Point Sound Source Research Articles

Neural-network-based sound source localization from unmanned aerial vehicles

As a mobile platform, unmanned aerial vehicles (UAV) can carry optics and acoustics sensors recording visual and audio information from ground. Over the past decade, UAVs are widely used in different applications, e.g., search and rescue, pipe leakage detection, etc. Compared with visual information, audio information is challenging to capture from UAVs due to the strong ego-noise generated by the rotating motors, propellers on the UAV as well as the motion of the UAV, which result in a low signal to noise ratio (SNR) of the received acoustics signals. With the contaminated signals, the performance of sound source localization algorithms, e.g., conventional beamforming, is severely degraded. To improve the quality of sound source localization result, different sound source enhancement algorithms have been proposed by researchers. In this paper, simulation experiments were conducted to study the potential of apply convolutional neural networks (CNN) to improve the beamforming result. It was found that with CNN, the estimation of a single point sound source location and source strength can be improved. The model's localization accuracy and source strength estimation accuracy were evaluated respectively.

Research on the influence mechanism of harmonic components on the noise distribution characteristics of converter transformers

In order to elucidate the sound source characteristics during the noise propagation process of converter transformers, a series of experimental studies were conducted based on finite element simulation and proportional prototype design of converter transformers. It was found that it was unreasonable to equate converter transformers with point sound sources in previous studies. On the contrary, it should be divided into dipole and multipole distribution characteristics. Meanwhile, research has found that the noise distribution of converter transformers exhibits dipole and dipole distribution characteristics under power frequency and harmonic excitation, respectively. The contribution of harmonic components at different frequencies in the formation process of bipolar sound sources was quantified through simulation and experiments, and the key harmonic frequencies for forming multipole sound sources were determined as paired combinations of 5, 7, 11, 13, 23, and 25. Based on the above research conclusions, a noise reduction approach for converter transformers based on bipolar and multipole boundary effects is proposed.

The Vibro-Acoustic Characteristics Analysis of the Coupled System between Composite Laminated Rotationally Stiffened Plate and Acoustic Cavities

In order to study vibro-acoustic characteristics between composite laminated rotationally stiffened plate and acoustic cavities in the coupled system, first-order shear deformation theory (FSDT) and modified Fourier series are used to construct a unified analysis model. The involved coupled systems primarily encompass three types: the coupled system between composite laminated rotationally stiffened plate and cylindrical-cylindrical cavities, spherical-cylindrical cavities, and conical-cylindrical cavities. First, the first-order shear deformation theory and the modified Fourier series are applied to construct the allowable displacement function of the composite laminated rotationally stiffened plate and the allowable sound pressure function of the acoustic cavities. Second, the energy functionals for the structural domain and the acoustic field domain are established, respectively. According to the continuity condition of the particle vibration velocity at the coupling boundary between the composite, laminated cylindrical shell and the enclosed cavity, the coupling potential energy between the stiffened plate and two acoustic cavities is introduced to obtain the energy functional of the coupled system. Third, the Rayleigh-Ritz method is utilized to solve the energy functional and, when combined with artificial virtual spring technology, the suggested theory may be used to study the vibro-acoustic characteristics of a coupled system with arbitrary elastic boundary conditions. Finally, based on validating the fast convergence and correctness of the model, this paper will analyze the impact of crucial parameters on vibro-acoustic characteristics. Furthermore, by incorporating internal point forces and point-sound source stimulation, a steady-state response analysis of the coupled system will be conducted. This research can give a theoretical foundation for the vibration and noise reduction of a vibro-acoustic coupling system.

Investigation on the time/frequency domain prediction model of radiation noise based on the source map

The main exterior noise sources of the high-speed train CRH380AM, such as pantograph and bogie, are studied by using the field test sound imaging data, and the equivalent point source spectrums are obtained here. Then, the prediction model of the exterior train noise is presented by using the moving point sound source radiation model in the time/frequency domain. The correctness and effectiveness of the model are verified by the field test data. The radiation contribution of local noise sources is analyzed by using this model, and the following conclusions are obtained: The largest noise sources are in the bogie areas, which provide the radiation contribution rate of about 80% when the train speed is above 300 km/h. The variation of the maximum radiation noise level can be ignored when the train formation or the pantograph lifting position is changed. The model can evaluate the radiated noise of similar vehicles quickly and accurately, which provides technical reference for acoustic optimization design of high-speed train.

