Room Acoustic Modeling Research Articles

An experimental investigation into the scattering properties of maximum length sequence diffusers and quadratic residue diffusers

Since the invention of Schroeder diffusers, extensive studies have been carried out on the prediction and measurement of diffusion coefficients and correlation scattering coefficients in the far field, providing valuable referring data for public. However, as another important evaluation index, the random-incidence scattering coefficients of Schroeder diffusers, which are popularly used in geometric room acoustic models for accurate predictions, have not yet been systematically studied in the diffusing field. This paper presents an experimental study on the scattering coefficients of two well-known Schroeder diffusers (maximum length sequence (MLS) diffusers and quadratic residue diffusers (QRDs)) in one 1:10 scaled-down reverberation room. The scattering coefficients of these Schroeder diffusers were compared to discover their variation laws as a function of well depth, well width, sequence length and the ratio of the maximum well depth to the wave length. To validate the accuracy and reliability of the scaled-down measurements, the scattering coefficients of six MLS diffusers, as well as their standard deviations, were also measured in a full-size reverberation room. The results measured in this study provide engineers and acousticians with some useful reference data in room acoustics design.

Time-domain modeling of wave-based room acoustics including viscothermal and relaxation effects in air.

Air absorption can be a significant source of attenuation, which should be considered in long-duration wideband acoustics simulations. In this short contribution, a time-domain model for three-dimensional wave propagation including viscothermal and relaxation effects (air absorption) is developed and coupled with locally reactive impedance wall conditions through a conservative energy framework. The model is discretised with a finite-difference time-domain method, and numerical stability is established with a discrete energy balance. Numerical examples are presented to demonstrate the proposed method.

Acoustical transmission of face coverings used to reduce coronavirus transmission in a classroom environment

The COVID-19 pandemic has caused many communities to require the wearing of face coverings, masks, and/or shields indoors to reduce the transmission rate of the virus, which includes educators and students in classroom settings. Several types of face coverings are studied, including standardized N95 and KN95, assorted cloth, and clear plastic face shields. They are evaluated on an acoustical head and torso simulator (HATS) setup in a classroom with two different locations for monitoring via a sound level meter. The HATS is used as a controlled and repeatable artificial voice or sound source, which creates white noise, artificial speech, and real speech signals. Sound levels throughout the classroom are measured to determine the direct field and reverberant field regions, and they are compared to a room acoustics model. Attenuation at octave band frequencies due to the face coverings are evaluated at a location of 2.0 m from the HATS, which is within the direct field to reduce the room acoustical effects, with evaluations repeated at a location near the back of the classroom (6.2 m) to include those room acoustical effects. The acoustic effects of the face coverings are compared to reported droplet transmission rates.

Adding air absorption to simulated room acoustic models.

Room acoustics models are often used in auditory research. The simplest implementations of these models ignore air absorption, and this lack can affect the room response, especially at high frequencies and for large simulated spaces. This letter proposes a method for adding air absorption to a simulated room impulse response calculated without air absorption. The procedure creates a time-varying lowpass filter that approximates air absorption as a function of distance. The existing absorption-free room response is passed through the filter to create a new response that incorporates air absorption effects.

Angle-Dependent Absorption of Sound on Porous Materials

Sound-absorbing materials are usually measured in a reverberation chamber (diffuse field condition) or in an impedance tube (normal sound incidence). In this paper, we show how angle-dependent absorption coefficients could be measured in a factory-type setting. The results confirm that the materials have different attenuation behavior to sound waves coming from different directions. Furthermore, the results are in good agreement with sound absorption coefficients measured for comparison in a reverberation room and in an impedance tube. In addition, we introduce a biofiber-based material that has similar sound absorption characteristics to glass-wool. The angle-dependent absorption coefficients are important information in material development and in room acoustics modeling.

Numerical geometric acoustics

We present a new approach to offline room acoustic modeling and simulation based on solving the eikonal equation, a nonlinear partial differential equation describing the arrival times of a high-frequency wavefront. We call the approach numerical geometric acoustics, since it combines some of the advantages of both numerical acoustics, where the acoustic wave equation or the Helmholtz equation are solved, and geometric acoustics, typically based on a variety of raytracing techniques. In our approach, reflection and diffraction effects are determined from boundary conditions connecting different eikonal problems generated by a recursion. This allows us to compute the multipath eikonal, a multivalued function parametrizing the arrival times of all acoustic rays propagating throughout a scene. Each branch of the multipath eikonal is computed by numerically solving the eikonal equation using a recently developed high-order semi-Lagrangian direct solver. This approach naturally encompasses spatially varying sound speeds. Our solver is compact and sufficiently high-order to allow us to transport the amplitude prefactor directly using paraxial raytracing. We discuss how to compute the acoustic parameter fields typical of precomputed room acoustic simulations used for virtual reality or games.

