Wave-based Acoustics Simulation Research Articles

Modeling source directivity by solving inverse problems

Directivity is an important property of a sound source in the real world. Howerver, majority of the wave-based acoustic simulation does not reflect directivity of a source. One of the reasons is that modeling of source directivity is not a simple task and remains a matter of research. In this talk, our attempts of modeling source directivity in time or frequency domains are briefly introduced.

Binaural Auralization of Room Acoustics with a Highly Scalable Wave-Based Acoustics Simulation

This paper presents a proposal of an efficient binaural room-acoustics auralization method, an essential goal of room-acoustics modeling. The method uses a massively parallel wave-based room-acoustics solver based on a dispersion-optimized explicit time-domain finite element method (TD-FEM). The binaural room-acoustics auralization uses a hybrid technique of first-order Ambisonics (FOA) and head-related transfer functions. Ambisonics encoding uses room impulse responses computed by a parallel wave-based room-acoustics solver that can model sound absorbers with complex-valued surface impedance. Details are given of the novel procedure for computing expansion coefficients of spherical harmonics composing the FOA signal. This report is the first presenting a parallel wave-based solver able to simulate room impulse responses with practical computational times using an HPC cloud environment. A meeting room problem and a classroom problem are used, respectively, having 35 million degrees of freedom (DOF) and 100 million DOF, to test the parallel performance of up to 6144 CPU cores. Then, the potential of the proposed binaural room-acoustics auralization method is demonstrated via an auditorium acoustics simulation of up to 5 kHz having 750,000,000 DOFs. Room-acoustics auralization is performed with two acoustics treatment scenarios and room-acoustics evaluations that use an FOA signal, binaural room impulse response, and four room acoustical parameters. The auditorium acoustics simulation showed that the proposed method enables binaural room-acoustics auralization within 13,000 s using 6144 cores.

High potential of small-room acoustic modeling with 3D time-domain finite element method

Applicability of wave-based acoustics simulation methods in the time domain has increased markedly for performing room-acoustics simulation. They can incorporate sound absorber effects appropriately with a local-reaction frequency-dependent impedance boundary condition and an extended-reaction model. However, their accuracy, efficiency and practicality against a standard frequency-domain solver in 3D room acoustics simulation are still not known well. This paper describes a performance examination of a recently developed time-domain FEM (TD-FEM) for small-room acoustics simulation. This report first describes the significantly higher efficiency of TD-FEM against a frequency-domain FEM (FD-FEM) via acoustics simulation in a small cubic room and a small meeting room, including two porous-type sound absorbers and a resonant-type sound absorber. Those sound absorbers are modeled with local-reaction frequency-dependent impedance boundary conditions and an extended-reaction model. Then, the practicality of time-domain FEM is demonstrated further by simulating the room impulse response of the meeting room under various sound absorber configurations, including the frequency component up to 6 kHz. Results demonstrated the high potential and computational benefit of time-domain FEM as a 3D small room acoustics prediction tool.

A Parallel Dissipation-Free and Dispersion-Optimized Explicit Time-Domain FEM for Large-Scale Room Acoustics Simulation

Wave-based acoustics simulation methods such as finite element method (FEM) are reliable computer simulation tools for predicting acoustics in architectural spaces. Nevertheless, their application to practical room acoustics design is difficult because of their high computational costs. Therefore, we propose herein a parallel wave-based acoustics simulation method using dissipation-free and dispersion-optimized explicit time-domain FEM (TD-FEM) for simulating room acoustics at large-scale scenes. It can model sound absorbers with locally reacting frequency-dependent impedance boundary conditions (BCs). The method can use domain decomposition method (DDM)-based parallel computing to compute acoustics in large rooms at kilohertz frequencies. After validation studies of the proposed method via impedance tube and small cubic room problems including frequency-dependent impedance BCs of two porous type sound absorbers and a Helmholtz type sound absorber, the efficiency of the method against two implicit TD-FEMs was assessed. Faster computations and equivalent accuracy were achieved. Finally, acoustics simulation of an auditorium of 2271 m3 presenting a problem size of about 150,000,000 degrees of freedom demonstrated the practicality of the DDM-based parallel solver. Using 512 CPU cores on a parallel computer system, the proposed parallel solver can compute impulse responses with 3 s time length, including frequency components up to 3 kHz within 9000 s.

