bluuebunny/crossref_metadata_2025 huggingface dataset:
Sound radiation from beams under the action of multiple random point forces
Authors: Peng H. , Keltie R. F.
Published: October 2005

The problem of acoustic radiation from infinite elastic beams driven by multiple stationary random point forces is analyzed. The expected value of the sound power is derived through integration of the surface intensity distribution over the entire beam. The reaction due to light fluid loading on the vibratory response of the beam is taken into account. With the input spectra being assumed as bandlimited white noise, the effects on the radiated sound power of the spatial correlation between two point forces are examined. It is is shown that there exists an optimal spacing distance between the two point forces, which will lead to a relative minimum in the radiated sound power. The physical explanation of this cancellation phenomenon is found in the reduction of the mean-square value of the vibratory level of the whole beam in the supersonic wave region. This reduction is produced by a modulation effect arising from the applied force function. A practical method to determine this optimal spacing distance is presented.
Wave propagation in a piezoelectric ceramic cylinder of arbitrary cross section with a circular cylindrical cavity
Authors: Paul H. S. , Venkatesan M.
Published: October 2005

Wave propagation in an infinite piezoelectric cylinder of arbitrary cross section with a circular cylindrical cavity is discussed. The boundary conditions on the inner surface of the cylinder are satisfied directly and on the outer surface they are satisfied using the Fourier expansion collocation method. The frequency equation that is applicable for the general cross section is obtained. Numerical calculations have been carried out for circular, elliptic, hexagonal, and parabolic cross sections for the ceramic material PZT-4. The results are tabulated and compared with the results obtained in the present case for the circular cylinder. The frequency versus the aspect ratio is plotted and the dispersion curves are also presented.
Data processing and accuracy analysis of damping measurements
Authors: Zhu G. H. , Crocker Malcolm J. , Rao Mohan D.
Published: October 2005

A method of curve fitting to process the data obtained from damping measurements of free decaying vibration is presented and compared with the logarithmic decrement method. In order to determine the accuracy of the two methods and the factors that influence the estimation error, a computer simulation is described, and the results have been estimated under different conditions of damping and noise. It is shown that the curve-fitting method is more accurate than the logarithmic decrement method for most conditions, and that, for values of damping and signal-to-noise most frequently encountered in practice, the optimum number of data points, for which the best estimate is obtained, is about 20. The method has been applied in the measurement of damping of a graphite epoxy tube specimen.
The calculation of sound power emission of sources in reverberation chambers
Authors: Zeng Li J. , Maa Dah You , Crocker Malcolm J.
Published: October 2005

The sound powers radiated by a monopole source and a dipole source in a reverberation chamber have been calculated. The calculation has shown that the sound power emission of an ideal sound source is greater in reverberant than free-field conditions. The smaller sound power radiation of an actual sound source in reverberant conditions has been shown to be due to the nonideal internal resistance of the source. The internal resistance of an actual sound source may be determined from the measured sound power emission ratio between reverberant and free-field conditions and the calculated sound power ratio.
Digital evaluation of the acoustics of small models: The midas package
Authors: Polack J. D. , Marshall A. H. , Dodd G.
Published: October 2005

Compared with more fashionable computer modeling, acoustical modeling is far from being superseded. In fact, there is often no alternative to acoustical modeling when designing an auditorium. Careful analysis of the laws of similarity shows that there remains some possibility of improving the acoustical testing of small models. This improvement does not solely concern transducers but the processing of impulse responses as well. Digital processing provides both accuracy of computation and compensation for air attenuation. Based on these principles, a computer-aided testing plant was designed and a computer package was written to drive it. A modular structure was selected as giving the maximum flexibility. Thus a digital evaluation of objective room-acoustical parameters can be achieved within a few minutes. So far, computer-aided acoustical modeling has proved well adapted for research and designing purposes.
Analysis of transient and steady-state weight covariance in an adaptive postbeamformer interference canceler
Authors: Godara Lal C.
Published: October 2005

A postbeamformer interference canceler (PIC) processes the signals derived from an antenna array by forming two beams using fixed beamforming weights. The weighted output of one beam, referred to as the interference beam, is subtracted from the other beam, referred to as the target beam. This article analyzes an algorithm to adjust the complex weight of the interference channel iteratively, studies the transient and steady-state behavior of the weight covariance, and derives the exact expression for the misadjustment.
The mutual coherence function in a scattering channel— A two-scale solution
Authors: Frankenthal Shimshon
Published: October 2005

By using the two-scale embedding procedure, an approximate expression for the mutual coherence function in a refractive and scattering channel is derived. The solution reduces to the known limiting monochromatic solutions, and provides a good approximation for the bichromatic coherence in a homogeneous scattering medium. Simple expressions are derived for both the coherence bandwidth and coherence time (Doppler spreading) in a quadratic channel with a quadratic scatterer. The possibility of inversion is explored.
High-frequency acoustic backscattering from a coarse shell ocean bottom
Authors: Stanic S. , Briggs K. B. , Fleischer P. , Sawyer W. B. , Ray R. I.
Published: October 2005

