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Holographic reconstructions of the sound field in the vicinity of a tied-down F-35 aircraft were achieved by applying multisource statistically optimized near-field acoustical holography to measure...

Sound field separation based on near-field acoustical holography has been developed worldwide, but with the increase in the number of sound sources, traditional measurement methods and calculation methods will generate more workload. To reduce the number of measuring points and save calculation time, the sound field separation of multiple coherent sources with a single measurement surface is proposed. On the basis of separating two coherent sources with this method, the separation formula of more sources based on an equivalent source method is given. Through numerical simulation, the effects of the number of holographic surface measuring points, measuring distance, array shape, and equivalent source number on the calculation accuracy of the sound field separation were compared at different frequencies. The correctness and effectiveness of the sound field separation method with a single surface are verified by actual experiments.

Results of investigation of the structure of the sound field near a supersonic isothermal air jet emanating from the nozzle of a jet engine under the conditions of existence of perturbations in its jet-edge generator by the direct shadow method are presented.

The acoustical characteristics of a room where the artistic performance is presented to the audience have a critical impact on the experience of both artists and spectators. It is important to know how the original aspects and the refurbishment works throughout the centuries are brought to the characterization of the sound field in such theatres, with positive and negative consequences. This paper presents the acoustical assessment of the Teatro Nuovo of Spoleto and the Teatro Alighieri of Ravenna, very important landmark centers for their historical and cultural activities. The acoustical characteristics have been gathered by placing the sound source on both the stage and orchestra pit, and the receivers in the stalls and balconies areas at different levels. It is of great interest to show the acoustical parameters of such Opera houses and some acoustical limits derived from intermediate interventions due to the need of the committees to allocate as many spectators as possible for income reasons. After an acoustic analysis of the existing conditions, the authors compare the acoustic behaviour inside the Teatro Nuovo of Spoleto using the image-source method (ISM) to investigate a change of ceiling configurations that occurred with the refurbishing works of the 20th century.

In this paper, a problem of sound generation of two-blade rotor sinusoidal shape during helicopter landing is solved. Near and far sound field characteristics have been calculated. A comparative analysis of obtained numerical results with results for Mach number 0.2

In existing partial field decomposition methods, the pressures are generally used as references. This paper is going to use the particle velocities as the references to decompose the sound field radiated by incoherent or partially coherent sources into mutually incoherent partial fields, and evaluate its performance by comparing with the method using pressure references. Both numerical simulations and experiment confirm the effectiveness of the method using particle velocity references for partial field decomposition and demonstrate its superiority over the method using pressure references, and it is also shown through numerical simulations that the particle velocity references almost always perform better than the pressure references as long as the references are located close to the sources and the directions of particle velocity references are perpendicular to the source plane as far as possible.

Nowadays, the sound source localization is widely applied in various fields, with a focus on arrays or algorithms. Meanwhile, acoustic metasurfaces have recently attracted enormous interest in material science. This paper proposed a kind of piezoelectric acoustic metasurface, whose structure is theoretically proved to be useful in sound field orientation or sound source localization. The metasurfaces consist of forty units made up of a resonance-like cavity and a piezoelectric composite sheet in air. By scanning through space and frequency, it has been investigated that the effective interval can reach $$30^\circ \le \theta \le 150^\circ $$ and $$-200\le x\le 200\,\hbox {cm}$$ under far-field and near-field scenario, respectively. Meanwhile, the bandwidth of the structure was evaluated to be up to 800–900 Hz in both scenarios. In addition, this paper analyzed three factors affecting the interval: frequency, the size of the metasurface, and the number of elements. The results of this paper has opened up a new way for sound source localization and metasurfaces.

In the measurement of the level difference between dwelling rooms, the low‐frequency modal density of the source room is not high enough for the incident sound field to be assumed as a random incidence, and the sound field is expected to be strongly influenced by the standing waves of the room modes. In this paper, an experimental method is proposed to analyze the characteristics of the incident sound fields in dwelling rooms, where the propagation mode expansion is applied to the complex sound pressure observed on the two layers of planar microphone array. The proposed method is applied to numerical models to simulate the incident sound fields to obtain information on its accuracy and application limitations, and the applicability of the method to ordinary rooms is discussed. In addition, the effect of room absorption on incident characteristics is demonstrated using the proposed method.