3D Interpolation in Wave-Based Acoustic Simulation

3D Interpolation in Wave-Based Acoustic Simulation

Experiences with industrial application of wave-based architectural acoustics simulations

Current state-of-the-art tools for simulation of acoustics in the built environment largely utilize geometrical acoustics technology, such as ray-tracing. Wave-based methods are known to be much more accurate than thatof geometrical acoustics methods with the accurate inclusion of wave-effects such as resonant behavior, diffraction, focusing, and interference, but the computational burden has been the roadblock preventing the practical commercial application. However, recent advancements in both numerical methodology and cloud computing are now enabling the industry to explore the benefits of this technology. In this talk, we will present the findings from multiple case-studies of practical application of a cloud-based wave-based acoustics simulation tool. The case-studies include several real-world industrial projects, but a study of the scenes provided in “GRAS—Ground truth for room acoustical simulation” is also presented. The results are compared to traditional modelling approaches and measurement where available. It is found that there are significant accuracy improvements to be gained from shifting towards the use of wave-based acoustical simulation tools, and with the lower levels of uncertainty, it is assessed that the new methods can enable more efficient and robust design processes in building design.

Local Time-Domain Spherical Harmonic Spatial Encoding for Wave-Based Acoustic Simulation

Volumetric time-domain simulation methods, such as the finite difference time domain method, allow for a fine-grained representation of the dynamics of the acoustic field. A key feature of such methods is complete access to the computed field, normally represented over a Cartesian grid. Simple solutions to the problem of extracting spatially encoded signals, necessary in virtual acoustics applications, result. In this letter, a simple time-domain representation of spatially encoded spherical harmonic signals is written directly in terms of spatial derivatives of the acoustic field at the receiver location. In a discrete setting, encoded signals may be obtained, at very low computational cost and latency, using local approximations with minimal number of grid points, and avoiding large convolutions and frequency-domain block processing of previous approaches. Numerical results illustrating receiver directivity and computed time-domain responses are presented, as well as numerical solution drift associated with repeated time integration.

Predicting absorption characteristics of single-leaf permeable membrane absorbers using finite element method in a time domain

Permeable membranes (PMs), which are air-permeable thin woven fabrics or non-woven fabrics, are attractive sound-absorbing materials used to control acoustics in buildings. Although the absorption characteristics of various PM absorbers have been studied extensively, it has not been established how to incorporate PMs into a wave-based acoustic simulation method known as the time-domain finite element method (TD-FEM). This paper presents a numerical model of limp PMs for TD-FEM as well as a computationally efficient TD-FEM for predicting sound fields including PMs. The limp PM model incorporates effects of both sound-induced vibration of PMs and the air permeability of PMs. Consequently, two material parameters are considered: the surface density and flow resistance of PMs. Verification of the limp PM model and efficiency evaluation of TD-FEM were first performed with an impedance tube problem. Then, reverberation absorption coefficients of single-leaf PM absorbers with a non-locally reacting rigid backed air cavity were predicted through simulation of a reverberation absorption coefficient measurement using the present TD-FEM at frequencies of 100 Hz to 2.5 kHz. The predicted results were compared with measured and theoretical values. To demonstrate the applicability of present TD-FEM, eight PMs, each with different flow resistance and surface density, were considered for comparison. Results revealed that the present TD-FEM with the limp PM model can predict the magnitude relation of absorption characteristics of single-leaf PM absorbers attributable to differences of material properties of PMs.

