Sound Field Model Research Articles

Shock wave negative pressure characteristics of underwater plasma sound source

The propagation process of intense acoustic shock wave, generated by the discharge of underwater plasma sound source, is analyzed based on a modified Rayleigh model. The bunching sound field model of underwater plasma sound source is established by using the Euler equation as the control equations. The formation mechanism of the shock wave negative pressure is analyzed theoretically and intuitively through the sound field charts obtained by simulation. The results demonstrate that the waters around the bunching wave will be stretched and form a zone of negative pressure with the combination of the rarefaction wave and the inertia of water. It will make the waters to form a discontinuous phenomenon if the stretching force is great than the ultimate tensile strength of the water, the phenomenon of cavitation bubble will appear at this time. Besides that, negative pressure will be aggravated by the diffracted wave generated at the edge of the energy-gathered reflector, and the shock wave negative pressure will reach the maximum value by the superimposition of the edge diffraction wave and the stretch wave. The reasons for the formation of the shock wave negative pressure is testified and revealed further by comparing the waveforms of simulation and experiment. The study results provide a theoretical guide for understanding the propagation law of underwater shock wave and further improving the design of the underwater plasma sound source.

Energy-based method for near-real time modeling of sound field in complex urban environments

Prediction of the sound field in large urban environments has been limited thus far by the heavy computational requirements of conventional numerical methods such as boundary element (BE) or finite-difference time-domain (FDTD) methods. Recently, a considerable amount of work has been devoted to developing energy-based methods for this application, and results have shown the potential to compete with conventional methods. However, these developments have been limited to two-dimensional (2-D) studies (along street axes), and no real description of the phenomena at issue has been exposed. Here the mathematical theory of diffusion is used to predict the sound field in 3-D complex urban environments. A 3-D diffusion equation is implemented by means of a simple finite-difference scheme and applied to two different types of urban configurations. This modeling approach is validated against FDTD and geometrical acoustic (GA) solutions, showing a good overall agreement. The role played by diffraction near buildings edges close to the source is discussed, and suggestions are made on the possibility to predict accurately the sound field in complex urban environments, in near real time simulations.

Modeling and visualization of the underwater sound field associated with underwater pile driving

As communities seek to expand and upgrade marine and transportation infrastructure, underwater noise from pile driving associated with marine construction is a significant environmental regulatory challenge. This work explores results of different transmission loss models for a site in Puget Sound and the effect of improved understanding of modeling on the extents of zones of influence. It has been observed that most of the energy associated with impact pile driving is less than about 1000 Hz. Here, analysis of the spectral content of pile driving noise is undertaken to ascertain the optimal surrogate frequency to model the broadband nature of the noise. Included is a comparison of a normal mode model, which is motivated by work presented by Reinhall and Dahl [JASA 130, 1209 (2011)], with other methods. A GIS (Geographic Information System) tool, ArcMap, is used to map the sound level over the bathymetry, which has proved to be a useful way of visualizing the impact of the noise. [Work supported by Washington Sea Grant.]

Energy-based method for near real-time modeling of sound field in complex urban environments

Prediction of the sound field in large urban environments has been limited thus far by the computational heaviness of standard numerical methods such as boundary element (BE) or finite-difference time-domain methods. Recently, a considerable amount of work has been devoted to developing energy-based methods for this application, and results have shown the potential to compete with conventional methods. However, these developments have been limited to 2-D models, and no real description of the phenomena at issue has been exposed. Here, the mathematical theory of diffusion is used to predict the sound field in complete 3-D complex urban environments. A 3-D diffusion equation is implemented by means of a simple finite-difference scheme and applied to two different types of urban configurations. This modeling approach is validated against BE and geometrical acoustic solutions, showing a good overall agreement. The role played by diffraction near the source is discussed, and suggestions are made on the possibility to accurately predict the sound field in complex urban environments in near real time simulations.

Computational methods in architectural acoustics.

Sound field modeling and auralization have been used in architectural acoustics for many years. Today, the technique of auralization can also be implemented with real‐time performance. Then it is part of the technology of virtual reality. Apparent simple scenarios of interaction, however, for instance, when a person is leaving a room and closes a door, require complex models of room acoustics and sound transmission. Otherwise the coloration, the loudness, and timbre of sound within and between rooms are not represented adequately. Still numerous approximations must be made to reach this goal. In the end, the resulting sound is not intended to be physically correct, but perceptively plausible. Knowledge about human sound perception is, therefore, a very important prerequisite to evaluate auralized sounds. In this paper the algorithms for sound field rendering and spatial reproduction are reviewed and discussed with regard to future research.

