bluuebunny/crossref_metadata_2025 huggingface dataset:
Scattering of plane waves from submerged objects with partially coated surfaces
Authors: Ferri Aldo A. , Ginsberg Jerry H. , Rogers Peter H.
Published: October 2005

This paper addresses the scattering of acoustic plane waves from submerged objects that are partially covered with a compliant coating. Beam incidence of a planar wave on cylinders of finite and infinite length are considered. The infinite cylinder is analyzed using a two-dimensional collocation technique, while a three-dimensional boundary element technique is used to study the finite cylinder. The coated and uncoated surfaces are modeled by assuming that the specific local impedance is constant along arcs of the cylindrical surfaces. It is shown that discontinuities in the impedance factor between adjacent regions leads to large pressure and normal velocity gradients on the surface in the vicinity of the discontinuity, but such effects have little influence on the scattered far-field pressure.
A comparison between two techniques for a source on a modified ground plane and an investigation of the case with a finite number of troughs
Authors: Sandström Sven-Erik
Published: October 2005

The far field is computed in three dimensions for an acoustic system radiating into the upper half-space. A source is situated on the boundary and in the neighborhood of a number of infinite and equidistant rectangular troughs. After Fourier transformation, the integral relation derived from Green’s theorem is transformed into a matrix equation for the coefficients of the eigenfunction expansions in the troughs. The far field is obtained through stationary-phase analysis of the Fourier-inversion integral. This approach is compared to earlier work based on a three-dimensional technique. By varying the number of troughs, it is possible to systematically observe the effects that are caused by the modification of the ground plane.
Comments on: ‘‘Properties of higher-order correlations and spectra for bandlimited deterministic transients’’ [J. Acoust. Soc. Am. 9
1, 975–988 (1992)]
Authors: Nielsen P. A.
Published: October 2005

The goal of this Letter is to clarify a very interesting result recently published in the article cited above. Specifically, it is shown here that the sampling frequency of the two-dimensional autobicorrelation function can be arbitrarily close to twice its highest frequency. However, if the original one-dimensional signal is sampled, then the sampling frequency must be at least three times its highest frequency. This latter result was presented by Pflug et al. [J. Acoust. Soc. Am. 91, 975–988 (1992)].
Vowel perception strategies of normal-hearing subjects and patients using Nucleus multichannel and 3M/House cochlear implants
Authors: Tartter Vivien C. , Hellman Sharon A. , Chute Patricia M.
Published: October 2005

Vowel perception strategies were assessed for two ‘‘average’’ and one ‘‘star’’ single-channel 3M/House and three ‘‘average’’ and one ‘‘star’’ Nucleus 22-channel cochlear implant patients and six normal-hearing control subjects. All subjects were tested by computer with real and synthetic speech versions of [i, i, u, u, q, 1, c, v, a, ε], presented randomly. Duration, fundamental frequency, and first, second, and third formant frequency cues to the vowels were systematically manipulated. Results showed high accuracy for the normal-hearing subjects in all conditions but that of the first formant alone. ‘‘Average’’ single-channel patients classified only real speech [hVd] syllables differently from synthetic steady state syllables. The ‘‘star’’ single-channel patient identified the vowels at much better than chance levels, with a results pattern suggesting effective use of first formant and duration information. Both ‘‘star’’ and ‘‘average’’ Nucleus users showed similar response patterns, performing better than chance in most conditions, and identifying the vowels using duration and some frequency information from all three formants.
Avoiding conflicts between the natural behavior of the animal and the demands of discrimination experiments
Authors: Harrison J. M.
Published: October 2005

Auditory discrimination experiments are traditionally designed without regard for ethological or ecological concerns, yet land dwelling mammals may have specialized behavior with respect to sound sources. Auditory discriminations occur under field conditions, and there is some fit or matching of the animal’s behavior to the acoustic environment. Understanding this fit requires a knowledge of specializations. Understanding the specializations may also guide the design of discrimination experiments. This paper reviews a number of auditory discrimination experiments that were designed to reveal some of the specialized behaviors. These experiments showed the following: (i) The position of a sound source is the dominant sensory dimension, over riding the quality of the sound; (ii) the effect of reinforcing a response in the presence of a sound is to strengthen the response of approaching the source. This effect is ubiquitous in discrimination tasks; (iii) sounds that are novel at the start of discrimination training more rapidly gain control of responding than sounds to which the animal has been pre-exposed; (iv) novel low-intensity sounds elicit approach and exploration of the source. These behaviors rapidly adapt. These four behavioral attributes are considered in terms of their impact upon behavior in the field, and of the requirements they impose on the design of experimental discriminations.
Principal component calibration models in the acoustic evaluation of zooplankton size spectra
Authors: Martínez Carlos M. , David Pascal M.
Published: October 2005

