Sound Intensity Distribution Research Articles

Deep-water ambient sound over the Atlantis II seamounts in the Northwest Atlantica).

Ambient sound was continuously recorded for 52 days by three synchronized, single-hydrophone, near-bottom receivers. The receivers were moored at depths of 2573, 2994, and 4443 m on flanks and in a trough between the edifices of the Atlantis II seamounts. The data reveal the power spectra and intermittency of the ambient sound intensity in a 13-octave frequency band from 0.5 to 4000 Hz. Statistical distribution of sound intensity exhibits much heavier tails than in the expected exponential intensity distribution throughout the frequency band of observations. It is established with high statistical significance that the data are incompatible with the common assumption of normally distributed ambient noise in deep water. Spatial variability of the observed ambient sound appears to be controlled by the seafloor properties, bathymetric shadowing, and nonuniform distribution of the noise sources on the sea surface. Temporal variability of ambient sound is dominated by changes in the wind speed and the position of the Gulf Stream relative to the experiment site. Ambient sound intensity increases by 4-10 dB when the Gulf Stream axis is within 25 km from the receivers. The sound intensification is attributed to the effect of the Gulf Stream current on surface wave breaking.

Research on Distribution of Sound Field Intensity in Substation Based on Noise Array Monitoring Sensor

Research on Distribution of Sound Field Intensity in Substation Based on Noise Array Monitoring Sensor

Phase space representation of sound field excited by a noise source in underwater acoustic waveguide.

The analysis of the field excited in a waveguide by a point noise source is performed using the phase space representation of this field given by the distribution of its amplitude in the depth-angle-time space. The transition from the traditional description of the field amplitude as a function of depth and time to phase space representation is performed using the coherent state expansion developed in quantum mechanics. In this paper, the correlation function of noise signals arriving at different points of the phase plane depth-angle is investigated. Numerical simulation data show that measurements of signal correlations in phase space, performed with the help of a receiving vertical antenna, can be used as input data in solving the problem of source localization and reconstruction of unknown parameters of the sound speed profile. It is shown that in phase space there is an analog of the classical interference pattern observed in the distribution of sound intensity in the distance-frequency plane. The slopes of striations in this interference pattern, as in the conventional one, are given by the Chuprov waveguide invariant.

Structure of interferogram and hologram of non-moving source in presence of shallow water internal waves

The results of holographic signal processing of the oceanographic experiment SWARM-95 on the coast of New Jersey are presented in the paper. The used acoustic signals were obtained on stationary acoustic track (non-moving airgun source) in the presence of shallow water intensive internal waves (IIW). The IIW led to significant 3D acoustic effects [Badiey et al., JASA 117(2), 613–625]. Within framework of holographic signal processing [Pereselkov and Kuz’kin, JASA 151(2), 666–676] the source interferogram (sound intensity distributions in frequency-time coordinates) is analyzed by two-dimensional Fourier transform (2D-FT). The result of the 2D-FT is called the Fourier hologram (source hologram). In result of holographic signal processing, the two separated sets of spectral spots are obtained in hologram domain. The first set of spectral spots corresponds to sound field in nonperturbed waveguide (without of IIW). The second set of spectral spots in hologram corresponds to hydrodynamic field perturbation by IIW. This structure of the hologram allows the reconstruction of interferogram of nonperturbed field for waveguide in the absence of IIW. The error in the reconstruction of the nonperturbed interferogram is estimated. [Work supported by grant from the Russian Science Foundation 23-61-10024.]

Design and performance of ultra-broadband composite meta-absorber in the 200Hz-20kHz range

In this study, a composite meta-absorber with a flexible size is proposed, and a genetic algorithm is used to optimize the geometric dimensions under normal incidence and free field conditions. With an overall thickness of 0.2 m, the quasi-perfect sound absorption is achieved in the 200 Hz - 20 kHz range. The sound pressure and sound intensity distributions inside the composite meta-absorber prove the incident sound wave is effectively localized inside the structure. Comparing the effective sound velocities in layers 1 and 10 with the sound velocity in air, it is possible to infer that the slow sound phenomenon is more pronounced at the bottom of THE composite meta-absorber, due to the different combinations of lateral plates and cavities. The coupling relationship between internal loss and radiation loss of the meta-absorber was revealed using the zero and pole method, proving the ultra-broadband and quasi-perfect sound absorption characteristics. Tests of the sound absorption coefficient in impedance tubes and reverberation chambers confirm the effective broadband sound absorption performance. The composite meta-absorber in this study can be directly used to reduce broadband noise. Moreover, it also provides ideas for the design of sound-absorbing metamaterials.