Vibrations of a thin, prestressed, fluid-loaded spherical shell forced by a point sound source

This paper investigates vibrations of and sound scattering by a thin elastic spherical shell when static pressures are different in the fluids inside and outside the shell. The work is motivated by stratospheric balloons being employed to carry acoustic sensors and by the proposed use of large, encapsulated gas bubbles for passive suppression of underwater sound [O. A. Godin and A. B. Baynes, J. Acoust. Soc. Am., 143, EL67–EL73 (2018)]. Linearized equations of motion of thin, prestressed shells are derived from first principles. Differences in the fluid-loading terms from previously proposed ad hoc models are identified and their significance is analyzed. Analytic solutions are derived for vibrations of a spherical shell excited by an incident spherical sound wave and for acoustic fields in the internal and external fluids. The results are verified against exact solutions in several particular cases. The mathematical model of the shell vibrations is applied to characterize the influence of the shell’s material properties on passive suppression of underwater noise and to quantify the effect of wave scattering by the balloon on performance of balloon-borne infrasound sensors in the atmosphere. [Work supported by ONR.]

Vibro-acoustic response of ribbed-panel-cavity systems due to an internal sound source excitation

An analytical solution is presented in this study for the vibro-acoustic analysis of a cavity coupled with a ribbed panel due to an internal point sound source excitation. The solution is validated by comparing the result with that obtained using finite element analysis. Generally good agreements are found between the results. The model is then used to examine the sound transmission either through a single ribbed–panel or multiple ribbed–panels separated by air gaps. Results demonstrate that the rib enhancement is effective to reduce the energy transmission controlled by the panel control modes. Whereas the attenuation of the energy transmission to the panels is more effective for the cavity control modes when multiple ribbed panels with air gaps are used. The result also shows that the depth of the air gaps will also play a part on the sound attenuation across the panel system where a larger air gap will lead to a better sound attenuation.

Scaling of the simulated pass-by measurement based on the vehicle's acoustic centre

Preliminary work by the IPEK - Institute of Product Engineering at KIT has shown that the simulated pass-by measurement for exterior noise homologation of vehicles has relevant optimization potential: the measurement can be carried out in smaller halls and with a smaller measurement setup than required by the standard and thus with less building construction cost and measurement effort. A prerequisite for this, however, is the scaling of the entire setup. For the scaling to work correctly, the sound sources of the vehicle must be combined to a single point sound source - the acoustic centre. Therefore, in a preliminary work, the IPEK developed a method, with the help of which the dominant sound sources of a vehicle can be localized and combined to an acoustic centre. In this work, the method is applied exemplarily on two test vehicles and their acoustic centres are determined. Afterwards, the measurement setups for both vehicles are scaled based on the acoustic centres, Finally, the simulated pass-by measurement with the scaled measurement setup is performed on an acoustic roller test bench and the scaled sound pressure levels are determined. To verify the overall method, the results of the scaled pass-by measurements are compared with the unscaled one and with measurements on the test track.

Dynamically adjustable directional acoustic radiation based on non-uniform cylindrical labyrinth structure