The sound-field auditory steady-state response (ASSR) is a promising measure for the objective validation of hearing-aid fitting in patients who are unable to respond to behavioral testing reliably. To record the sound-field ASSR, the stimulus is reproduced through a loudspeaker placed in front of the patient. However, the reverberation and background noise of the measurement room could reduce the stimulus modulation used for eliciting the ASSR. As the ASSR level is heavily dependent on the stimulus modulation, any reduction due to room acoustics could affect the clinical viability of sound-field ASSR testing. This study investigated the effect of room acoustics on the level and detection rate of sound-field ASSR. The study also analyzed whether early decay time and an auditory-inspired relative modulation power model could be used to predict the changes in the recorded ASSR in rooms. A monaural auralization approach was used to measure sound-field ASSR via insert earphones. ASSR was measured for 15 normal-hearing adult subjects using narrow-band CE-Chirps® centered at the octave bands of 500, 1000, 2000, and 4000 Hz. These stimuli were convolved with simulated impulse responses of three rooms inspired by audiological testing rooms. The results showed a significant reduction of the ASSR level for the room conditions compared with the reference anechoic condition. Despite this reduction, the detection rates for the first harmonics of the ASSR were unaffected when sufficiently long recordings (up to 6 min) were made. Furthermore, the early decay time and relative modulation power appear to be useful predictors of the ASSR level in the measurement rooms.

The simulation of external sound field is one of the key problems in the radiated noise calculation of underwater structure. The influence of external acoustic environmental factors, such as limited water depth and free surface, is also lack of enough research at present. Firstly, the calculation method of underwater radiated noise is verified by a stiffened cylindrical shell, and then the area size, shape and element size of the external sound field is discussed. Finally, the effect of finite water depth and free surface on the radiated sound field is analyzed. The results can provide a reference for the calculation of radiated noise of underwater structure.

Internal solitary wave is a universal phenomenon in ocean which can bring enormously significant impact to sound propagation. To our knowledge, most previous acoustic-based methods on the problems of the effect of internal solitary waves on acoustic propagation were done in the frequency domain. It is hard to make inconsistent spatial variation of sound speed with these methods. Therefore, a time domain model based on the lattice Boltzmann method is presented to simulate the sound propagation with and without internal solitary waves. The mechanisms of how the internal solitary waves influence the acoustic propagation involved is investigated. Through compare with and without solitary wave, the main result is this wave will changed the distribution of sound field and interfere with the structure of it.

A two-dimensional (2D) meshless model based on the vortex method is developed to predict the aerodynamic noise of a noncompact open cavity, which calculates the flow and sound field results...

A three-dimensional analytical solution is constructed for the model of an inhomogeneous hydroacoustic waveguide with a cylindrical inhomogeneity within the sedimentary layer. A numerical-analytical method for finding the velocity potential is proposed, for which undefined coefficients for normal modes are determined from the corresponding infinite system of linear algebraic equations. The asymptotic behavior of the amplitude coefficients in the system is investigated. Sound fields with variation of the parameters of the problem are numerically studied.

The sound field characteristics in a trapezoidal enclosure surrounded by a flexible wall, which is adjacent to the tilted one, are investigated and compared with the case of a rectangular enclosure. The acoustic modes of trapezoidal enclosure are obtained by the coupling of the modes of rectangular enclosure that bounds it. The coupling system model is then built between trapezoidal enclosure modes and flexible wall modes using modal coupling theory. Based on the coupled system model, the effect of flexible wall modal density on the resonance frequencies and the decay times of coupled system are analyzed. Compared with the case of rectangular enclosure, the variation of the resonance frequency and the decay time of enclosure-controlled system mode is determined by its mode indices and tilted wall location when the panel modal density is changed. When the modal indices of trapezoidal sound field in the two directions unparallel to the tilted wall are equal to zero simultaneously, the effect of inclination angle on the resonance frequencies and decay times of these coupled system modes can be neglected. Otherwise, the coupling system modes behaviors are changed with the elevation angle. In addition, the coupling selection between the modes of trapezoidal enclosure and flexible wall is discussed in detail.