Acoustic bottom backscattering measurements were taken in a coarse shelly area 27 miles east of Jacksonville, Florida Data from sidescan sonar, underwater television, stereo photography, high-resolution bathymetry, and sediment core analysis were used to locate and classify the experimental area. Bottom backscattering measurements were made as a function of frequency (20–180 kHz), grazing angle (5°–30°), and azimuthal angle. Backscattering strengths were found to follow Lambert’s law, had a slight negative frequency dependence, and were consistent with measurements taken in other shelly areas. There was no azimuthal dependence of the scattered signals over the range of grazing angles and frequencies used. Bottom roughness had a Gaussian distribution and the ping-to-ping scattered signal envelope distributions were non-Rayleigh. Comparison of scattering strengths from several shelly areas showed little correlation with measured rms roughness. Scattering strength predictions made using a composite roughness model developed by Jackson et al. [J. Acoust. Soc. Am. 79, 1410–1422 (1986)] were compared to scattering strength measurements taken at 20, 40, and 60 kHz.
Reflection coefficient null of acoustic waves at a liquid–anisotropic-solid interface
Authors: Arikan Orhan , Telatar Emre , Atalar Abdullah
Published: October 2005

The reflection coefficient of acoustic waves incident on a liquid–solid interface from the liquid side is numerically calculated for a general anisotropic solid oriented in any arbitrary direction. The reflection coefficient depends, in general, on polar and azimuthal angles of incidence. Results are presented for various crystalline materials of different symmetry classes. A null in the reflection coefficient amplitude is detected at a particular incidence angle for every anisotropic material that supports pseudosurface waves. The null in the reflection corresponds to the excitation of the pseudosurface wave on the interface surface, and it has typically a very narrow angular aperture. The angular position of the null is very critical and highly dependent on the elastic parameters of the anisotropic solid.
Kanamycin induced low-frequency hearing loss in the budgerigar (M
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Authors: Hashino Eri , Sokabe Masahiro
Published: October 2005

The chronic effects of kanamycin (KM) on hearing in the budgerigar were investigated by behavioral audiometry. The birds received a daily intramuscular injection of KM (100 mg/kg or 200 mg/kg) for 10 successive days, and absolute thresholds between pre- and post-treatment were compared. KM induced both transient and permanent low-frequency specific hearing loss; i.e., the elevation of threshold for frequencies below 1 kHz was greater than that for frequencies above 1 kHz. Moreover, the degree of hearing loss was dose dependent. The low-frequency selective effects of KM in the present study were contrary to the high-frequency specificity of aminoglycoside ototoxicity in mammals. To assess the effect of KM on auditory frequency resolution, critical ratios were estimated in pathological birds with low-frequency specific hearing loss. There was a linear relation between shift in critical ratio and shift in absolute threshold, suggesting that the increase in the critical ratio is due to a decrease in the efficiency of the detector mechanism rather than a change in the spectral resolving power of the birds.
Acoustic radiation from a shell with internal structures
Authors: El-Raheb M. , Wagner P.
Published: October 2005

A method is developed to compute frequency response and acoustic radiation of a complex shell. The axisymmetric geometry of the shell includes cylindrical, conical, and spherical segments stiffened by discrete rings and bulkheads. The shell is coupled to internal masses and elastic frames. Shell segments are treated by transfer matrices. Rings, bulkheads, frames, and concentrated masses are treated by impedances at junctions of segments. The shell is coupled to an external acoustic fluid treated by Green’s function and curved surface elements. A major issue facing the method’s treatment of the fluid would be lack of existence or uniqueness encountered in the uncoupled, external acoustic problem at characteristic wavenumbers. By using a simple spherical shell, without internal structures, this potential hindrance is shown not to arise. A fuller application of the method awaits subsequent results.
Nearfield effects in acoustic scattering by submerged rigid bodies and elastic shells
Authors: Gaunaurd G. C. , Werby M. F.
Published: October 2005

Old classic formulas to evaluate the farfield, general, differential scattering cross sections, and the farfield sonar or backscattering cross sections of submerged solid bodies and elastic shells are modified and generalized here to their nearfield region of validity. The formulation is developed in 2-D by means of normal mode series, and in 3-D by means of the extended boundary condition (EBC) approach. The nearfield expressions, which are the ones valid in the close proximity of targets, are shown to asymptotically reduce to the standard ones defined in their farfields as the distance between target and observation point increases. Many calculated examples are exhibited of bistatic angular distributions plotted versus aspect angle, and of backscattering cross sections plotted versus frequency, both in 2-D and 3-D, all evaluated in the nearfield. In the cases examined, which here include cylindrical shells and rigid spheroidal bodies, it is shown that the farfield values, given by the usual farfield expressions, are reached at distances of about five shell diameters (or spheroidal lengths) away. In connection with nearfield evaluations of scattering cross sections, it is of interest to predict the sound-pressure fields transmitted inside a submerged, air-filled shell. These internal fields in cylindrical shells have been studied here. Isobaric contours of the internally transmitted pressures are displayed in various graphs. These plots quantitatively show the spatial variations of the high-pressure points (quasicaustics) that are developed internally, due to the resonance vibrations of the shell and its internal air column. The shell vibrations are mostly due to (flexural) Lamb waves circumferentially propagating around it.
Model-based passive ranging
Authors: Candy James V. , Sullivan Edmund J.
Published: October 2005

