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On 13–15 January 2022, the Hunga Tonga–Hunga Ha'apai underwater volcano erupted. This powerful eruption generated infrasonic waves with amplitudes of thousands of Pascals in the near field. The ground infrasonic stations in China, located approximately 10 000 km from the Hunga volcano, also received waves with frequencies from 0.01 to 0.05 Hz. However, the amplitude reached 17 Pa, which is higher than the predicted amplitude using the absorption model without considering the dispersion effect in the thin thermosphere. At high altitudes, dispersion exists and the sound speed depends on the ratio of the molecular mean collision ratio to sound frequency, which is proportional to the ratio (frequency/pressure). And attenuation coefficients are complex to model. We simulate dispersive sound speeds and attenuation coefficients at different frequencies according to theory and our experimental data. In the thermosphere, the dispersion effect causes noticeable changes of sound speed and then affects wave propagation paths in the far field. The abnormal attenuation coefficient has a smaller impact on thermospheric returns than that of the dispersive sound speed, but it is also not negligible. It explains the large amplitude of thermospheric signals received in our infrasound stations. This article is part of the theme issue 'Celebrating the 15th anniversary of the Royal Society Newton International Fellowship'. [ABSTRACT FROM AUTHOR]

The orchestra pit is not a friendly workplace for musicians, and the need to ensure their interaction with the stage and audience places very high demands on this interior. The aim of the considerations presented in the article was to analyse the various possibilities of acoustic adaptation of the orchestra pit against the background of obtaining the expected effects. The conducted simulation studies and the use of the results of the experimental studies carried out in the well-equipped orchestra pit of the Krakow Opera allowed for the indication of representative acoustic parameters useful for the assessment of the results of acoustic treatment. Based on the comparison of the reverberation time T20 and EDT for various variants of the orchestra pit interior, the confirmation of the legitimacy of using sound diffusing and absorbing systems was obtained. They spread the energy of the first sound reflections in time and reduce the risk to the musicians' hearing. Reflective elements and sound dispersing within the orchestral will ensure adequate audibility between the musicians. [ABSTRACT FROM AUTHOR]

With the proposal of the concept of parity-time-symmetry, more and more exotic properties are being unearthed in non-Hermitian systems. In this work, we investigate the related acoustic feature and phenomenon in two-dimensional phononic crystals with a complex modulus by introducing the balanced loss and gain. Different from Hermitian properties, partial band degeneracy has occurred in the dispersion diagram, leading to higher density of states, and self-collimated wave propagation has been predicted at the merged frequency. More importantly, the input locations of the point source have a significant impact not only on the direction of self-collimation waves but also on the intensity profiles of the pressure field, which is not achieved in self-collimation of Hermitian systems. We also propose a digital single-pole double-throw switch, which corresponds to two special self-collimating situations. Our finding provides an effective approach for controlling the wave direction and designing more digital acoustic functional devices in non-Hermitian systems. [ABSTRACT FROM AUTHOR]

The establishment of a soundscape baseline might allow the rapid detection of significant environmental changes and could potentially be a holistic instrument for biome conservation. Due to the diversity and variability of the sounds produced in an ecosystem, the establishment of a baseline is complex. Thus we evaluated if, in an ever-changing soundscape, it was possible to find dominant acoustic features on a monthly and hourly scale. Dominant power spectrums (PSs) in an area of premontane moist forest were identified by correlating PSs from February to December 2015, calculating the linear correlation between them, and defining a set of PSs that were strongly correlated (Pearson > = 0.95) to most of the obtained PSs. For any two PSs, the Pearson coefficient > = 0.95 accounted for an equivalence relation between the PSs; these relations allowed us to group spectrums into a few sets. In the daytime, 7.3% (eight out of 109 PSs) of the PSs (i.e., the dominant spectrums) were strongly correlated to 80.7% of the obtained PSs; the remaining 19.3% were singular PSs, weakly correlated to other diurnal PSs. During the night, 6.06% (four out of 66 PSs) of the PSs (i.e., the dominant spectrums) were strongly correlated to 53.0% of the obtained PSs; the remaining 47.0% were singular PSs, weakly correlated to other nocturnal PSs. Strong correlations between the PSs on an hourly scale and monthly scale could be used to denote features that prevail over time. The occurrence of strong associations between PSs (i.e., > 0.98) in spectrums from different months suggests that the generation of sound in the studied forest has a well-defined frequency distribution. [ABSTRACT FROM AUTHOR]

