bluuebunny/crossref_metadata_2025 huggingface dataset:
Angle–time–frequency resolution of the noise field generated by wind-induced breaking waves
Authors: Finette S. , Heitmeyer R. M.
Published: October 2005

This paper describes a model of the noise field generated by waves breaking on the ocean surface and the angle–time–frequency resolution of that noise field. The model takes into account the discrete space-time structure of the noise sources and thus differs from models based on the continuous source sheet assumption. This is done using a stochastic model to specify the locations, occurrence times, and radiated noise waveforms for the individual breaking waves and then computing the noise field as the superposition of the noise contributions from those breaking waves. The angle–time–frequency resolution of the noise field is obtained by applying a time–frequency resolution algorithm to the output of a beamformer as a function of the steering angle. To describe the properties of the 3-D noise resolution, we assume a vertical array in a shallow-water acoustic environment and use recently obtained experimental estimates of the acoustic coverage and the source level and waveform-duration probability densities to determine the breaking wave source model parameters. The examples presented indicate that the breaking wave noise is largely confined to two angular sectors, the high-angle sector looking toward the ocean surface and the sector containing the discrete mode propagation energy. The high-angle noise exhibits a large temporal variability, characterized by a small number of large broadband bursts, and is only weakly dependent on the acoustic environment. On the other hand, the discrete mode noise shows less temporal variability, characterized by a larger number of smaller broadband bursts, and is strongly dependent on the acoustic environment. Finally, the angle–frequency structure of the low-level noise in the downward-looking direction represents an example of imaging the bottom with surface-generated ambient noise and suggests that ambient noise measurements might be used to estimate sediment thickness.
Encoding the fundamental frequency of a complex tone in the presence of a spectrally overlapping masker
Authors: Carlyon Robert P.
Published: October 2005

A series of experiments investigated listeners’ ability to encode the fundamental frequency (F0) of a group of harmonics (the ‘‘target’’) in the presence of a second, spectrally overlapping, group (the ‘‘masker’’). Experiment 1a was a sequential F0 discrimination task between two targets, whose F0s were geometrically centered on 210 Hz, in the presence of a 210-Hz masker. The target and the masker were bandpass filtered identically, either from 20 to 1420 Hz (‘‘low-frequency’’ condition) or from 3900 to 5400 Hz (‘‘high-frequency’’ condition). In the low-frequency condition the masker affected performance only moderately, regardless of whether it was gated synchronously with, or was turned on 150 ms before and off 150 ms after, each 200-ms target. In the high-frequency condition, the synchronous masker also had a moderate effect, but the asynchronous masker reduced performance dramatically. Whatever the masker gating, listeners did not hear the combination of the masker and target in this region as a mixture of two complex tones, but experienced a unitary noiselike or ‘‘crackle’’ percept. Experiment 1b showed that the large deterioration seen in the high-frequency condition of experiment 1a could be obtained in the low-frequency condition by reducing the F0 to 62.5 Hz, suggesting that the resolvability of adjacent harmonics was important for the effect.

Experiment 2 required listeners to detect a difference in F0 (‘‘ΔF0’’) between two simultaneous groups of components, one filtered in the high region and the other in the low region. Performance was only slightly degraded by a continuous masker filtered in the low region, but was reduced to chance by a masker in the high region. Experiment 3 showed that, as the ΔF0 between a masker and a target in the low region increased from 1% to 8%, listeners identified the mixture as sounding progressively ‘‘less fused,’’ but this was not the case in the high region. It is concluded that listeners are poor at extracting the F0s of two groups of unresolved harmonics in the same frequency region. The experiments provide no evidence that listeners can use the leading part of an asynchronous masker to identify its F0 and thereby help extract the target’s F0 from the mixture.
On the pitches of the components of a complex tone
Authors: Hartmann William Morris , Doty Sandra L.
Published: October 2005