In this work, a cylindrical four-channel non-uniform labyrinth structure is constructed. The ring shaped metamaterial designed by using the rotational anisotropy of the structure can control sound wave and achieve dynamically adjustable directional sound radiation. The cylindrical non-uniform labyrinth structure comprised of four channels has dipole resonance characteristic. At the dipole resonance frequency, sound waves can radiate from the openings of two sector channels that occupy a large proportion. At this time, the cylindrical non-uniform labyrinth structure can be approximately regarded as a dipole sound source. For the cylindrical uniform labyrinth structure, the sound transmission property will not change as it rotates around its center. However, when the cylindrical non-uniform labyrinth structure rotates around its own center, the position of the dipole sound source and the direction of the radiated sound wave also change. Placing a point sound source in the center of the circular metamaterial composed of 18 non-uniform labyrinth structures, and adjusting the rotation angle of the circular non-uniform labyrinth structure so that each structure lies in the conductive or cut-off state, the propagation of the point sound source in all directions can be controlled. The propagation characteristics of these structures are utilized to achieve dynamically adjustable directional sound radiation. In addition, the influence of the rotation angle of the cylindrical non-uniform labyrinth structure on the transmitted sound wave is studied, and the switching effect of the non-uniform cylindrical labyrinth structure in the constructed sound source system is explored, which provides a new idea for constructing simple directional radiation acoustic equipment.

Analysis on the seismic wave caused by low frequency sound source in shallow sea based on multi-transmitting formula artificial boundary

The elastic waves propagating in seabed caused by sailing ships are called ship seismic waves, which can be used to identify ship targets. The wave components and the influences of source frequency, source depth and depth of seawater to the seismic waves are important to the application of seismic wave to detect ship targets. Thus, a forward numerical simulation of seismic waves in shallow sea excited by low frequency sources in time domain was carried out with finite element method based on the Multi-Transmitting Formula artificial boundary. The numerical results show that the body waves and conical waves decay faster in space, but the interface wave decays relatively slow. Multi-transmitting Formula (MTF) artificial boundary has achieved good transmitting effect for longitudinal wave, upstream and downstream acoustic wave and transverse wave. When the source frequency is very low and the seawater layer is shallow, due to the effect of low-frequency cutoff, there is no normal mode wave which can propagate without attenuation in the seawater waveguide, and only the interface wave is propagating near the sea bottom surface. When the frequency of the source or the depth of the seawater layer increases, the effect of low frequency cutoff in the shallow water waveguide is weakened, and the normal mode waves propagating in seawater layer are gradually excited. The intensity of the interface wave caused by low-frequency point sound source mainly depends on the distance between the source and the seafloor.

Element Differential Method for Computational Acoustics in Time Domain

In this paper, a new robust numerical method, named element differential method (EDM), is developed to solve computational acoustic problems in time domain. The key aspect of the method is the direct differentiation of shape functions of the isoparametric elements used to characterize the geometry and physical variables, which can be utilized to evaluate the spatial partial derivatives of the physical variables appearing in the governing equations and boundary conditions. Moreover, a unique collocation technique is proposed to form the system of equations, in which the governing equation is collocated at internal nodes of elements and the acceleration equilibrium equation is collocated at interface nodes between elements and outer surface nodes. EDM is a strong-form numerical method that doesn’t require a variational principle or a control volume to set up the computational scheme, and no integration is performed. Based on the Newmark difference technique, a time marching solution scheme is developed for solving the time-dependent system of equations. For the point sound source expressed in terms of the Dirac function, a sound source density function is proposed to approximate the point sound source to make it handleable in EDM. Three numerical examples are given to demonstrate the correctness and application potential of the developed method.

Acoustic field characteristic analysis of the rotary acoustic cavity coupled system

The rotary acoustic cavity coupled system can be generated in working conditions of aviation, aerospace, ship, machinery, and other fields. The rotary acoustic cavity includes cylindrical, spherical, and conical acoustic cavities, which integrates into the unified analysis model by iso-parametric transformation in finite element method. To study the acoustic field characteristic of rotary acoustic cavity coupled system, a unified analysis model of rotary acoustic cavity coupled system is established: First, the acoustic field characteristic of the coupled system is researched by improved Fourier series method, and the admissible sound pressure function is constructed by three-dimensional modified Fourier series. Then, the acoustic field domain energy functional is established, and the coupled domain energy functional including the coupled potential energy between the sound cavities is introduced to acquire the total energy functional of the coupled system. Finally, the energy equation is solved by Rayleigh–Ritz method, and the natural frequency and corresponding mode of the coupled system are obtained. The unified analysis model demonstrates excellent convergence and accuracy, which is verified by the results of finite element method. Sound pressure responses of the coupled system are obtained by introducing the internal point sound source excitation. The effect of relevant parameters of the coupled system on natural frequency and sound pressure response is investigated, which can provide theoretical guidance for vibration and noise reduction.