Passive localization by use of acoustic propagation models, sometimes called ‘‘matched field processing’’ is usually carried out in three steps. First, some appropriate model is selected. Then, model parameters, usually taken from archival data or from auxiliary measurements, are introduced into the model. Finally, acoustic measurements of the field radiated by the source to be located are made that, in combination with the properly parametrized model, allow a solution for the source coordinates to be carried out. Here, such a model-based approach is used in conjunction with a normal-mode model. By coupling the procedure with a parameter estimation/identification scheme and using a horizontal (towed) array instead of the usual vertical array, it is shown that the model parameters need not be known a priori in order to carry out the solution. This is in contrast to the standard approach in which the modal functions must be computed directly from the model (wave equation) in order to solve the problem. It is still necessary to base the calculation on a model, but, surprisingly, the sound velocity profile, the ocean depth, and ocean bottom properties need not be known explicitly, since sufficient information to determine the range of the source can be inferred directly from the measured data themselves. Using a sophisticated acoustic propagation model to generate simulated data, coupled with various array processing techniques, the feasibility of the approach is demonstrated.
The precedence effect: No evidence for an ‘‘active’’ release process found
Authors: Blauert Jens , Canévet Georges , Voinier Thierry
Published: October 2005

Hafter et al. [Auditory Function: The Neurobiological Bases for Hearing (Wiley, New York, 1988)] have reported that ‘‘post-onset adaptation,’’ as measured with trains of high-frequency clicks in a lateralization paradigm, can instantly be released by presentation of an additional, short trigger signal, which is spectrally different from the click trains. As post-onset saturation may be one of the psychoacoustic components of the precedence effect, it has been investigated whether suitable trigger signals might also induce a release from echo inhibition. However, no evidence for such an ‘‘active’’ release process could be observed in a number of exploratory precedence-effect settings.
Detection of gaps in sinusoids and pulse trains by patients with cochlear implants
Authors: Shannon Robert V.
Published: October 2005

Gap detection thresholds were measured in patients with the Nucleus and Symbion cochlear implants as a function of several current waveform parameters. Detection of gaps in an electrical sinusoidal stimulus or in a train of biphasic pulses by implanted patients was similar to detection of gaps in comparable acoustic stimuli by normal listeners. Threshold gaps were 20–50 ms for low-level stimuli and improved with stimulus level to 2–5 ms for high-level stimuli. Gap detection performance was not affected by the electrode position in the cochlea or by the distance between stimulating electrodes. The data from most patients were well fitted by a trading relation between the duration of the gap and the square of stimulus intensity, indicating energy detection. The similarity of gap thresholds for normal subjects and implant patients suggests that many details of the peripheral neural activity are probably not important for this task, and that there is no retrocochlear loss of auditory temporal resolution with sensorineural hearing loss.
Kinematic, acoustic, and perceptual analyses of connected speech produced by Parkinsonian and normal geriatric adults
Authors: Forrest Karen , Weismer Gary , Turner Greg S.
Published: October 2005

Acoustic and kinematic analyses, as well as perceptual evaluation, were conducted on the speech of Parkinsonian and normal geriatric adults. As a group, the Parkinsonian speakers had very limited jaw movement compared to the normal geriatrics. For opening gestures, jaw displacements and velocities produced by the Parkinsonian subjects were about half those produced by the normal geriatrics. Lower lip movement amplitude and velocity also were reduced for the Parkinsonian speakers relative to the normal geriatrics, but the magnitude of the reduction was not as great as that seen in the jaw. Lower lip closing velocities expressed as a function of movement amplitude were greater for the Parkinsonian speakers than for the normal geriatrics. This increased velocity of lower lip movement may reflect a difference in the control of lip elevation for the Parkinsonian speakers, an effect that increased with the severity of dysarthria. Acoustically, the Parkinsonian subjects had reduced durations of vocalic segments, reduced formant transitions, and increased voice onset time compared to the normal geriatrics. These effects were greater for the more severe, compared to the milder, dysarthrics and were most apparent in the more complex, vocalic gestures.
Masked tonal hearing thresholds in the beluga whale
Authors: Johnson C. S. , McManus M. W. , Skaar D.
Published: October 2005