Three-Dimensional Modeling of Sound Field Holograms of a Moving Source in the Presence of Internal Waves Causing Horizontal Refraction

In this paper, we study the variations of holograms of a moving source in an inhomogeneous ocean waveguide. It is assumed that intense internal waves (internal solitons) are the reason for the inhomogeneities of the shallow water waveguide. The results of 3D modeling of the sound field considering horizontal refraction by internal waves are presented. In the context of 3D modeling, the interferogram (sound intensity distributions in frequency–time coordinates) and hologram (2D Fourier transform of the interferogram) of moving sources are analyzed. The hologram consists of two disjoint regions corresponding to the unperturbed field and the field perturbed by internal waves. This structure of the hologram allows for the reconstruction of the interferogram of the unperturbed field in a waveguide in the absence of intense internal waves. The error in the reconstruction of the unperturbed interferogram is estimated.

A study on non-destructive testing of geometrical parameters of self-piercing riveting joints using an acoustic microscope with a scanning focusing converter

ABSTRACT A non-destructive technique was proposed for geometrical parameters’ measurement of self-piercing riveting (SPR) joints based on ultrasonic C-scan image. Firstly, in order to enhance the detection precision, the characteristics of the ultrasonic echo signal at the edge of internal structure were analysed, and a theoretical formula on its sound intensity distribution was established. Then, an image segmentation process for the detection of SPR expansion diameter was suggested. Results showed that taking the greyscale value at the ‘inflection point’ from the C-scan image as the threshold of the segmentation, the non-destructive test results can get good correlation with the metallographic cross section, which provides a new method on the quality evaluation of SPR by using non-destructive test.

Acoustic far-field prediction based on near-field measurements by using several different holography algorithms.

Near-field acoustical holography (NAH) is a useful tool for sound field reconstruction and sound source identification. In NAH, a basis model is first selected to represent the physical sound field, and then a near-field measurement is made with a microphone array. Next, the parameters in the selected model can be estimated based on the measurements by using an inverse approach, resulting in the sound field near the source being reconstructed so that the sound source location can be identified. But, in addition to being able to reconstruct the near-field of a source, the far-field can also be predicted with the identified sound source model. A significant amount of work has been performed to study the near-field reconstruction capability of different NAH algorithms, but there has been a limited number of publications in which the far-field prediction accuracy, based on the near-field measurement constructed model, has been considered. In the present experimental work, two multi-transducer loudspeakers were placed side-by-side to create a multi-component sound source, and two sets of measurements were conducted: an intensity probe scanned the sound field generated by the loudspeakers in both the near-field (0.05 m) and far-field (0.48 m) such that the true near- and far-field intensity spatial distributions and total sound power could be identified. Then, based on the near-field pressure measurements, four acoustical holography algorithms, statistically optimized near-field acoustical holography, wideband acoustical holography, l1-norm minimization, and a hybrid compressive sampling method were used to predict the near- and far-field sound intensity distributions. The near- and far-field prediction results were compared with the direct measurement, and the sound field reconstruction accuracy was studied. It was found that all of the algorithms were able to reconstruct the near-field well when the near-field measurements were used to construct the model. It was found that with the abovementioned models, far-field reconstructions could correctly predict the spatial sound field distribution, but in all of the cases, the total sound power was underestimated.

Analisis Akustik Bunyi Sibilant Bahasa Jepang pada Pembelajar Bahasa Jepang di Indonesia yang Berbahasa Ibu Bahasa Jawa

Abstract
 This study aims to analyze the characteristics of Japanese sibilant sound observed from the acoustic analysis. The data of this study were in the form of sound samples from 16 respondents who spoke Javanese in Japanese language learners at the university and 8 Japanese native speakers. The respondents were asked to pronounce vocabulary containing Japanese sibilant sounds at the beginning and middle of a total of 72 words which have meaning. Then, the sample of Indonesian and Japanese respondent's sound was measured using Praat software to find their duration, intensity and Center of Gravity (CoG) of the sibilant sound. The measurement results are carried out an analysis of 2 factors, namely consonant type and sound position, using anova statistics. The duration, intensity and Center of Gravity measurement results show that the two factors (consonant type and sound position) are statistically significant. The distribution of sibilant sound duration is from 68 ms to 144 ms, and the distribution of sibilant sound intensity is from 50 dB to 60 dB. The results of the Center of Gravity (CoG) measurements show that among the learners, the CoG values ​​are in the average range of /s/ = 7 kHz, /z/ = 6 kHz, /ɕ/ = 5 kHz, and /ʑ/ = 4 kHz, while among the native speakers, the CoG values ​​are in the average range of /s/ = 8 kHz, /z/ = 8 kHz, /ɕ/ = 6 kHz, and /ʑ/ = 6 kHz.
 Key words: (a) acoustic analysis, (b) Japanese sibilant, (c) duration, (d) Center of Gravity (CoG)