Reliable species identification is vital for survey and monitoring programs. Recently, the development of digital technology for recording and analyzing vocalizations has assisted in acoustic surveying for cryptic, rare, or elusive species. However, the quantitative tools that exist for species differentiation are still being refined. Using vocalizations recorded in the course of ecological studies of a King Rail (Rallus elegans) and a Clapper Rail (Rallus crepitans) population, we assessed the accuracy and effectiveness of three parametric (logistic regression, discriminant function analysis, quadratic discriminant function analysis) and six nonparametric (support vector machine, CART, Random Forest, k‐nearest neighbor, weighted k‐nearest neighbor, and neural networks) statistical classification methods for differentiating these species by their kek mating call. We identified 480 kek notes of each species and quantitatively characterized them with five standardized acoustic parameters. Overall, nonparametric classification methods outperformed parametric classification methods for species differentiation (nonparametric tools were between 57% and 81% accurate, parametric tools were between 57% and 60% accurate). Of the nine classification methods, Random Forest was the most accurate and precise, resulting in 81.1% correct classification of kek notes to species. This suggests that the mating calls of these sister species are likely difficult for human observers to tell apart. However, it also implies that appropriate statistical tools may allow reasonable species‐level classification accuracy of recorded calls and provide an alternative to species classification where other capture‐ or genotype‐based survey techniques are not possible. Reliable species identification is vital for survey and monitoring programs. We assessed the accuracy and effectiveness of three parametric and six nonparametric statistical classification methods for differentiating between the vocalizations of King and Clapper rails. This work suggests that appropriate statistical tools may allow reasonable species‐level classification accuracy of recorded calls and provide an alternative to species classification where other capture‐ or genotype‐based survey techniques are not possible. [ABSTRACT FROM AUTHOR]

Acoustic scattering by a single bubble is the most basic problem for bubble detection. For a two-phase flow, the subject of forced oscillations of a pair of bubbles is important because it controls how bubbles interact with each other. Attempts to incorporate interactions between bubbles have traditionally used a multiple scattering methodology. The proposed approach uses a bi-spherical coordinate system and is limited to a description of a sufficiently long-wave acoustical field, so that the bubbles are homobaric, and the medium in the vicinity of the bubbles can be considered incompressible. The choice of a specific coordinate system allows the authors to take into account the internal symmetry inherent in this problem and provides a partial summation on only the most important contributions to the multiple scattering series. A closed form solution was derived for the scattered acoustic field that determines its parametric dependence on bubbles sizes and the separation distance. [ABSTRACT FROM AUTHOR]

Novel acoustic liner designs often incorporate new materials with non-uniform impedance distributions. Therefore, new methods are required for their modelling and analysis. In this paper, a theoretical model is developed to investigate the scattering of sound waves from an axially symmetrical flow duct with a semi-infinite, azimuthally non-uniform acoustic lining on the duct wall. More specifically, the incorporation of Fourier series expansions into the Wiener–Hopf method leads to an analytical model with a matrix kernel, which is further factorised by using the pole-removal method to obtain a closed-form solution. A new mathematical method is developed to solve the residues associated with the pole-removal technique. The proposed model has been verified and validated by comparing with corresponding computational results. In addition to shedding light on the possible physical effect of azimuthally non-uniform liners along with an axial hard–soft interface, the current model enhances the theoretical modelling capability for a complicated set-up of practical importance, and can be used to investigate new liner designs for passive noise control in flow ducts. [ABSTRACT FROM AUTHOR]

Dispersion Theory [DT; Liljencrants and Lindblom (1972). Language 12(1), 839-862] claims that acoustically dispersed vowel inventories should be typologically common. Dispersion is often quantified using triangle area between three mean vowel formant points. This approach is problematic; it ignores distributions, which affect speech perception [Clayards, Tanenhaus, Aslin, and Jacobs (2008). Cognition 108, 804-809]. This letter proposes a revised metric for calculating dispersion which incorporates covariance. As a test case, modeled vocal tract articulatory-acoustic data of stop consonants [Schwartz, Boe, Badin, and Sawallis (2012). J. Phonetics 40, 20-36] are examined. Although the revised metric does not recover DT predictions for stop inventories, it changes results, showing that dispersion results depend on metric choice, which is often overlooked. The metric can be used in any acoustic space to include information about within-category variation when calculating dispersion. [ABSTRACT FROM AUTHOR]

The aim of this work is to derive sharp quantitative estimates of the qualitative convergence results developed by Li et al. (2015) for regularized full- and partial-cloaks through transformation optics approach. LetΓ0be a compact set in ℝ3andΓδbe aδ-neighborhood ofΓ0forδ∈ℝ+.Γδrepresents the virtual domain used for the blow-up construction. By incorporating suitably designed lossy layers, it is shown that if the generating setΓ0is a generic curve, then one would have an approximate full-cloak withinδ2to the perfect full-cloak, whereas ifΓ0is the closure of an open subset on a flat surface, then one would have an approximate partial-cloak withinδto its perfect counterpart. The estimates derived are independent of the contents being cloaked; that is, the cloaking devices are capable of nearly cloaking an arbitrary content. Furthermore, as a significant by-product, our argument allows the relaxation of the convexity requirement onΓ0by Li et al. (2015), which is critical for the Mosco convergence argument therein. [ABSTRACT FROM PUBLISHER]

In this study, the acoustic dissipation is investigated experimentally in wooden pipes of different species commonly used in woodwind instrument making: maple (Acer pseudoplatanus), pear wood (Pyrus communis L.), boxwood (Buxus sempervirens), and African Blackwood (Dalbergia melanoxylon). The pipes are parallel to the grain, except one which forms an angle of 60° with the fiber direction. An experimental method, involving input impedance measurements with several lengths of air column, is introduced to estimate the characteristic impedance and the attenuation factor in the pipes. Their comparison reveals significant differences of acoustic dissipation among the species considered. The attenuation factors are ranked in the following order from largest to smallest: maple, boxwood, pear wood, and African Blackwood. This order is the same before and after polishing the bore, which is an essential step in the making process of wind instrument. For maple, changing the pipe direction of 60° considerably increases the attenuation factor, compared to those of the other pipes, parallel to the grain. Further, polishing tends to reduce the acoustic dissipation in the wooden pipes, especially for the most porous species. As a result, the influence of polishing in the making procedure depends on the selected wood species. [ABSTRACT FROM AUTHOR]