Masked tonal thresholds were measured for a beluga whale at one noise level and 32 frequencies between 40 Hz and 115 kHz. Critical ratios were estimated and compared with those previously measured for the bottlenose dolphin. Beluga whale critical ratios were found to be about 3 dB lower than those of the bottlenose dolphin. Absolute tonal thresholds were extended below previous measurements to 40 Hz.
Spherical nearfield calibration array for three-dimensional scanning
Authors: Van Buren A. L.
Published: October 2005

Nearfield calibration arrays (NFCAs) are used to determine the farfield acoustic radiation from a transducer by measurements made in the nearfield. The original Trott NFCAs [W. J. Trott, Underwater Sound Ref. Lab. Rep. No. 55 (1961); also J. Acoust. Soc. Am. 36, 1557–1568 (1964)] were planar arrays. More recently, cylindrical NFCAs have been developed for determining the azimuthal radiation pattern of an enclosed transducer. This paper describes a spherical NFCA for determining the full three-dimensional radiation pattern of an enclosed transducer. In theory, the NFCA consists of a large number of discrete hydrophone elements arranged over a spherical surface in N equispaced constant latitude bands. In practice, the array can be synthesized by use of a single semicircular arc containing relatively few elements and by either rotation of the transducer or revolution of the arc about the polar axis. Individual hydrophone sensitivities (both amplitude and phase) are adjusted so that the NFCA serves as a plane-wave filter for acoustic radiation originating from inside the sphere. The relative sensitivities, called shading coefficients, are computed using the NFCA reciprocity principle and a least-squares procedure. Only a few sets of N/2 [or (N+1)/2, if N is odd] shading coefficients are required for full three-dimensional operation of the NFCA over a frequency range of 3 oct or more. Design criteria are discussed and example numerical results are presented.
Phase velocity of Lamb waves on a spherical shell: Approximate dependence on curvature from kinematics
Authors: Marston Philip L.
Published: October 2005

The phase velocity cl along the outer surface of a thick shell for Lamb waves may be calculated as a function of frequency by use of Watson transform methods. For thick shells, this cl is offset from Lamb’s result for a flat plate of the same thickness h. This discrepancy may be removed by distinguishing the velocity along the outer surface (of radius a) from the velocity along a curve corresponding to the average radius [a−(h/2)] for the shell. The resulting expression in h/a facilitates an improved approximation of cl from Lamb’s analysis. The approximations may be useful in scattering calculations for cases where cl exceeds the speed of sound in the surrounding fluid.
Comments on ‘‘On the measurement of glottal flow’’ [J. Acoust. Soc. Am. 8
4, 888–900 (1988)]
Authors: McGowan Richard S.
Published: October 2005

This letter indicates the possibility of rotational air motion in regions where rotational motion is not produced. This has application to the region above the glottis, where static models have shown the existence of rotational motion.
Effects of two-dimensional topographies using the discrete wavenumber-boundary integral equation method in P–S
V cases
Authors: Gaffet Stéphane , Bouchon Michel
Published: October 2005

The effect of topography on surface motion is studied in the case of incident P and SV waves and in presence of an explosive source. The discrete wavenumber-boundary integral equation method is formulated for this case and is applied to the problem of diffraction of an elastic wave field by a ridge-shaped topography. The amplitude of the scattered field, which mostly consists of surface P waves and Rayleigh waves, is strongly dependent on the steepness of the topography. The generation of surface waves by an explosion located in the vicinity of the ridge topography is studied and an increase in Rayleigh wave amplitude and a broadening of the Rayleigh pulse when the explosion occurs within the ridge is found.
Scattering from multiple gratings of compliant tubes in a viscoelastic layer
Authors: Radlinski Ronald P.
Published: October 2005

Previous studies of scattering from multiple gratings of resonant compliant tubes in water determined that noncompliant, antisymmetric structural modes excited by evanescent waves severely degraded the reflectivity of closely packed gratings. Also, low-frequency performance was diminished by transmission resonances due to the spring–mass–spring configuration of the two compliant gratings separated by a fluid mass. In this paper, encapsulating a single grating in a layer of elastomer whose shear properties are well below its rubber–glass transition region is shown to only reduce the maximum insertion loss. For two gratings, both the transmission resonances and the evanescent wave excitations are mitigated by encapsulation in a rubberlike material. Insertion loss performance with an encapsulant whose shear properties are in the rubber–glass transition region occurs at reduced bandwidths and shifted frequency responses. The mathematical model for gratings in fluid is extended to include the viscoelastic layer and calculations from this model are compared with experiments.
Dispersion relations of plate modes in anisotropic polycrystalline sheets
Authors: Hirao M. , Fukuoka H.
Published: October 2005

