Sound Field Model Research Articles

Frequency-domain sound field from the perspective of band-limited functions.

A model that approximates the sound field well is useful in various fields, such as acoustic signal processing and numerical simulation. We have proposed an effective model in which the wideband instantaneous sound field is regarded as an element of a spherically band-limited function space, using the reproducing kernel of that space. In this paper, the frequency-domain sound field is regarded as an element of some band-limited function space, and a representation of the field as a linear combination of the reproducing kernel in that space is proposed. This model has the strongest representational capacity of all function systems when we know only the sound pressure information at arbitrary positions. The proposed model can be considered a generalization of the existing three-dimensional sound field model using the reproducing kernel of the solution space of the Helmholtz equation to the spatial dimension. One of the advantages of capturing the frequency-domain sound field in this way is the simplicity achieved for the estimation formula of the wavenumber spectrum. Two numerical simulations were conducted to validate the proposed methods.

Mixed Reality visualization of sound field using the room impulse responses modeled by room geometry and physical model

For room acoustic design and detecting noise problems, the sound field visualization is useful to understand sound propagation in a room. In our previous study, we proposed the Mixed Reality (MR) visualization system for steady sound field with mapping the three-dimensional sound intensities measured by moving a microphone array. To visualize the transient sound field, time-synchronization of multi-point measurements is required. However, the measurement time for the transient sound field becomes significantly larger compared to the stationary sound field. In this study, we proposed the Mixed Reality visualization of sound propagation based on sound field modeling. From smaller measured data, we estimate the transient sound field by spatial interpolation based on the equivalent sound sources and room shape acquired by Simultaneous Localization and Mapping. The estimation results were visualized by MR technology using Microsoft HoloLens2.

Modeling and reproduction of sound field by moving complex sound source

Previously, Wave Field Synthesis (WFS), Near-field Compensated Higher-Order Ambisonics (NFC-HOA), Boundary Surface Control (BoSC), and the Spectral Division Method (SDM) have been proposed as sound field synthesis methods. These methods are based on matching the acoustic physical quantities at the boundary of the reproduced sound field with those of the desired sound field. Sound field synthesis techniques can be classified into data-based and model-based methods. The former aim at reproducing sound fields captured by microphone arrays, while the latter aim at synthesizing sound fields based on mathematical models. Most existing sound field reproduction methods only consider simple sound source models, such as static point sources, instead of sound sources with complex radiation properties. To generate a more realistic sound image, this study investigated the formulation of a sound field generated by a sound source with complex radiation properties moving along arbitrary trajectories in a spherical harmonic domain, and reproduced the sound field using loudspeaker arrays.

Three-dimensional sound field reproduction using reflected sounds based on pressure-matching with equivalent sources

Three-dimensional sound field reproduction generally requires more loudspeakers as the arrival direction of the desired sound increases. In particular, to reproduce the sound field in the vertical direction, the number of loudspeakers is significantly increased. In this study, we propose a three-dimensional sound field reproduction method that use the sound reflections from the floor surface to reduce the number of loudspeakers in the vertical direction. First, the sound field driven by each loudspeaker is modeled by considering the primary reflection. Second, based on the pressure matching method with the loudspeaker sound field models, the sound field is reproduced from the unplaced direction of the loudspeakers using the primary reflected sounds. Via simulation experiments, we evaluate the reproduction accuracy of the proposed method in the horizontal and elevation planes.

A grating lobes suppression method for a steerable parametric array loudspeaker

A parametric array loudspeaker (PAL) is a highly directional sound source with small aperture size. To achieve accurate sound projection, the steerable PAL is implemented by the use of the phased array technology. In this paper, the sound field model based on the Westervelt equation of a practical steerable PAL is presented, and a quasi-linear approximation is adopted to obtain the spatial sound pressure distribution. By applying the phased array technology, the audio beam can steer to the target direction. However, the grating lobe arises when the transducers are spaced more than half a wavelength, which disturbs the effect of beam steering. We further propose the grating lobes suppression method and apply it to the steerable PAL. Simulation results validate the performance of the proposed method.

Sound Field Modelling and Noise Reduction for a Forklift Power Compartment Based on Perfectly Matched Layer and Acoustic Packaging Design

The core goal of this paper is to put forward a feasible scheme of noise reduction for a target forklift on the basis of solving the problem of vibration and acoustic radiation from complex structures in infinite domain. Based on the previous report and vibration acceleration tests, the acoustic virtual wind tunnel model of forklift power compartment was established using finite element method and boundary element method, in which the perfectly matched layer was first applied to simulate the attenuation propagation of sound waves in air. In addition, according to the distribution characteristics of sound pressure field with different frequencies, the acoustic energy mainly radiated through the bottom and right side, and concentrated in the low frequency. Consequently, the acoustic packaging design for the whole forklift power compartment was presented, and a satisfying noise reduction effect was achieved.