The pitches of the harmonics (numbers 1, 2, 3, 4, 5, 7, 9, and 11) of a complex tone were measured in a matching experiment. The harmonics to be matched were mistuned (8% or less) either positively, or negatively, or not at all. For all mistuned harmonics and all listeners the matching pitches were found to be exaggerations of the mistunings, i.e., the data exhibited pitch shifts with the same sign as the mistunings. This result is shown to be contrary to place models of pitch perception, such as the spectral pitch algorithm of Terhardt, in which pitch shifts are caused by the interaction of excitation patterns for the individual harmonics. An alternative model, in which pitch is determined by neural timing, also fails to account for the data. However, a hybrid model, combining effects of excitation pattern interaction with neural timing, does agree with most of the data.
Some effects of filtered contexts on the perception of vowels and fricatives
Authors: Watkins Anthony J. , Makin Simon J.
Published: October 2005

When a phrase is filtered to simulate the effects of a transmission channel, a vowel played shortly afterward is heard as if there is perceptual compensation for the filter. However, a transmission channel would also have an effect on sounds that arrive after the vowel. The present experiments ask whether vowel test sounds are affected by the filtering of a subsequent affricate when there are no other sounds present. Effects on other types of test sounds from different subsequent sounds are measured as well. The experiments also ask whether these effects occur when there is information about the channel in a precursor phrase. Listeners identified words from continua between /itsh/ and /εtsh/, /æpt/ and /inverted open aye pt/, or /sl schwa/ inverted closed omega and /flschwa inverted closed omega/. Filters’ frequency responses were the difference of spectral envelopes from the end-point test sounds. The perceptual midpoints of all the continua were shifted in a manner consistent with compensation when the precursors were filtered, as well as when sounds subsequent to the test sound were filtered and there were no precursors. Also, when filtered precursors were present, the shifts increased when filtering was added to sounds subsequent to the test sound. These results indicate that mechanisms of perceptual compensation for filtering by transmission channels use information in preceding sounds in combination with information in following sounds and that these mechanisms operate between different types of speech sounds.
Spherical inclusion characterization by the acoustical microscope: Axisymmetric case
Authors: Lobkis O. I. , Maslov K. I. , Kundu T. , Zinin P. V.
Published: October 2005

In this paper it is shown how one can obtain the diameter and depth of a solid spherical inclusion in a solid half-space directly from the location of the peaks of its V(z) curve. Simplified expressions of V(z) curves presented in this paper have been experimentally verified by generating V(z) curves of a spherical inclusion in pure epoxy. The inclusion diameter and depth are predicted from the experimentally generated V(z) curves. Experimental predictions are found to be very close to the true values; errors associated with all predictions are less than a few percent.
Coincidence echo statistics
Authors: Foote Kenneth G.
Published: October 2005

Two scatterers at similar range give an echo which may appear to be due to a single scatterer. Methods for determining target strength that depend on resolving single scatterers may fail in this instance. Statistics associated with the described special case of coincidence are derived and illustrated by theoretical computation for the SIMRAD EK500 echo sounder system with the ES38B split-beam transducer resonant at 38 kHz. Connections to angle measurement in radar and swath bathymetry and to bottom-scattering-strength measurement are noted.
Estimation of the orientation distribution of short-fiber composites using ultrasonic velocities
Authors: Dunn Martin L. , Ledbetter Hassel
Published: October 2005

A method for estimating the orientation distribution function (ODF) of short-fiber composites using measured ultrasonic velocities is presented. The method is based on the coupling of (i) a forward micromechanics model of the effective ultrasonic velocities of the textured composite in terms of the coefficients in an expansion of the ODF in generalized spherical harmonics, (ii) ultrasonic measurements of the velocities, and (iii) an inversion algorithm to obtain the coefficients of the ODF from the measured velocities and the forward model. The approach is used to determine the ODF coefficients for a transversely isotropic short-fiber SiC/Al metal-matrix composite. The ODF coefficients obtained by inversion of ultrasonic velocities agree reasonably with those obtained from neutron-diffraction pole figures. Corresponding elastic constants predicted with these coefficients also agree well with independently measured elastic constants.
Flexural vibration of piezoelectric composite hollow cylinder
Authors: Paul H. S. , Nelson Vazhapadi K.
Published: October 2005

