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Numerical simulation method based on Powell vortex sound theory is adopted to explore the mechanisms of acoustic field distribution characteristics of a centrifugal pump with different blade outlet angles. Results reveal that with the increasing of the angle, the fluctuation range of acoustic source at the tongue in time domain extends, which causes the same fluctuation characteristics of acoustic pressure. As the angle increases from 15° to 35°, the total acoustic source intensity (TASI) and total acoustic pressure level (TAPL) at the tongue increase by 1.68% and 2.54% on average under various rotational speeds, respectively. Additionally, the TASI and TAPL show the similar directivity characteristics under different angles, and the change of the angle has slight effect on the extremum distribution characteristics. Besides, the A-weighted average acoustic pressure level (L p) and A-weighted average acoustic source intensity level (L a) are adopted to describe the overall level of TAPL and TASI. When the angle increases from 15° to 35°, the L a and L p increase gradually and increase by 1.59% and 2.21% on average under various rotational speeds, respectively. The study reveals the acoustic source and acoustic pressure distribution characteristics in time and frequency domain qualitatively and quantitatively, and manifests that the distribution and variation patterns of acoustic source lead to those of acoustic pressure. The conclusions could lay a foundation for the empirical formula proposition between acoustic pressure and acoustic source. [ABSTRACT FROM AUTHOR]

Abstract The three-dimensional (3D) acoustic intensity probe is not popularly used for the source localization of acoustic source because of the large error even though the technique has been well known. In particular, the measured direction-of-arrival strongly depends on the frequency, which is a detrimental drawback that hampers the use of this method. Such spectral bias error, due to the discrete positioning and spacing of sensors surrounding the acoustic center, fluctuates in a nearly regular spectral pattern when a 3D acoustic intensity probe configured in a tetrahedral shape is used. In this work, two error compensation methods are tried: The first method is to adopt a double-module configuration, which is formed by the connected assembly of two intensity modules, but with different locations of acoustic centers for a spatial averaging effect. The second one is the 1/3-octave band averaging of the measured intensity spectrum within the effective measurement range. Because two probe modules are attached, they concatenate 1–3 sensors in the overlap position. Four double-module probes different in assembly configuration of involved two single-modules are tested: modules having a same acoustic center but twisted by 60°, inverted modules sharing one microphone and twisted by 60°, symmetric modules having the joint angle of 60° in the sharing edge, symmetric modules to a common face thus sharing three microphones. Measurements are conducted in an anechoic chamber by changing the source positions for 4 azimuth and 3 elevation angles. The results reveal that the maximum mean bias error of about 4° can be obtained by the double-module 3D acoustic intensity method, depending on the module configuration and angular source position. This contrasts to the fluctuating direction-of-arrival within about ±10° error range, which is obtained by each single-module in a concatenated double-module. In particular, when the band averaging technique is applied to the measured data by the probe module composed of the inverted single modules, the maximum bias error can be reduced to less than 1° in both azimuth and elevation angles. [ABSTRACT FROM AUTHOR]

• Performance analysis of arrays of acoustic vector sensors (AVSs) for underwater surveillance. • Frame hosting the AVSs is not acoustically transparent introducing phase/gain mismatch of signals. • Coherent processing of acoustic intensities at each AVS with adaptive equalization of distortions. • Analysis of real data collected at sea with a bottom node with 2 AVSs and a towed array of 5 AVSs. • Comparison with Cramer-Rao Lower Bound of DOA estimation (the method is asymptotically efficient). This paper introduces a method to coherently combine the signals collected by the directional and omnidirectional channels of an Acoustic Vector Sensor array when the supporting frame is introducing a phase and gain mismatch error. The proposed method adaptively estimates the distortion introduced by the supporting frame and corrects the measurements at the sensors before their coherent combination. The paper evaluates the Cramer-Rao Lower Bound for Direction of Arrival estimation and compares the bound with simulated data and real data collected at sea. The proposed method is asymptotically efficient, reaching the lower bound for sufficiently large values of the signal to noise ratio. [ABSTRACT FROM AUTHOR]