The relative importance of suspended particles and turbulence as backscattering mechanisms within a hydrothermal plume located on the Endeavour Segment of the Juan de Fuca Ridge is determined by comparing acoustic backscatter measured by the Cabled Observatory Vent Imaging Sonar (COVIS) with model calculations based on in situ samples of particles suspended within the plume. Analysis of plume samples yields estimates of the mass concentration and size distribution of particles, which are used to quantify their contribution to acoustic backscatter. The result shows negligible effects of plume particles on acoustic backscatter within the initial 10-m rise of the plume. This suggests turbulence-induced temperature fluctuations are the dominant backscattering mechanism within lower levels of the plume. Furthermore, inversion of the observed acoustic backscatter for the standard deviation of temperature within the plume yields a reasonable match with the in situ temperature measurements made by a conductivity-temperature-depth instrument. This finding shows that turbulence-induced temperature fluctuations are the dominant backscattering mechanism and demonstrates the potential of using acoustic backscatter as a remote-sensing tool to measure the temperature variability within a hydrothermal plume. [ABSTRACT FROM AUTHOR]

Nonlinear phenomena of the planar and quasi-planar magnetoacoustic waves are considered. We focus on deriving of equations which govern nonlinear excitation of the non-wave motions by the intense sound in initially static gaseous plasma. The plasma is treated as an ideal gas with finite electrical conductivity permeated by a magnetic field orthogonal to the trajectories of gas particles. This introduces dispersion of a flow. Magnetoacoustic heating and streaming in the field of periodic and aperiodic magnetoacoustic perturbations are discussed, as well as generation of the magnetic perturbations by sound. Two cases, corresponding to magnetosound perturbations of low and high frequencies, are considered in detail. [ABSTRACT FROM AUTHOR]

Compact loudspeaker arrays have wide potential applications as portable personal audio systems that can project sound energy to specified regions. It is meaningful to investigate the scattering effects on the array performance since the scattering of the users' heads is inevitable in practice. A five-channel compact endfire array is established and the regularized acoustic contrast control method is evaluated for the scenarios of one moving listener and one listener fixed in the bright zone while another listener moves along the evaluation region. Both simulations and experiments verify that the scattering has limited influence on the directivity of the endfire array. [ABSTRACT FROM AUTHOR]

This Letter reports on the experimental validation of a two-dimensional acoustic hyperbolic metamaterial slab optimized to exhibit negative refractive behavior. The slab was designed using a topology optimization based systematic design method allowing for tailoring the refractive behavior. The experimental results confirm the predicted refractive capability as well as the predicted transmission at an interface. The study simultaneously provides an estimate of the attenuation inside the slab stemming from the boundary layer effects--insight which can be utilized in the further design of the metamaterial slabs. The capability of tailoring the refractive behavior opens possibilities for different applications. For instance, a slab exhibiting zero refraction across a wide angular range is capable of funneling acoustic energy through it, while a material exhibiting the negative refractive behavior across a wide angular range provides lensing and collimating capabilities. [ABSTRACT FROM AUTHOR]

Precise acoustical leak detection calls for robust time-delay estimates, which minimize the probability of false alarms in the face of dispersive propagation, multiple reflections, and uncorrelated background noise. Providing evidence that higher order modes and multi-reflected signals behave like sets of correlated noise, this work uses a regression model to optimize residual complexity in the presence of both correlated and uncorrelated noise. This optimized residual complexity (ORC) is highly robust since it takes into account both the level and complexity of noise. The lower complexity of the dispersive modes and multiple reflections, compared to the complexity of the plane mode, points to the robustness of ORC against multiple reflections and dispersion. Experimental investigations using recorded sounds of gas leaking from a pipe confirm the robustness of ORC against multiple reflections. Numerical simulations also show robustness against dispersive modes, even when they disturb the linearity of the cross-spectrum phase. Comparisons with other methods—mutual information, cross correlation, and residual complexity—underline the general advantages of ORC in terms of robustness in the presence of reflection and dispersion, against both correlated and uncorrelated noise, and to short signals. [ABSTRACT FROM AUTHOR]

Generic predictions for acoustic dispersion and absorption in the atmospheres of Mars and Venus are presented. For Mars, Pathfinder and Mars Express ambient data and averaged thermophysical parameters are used as inputs to a preliminary model based on the continuum approximation for Mars' thin atmosphere--the need for Boltzmann-based treatment is discussed in the context of Knudsen numbers. Strong absorption constrains acoustic sensing within the Martian planetary boundary layer. For the dense atmosphere of Venus, the van der Waals equation of state is used. The thermophysical and transport parameters were interpolated at the ambient conditions. Acoustic sensing is discussed at 50 km above Venus' surface, a level where aerostats (e.g., European Space Agency's EVE) and manned airships (e.g., NASA's HAVOC) may be deployed in the future. The salient atmospheric characteristics are described in terms of temperature, pressure, and convective stability profiles, followed by wavenumber predictions, and discussions of low- and high-frequency sensing applications. At low frequencies, emphasis is placed on infrasound. A simple generation mechanism by Martian dust devils is presented, yielding fundamental frequencies between 0.1 and 10 Hz. High-frequency sensing is exemplified by ultrasonic anemometry. Of the two environments, Venus is notably more dispersive in the ultrasonic range. [ABSTRACT FROM AUTHOR]