The free vibration of a laminated hollow circular cylinder with traction-free surfaces is studied by taking care of continuity conditions at the interfaces. The frequency equations are obtained for the composite cylinder composed of two different piezoelectric materials belonging to the 6mm class and a hypothetical linear elastic material with voids (LEMV) as bonding layers. Numerical results for complex-valued frequency are carried out for the composite cylinder ceramic-1/LEMV/ceramic-2. The dispersion curves for the flexural vibration of a composite hollow cylinder with voids and without voids are obtained and are compared with that of a hollow cylinder of piezoelectric material.
Propagant phase in reverberant environments
Authors: Fletcher N. H. , Thwaites S.
Published: October 2005

The phase of the transfer function between two points in an extended system can be easily measured if it is taken to be the accumulated phase obtained by smoothly raising the measurement frequency from zero to the reference frequency. Lyon et al., in an extended series of papers [most recently J. Acoust. Soc. Am. 95, 286–296 (1994)], have examined the behavior of this accumulated phase in systems of two and three dimensions and have elucidated the concept of a reverberant phase which is independent of the separation between the two measurement points, provided they are far enough apart, but which rises sharply with increasing frequency. In some applications, for example, in nondestructive testing of extended structures, it is important to be able to observe simple wave-propagation behavior and in particular to measure the propagant phase as a function of frequency and position. The conditions under which this is possible are investigated, and are shown to impose constraints on the ratio between the propagation distance and the size of the structure under test, and either the material damping coefficient or the reflection coefficient at the domain boundaries. These results, which represent an extension of those of Lyon et al., are discussed in terms of the distribution of zeros of the transfer function in the complex frequency plane. Many platelike structures of practical interest are found to satisfy these conditions, so that measurement of propagant phase behavior can provide the basis for a useful technique of nondestructive examination.
Analysis of periodically forced nonlinear Hill’s oscillator with application to a geared system
Authors: Padmanabhan C. , Singh Rajendra
Published: October 2005

Although nonlinear systems subject to combined parametric and external excitations have been examined in some depth, very few of these investigations have addressed the influence of a mean (time-invariant) load on the system response. In particular, the importance of the mean load effect has been highlighted in the study of whirling asymmetric shafts, where significant changes in system response and stability occur under the influence of gravity. The present paper intends to characterize the specific effect of mean load on the dynamic behavior of a Hill’s oscillator with a clearance-type nonlinearity while also being subjected to a periodic base displacement excitation. The parametric continuation technique and method of harmonic balance would be used for this purpose. Issues discussed would include the coupling between the mean load and the dynamic response amplitude, interaction between the parametric excitation effect and the clearance nonlinearity, and comparison between time-invariant and time-varying systems. Further, a geared system has been analyzed as a practical application of the nonlinear Hill’s equation examined. Earlier studies on gear dynamics have been reexamined to provide improved correlation with prior experimental data; new interpretations for some of the nonlinear phenomena in the experimental data has also been provided based on our study.
Fast, efficient calculation of rays and travel times with ray perturbation theory
Authors: Pulliam Jay , Snieder Roel
Published: October 2005

A ray perturbation formulation for the calculation of rays and travel times in isotropic inhomogeneous media is presented. The ray perturbation theory employed is of first order for the ray deflection and of second order for the travel time. The initial slowness model is parametrized in terms of triangular cells; values are assigned initially to grid nodes and the slowness gradient is assumed to be constant between nodes. The assumption of a constant slowness gradient within a cell leads to a simplification of the ray perturbation equations and a straightforward analytic solution for ray segments in the cells. Imposing boundary conditions that require continuity at cell interfaces leads to a separate tridiagonal system of equations for each component of the ray-path location vector, which produces an extremely efficient algorithm. The accuracy and speed of this scheme with a 2-D synthetic crosswell experiment is evaluated. The computation times for the calculations described in this paper depend only on the number of nodes that influence each ray, not the total number of nodes parametrizing the model, so the method promises an even greater increase in speed for 3-D applications.
Transient analytic and numerical results for the fluid–solid interaction of prolate spheroidal shells
Authors: Jones-Oliveira Janet B.
Published: October 2005