The theoretical basis of application of PCR (principal components regression) methods to the estimation of zooplankton size spectra by multifrequency acoustical methods is presented. Preliminary performance studies on simulated data are preformed to test the capacities of this technique as a function of the acoustic signal-to-noise ratio (SNR) and the type of acoustic scattering model. The results are compared with those obtained with a non-negative least squares (NNLS) algorithm, and finally, an application to a real data matrix is shown. The main advantage over the NNLS method is that it avoids the knowledge of the scattering responses for each class of particles. The results obtained on simulated data indicate that PCR calibration models are good alternatives for the estimation of size spectra, in the range tested. For all the conditions analyzed, the error estimators and correlation coefficients show a better fit than NNLS models. The real data matrix tested is particularly complex, avoiding the use of the NNLS method. The PCR method, however, gives acceptable results for most classes, despite the undetermination of the acoustic data matrix (five frequencies for 26 groups). The addition of nonacoustical variables to the acoustic data set, correlated with the spatial distribution of organisms, increases the precision of the estimates. Further analysis will be made to test the capacities of this technique in the presence of a more complex noise structure and nonlinear phenomena.
Lateral low-frequency components of reflected sound from a canopy complex comprising triangular plates in concert halls
Authors: Nakajima Tatsumi , Ando Yoichi , Fujita Keisuke
Published: October 2005

Applying the diffraction integral of Rubinowicz, the transfer functions (TFs) for reflection by canopy panels of various shapes were calculated. Numerical calculation of TF shows that the optimum interior angle of an isosceles triangle giving a flat response lies between 90° to 120°. And, the use of a number of canopy panels above both sides of a concert hall helps to control lateral low-frequency components for the audience area, and produces a small value of interaural cross correlation (IACC). It is interesting to observe that the interior angle of the triangular panels composing the canopy in the Tanglewood Music Shed falls in the optimum range. The TFs of large triangular panels suspended in front of the top of the proscenium arch in Fujita Hall, a concert hall designed by us, indicate the existence of relatively strong low-frequency components of reflection from lateral directions to a listener at the front section of the hall. Further, higher frequency components of the reflections tend to arrive near to the median plane of each listener.
Modal properties and eigenvalue veering phenomena in the axisymmetric vibration of spheroidal shells
Authors: Chen Pei-Tai , Ginsberg Jerry H.
Published: October 2005

The axisymmetric free vibration properties of arbitrarily slender thin spheroidal shells are investigated by implementing the method of assumed modes in conjunction with energy functionals derived from classical linear bending theory. Loci depicting the dependence of the natural frequencies on aspect ratio are constructed for aspect ratios ranging from a sphere to a prolate spheroid whose length is seven times its diameter. At certain aspect ratios, loci associated with different eigensolutions come close, then veer away without intersecting. Modal properties, such as the number of nodes in the mode associated with increasing root number for the eigenvalue, are found to change irregularly when veering occurs. An analysis of the partitioning of strain energy between membrane and bending effects is performed in conjunction with an earlier general study of eigenvalue veering phenomena. The analysis demonstrates that veering results in mixing of membrane and bending effects, such that it no longer is meaningful to classify the natural modes by their stored energy. A corollary of the analysis is the recognition that membrane shell theory ceases to be useful for spheroidal shells beyond an aspect ratio of 1.5. Further investigation shows that, in addition to physical causes, two eigenvalue loci might veer as the result of approximation error. The modal properties in such cases are interchanged between the nonintersecting loci, such that when viewed macroscopically all properties seem to change gradually along intersecting loci.
Mode shape analysis of angle-ply-laminated composite shallow shells
Authors: Qatu Mohamad S.
Published: October 2005

This work represents the first known comprehensive study concerned with the natural mode shapes of angle-ply-laminated composite shallow shells having rectangular planform and various boundary conditions. The Ritz method with algebraic polynomial displacement functions is used. Convergence studies are made which demonstrate that reasonably accurate results are obtainable before ill conditioning starts to cause problems. Shallow shells with spherical, circular cylindrical, and hyperbolic paraboloidal curvatures and completely free, cantilevered, and doubly cantilevered (i.e., two adjacent edges clamped and the others free) boundary conditions are considered. The effects of the fiber orientation, curvature, and boundary conditions upon the mode shapes are studied. Nodal line crossing in the mode shapes, which exists for most of the cross-ply shells, is replaced by curve veering for angle-ply ones. A gradual change in the mode shapes is observed as the lamination angle increases. Lamination, curvature, and boundary condition change the mode shape characteristics drastically. The information presented in this paper should be useful for engineers and researchers who are interested in the acoustical characteristics of these structural elements.
Auditory-nerve action potentials form a nonrenewal point process over short as well as long time scales
Authors: Lowen Steven B. , Teich Malvin C.
Published: October 2005