The presence of texture can explain the anisotropy of ultrasonic propagation velocities in polycrystalline materials. This paper derives dispersion relations with which the phase velocities can be calculated for plate modes guided along an arbitrary direction in the plane of an orthorhombic sheet. The effect of texture is brought into the analysis through the crystallites’ orientation distribution coefficients (ODCs). The dispersion relations are split into two parts, one for the P–SV motion and the other for the SH motion. The result for the symmetric P–SV motion approaches the angular variation in the velocity of the lowest (S0) mode with decreasing frequency. The anisotropy in Rayleigh surface wave velocity is also derived as a solution in the high-frequency limit. These limiting solutions are useful for the nondestructive characterization of texture from ultrasonic velocity measurements.
Nonlinearly generated spectral components in the nearfield of a directive sound source
Authors: Kamakura Tomoo , Hamada Naoaki , Aoki Kenich , Kumamoto Yoshiro
Published: October 2005

Nonlinear propagation of sound waves generated by a directive ultrasound source in air is discussed theoretically and experimentally. The circular source of 21 cm in radius consists of 1410 small PZT bimorph transducers, whose resonance frequency is 28 kHz. For a single-frequency wave excitation, sound pressures of the fundamental, second, and third harmonics are measured and are compared with the numerical results using a method of Aanonsen et al. [J. Acoust. Soc. Am. 75, 749–768 (1984)]. Extending their initial condition to the case of a two-frequency wave excitation, propagation curves and beam patterns of the difference frequency sound are obtained and compared with the measured data. All observations quantitatively agree very well with the numerical calculation. Nonlinear attenuation of spectral components by increasing the source pressure is clearly confirmed.
Transient response of an elastic spheroid—Surface waves and quasicylindrical modes
Authors: Williams Kevin L. , Sammelmann Gary S. , Trivett David H. , Hackman Roger H.
Published: October 2005

The low kL/2 transient response of an elastic spheroid to an acoustic wave incident along the axis of symmetry is analyzed. The emphasis is upon a direct theoretical and experimental determination of the group velocity of the lowest elastic mode of the spheroid. With these results, a critical examination is made of the consequences of two different physical pictures that have been proposed for the low kL/2 elastic response of such targets (the surface wave and ‘‘quasicylindrical’’ mode pictures). Large discrepancies are found between predictions of the group velocity based on the surface wave picture and both the T-matrix analysis and the experimental results presented here. In contrast, the predictions of the quasicylindrical mode picture are found to be in excellent agreement with these results. It is concluded that, although the surface wave description is useful at high kL/2, the quasicylindrical mode picture provides a more meaningful description of resonance phenomena in the low-to-medium kL/2 region.
Detection of oil-derivative contamination of water surfaces by statistical analysis of scattered acoustical signals
Authors: Pogorzelski Stanislaw J.
Published: October 2005

The statistical distribution of the amplitude of the acoustical signal scattered by a water surface undulated by an air stream was studied under laboratory conditions. The surface was covered with layers of oil substances of different physical properties. Statistical parameters of the distribution were determined as functions of the speed of the air stream and the thickness of the oil layer. Values of the obtained parameters differ from those expected for the scattering on the surface of clean water. Simultaneous analysis of all the statistical parameters could be a starting point for determining the weight fraction of the given substance and its thickness.
Optoacoustic observation of internal relaxation in liquid CS2
Authors: Thompson Charles H. , Cheyne Stanley A. , Bass Henry E. , Raspet Richard
Published: October 2005

Relaxation of liquid CS2 following absorption of a short pulse of 337-nm UV radiation has been experimentally observed using an optoacoustic technique. A theoretical description of the optoacoustic signal based on a delta function response formulation that accounts for multiple relaxation has been developed and computational results compared to theory. Agreement requires adopting an energy transfer scheme that includes a relatively slow rate (11×106 s−1) between initial photon absorption and transfer to translation.
Laminated piezopolymer plates for torsion and bending sensors and actuators
Authors: Lee C.-K. , Moon F. C.
Published: October 2005

A set of piezopolymer devices has been developed based on a composite laminate theory for piezoelectric polymer materials. By using different combinations of ply angles and electrode patterns, a piezopolymer/metal shim plate structure was built that exhibited both bending and torsion deformation under an applied electric field. A set of torsion-beam sensor structures was also built that could distinguish between bending and torsion or between different vibration modes. These devices were based on a general theory of piezoelectric laminates. The experimental results agreed quite closely with the theoretical predictions. These integrated sensor–actuator devices may find application in the control of microactuators or may be used for modal control of larger continuous structures.
A note on ‘‘Information conveyed by vowels’’
Authors: Ladefoged Peter
Published: October 2005

In an early experiment using synthetic speech, it was shown that raising or lowering the formants in an introductory sentence affected the identification of the vowel in a following test word [P. Ladefoged and D. Broadbent, J. Acoust. Soc. Am. 29, 98–104 (1957)]. This experiment has now been replicated using natural speech produced by a phonetician using two different overall settings of the vocal tract.
A bistatic, high-frequency, under-ice, acoustic scattering model. II: Applications
Authors: Bishop Garner C.
Published: October 2005