A transient solution is presented which models the fluid–solid interaction of a thin elastic prolate spheroidal shell loaded end-on by a nonconservative acoustic shock wave. Solutions to the Lagrangian equations of motion are provided for the normal and tangential shell displacement fields, as well as for the incident, scattered, and radiated fluid pressure fields. The explicit analytic solutions converge uniformly and absolutely to the exact solution of the actual coupled differential equations over the entire temporal and spatial domains both in the structure and in the fluid. Numerical results for the free vibrations and for the transient fluid–solid interactions of a fluid-loaded prolate spheroidal shell are presented. As in the case for the spherical geometry, the fluid loading is shown to down shift the frequencies and to introduce additional proliferant structural frequencies. Long time history plots of the shell displacements are presented for the submerged shock-loaded low aspect ratio case. Insights into the qualitative and quantitative effects of the fluid on the structural response are revealed. DOE−MACSYMA was used extensively to develop and verify the solutions.
Use of quantitative measures of auditory brain-stem response peak amplitude and residual background noise in the decision to stop averaging
Authors: Don Manuel , Elberling Claus
Published: October 2005

An objective quantitative approach to the decision of when to stop averaging sweeps in auditory brain-stem response (ABR) testing is presented. This decision is based on (1) the knowledge of the amplitude distributions of wave V in the ABRs of normal hearing individuals for varying stimulus levels, (2) calculated estimates of the residual background noise in the average, and (3) use of a quantitative statistical detector of an evoked potential. Several reasons for terminating an average are presented along with a specific protocol for each of the reasons. These protocols provide a general but consistent framework to address the issue of when to stop averaging and should improve the efficiency of ABR testing. Furthermore, it is quite possible to automate the procedure and the decision process.
Approximating the response of reverberant systems: Applications to proportional damping, added impedance, and feedback control
Authors: Clark Robert L.
Published: October 2005

Approximate methods for computing the response of reverberant systems are reviewed in light of recent discussions on ‘‘modal methods’’ provided by Pan [J. Acoust. Soc. Am. 93, 1641–1643 (1993); 97, 691–694 (1995)] and Franzoni and Dowell [J. Acoust. Soc. Am. 97, 687–690 (1995)]. Cross coupling of admissible functions used in the assumed modes approach is discussed with respect to inherent system tamping, dissipative impedances, and proportional colocqted feedback convrol. The dissipatite impedance and colocated, rate-feedback control are observed to have an identical form and thus the number of admissible functions required to converge the closed-loop model will, in general, exceed the number of admissible functions required to converge the open-loop model over the same bandwidth due to the cross coupling resulting from the feedback.
Trumpet sound simulation using a two-dimensional lip vibration model
Authors: Adachi Seiji , Sato Masa-aki
Published: October 2005

Trumpet sound simulation is carried out with a two-dimensional lip vibration model, where the lips execute both swinging and stretching motions. This model allows lips to operate on both the lower and higher frequency sides of the air-column resonance frequencies. Oscillations generated by the total sound production system are on both the lower and higher frequency sides in the first through third resonance modes, while in the fourth and higher modes they are realized only on the lower side. From each resonance mode, an oscillation having the least frequency deviation against a change in lip eigenfrequency and also having sufficient amplitude is selected as the optimum oscillation of the resonance mode. It is found that these oscillations in the lower modes have positive phase differences between lip vibration and mouthpiece pressure, whereas those in the higher modes have negative ones. This result closely matches the transition of lip vibration states from the one modeled by the outward-striking valve at the second mode (i.e., the lowest mode among those used musically) to that modeled by the laterally striking valve at the higher modes, which is observed in the simultaneous measurement of mouthpiece pressure and lip vibration.
Nature of the lip reed
Authors: Chen Fang-Chu , Weinreich Gabriel
Published: October 2005

