Propagation In Rooms Research Articles

Reduced basis methods for numerical room acoustic simulations with parametrized boundaries.

The use of model-based numerical simulations of wave propagation in rooms for engineering applications requires that acoustic conditions for multiple parameters are evaluated iteratively, which is computationally expensive. We present a reduced basis method (RBM) to achieve a computational cost reduction relative to a traditional full-order model (FOM) for wave-based room acoustic simulations with parametrized boundaries. The FOM solver is based on the spectral-element method; however, other numerical methods could be applied. The RBM reduces the computational burden by solving the problem in a low-dimensional subspace for parametrized frequency-independent and frequency-dependent boundary conditions. The problem is formulated in the Laplace domain, which ensures the stability of the reduced-order model (ROM). We study the potential of the proposed RBM in terms of computational efficiency, accuracy, and storage requirements, and we show that the RBM leads to 100-fold speedups for a two-dimensional case and 1000-fold speedups for a three-dimensional case with an upper frequency of 2 and 1 kHz, respectively. While the FOM simulations needed to construct the ROM are expensive, we demonstrate that the ROM has the potential of being 3 orders of magnitude faster than the FOM when four different boundary conditions are simulated per room surface.

Numerical modelling of sound propagation in rooms bounded by walls with rectangular-shaped irregularities and frequency-dependent impedance

The objective of the work presented here was to develop a numerical model for simulating sound propagation in a confined environment while accurately taking account of the acoustic scattering and diffraction effects generated by the presence of geometrical relief on the room surfaces. To achieve this, two methods were combined: the Adaptive Rectangular Decomposition (ARD) method, for simulating the propagation in the enclosed space, and the Finite-Difference Time-Domain (FDTD) method, for accurately modelling the complex boundaries of the room being studied. Firstly, this paper presents a way of improving how account is taken of the Perfectly Matched Layers (PMLs) used to simulate absorption of the waves at the boundaries of the domain. It then describes in detail the method of creating Digital Impedance Filters (DIFs) and the way in which they were incorporated into the ARD method in order to simulate surfaces having relief and that are characterized by frequency-dependent impedance. The model was then compared with theoretical results obtained using the Kobayashi Potential (KP) method and with measurements of the reflected pressure field above a surface containing rectangular cavities under semi-anechoic conditions. Finally, another application of the numerical model was implemented in a real room delimited by surfaces having geometrical relief.

The perceptual evaluation of acoustical environments I: Simulated environments

The successful design and development of numerical models for the sound propagation in rooms crucially depends on the existence of appropriate measures for the quality assessment of the modeling results. In the perceptual domain, these should include single-number measures for the overall assessment of the simulation as well as differential measures, enabling experts to identify specific shortcomings in the selected modeling approach and its implementation. In the SEACEN consortium, the “authenticity” and the “plausibility” of virtual acoustic environments has been established, measuring the perceived identity with an external (given) or internal reference. Moreover, a Spatial Audio Quality Inventory (SAQI) was developed by a focus group of experts for virtual acoustics, as a metric for the differential diagnosis of virtual environments.

Signal processing for hemispherical measurement data

To realistically model the sound propagation in rooms, a detailed knowledge of the reflection properties of the surrounding surfaces is required. In this context, the reflection properties include both the sound absorption as well as scattering. In order to be able to measure the angle-dependent reflection properties of surfaces in-situ, a hemispherical microphone array was recently designed and built. For a reduction of the required hardware an efficient, rotationally symmetric sampling was chosen, so that 28 microphones on two concentric semicircles are employed to measure a total of over 3000 positions on a hemisphere in just over 15 minutes. This contribution will give an overview over the required signal processing steps to process the measurement data from such a microphone array. Special emphasis will be placed on the determination of the microphone positions and the special case of data available on a hemispherical surface. Also, the sound field model used to determine the impedance on the surface will be explained. Preliminary results will be presented.

Noise immunity of the wireless communications scheme based on ultrawideband chaotic radio pulses in multipath channels

The problem of determining the noise immunity of wireless data transmission based on ultrawide-band (UWB) chaotic radio pulses in the multipath channel with white noise is substantiated. The results have been calculated via numerical simulation using the multipath channel models describing UWB signal propagation in rooms of different classes at distances as long as several tens of meters. The direct chaotic communications method is shown to have the noise immunity high enough to employ this scheme in practical wireless applications where information is transmitted under severe conditions of multipath propagation. In this case, the ultimate data transfer rates are found to 25 Mb/s.

