bluuebunny/crossref_metadata_2025 huggingface dataset:
Measuring longer tubular objects using acoustic pulse reflectometry
Authors: Sharp David B. , Campbell D. Murray
Published: July 2002

Acoustic pulse reflectometry is a noninvasive technique for measuring the internal dimensions of tubular objects. A sound pulse is produced using a loudspeaker and injected into the object under investigation via a source tube. The resultant object reflections are recorded by a microphone embedded in the wall of the source tube. Analysis of the reflections yields information about the bore profile of the object. At present, there is a restriction on the length of object that can be measured using the standard reflectometer. This restriction arises because after the object reflections pass the microphone they undergo further reflection at the loudspeaker. These source reflections return to the microphone as unwanted signal. Hence, there is only a finite time over which the object reflections can be accurately recorded which, in turn, limits the length of object that can be measured. In this paper, a method for removing the length restriction is described and preliminary results are presented. The method involves the cancellation of the incoming object reflections at the loudspeaker, thus preventing the formation of source reflections. [Work supported by EPSRC.]
Acoustic monitoring of the curing process in cement and concrete
Authors: Tittmann Bernhard R. , Tavossi Hasson M. , Cohen-Tenoudji Frederic
Published: July 2002

Acoustic wave velocity and attenuation measurements are used to monitor cement and concrete during hardening. The measured acoustic parameters can then be used to investigate the curing process. The goal of this work is to determine the time required for a given mixture of concrete to be hard enough for the removal of the molds, in order to speed up the construction process. Currently this removal time is unpredictable. In addition concrete, mortar, and cement, before hardening, can be considered as examples of granular materials. The shear, rigidity moduli, and acoustic wave velocity of these materials can differ from the values obtained by applying effective-medium theories and Biots theory. The complete description of the mechanical properties of these materials requires the consideration of discrete nature of the solid constituents and the effects of contacts between the grains. These effects are included in the theoretical description of the process. The methods of acoustic microscopy are also applied to investigate the surface and subsurface physical changes of cement during hardening. Theoretical and experimental results of this investigation will be presented.
Sound propagation in gas-filled rigid-framed porous media: General theory and new experimental and numerical data
Authors: Lafarge Denis , Henry Michel , Firdaouss Mouaouia , Guermond Jean-Luc
Published: July 2002

The acoustic properties of gas-filled porous media have been the subject of extensive theoretical and experimental work. However, even in the simplest case of rigid-framed materials, most of the theoretical developments found in the acoustical literature remain largely empiric or semiphenomenologic. This is due to the complicated microstructure of porous materials in general. Starting with first principles and using a simple two-scale analysis, a general formulation of the problem of (linear) long-wavelength sound propagation in gas-filled media is provided in terms of two independent permeabilities. One of these—the viscous dynamic permeability—is well known. Its thermal analog, the thermal dynamic permeability, is new in the acoustical context. It can be related to a notion of ‘‘mean survival time’’ in diffusion-controlled reactions. The exact connection between the microgeometry and the frequency-dependent dynamic permeabilities is obtained in terms of independent geometrical distribution functions. Useful analogies with the dispersion of electric and magnetic permeabilities are noted. New experimental and numerical data demonstrate the usefulness of the scaling functions proposed by Wilson et al. and Pride et al. Different limitations of the general modeling and the mentioned scaling functions are also noted.
Electric-field influence on Lamb and SH wave properties in LiNBO3 plates
Authors: Zaitsev B. D. , Joshi S. G. , Kuznetsova I. E.
Published: July 2002

Presently, acoustic devices using an electrically controlled time delay are highly promising. They include acoustic phase shifters, amplitude and phase modulators, and transversal filters with electrically controlled amplitude-frequency characteristics. Lithium niobate is one of the most promising materials with the anisotropic nonlinear electroacoustic interaction studied for bulk (BAW) and surface (SAW) acoustic waves. This paper is devoted to the theoretical investigation of electrically controlled characteristics of acoustic waves in plates of lithium niobate. The main crystallographic cuts and various thicknesses of plate under the action of different orientations of an external electric field have been investigated. It was confirmed that the dependence of velocity on an electric-field intensity has a complex nature as well as for SAW and BAW. Therefore, even and odd portions of analyzed dependencies have been introduced and studied separately. It was found that mentioned portions are functions not only of wave propagation direction and electric-field orientation but of plate thickness. It allows the changing of the nature of velocity dependence on electric-field intensity from a quadratic law to a linear one. Another advantage is the possibility of providing a significant electric-field intensity by using low voltage due to thin thickness of plate.
Heckls influence on SEA development
Authors: Lyon Richard H.
Published: July 2002

Manfred Heckl was at Bolt Beranek and Newman Inc. in the early 1960s during the development of the basic SEA ideas and applications. As various concepts, formulas, and experimental results emerged, he constantly showed how those results related to the earlier work of Westphal, Cremer, and others. Four areas are particularly fresh in my mind—the use of transmissibility notions for connected plates, the use of reciprocity to calculate SEA results, the modal density of cylindrical structures, and the edge damping of plate structures. In every case, Manfred was able to bring fresh insights to the discussions. Although his name is not on many SEA papers, his contributions and influence were strong and are not forgotten.
Ambiguity in prominence perception in spoken utterances of American English
Authors: Dilley Laura C. , Shattuck-Hufnagel Stefanie
Published: July 2002

