Beam-tracing model for predicting sound fields in rooms with multilayer bounding surfaces

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.

Section: Phased Beam Tracing and Its Simulation Error A Phased Bmentioning

confidence: 91%

“…8,11,[16][17][18] If an intersecting polygon is detected, there are two solutions: The original beam is followed by its central axis ray 3,8,11 or the original beam can be split. 16,17 Beam-splitting algorithms make simulations more accurate, but they become computationally voracious.…”

Section: Phased Beam Tracing and Its Simulation Error A Phased Bmentioning

confidence: 99%

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

2012

“…Another problem of PBTM arises when beams intersect more than one surface. If an intersecting polygon is detected, there are two solutions: The original beam is followed by its central axis ray 4,20,22 or the original beam can be split. 24,25 Beam-splitting algorithms possibly make simulations more accurate, but they are computationally voracious.…”

Section: Phased Beam Tracing Methodsmentioning

confidence: 99%

“…Furthermore, an advanced transfer-matrix approach for multilayer boundary surfaces can be incorporated to a phased beam tracing method. 4 Surface impedance boundary conditions are likely to be superior to absorption boundary conditions because they fully describe the physical characteristics of the boundary, i.e., the magnitude and phase changes on reflections. It has been reported that phased geometrical acoustics simulations using surface impedances as boundary conditions agree well with measurements and reference calculations.…”

Section: Introductionmentioning

confidence: 99%

Absorption and impedance boundary conditions for phased geometrical-acoustics methods

2012

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.

“…In this study, the beam tracing method [23][24][25] is employed to simulate the sound propagation in a reverberation chamber. Triangular beams, which are emitted from a source, are followed by their central axes ͑hereafter rays͒ without splitting algorithm.…”

Section: Angular Distribution Of Energy Density As a Weighting Fumentioning

confidence: 99%

A correction of random incidence absorption coefficients for the angular distribution of acoustic energy under measurement conditions

2009

Most acoustic measurements are based on an assumption of ideal conditions. One such ideal condition is a diffuse and reverberant field. In practice, a perfectly diffuse sound field cannot be achieved in a reverberation chamber. Uneven incident energy density under measurement conditions can cause discrepancies between the measured value and the theoretical random incidence absorption coefficient. Therefore the angular distribution of the incident acoustic energy onto an absorber sample should be taken into account. The angular distribution of the incident energy density was simulated using the beam tracing method for various room shapes and source positions. The averaged angular distribution is found to be similar to a Gaussian distribution. As a result, an angle-weighted absorption coefficient was proposed by considering the angular energy distribution to improve the agreement between the theoretical absorption coefficient and the reverberation room measurement. The angle-weighted absorption coefficient, together with the size correction, agrees satisfactorily with the measured absorption data by the reverberation chamber method. At high frequencies and for large samples, the averaged weighting corresponds well with the measurement, whereas at low frequencies and for small panels, the relatively flat distribution agrees better.