An isotropic sound field model composed of a finite number of plane waves

An isotropic sound field model composed of a finite number of plane waves

Towards assessing the impact of anthropogenic sound on fishes: Gaps, perspectives, and a case study of a large floating bridge

Underwater anthropogenic sound can cause physical, physiological, and behavioral impacts on fishes. With the development of marine energy facilities, the impact of man-made underwater sound on fishes has become a growing regulatory concern. Large gaps remain in how to perform an underwater sound assessment. Such gaps mainly reside in scientific evidence, regulatory criteria, sound characterization metrics, sound field modeling, and instrumentation for field measurement. This paper reviewed existing work on underwater sound assessment for fishes to identify critical gaps and provide perspectives on how to deal with these gaps, demonstrated with a case study on the impact of the Hood Canal Bridge traffic sound on migrating steelhead smolts in Washington State, U.S. We also provide perspectives on future research directions to bridge the identified gaps for aquatic ecological assessment.

A Correction Method for the Measurement of Frequency-Dependent Attenuation Coefficient With Curved Surface Specimens Using Normal Contact Transducer

The ultrasonic pulse-echo technique has been widely employed for the measurement of the frequency-dependent attenuation coefficient in polycrystalline metals. However, the nonuniform thickness of the coupling layer between the transducer piston and the curved surface is inevitable for curved specimens, resulting in a significant overestimation. In addition, the curved surface also affects the diffraction loss caused by the divergence and convergence of ultrasonic beams during the propagation path. In this study, a correction method is proposed for the experimental calculation of the frequency-dependent attenuation with the curved surface components using a contact transducer. First, with the analysis of the nonuniform coupling layer created by the curved surface and transducer piston, the integral over the effective cross-sectional area is introduced to determine the reflection coefficient. Second, an equivalent rectangular transducer sound field model is proposed to calculate the diffraction loss for different curvatures and propagation distances based on the multi-Gaussian beam (MGB) theory. Then, a correction model is established to compensate for the deviation caused by the curved surfaces. To verify the feasibility of the proposed method, two cylindrical bars and five blanks with different curvatures were designed. The experimental results show that the proposed correction method can effectively eliminate the deviation caused by the curved surface and improve the stability of measurement. With the correction, the variation of the attenuation spectrum for the curved specimens is reduced by approximately 5%. This facilitates researchers to better develop and use frequency-dependent attenuation coefficients of materials for further applications.

Study on ultrasonic nondestructive evaluation method for grain size of magnesium alloy components with complex profile

In order to solve the problems of difficult measurement, inaccurate results and serious interference of diffusion and attenuation in the nondestructive evaluation of grain size of magnesium alloy components with complex profile, the sound field models of plane, cylindrical and conical parts based on the multiple Gaussian sound beam method are studied, and the attenuation mechanism of ultrasonic propagation in the medium of complex components and the diffusion and attenuation components in curved test blocks are analyzed, An evaluation method of ultrasonic attenuation of grain size based on diffusion loss correction is proposed to eliminate the influence of complex components on the total amount of ultrasonic attenuation. The results show that the ultrasonic nondestructive evaluation method of grain size based on sound velocity diffusion correction can effectively reduce the system error and improve the accuracy of grain size evaluation of magnesium alloy components with complex profile.

Machine-learning-based estimation of absorption coefficients from transfer functions modeled by equivalent sources

In the field of room acoustics, it is important to find the absorption coefficients of the wall surface, which is a boundary condition for modeling the room acoustic field. However, it is not easy to measure the acoustic impedances of the entire room because it requires many measurement points near the wall surface. Recently, a method to estimate the acoustic impedance and absorption coefficients by using both measurement and simulation methods has been proposed. However, a large number of measurement points are required to obtain sufficient estimation accuracy. In this study, we proposed estimation method of the sound absorption coefficients using machine learning with virtually increasing the number of microphones. First, the transfer functions at the virtual microphones are obtained from small number of transfer functions based on the sound field modeling by sparse equivalent sources. Then, the both transfer functions at the virtual and real microphones are used as the training data for machine learning. To evaluate estimation accuracy of the proposed method, we conducted the two-dimensional simulation experiments based on the boundary element method.

Attenuation and dispersion of leaky Rayleigh wave in polycrystals.