The extraordinary transmission in density-near-zero (DNZ) acoustic metamaterials (AMs) provides possibilities to manipulate acoustic signals with extremely large effective phase velocity and wavelength. Here, we report compact transformable acoustic logic gates with a subwavelength size as small as 0.82λ based on DNZ AMs. The basic acoustic logic gates, composed of a tri-port structure filled with space-coiling DNZ AMs, enable precise direct linear interference of input signals with considerably small phase lag and wavefront distortion. We demonstrate both theoretically and experimentally the basic Boolean logic operations such as OR, AND, XOR, and NOT with wide operational frequency ranges and controllability, by adjusting the phase difference between two input signals. More complex logic calculus, such as "I1+I2×I3," are also realized by cascading of the basic logic gates. Our proposal provides diverse routes to construct devices for acoustic signal computing and manipulations. [ABSTRACT FROM AUTHOR]

Acoustic rainbow trapping represents the phenomenon of strong acoustic dispersion similar to the optical “trapped rainbow,” which allows spatial-spectral modulation and broadband trapping of sound. It can be realized with metamaterials that provide the required strong dispersion absent in natural materials. However, as the group velocity cannot be reduced to exactly zero before the forward mode being coupled to the backward mode, such trapping is temporary and the local sound oscillation ultimately radiates backward. Here, we propose a gradient metasurface, a rigid surface structured with gradient perforation along the wave propagation direction, in which the inherent thermal and viscous losses inside the holes are considered. We show that the gradually diminished group velocity of the structure-induced surface acoustic waves (SSAWs) supported by the metasurface becomes anomalous at the trapping position, induced by the existence of the inherent losses, which implies that the system's absorption reaches its maximum. Together with the progressively increased attenuation of the SSAWs along the gradient direction, reflectionless spatial-spectral modulation and sound enhancement are achieved in simulation. Such phenomenon, which we call as absorptive trapped rainbow, results from the balanced interplay among the local resonance inside individual holes, the mutual coupling of adjacent unit cells, and the inherent losses due to thermal conductivity and viscosity. This study deepens the understanding of the SSAWs propagation at a lossy metasurface and may contribute to the practical design of acoustic devices for high performance sensing and filtering. [ABSTRACT FROM AUTHOR]

A method is proposed to evaluate in a non-contact way the phase velocity dispersion curves of circumferential waves around a shell of arbitrary shape immersed in a fluid. No assumptions are made about the thickness or the material of the shell. A geometrical model is derived to describe the shape of the radiated wavefronts in the surrounding fluid, and predict the positions of its centers of curvature. Then the time-reversal principle is applied to recover these positions and to calculate the phase velocity of the circumferential waves. Numerical finite-difference simulations are performed to evaluate the method on a circular and on an elliptic thin shell. Different dispersion curves can be recovered with an error of less than 10%. [ABSTRACT FROM AUTHOR]

A procedure and the experimental data of the dispersion dependences of the velocity and ultrasonic attenuation coefficient as measured by the resonance method in samples with a thickness below 1 mm at frequencies up to 100 MHz are presented. It is shown that structural inhomogeneities exert an influence on the acoustic properties of thin samples. [ABSTRACT FROM AUTHOR]

A model of the formation of a series of multiple reflections due to the propagation of acoustic waves that are radiated by an electromagnetic-acoustic trough transducer over the elliptical cross section of a bar is proposed. The impact of the deviation from a round cross section on the informative parameters of the obtained oscillogram is studied. [ABSTRACT FROM AUTHOR]

This paper presents experimental results for wave propagation in an anisotropic multilayered structure with linearly varying cross section. Knowing the dispersion and wave propagation properties in such a structure is of great importance for non-destructive material testing and structural health monitoring applications for accurate damage detection and localization. In the proposed study, the wavefield is generated by a circular piezoelectric wafer active sensor and measured by a scanning laser-Doppler-vibrometer. The measurements are compared with a theoretical group delay estimation and a signal prediction for the antisymmetric wave motion along the non-uniform propagation path. The required dispersion curves are derived from the well-known global matrix method for segments of constant thickness. A multidimensional frequency-wavenumber analysis of linescan data and the full wavefield provides further insight of the adiabatic wave motion because the wavenumber changes along the tapered geometry of the waveguide. In addition, it is demonstrated that a terahertz time-domain system can be used in glass-fiber reinforced plastic structures as a tool to estimate the thickness profile of thin structures by means of time-of-flight measurements. This information is particularly important for guided wave-based diagnostics of structures with unknown thickness. [ABSTRACT FROM AUTHOR]

This paper describes an original imaging technique, named Locadiff, that benefits from the diffuse effect of ultrasound waves in concrete to detect and locate mechanical changes associated with the opening of pre-existing cracks, and/or to the development of diffuse damage at the tip of the crack. After giving a brief overview of the theoretical model to describe the decorrelation of diffuse waveforms induced by a local change, the article introduces the inversion procedure that produces the three dimensional maps of density of changes. These maps are interpreted in terms of mechanical changes, fracture opening, and damage development. In addition, each fracture is characterized by its effective scattering cross section. [ABSTRACT FROM AUTHOR]