For most words of English in most spoken contexts, the location of the main stress syllable is clear. However, for words in which (a) the main lexical stress is not obvious from the phoneme string alone (e.g., main-stress-ambiguous words like ‘‘digest’’ and ‘‘increase,’’ and certain proper names), and (b) the possible positions for the main stress consist of adjacent full-vowel syllables, an ambiguity in the location of the prominence and, consequently, in the identity of the lexical item (for main-stress-ambiguous words) is observed when these words occur in contexts with certain F0 configurations extending across the adjacent full-vowel syllables (e.g., a rise followed by a peak, or a peak followed by a fall; F0 peaks frequently dissociate from lexically stressed syllables [Ladd (1996)]). In these cases, the syllable affiliation of the main lexical stress is unclear; either the peak or movement (rise or fall) in the F0 contour can be heard as the prominence. This suggests that listeners interpret F0/syllable alignment in light of their language knowledge and a set of perceptual proclivities [Handel (1989)]. When the language fails to specify enough information or two perceptual proclivities are in conflict, perceptual ambiguity can result.
Intonation of noun phrases in Unangan (Eastern Aleut)
Authors: Taff Alice , Wegelin Jacob
Published: July 2002

This paper reports on the intonation patterns of Unangan. The effect of syntactic structure on intonation was investigated. Data for this study are taken from recordings of 12 fluent speakers each providing around 20 sentences in Unangan elicited by English stimuli. Numerical results of entire pitch tracks generated on the Kay CSL 4300B were subjected to statistical analysis. Exploratory plots of batches of sentences were produced using a smoother. When utterances are grouped by speaker, Unangan words have been shown to have an intonation contour whereby each word attains a maximum in its first half, ending lower than it starts. The combination of highs at each word beginning with the downtrending of sentences creates the overall sentence shape of a cascade, each word a step in the falls [Taff and Wegelin, UCLAWPP (1997)]. Building on that study, this investigation looks at plots of same sentences compared across speakers finding that in the possessor/possessed construction (e.g., cormorant’s neck) the second word in the phrase is higher in pitch than the first, contrary to the lowering of each successive word described above. Results indicate that intonation in this language is closely related to its syntax. [Work supported by NSF.]
Effects of prosodic structure on consonant weakening
Authors: Lavoie Lisa M.
Published: July 2002

While the effects of lexical stress are most obvious on vowels, consonants also show evidence of prosodic structure. In English, stress conditions the flapping of alveolar stops and Turk [‘‘Effects of Position in Syllable and Stress on Consonant Articulation,’’ Ph.D. dissertation, Cornell University, 1993] has shown that labial stops also shorten in the flapping environment. This study investigates the strength of intervocalic consonants as a function of word stress, position-in-word, and speech rate. Two stress pairs of closely matched disyllabic words (one for word-initial, one for word-medial) were recorded for 16 English consonants at three rates of speech. Words for [v] are as follows, with the stressed syllable capitalized: VENdor, veNEER; SEver, seVERE. Results for fricatives will be reported, including the following tendencies for fricatives which are the onset to an unstressed syllable: voiced fricatives are more fully voiced, some fricatives are shorter, more formant structure is evident in the noise, and transitions to the following vowel may be longer. Findings for each speech rate will be compared to determine how the rate may impact consonant behavior. Each correlate will be evaluated with respect the hypothesis that consonants in unstressed syllables are more vowellike.
Reconstruction and projection of interior sound fields using a spherical measurement array
Authors: Williams Earl G.
Published: July 2002

A spherical surface populated with microphones is placed within an aircraft fuselage or automotive cabin, and the sound field is determined throughout the interior of the source. This hypothetical experiment is the goal of the measurement system which will be discussed. The output from this spherical antenna is processed using mathematical and signal processing techniques to solve both a forward (projection) and an inverse (reconstruction) problem when no sources are within the array. The forward projection provides the field inside the measurement surface. The field outside is computed by solving an inverse problem providing a reconstruction of pressure and velocity in a spherical region up to the external enclosing boundaries. The accuracy of a proposed measurement system for both the forward and inverse modes of operation will be discussed. This discussion includes number of sensors and sensor placement schemes, and, most importantly, the effect of ambient noise and SNR on the projections and reconstructions, including the maximum reconstruction distances from the measurement sphere which can be obtained. [Work supported by ONR and NASA.]
Some nonlinear aspects of the ear as a sound detector and a sound emitter: Comparisons with properties of musical instruments
Authors: Tubis Arnold , Talmadge Carrick L. , Long Glenis R.
Published: July 2002