A physics-enhanced multi-plane acoustic hologram deep neural network (PhysenNet_MPAH) approach is proposed for generating multi-plane acoustic hologram. By combining a convolutional neural network with a physical model, the PhysenNet_MPAH approach can generate high-quality acoustic holograms for holographic rendering of targeted acoustic intensity fields at multiple planes. This approach is capable of reconstructing both strong and weak-targeted multi-plane fields, with superior quality compared to traditional iterative angular spectrum approach. The reconstructed multi-plane acoustic fields are also demonstrated to be useful for three-dimensional particles manipulation, indicating potential applications in dynamic particles manipulation and volumetric display. • A physics-enhanced multi-plane acoustic hologram neural network is proposed for generating multi-plane acoustic holograms. • The PhysenNet_MPAH method is able to reconstruct both the strong and weak-targeted multi-plane fields, with superior quality. • The reconstructed multi-plane acoustic fields can be used for 3D particle manipulation. [ABSTRACT FROM AUTHOR]

Acoustic vector sensors (AVS) are increasingly utilized for remote target passive perception, but accurate direction-of-arrival (DOA) estimation remains a formidable challenge, particularly in the presence of heavy background noise. In this paper, we propose a novel DOA estimation method that utilizes complex acoustic intensity measurements (CAIM) and unsaturated bistable stochastic resonance with linear amplitude response constrained (LAR-UBSR). The proposed method aims to exploit the excellent denoising performance of stochastic resonance (SR) to enhance the accuracy of DOA estimation. The proposed LAR-UBSR method is based on the theoretical analysis of the signal pre-processing requirements of CAIM, which determines the linear amplitude response and fixed phase shift. LAR-UBSR achieves a stable phase shift and linear amplitude response by utilizing the unsaturated potential well and limited potential parameters adjustment method of SR. We analyze the amplitude response linearity of LAR-UBSR under different signal-to-noise ratios (SNRs) and a wide range of frequencies, demonstrating a larger linear amplitude response interval that meets the signal pre-processing requirements of CAIM. Numerical analysis and application verification show that the proposed DOA method outperforms existing methods, particularly under low SNR conditions. The results suggest the potential for high-accuracy DOA estimation using nonlinear signal processing strategies in the presence of heavy background noise. • Theoretical analysis underscores the importance of a linear amplitude response and stable phase shift in AVS signal pre-processing for accurate DOA estimation. • The LAR-UBSR method fulfills these pre-processing requirements, expanding the linear amplitude response range across various conditions. • The novel LAR-UBSR enhanced CAIM-based DOA estimation excels, especially in noisy environments. • The effectiveness of the LAR-UBSR enhanced CAIM method was verified through open-lake experiments. [ABSTRACT FROM AUTHOR]

Sound source DOA estimation using first-order differential microphone arrays (DMAs) has been demonstrated as a promising means for the applications where the size of arrays is restricted. The existing methods for DOA estimation of multiple speech sources with first-order DMAs, however, are shown sensitive to noise and room reverberation. To combat the problem, we propose a DOA estimation algorithm by exploring the redundancies of two orthogonal first-order DMAs in sound intensity measurement. In particular, the reliable time–frequency points for DOA estimation can be effectively singled out by the proposed algorithm and thus leads to better DOA estimation performance in noisy and reverberant environments. Moreover, the proposed algorithm has a closed form solution, and no time-consuming search process over spatial space is required. Simulation and real experimental results have demonstrated the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

The authors applied the Finite Element Method (FEM) to analyze the electro-mechanical transformation and micro dynamical characteristics of a piezoelectric panel loudspeaker with triple layered piezoelectric ceramic slices in 2 × 2 rectangular arrangements. According to the simulated micro-vibration data, the authors built an acoustic analysis model combined with a linear superposition method to rapidly obtain the Sound Pressure Level (SPL) frequency response. FEM calculations of resonant modes, resonant frequencies, and the amplitude at the center of the diaphragm were in good agreement with measured values. The measured SPL frequency response agreed with the simulation, supporting the FEM model and the SPL frequency response calculation method proposed in this paper. In addition, an improved structure by addition of an elastic mat was illustrated and demonstrated to provide a smoother low-frequency SPL frequency response verified by both measurement and simulation methods. [ABSTRACT FROM AUTHOR]