All the current sound field separation methods based on particle velocity are apply measurement surfaces or a single measurement surface with pressure-velocity. In order to acquire less measurement data and efficient calculation, a sound field separation method with single holographic surface based on particle velocity is proposed. According to the principle of equivalent sources near-field acoustical holography technique, this method can separate directly the sound filed information radiated by target source from coherent sound fields. Numerical simulation analyzed the results with different frequencies and signal-to-noise ratio (SNR). The results show that this method can separate the coherent sources accurately and efficiently.

The low-frequency properties of a room (where statistical methods in the standards cannot be applied directly) are often hard to estimate due to strong modal behaviour. The situation gets complicated by the fact that variations in the furnishing can have an impact on the modal patterns and therefore can also influence the results of measurements at certain points, in spite of the room properties being the same. The latter can hinder the achievement of acoustic comfort in dwellings, even if they comply with the current regulations, especially due to the fact that low-frequency noise is left outside the scope, since the standards currently in force do not require measurements below 100 Hz (albeit Sweden set 50 Hz as lower limit). This article aims to study variations of the sound field that results of varying the position of three moderately absorbing boards, which emulate how very sparse furniture can impact the sound field when relocated in the room. Furthermore, the potential of numerical models as prediction tools for such problems is pointed out.

This work is part of a study of the interactions of ear canal (EC) sound with tympanic membrane (TM) surface displacements. In human temporal bones, the ossicles were stimulated mechanically “in reverse” to mimic otoacoustic emissions (OAEs), and the sound field within the ear canal was sampled with 0.5–2 mm spacing near the TM surface and at more distal locations within the EC, including along the longitudinal EC axis. Sound fields were measured with the EC open or occluded. The reverse-driven sound field near the TM had larger and more irregular spatial variations below 10 kHz than with forward sound stimulation, consistent with a significant contribution of nonuniform sound modes. These variations generally did not propagate more than ∼4 mm laterally from the TM. Longitudinal sound field variations with the EC open or blocked were consistent with standing-wave patterns in tubes with open or closed ends. Relative contributions of the nonuniform components to the total sound pressure near the TM were largest at EC natural frequencies where the longitudinal component was small. Transverse variations in EC sound pressure can be reduced by reducing longitudinal EC sound pressure variations, e.g., via reducing reflections from occluding earplugs.

We have investigated the distribution of sound pressure levels in the Helmholtz resonators over a wide range of frequencies. Computer simulation of the sound field at the resonator was performed by using a finite element method and an experimental research. We have established the existence of many resonance frequencies at the resonator and show the distribution of the maxima and minima of sound pressure levels within the volume of the resonator. It has been revealed that the distribution of the resonator's resonance frequencies does not obey the harmonic law. That makes it possible to consider resonance properties of the resonator similarly to the oscillations in a membrane or a bell. The second resonance frequency of the resonator is 6‒9 times higher than the first resonance frequency corresponding to the Helmholtz resonance. Simulation of sound field in the resonator showed the presence of nodal lines in the distribution of the sound pressure in both the resonator's volume and its throat. It has been established that the number of nodal lines for the first frequencies is one unity less than the resonance number. A common feature to all distributions is that when a measuring point approaches the edge of the resonator throat, the level of sound pressure decreases. In addition, the study has found the possibility to generate resonance only within the resonator's volume without distinct nodal lines in the throat. Comparative analysis of data acquired from experiment and during computer simulation has revealed a high level of reliability of the results obtained. Error in determining the resonance frequency did not exceed 0.8 %. That makes it possible, when further determining the sound field in the systems of resonators, to employ computer simulation instead of resource-intensive experimental studies. The existence of many resonances at the Helmholtz resonator enables the construction of broadband devices, which could be based on using a given type of resonators

In this study, simulations of a scale model of an unfurnished rectangular room with an absorbing ceiling using an energy-based geometrical acoustic model and a phased geometrical acoustic model are compared to measurements. This room can represent a typical classroom or office. This comparison concluded that the phased model can capture more details of the sound field, particularly at low frequencies. For accurate predictions, precise surface descriptions are needed for the phased GA method, which are not always available. The main drawback of the phased model is a longer calculation time.