Reed instruments have been categorized into two families since Helmholtz: the ‘‘striking inward’’ and the ‘‘striking outward’’ reeds. In an attempt to clarify the question to which family the lips of the brass player belong, a Helmholtz resonator with active feedback was used as a single-mode brass instrument and the playing frequencies generated by three trumpet players were measured. By adjusting the gain and the phase in the feedback loop, the resonant frequency and the quality factor of the resonator can be varied. The acoustic impedance at the mouthpiece is measured by a novel method without removing the player’s lips. The results show that with extreme efforts the players can generate playing frequencies both lower and higher than the corresponding air column resonance, but that the playing frequency under normal playing conditions (the ‘‘most comfortable note’’) is almost always higher than the corresponding air column resonance. This supports the view that human lips function as ‘‘striking outward’’ reeds.
Acoustic energy quantities and radiation force in higher approximation. II. Boundary conditions of the Earnshaw–Riemann solution
Authors: Beissner K.
Published: October 2005

The well-known, nonlinear, plane-progressive Earnshaw–Riemann wave solution is applied to calculate the acoustic intensity and the Langevin radiation pressure up to the fourth order of approximation. In doing so, it appears necessary to use this solution in a form slightly differing from that widely found in the acoustics literature. Certain results obtained recently are corrected.
Local variations of slow wave attenuation in air-filled permeable materials
Authors: Nagy Peter B.
Published: October 2005

The previously reported [P. B. Nagy, J. Acoust. Soc. Am. 93, 3224 (1993)] anomalous high-frequency attenuation of slow wave transmission through air-filled porous plates was further investigated by a novel experimental means. In order to investigate the heterogeneous nature of the pore structure, the experimental system was modified so that the spatial variation of the transmitted acoustic field could be measured by a sharply focused receiver. The experimental results indicate that the observed attenuation is mainly due to viscous losses. Owing to the a couple of simple technical modifications and improvements such as beam focusing, automated scanning, increased dynamic range, and greatly accelerated data acquisition, it became possible to use the slow wave transmission method as an ultrasonic imaging technique. This novel approach can be used to study the heterogeneous pore structure in permeable solids with a few-millimeter-resolution in the 100- to 500-kHz frequency range.
Investigation of the dispersion relations of surface acoustic waves propagating on a layered cylinder
Authors: Kawald U. , Desmet C. , Lauriks W. , Glorieux C. , Thoen J.
Published: October 2005

The propagation of pulsed surface acoustic waves (SAW) on a layered cylinder has been investigated both theoretically and experimentally. The pulses were generated by a ‘‘line-source’’ pulsed laser and detected by an optical beam deflection technique providing information on pulse dispersion in a fully contactless way. The sample investigated was a hollow steel tube fitted tightly to a massive cylinder of a tin alloy. The theoretical dispersion relation for surface waves propagating in this system, under the assumption that the wave fields are uniform along the cylinder axis, was derived and good agreement with the experimental results was found. These results confirm the applicability of an optical, contactless technique for the characterization of layers on curved substrates.
Behavior of extensional modes in a thin rod immersed in a viscous medium
Authors: Liu Yuan , Viens Martin , Cheeke David
Published: October 2005

A viscoelastic model is established for the coupled motion in a thin solid rod and an infinite viscous medium surrounding it, starting from the basic laws of elastic and fluid mechanics. The effect of various material parameters of the surrounding medium on the propagation of acoustic waves along the rod is investigated using numerical calculations. It is demonstrated that, at low frequencies, the fundamental radial–axial mode (R01) responds most to changes in the material parameters of the surrounding medium related to shear motion in a manner similar to that of the fundamental torsional mode (T00). Based on this effect, a model miniature viscosity and density sensor is proposed and tested in viscous liquids. The attenuation in the device agrees well with the theoretical model and exhibits an approximately linear dependence on the square root of the product of the density and the shear viscosity of the surrounding medium. This work shows that simple traditional acoustic technology can be used to develop small size, low-cost sensors for liquid viscosity and density measurement with the possibility of on-line applications.
Acoustical laser with mechanical pumping
Authors: Zavtrak Sergei T.
Published: October 2005