The firing patterns of auditory-nerve action potentials exhibit long-term fractal fluctuations that do not arise from the distribution of the interevent intervals, but rather from the ordering of these intervals. Using the serial interevent-interval correlation coefficient, the Fano-factor time curve, and shuffling of interevent intervals, it is shown that adjacent intervals for spontaneous firings exhibit significant correlation. The events are therefore nonrenewal over short as well as long time scales.
The determination of the far field of an acoustic radiator from sparse measurement samples in the near field
Authors: Borgiotti Giorgio V. , Rosen Erik M.
Published: October 2005

The near-field to far-field projection procedure here introduced has the following novel features. (1) The measured near-field samples do not need to belong to a separable coordinate surface. (2) The number of samples is, in principle, as small as the theoretical number of degrees of freedom of the far field, related to the dimensions of the source in wavelengths. (3) The samples do not need to belong to a regular grid. (4) If the projection is sought only within a limited angular sector, a further reduction of the number of measurement samples is possible. The technique is based on the identification from the measured data of an equivalent monopolar distribution of acoustic sources on a surface completely surrounding the radiator. The far field of these sources, straightforwardly computed, constitutes the estimate of the far field of the radiator. The identification is based on the pseudo inversion of the matrix representing the mapping of the equivalent sources into near-field samples, which is obtained by resorting to the singular value decomposition of the matrix. Representative results of the extensive numerical simulations are here included.
Optimal near-field measurement in the presence of noise and reflections
Authors: Stoughton Roland
Published: October 2005

An algorithm is presented for reconstructing, with minimum mean-squared error (MMSE), the radiated or scattered near or far field from near-field measurements. The effects of multipath and spatially correlated noise are included. The algorithm provides an estimate of its squared error in any situation that can be used to guide sampling and sensor array design. A numerical example relevant to wind-tunnel measurements is presented.
Experimental and theoretical study of elastic wave dispersion in a liquid bilayer
Authors: Laperre J. , Thys W.
Published: October 2005

A model is constructed to express the normal dispersion curves of a liquid bilayer in terms of the dispersion curves of its two constituent layers. The idea is illustrated with a numerical example and later experimentally confirmed with another example.
Improvement of the acoustic and hygroscopic properties of wood by a chemical treatment and application to the violin parts
Authors: Yano H. , Minato K.
Published: October 2005

A chemical treatment was applied to a wood specimen and some parts of a violin. Formaldehyde cross linkings formed between hydroxyl groups of wood constituents decreased the internal friction (Q−1) of a sitka spruce specimen as much as 40% and 45% in the fiber and cross fiber directions, respectively, in the frequency range of 150–500 Hz. The degree of reduction in Q−1 was smaller at high frequencies and larger at low frequencies. The specific dynamic Young’s modulus (E/γ) at 20 °C, 65% RH increased 10% in the cross fiber direction, though it hardly increased in the fiber direction within the frequency range examined. The changes of specific gravity in the air-dried state were negligibly small. The variations of acoustic properties and dimensions of the wood against humidity change were reduced markedly because of the decreases of hygroscopicity. By a sensory evaluation test, a violin having a treated bridge was judged to be more bright, sonorous, and less poor, dull, and comprehensively better than the same violin having an untreated bridge. The effect of the treatment was more pronounced when the top plate, bass bar, and sound post were treated in addition to the bridge. The variation in sound spectra and the decrease in tuned frequency of violin against humidity change diminished as a result of the treatment.
The influence of talker differences on vowel identification by normal-hearing and hearing-impaired listeners
Authors: Nábělek Anna K. , Czyzewski Zbigniew , Krishnan Lata A.
Published: October 2005

Vowel identification was tested in quiet, noise, and reverberation with 20 normal-hearing subjects and 20 hearing-impaired subjects. Stimuli were 15 English vowels spoken in a /b–t/ context by six male talkers. Each talker produced five tokens of each vowel. In quiet, all stimuli were identified by two judges as the intended targets. The stimuli were degraded by reverberation or speech-spectrum noise. Vowel identification scores depended upon talker, listening condition, and subject type. The relationship between identification errors and spectral details of the vowels is discussed.
Ultrasonic attenuation in articular cartilage
Authors: Senzig David A. , Forster Fred K. , Olerud John E.
Published: October 2005