Statistical characteristics of an ensemble of ultrawideband communications channels under the conditions of multipath signal propagation in rooms

The estimates of data rates in the ultrawideband direct chaotic scheme of data transmission in rooms, which can be achieved at a specified level of error probability under the conditions of multipath signal propagation in wireless communications networks, are presented. The estimates have been obtained via direct numerical simulation of energy reception of chaotic signals at the output of communications channels. The channel impulse responses were formed according to the statistical model developed by the IEEE 802.15 working group for indoor applications. In the approximation of a dominant reverberation interference (multipath propagation), the portion of channels making it possible to transmit data with rates from 10 to 50 Mb/s and the practically important error probability (Pb ∼ 10−5−10−4) is determined for the chaotic signal bandwidths Δf = 500 and 2000 MHz. It have been first revealed that, in the given ensemble of channels, the small portion of channels (5–20%) with high levels of error probability Pb substantially affects the dependence of the error probability averaged over the given type of channels (\( \bar P_b \) (R)) on the transmission rate. It has been demonstrated that quantity \( \bar P_b \) (R) is the practically important characteristic of noise immunity for the significant portion (∼80–95%) of channels of the given type.

Numerical analysis of sound propagation in rooms using the finite difference time domain method

Impulse response is an important quantity for room acoustics. To predict the impulse response, several types of calculation methods based on wave theory, such as the boundary element method (BEM), finite element method (FEM) and finite difference method (FDM), are being investigated. Among them, the authors are exploring application of the finite difference time domain (FDTD) method to calculate room sound fields. Using the method, by which the acoustical quantities at discrete grid points of a closed field are successively solved step-by-step according to vector operations, the impulse responses can be obtained directly in a time domain using little computer memory storage. Furthermore, changes of spatial distributions of room sound fields in time can be obtained easily by storing the sound pressure at grid points and displaying them by animation. In this presentation, several examples of the FDTD analyses of room impulse responses are reported and computer animation of their room sound fields is introduced. In addition, examination of the applicability of prediction of the impulse responses by comparison with in situ measurement of a small hall is discussed.

Visualization of sound propagation and scattering in rooms.

This paper presents visualization of transient sound propagation in 2-dimensional room sound fields in which the typical shapes of concert halls are modeled by applying the finite difference time domain method. As a basic study on room acoustic design, sound propagation in rooms, scattering effect of acoustic diffusers and reflection characteristics of suspended panel arrays are investigated. Through the investigation, it has been confirmed that this kind of visualization technique is very effective to get intuitive comprehension of complex acoustic phenomena which occur in rooms. The technique can be useful tool for discussion on room and acoustic treatment between acoustic engineers and architects.

Simulation of the transient and steady-state sound propagation in rooms using a new combined ray-tracing/image-source algorithm

A new method for the calculation of room acoustical impulse responses is described, which is based on two well-known computer algorithms, the ray-tracing and the image-source models. With the new method, the procedure of sieving the ‘‘visible’’ image sources out of the enormous quantity of possible sources is carried out by examination of the histories of sound particles. From the obtained list of visible image sources, the impulse response of the enclosure is easily constructed. The new method combines the advantages of the ray-tracing process, namely, the relatively slow increase of computation time with the length of the impulse response, with the accuracy inherent to the image-source model, which is even sufficient to calculate the Fourier transform, i.e., the steady-state transmission function of the room, or to convolve the impulse response with sound signals.

Room acoustics and listening

The physical basis for sound propagation in rooms may be described by a time‐domain model of reflection from the walls. Reflections arriving soon after direct source‐to‐listener transmission produce a perception of spectral “coloration” while later arrivals contribute “echo.” Directional perception and listener preference for rooms are heavily influenced by such underlying phenomena. These perceptual effects can be quantified and directly related to their physical bases through use of psychophysical testing and interpretation methods, such as multidimensional scaling, combined with computer techniques for creating and modifying sound fields measured in actual or synthetic enclosures. Examples of such approaches, including diotic/dichotic image models of small rooms, modification of concert‐hall transfer functions, and manipulation of responses measured directly in the ear‐canal of listeners, are used ot illustrate the current state of the art.