Model-Based Dereverberation Preserving Binaural Cues

The ability of the human auditory system for sound localization mainly depends on the binaural cues, especially interaural time and level differences (ITD and ILD). In the context of digital hearing aids and binaural audio transmission systems, these cues can be severely degraded by independent bilateral signal processing such as dereverberation or noise reduction. This contribution presents a novel two-stage binaural dereverberation algorithm which explicitly preserves the binaural cues. The first stage is based on a statistical model of the room impulse responses (RIR) and comprises a spectral subtraction rule which reduces late reverberation only. It includes a smoothing process of the spectral gains to reduce musical tones. In a second stage, the residual reverberation is attenuated by a dual-channel Wiener filter. This is derived from a coherence model of the reverberant sound field taking into account shadowing effects of the head. The overall binaural-input binaural-output structure efficiently reduces both early and late reverberation. In experiments as well as informal listening tests using measured binaural room impulse responses, the proposed algorithm significantly improves speech quality according to objective and subjective measures.

Modeling of sound fields in urban streets using a one‐dimensional transport equation model.

This paper presents a one‐dimensional transport equation model for acoustic field predictions in urban streets. Considering urban streets as elongated enclosures, acoustic properties of the surfaces are typically quite different. For example, the top and two ends are often open and the streets are usually reflective. A recently developed one‐dimensional transport equation [Jing et al., J. Acoust. Soc. Am. 125, 2735 (2009)] is extended to model non‐uniform absorption and scattering coefficients and is applied to urban streets acoustic predictions. This paper discusses preliminary experimental results obtained from a tenth scale‐model to validate the model.

On the applicability of the spherical wave expansion with a single origin for near-field acoustical holography

The spherical wave expansion with a single origin is sometimes used in connection with near-field acoustical holography to determine the sound field on the surface of a source. The radiated field is approximated by a truncated expansion, and the expansion coefficients are determined by matching the sound field model to the measured pressure close to the source. This problem is ill posed, and therefore regularization is required. The present paper investigates the consequence of using only the expansion truncation as regularization approach and compares it with results obtained when additional regularization (the truncated singular value decomposition) is introduced. Important differences between applying the method when using a microphone array surrounding the source completely and an array covering only a part of the source are described. Another relevant issue is the scaling of the wave functions. It is shown that it is important for the additional regularization to work properly that the wave functions are scaled in such a way that their magnitude on the measurement surface decreases with the order. Finally, the method is applied on nonspherical sources using a vibrating plate in both simulations and an experiment, and the performance is compared with the equivalent source method.

3-D Model of sound pressure field in a meridinal section plane of fruit

A theoretical model was suggested for qualitative evaluation of a sound pressure field in fruit tissue, as affected by ultrasonic probe dimensions and fruit properties. The classic directivity pattern of an ideal fluid model, expressed by Bessel function of the first kind, was extended to include energy dissipation of a real material. The directional characteristics of wave propagation, as influenced by transmitter frequency and diameter, and by fruit properties, were discussed. The model indicates how to select the parameters of the ultrasonic transducer (transducer diameter, frequency and excitation power) to control the magnitude and directivity of the ultrasonic waves in the fruit tissue. The suggested theoretical model represented fairly well the experimental sound wave distribution over the half-cut surface of potato and avocado ( R 2 > 0.862 and 0.977, respectively); the same theoretical model could not represent the sound wave distribution over a half-cut melon. Results of the study were applied in a new probe design for ultrasonic testing of whole fruit.

Modeling the sound field of open spaces using a diffusion equation model

Steady-state and transient sound field modeling of open spaces, such as urban squares, courtyard-type traditional Chinese theaters, is discussed in this paper. It is well known that the application of the statistical room-acoustic theory is strongly limited in this case, because of the high non-uniformity of the absorption coefficient. In this study, a diffusion equation along with a recently proposed modified boundary condition [Y. Jing and N. Xiang, J. Acoust. Soc. Am., 123, 2008, 145-153] is used to predict the acoustic characteristics of open spaces, in terms of both sound pressure level distributions and reverberation times. Three different types of open spaces are presented, including urban squares, quasi-cubic open rooms, and urban streets. This paper will compare the simulation results with the experimental results conducted in all these three cases (scale model), to verify the validity and efficiency of the diffusion equation model.