The interaction between the sound field outside an elastic structure and its boundary is of paramount importance in the field of acoustics. This paper describes the global acoustic impedance in the form of impedance integral operator and impedance matrix for the analysis of elastic structures. In general, the excitation applied locally to the structure can induce vibration on the entire structure surface and hence the global acoustic impedance is introduced to characterize the relationship between the resultant sound pressure and acoustic particle velocity. The main advantage of the global acoustic impedance over the local acoustic impedance is that it facilitates improved physical insights into the sound field due to the presence of excitation sources. Furthermore, the acoustic impedance of an elastic spherical shell in matrix form is solved and analyzed by solving the finite element equation of structural dynamics with programming techniques. The impedance matrix is subsequently taken as the boundary condition to investigate the acoustic scattering from the elastic shell structure using the acoustic boundary element method. Explanations for the difference between the acoustic scatterings calculated based on the global acoustic impedance and the local acoustic impedance are offered.

Yost and Brown (2013, JASA 133) investigated the ability of listeners to localize two simultaneously presented, independent noises presented over loudspeakers from different locations. These experiments demonstrated that SAM noises that were out of phase at two spatially-separated loudspeakers led to better localization performance than when the SAM noises were in phase at each loudspeaker. Performance was improved at SAM rates as high as 200 Hz as compared to non-SAM noise. Yost and Brown hypothesized that listeners’ behavior might be explained as a temporal-spectral (T-S) analysis, and showed that such an approach could, qualitatively, account for some of their behavioral data. This presentation will explore the degree to which a quantitative, biologically-inspired peripheral/brainstem auditory model can predict some of the listener performance presented in Yost and Brown 2013. Specifically, the model structure includes simulated auditory nerve response using the Zilany et al. model (JASA, 2014) with rate-count-based estimation of interaural differences of time and intensity as they occur in the presented stimuli recorded with a KEMAR manikin.

A far-field solver based on the acoustic analogy of Ffowcs Williams and Hawkings for acoustic problems with convection and vortical waves was implemented in the open source package Overture. The numerical calculations of CAA test cases showed good agreement with analytical solutions or results from measurements and simulation data from the literature. This paper presents the implemented solver and its verification. In futher work, the developed framework will be used to investigate jet-flap interaction and the emitted sound field, numerically.

A round jet with \(Re=3600\) and \(M=0.9\) as well as two planar nozzle-wing flap configurations were simulated by using LES. An evaluation was proposed to predict the effect of the instantaneous Lighthill sources, S, their linear components, \(S^{\mathrm {l}}\), and non-linear components, \(S^{\mathrm {n}}\). The simulations indicate that conclusions can be made regarding the directional characteristic of the emitted sound field. These findings were used in investigations of a nozzle-wing-flap configuration. The wing-nozzle configuration showed increased values of the mean Lighthill source terms on the bottom of the wing and flap, contrary to the case of an isolated wing.

The sound field near the tympanic membrane (TM) is estimated based on acoustic data measured at the tip of a probe inserted into the ear canal, from which the area-distance function of the ear canal is calculated. Such information has the potential to quantify the sound input to the middle ear at high frequencies. Spatial variation in the ear-canal cross-sectional area is described acoustically by quantifying forward and reverse sound waves between the probe tip and a near-TM location. A causal acoustic reflection function (RF) measured in the time domain at the probe tip is used to calculate area-distance functions of the ear canal. Area-distance functions are compared with plane-wave methods based on layer peeling and Ware-Aki algorithms. A time-domain model of viscothermal wall loss is devised and applied to ear-canal data, with area-distance functions compared between loss-less and lossy methods. This model is applicable to time-domain RF calibrations using measured data in short tubes. Specification of the near-TM sound field may benefit the interpretation of data from physiological tests such as otoacoustic emission and auditory brainstem responses and high-frequency behavioral tests such as extended audiometry and tests of spatial processing of sound.