Study on noise characteristics of a novel equal-thickness screen

As the key unit in coal preparation and utilization, equal-thickness screens characterized by a large capacity and high efficiency have been extensively applied in coal preparation plants. Recently, the noise pollution caused by the screening of coal has become more and more serious. Reducing the noise of vibrating screens is the key to control the noise of coal preparation plants. In this article, the noise test system was used to measure three-dimensional (3D) sound intensity of the equal-thickness screen. According to the analysis of sound intensity distribution and spectral coherence, the main sources of noise were identified. The main sources of noise of equal-thickness screen were vibration motors, side panel, screen surface and damping supports. A displacement model was fitted to the experimental data, and the kinematics of the sieve body was studied. The results showed that the amplitude of the sieve body decreased as the distance from the feeding end (towards the discharge end). Similarly, the intensity of the noise decreased about 2 dB in the same direction (from the feeding end to discharge end). However, in the direction perpendicular to the movement of the material, the noise distribution was symmetrical. Finally, various noise reduction measures were also put forth. It could be seen that when the composite spring was adopted as the damping support and the structures of vibration motors, screen surface and side panel were changed, the noise could be effectively reduced.

Intensity Based Spatial Soundfield Reproduction Using an Irregular Loudspeaker Array

Sound intensity is an acoustic quantity closely linked with human perception of sound location, and it can be controlled to create a high level of realism to humans in soundfield reproduction systems. In this article, we present an intensity matching technique to optimally reproduce sound intensity over a continuous spatial region using an irregular loudspeaker array. This avoids several known limitations in the previous works on intensity based soundfield reproduction, such as a single sweet spot for the listener and a regular loudspeaker geometry that is difficult to implement in real-world applications. In contrast to the previous works, the new technique uses a cost function we built to optimize sound intensity over space by exploiting spatial sound intensity distributions. The spatial sound intensity distribution is represented by spherical harmonic coefficients of sound pressure, which are widely used to describe a spatial soundfield. Compared to the conventional spatial soundfield reproduction method of pressure matching in the spherical harmonic domain and the HOA $max$ - $r_E$ decoding method optimizing sound intensity at a single position, we show that the intensity matching technique has better overall performance with two different irregular loudspeaker layouts through simulations. The impact of microphone noise on reproduction performance is also assessed. Finally, we carry out perceptual localization experiments to validate the proposed method.

Estimating Traffic Intensity Employing Passive Acoustic Radar and Enhanced Microwave Doppler Radar Sensor

Innovative road signs that can autonomously display the speed limit in cases where the traffic situation requires it are under development. The autonomous road sign contains many types of sensors, of which the subject of interest in this article is the Doppler sensor that we have improved and the constructed and calibrated acoustic probe. An algorithm for performing vehicle detection and tracking, as well as vehicle speed measurement, in a signal acquired with a continuous wave Doppler sensor, is discussed. A method is also experimentally presented and studied for counting vehicles and for determining their movement direction by means of acoustic vector sensor application. The assumptions of the method employing spatial distribution of sound intensity determined with the help of an integrated three-dimensional (3D) sound intensity probe are discussed. The enhanced Doppler radar and the developed sound intensity probe were used for the experiments that are described and analyzed in the paper.

Fundamental study on enlarge of a loop-tube-type thermoacoustic system—Measurement of onset temperature and sound field in cross-sectional area change