A new simple scheme of an acoustical laser with mechanical pumping is suggested. In accordance with this scheme the pumping is created by a piezoelectric emitter of the piston type. The liquid with dispersed particles (gas bubbles) plays the role of an active medium. Phase bunching of the particles is realized by acoustical radiation forces. Generation conditions for this acoustical laser are evaluated. It is shown that two types of losses must be overcome for the beginning of the generation. The first type results from the energy dissipation in the active medium and the second one is caused by radiation losses at the boundaries of the resonator.
Near-field computation for sound propagation above ground—Using complex image theory
Authors: Li Y. L. , White Michael J.
Published: October 2005

In this paper, a very simple method is introduced for the efficient computation of the sound field in the near region above an impedance ground or an extended reaction ground. The procedure is based on complex image theory. Using Prony’s method, the slowly varying factor in the integrand of the Sommerfeld integral is approximated by a short series in terms of complex exponential functions. The result can be exactly evaluated by the Sommerfeld identity. A new closed-form approximate expression of the sound field is obtained, which is represented as the original source, its quasistatic image, and several ‘‘images’’ with complex amplitudes and positions. Avoiding numerical evaluation of the Sommerfeld integral makes these closed-form expressions computationally very efficient. The representation of the field with complex images makes the formula useful in measurement of ground impedance or in other cases requiring repeated mapping of the sound field. Numerical results show that these closed-form Green’s functions are very accurate for the computation of the near field.
Discrete tones generated by a supersonic jet ejector
Authors: Krothapalli Anjaneyulu , Hsia Y. C.
Published: October 2005

Results of an experimental investigation are presented that describe the characteristics of discrete sound generated by a constant area ejector that uses an underexpanded rectangular jet as the primary flow. The variation of screech tones, which are commonly observed in the spectrum of free shock-containing jets with stagnation pressure and area ratio, show a staging behavior due to the presence of the ejector duct. Such a behavior is explained with the use of a feedback loop. In addition to screech tones, a different type of resonant oscillation within the duct is identified. These consist of acoustic resonances whose frequencies and mode shapes are related to the unsteady flow in the duct and the size of the duct. Two dominant symmetric (varicose) and antisymmetric (flapping) modes of the primary jet determine the nature of the ejector tones that are observed in the spectrum. Using a phase-locked schlieren system, different longitudinal and transverse duct modes are photographed.
Acoustic scattering from fish swimbladders
Authors: Ye Zhen
Published: October 2005

It is well known that the acoustic scattering from a swimbladder fish is dominated by the gas-filled swimbladder. In this paper, the sound backscattered by a fish swimbladder of an arbitrary geometrical shape is studied. Particular attention is paid to the scattering at low frequencies, i.e., the acoustic wavelength is much larger than the size of swimbladder. A surface average approach is presented to study the sound scattering by the fish swimbladder. A formula is derived for the low-frequency scattering function of an arbitrary swimbladder, incorporating the familiar resonance feature of a gas-filled scatterer. The theory is applied to a prolate spheroid gas bubble, yielding favorable results compared to that obtained by a rigorous approach. As an application, the theory is also used to study the low-frequency acoustic scattering of some fish, and the results are compared with some existing experimental data. It is shown that the theoretical results agree reasonably well with the data for frequencies near or below resonance frequencies, but significant discrepancy remains for higher frequencies.
Acoustic travel-time perturbations due to shallow-water internal waves and internal tides in the Barents Sea Polar Front: Theory and experiment
Authors: Lynch James F. , Jin Guoliang , Pawlowicz Richard , Ray Douglas , Plueddemann Albert J. , Chiu Ching-Sang , Miller James H. , Bourke Robert H. , Parsons A. Rost , Muench Robin
Published: October 2005