Optimization-based method for the calibration of geometrical acoustic models

Uncertainty of the final results of room acoustic modelling is a result of uncertainties of many model input parameters, which have to be discovered and limited if possible. It can be done by model calibration. In this paper, a detailed procedure of room acoustic model calibration is proposed. It is based on detection and limitation of possible sources of discrepancies between measured and simulated selected room acoustic parameters defined in ISO 3382-1 standard. As independent parameters which describe the variability of the acoustic field in the room the most accurately, clarity C80 and early decay time EDT are suggested. Based on uncertainty analysis, sound absorption coefficients of all materials used in the interior and selected sound scattering coefficients as well as positions of the receivers are chosen to be input parameters adjusted in the model calibration process. Correction of these parameters is done using optimization algorithms in order to accelerate the procedure. Methods for choosing key ray-tracing simulation parameters are presented, according to which it is possible to obtain repeatable results in the shortest possible time. All analyses are done for five different interiors (three philharmonics and two churches). Correctness of sound absorption/scattering coefficients calculated in the calibration process is validated in the comparison of simulation and measurement results, using a different sound source position. Obtained results are specific for analysed rooms, but proposed methodology is universal for all kinds of room acoustic models.

Time-domain impedance boundary condition modeling with the discontinuous Galerkin method for room acoustics simulations.

The time-domain nodal discontinuous Galerkin (TD-DG) method is emerging as a potential wave-based method for three-dimensional (3D) room acoustics modeling, where high-order accuracy in the low frequency range, geometrical flexibility, and accurate modeling of boundary conditions are of critical importance. This paper presents a formulation of broadband time-domain impedance boundary conditions (TDIBCs) of locally-reacting surfaces in the framework of the TD-DG method. The formulation is based on the approximation of the plane-wave reflection coefficient at normal incidence in the frequency domain using a sum of template rational functions, which can be directly transformed to the time-domain. The coupling of the TDIBCs with the discontinuous Galerkin discretization is achieved through the characteristic waves of the upwind flux along the boundary, where a series of first-order auxiliary differential equations is time-integrated in a high-order way. To verify the performance of the formulation, various numerical tests of single reflection scenarios are shown to demonstrate the cost efficiency and memory-efficiency of high-order basis functions, among which a 3D application to an impedance boundary of rigidly backed glass-wool baffle for room acoustic purposes is presented.

Room acoustic modeling and auralization at an indoor firing range.

Reverberation time measurements were conducted in the 21-lane indoor firing range at Wright Patterson Air Force Base. Long reverberation times resulted in poor speech transmission indices (STI) which required acoustical treatments within the range. After treatment, reverberation times were significantly reduced and STI was dramatically enhanced. Standard Sabine and Eyring models failed to accurately predict the reverberation times. A computer simulation of the range was developed to predict room acoustic conditions and auralize speech performance for perceptual evaluation in the range.

Sound diffraction prediction of a rectangular rigid plate using the physical theory of diffraction

For the purpose of numerical efficiency in room acoustic modeling, the physical theory of diffraction (PTD) is applied to approximate solutions of a finite-sized, rigid rectangular plate. The application of the PTD enables sound diffraction contributions from the two edge pairs of the rigid plate to be predicted separately while ignoring the edge waves around the corners in far-field. This paper discusses numerical implementations of the theoretical predictions to show the efficiency of the application of the PTD in finite-sized objects. The numerical results implemented will also be compared with preliminary experimental results carried out using an acoustical goniometer.

A round robin on room acoustical simulation and auralization.