We have worked to improve the output of the thermoacoustic system to expand the range of system applications. The onset temperature of a loop-tube-type thermoacoustic system was experimentally examined under changes to cross-sectional area in a loop tube. The total length of the system was not varied. This cross-sectional area, i.e., inner diameter was set to values of 24.2, 42.6, and 95.6 mm; onset temperatures at these diameters were found to be 623, 329, and 121 °C, respectively. The sound field in the system was measured to investigate the reason why the onset temperature varies depending on the inner diameter. The sound pressure distribution, particle velocity distribution, sound intensity distribution, and phase difference distribution of sound pressure and particle velocity in the system required for evaluation of the thermoacoustic system were measured. It is confirmed that the sound field is different depending on the inner diameter. It is found that the oscillation frequency is different depending on the inner diameter. The oscillation frequency of system with an inner diameter of 24.2 mm shows two-wavelength resonance. The oscillation frequencies of the other system showed one-wavelength resonance. In addition, dissipation is confirmed to increase as the inner diameter decreased.We have worked to improve the output of the thermoacoustic system to expand the range of system applications. The onset temperature of a loop-tube-type thermoacoustic system was experimentally examined under changes to cross-sectional area in a loop tube. The total length of the system was not varied. This cross-sectional area, i.e., inner diameter was set to values of 24.2, 42.6, and 95.6 mm; onset temperatures at these diameters were found to be 623, 329, and 121 °C, respectively. The sound field in the system was measured to investigate the reason why the onset temperature varies depending on the inner diameter. The sound pressure distribution, particle velocity distribution, sound intensity distribution, and phase difference distribution of sound pressure and particle velocity in the system required for evaluation of the thermoacoustic system were measured. It is confirmed that the sound field is different depending on the inner diameter. It is found that the oscillation frequency is different dependi...

Improvement of ultrasonic heat transfer enhancement using acoustical focusing and resonance properties

This paper is aiming to improve the ultrasonic heat transfer enhancement by controlling the sound intensity distribution and constructing an acoustic focusing field, which can reduce energy dissipation and dramatically enhance the local sound intensity of heat transfer surface. Two design criteria are proposed to construct the acoustic focusing field by utilizing acoustic interference and acoustic resonance. Correspondingly, an elliptical acoustic focusing tank is designed and fabricated. Two-dimensional simulation and experimental tests of sound intensity distribution in the elliptical acoustic focusing tank are performed to verify the theoretical conception and design. In addition, the heat transfer coefficients are measured at different locations in the elliptical tank under natural convection, using a square tank as a control. The experimental results show that the elliptical acoustic focusing tank can promote the intensity of the whole sound field, especially the focus region compared with the square tank. The heat transfer coefficient and heat transfer enhancement rate anywhere in the elliptical tank is higher than that in the square tank. The maximum heat transfer enhancement rate of the elliptical tank is 55.3% in natural convection, which is 47.1% higher than that of the square tank under the same condition.

Fast spatial scanning of 3D ultrasound fields via thermography

We propose and demonstrate a thermographic method that allows rapid scanning of ultrasound fields in a volume to yield 3D maps of the sound intensity. A thin sound-absorbing membrane is continuously translated through a volume of interest while a thermal camera records the evolution of its surface temperature. The temperature rise is a function of the absorbed sound intensity, such that the thermal image sequence can be combined to reveal the sound intensity distribution in the traversed volume. We demonstrate the mapping of ultrasound fields, which is several orders of magnitude faster than scanning with a hydrophone. Our results are in very good agreement with theoretical simulations.

Counting and tracking vehicles using acoustic vector sensors

A method is presented for counting vehicles and for determining their movement direction by means of acoustic vector sensor application. The assumptions of the method employing spatial distribution of sound intensity determined with the help of an integrated 3D intensity probe are discussed. The intensity probe developed by the authors was used for the experiments. The mode of operation of the algorithm is presented in conjunction with noise characteristics produced by moving vehicles. The optimization of the algorithm is based on measurements of intensity of sound emitted by the vehicle under controlled conditions. A test setup was built for this purpose with the use of measuring devices installed along a road with varying traffic flow. Reference data on the number of vehicles and traffic directions were prepared employing a recorded video and a reference traffic analyzer operating in lidar technology. It is shown that the developed acoustic method may contribute to an increase of effectiveness of commonly used vehicle counting systems employing inductive loops or Doppler radars. [Project financed by the by the Polish National Centre for Research and Development (NCBR) from the European Regional Development Fund under the Operational Programme Innovative Economy No. POIR.04.01.04-00-0089/16 “INZNAK—Intelligent road signs...”.]A method is presented for counting vehicles and for determining their movement direction by means of acoustic vector sensor application. The assumptions of the method employing spatial distribution of sound intensity determined with the help of an integrated 3D intensity probe are discussed. The intensity probe developed by the authors was used for the experiments. The mode of operation of the algorithm is presented in conjunction with noise characteristics produced by moving vehicles. The optimization of the algorithm is based on measurements of intensity of sound emitted by the vehicle under controlled conditions. A test setup was built for this purpose with the use of measuring devices installed along a road with varying traffic flow. Reference data on the number of vehicles and traffic directions were prepared employing a recorded video and a reference traffic analyzer operating in lidar technology. It is shown that the developed acoustic method may contribute to an increase of effectiveness of common...