During August 1992, a combined acoustics/physical oceanography experiment was performed to study both the acoustical properties and the ocean dynamics of the Barents Sea Polar Front in the region near Bear Island. Oceanographic observations from shipboard hydrography and moored sensors allowed the construction of the internal wave frequency spectrum for the area. A rapidly sampled tomographic section from a 224-Hz, 16-Hz-bandwidth acoustic source to a 16-element vertical receiving array enabled the monitoring of travel-time fluctuations over the internal wave frequency band. To describe the measured acoustic fluctuations, theoretical expressions have been developed for the travel-time variances which are functions of the internal wave oceanographic field, the local acoustic propagation characteristics, and the acoustical system’s properties. Both ray and mode theory expressions are generated, as the experiment was performed in shallow water and both ray and mode arrivals were resolvable. Comparison of the theory with the data shows generally good agreement. However, due to the fact that the internal wave study is a secondary objective of this experiment, the data are not of the quality eventually hoped for. Directions for future research in this area are outlined and discussed.
Temporal evolution of under ice reflectivity
Authors: Laible Henry A. , Rajan Subramaniam D.
Published: October 2005

Multiyear Arctic Sea ice is a heterogeneous material whose acoustic properties are functions of time and space. Over the past few years a number of investigators have studied the reflectivity of sound at the ice–water interface for sound incident from the water. The studies have considered reflections of low- and high-frequency sound for fixed times of the year. From data collected in a recent year-long field experiment conducted in the Arctic, the reflection coefficient at the ice–water interface for sound incident from the water column has been determined as a function of time. The purpose of this paper is to study the temporal evolution of the reflection coefficient with a view to explain the observed fluctuations in the magnitude of the reflection coefficient. A thermodynamic model of ice growth was used to obtain the temperature and salinity structure of the ice for each month of the year and an elastic model was used to calculate the corresponding compressional and shear wave speeds. The reflection coefficient was calculated and the results were compared for various changes in the input parameters to the models. Correlation exists between the model and field measurements of reflection coefficient during the months of September–April. The model does not predict the behavior observed during June–August. It is believed that the reason for the discrepancy is associated with a change in water column properties during this time.
Matched-phase noise reduction
Authors: Fitzgerald Raymond M.
Published: October 2005

In their recent paper, Orris et al. (OMK) [J. Acoust. Soc. Am. 96, 3499–3503 (1995)] present the ‘‘matched-phase noise reduction’’ technique, which they characterize as a ‘‘method for improving signal-to-noise ratios in noise dominated data, given the shape of the noise spectrum.’’ They derive an optimum ‘‘filter,’’ analyze its properties, provide ‘‘an example in which a signal can be retrieved from noise at a level more than 100 dB higher than the signal,’’ and suggest practical applications for the method in underwater acoustics scenarios ‘‘where the frequency spectrum is known approximately.’’ The present paper analyzes the OMK technique in terms of estimators that best approximate the unknown signal and noise and arrives at conclusions which differ from those of OMK. The demonstration of signal recovery reported by OMK is shown to result from their synthesis of an atypical noise realization. Limitations of their technique under more typical conditions are derived.
On a choice of the optimum sounding signal for time-delay spectrometry
Authors: Yaremchuk A. I.
Published: October 2005

The time-delay spectrometry method is reviewed from a general standpoint. All sounding signals that allow the measurement of the response function of a system under study are presented. It is shown that an exact evaluation of the response function can be done only in an adiabatic regime. A simple mechanical model describing TDS system performance is proposed and used for investigation of the inverse problem. A perturbation theory that enables one to obtain the asymptotic solution is formulated. The periodic case is discussed.
Role of articulation in speech perception: Clues from production
Authors: Lindblom Björn
Published: October 2005