A compressive nonlinearity in the mechanics of the cochlea is responsible for (1) the dynamic detection range of about 120 dB; (2) the level-dependent modification of the ability to detect one tonal component in the presence of another (masking); (3) the stabilization of cochlear self-oscillations, which are associated with sounds broadcast from the ear (spontaneous otoacoustic emissions); and (4) the psychoacoustic detection and detection in the ear canal of frequency components (intermodulation distortion products) not present in the original acoustic signal. The spontaneous otoacoustic emission spectra are characterized by quasi-regular frequency spacings, with some ears having over 30 narrow-band spectral peaks. The intermodulation distortion level is higher than that claimed for mediocre stereo systems and varies with frequency. Several interesting analogies between the modeling of otoacoustic emissions and the sound spectra of musical wind instruments are discussed. [Work supported by NIDCD.]
On the rating of high-energy impulsive sounds: Optimization of a level-dependent conversion procedure with the help of new field survey results
Authors: Vos Joos , Buchta Edmund
Published: July 2002

A few years ago, Schomer [Noise Control Eng. J. 42(5), 179–191 (1994)] developed a new rating procedure for high-energy impulsive sounds, in which a level-dependent conversion of the C-weighted sound exposure levels (CSELs) of the impulses into A-weighted sound exposure levels (ASELs) of equally annoying vehicle sounds was applied. In a recent reanalysis, Vos [Noise Control Eng. J. 45(3), 123–131 (1997)] showed that at least for artillery sounds, the optimal parameter values to be used in this level-dependent conversion procedure were different from those suggested by Schomer. The experimental results from a new field survey on the community response to artillery and road-traffic sounds (Buchta and Vos, these proceedings) provide a new opportunity to optimize the conversion procedure. The present effort is especially interesting because here, in contrast to previous analyses, large sets of different CSEL values per noise zone are available (for most of the zones the impulses originating from tens of different firearm/shooting range combinations were considered), and the annoyance ratings for the impulsive and road-traffic sounds had been determined with similar questions and for the same group of respondents, facilitating a comprehensive estimate of the adequate parameter values.
Scale modeling of railway noise barriers
Authors: Hothersall David C. , Horoshenkov Kirill V. , Morgan Philip A.
Published: July 2002

Noise barriers are an efficient way of reducing the noise from railways, particularly the noise produced in the region of the rails and wheels. Several designs of noise barrier have been suggested in the literature which aim to improve the insertion loss over that obtainable from a plane screen of the same height. The positioning of these barriers is governed by the limitations imposed by the structure gauge of the railway. Scale modeling has been carried out in a humidity-controlled anechoic chamber at a scale of 1:20. Appropriate materials have been selected to model the impedance of the track ballast, absorbing barrier surfaces and grassland at the reduced scale. To model the interaction between the side of the train and the barrier realistically, models appropriate for a high-speed train cross section have been used. Experimental results for the insertion loss of shaped and multiple-edge barriers are compared with the results from numerical modeling. The efficiency of each of the designs is assessed. The generation of time histories for the passage of trains and the calculation of noise indices are considered.
Surface waves over a convex impedance ground
Authors: Li Kai Ming , Wang Qiang
Published: July 2002

Laboratory experiments are reported for the study of surface waves above a convex impedance surface. Monopole, horizontal dipole, and vertical dipole sources are used in these experiments. The model ground surface is an open-meshed rubber mat with a hole size of 22-mm square and 12-mm depth. The rubber mat is then laid on a rigid masonite curved surface. There are generally good agreements between measurements and predictions based on the residue series theory. In an earlier theoretical study [see J. Acoust. Soc. Am. 89, 107–114 (1991)], Raspet et al. have identified the contribution due to the surface wave poles. However, the present experimental results have suggested that the surface wave pole contributions not only contain the surface waves but also include the creeping waves. The experimental results also show that there are two groups of waves, which are well separated, arriving at different times. The earlier group of waves may be attributed to the creeping waves, while the later group of waves is identified as the surface waves. [Work supported by EPSRC and an Open University Studentship.]
Acoustic determination of scale and structure constants in fluctuating fluid
Authors: Mellert Volker , Schwarz-Roehr Bernhard
Published: July 2002

The power spectrum of tubulence (e.g., fluctuating wind, v, and temperature T) is characterized by structure constants, which are related to scale and strength of fluctuation. The von Kármán spectrum is a common model for atmospheric turbulence, and is determined by intensity and scale parameters c2v c2T and L0. The quantities are usually measured by recording time series, e.g., of v and T, at one location. Required is a frozen turbulent structure, being carried along the sensor by an average flow. This measuring method fails if the average movement of the fluid is insufficient. However, sound waves provide an easy and fast tool for determining the desired parameters. The complex amplitude A(r) of the wave is changed by the refractive index fluctuations. Successive wavefronts ‘‘see’’ different spatial representations of the turbulence. Evaluating the statistics of this ensemble yields the desired parameters, provided a theory of wave propagation through turbulence is available. Based on the parabolic equation method, analytical results have been derived allowing for the calculation of the structure constants (Ostashev et al., accepted for publication in J. Acoust. Soc. Am.). Spatial correlation 〈A(r1)⋅A(r2)〉 yields c2v, c2T, and L0 acoustically. Results are compared with ‘‘classical’’ sensor measurements in the atmospheric boundary layer.
Inclined acoustic sounding of the atmospheric boundary layer
Authors: Chunchuzov Igor P.
Published: July 2002