Previous studies have utilized articular cartilage from joints as a model to investigate the influence of various constituents in a connective tissue matrix on ultrasonic properties. These studies have assumed a degree of homogeneity of articular cartilage taken from the same joint. However, tactile loads on articular cartilage vary significantly with location in a joint, and the effects of mechanical load on the connective tissue matrix and the resulting effects on ultrasonic properties are not known. This work reports the variations in acoustical properties of bovine articular cartilage from the stifle (knee) joint both among different joints and within each joint. A pulse-echo transmission technique was used to measure acoustic attenuation in the frequency range of 10 to 40 MHz. The attenuation coefficient was characterized by the integrated attenuation (mean value) over the frequency bandwidth considered. Integrated attenuation averaged over each joint varied among joints from 3.2 to 7.5 NP/cm (6.0±2.0, mean ±s.d.). Additionally, a linear regression (r=0.59) of all the data versus location along the patellar groove indicated that within joints integrated attenuation increased from proximal to distal locations by 6% to 60% (32±25, mean ±s.d.). The variations observed among joints and along the patellar groove within a given joint suggest that studies utilizing articular cartilage to determine the role of connective tissue constituents on acoustic properties require control for joint and location. An additional outcome of this study was the observation that damage to the load-bearing surface of articular cartilage may be detectable ultrasonically through characteristics of the acoustic reflection from the articular surface.
Inferring articulation and recognizing gestures from acoustics with a neural network trained on x-ray microbeam data
Authors: Papcun George , Hochberg Judith , Thomas Timothy R. , Laroche François , Zacks Jeff , Levy Simon
Published: October 2005

This paper describes a method for inferring articulatory parameters from acoustics with a neural network trained on paired acoustic and articulatory data. An x-ray microbeam recorded the vertical movements of the lower lip, tongue tip, and tongue dorsum of three speakers saying the English stop consonants in repeated CE syllables. A neural network was then trained to map from simultaneously recorded acoustic data to the articulatory data. To evaluate learning, acoustics from the training set were passed through the neural network. To evaluate generalization, acoustics from speakers or consonants excluded from the training set were passed through the network. The articulatory trajectories thus inferred were a good fit to the actual movements in both the learning and generalization conditions, as judged by root-mean-square error and correlation. Inferred trajectories were also matched to templates of lower lip, tongue tip, and tongue dorsum release gestures extracted from the original data. This technique correctly recognized from 94.4% to 98.9% of all gestures in the learning and cross-speaker generalization conditions, and 75% of gestures underlying consonants excluded from the training set. In addition, greater regularity was observed for movements of articulators that were critical in the formation of each consonant.
Acoustic measures for linguistic features distinguishing the semivowels /w j r l/ in American English
Authors: Espy-Wilson Carol Y.
Published: October 2005

Acoustic properties related to the linguistic features which characterize the semivowels in American English were quantified and analyzed statistically. The features can be divided into those which separate the semivowels from other sounds and those which distinguish among the semivowels. The features of interest are sonorant, syllabic, consonantal, high, back, front, and retroflex. Acoustic correlates of these features were investigated in this study of the semivowels. The acoustic correlates, which are based on relative measures, were tested on a corpus of 233 polysyllabic words, each of which was spoken once by two males and two females. For the most part, the appropriate distinctions are made by the chosen acoustic properties for features. However, for each property, there was some overlap in the acoustic correlates of features for the sounds being distinguished. An examination of the sounds in the overlap regions reveals that their surface manifestation varies substantially from the canonical form. In large part, the observed variability can be explained in terms of changes due to feature spreading and lenition.
Asymptotic modal analysis for sound fields of a reverberant chamber
Authors: Kubota Yuji , Dowell Earl H.
Published: October 2005

Asymptotic modal analysis (AMA) has been applied to the sound fields of a reverberant chamber under narrow-band excitation by point sources. The result in the form usually given by geometrical acoustics also has been obtained by studying the asymptotic behavior of the result of wave or normal mode theory. A few numerical examples for a rectangular chamber are carried out to illustrate the way in which the asymptotic limit is approached. It is shown that the accuracy of the results depends on the number of modes in a frequency band of interest, the source position, and the chamber shape. A supplementary expression to improve the accuracy of the asymptotic theory has been derived for the case of a flat room, in which case the conventional geometrical acoustics type result is less accurate. The spatial distribution of the (mean-square) sound pressure also has been discussed. It is shown that, asymptotically, the sound pressure at all points of the chamber becomes the same except for some special regions, and that a large sound pressure appears at those exceptional regions. The regions near the walls and near the lines through the source perpendicular to the walls are special.
Optimum kernels for oversampled signals
Authors: Huestis Stephen P.
Published: October 2005

For an oversampled bandlimited acoustic signal, the sampling kernel is nonunique. Niland [R. A. Niland, J. Acoust. Soc. Am. 86, 1805–1812 (1989)] presents a formalism for constructing a kernel that is most concentrated near the origin. By exploiting the most general form for the sampling kernel, Niland’s result is seen to be nonoptimal. The form of the kernel which is in fact optimal by his measure is derived and illustrated.
Jet behavior in the flute
Authors: Coltman John W.
Published: October 2005