A model that has been developed to calculate the scatter produced by a high-frequency acoustic pulse that originates from a stationary and arbitrarily located source; is incident on and scattered from an under-ice surface characteristic of pack ice regions of the interior Arctic; and is detected by a stationary and arbitrarily located receiver is used to calculate a variety of acoustic data. Scattering from small-scale surface roughness produced by ice blocks as well as from large-scale surface roughness produced by ice keels is calculated and discussed. The effects of physical parameters on the scatter of a high-frequency plane wave from an ice block whose physical and geometric parameters are characteristic of those found in the Arctic are calculated and discussed briefly. The ice block scattering model is modified to calculate the near field target strength of a circular ice piston as a function of incidence angle. When measured and modeled facet target strength data are compared, it is shown that, near normal incidence, measured and modeled target strength levels agree reasonably well, but that the details of their dependence on incidence angle are different and that differences between the measured and modeled target strength data increase as frequency increases. Monostatic reverberation time series, facet target strength distributions, and correlation data are calculated and compared with measured data for three Arctic sites, and it is shown that measured and modeled data agree reasonably well. For the Chukchi Sea site, a variety of monostatic and bistatic time series, distribution, and correlation data are calculated and discussed for ice keels and flat ice features as well as for the entire under-ice surface. It is shown that the predominant large-scale, under-ice scatterers are ice keels; that ice keels increase reverberation levels; that the facets of ice blocks from which ice keels are composed produce high-level echos or glints; that generally the spatial location of these high-level echoes depends on source–receiver location, although some may persist from one location to the next; and that high-level echos from ice facets are one of the principal means by which ice keels increase high-frequency, under-ice reverberation.
The generation of infrasonic ambient noise in the ocean by nonlinear interactions of ocean surface waves
Authors: Kibblewhite A. C. , Wu C. Y.
Published: October 2005

Expressions for the spectra of infrasonic ocean noise and microseisms induced by nonlinear wave interaction are derived theoretically for an ocean environment modeled as a water layer overlying a solid half-space. A series of spectral transfer functions relating the source pressure field induced by the wave action to the underwater acoustic noise field and that of the microseisms this generates in the seabed are defined and calculated. The effect of bottom reflections on the transfer function is examined and an estimate of the contribution of the Rayleigh wave component of the microseism signal received onshore is also made.
The 1984 bottom-mounted Gulf Stream tomographic experiment
Authors: Agnon Yehuda , Malanotte-Rizzoli Paola , Cornuelle Bruce D. , Spiesberger John L. , Spindel Robert L.
Published: October 2005

In this paper, data from a Gulf Stream tomographic experiment carried out in October 1984 are analyzed. The experiment used acoustic sources and receivers bottom mounted beneath the stream to measure Gulf Stream dynamics. However, due to an unfortunate electronic malfunction of the source, only 2 days of acoustically measured travel time data are available. Nevertheless, some new and positive results are obtained. Bottom reflected acoustic rays having up to two bottom bounces are unambiguously identified by solving the direct problem of tracing rays both in a reference climatological profile and in actual range-dependent sound-speed sections from a hydrographic survey carried out during the experiment. It is also shown that these rays do not appear to be affected by important nonlinearities so that they can be used to provide consistent results in inverse solutions.
Comparison of target monitoring and two-ear monitoring dichotic listening procedures
Authors: Speaks Charles , Niccum Nancy , Leathers Ruth , Katsuki-Nakamura Jun
Published: October 2005

The dichotic listening performance of 40 listeners was assessed for consonant–vowel (CV) nonsense syllables with two procedures. One was a conventional two-ear monitoring task in which listeners attended to both ears and provided two responses for each pair of syllables. The ear advantage was described by %RE−%LE. The second was target monitoring, a yes/no task in which listeners attended to only one ear and listened for the presence of a target syllable. That procedure provided both hit and false alarm rates for each ear, and the ear advantage was described by P(C)maxRE−P(C)maxLE, which is insensitive to decision variables. Although both procedures yielded mean right-ear advantages (REA), the mean REA of +7.5% with two-ear monitoring was significantly different from the mean REA of +2.6% with target monitoring. In addition, although 62% of the listeners had a significant REA with the conventional procedure, only 40% had a significant REA with target monitoring. Decision variables, which are not controlled with conventional dichotic testing methods, may contribute to the ear advantage as it is described frequently in the literature.
Comment on ‘‘A cochlear model for acoustic emissions’’ [J. Acoust. Soc. Am. 8
4, 222–229 (1988)]
Authors: Wit Hero P.
Published: October 2005

The model proposed by Furst and Lapid in the article ‘‘A cochlear model for acoustic emissions’’ [J. Acoust. Soc. Am. 84, 222–229 (1988)] predicts properties for spontaneous otoacoustic emissions that are not in accordance with experimentally obtained results.
A slender-body approximation in scattering theory
Authors: Tran Van Nhieu Michel
Published: October 2005