The method of inclined acoustic sounding of the atmospheric boundary layer has been proposed and realized experimentally. The method is based on the phenomena of the waveducted sound propagation along ground surface under the presence of the positive wind shear. In the experiment the wind velocity profiles and their large-scale time fluctuations were continuously controlled with the SODAR up to the height of 300 m and with the anemometers placed at the mast of 56 m height. The fluctuations of the acoustic pulse travel time with the periods in the range of 3–30 min were measured between the special pulse generator and the three receivers placed on the ground surface 2.5 km apart from each other, forming a horizontal triangle antenna. The obtained cross coherence and phase spectra between the pulse travel time and the wind velocity fluctuations show a peak of coherence with the maximum of about 0.8 to 0.9 for the period of 8 min. Such low-frequency wind velocity fluctuations near the ground surface are thought to be caused by the gravity wave modes propagating in the stable stratified troposphere with the periods close to the Brunt–Vaisalla period. The inclined acoustic sounding is proposed to be used for the acoustic tomographic monitoring of the three-dimensional wind field in the atmospheric boundary layer.
Direct and inverse obstacle scattering by shape deformation
Authors: Roy Dilip N. Ghosh , Warner Jeremy A. , Couchman Luise
Published: July 2002

The results of direct and inverse scattering of plane acoustic waves from penetrable and impenetrable objects are reported here. It is assumed that the scatterer boundary is a superposition of an arbitrary deformation on an underlying simple geometry. The direct problem is solved via the Padé extrapolation of the boundary variations. This results in solving only certain algebraic recursion relations and requires neither Green’s function nor integral representations. The inverse problem of recovering the obstacle’s shape and material parameters from the far-field scattering data is solved by Gauss–Newton minimization. The calculation of the scattered field and its Jacobian involves no more than solving a series of Helmholtz scattering problems in the same domain, namely, exterior to the simple shape instead of the iteratively updated deformed surfaces, leading thereby to substantial computational simplifications. Moreover, since no integral equation is used, the ambiguity in the solution because of the interior eigenvalues does not arise. Several two-dimensional obstacles of various shapes are inverted for their boundaries as well as their material parameters of mass density and wave number. Finally, the procedures described can be extended straightforwardly to transmission and three-dimensional problems.
Interaction of an acoustic plane wave with a circular elastic plate in water
Authors: Eudeline Yannick , Duflo Hugues , Izbicki Jean-Louis , Duclos Jean
Published: July 2002

An experimental investigation of the interaction of an acoustic plane wave with a circular elastic plate is presented. The experimental setup consists of a duraluminum 2-mm-thick disk with different values of the radius (between 10 and 50 mm). Monostatic and bistatic experiments are performed. In the first case a transducer turns around the disk (in the perpendicular plane), sends the incident wave, and receives the diffracted signal in each observation direction. In the second experiment we use two transducers, the emitter and the receiver which turns around the circular plate. In each observation direction, we have calculated the FFT of the diffracted signal for frequencies lower than 3 MHz. We have represented the results in a two-dimensional image in which appears the spectral response of the plate. Two kinds of results are obtained: (i) Lamb waves propagation on the plate which are detected by their angular reemission of energy in water, (ii) particular frequencies are also detected close to eigenfrequencies of the circular plate in vacuum.
A new model to predict echoes of large, smooth targets, with finite dimension transducers, at a low cpu cost
Authors: Berton Jean-Luc , Riffard Cecile , Dominjon Christian , Dedieu Dominique
Published: July 2002

A model called SYTRAC.L, for the prediction of echoes from large, hard reflectors, facing finite dimensions transducers, is proposed. For great reflectors, the introduction of the acoustic ray theory allows low cpu costs and more reasonable memory needs, with comparison with other methods where a numerical integration is performed on the reflector, since this integration is eliminated. In a first stage, this model does not take into account reflector edge diffraction effects, but these are being introduced with GTD approaches. The validation of the formulation and of the numerical implementation was done by comparison with analytical results in two canonical configurations. Experimental comparisons for plane and cylindrical reflectors have also been performed. This model is used to estimate the accuracy of telemetries on large structures, at distances less or greater than the far-field limit. As an example, results of a parametric study of echo characteristics from cylindrical and plane targets are described according to their distance and tilting.
On the preferred delay time of a single reflection for cellists
Authors: Sato Shin-ichi , Ando Yoichi , Ota Saho
Published: July 2002

In order to attain a knowledge of designing the stage enclosure in a hall, the subjective preference of sound fields with a single reflection for alto-recorder players has been reported [I. Nakayama, Acustica 54, 217–221 (1984)]. In this study, subjective preference judgments of sound fields with a single reflection were performed by cello players. It is examined whether or not preferred delay time of reflection is dependent on the effective duration (τe) of the autocorrelation function (ACF) of the music signals performed by each player and the amplitude of the reflection. [Work was supported by the Grant-in-Aid for Scientific Research JSPS.]
Some recent experiences with the acoustical design of orchestra pits
Authors: Paoletti Dennis , Graffy Kurt , Tedford Larry
Published: July 2002