Time snapshot profiles of an acoustically excited flute jet were measured with a Pitot tube and with a hot wire anemometer. Both methods showed the jet broadened substantially under excitation, and developed a subsidiary peak on the side opposite the main moving peak. Variation of phase, jet swing, and inferred current signal amplitude with drive intensity and frequency, and response to a complex wave were consistent with pressure gradient as the stimulus for the jet motion, rather than acoustic velocity or negative displacement. Observation of signals generated by the jet when blowing a nonresonant flute tube and embouchure while excited by either simple or complex waves in the same tube, gave overall transfer functions that were consistent with the assumption of jet response to acoustic velocity in conjunction with tube drive by injected jet current.
Specific acoustic impedance measurements of an air-filled thermoacoustic prime mover
Authors: Arnott W. Pat , Bass Henry E. , Raspet Richard
Published: October 2005

Thermoacoustic heat engines can be used to produce sound from heat and to transport heat using sound. The air-filled prime mover studied is a quarter wavelength resonator that produces sound at nominally 115 Hz for a temperature difference of ΔT=176 K. Specific acoustic impedance at the mouth of the prime mover was measured as a function of the temperature difference between the hot and cold heat exchangers. The real part of the impedance changes sign for sufficiently large temperature differences, indicating the possibility of sound production. The theoretically predicted radiation impedance of an open pipe was compared to the measured impedance curves. The operating point was confirmed from the intersection of these experimental and theoretical impedance curves. These measurements allow for analysis of the prime mover as a sound source as discussed in a recent theoretical paper [T. B. Gabrielson, J. Acoust. Soc. Am. 90, 2628–2636 (1991)].
Variable domain transform and the detection of frequency modulation pulses
Authors: Roosnek Nico
Published: October 2005

In this article a method is described for the detection of linear frequency modulation (FM) pulses with unknown frequency rate parameters in a noisy environment. The method, which is equivalent to the wavelet transform, enhances the signal towards noise. The technique is based on the variation of the domain after which a Fourier transform is applied, or for short called ‘‘variable domain transform.’’ The enhancement is in the order of pulse compression. The computational speed is of the order of that of the fast Fourier transform. The method is also applicable for other signal forms. A criterion is given for the type of signals that can be processed in that manner. An actual signal is analyzed and discussed.
Modal-slowness analysis of plate vibrations
Authors: Fricke J. Robert , Baggeroer Arthur B.
Published: October 2005

A methodology for analyzing complicated plate vibrations is presented. It is based on the Radon transform and unravels the modal structure excited by transient broadband pulses. The difference in phase velocity between flexural and longitudinal plate waves is exploited to this end. Array data collected in the x–t domain is mapped into the slowness-tau p–τ domain. In this domain, the flexural and longitudinal mode are isolated from one another and may be analyzed individually. Several analysis tools are developed and demonstrated for two plate models: a flat, finite-width steel plate and the same plate with a small steel block in welded contact. Examples of the analysis results are estimates for modal waveform and dispersion, modal energy content, and modal transfer functions relating incident and scattered waves at an impedance discontinuity in the plate.
Evaluation of interference effect in the energy investigation of echoes scattered by an uncorrelated planar distribution of spherical targets
Authors: Sun Zhigang , Gimenez Gérard
Published: October 2005

In this paper, an evaluation function is proposed to determine the interference effect in the energy investigation of echoes scattered by a random distribution of spherical targets. The application of this function to an uncorrelated planar distribution of spheres leads to an analytical formula that has the advantage of being independent of either exciting signal of the sonar system or properties of particular spheres and therefore can be used to any kind of spherical isotropic targets. In the estimation of underwater target abundance by the echo squared integration method, this formula provides a fast way to evaluate the interference contribution of echoes.
The short pulse method of isolation and identification of resonances: Comparison with a quasiharmonic method and application to axisymmetrical scatterers
Authors: Rembert P. , Cand A. , Pareige P. , Talmant M. , Quentin G. , Ripoche J.
Published: October 2005

Several experimental methods using quasiharmonic insonification lead to a direct verification of the resonance scattering theory. They provide, for elastic cylindrical targets, the resonance frequencies and the mode number of each of them. Pulsed techniques already existing only allowed the resonance frequency determination. Recently, a short pulse method of isolation and identification of resonances (short pulse MIIR) has been initiated. It completes previous works and allows a complete comparison with theoretical and quasiharmonic experimental results. This method consists in digitizing the time signals that characterize the scattering from an elastic target insonified by a short pulse for different angular positions of the receiving transducer. For each acquired signal a resonance spectrum is obtained after a spectral amplitude analysis. From these data, computer processing allows the plotting of identification patterns and by the same way the knowledge of the mode of vibration at a given resonance frequency. Even if this method is not restricted to cylindrical scatterers, this paper presents the identification of resonances by means of the short pulse MIIR of targets as cylinders, shells and water-filled shells and cavities. The accuracy and the possibility for separating overlapping resonances are also discussed.
Scattering of hydrodynamic pressure pulses by coating inhomogeneities
Authors: Domaradzki J. Andrzej , Shah Kishan , Crighton David G.
Published: October 2005