On the basis of the principle of stationary phase, Chuprov [Ocean Acoustics: Current State (Nauka, Moscow, 1982)] proposed a scalar parameter--the waveguide invariant β, to interpret the dispersive properties of underwater acoustic waveguide. It has been found that β may be useful in many applications in underwater acoustics. A reasonable prediction of the value of β is often necessary in such applications. It was known that β has some "canonical" values for waveguides with simple sound speed profiles (SSP). When a thermocline exists, β for refractive modes (with a turning point) is no longer constant and can even change its sign. In this paper, by dividing the SSP into the nonrefractive part and the refractive part, a clear explanation of how the value of β is affected by the thermocline is presented. The results show that β can be positive and increase continually from around 1 to +∝; or negative from -∝ to about -3. An analytic criterion of the sign of β is developed. This method can also be used to analyze the value of β for any other kind of SSP. [ABSTRACT FROM AUTHOR]

This paper presents a quantitative study of conversion of evanescent Lamb waves into propagating in isotropic plates. The conversion is substantiated by prescribing time-harmonic Lamb displacements/tractions through a narrow aperture at an edge of a semi-infinite plate. Complex-valued dispersion and group velocity curves are employed to characterize the conversion process. The amplitude coefficient of the propagating Lamb modes converted from evanescent is quantified based on the complex reciprocity theorem via a finite element analysis. The power flow generated into the plate can be separated into radiative and reactive parts made on the basis of propagating and evanescent Lamb waves, where propagating Lamb waves are theoretically proved to radiate pure real power flow, and evanescent Lamb waves carry reactive pure imaginary power flow. The propagating power conversion efficiency is then defined to quantitatively describe the conversion. The conversion efficiency is strongly frequency dependent and can be significant. With the converted propagating waves from evanescent, sensors at far-field can recapture some localized damage information that is generally possessed in evanescent waves and may have potential application in structural health monitoring. [ABSTRACT FROM AUTHOR]

We describe a way to generate and detect arbitrary frequency components in time-resolved surface acoustic wave imaging based on optical pumping and probing with a periodic light source. The detailed theory of the technique, based on beam modulation and Fourier analysis, for a variety of possible experimental configurations is presented, followed by experimental data for a glass substrate covered with a thin gold film. We show how the acoustic dispersion relation can be obtained to arbitrary frequency resolution, not limited by the laser pulse repetition rate. [ABSTRACT FROM AUTHOR]

The use of Global Navigation Satellite System (GNSS)-tracked Lagrangian drifters allows more realistic quantification of fluid motion and dispersion coefficients than Eulerian techniques because such drifters are analogs of particles that are relevant to flow field characterization and pollutant dispersion. Using the fast-growing real-time kinematic (RTK) positioning technique derived from GNSS, drifters are developed for high-frequency (10 Hz) sampling with position estimates with centimeter accuracy. The drifters are designed with small size and less direct wind drag to follow the subsurface flow that characterizes dispersion in shallow waters. An analysis of position error from stationary observation indicates that the drifter can efficiently resolve motion up to 1 Hz. The result of the field deployments of the drifter in conjunction with acoustic Eulerian devices shows a higher estimate of the drifter streamwise velocities. Single particle statistical analysis of field deployments in a shallow estuarine zone yielded estimates of dispersion coefficients comparable to those of dye tracer studies. The drifters capture the tidal elevation during field studies in a tidal estuary. [ABSTRACT FROM AUTHOR]

The estimation of slowness (the reciprocal of velocity) and attenuation dispersion of borehole acoustic and surface seismic data is key to a variety of applications. The emerging broadband approach for dispersion extraction of multiple modes has shown significant advantages over traditional narrowband approaches. In this letter, Cramér-Rao bounds (CRBs) are established to characterize the best achievable performance of any unbiased broadband estimator of the dispersion. One noteworthy observation from the derived CRBs is that the same estimation accuracy can be achieved between the angular wavenumber and the attenuation and, between the group slowness and the attenuation rate. The broadband CRB is also shown to include the narrowband CRB as a special case and it quantifies the performance benefit of the broadband approach. [ABSTRACT FROM AUTHOR]

A simple analytical model for the interaction between a plane jet issued from a flue and a transverse acoustic disturbance is developed in this paper. The model is inspired by direct flow simulation results confronted to experimental data. The interaction is expected to take place in the vicinity of the separation points of the jet. The influence of the detailed geometry of the channel end on the jet receptivity is discussed, and more specifically the chamfer geometries found in flute-like musical instruments. The simplified model explains quite well the difference between the jet response of a flue with square edges compared to a chamfered flue exit. The effect of rounded, lip-like flue exit is not well captured by the model. [ABSTRACT FROM AUTHOR]