A round robin was conducted to evaluate the state of the art of room acoustic modeling software both in the physical and perceptual realms. The test was based on six acoustic scenes highlighting specific acoustic phenomena and for three complex, "real-world" spatial environments. The results demonstrate that most present simulation algorithms generate obvious model errors once the assumptions of geometrical acoustics are no longer met. As a consequence, they are neither able to provide a reliable pattern of early reflections nor do they provide a reliable prediction of room acoustic parameters outside a medium frequency range. In the perceptual domain, the algorithms under test could generate mostly plausible but not authentic auralizations, i.e., the difference between simulated and measured impulse responses of the same scene was always clearly audible. Most relevant for this perceptual difference are deviations in tone color and source position between measurement and simulation, which to a large extent can be traced back to the simplified use of random incidence absorption and scattering coefficients and shortcomings in the simulation of early reflections due to the missing or insufficient modeling of diffraction.

Some contributions of Murray Hodgson to room acoustics modeling

This presentation focuses on some of the many contributions of Murray Hodgson (1952–2017) concerning room-acoustic modeling. The concepts of sound field diffuseness and diffuse reflections have always been of major interest for Murray, his studies associating most of the time numerical modeling and measurements on scale models or real-scale rooms. His most cited paper [JASA 89, 1990] proposes to include diffuse surface reflections in ray-tracing simulations, and is a milestone in room acoustics prediction as most standard room-acoustic prediction softwares now include surface diffusivity. Another extensively cited paper [App. Ac. 49, 1996] discusses the applicability of diffuse field theory according to room shape and to absorption distribution and magnitude. The conclusions of this study are still greatly useful to researchers, students, and practitioners. Another important focus of Murray’s research has been the acoustics of « fitted » rooms (i.e., rooms containing many obstacles such as industrial workrooms, classrooms…), and was the topic of many of his papers. This presentation will review some contributions of Murray on this research topic.

Personalization Method for HRTF Based on Multi-Dimensional Physiological Parameters

Head-Related Transfer Function (HRTF) is the most important factor to achieve Auditory Space Modeling(ASM). HRTF has many applications in the areas of room acoustic modeling, spatial hearing and multimedia. For the reason that HRTF is related to the location and frequency of sound source and the physiological structures of the listener, customization of HRTF becomes the bottle-neck problem of the research and application of ASM. This paper, based on the measured data offers the personalization method of the HRTF based on the multi-dimensional physiological parameters, and the method is verified through the spectral distortion and the subjective auditory localization experiments. The results show that database matching can obtain the personalized HRTF efficiently and in the spatial hearing experiment the personalized HRTF can reduce the front-back confusion of auditory localization and improve the accuracy.

Spatial Sound Rendering – A Survey

Simulating propagation of sound and audio rendering can improve the sense of realism and the immersion both in complex acoustic environments and dynamic virtual scenes. In studies of sound auralization, the focus has always been on room acoustics modeling, but most of the same methods are also applicable in the construction of virtual environments such as those developed to facilitate computer gaming, cognitive research, and simulated training scenarios. This paper is a review of state-of-the-art techniques that are based on acoustic principles that apply not only to real rooms but also in 3D virtual environments. The paper also highlights the need to expand the field of immersive sound in a web based browsing environment, because, despite the interest and many benefits, few developments seem to have taken place within this context. Moreover, the paper includes a list of the most effective algorithms used for modelling spatial sound propagation and reports their advantages and disadvantages. Finally, the paper emphasizes in the evaluation of these proposed works.

FDTD Methods for 3-D Room Acoustics Simulation With High-Order Accuracy in Space and Time

Time-domain finite difference (FDTD) methods are popular tools for three-dimensional (3-D) room acoustics modeling, but numerical dispersion is an inherent problem that can place limitations on the usable bandwidth of a given scheme. Compact explicit 27-point schemes and “large-star” schemes with high-order spatial differences offer improvements to the simplest scheme, but are ultimately limited by their second-order accuracy in time. In this paper, we use modified equation methods to derive FDTD schemes with high orders of accuracy in both space and time, resulting in significant improvements in numerical dispersion as compared to the aforementioned schemes. In comparison to such schemes, the high-order accurate schemes presented in this paper use significantly less memory and fewer operations when low error tolerances in numerical phase velocities are critical, leading to higher usable bandwidths for auralization purposes. Simulation results are also presented, demonstrating improved approximations to modal frequencies of a shoe-box room and free-space propagation of a bandlimited pulse.