Directional Sources in Wave-Based Acoustic Simulation

Volumetric wave-based acoustic simulation relies on the complete solution to the three-dimensional wave equation over a spatial grid. Detailed modeling of sources, however, requires interpolation over the grid, which is complicated by the directional character of the source itself. In this paper, a new model of point sources of arbitrary directivity and location with respect to an underlying grid is presented. The model is framed in the spatio-temporal domain directly through the differentiation of Dirac distributions, leading to a spatial Fourier-based approximation strategy. Various approximants are presented, of both separable and nonseparable type, which allow for optimization over a specified wavenumber range. Such approximants are then employed in a finite difference time domain setting, yielding numerical results for sources of various types, which are then compared against exact solutions.

Numerical study on the absorption performance of MPP sound absorber installed in small rectangular rooms

Sound absorbers using microperforated panel (MPP) are one of the most promising alternatives of the next-generation sound absorbing materials, thanks to the superior material performances in durability, weatherability, recyclability, and flexibility of design, as well as the attractive broadband sound absorption characteristics. Many previous researches focus on the development of absorbers itself. However, in order to bring out the absorption performance sufficiently or to use it appropriately in room acoustics applications, it is important to understand the absorption effect of MPP absorbers on sound fields in rooms. For the purpose, recently, highly accurate wave-based acoustics simulation techniques such as FEM can be used to analyze sound fields in practical sized rooms with MPP absorbers. This paper presents the absorption performance of MPP absorbers installed in a small rectangular room of 91 m3 using 3D-FEM in frequency domain. Both the steady-state and the unsteady-state sound fields are calculated up to 1 kHz under the various absorber locations. The unsteady-state sound fields are calculated using inverse Fourier transform of transfer functions of rooms. The results are compared to explore the optimum sound absorber locations.

Energy decay analysis of non-diffuse sound fields in rectangular rooms

Rectangular rooms with irregular aspect ratio or nonuniform absorption distribution apt to have non-diffuse sound fields, where the curvature of energy decay curve occurs in the reverberation process. In general, this curvature leads to longer reverberation times than the estimates by the Sabine or Eyring formula; however it can be suppressed to a certain extent with diffusive wall surfaces. Recently the author has proposed a new approximate theory of reverberation in rectangular rooms with specular and diffuse reflections. In this paper, the validity of the theory is investigated by two case studies with geometrical and wave-based acoustic simulation. In the first study, energy decay in a variety of rectangular rooms with changing the aspect ratio, the absorption distribution and the scattering coefficient, is simulated with the image source method and the ray tracing method. In the second study, a two-dimensional FDTD analysis is performed to demonstrate the frequency dependence of energy decay in a variety of rectangular rooms with flat or corrugated walls. Finally, the simulated results are compared with the theoretical ones, and the validity and the limitation of the approximation are discussed.

Validation of adaptive rectangular decomposition for three-dimensional wave-based acoustic simulation in architectural models

Computer-based simulation is an increasingly popular way to predict the acoustics of real-world architectural designs. Most commercial acoustic simulation tools are based on geometric techniques and cannot accurately model low-frequency diffraction and other wave phenomena. Numerical wave simulation techniques can model these effects, but are less commonly used, since they are compute- and memory-intensive, and cannot scale to large spaces. Moreover, it is challenging to ensure that numerical methods do not suffer from high dispersion errors. Recent techniques have begun to overcome these limitations. One such method is adaptive rectangular decomposition (ARD), which combines analytical solutions to the wave equation in rectangular subdomains with a finite difference stencil for interface handling between subdomains, resulting in high-performance wave simulation with low dispersion error. ARD, along with high-performance ray tracing, are available as part of Impulsonic’s IPL SDK, a software development kit that allows custom acoustic simulation tools to be easily built with state-of-the-art simulation technology. In this paper, we evaluate the performance and accuracy of the IPL SDK and ARD, by analyzing simulation results and comparing them against measurements obtained for real-world architectural designs.