Sound generation by a deterministic, hydrodynamic pressure pulse in a fluid flowing over a compliant coating with an embedded void inhomogeneity is investigated. The inhomogeneity is represented by an acoustic monopole and its strength is found for several models of the pressure pulse. The far-field acoustic pressure is calculated for all models and is compared with the sound generated by a statistically stationary turbulent boundary layer. It is found that for certain parameters of the coating, the intensity of scattered sound generated by a deterministic pulse may exceed by 10–40 dB the intensity of sound estimated for the statistical turbulent boundary layer forcing.
Acoustic wave scattering from thin shell structures
Authors: Norris Andrew , Vasudevan Naresh
Published: October 2005

A general asymptotic theory is developed to describe the acoustic response of heavily fluid-loaded thin shells in the midfrequency regime between the ring and coincidence frequencies. The method employs the ideas of matched asymptotic expansions and represents the total response as the sum of an outer, or background response, plus an inner or resonant contribution. The theory is developed for thin shells with smoothly varying material and geometrical properties. First, a suitable background field is found which satisfies neither the rigid nor the soft boundary conditions that have been typically employed, but corresponds to an impedance boundary condition. The background field is effective throughout the midfrequency as well as the strong bending regimes. The corresponding inner or resonance field is also valid in the same range. The approach taken is to represent these fields as inverse power series in the asymptotically small parameter 1/kR, where R is a typical radius of curvature of the shell and k is the fluid wave number. The leading-order terms in the series differ in the inner and outer expansions, in such a way that the displacement tangential to the surface is negligible in the outer (background) region, but dominates the scattering near resonances. The resonances can therefore be associated with compressional and shear waves in the shell. A uniform asymptotic solution is derived from the combined outer and inner fields. Numerical results are presented for the circular cylinder and the sphere and comparisons are made with exact results for these canonical geometries. The results indicate that the method is particularly effective in the midfrequency range. The strong bending regime is also well represented, especially for cylindrical scatterers.
Acoustic harmonic radiation and scattering from shells of revolution using finite element and internal source density methods
Authors: Stepanishen Peter R. , Chen Huo-Wang
Published: October 2005

Acoustic axisymmetric harmonic radiation and scattering from fluid-loaded shells of revolution is addressed in the present paper using an in-vacuo modal vector expansion for the velocity field of the shell. The in-vacuo modal vectors for a specific shell are obtained via the use of finite element methods. As a result of the fluid loading the in-vacuo modes of the shell become coupled; hence, the modal velocity coefficients are described by a coupled set of algebraic equations which include mode-dependent mechanical impedances for the shell and mode-dependent acoustic radiation impedances for the fluid. The mode-dependent acoustic radiation impedances are obtained via the use of an internal monopole source density method. This method eliminates the need to use surface integral equation methods with their inherent problems to evaluate the acoustic radiation impedances. Extensive numerical results are presented for spheroidal and spherical shells. In-vacuo mode shapes and natural frequencies are first presented and then used to obtain the associated acoustic radiation impedances. Finally, the response of fluid-loaded point excited spherical and spheroidal shells are presented and discussed.
A fast algorithm to solve the inverse scattering problem in layered media with arbitrary input
Authors: Tenenbaum Roberto A. , Zindeluk Moysés
Published: October 2005

A new sequential algorithm to solve the one-dimensional inverse scattering problem in layered media with arbitrary inlet pulse is presented. The procedure consists of the mathematical inversion of the exact algebraic solution for the direct problem derived in Tenenbaum and Zindeluk [J. Acoust. Soc. Am. XX, XXXX–XXXX (1992)] and features computational efficiency together with improved numerical stability. Simulated examples of successful impedance profile identification with noisy data are reported and a detailed analysis of the stability improvement is provided. Impact tests on variable cross-section long bars monitored with strain gauges are also reported and the method is applied to actual parameter profile identification, with success.
Extensional stress waves in one-dimensional elastic waveguides
Authors: Drumheller Douglas S.
Published: October 2005

Computations of linear, one-dimensional wave propagation problems are often accomplished with integral transform methods. Time-domain approaches that usually involve a infinite-difference or method-of-characteristics approach have usually been reserved for nonlinear problems. However, time-domain algorithms have unique advantages for many problems with complex combinations of geometry, internal energy sources, and boundary conditions. One such algorithm will be examined in this work. It was originally developed for an unusual waveguide problem—acoustical wave transmission through drill strings that are used to drill geothermal and petrochemical wells. The development of this algorithm takes advantage of a unique property of the linear problem. The result is a computational method that is a combination of the finite-difference and characteristics methods. A variety of example problems are treated in this work. They involve linear elastic, ferroelectric, and fading-memory materials. Examples are given of solutions to the coupled mechanical and electrostatic field equations, and to problems with nonhomogeneous material properties.
Effect of intensity slopes on the perception of vowel duration
Authors: Nishinuma Yukihiro , Santi Serge
Published: October 2005