The problem of the scattering of a plane wave by a general slender body of arbitrary cross section with a constant surface impedance is treated by a formalism based on the matched asymptotic method. It is shown that the scattered pressure may be determined by the resolution of a set of 2-D problems when using the slender-body approximation that is valid for wavelengths of the order of magnitude or greater than the characteristic cross-section length of the body. In the case of axisymmetric bodies, an expression for the scattered field can be obtained explicitly. The contributions of the insonified end section are analyzed from a paraboloidal geometry model, and simplified solutions are proposed for rigid and soft conditions. Some theoretical and numerical results for the farfield directivity are presented to illustrate the theory.
Green’s functions for propagation of sound in a simply moving fluid
Authors: Lakhtakia Akhlesh , Varadan Vijay K. , Varadan Vasundara V.
Published: October 2005

Two approaches involving the spatial and temporal Fourier transforms have been used to derive time- and space-dependent Green’s functions pertinent to the propagation of sound waves in a fluid that is moving with a constant velocity v. The two approaches give rise to differing interpretations of the observations made by a stationary observer vis-à-vis those made by an observer moving with the fluid. The properties of the causal and the noncausal Green’s functions are analyzed, and are shown to be equivalent.
Responses of ‘‘high-spontaneous’’ auditory-nerve fibers to consonant–vowel syllables in noise
Authors: Geisler C. Daniel , Gamble Theresa
Published: October 2005

Responses of ‘‘high-spontaneous’’ single auditory-nerve fibers in anesthetized cat to nine different spoken stop and nasal consonant–vowel syllables presented in four different levels of speech-shaped noise are reported. The temporal information contained in the responses was analyzed using ‘‘composite’’ spectrograms and pseudo-3D spatial-frequency plots. Spectral characteristics of both consonant and vowel segments of the CV syllables were strongly encoded at S/N ratios of 30 and 20 dB. At S/N=10 dB, formant information during the vowel segments was all that was reliably detectable in most cases. Even at S/N=0 dB, most vowel formants were detectable, but only with relatively long analysis windows (40 ms). The increases (and decreases) in discharge rate during various phases of the responses were also determined. The rate responses to the ‘‘release’’ and to the voicing of the stop-consonant syllables were quite robust, being detectable at least half of the time, even at the highest noise level. Comparisons with psychoacoustic studies using similar stimuli are made.
Auditory filter characteristics and consonant recognition for hearing-impaired listeners
Authors: Dubno Judy R. , Dirks Donald D.
Published: October 2005

To examine the association between frequency resolution and speech recognition, auditory filter parameters and stop-consonant recognition were determined for 9 normal-hearing and 24 hearing-impaired subjects. In an earlier investigation, the relationship between stop-consonant recognition and the articulation index (AI) had been established on normal-hearing listeners. Based on AI predictions, speech-presentation levels for each subject in this experiment were selected to obtain a wide range of recognition scores. This strategy provides a method of interpreting speech-recognition performance among listeners who vary in magnitude and configuration of hearing loss by assuming that conditions which yield equal audible spectra will result in equivalent performance. It was reasoned that an association between frequency resolution and consonant recognition may be more appropriately estimated if hearing-impaired listeners’ performance was measured under conditions that assured equivalent audibility of the speech stimuli. Derived auditory filter parameters indicated that filter widths and dynamic ranges were strongly associated with threshold. Stop-consonant recognition scores for most hearing-impaired listeners were not significantly poorer than predicted by the AI model. Furthermore, differences between observed recognition scores and those predicted by the AI were not associated with auditory filter characteristics, suggesting that frequency resolution and speech recognition may appear to be associated primarily because both are degraded by threshold elevation.
Frequency discrimination near the spectral edge of simultaneous and forward maskers
Authors: Fantini Deborah A.
Published: October 2005

The effects of the presence of an amplitude discontinuity in the spectrum of a noise masker on frequency discrimination performance were examined. First, detection thresholds as a function of masker level were obtained for pure-tone signals masked by either simultaneous or forward white and low-pass maskers. Then frequency discrimination thresholds were obtained using four masker levels that were chosen to yield predetermined masked thresholds, with signal levels corresponding to each of three sensation levels above these masked thresholds. The principal results indicate that frequency discrimination is poorer in simultaneous low-pass noise than in simultaneous white noise, and that this difference in performance increases with increasing sensation level and with increasing masker level. These results are inconsistent with an explanation based on the pitches generated at spectral edges (‘‘edge pitch’’), pitch shifts, or disruption of phase-locking information, but are generally consistent with an explanation based on lateral suppression. It is proposed that a release from suppression may occur in filtered noise backgrounds at high noise levels and at high sensation levels. The reduced suppression may result in poorer frequency discrimination due, in part, to reduced signal detectability.
Comments on the deep six sound channel
Authors: Ramos P. A. , Palmer D. R.
Published: October 2005

Some features of the deep six sound channel [J. C. Miller, J. Acoust. Soc. Am. 71, 859–862 (1982)], which may be important to those who wish to use the model in various applications, are noted and discussed.
A laser study of transient Lamb waves in thin materials
Authors: Hutchins D. A. , Lundgren K. , Palmer S. B.
Published: October 2005