Precursor field theory has been developed to describe the dynamics of electromagnetic field evolution in causally attenuative and dispersive media. In Debye dielectrics, the so-called Brillouin precursor exhibits an algebraic attenuation rate that makes it an ideal pulse waveform for communication, sensing, and imaging applications. Inspired by these studies in the electromagnetic domain, the present paper explores the propagation of acoustic precursors in dispersive media, with emphasis on biological media. To this end, a recently proposed causal dispersive model is employed, based on its interpretation as the acoustic counterpart of the Cole-Cole model for dielectrics. The model stems from the fractional stress-strain relation, which is consistent with the empirically known frequency power-law attenuation in viscoelastic media. It is shown that viscoelastic media described by this model, including human blood, support the formation and propagation of Brillouin precursors. The amplitude of these precursors exhibits a sub-exponential attenuation rate as a function of distance, actually being proportional to z-p, where z is the distance traveled within the medium and 0.5 <; p <; 1. The precursors identified in this work facilitate the design of optimal waveforms for propagation in complex media, creating new possibilities for acoustic-pulse-based communication and imaging systems. [ABSTRACT FROM AUTHOR]

In this paper, the propagation of acoustic waves along a duct system, where a semi-infinite circular rigid pipe with a rigid end face is placed axially inside an infinite circular rigid pipe is analyzed rigorously. First, direct Fourier transform is applied and the problem is reduced into the solution of a modified Wiener-Hopf equation of the second type from which the reflection and transmission coefficients are determined. Then the bifurcated circular waveguide problem is solved by applying direct Fourier transform again to reduce the problem into the solution of a Wiener-Hopf equation and the resulting transfer coefficients are taken into account when applying the building block method. Building block method is one of the scattering matrix techniques where reflection and transmission characteristics of each discontinuity in a duct are first determined independently and then taken into account as scattering matrices in order to analyze the original problem. At the end of the analysis, numerical results are presented comparing two approaches of formulation and illustrating the effects of the radii of the pipes and frequency. [ABSTRACT FROM AUTHOR]

What are the features that impersonators select to elicit a speaker's identity? We built a voice database of public figures (targets) and imitations produced by professional impersonators. They produced one imitation based on their memory of the target (caricature) and another one after listening to the target audio (replica). A set of naive participants then judged identity and similarity of pairs of voices. Identity was better evoked by the caricatures and replicas were perceived to be closer to the targets in terms of voice similarity. We used this data to map relevant acoustic dimensions for each task. Our results indicate that speaker identity is mainly associated with vocal tract features, while perception of voice similarity is related to vocal folds parameters. We therefore show the way in which acoustic caricatures emphasize identity features at the cost of loosing similarity, which allows drawing an analogy with caricatures in the visual space. [ABSTRACT FROM AUTHOR]

A theoretical model is developed for the sound scattered when a sound wave is incident on a cambered aerofoil at non-zero angle of attack. The model is based on the linearization of the Euler equations about a steady subsonic flow, and is an adaptation of previous work which considered incident vortical disturbances. Only high-frequency sound waves are considered. The aerofoil thickness, camber and angle of attack are restricted such that the steady flow past the aerofoil is a small perturbation to a uniform flow. The singular perturbation analysis identifies asymptotic regions around the aerofoil; local ‘inner’ regions, which scale on the incident wavelength, at the leading and trailing edges of the aerofoil; Fresnel regions emanating from the leading and trailing edges of the aerofoil due to the coalescence of singularities and points of stationary phase; a wake transition region downstream of the aerofoil leading and trailing edge; and an outer region far from the aerofoil and wake. An acoustic boundary layer on the aerofoil surface and within the transition region accounts for the effects of curvature. The final result is a uniformly-valid solution for the far-field sound; the effects of angle of attack, camber and thickness are investigated. [ABSTRACT FROM AUTHOR]

A new method for producing polyfluoroalkylacrylate latexes for surface modification of chemical fibers using ultrasonic dispersion was examined. The influence of ultrasound (US) on the principal kinetic parameters of the polymerized systems and the colloidal and chemical properties of the resulting latexes were studied. It was shown that finely dispersed latex produced by mini-emulsion polymerization using US was significantly more effective for surface modification of fibers. [ABSTRACT FROM AUTHOR]

Two effective medium models are presented and used to predict complex reflection and transmission coefficients of finite periodic arrays of resonant elastic shells as well as their effective density and bulk modulus at low frequencies. Comparisons with full multiple scattering theory and measurements show that the self-consistent model fails to correctly predict the shape of the transmission/reflection curves when scatterer resonances are close to the first Bragg bandgap. The low frequency grating model, which neglects the evanescent modes and considers scattered wave propagation only in the same direction as the incident one, gives a much better agreement with both measurements and the full multiple scattering theory. Moreover, because it does not require the wavelength to strongly exceed the size of scatterers, the model gives reliable predictions even at frequencies around the first periodicity related bandgap. In contrast to the self-consistent model, the low frequency grating model is applicable when the resonant scatterers have more than two low frequency resonances. [ABSTRACT FROM AUTHOR]

The sound scattering from a finite vacuumed cylindrical shell simultaneously loaded with the bulkheads and the ribs are studied. The motions of the shell are described by the Donnell equations. Each rib is modeled as a rod of circular curvature where only the normal force is applied. The motions of the bulkheads are decomposed into the out-plate bending motions and the in-plate extensional motions, which are independent of each other. The backscattered sound field is analyzed via the frequency-angle spectra. Compared against the backscattered sound from a ribbed cylindrical shell, the Bloch-Floquet waves disappear at low frequencies but still exist at mid and high frequencies. The Bragg scattering excited by the ribs is unchanged at mid and high frequencies. Besides the ribs' Bloch-Floquet waves and Bragg scattering, there exists the Bragg scattering excited by the bulkheads. The backscattering from a cylindrical shell loaded with just the bulkheads is calculated. When the spacing and the thickness of the bulkheads are equal to those of the ribs, the crests of the Bragg scattering and the Bloch-Floquet waves on the frequency-angle spectra are almost the same as those of the ribbed cylindrical shell. The resonances of the bulkheads are also excited in this case. [ABSTRACT FROM AUTHOR]