The discrimination of duration was investigated using synthetic vowels with negative intensity changes (0, −6, −12, and −18 dB). Test stimulus durations ranged from 100 to 300 ms in steps of 20 ms and the standard stimulus was 200 ms in duration and had a uniform intensity. Stimulus pairs were presented to 20 subjects whose task was to state which vowel in the pair sounded longer (forced choice; method of constant stimuli). The data indicate that a drop in intensity of more than 12 dB results in a significant decrease in discriminability of duration differences.
Consonant recognition by some of the better cochlear-implant patients
Authors: Tyler Richard S. , Moore Brian C. J.
Published: October 2005

Fifty-four of the better cochlear-implant patients from Europe and the United States were tested on two consonant recognition tests using nonsense syllables. One was produced in an accent appropriate for their own language by a male and a female talker. Recorded tokens of /ibi, idi, igi, ipi, iti, iki, ifi, ivi, i1i, isi, izi, imi, ini/ were presented. With the French syllables, six patients with the Chorimac device averaged 18% correct (6%–29%). With the German syllables, nine patients with the 3M/Vienna device averaged 34% correct (17%–44%), ten patients with the Nucleus device (tested in Hannover) averaged 31% correct (19%–42%), and ten patients with the Duren/Cologne device averaged 27% correct (10%–56%). With the English syllables, ten patients with the Nucleus device (tested in the United States) averaged 42% correct (29%–62%), and nine patients with the Symbion device averaged 46% correct (31%–69%). An information-transmission analysis and sequential information-transfer analysis of the confusions suggested that different implants provided differing amounts of feature information. The place of articulation feature was typically the most difficult to code for all implants. In the second test a male and a female talker recorded the stimuli /ibi, idi, igi, imi, ini, i1i, isi, izi/ in a single manner that was appropriate for all three languages. Six patients with the Chorimac device averaged 27% (13%–48%), ten patients with the Duren/Cologne implant averaged 29% (15%–75%), ten patients with the Nucleus device (tested in Hannover) averaged 40% (25%–58%), ten patients with the Nucleus device (tested in the United States) averaged 49% (40%–60%), nine patients with the Symbion device averaged 61% (40%–75%), and nine patients with the 3M/Vienna device averaged 41% (29%–52%) correct.
Frequency discrimination in forward and backward masking
Authors: Turner Christopher W. , Zeng Fang-Gang , Relkin Evan M. , Horwitz Amy R.
Published: October 2005

Frequency difference limens for pure tones preceded by a forward masker or followed by a backward masker were obtained across a wide range of signal levels. Relkin and Doucet [Hear. Res. 55, 215–222 (1991)] have shown that at a masker-signal delay of 100 ms, the thresholds of high-SR (spontaneous rate) auditory-nerve fibers are recovered, while the low-SR fiber thresholds are not. Therefore, forward-masked frequency discrimination potentially offers a method to investigate the role of low-SR fibers in the coding of frequency. It has been shown that when an intense forward masker is presented 100 ms before a pure-tone signal, intensity difference limens are elevated for mid-level signals [Zeng et al., Hear. Res. 55, 223–230 (1991)]. However, Plack and Viemeister [J. Acoust. Soc. Am. 92, 3097–3101 (1992)] have shown that a similar elevation in the intensity difference limen is obtained under conditions of backward masking, where selective adaptation of the auditory neurons would not be expected to occur. A condition of backward-masked frequency discrimination was therefore included to investigate the role of interference resulting from adding additional stimuli to a discrimination task. For signals at 1000 and 6000 Hz, there was no effect of a forward masker upon frequency difference limens. For the backward-masked conditions, an elevation of the frequency difference limen was observed at all signal levels, demonstrating that the effects of forward and backward maskers upon frequency discrimination are dissimilar and suggesting that cognitive effects are present in backward-masked discrimination tasks. This difference between intensity and frequency discrimination supports the idea that intensity and frequency are encoded in different manners by the auditory system. The absence of an effect of forward masker on frequency discrimination suggests that the rate response of low-SR fibers does not contribute useful information to a frequency discrimination task.
The ‘‘proportion-of-the-total-duration rule’’ for the discrimination of auditory patterns
Authors: Kidd Gary R. , Watson Charles S.
Published: October 2005