Measurements of acoustic impedance and their data application to calculation and audible simulation of sound propagation

Acoustic impedance determines the boundary condition of each sound field, but collections of actual values to evaluate sound fields are insufficient. Therefore, measurements of acoustic impedance using a particle velocity sensor were taken on different fields. Such measurement results were used for sound propagation calculations. Frequency characteristics of sound propagation on grass, snow-covered, and porous drainage pavement surfaces showed fair correspondence with field measurement results. Subsequently, fine calculations in the frequency domain were converted to impulse responses for each sound field model. Convolution operations based on the impulse response and on voice, music, and other noise sources readily produced an ideal sound field for the audible sound file. Furthermore, simulations of noise from a car running through a paved drainage area, with noise reduction effects, were attempted as advanced applications.

Sound field modeling in a street canyon with a diffusion equation

The transport theory of sound particles is applied to the sound field modeling in an empty street canyon with partially diffusely reflecting facades. A diffusion equation is then derived to predict the sound field distribution and the sound decay in the street. The main parameter, namely the diffusion coefficient, is a function of the street width and the acoustic reflection laws of both building facades. For a single rectangular street, analytical solutions can be found. For more complex urban spaces, a finite-element based approach is proposed. Several numerical examples are given, like the sound propagation in a street with a nonuniform cros section, and in street intersections, for point and line sources. In comparison with ray-tracing-based models, the diffusion model requires less computation time and could be applied to the calculation of a sound map for large urban areas. However, at the present time, the diffusion coefficient can be calculated only for simple building reflection laws, like the Lambert’s one.

Measurements of acoustic impedance and their application to sound propagation calculations and audible simulations

Acoustic impedance is an important value that determines the boundary condition of each sound field, but collections of actual values are not sufficient for evaluation of many sound fields. First, measurements using a particle velocity sensor for acoustic impedance were tested on various fields. Such measurement results were applied to calculations of sound propagation. Frequency characteristics of sound propagation were obtained along such surfaces as fields of lawns and snow, and areas paved by porous asphalt for drainage. Those characteristics showed fair correspondence with inspected field measurement results. Then, fine calculations in the frequency domain were converted to the impulse response for each sound field model. Convolution operations based on the impulse response and on voice, music, and some noise sources readily produced an ideal sound field to the audible sound file. Furthermore, simulations of the noise, including noise reduction effects from a car running through a drainage pavement area, were executed as advanced applications. Our measurement method of acoustic impedance is inferred to be useful. Calculated sound propagation characteristics based on the measured acoustic impedance correspond to actual propagation characteristics. Audible simulation will be effective as a future means of sound-field evaluation. [Research supported by KAKENHI.]

Sparseness‐based 2ch blind source separation in reverberant environments based on direction‐of‐arrival estimation with a reliability measure

We present a novel sparseness‐based 2ch blind source separation (BSS) method based on robust direction‐of‐arrival (DOA) estimation that enables reasonable separation of source signals even in a highly reverberant environment. DOA estimation for BSS is not easy in reverberant environments since reflected sound waves behave as coherent interferences in the observed signals and make ambiguous the sound source direction. Our key idea to solve this problem is to find and integrate clean, reliable time‐frequency fragments through the observation with a reliability measure. For that, (1) based on a diffused sound field model of reverberation, a theoretical correlation matrix is introduced for whitening the coherent interferences, (2) the DOA of each time‐frequency bin is estimated with reliability by utilizing information of neighboring bins, and (3) the reliability‐weighted DOAs are integrated over the whole time‐frequency bins. After that, separated signals are obtained by time‐frequency masking or inverse filtering. Experimental results including comparison with other methods are also reported.

Sound-field modeling in architectural acoustics by a transport theory: Application to street canyons

The transport theory of sound particles is applied to the sound field modeling in architectural acoustics. A theoretical description is proposed for empty enclosures with complex boundary conditions, including both specular and diffuse reflections. As an example, the model is applied to street canyons. Therefore, an asymptotic approach is proposed to reduce the transport equation to a diffusion equation defined by only one parameter, the diffusion coefficient. This coefficient is a function of the reflection law of the building façades, the ratio of specular and diffuse reflections, as well as the street width. The model is then compared to Monte Carlo simulations of the propagation of sound particles in complex enclosures. As expected by the asymptotic approach, the model is in agreement with numerical results, but mainly for small street width and very diffuse reflections. Finally, a discussion is proposed in the conclusion, on the model's capabilities.