In this work, we use the characteristic equation of leaky Rayleigh waves (LRWs) and a unified approach of bulk waves proposed by Stanke and Kino [J. Acoust. Soc. Am. 75, 665-681 (1984)] to calculate the attenuation and velocity dispersion of LRWs in polycrystals. Numerical results demonstrate that the total attenuation including the leakage attenuation and scattering attenuation is proportional to frequency and independent of grain size in the Rayleigh scattering regime. Meanwhile, the variation of phase velocity in all scattering regimes remains at ∼0.7% according to the theoretical expectation; this means that the velocity dispersion of the LRWs can be ignored, consistent with the conventional viewpoint. Measurements are conducted on stainless steel at different ultrasonic frequencies (all in the Rayleigh scattering regime). The non-paraxial sound field model is used here to eliminate the diffraction loss and to obtain the total attenuation. Experimental results verify that LRWs have very little velocity dispersion. Meanwhile, experimental fitting data reveal that the modified theoretical model can be used to evaluate the total attenuation (only ∼2% discrepancies) of LRWs under the consideration of the diffraction effect. The relative errors between experimental scattering attenuation and theoretical value ranged from 11% to 18%, mainly owing to the effect of surface roughness and measurement inaccuracy.

Study on passive location method of shallow water acoustic source with single hydrophone

In order to meet the needs of target detection in shallow water with concealed and low energy consumption platform, the Bayesian estimation theory was applied to underwater acoustic location. The underwater acoustic location model was established based on probability density function as the description of sound source state, so as to overcome the problems of unstable shallow water environment and mismatching of sound field model. Histogram filtering method is used to solve the integral solution in the process of posterior probability estimation of sound source state. The hierarchical grid histogram filtering method is proposed for the first time, which effectively improves the efficiency of histogram filtering iterative algorithm. The measured data and simulation results of SWelleX-96 show that the depth positioning accuracy can reach 35 m and the distance positioning accuracy can reach 0.69 km within the range of 200 m deep and 10 km long in shallow water environment, and the efficiency of the algorithm can be improved by N1/2 times.

Sound Field Modeling Method and Key Imaging Technology of an Ultrasonic Phased Array: A Review

An ultrasonic phased array consists of multiple ultrasonic probes arranged in a certain regular order, and the delay time of the excitation signal sent to each array element is controlled electronically. The testing system model based on ultrasonic propagation theory is established to obtain a controllable and focused sound field, which has theoretical and engineering guiding significance for the calculation and analysis of ultrasonic array sound fields. Perfecting array theory and exploring array imaging methods can obtain rich acoustic information, provide more intuitive and reliable research results, and further the development of ultrasonic phased-array systems. This paper reviews the progress of research on the application of ultrasound arrays for non-destructive testing (NDT) and brings together the most relevant published work on the application of simulation methods and popular imaging techniques for ultrasonic arrays. It mainly reviews the modeling approaches, including the angular spectrum method (ASM), multi-Gaussian beam method (MGB), ray tracing method, finite element method (FEM), finite difference method (FDM), and distributed point source method (DPSM), which have been used to assess the performance and inspection modality of a given array. In addition, the array of imaging approaches, including the total focusing method (TFM), compression sensing imaging (CSI), and acoustic nonlinearity imaging (ANI), are discussed. This paper is expected to provide strong technical support in related areas such as ultrasonic array testing theory and imaging methods.

Scattering characteristics analysis of conformal array based on sound field prediction method

In order to study the problem that the array manifold of conformal arrays deviates from the ideal value due to the sound scattering caused by the rigid baffles of arrays, in this paper, the influence of the scattering phenomenon caused by the rigid baffle on the receiving response of array is analyzed by using sound field prediction method based on a conformal array-semi-cylindrical volume array. The sound field distribution of conformal array at different angles is calculated by using the sound field modeling and simulation. Based on the above distribution, an actual array manifold is constructed under consideration of rigid barrier, and its variation under the influence of scattered sound is analyzed. The variation is described by two physical quantities defined in this paper: the first-order response composed of amplitude and phase and the second-order response composed of cross-correlation. Simulation shows that compared with the ideal model, the scattered signals generated by rigid baffles on conformal array varies with the azimuth and signal-to-noise ratio(SNR), which further leads to the deviation of each hydrophone of conformal array. The experimental data verifies that the simulation results are basically consistent with the actual situation. The effect of the scattering on the conformal array should be considered when designing and performing in practice.

Realizing the second harmonic acoustic focusing based on an artificial bubble array

Ultrasonic imaging technologies possess extensive applications in modern medical diagnosis and treatment. In this paper, a designed artificial bubble array is utilized to establish a multi-scattering sound field model to describe the nonlinear vibration of the artificial bubble array, combining nonlinear acoustics and multi-scattering theory. With the results of the effective medium model, the correctness and reliability of the multi-scattering model are verified. Furthermore, under different incident frequencies and different bubble array parameters, the distributions of fundamental and second harmonic sound pressure fields produced by nonlinear vibration of the artificial bubble array are investigated. Via a judicious design of structural parameters, both fundamental and second harmonic acoustic focusing at specific locations inside the bubble array and second harmonic acoustic focusing outside the array under a specific incident frequency are realized.