A method is described by which transient ultrasonic Lamb waves may be generated and detected within thin materials, using laser techniques. The material is thin enough that only the two lowest-order modes of Lamb waves need be considered. These are the a0 mode, which is dispersive in the thin plate limit, and the s0 mode, which is not. Signal processing techniques were used to determine the dispersion characteristics of the a0 mode, and the velocity of the s0 mode, in both aluminum and metallic glass samples. From these measurements, it was possible to estimate both the thickness of the samples and their elastic constants. The errors involved in such a measurement are discussed.
Correlation after asymmetrical clipping
Authors: Weston David E.
Published: October 2005

A general formula is derived for the correlation coefficient between clipped waveforms, or among detection sequences, for the case where the clipping is asymmetric or the detection probability departs from 50%. The analytic arcsine law for symmetrical clipping is rehearsed, and new analytic forms are found for asymmetrical clipping with high positive correlation, numerically low correlation, and high negative correlation.
Inner hair cell responses to tonal stimulation in the presence of broadband noise
Authors: Dolan David F. , Nuttall Alfred L.
Published: October 2005

The effects of broadband noise (BBN) on the tone-evoked dc receptor potential from inner hair cells of guinea pigs were measured. The effects of the noise were: suppression of the receptor potential, no net change, or greater depolarization relative to the tone alone, evoked receptor potential. The effects appear to be consistent with a two-tone suppression hypothesis. The time course of the suppression effect is immediate and constant in time. This observation suggests no obvious involvement of a local feedback loop in outer hair cells or one depending on the efferent nerves. Inner hair cell ‘‘sensitivity’’ is a variable in the magnitude of the suppression. Comparison of masked, tone-evoked dc receptor potential intensity functions to responses from auditory-nerve fibers (taken from the literature for experiments using a similar paradigm) differentiates the phenomena of suppression and adaptation in the auditory periphery.
Solid particle motion induced by a point source above a poroelastic half-space
Authors: Attenborough Keith , Richards Trevor L.
Published: October 2005

By using a modified Biot model of the poroelastic half-space and the classical approach to determination of the field at a fluid/solid boundary, the wave contributions to the solid surface particle velocity due to a point source in air above an air-filled poroelastic solid are identified and evaluated. The evaluation involves both a new method of approximation of the branch-cut integrals and the light fluid limit when searching for surface-wave modes. The significant contributions are found to be from the direct and ground waves in air and from a surface wave which may be described as an air-coupled Rayleigh wave. The parameter combination that maximizes the air-coupled Rayleigh-wave contribution is identified.
Sonar beamforming based upon monaural localization techniques
Authors: Tollman Peter A. , Denbigh Philip N.
Published: October 2005

Sonar beamforming is usually accomplished using multielement transducer arrays. A novel alternative beamforming system is proposed, which uses a single fixed active element placed within an irregular reflecting surface. The proposed system is based upon one suggested mechanism of monaural localization. Interference resulting from reflections off the surface modifies the spectra of incoming acoustic signals. The signal source is located by correlating the output signal spectrum with the known spectral responses of the receiving system for all angles. Computer simulations and tests using an experimental active system indicate that the proposed technique could be a useful alternative in certain sonar applications.
An acoustic waveguide with variable cross section
Authors: Razavy M.
Published: October 2005

The modes of propagation and the allowed range of frequencies for an acoustic waveguide with variable cross section have been found by solving the wave equation in elliptic cylinder coordinates. This waveguide is formed by two parallel planes and two surfaces obtained by the translation of two branches of hyperbola perpendicular to the planes, so that the cross section is a rectangle with variable length. Numerical results for relevant physical quantities are given.
Matched field processing in shallow water for range, depth, and bearing determination: Results of experiment and simulation
Authors: Ozard John M.
Published: October 2005

Recent theoretical studies have investigated high-resolution methods for estimating source position in a shallow-water waveguide. In this paper, an eigenvector method and a geophysical model based on several types of seismic data are used to estimate the bearing, depth, and range of a moving submerged source in the presence of an interfering surface source at the same range and bearing. The receiver was a sparse horizontal array of four sensors on the bottom (depth 82 m). A variant of the eigenvector method known as the MUSIC method was employed for measured and test field matching and a normal mode model was employed to calculate the test field. The data analyzed were obtained by towing a submerged source directly below the stern of the CFAV Endeavour, so that the surface and submerged sources were essentially at the same range and bearing. Source bearing estimates for the data showed that source bearings were usually well defined although somewhat ambiguous. The presence of the deep source was indicated at 15 and 19.5 Hz but the ranges were completely ambiguous. Simulations produced similar results for the same small number of sensors and a small number of propagating modes. However, simulations also showed that, with a horizontal array of 15 hydrophones and a signal-to-noise ratio of 10 dB, unambiguous resolution of depth, bearing, and range would be obtained.