It has been known that the application of diffuse field theory to the sound field with a non-single-exponential sound decay did not comply well with listeners’ experience. Recent researches have concentrated on quantifying and controlling the non-single-exponential decay processes in rooms. However, the effect of non-single-exponential sound decay on listeners’ reverberance has not been clearly known in spite of its importance. The present work tried to explore the relationship between the non-single-exponential decay of sound in rooms and the listener’s reverberance, and further to develop a simple way of predicting subjective reverberance caused by non-single-exponential decay processes. A series of listening experiments were carried out with various computer generated non-single-exponential sound decay patterns using a two alternative forced choice (2AFC) paired comparison method. A simple way of predicting listeners’ reverberance for non-single-exponential sound decays was proposed by combining the results of subjective tests and the analysis of Schroeder decay curves using decay rates at multiple fixed intervals and their effects on listeners’ reverberance. The correlation analyses suggested that the proposed method could predict listeners’ reverberance caused by non-single-exponential sound decays better than conventional parameters within the range of non-single-exponential decay patterns examined in the present work. [ABSTRACT FROM AUTHOR]

Noise annoyance due to aircraft flyover noise was assessed under laboratory conditions. The main objectives of the study were: (i) to identify influential acoustical features of noise annoyance, (ii) to propose noise indices to characterize these acoustical features and (iii) to enhance annoyance models including influential acoustical and non-acoustical variables. Therefore, a verbalization task was performed by the participants of the experiment to collect their whole impression concerning the aircraft flyover noises for which they rated annoyance. This verbalization task highlights that noise annoyance was influenced by three main acoustical features: (i) the spectral content, (ii) the temporal variation and (iii) the perceived sound intensity. Four combinations of noise indices were used to propose multilevel annoyance models, in combination with the individual noise sensitivity. Noise sensitivity was found to highly contribute to annoyance models and should therefore be considered in future studies dealing with noise annoyance due to aircraft noise. Different combinations of noise indices coupled with noise sensitivity were found to be promising for future studies that aim to enhance current annoyance models. [ABSTRACT FROM AUTHOR]

Headphone rendering of nearby virtual sound sources represents to date an open issue in 3-D audio, due to a number of technical challenges and temporal requirements involved in the measurement of individual Head-Related Transfer Functions (HRTFs). In order to tackle this problem, we propose a filter model of near-field effects based on the Distance Variation Function (Kan et al., 2009). Thanks to its simple structure and low order, the model can be applied to any far-field virtual auditory display to yield a realistic and computationally efficient near-field compensation of spectral and binaural effects. The model is subjectively evaluated in two psychophysical experiments where the relative distance of pairs of virtually rendered sound sources is judged. Results show that even though sound intensity overshadows subtler near-field effects when it is available as a cue for distance, the model is capable of offering relative distance information of near lateral virtual sources when intensity cues are removed. Furthermore, performances of the model in relative distance rendering are compared to those of alternative near-field rendering methods available in the literature. [ABSTRACT FROM AUTHOR]

A rectangular cavity inside a two-dimensional sonic crystal was theoretically and experimentally characterized by examining its response to a cylindrical source emitting narrow-band filtered noise bursts with central frequencies ranging from 2 to 12 kHz. A broadband intensity resonance was observed for frequencies within the full band-gap region of the sonic crystal (5.5–6.5 kHz). Unlike ordinary resonances, this broadband resonance depends on the reflection properties of the sonic crystal forming the surrounding walls rather than on the geometry of the cavity. [ABSTRACT FROM AUTHOR]

This paper studied the acoustic wave propagation in a waveguide with continuous right-angled corners, with emphasis on the effect brought by the distance between the corners. The numerical analyses showed that at middle to high frequencies, the transmission loss ( TL ) of a multi-cornered waveguide was 2–5 dB higher than that of single-cornered and varied with frequency. To explain the performance at peaks and dips in the TL curve, analyses on eigenmodes and sound intensity distribution were conducted. The performance of multi-cornered waveguides was experimentally investigated, which fit well with the numerical results. The present study indicates that, for a waveguide with continuous corners, its acoustic performance is not simply a “summation” of two individual single-cornered ones. Both the standing wave modes and the evanescent modes between the corners lead to its complicated frequency performance. [ABSTRACT FROM AUTHOR]

