and receiver locations in predicting room transfer functions by a phased beam tracing method

Jeong

2012

The accuracy of a phased beam tracing method in predicting transfer functions is investigated with a special focus on the positions of the source and receiver. Simulated transfer functions for various source-receiver pairs using the phased beam tracing method were compared with analytical Green's functions and boundary element solutions up to the Schroeder frequency in simple rectangular rooms with different aspect ratios and absorptions. Only specular reflections were assumed and diffraction was neglected. Three types of error definitions were used: average error level over a narrow band spectrum, average error level over a 1/3 octave band spectrum, and dissimilarity measure. The narrow band error and dissimilarity increased with the source-to-receiver distance but converged to a certain value as the reverberant field became dominant. The 1/3 octave band error was found to be less dependent on the source-receiver distance. The errors are increased as the aspect ratio becomes more disproportionate. By changing the wall absorption from 0.2 to 0.8 for a rectangular room, the average narrow and 1/3 octave band error are deviated by around 1.5 dB. A realistic nonuniform distribution of the absorption increases the error, which might be ascribed to wave phenomena evoked by the impedance-discontinuous boundary.

“…Three room configurations representing a small, empty office (Room 1: dimensions 3 x 3 x 3 m3), a corridor (Room 2: dimensions 10 x 3 x 3 m3) and a small, empty industrial workshop (Room 3: dimensions 3 x 3 x 10 m3) were studied by Hodgson and Wareing [2]. They used various multilayer boundary conditions for the surfaces of these rooms, based on which twelve room configurations were considered.…”

Section: Test Configurationsmentioning

confidence: 99%

“…It is the intent of this work to study the effects of different surface-reaction models on the steady-state characteristics and temporal variations of the sound-pressure fields in various room configurations. This has already been done in part by Hodgson and Wareing [2], who investigated the effects of modeling surfaces as of local or of extended reaction on steady-state sound-pressure levels in twelve room configurations. The aim here is to revisit the configurations used by Hodgson and Wareing [2] and investigate them further in terms of their transient response and associated room-acoustical parameters.…”

Section: Introductionmentioning

confidence: 99%

“…This has already been done in part by Hodgson and Wareing [2], who investigated the effects of modeling surfaces as of local or of extended reaction on steady-state sound-pressure levels in twelve room configurations. The aim here is to revisit the configurations used by Hodgson and Wareing [2] and investigate them further in terms of their transient response and associated room-acoustical parameters. Moreover, the significance of modeling interference effects is investigated: in the first stage, only phase changes on surface reflection are ignored; in the second stage, all phase effects are ignored (energy-based modeling).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Energy- and wave-based beam-tracing prediction of room-acoustical parameters using different boundary conditions

Yousefzadeh

Hodgson

2012

Self Cite

A beam-tracing model was used to study the acoustical responses of three empty, rectangular rooms with different boundary conditions. The model is wave-based (accounting for sound phase) and can be applied to rooms with extended-reaction surfaces that are made of multiple layers of solid, fluid, or poroelastic materials—the acoustical properties of these surfaces are calculated using Biot theory. Three room-acoustical parameters were studied in various room configurations: sound strength, reverberation time, and RApid Speech Transmission Index. The main objective was to investigate the effects of modeling surfaces as either local or extended reaction on predicted values of these three parameters. Moreover, the significance of modeling interference effects was investigated, including the study of sound phase-change on surface reflection. Modeling surfaces as of local or extended reaction was found to be significant for surfaces consisting of multiple layers, specifically when one of the layers is air. For multilayers of solid materials with an air-cavity, this was most significant around their mass-air-mass resonance frequencies. Accounting for interference effects made significant changes in the predicted values of all parameters. Modeling phase change on reflection, on the other hand, was found to be relatively much less significant.