Beamforming of plane-wave ultrasound echo signals in the Fourier domain provides fast and accurate image reconstruction. Conventional implementations perform a k-space interpolation from the uniform sampled grid to a nonuniform acoustic dispersion grid. In this paper, we demonstrate that this step can be replaced by a nonuniform Fourier transform. We study the performance of the nonuniform fast Fourier transform (NUFFT) in terms of signal-to-noise ratio and computational cost, and show that the NUFFT offers an advantage in the trade-off between speed and accuracy, compared with other frequency-domain beamforming strategies. [ABSTRACT FROM PUBLISHER]

Spectro-temporal modulations of speech encode speech structures and speaker characteristics. An algorithm which distinguishes speech from non-speech based on spectro-temporal modulation energies is proposed and evaluated in robust text-independent closed-set speaker identification simulations using the TIMIT and GRID corpora. Simulation results show the proposed method produces much higher speaker identification rates in all signal-to-noise ratio (SNR) conditions than the baseline system using mel-frequency cepstral coefficients. In addition, the proposed method also outperforms the system, which uses auditory-based nonnegative tensor cepstral coefficients [Q. Wu and L. Zhang, 'Auditory sparse representation for robust speaker recognition based on tensor structure,' EURASIP J. Audio, Speech, Music Process. 2008, 578612 (2008)], in low SNR (≤ 10 dB) conditions. [ABSTRACT FROM AUTHOR]

The accuracy of a phased beam tracing method in predicting transfer functions is investigated with a special focus on the positions of the source and receiver. Simulated transfer functions for various source-receiver pairs using the phased beam tracing method were compared with analytical Green's functions and boundary element solutions up to the Schroeder frequency in simple rectangular rooms with different aspect ratios and absorptions. Only specular reflections were assumed and diffraction was neglected. Three types of error definitions were used: average error level over a narrow band spectrum, average error level over a 1/3 octave band spectrum, and dissimilarity measure. The narrow band error and dissimilarity increased with the source-to-receiver distance but converged to a certain value as the reverberant field became dominant. The 1/3 octave band error was found to be less dependent on the source-receiver distance. The errors are increased as the aspect ratio becomes more disproportionate. By changing the wall absorption from 0.2 to 0.8 for a rectangular room, the average narrow and 1/3 octave band error are deviated by around 1.5 dB. A realistic non-uniform distribution of the absorption increases the error, which might be ascribed to wave phenomena evoked by the impedance-discontinuous boundary. [ABSTRACT FROM AUTHOR]

Active structural acoustic control has been an area of research and development for over two decades with an interest in searching for an 'optimal' error quantity. Current error quantities typically require the use of either a large number of transducers distributed across the entire structure, or a distributed shaped sensor, such as polyvinylidene difluoride. The purpose of this paper is to investigate a control objective function for flat, simply-supported plates that is based on transverse and angular velocity components combined into a single composite structural velocity quantity, termed Vcomp. Although multiple transducers are used, they are concentrated at a single location to eliminate the need for transducers spanning most or all of the structure. When used as the objective function in an active control situation, squared Vcomp attenuates the acoustic radiation over a large range of frequencies. The control of squared Vcomp is compared to other objective functions including squared velocity, volume velocity, and acoustic energy density. The analysis presented indicates that benefits of this objective function include control of radiation from numerous structural modes, control largely independent of sensor location, and need to measure Vcomp at a single location and not distributed measurements across the entire structure. [ABSTRACT FROM AUTHOR]

The waveguide invariant β is affected by the shallow-water environment. The effect due to bottom sediment on β is investigated in this paper. It is found that the effect of sediment bottom can be concentrated on one parameter P-the bottom reflection phase-shift parameter. For a Pekeris waveguide, under Wentzel-Kramers-Brillouin (WKB) approximation, a very simple analytic relation is given: β ≈ 1 + P/(k0Heff), where Heff is the 'effective depth,' and Heff = H + P/2k0. The value of β related to different high-speed sediments (including layered sediment) ranges from 1.0 to 1.5. Some numerical examples including the layered sediment case are conducted to verify this result. Good agreement between the results calculated by KRAKEN and by WKB with parameter P has been found. Hence, the application of parameter P provides a model-free platform to investigate the bottom effect on the waveguide invariant β in shallow-water. [ABSTRACT FROM AUTHOR]