• Analytical solution for an acoustic field inside rectangular-cylindrical enclosures. • Complex eigenfrequencies of a rectangular-cylindrical enclosure. • Absorption by an impedance quarter - cylindrical ceiling. • Distribution of the acoustic sound intensity vector. • Acoustic spaces coupled by the continuity conditions. Enclosures with a mixed rectangular-cylindrical geometry are common in sacred, historic and modern buildings. Therefore, obtaining efficient analytical formulas for describing the sound radiation inside such structures is of practical importance. These formulas can be implemented in open-source software and can aid in the analysis of acoustic fields. In this study, the problem of sound radiation by a point source located inside a rectangular enclosure with a sound-absorbing quarter-cylindrical ceiling was analytically solved. The formulas presented in this paper can also be used to obtain the eigenfrequencies and eigenfunctions. To obtain the analytical solution, two connected subregions, namely rectangular space, and quarter-cylinder, were considered, and the continuity conditions were imposed on the region's coupling interface. The acoustic field was described using the solution for a rigid-walled room and the additional components containing the Fourier and Dini series. These components allow the solution to satisfy the impedance boundary condition and the continuity conditions. The formulas and their computer implementation were validated using the finite element method (FEM). A good agreement was achieved between results given by both methods. The numerical analysis demonstrated that the use of the formulas is less time-consuming than using FEM when the frequency is greater than 150 Hz. Moreover, compared to FEM, the analytical solution can be applied to higher frequencies for which the use of FEM requires hardware with high computing capability. [ABSTRACT FROM AUTHOR]

• Simulates a pure sinusoidal plane wave as the reference signal for the p-p intensity probe. • Generates acoustic intensity/particle velocity levels with a known amplitude for intensity instrument calibration. • Accurate and definable reference intensity and particle velocity level traceable to recognized standards, pressure, and time. • Allows multiple choices of spacers or incident angles without dismantling or orienting the probe during calibration. The calibration of sound intensity instruments—in particular, with respect to instruments' sensitivity to both sound intensity and particle velocity in the rated frequency range—is challenging for laboratories worldwide. The commonly used approach is to measure the pressure sensitivity and phase difference of a pair of microphones, and electrically test the analyzer. The intensity instrument cannot be fully calibrated if only the components of the intensity measurement system are calibrated. Ideally, the sound intensity instrument should be calibrated as a system, along with all its parameters being compared with traceability to recognized standards; this will increase the confidence in the validity of measurement results. Currently, calibration below 50 Hz is still not feasible. To meet this requirement, the Beijing Aerospace Institute of Metrology and Measurement Technology has developed a double coupler calibration system capable of generating an intensity or particle velocity level of known amplitude and direction traceable to recognized standards. This paper covers the principle of the double coupler technique, design of the system, and generation of the reference intensity signal. The calibration results are in good agreement with the theoretical calculation results. [ABSTRACT FROM AUTHOR]

• Acoustic intensity equations were derived for an isotropic solid medium. • Simulation results and experimental reverberation time are in good agreement. • The attenuations of bulk waves were retrieved using an inverse problem method. Classical ultrasonic testing (UT) is a method used to evaluate the parameters of materials using mechanical wave. Most of these methods provide local information about the properties of the medium along the direct paths between emitter and receiver. Yet, some of these methods depend on the coda or late reflections, which provide global information about the medium. In this work, a method inspired by room acoustic techniques is proposed to determine medium properties. In fact, the reverberated signal is highly sensitive to mechanical parameters and boundary conditions. In acoustic room theory, which uses these reverberated signals, for determination of the reverberation time which is very useful to enhance the sound quality of rooms. However, this technique only uses one propagation mode, since the wave propagates through the air inside the acoustic room. Considering that a solid medium is analogous to the acoustic cavity, the walls are equivalent to boundary conditions. Firstly, a model is developed to estimate the acoustic intensity of each propagation mode taking into account the coupling due to mode conversion. It allows the reverberation time to be estimated in solid medium. Secondly, an experimental setup is proposed. A five piezoelectric (PZT) patches, randomly distributed on an aluminum block, one acting as an emitter and the others as receivers to perform experimental reverberation time measurements. Finally, a comparison between the simulated and experimental is done, and inverse problem solving is performed to retrieve the attenuations. A good agreement between the retrieved and literature attenuation values of both bulk waves has been observed in aluminum. [ABSTRACT FROM AUTHOR]