A number of recent projects including work for the San Francisco and Houston Operas have included acoustical designs for new and/or renovated orchestra pits. This paper will review some of those projects, their criteria, design, measurements, and evaluations.
Acoustics of the avian vocal tract
Authors: Fletcher Neville , Tarnopolsky Alex
Published: July 2002

The avian vocal tract can appropriately be modeled on a source-filter basis, with the pressure-controlled syrinx valve providing the wideband harmonic source and the vocal tract the linear passive filter. This filter consists of four parts: the bronchial tubes above the syrinx valves, the trachea, the mouth with included tongue, and the beak. Each of these can be modeled and its behavior calculated quantitatively using standard methods [Fletcher, Acoustic Systems in Biology (Oxford U. P., New York, 1992)]. The long trachea defines the main resonance frequencies, upon which the bronchial resonances impose formant bands. The mouth, the cross section of which can be varied by changing the tongue position, influences particularly the frequencies of the first two tracheal resonances, but also the harmonicity of the upper system resonances. The beak behaves as a slotted tapered transmission duct, and contributes an end-correction to the system, the magnitude of which is a strong function of both beak gape and frequency. This paper reports the numerical results of such a theoretical analysis, compares these with experimental measurements upon appropriate model systems, and discusses the implications of the results for the understanding of avian vocalization.
The Scripps Pier Bubble Experiment of 1997 and overview of rip events and their effects on acoustics measurements
Authors: Caruthers Jerald W. , Elmore Paul A. , Stanic Stephen J. , Goodman Ralph R.
Published: July 2002

An experiment to determine the dynamics, distributions, and acoustic effects of bubbles in shallow water just offshore from active surf was performed in the Spring of 1997. The region of interest was just North of the pier at the Scripps Institution of Oceanography. An area from a few tens of meters to a thousand meters from the beach was instrumented by several researchers. An effort was made to acquire a comprehensive dataset of coastal dynamics, bubble distributions, and acoustic propagation. A major emphasis was placed on a smaller region approximately 400 m2 in area and about 300 m offshore, where most of the instruments were clustered. The purpose of this paper is to provide an overview of the experiment, a summary of the runs made over the several days of experiments, and a context for the observed rip events based on an acoustic device known as the ‘‘Delta-Frame.’’ Two rip events (Run 5, event starting about 14:48 PST 7Mar97 and Run 7, event starting about 15:38 PST 8Mar97) selected for coordinated analyses and presentations to follow will be highlighted. [Work supported by ONR.]
Sound radiation by a bubble encountering a vortex ring
Authors: Kolaini Ali R.
Published: July 2002

The dynamics of a bubble and subsequent acoustic radiation interacting with a vortex ring created by an underwater nozzle are studied both theoretically and experimentally. The velocity field of the flow containing the bubble may be represented as a ‘‘basic flow’’ related to the vortex ring and a ‘‘secondary flow’’ related to the bubble motion [G. Chahine, 20th Symposium on Naval Hydrodynamics (1994)]. The ‘‘bubble flow’’ is assumed to be irrotational satisfying the Laplace equation. The vortex related velocities are given by the stream function and are taken into account by imposing ‘‘correct’’ kinematics and dynamic boundary conditions at the bubble surface. The interaction of the bubble with a vortex ring has been shown to cause severe deformation. Under special circumstances the deformed bubble may be at resonance with these vortex filaments and force it to radiate sound to the far field. The boundary integral technique (BIT) is employed to solve governing equations. The BIT is utilized to simulate the ‘‘bubble flow,’’ its surface distortions and subsequent acoustic radiation. The critical parameters responsible for the acoustic re-excitation of the bubble encountering the vortex filaments are discussed in some details. Some conclusions are arrived at on the acoustical characteristics of the bubble encountering a fully developed turbulent flow field. [Work supported by ONR.]
Influence of air loading and dissipation on plate transducer amplitude
Authors: Ballato Arthur
Published: July 2002

Air-loaded plate transducers driven piezoelectrically are used in a variety of modern applications such as optical modulators, microactuators, and certain types of resonant acoustic sensors and frequency control elements. For these uses it is necessary or desirable to know the maximum mechanical amplitudes obtainable, and how these are limited by the various internal dissipation mechanisms and the loading of the ambient fluid. Internal conduction, dielectric, and acoustic viscosity losses are incorporated, and, by introducing of a complex piezoelectric coupling coefficient, changes in critical frequencies and amplitudes are traced with variations in type and size of dissipation mechanism, and the ambient loading. The analysis also shows that the unavoidable interfacial stresses existing between the crystal plate surfaces and the exciting electrodes can become exceedingly large at the frequencies commonly used for frequency control of cellular communications. Because the various devices covered usually form components of an overall circuit design, a number of alternative equivalent electrical circuits are also provided whereby the physics of these structures may be rendered and readily interpreted in network terms.
Psychometric functions for gap detection
Authors: Florentine Mary , Buus So/ren , Geng Wei
Published: July 2002