On Diffraction of a Point Sound Source by an Infinite Wedge

On Diffraction of a Point Sound Source by an Infinite Wedge

Vibro-acoustic characteristics analysis of the rotary composite plate and conical–cylindrical double cavities coupled system

PurposeThe purpose of the study is to obtain and analyze vibro-acoustic characteristics.Design/methodology/approachA unified analysis model for the rotary composite laminated plate and conical–cylindrical double cavities coupled system is established. The related parameters of the unified model are determined by isoparametric transformation. The modified Fourier series are applied to construct the admissible displacement function and the sound pressure tolerance function of the coupled systems. The energy functional of the structure domain and acoustic field domain is established, respectively, and the structure–acoustic coupling potential energy is introduced to obtain the energy functional. Rayleigh–Ritz method was used to solve the energy functional.FindingsThe displacement and sound pressure response of the coupled systems are acquired by introducing the internal point sound source excitation, and the influence of relevant parameters of the coupled systems is researched. Through research, it is found that the impedance wall can reduce the amplitude of the sound pressure response and suppress the resonance of the coupled systems. Besides, the composite laminated plate has a good noise reduction effect.Originality/valueThis study can provide the theoretical guidance for vibration and noise reduction.

Sound field reconstruction method of spatial point sound source to accurately calibrate microphone arrays

The common methods to calibrate microphone array are those that calibrate each microphone. Different from these methods, this article proposes a simulated point sound source calibration method without calibrating each microphone. Suppose there is a microphone array in the sound field of the point source, according to the positional relationship between the array and the source, the dynamic sound signal of every microphone can be calculated. A microphone array calibration device (MACD) is designed to input the dynamic signals calculated into the actual microphone array by the coupling cavity standard sound sources. By comparing the position of the simulated point source with that located by array, position error correction curves are fitted to calibrate the positioning accuracy of microphone array. The experimental results reveal validity of the proposed method.

A point sound source location and detection method based on 19-element hemispheric distributed acoustic pressure sensor array

To solve the key problem of diagnosing the operating condition of an oil transfer pump unit in a 3D closed space, this paper presents an approach for a point sound source location and detection method based on a hemispheric distributed sound pressure sensor array. The array model consists of 19 sound pressure sensors acting in the radial direction and uniformly distributed over the hemispherical surface. A spatial rectangular coordinate system is established by taking the projection point of the central sensor arranged at the apex of the hemisphere to the ground as the origin of the spatial coordinates. With reference to the central sensor, the point sound source is located by selecting the maximum measured sound level and its spatial coordinate in each of the three layers of sensors surrounding it as parameters and using a triangular or a quadrilateral area location algorithm based on virtual instrument technology. According to the location of the source, the A-weighted sound level of the sound source point is derived by the inversion of the sound field distribution law. Results show that the triangular and quadrilateral area location algorithms are both effective. The errors in location become larger for a measured sound source far from the centre.

Method for localisation of sound sources and aggregation to an acoustic centre

Preliminary work by the IPEK - Institute of Product Engineering at KIT has shown that the simulated pass-by measurement for exterior noise homologation of vehicles has relevant optimization potential: the measurement can be carried out in smaller halls and with a smaller measurement setup than required by the norm and thus with less construction cost and effort. A prerequisite for this however is the scaling of the entire setup. For the scaling in turn, the sound sources of the vehicle must be combined to a single point sound source - the acoustic centre. Previous approaches for conventional drives assume a static centre in the front part of the vehicle. For complex drive topologies, e.g. hybrid drives, and unsteady driving conditions, however, this assumption is not valid anymore. Therefore, with the help of an acoustic camera, a method for localizing the dominant sound sources of the vehicle and a software-based application for summarizing them to an acoustic centre were developed. The method is able to take into account stationary, unsteady and sudden events in the calculation of the acoustic centre, which is moved as a result. Using substitute sound sources and two vehicles, the method and the used measurement technology were examined and verified for their applicability.