Рассматриваются особенности работы гидроакустических комбинированных приемников, образующих вертикально ориентированную антенну, в мелком море в инфразвуковом диапазоне частот. Данное исследование связано с решением проблемы определения координат и параметров движения определенной цели путем активно-пассивной локации и измерения характеристик наблюдаемого при этом поля шумов. Актуальность представляет анализ пространственно-частотной и пространственно-временной структуры звукового поля. Для проведения эксперимента использовался НИС «Юрий Молоков», буксирующий низкочастотный излучатель ЛЧМ-сигналов. Пространственно-частотная структура звукового поля исследуется путем спектрального анализа дискретных составляющих вально-лопастного звукоряда буксирующего судна в диапазоне частот 1–20 Гц. Исследование пространственно-временной структуры поля производится путем корреляционной обработки ЛЧМ сигналов на апертуре вертикально ориентированной антенны в диапазоне частот 30–60 Гц. Результаты спектральной обработки принятых сигналов позволяют получить оценки помехоустойчивости комбинированного приемника, причем повышенная помехоустойчивость реализуется при использовании полного набора из 16 информативных параметров, характеризующих энергетическую структуру звукового поля. Это в итоге позволяет исследовать вертикальную структуру звукового поля и произвести идентификацию формирующих его нормальных волн. Из полученных результатов корреляционной обработки сложных ЛЧМ-сигналов вытекают также оценки пространственно-временной структуры звукового поля и коэффициентов корреляции на апертуре вертикально ориентированной антенны в различных каналах комбинированных приемников. The article considers the features of composite underwater acoustic receivers forming a vertically oriented antenna in conditions of shallow sea in the infrasound frequency band. This research targets the problem of positioning and motion parameters characterization of the given target object using active-passive location and measurement of observed noise field parameters. Its particular significance is the analysis of space-frequency and space-time structures of the sound field. The experimental research was performed involving the research vessel "Yuriy Molokov" towing low-frequency transducer of LFM signals. The space-frequency structure of the sound field was studied by spectral analysis of discrete components of the vane-lobe tone series of the towing vessel in the band 1–20 Hz. The study of the space-time structure of the field was performed by correlation processing of LFM signals on the aperture of the vertically oriented antenna in the frequency band of 30–60 Hz. The results of spectral processing of the received signals allow estimating the noise-sustainability of the composite receiver. Moreover, the increased noise-sustainability is achievable when using the full set of 16 informative parameters describing the energetic structure of the sound field. That allows studying the vertical structure of the sound field and performing identification of the normal waves participating in its formation. Also, obtained results of correlation processing of composite LFM signals give estimates of the space-time structure of the sound field and correlation coefficients on the aperture of a vertically oriented antenna in different channels of the composite receiver.

The sound field properties for non-cavitating marine propellers are studied using FW-H (Ffowcs William-Hawkings) acoustic analogy and BEM (Boundary Element Method) approach. For the first time, the FW-H formula to calculate acoustic pressure generated by the propeller wake sheet is proposed. The corresponding sound signal can be dominant up to several kilometres. Secondly, non-physical fictitious volume flux is observed when the permeable FW-H approach is used together with BEM. The reason is explained and a virtual source correction method is proposed to solve this problem. Furthermore, analytical analyse show that the second thickness term and the first two loading terms in Farassat 1A formula are important, and the others are negligible. The numerical studies show that the permeable FW-H approach produces underestimation when compared to the direct FW-H method, and the underestimation is severer for larger permeable surface and higher frequency. It is also found that the first loading term in Farassat 1A formula is the dominant source term in the direct FW-H method, while the first thickness term is dominant when the permeable FW-H approach is used.

This paper focuses on the distribution characteristics of the radiation noise for a full-ceramic angular contact ball bearing (FCACBB). A model for calculating the radiation noise of a FCACBB was established based on the bearing dynamic characteristics and sound radiation theory, and the effectiveness and accuracy of the method were verified by corresponding experiments. The variation of the radiation noise for a FCACBB with the rotational speed was analyzed. The directivity of the sound field in the circumferential direction was found. The variation trends of the radiation noise in the friction load zone and the impact load zone were discussed. The attenuation of the radiation noise in the radial direction and in the axial direction was investigated. The directivity angle and the degree of directivity of the sound field were explored at different radial and axial distances. The results show that the inhomogeneous contacts between the bearing components in the circumferential direction result in different degrees of friction and impact vibration at different locations, which makes the radiation noise of the FCACBB have a larger component in the radial direction than in the axial direction. The conclusions can provide a reference for predicting the radiation noise of FCACBBs and further optimizing the sound field.