• Acoustic discomfort in helicopter cabins can be predicted using internal noise loudness. • The overall discomfort related to noise and vibration in helicopter cabins can be predicted using specific discomfort indicators for noise and for vibrations. • The global discomfort model shows a similar contribution from the two sources with an interaction term which disadvantages comfort if one of the sources is dominant. Noise and vibrations are major sources of discomfort in helicopter cabins and helicopter manufacturers are seeking to estimate passenger discomfort based on noise and vibration measurements. To this end, series of perceptive experiments have been conducted to link subjective assessments of discomfort to objective measurements. Firstly, it has been shown that noise discomfort is governed by perceived intensity and an acoustic comfort equation has been established based on a sound loudness metric. A second series of tests is presented in this document and aims to estimate the global discomfort due to simultaneous noise and vibrations. Discomfort indicators specific to noise and vibrations were used to create a global discomfort equation. This equation shows a similar contribution to the global discomfort from the two sources but demonstrates an interaction term which disadvantages comfort if one of the sources is dominant. [ABSTRACT FROM AUTHOR]

The effects produced by high-intensity ultrasound application during the acid pretreatment of biomass can enhance its later conversion into bioethanol. Therefore, it is interesting to evaluate how residues, such as cassava bagasse (CB), affect the actual acoustic field applied and, thus, the magnitude of its effects. For this, calorimetric method was used to estimate acoustic energy and the efficiency of electric-acoustic energy conversion in acid suspensions containing different CB concentrations (2–10%). Tests were carried out under different input powers, from 160 to 400 W (24 kHz), at different distances (1.5–5.5 cm) from the sonotrode. Thus, the experimental acoustic intensity measured varied from 12.90 to 68.57 W·cm−2, the highest values being registered in the suspensions with the lowest CB content (65.55–36.81% of conversion yield close to the sonotrode). Attenuation was also addressed during sound wave propagation, finding a constant value of 0.021 cm−1. Polynomial models were well fitted to acoustic parameters and acoustic intensity exhibited a high correlation ( r >0.87 and p value ≤ 0.05) with the experimental thermophysical properties of the suspensions. [ABSTRACT FROM AUTHOR]

Mechanical faults are major fault types in gas insulated switchgear (GIS). The vibration and acoustic signature provide valuable health indicator for GIS. This paper proposes a novel mechanical defect detection and identification approach for GIS using acoustic imaging. The vibration modals of a three-phase-in-one-tank GIS bus tube under different natural frequencies are investigated. An acoustic pressure sensor matrix is designed to obtain the acoustic intensity nephogram of the GIS. The gray-level co-occurrence matrix (GLCM) is used to extract the characteristics of the nephogram. Five eigenvalues, including angular second moment, contrast, entropy, correlation, and inverse different moment, are analyzed for three types of mechanical defects (i.e., loose anchor bolts, loose disc insulator bolts, and poor switchgear contact). A mechanical defect diagnostic approach for GIS is developed using the variation percentage of the averaged values of contrast as the key indicator. The effectiveness of the approach is validated using experimental data. [ABSTRACT FROM AUTHOR]

Condition monitoring of gear trains by classic techniques based on vibrations and/or extensometry measurements requires the preparation of the sensor contact surfaces and the cables installation. In the case of planetary gear trains, this task is more difficult due to their compactness and the complexity of the relative movements among their different elements. As an alternative, the authors studied the possibility of using acoustic measurements for the planetary gear-set characterisation, as well as for predictive maintenance of this mechanical system. In order to perform this study, a suitable measurement equipment was selected and a bespoke software was developed to control it, to process the data, as well as to represent the results. This informatic tool was used to perform the acoustic characterisation, in which acoustic pressure and intensity measurements were combined with advanced algorithms, such as sincronous-average technique. In this study, two different failures were experimentally recreated in a commercial gearbox, representing the results by frequency and order spectra and intensity maps. The obtained results were compared with those obtained in the box without defect. [ABSTRACT FROM AUTHOR]