To determine the form of psychometric functions for gap detection, three normal listeners were tested at octave frequencies from 0.25 to 8 kHz using a constant-stimulus procedure with a cued yes–no paradigm. The gaps were carried by bandpass noises with an overall level of 85 dB SPL and a bandwidth equal to three auditory-filter bandwidths. To avoid audibility of spectral splatter, the bandpass noise was presented in a complementary notched-noise masker with a spectrum level 10 dB below that of the signal and a bandwidth equal to nine auditory-filter bandwidths. Gap durations were chosen randomly from one of six fixed values (seven at 0.25 kHz) ranging from 0.5 Minimal Detectable Gap durations (MDG) to 2 MDGs (2.8 MDGs at 0.25 kHz). An inaudible gap of 0.5 ms was included as a control condition. Although the false-alarm rate varied among the listeners, the slopes of the psychometric functions were quite similar. The slopes increased as the test frequency increased up to 2 kHz, but remained constant at the higher frequencies. These results indicate that stimulus variability is not important in determining gap-detection thresholds at 2 kHz and above.
Suppression and the upward spread of masking
Authors: Oxenham Andrew J. , Plack Christopher J.
Published: July 2002

For signals well above a masker in frequency, signal level at threshold grows more rapidly than masker level, leading to the upward spread of masking (USM). It is unclear whether USM is due to a relative increase in masker excitation or an increase in suppression with increasing masker level. Thresholds were measured using a 4-kHz signal, gated with a 10-ms Hanning window. The masker was a 500-Hz-wide random Gaussian noise, centered at either 4 kHz (on frequency) or 2.4 kHz (off frequency) and gated with 2-ms ramps. Masker levels ranged from 50–90 dB SPL. In simultaneous-masking conditions, the signal was temporally centered in a 400-ms masker. In nonsimultaneous conditions, where no suppression should occur, the signal was in a brief gap between two 200-ms maskers. Results are qualitatively consistent with an explanation based on the characteristics of the basilar-membrane input-output function. At higher signal levels, the differential compression of masker and signal produces USM even in nonsimultaneous conditions (no suppression). At low signal levels (below about 40 dB SPL) the basilar-membrane response to single tones is nearly linear and nonlinear USM is only observed in simultaneous-masking conditions. [Work supported by the Wellcome Trust and the Royal Society.]
Detection of differences in rate of frequency change in gliding tones
Authors: Madden John
Published: July 2002

The purpose of the study was to measure discrimination for glides in frequency, based on discrimination of rate of frequency change. Changes in frequency transition span and duration were eliminated as confounding cues by using signals of equal frequency span and duration that smoothly changed in rate at the half-way point in their duration. That is, each signal consisted of a first segment at one rate of frequency change, a brief rate transition segment, and a second segment at another rate of frequency change. The listeners compared a standard signal during which there was no change in rate (a linear glide) with a target signal during which the second segment changed at a greater rate than the first. The task was to indicate which signal changed in rate. Discrimination thresholds were obtained for signals with a range of center frequencies, frequency spans, and durations. Both up- and down-glides were used. Preliminary results indicate that discrimination thresholds are relatively constant for center frequencies from 0.5 kHz to 2 kHz, but increase by a factor of 2.5 at 6 kHz. [Work supported by Research Grant Number 1 R15 dc 02662-01 from the National Institute on Deafness and Other Communication Disorders, National Institutes of Health.]
Complex resonances of elliptic cylinders
Authors: Ancey Stéphane , Folacci Antoine , Gabrielli Paul
Published: July 2002

Complex resonances of elliptic cylinders of arbitrary eccentricities (including the limit cases of the circular cylinder and the strip) are exactly determined by solving the Helmholtz equation with the Sommerfeld’s radiation condition at infinity and various boundary conditions on the scatterer. Resonances are then fully classified along the two irreducible representations A1 and A2 of the symmetry group C2 of the scatterer. This spectrum of resonances is also asymptotically recovered (i) by using the ordinary geometrical theory of diffraction, and (ii) by applying the method of the Gutzwiller–Voros spectral determinant. This last technique could be developed in acoustic multiple scattering. Indeed, in this context, because of the complexity of the system of rays and its chaotic behavior, ordinary geometrical theory of diffraction fails to provide accurate results.
Piezoelectric thin shell theoretical model and eigenfunction analysis of radially polarized ceramic cylinders
Authors: Ebenezer D. D. , Abraham Pushpa
Published: July 2002