Deep learning-enhanced single point sound source localization for spherical microphone array

In this contribution, we present a high-resolution and accurate sound source localization via a deep learning framework. While the spherical microphone arrays can be utilized to produce omnidirectional beams, it is widely known that the conventional spherical harmonics beamforming (SHB) has a limit in terms of its spatial resolution. To accomplish the sound source localization with high resolution and preciseness, we propose a convolutional neural network (CNN)-based source localization model as a way of a data-driven approach. We first present a novel way to define the source distribution map that can spatially represent the single point source's position and strength. By utilizing paired dataset with spherical harmonics beamforming maps and our proposed high-resolution maps, we develop a fully convolutional neural network based on the encoder-decoder structure for establishing the image-to-image transformation model. Both quantitative and qualitative results are demonstrated to evaluate the powerfulness of the proposed data-driven source localization model.

Electroacoustic analysis of a directional moving-coil microphone using combined lumped-parameter models and BEM

This article presents a lumped-parameter model combined with external sound pressure field simulation, based on the boundary element method (BEM) for utilization in a directional microphone. A study about microphone capsule of a typical handheld moving-coil microphone with hyper-cardioid pattern has been conducted. In the BEM simulation, a simplified 3D model of the capsule that met sound waves which radiated from a point sound source has been taken into account. The blocked average pressure at the openings of the capsule is used to drive the lumped element equivalent circuit model. Through the model, the sensitivity, directivity, and impedance of the microphone were analyzed. Hence, the proximity effect is observed and discussed. To verify our simulation, the microphone characteristics were experimentally measured by B&K devices with SoundCheck software in an anechoic chamber. The simulation data are in good agreement with the measurement data at low and medium frequencies below 13 kHz, and there were larger errors at higher frequencies, which may indicate that the lumped parameters is less applicable at higher frequencies. The proposed method gains more precise and comprehensive prediction for the microphone characteristics, which therefore could be utilized in optimizing the choice of materials and size of the microphone capsule design.

Experimental study on a compact lined circular duct for small-scale propeller noise reduction

In a recent work by the authors, an optimal sound absorber with a compact scale consisting of multiple inhomogeneous Helmholtz resonators with extended necks (HRENs) was designed and demonstrated for effective sound absorption in a prescribed frequency range. The development of HREN-based absorber provides a promising potential for sound absorption in a compact dimension. The present study aims to line the compact optimal absorber in a circular duct for noise attenuation. A rigid duct with the same configuration is fabricated for comparison. The acoustic performances of the lined duct and the rigid duct are experimentally evaluated by using two linear microphone arrays in an anechoic chamber. Two types of noise sources are considered: a point sound source and a rotating propeller. The experimental results reveal that a significant noise reduction is achieved by the lined duct for both the point source and the propeller noise source in the target frequency range when comparing to the rigid duct.

Propagation characteristics of low-frequency acoustic wave in full waveguide of shallow water based on time-domain finite element method

In order to clarify the propagation mechanism and characteristics of low-frequency sound signals in shallow sea with elastic bottom, using the Time-domain Finite Element Method (TDFEM), a time-domain numerical calculation model of the low-frequency sound field in shallow sea full-waveguide under the action of a point sound source is established. With this model, The influence of seabed acoustic parameters’ and seabed topography’ changes on the sound propagation characteristics in full-waveguide is simulated and analyzed. The results show that when there is a shear wave effect on the seabed, low-frequency sound waves will excite the Scholte wave propagating on the bottom boundary of the seabed. The greater the seabed acoustic impedance, the faster the excited Scholte wave velocity and the large the amplitude. At the same time, there will be acoustic energy leakage phenomenon in the inclined seabed.