Acoustic waves are fascinating phenomena in gases, liquids or solids with numerous physical and technical aspects. Air is the medium of interest when it comes to audible sound. The gas dynamics of air determine the equations of the sound pressure and other field quantities from which the wave equation can be derived and solved for basic wave types. Properties of the waves such as frequencies and sound levels are associated with the human hearing sensation. The chapter on fundamentals of acoustics deals with the introduction into sound field physics and terminology of acoustics.

In the situation that vibrating objects are located above a reflecting plane, an independent-equivalent source method (I-ESM) regards the reflections due to the plane as being radiated by equivalent sources placed under the plane and then the half-space sound field is reconstructed by matching the measured pressure with the equivalent sources distributed within the vibrating object and those substituting for reflections. But, this method heavily depends on the equivalent source configuration and may obtain bad reconstruction results if the equivalent sources are arranged incorrectly. This paper deals with the optimization of the equivalent source configuration to ensure I-ESM always perform well. Through numerical simulations and experiments, the influence of equivalent source configurations on the reconstruction accuracy was studied and optimal configurations were acquired and confirmed.

The ray description of sound phenomena contains inevitable approximations that do not allow to describe acoustic processes adequately in certain cases, especially when it is necessary to reveal important subtle characteristics of the sound field, for example, near caustic surfaces. An alternative to the ray approach is the wave description.

Due to the energy conservation law, traditional active noise control system cannot realize the suppression of omnidirectional sound field and will bring fluctuation effect in the far field. This paper presents a method of sound field control using beam deflection to overcome the shortcomings of traditional active noise control system. The principle of beam deflection is firstly derived based on the principle of beam forming. Two methods including conventional beam deflection and optimal beam deflection are proposed. Then technical route of the sound field control using beam deflection is given. Finally, simulations are performed and the results show that proposed method can effectively suppress the energy of a controlled sound source in the predetermined direction.

To measure the air-borne sound and floor impact sound insulation performance, the sound field correction of the receiving room was conducted using reverberation time. Reverberation time is varied by environmental conditions, characteristics of sound source, position of sound source and microphones, etc. The sound field correction method on a rubber ball impact sound was standardized. In this study, the reverberation time was measured and compared using an omni-directional loud-speaker, a half-omni-directional loud-speaker, and a sub-woofer. Reverberation times at below 500 Hz bands became shorter when the height of the Omni-directional loud-speaker was increased. The reverberation times measured with the omni-directional loud-speaker at 1.7 m height were similar with the reverberation times measured with the half-omni-directional loud-speaker. For the measurement of reverberation time in low frequency below 80 Hz band, sub-woofer was installed on the floor. Reverberation times measured with sub-woofer were shorter than reverberation times measured using the half omni-directional loud-speaker, and the deviation was smaller. In order to make a correction for the receiving room sound field condition on light-weight impact sound, the height of the omni-directional loud-speaker should be approximately 1.7 m. In addition, for the sound field correction of the rubber ball impact sound at below 100 Hz bands, the use of sub-woofer for sufficient generation of sound energy in the low-frequency band is needed.

A first principles understanding of the sound field produced by multirotor drones in hover is presented. Propeller diameters ranging from 8 to 12 in. are examined and with configurations comprising...

By using experimental results and taking into account the characteristics of shaping in the focal region, we theoretically demonstrate the plasma ellipsoid model and calculate the breakdown threshold and the directivity of the sound filed. It is found that the predictions in our theoretical model well agree with the results of experiments.

The paper presents the results of processing measurement data on the spatiotemporal structures of sound fields in Lake Ladoga. Measurements were taken with an extended vertical receiver array. The aim of processing was to isolate the field components that were stable with respect to small variations in the waveguide parameters. Since a model of the medium is inevitably inaccurate, such components can be predicted with greater accuracy than the total field. In terms of the ray approach, a stable component is generated by a beam of rays propagating over close trajectories. The discussed experiment analyzed sound fields excited by a point source that emitted wideband pulses, as well as the fields of wave beams excited by the emitting vertical array at fixed frequencies. In both cases, the processing results showed that the isolated stable components, as expected, coincide substantially better with the prediction of theoretical calculation (by the wide angle parabolic equation method) than with the total wave field.