Experimental and theoretical characterisation of sonochemical cells. : Part 2: cell disruptors (Ultrasonic horns) and cavity cluster collapse

Cavitation theory is used to predict the acoustic pressure at the boundary of the inertial/non inertial threshold for a range of bubble sizes. The sound field generated from a commonly employed sonoelectrochemical cell is modelled. The model is tested with a calibrated hydrophone far from the transducer to avoid spatial averaging. This allows the model to provide the absolute pressure amplitude as a function of axial distance from the source. An electrochemical technique for detecting both inertial and non-inertial cavitation within the solution is employed. This technique uses a dual microelectrode to map the boundary between the regions where inertial cavitation occurs (associated with surface erosion), and where it does not. This zone occurs close to the transducer for the microelectrode employed (<1.5 mm). Further characterisation of the inertial cavitation zone is achieved by imaging of multibubble sonoluminescence (MBSL). The pressures at the boundary between inertial and non inertial cavitation that are determined from the electrochemical and imaging experiments are compared to a sound field model and cavitation theory. Qualitative arguments for the invasive nature of the electrode into the sound field are proposed. Evidence for cavity cluster collapse and shock wave emission is presented and discussed in relation to luminescence, the electrochemical experiments and cavitation theory.

Sound field modeling in a street canyon with partially diffusely reflecting boundaries by the transport theory

The transport theory, applied to the concept of sound particles, seems to be well adapted to predict the sound propagation in urban areas, including most complex effects, like diffuse scattering by building facades, atmospheric attenuation, scattering by urban objects in streets, etc. In this paper, the transport theory is then applied to the sound field modeling in an empty street canyon with partially diffusely building facades. In this case, the temporal and spatial distribution of sound energy in a street is the solution of a transport equation, with mixed specular-diffuse boundary conditions. Using an asymptotic approach, the transport equation may be reduced to a diffusion equation for the sound energy, where the diffusion coefficient depends only on the building facades properties. Comparisons with experiments show that the diffusion model gives consistent results with experimental data, both for the sound attenuation level and the reverberation time.

Reverberated sound field modeling in coupled rooms using a diffusion equation

Sound modeling in coupled rooms has attracted considerable attention in the past, but accurate and operational models are still needed. In recent papers, a diffusion equation based model has been applied with success to unusual room shapes. This approach allows nonuniform repartition of energy, and is especially relevant in room acoustics for long rooms or complex spaces such as networks of rooms. The present work aims at validating the behavior of the diffusion model in the case of two acoustically coupled rooms separated by an open area. In this purpose, the time-dependent diffusion equation is solved in three dimensions using a finite-element solver. It allows one to predict both sound attenuation and reverberation time at any point of the coupled rooms. Parameters influencing the coupling, i.e., room relative sizes, aperture size and room absorption areas, are investigated. Results are then compared with the classical statistical theory of coupled rooms. Finally, a comparison with experimental data in two coupled classrooms is also provided.

Computer modeling of sound fields in the ocean with fine-structured inhomogeneities

The results of a computer modeling of sound propagation in the ocean with fine-structured inhomogeneities are presented. The modeling was performed using a wave code based on the wide-angle approximation, which allows one to estimate the effects of sound field perturbations. These effects include the insonification of the geometric shadow zones and the abnormal attenuation of low-frequency sound in the course of its propagation in an oceanic waveguide. Calculations clearly demonstrate that the fine-structured inhomogeneities of the sound velocity considerably affect the sound propagation in the ocean.

A measurement method of the flow rate in a pipe using a microphone array.

A method of measuring the flow rate in a pipe is proposed. The method utilizes one-dimensional acoustic pressure signals that are generated by a loud speaker. A microphone array mounted flush with the inner pipe wall is used to measure the signals. A formula for the flow rate, which is a function of the change of wave number, is derived from a simple mathematical model of sound field in the pipe conveying a viscous fluid. The change of the wave number, which is one of the results caused by flow, is estimated from the recursive relation among the measured microphone array signals. Since measurement errors, due to extraneous measurement noise and mismatch of response characteristics between microphones, exist in the estimated flow rate, a method of compensating the errors is proposed. By using this measurement method, the flow rate can be obtained more accurately than that of our previous method. To verify applicability of the measurement method, numerical simulation and experiments are performed. The estimated flow rates are within 5% error bound.