A piezoelectric thin shell theoretical model of radially polarized ceramic cylinders is first developed. An eigenfunction approach is then used to determine the displacement, stress, electric field, and input electrical admittance of the cylinder. In the model, the effect of bending strain is included and it is assumed that the electric field varies linearly between the electrodes. The electrostatic condition is then used to express the electric field in terms of the displacement. Next, the equations of motion and the boundary conditions are derived by using Hamilton’s variational principle. They have the same form as the corresponding equations for a thin elastic shell and are solved after expressing the frequency-dependent displacement as the sum of the static displacement and a weighted sum of the eigenfunctions of the short-circuited cylinder. The eigenfunctions are determined here by using a general method and, therefore, cylinders with arbitrary boundary conditions can be analyzed. It is shown that experimental resonance frequencies and input electrical admittance of free-free cylinders are in good agreement with those computed here and that the electric field is in good agreement with results obtained by other investigators who used a numerical method to solve the equations.
Active target detection in the ocean: Optimizing performance and cost
Authors: Michalopoulou Zoi-Heleni
Published: July 2002

The goal of this work is to design a processor for underwater target detection with superior performance to the commonly used matched filter without the efficiency penalties of the optimal filter. The theoretically optimal filter for active detection in the ocean is a correlator between the received signal and the convolution of the transmitted signal and the impulse response of the ocean. This filter is seldom employed because of the considerable computational overhead. The practically preferred method is a standard matched filter that correlates the transmitted signal to the received signal. It is computationally efficient but analytically suboptimal because it ignores the effects of the propagation medium on the transmitted signal. The standard filter is also preferable because of its attractive property of portability across environments, this feature stemming from deliberate disregard of the physics of the propagation medium. Here, the potential for improving detection performance is explored through modified matched filters that retain the portability property but do not resort to the exhaustive multiparameter grid searches of the optimal filter. [Work supported by ONR Ocean Acoustics, through Grant No. N000149710600.]
The form of the normal mode that ensures escape with certainty from a surface channel
Authors: Floyd Edward R.
Published: July 2002

Surface channels trap those rays that are reflected internally before reaching a deep sound channel according to classical geometric ray tracing. In the wave representation, some leakage of trapped normal modes does occur. Recent advances in wave propagation [E. R. Floyd, Anal. Fond. L. Broglie 20, 263–279 (1995)] have shown that a wave function having subbarrier energy but with a particular compound modulation in amplitude and wave number does tunnel through a barrier with certainty and without reflection. Herein, a normal mode with a particular compound modulation is shown to escape from a surface channel with certainty and without reflection. These normal modes with compound modulations, which may be unfamiliar to many workers, are solutions to the wave equation. The investigation considers a bottomless sound velocity profile, C(z), whose reciprocal square, C−2(z), forms a surface channel over the deep sound channel by two piecewise-continuous linear segments. The findings are generalized to include various surface and deep sound channels. While the quantum tunneling problem was originally solved in a trajectory representation [analogous to rigorous ray tracing, cf. E. R. Floyd, J. Acoust. Soc. Am. 80, 877–887 (1986)], herein a wave representation is used.
Inclusion of continuum effects in coupled-mode theory using leaky modes
Authors: Knobles David P. , Koch Robert A. , Westwood Evan K. , Stotts Steven A.
Published: July 2002

A difficulty with coupled-mode algorithms for acoustic propagation in sloping, shallow-water regions is properly including the modal continuum. The disadvantage of the standard false-bottom approach is that a large number of modes are needed to represent the continuum, which makes the coupled-mode solution less practical. A leaky mode decomposition requires significantly fewer modes to represent the continuum. However, because the leaky modes are not bounded in the lower half-space, the overlap integrals involved in computing the coupling coefficients are undefined. In addition, the branch line integral, which is not included in the usual coupled-mode formalism, can become significant as modes undergo the transition between being trapped and being leaky. In this work, the approach of inserting a small attenuation gradient in the lower half-space is taken. The half-space gradient makes the mode functions have Airy-function solutions, eliminates the branch cut, replaces it by a series of modes, and makes the leaky modes well behaved at infinite depth. Using the differential form of the coupled-mode equations, overlap integrals can be computed analytically using well-known formulas for Airy functions. The accuracy and efficiency of the approach is evaluated using the ASA benchmark wedge problem as a test case. [Work supported by ONR.]
Prediction of ambient noise in the ocean, the missing components
Authors: Cato Douglas H.
Published: July 2002

The main components of ambient noise in the ocean were established by pioneers in ambient noise [V. O. Knudsen, R. S. Alford, and J. W. Emling, J. Marine Res. 7, 410–429 (1948); G. M. Wenz, J. Acoust. Soc. Am. 34, 1936–1956 (1962)] and prediction methods are generally based on the results of these studies. Most measurements were made in regions of high shipping densities where traffic noise usually obscured other components of ambient noise at low frequencies (below 200 Hz), so these do not appear in most prediction methods, even though their presence was noted in the early studies. Biological noise was also recognized as important, and widely studied, but is also not usually included. Studies of ambient noise near Australia, where shipping densities are generally lower, have shown the importance of low-frequency wind-dependent noise. Biological noise is also a major component in this part of the world, often being the dominant noise in tropical waters. Biological choruses are widespread and occur with diurnal regularity. These results are not inconsistent with measurements in other parts of the world. This paper discusses important components of ambient noise that are often missing from prediction methods.
Imaging of supersonic surface fields on a cylindrical shell
Authors: Corrado Charles N. , DiPerna Daniel T. , Conti Matthew
Published: July 2002