A principle of auditory perception that governs the detectability of changes in components in unfamiliar sequences of tones is demonstrated in four experiments. The proportion-of-the-total-duration (PTD) rule can be stated as follows: Each individual component of an unfamiliar sequence of tones is resolved with an accuracy that is a function of its proportion of the total duration of the sequence or ‘‘pattern.’’ An adaptive-tracking frequency-discrimination task was used in all experiments. Experiment 1 demonstrated that the PTD rule holds over a wide range of total pattern durations, numbers of components, and component durations. Experiment 2 demonstrated that the PTD rule governs discrimination performance despite variation in the relative durations of context and target tones. Experiment 3, using a variable temporal position for the target, confirmed that the PTD effect does not require that a listener be able to anticipate the temporal location of the target tone. Experiment 4, using two target tones, showed that the PTD rule applies to the proportional duration of individual components within patterns and not to the total proportional duration of nonadjacent components within the pattern. These findings are incompatible with performance limitations based on a fixed-duration short-term memory capacity and with versions of informational limitations in which the amount of information in a pattern varies either with the number of components or with the total pattern duration. The PTD rule appears to reflect the way listeners distribute their attention when presented with unfamiliar complex sounds that have no structural properties (other than proportional duration) that significantly increase the salience of individual components.
Detection of combined frequency and amplitude modulation
Authors: Moore Brian C. J. , Sek Aleksander
Published: October 2005

This article is concerned with the detection of mixed modulation (MM), i.e., simultaneously occurring amplitude modulation (AM) and frequency modulation (FM). In experiment 1, an adaptive two-alternative forced-choice task was used to determine thresholds for detecting AM alone. Then, thresholds for detecting FM were determined for stimuli which had a fixed amount of AM in the signal interval only. The amount of AM was always less than the threshold for detecting AM alone. The FM thresholds depended significantly on the magnitude of the coexisting AM. For low modulation rates (4, 16, and 64 Hz), the FM thresholds did not depend significantly on the relative phase of modulation for the FM and AM. For a high modulation rate (256 Hz) strong effects of modulator phase were observed. These phase effects are as predicted by the model proposed by Hartmann and Hnath [Acustica 50, 297–312 (1982)], which assumes that detection of modulation at modulation frequencies higher than the critical modulation frequency is based on detection of the lower sideband in the modulated signal’s spectrum. In the second experiment, psychometric functions were measured for the detection of AM alone and FM alone, using modulation rates of 4 and 16 Hz. Results showed that, for each type of modulation, d′ is approximately a linear function of the square of the modulation index. Application of this finding to the results of experiment 1 suggested that, at low modulation rates, FM and AM are not detected by completely independent mechanisms. In the third experiment, psychometric functions were again measured for the detection of AM alone and FM alone, using a 10-Hz modulation rate. Detectability was then measured for combined AM and FM, with modulation depths selected so that each type of modulation would be equally detectable if presented alone. Significant effects of relative modulator phase were found when detectability was relatively high. These effects were not correctly predicted by either a single-band excitation-pattern model or a multiple-band excitation-pattern model. However, the detectability of the combined AM and FM was better than would be predicted if the two types of modulation were coded completely independently.
Coherent acoustical radiation from breaking waves
Authors: Farmer David M. , Ding Li
Published: October 2005

Observations of sound radiated by breaking surface waves have been detected with a four-hydrophone array in the open ocean. Time delay measurement is used to evaluate the position of individual breaking events. However, the coherence between different pairs of hydrophones is anisotropic. Together with the spectral distribution, these signals are interpreted in terms of the spatial distribution and nature of the sound generation mechanism.
Ground parameter information for propagation modeling
Authors: Attenborough Keith
Published: October 2005

The relative success of various simplified ground impedance models at fitting data obtained from direct and indirect measurements is reviewed. A new two-parameter approximation for the normal surface impedance of a nonhard-backed layer structure is introduced. A two-parameter model of this form is shown to have wide success in fitting recent ground impedance and excess attenuation data obtained by a variety of techniques. Further evidence is produced of the unreliability that would be associated with extrapolation of fits based on the single-parameter semiempirical model widely used at present outside the frequency range of the fitted data. By refitting classical ground impedance data and tabulating resulting parameters along with those obtained more recently, a menu of ground types, best-fit models, associated parameter values and frequency ranges of fits has been compiled.
Cross-talk artifacts in spatial spectrum estimation with a sensor array
Authors: Krolik Jeffrey , Swingler David
Published: October 2005

Cross-talk between output channels is a common problem that can occur in the wet-end or dry-end electronic cabling of a sensor array. This paper examines artifacts in spatial spectral estimates caused by cross-talk between sensor output channels. It is shown that cross-talk can result in spurious peaks in spatial spectral estimates, particularly for high resolution methods that involve the covariance matrix inverse. An analysis of the eigenvalues and eigenvectors of the array output covariance matrix in the presence of cross-talk contamination is given in the noise-only case. Cross-talk contamination is linked to a reduction in the magnitude of the smallest eigenvalue of the covariance matrix and thus the most pronounced artifacts are found in spatial spectral estimates that involve eigenvalue reciprocals. Various examples using both simulated and real towed-array data are discussed.