Human listeners seem to have an impressive ability to recognize a wide variety of natural sounds. However, there is surprisingly little quantitative evidence to characterize this fundamental ability. Here the speed and accuracy of musical-sound recognition were measured psychophysically with a rich but acoustically balanced stimulus set. The set comprised recordings of notes from musical instruments and sung vowels. In a first experiment, reaction times were collected for three target categories: voice, percussion, and strings. In a go/no-go task, listeners reacted as quickly as possible to members of a target category while withholding responses to distractors (a diverse set of musical instruments). Results showed near-perfect accuracy and fast reaction times, particularly for voices. In a second experiment, voices were recognized among strings and vice-versa. Again, reaction times to voices were faster. In a third experiment, auditory chimeras were created to retain only spectral or temporal features of the voice. Chimeras were recognized accurately, but not as quickly as natural voices. Altogether, the data suggest rapid and accurate neural mechanisms for musical-sound recognition based on selectivity to complex spectro-temporal signatures of sound sources. [ABSTRACT FROM AUTHOR]

The 'combined-stimulation advantage' refers to an improvement in speech recognition when cochlear-implant or vocoded stimulation is supplemented by low-frequency acoustic information. Previous studies have been interpreted as evidence for 'super-additive' or 'synergistic' effects in the combination of low-frequency and electric or vocoded speech information by human listeners. However, this conclusion was based on predictions of performance obtained using a suboptimal high-threshold model of information combination. The present study shows that a different model, based on Gaussian signal detection theory, can predict surprisingly large combined-stimulation advantages, even when performance with either information source alone is close to chance, without involving any synergistic interaction. A reanalysis of published data using this model reveals that previous results, which have been interpreted as evidence for super-additive effects in perception of combined speech stimuli, are actually consistent with a more parsimonious explanation, according to which the combined-stimulation advantage reflects an optimal combination of two independent sources of information. The present results do not rule out the possible existence of synergistic effects in combined stimulation; however, they emphasize the possibility that the combined-stimulation advantages observed in some studies can be explained simply by non-interactive combination of two information sources. [ABSTRACT FROM AUTHOR]

This work investigates the acoustical properties of a multilayer porous material in which periodic inclusions are embedded. The material is assumed to be backed by a rigid wall. Most of the studies performed in this field used the multipole method and are limited to circular shape inclusions. Here, a mode matching approach, more convenient for a layered system, is adopted. The inclusions can be in the form of rigid scatterers of an arbitrary shape, in the form of an air-filled cavity or in the form of a porous medium with contrasting properties. The computational approach is validated on simple geometries against other numerical schemes and with experimental results obtained in an anechoic room on a rigid grating embedded in a porous material made of 2 mm glass beads. The method is used to study the acoustic absorption behavior of this class of materials in the low frequency range and at a range of angles of incidence. [ABSTRACT FROM AUTHOR]

Previous studies investigating sensitivity to step changes in tempo and prediction of tone onset time have generally utilized isochronous sequences. This study investigates subjects' ability to detect deviations from a gradual change in the tempo of a tone sequence (experiment 1) and their judgment of the perceptually optimal timing of this tone (experiment 2). In experiment 1, inter-onset-intervals within pairs of eight-tone sequences followed a geometric progression to create a gradual tempo change. In one sequence, the final tone was presented either earlier or later than specified by the progression. Subjects performed well at detecting deviations that exaggerated the tempo progression but poorly when it was counteracted. Experiment 2 used similar pairs except that the final tone was always presented earlier in one sequence than the other. Final interval length was adaptively adjusted to subjects' judgments; it was adjudged in best agreement with the progression when its length was roughly half way between the mathematically correct value and the length of the penultimate interval. The data support 'multiple-look' and entrainment models of tempo sensitivity and suggest that temporal prediction is based less on the tempo contour of a whole sequence than on the duration of the preceding interval. [ABSTRACT FROM AUTHOR]

Theoretical and experimental determination of sonic band structures of two-dimensional (2-D) arrays of rigid cylinders in air is reported. We present measurements for square and triangular lattices. A variational method is employed to calculate the acoustic dispersion relation. Experimentally, a transmission technique and the analysis of the phase delay between the incident and scattered waves by the structure are used to construct the acoustic bands. The comparison between theory and experiments allows to fully characterize the band gaps and it has also demonstrated the existence of deaf bands; i.e., bands which cannot be excited due to symmetry reasons. For the case of square lattice we show that the structure with a filling fraction of 0.41 has a full acoustic gap [ABSTRACT FROM PUBLISHER]

An introduction is presented in which various topics within the issue are discussed including supercritical aggregation equation, a perturbative model for predicting high-Reynolds-number, and the scattering of plane acoustic waves through circular semi-infinite pipe.

Although transcranial photoacoustic imaging has been previously investigated by several groups, there are many unknowns about the distorting effects of the skull due to the impedance mismatch between the skull and underlying layers. The current computational methods based on finite-element modeling are slow, especially in the cases where fine grids are defined for a large 3-D volume. We develop a very fast modeling/simulation framework based on deterministic ray-tracing. The framework considers a multilayer model of the medium, taking into account the frequency-dependent attenuation and dispersion effects that occur in wave reflection, refraction, and mode conversion at the skull surface. The speed of the proposed framework is evaluated. We validate the accuracy of the framework using numerical phantoms and compare its results to k-Wave simulation results. Analytical validation is also performed based on the longitudinal and shear wave transmission coefficients. We then simulated, using our method, the major skull-distorting effects including amplitude attenuation, time-domain signal broadening, and time shift, and confirmed the findings by comparing them to several ex vivo experimental results. It is expected that the proposed method speeds up modeling and quantification of skull tissue and allows the development of transcranial photoacoustic brain imaging. [ABSTRACT FROM AUTHOR]