A Scalable Algorithm for Physically Motivated and Sparse Approximation of Room Impulse Responses With Orthonormal Basis Functions

Parametric modeling of room acoustics aims at representing room transfer functions by means of digital filters and finds application in many acoustic signal enhancement algorithms. In previous work by other authors, the use of orthonormal basis functions (OBFs) for modeling room acoustics has been proposed. Some advantages of OBF models over all-zero and pole-zero models have been illustrated, mainly focusing on the fact that OBF models typically require less model parameters to provide the same model accuracy. In this paper, it is shown that the orthogonality of the OBF model brings several additional advantages, which can be exploited if a suitable algorithm for identifying the OBF model parameters is applied. Specifically, the orthogonality of OBF models does not only lead to improved model efficiency (as pointed out in previous work), but also leads to improved model scalability and model stability. Its appealing scalability property derives from a previously unexplored interpretation of the OBF model as an approximation to a solution of the inhomogeneous acoustic wave equation. Following this interpretation, a novel identification algorithm is proposed that takes advantage of the OBF model orthogonality to deliver efficient, scalable, and stable OBF model estimates, which is not necessarily the case for nonlinear estimation techniques that are normally applied.

First international round robin on auralization: Results of the perceptual evaluation

The round robin on auralization aimed at a systematic evaluation of room acoustic modeling software by means of comparing simulated and measured impulse responses. While a physical evaluation by means room acoustical parameters and spectro-temporal comparisons is addressed in an accompanying talk, here, we focus on an evaluation of perceptual differences arising in complex room acoustical scenarios. In these cases, a mere physical evaluation might not be able to predict the perceptual impact of the manifold interaction of different sound propagation phenomena in enclosed spaces such as reflection, scattering, diffraction, or modal behavior. For this purpose, dynamic auralizations of binaural room impulse responses that were simulated with different room acoustical modeling softwares were evaluated against their measured counterparts. For this purpose, listening tests were conducted using “plausibility” and “authenticity” as overall quality criteria and the Spatial Audio and Quality Inventory (SAQI) for a differential diagnosis of the remaining differences.

Оценка адекватности математических моделей акустических передаточных функций для помещений с произвольной геометрией

Оценка адекватности математических моделей акустических передаточных функций для помещений с произвольной геометрией

Crowd noise simulation system for sound environment evaluation of public spaces

Aiming at the prediction and evaluation of sound environment of public spaces, a simulation-based auralization system is developed for reproducing background crowd noise. The system combines room acoustics modeling using a ray tracing method with a six-channel sound field reproduction system in an anechoic room. As sound sources, footsteps and voices of pedestrians moving on a floor, and HVAC noise from a ceiling are modeled. In a preliminary examination simulating several existing public spaces, a general correspondence to real sound field are confirmed in noise level and auditory impressions such as noisiness, liveness, and so on. Next, simulating a variety of imaginary rooms with changing room dimensions, absorption and pedestrian density, a subjective experiment of auditory pairwise comparisons is carried out. The results show that the noisiness fairly corresponds with the noise level, whereas the feeling of reverberation does not clearly related to the reverberation time, which may be due to the continuous overlap of sounds.

Evaluation of Loudspeaker-Based Virtual Sound Environments for Testing Directional Hearing Aids.

Assessments of hearing aid (HA) benefits in the laboratory often do not accurately reflect real-life experience. This may be improved by employing loudspeaker-based virtual sound environments (VSEs) that provide more realistic acoustic scenarios. It is unclear how far the limited accuracy of these VSEs influences measures of subjective performance. Verify two common methods for creating VSEs that are to be used for assessing HA outcomes. A cocktail-party scene was created inside a meeting room and then reproduced with a 41-channel loudspeaker array inside an anechoic chamber. The reproduced scenes were created either by using room acoustic modeling techniques or microphone array recordings. Participants were 18 listeners with a symmetrical, sloping, mild-to-moderate hearing loss, aged between 66 and 78 yr (mean = 73.8 yr). The accuracy of the two VSEs was assessed by comparing the subjective performance measured with two-directional HA algorithms inside all three acoustic environments. The performance was evaluated by using a speech intelligibility test and an acceptable noise level task. The general behavior of the subjective performance seen in the real environment was preserved in the two VSEs for both directional HA algorithms. However, the estimated directional benefits were slightly reduced in the model-based VSE, and further reduced in the recording-based VSE. It can be concluded that the considered VSEs can be used for testing directional HAs, but the provided sensitivity is reduced when compared to a real environment. This can result in an underestimation of the provided directional benefit. However, this minor limitation may be easily outweighed by the high realism of the acoustic scenes that these VSEs can generate, which may result in HA outcome measures with a significantly higher ecological relevance than provided by measures commonly performed in the laboratory or clinic.