Conventional imaging techniques represent a radiating body as a distribution of equivalent monopole sources. This paper presents a more rigorous approach for imaging the supersonic components of both surface pressure and normal velocity produced by scattering or radiation from a nominally cylindrical body. The technique employs the Helmholtz integral equation to relate monopole and dipole strengths. A modal expansion of the surface pressure on a baffled cylinder forms the basis for determining an array-weighting function used to estimate the surface fields. The technique makes use of acoustic pressure data measured in a horizontal plane at ranges where the evanescent field is insignificant. No far-field constraints are imposed in the derivation of the method, allowing the measurements to be conducted within the geometric near-field of the body. When the array is located in the far field, this method is shown to yield similar array-weighting functions to a method derived by Williams [E. G. Williams, J. Acoust. Soc. Am. 99, 2022 (1996)]. Mid-frequency, 2≤ka≤20, scattering and radiation data from measurements of a ribbed cylindrical shell are used to illustrate the technique. The intensity images reveal membrane wave and rib scattering processes in both the time and frequency domains. [Work supported by NSWC and ONR.]
Feasibility of using imperfect microphone arrays in noise source location
Authors: Bhatt Tarun , Houghton J. Richard , Darvennes Corinne M.
Published: July 2002

Microphone arrays are being used in many applications such as noise source location, sound intensity measurement, or acoustic holography. For the purpose of source location using the unwrapped phase method, it is important to use phase-matched microphones. The paper studies the feasibility of replacing phase-matched microphones with an array of unmatched microphones and of finding faulty microphones within the array. For this purpose, two sets of tests were performed. With the first set, the microphone characteristics were measured. An electronic circuit provided time delays, i.e., phase information, between the microphones, and narrow and wideband source signals supplied frequency responses for all the microphones. With the second set of tests, optimization techniques and neural network methods were used to locate a noise source with (1) a matched microphone array, (2) an unmatched array, and (3) an array containing faulty microphones. Comparison of the data from the various microphone arrays is presented in this paper. The feasibility of using unmatched arrays with optimization and/or neural network methods is discussed. It is also demonstrated that a microphone with a significant signal-to-noise ratio and/or a large phase error can be pinpointed within the microphone array.
Comparison between subcritical penetration models and in situ data
Authors: Maguer Alain , Pouliquen Eric , Bovio Edoardo , Fox Warren L. J. , Schmidt Henrik
Published: July 2002

This paper presents the recent results of a study whose overall objectives are to determine the mechanism(s) contributing to anomalous high-frequency sound penetration into sediments, and to quantify the results for use in sonar performance prediction for the detection of buried objects. To date, several mechanisms have been hypothesized in order to explain this phenomenon, the most frequently mentioned being: (a) the existence of a Biot slow wave in the sediment, (b) surface roughness, and (c) scattering of the evanescent wave by volume inhomogeneities within the sediment. In situ acoustic measurements were performed on a sandy bottom whose geoacoustic properties were carefully identified. A parametric array mounted on a tower moving on a rail was used to insonify hydrophones located above and below the sediment interface. An extensive data set covering a wide range of grazing angles (both above and below the estimated critical angle) and frequencies (2–50 kHz) was acquired and processed. The results are compared to models for the three mechanisms stated in an attempt to explain the anomalously high sound-pressure levels measured. Dependence on frequency, depth into the sediment, and grazing angle is explored.
Aspects of a damped surface wave in the Fourier diamond spaces. New surface wave analysis method (SWAM)
Authors: Martinez Loïc , Duclos Jean , Tinel Alain
Published: July 2002

A damped surface wave (complex wave number K=K′+jK″) is described by its space-frequency representation S(x,ω)=exp(jK(ω)x). The wave-number-frequency representation Ksi(k,ω) is the spatial Fourier transform of S(x,ω). A Ksi-cut versus k is a k-Breit Wigner form (square modulus maximum for k=K′,K″ half-width). A Ksi-cut versus ω is then shown to be an ω-Breit Wigner form (square modulus maximum for ω=Ω′, with an Ω″ half-width). New interesting properties are found: the phase velocity is Cp=Ω′/K′ and the group velocity is Cg=Ω″/K″. The wave-number-time representation N(k,t) is the inverse frequency Fourier transform of Ksi(k,ω). N(k,t) is then shown to be N(k,t)=exp(jΩ(k)t). The space-time representation s(x,t) is obtained by inverse frequency (respectively, wave number) Fourier transform of S(x,ω) [respectively of N(k,t)]. The four spaces s, S, Ksi, and N are the four Fourier diamond spaces. Used on s(x,t) experimental datas, the two cuts properties are the basis of the surface wave analysis methods (SWAM). Those methods identify the complex K (respectively, Ω) using k-ARMA (respectively ω-ARMA) models. Using SWAM on a cylindrical shell, the A-wave is experimentaly fully characterized. The agreement with theoretical results is excellent.