Wavepacket modeling of the jet noise source

This study is motivated by the need for physical models for the jet noise source to be used in practical noise prediction schemes for propulsion–airframe integration concepts. The basis for the source model is an amplitude-modulated traveling wave—the wavepacket. The source is parameterized and the parameters are determined by minimizing the difference between the modeled and experimental sound intensity distributions in the far field. Even though the pressure signal that reaches the far field is highly filtered, sufficient information is available to construct a wavepacket with reasonable physical characteristics. A simple stochastic extension of this concept shows a connection between the shape of the far-field sound pressure level spectrum and the emission polar angle. It suggests that the broadening of the spectrum with increasing polar angle from the downstream axis can be explained on the basis of a single noise source (the wavepacket), rather than the prevailing model of two distinct noise sources, one coherent and the other incoherent.

Transmission Loss of Membrane-Type Acoustic Metamaterial with Negative Effective Mass

The transmission loss (TL) of membrane-type acoustic metamaterials consisting of small mass and rubber membrane was studied. By establishing a mass-spring equivalent model of metamaterial structural unit, which regards rubber membrane as having the dual role of damping force and spring force, we demonstrated that effective mass density of this membrane-type acoustic metamaterial was negative in the band gap range by theoretical analysis. Based on the theory of plane wave propagation, we studied the sound insulation of this membrane-type acoustic metamaterial. The result showed that membrane-type metamaterial was based on the principle of dipole resonance, which made the membrane-type acoustic metamaterial appear high reflection and low transmission phenomenon so as to achieve the aim of reducing noise. By optimal design, the sound attenuation frequency range of this membrane-type acoustic metamaterial was reduced to 20Hz-100Hz, greatly enhancing the ability of this metamaterial in terms of low-frequency sound insulation. We obtained the distribution of sound intensity at the optimum transmission frequency and the best reflection frequency by coupled acoustic-structural analysis. The best sound insulation frequency was matched with the second order and the third order eigenfrequency of this membrane-type acoustic metamaterial unit, and the strain energy was concentrated at the joint of small mass and the membrane. The total sound insulation of acoustic metamaterial plate was better than the single metamaterial unit.

Sound Intensity Distribution Around Organ Pipe

Abstract The aim of the paper was to compare acoustic field around the open and stopped organ pipes. The wooden organ pipe was located in the anechoic chamber and activated with a constant air flow, produced by an external air-compressor. Thus, a long-term steady state response was possible to obtain. Multi-channel acoustic vector sensor was used to measure the sound intensity distribution of radiated acoustic energy. Measurements have been carried out on a defined fixed grid of points. A specialized Cartesian robot allowed for a precise positioning of the acoustic probe. The resulted data were processed in order to obtain and visualize the sound intensity distribution around the pipe, taking into account the type of the organ pipe, frequency of the generated sound, the sound pressure level and the direction of acoustic energy propagation. For the open pipe, an additional sound source was identified at the top of the pipe. In this case, the streamlines in front of the pipe are propagated horizontally and in a greater distance than in a case of the stopped pipe, moreover they are directed downwards. For the stopped pipe, the streamlines of the acoustic flow were directed upwards. The results for both pipe types were compared and discussed in the paper.

Near field acoustic holography measurements of carbon nanotube thin film speakers.

Carbon nanotube (CNT) thin film speakers produce sound with the thermoacoustic effect. Better understanding of the physical acoustic properties of these speakers will drive future design improvements. Measuring acoustic properties at the surface of the CNT thin film is difficult because the films, themselves, do not vibrate, are fragile and have a high surface temperature. In order to measure the surface particle velocity and sound pressure level (SPL), near field acoustic holography (NAH) has been used by employing probe microphones. NAH images the acoustic quantities of the source system using the set of acoustic pressure measurements on a hologram parallel to the source surface. It is shown that the particle velocity at the surface of an open-air, double-sided speaker is nominally zero, as expected. However, the SPL distribution is not uniform on the source surface, contrary to common lumped parameter model assumptions. Also, particle velocity and sound intensity distributions on the hologram have been obtained in this study. Finally, measured directivity patterns of the planar CNT speaker are reported.