Analysis of the sound field above finite absorbers in the wave-number domain.

This study examines the edge diffraction effect when a sound wave impinges and reflects off finite porous absorbers, flush-mounted in an infinite hard baffle. A theoretical analysis of the diffraction is given by taking a two-dimensional spatial Fourier transform of a plane wave impinging on a finite absorber. Numerical experiments are also presented to simulate the sound field above infinite and finite locally reactive absorbers and the measurement with an array of pressure sensors. In such cases, a regularized solution is used to separate the incident and reflected plane wave components, in the wave-number domain, including both propagating and evanescent waves. The properties of the wave-number spectrum are associated either with the specular reflection or with the diffracted components, caused by the interaction of the sound wave with the finite absorber. From the regularized solution, it is possible to reconstruct the surface impedance and the absorption coefficient of the sample. The influence of Gaussian noise on such measurements is also investigated. The use of propagating and evanescent waves on the sound field model led to an estimation of the absorption coefficient that depends just slightly on the size of the sample, which is a desired feature for in situ measurement methods.

Enhancing binaural rendering of head-worn microphone arrays through the use of adaptive spatial covariance matching.

In this article, the application of spatial covariance matching is investigated for the task of producing spatially enhanced binaural signals using head-worn microphone arrays. A two-step processing paradigm is followed, whereby an initial estimate of the binaural signals is first produced using one of three suggested binaural rendering approaches. The proposed spatial covariance matching enhancement is then applied to these estimated binaural signals with the intention of producing refined binaural signals that more closely exhibit the correct spatial cues as dictated by the employed sound-field model and associated spatial parameters. It is demonstrated, through objective and subjective evaluations, that the proposed enhancements in the majority of cases produce binaural signals that more closely resemble the spatial characteristics of simulated reference signals when the enhancement is applied to and compared against the three suggested starting binaural rendering approaches. Furthermore, it is shown that the enhancement produces spatially similar output binaural signals when using these three different approaches, thus indicating that the enhancement is general in nature and could, therefore, be employed to enhance the outputs of other similar binaural rendering algorithms.

Back-projection method with fast time-delay correction for photoacoustic tomography reconstruction based on a focused sound field model

Photoacoustic tomography is a rapidly developing imaging technology, which can provide structural and functional information of biological tissues. It can integrate the advantage of high optical contrast from optical imaging with those from high penetration depth from ultrasound imaging. However, the existing back-projection algorithm in photoacoustic tomography equates the ultrasonic transducer scanning around the target to a point detector, which leads to a notable tangential blur in the eccentric imaging regions, and thus seriously degrading the image quality. In this paper, we propose a novel photoacoustic tomography reconstruction algorithm, which employs a focused sound field equivalent model to overcome the sound field distortion caused by the transducer’ finite aperture effect and can quickly and effectively restore the elongated tangential resolution in the eccentric imaging regions. Simulation results show that for the target with a diameter of 5 mm and a distance of 6 mm from the rotation center, the tangential resolution is improved by at least twice. Experimental results show that this method can effectively restore the image tangential blur in the off-center regions, where the tiny structures of complex targets can be detected. This new method provides a valuable alternative to the conventional back-projection method and plays an important guiding role in the design of photoacoustic tomography systems based on circle/sphere scanning.

Parametric Ambisonic Encoding of Arbitrary Microphone Arrays

This article proposes a parametric signal-dependent method for the task of encoding microphone array signals into Ambisonic signals. The proposed method is presented and evaluated in the context of encoding a simulated seven-sensor microphone array, which is mounted on an augmented reality headset device. Given the inherent flexibility of the Ambisonics format, and its popularity within the context of such devices, this array configuration represents a potential future use case for Ambisonic recording. However, due to its irregular geometry and non-uniform sensor placement, conventional signal-independent Ambisonic encoding is particularly limited. The primary aims of the proposed method are to obtain Ambisonic signals over a wider frequency band-width, and at a higher spatial resolution, than would otherwise be possible through conventional signal-independent encoding. The proposed method is based on a multi-source sound-field model and employs spatial filtering to divide the captured sound-field into its individual source and directional ambient components, which are subsequently encoded into the Ambisonics format at an arbitrary order. It is demonstrated through both objective and perceptual evaluations that the proposed parametric method outperforms conventional signal-independent encoding in the majority of cases.