The relative roles played by signal properties and nonsignal information in speech perception are first examined. The evidence strongly suggests that phonetic percepts are never knowledge-innocent records of the raw signal. That conclusion is drawn not only about ‘‘higher’’ levels of language processing, but is seen to apply also to the perception of elementary phonetic stimuli. A review of a broad range of facts about production highlights the fact that speech production is adaptively organized. That circumstance suggests that the signal does not encode articulatory or acoustic/auditory invariants, but plays the role of supplementing the multimodal information already in place in the listener’s speech processing system. It is accordingly proposed that phonetic signals are not invariants wrapped in ‘‘noise,’’ but are products of listener-dependent adaptations that transform speech patterns in principled and, therefore, interpretable ways. Do listeners form speech percepts by way of intermediate articulatory representations? There seem to be strong both theoretical and methodological reasons to doubt that they do.
Critique: Articulatory-acoustic relations and their role in speech perception
Authors: Stevens Kenneth N.
Published: October 2005

These remarks are in response to ‘‘Role of articulation in speech perception: Clues from production,’’ by Björn Lindblom. It is suggested that the form in which the lexicon is stored includes both segments and distinctive features, and this representation is neutral with respect to the articulatory and the acoustic domains. The process by which features are determined from the sound requires that patterns of acoustic properties be identified. In developing models of speech perception, knowledge of articulatory-acoustic relations can be a guide in defining these properties, but it is not necessary for the models to assign primary status to articulation.
Shock waves in trombones
Authors: Hirschberg A. , Gilbert J. , Msallam R. , Wijnands A. P. J.
Published: October 2005

Based on physical models of musical instruments and of the human voice, a new generation of sound synthesizers is born: virtual instruments. The models used for wind instruments are simple feedback loops in which a nonlinear sound source drives a linear filter representing the pipe of the instrument. While very rewarding musical sounds have been obtained with these models, it has become obvious that some essential phenomena escape such a description. In particular the brightness of the sound generated by trombones is expected to be due to the essential nonlinearity of the wave propagation in the pipe. At fortissimo levels this leads to shock wave formation observed in our experiments both from pressure measurements and flow visualization. A modest modification of the physical model could already take this phenomenon into account. The key idea is that the nonlinear effect is essential for the transfer of sound from the source toward the listener, but can be ignored in a model of the generation of the pipe oscillations.
Sound propagation in ducts with bulk reacting lining in the presence of laminar mean flow
Authors: Gogate G. R. , Munjal M. L.
Published: October 2005

In this Letter the problem of sound propagation in ducts lined with bulk reacting material in the presence of laminar mean flow is considered. The boundary conditions appropriate for the cases of circular and two-dimensional rectangular ducts with bulk reacting linings are formulated by making use of the analytical solutions of the sheared flow wave equations presented by the authors in their earlier work. These are then solved numerically. Results showing the effect of sheared mean flow on the attenuation of the lowest mode, and the comparison of locally reacting and bulk reacting linings are presented.
Active matched-field tracking
Authors: Bucker Homer
Published: October 2005

By extending the definition of the covariance matrix, an algorithm is proposed for active matched-field tracking. The new algorithm is similar to matched-field tracking in that data is first collected over an extended period of time (∼3–5 min in the underwater problem). Then the algorithm sorts through the data to find possible source tracks that are mostly defined by their end points, A and B.
Comments on ‘‘Chemical treatment of wood for musical instruments’’ [J. Acoust. Soc. Am. 96, 3380–3391 (1994)]
Authors: Holz D.
Published: October 2005

In the paper under discussion, the authors conducted a survey on several qualities of resonant wood, particularly conifer, in view of their suitability for violin top plates and piano soundboards. They reported their experiments with several agents, especially with formaldehyde to improve certain physical properties. It will be shown that the discussion about acoustical magnitudes of resonant wood, although detailed, should be complete and that some results do not correspond to previous knowledge.
Experimental observation of subharmonic oscillations in Infoson bubbles
Authors: Lotsberg O. , Hovem J. M. , Aksum B.
Published: October 2005

This paper reports the result of an experimental study of nonlinear emission from gas-filled bubbles with particular emphasis on the subharmonic emission. The gas bubbles are Infoson, a contrast agent for use in echocardiology consisting of small gas-filled microspheres with a mean diameter of approximately 4 μm. Pulsed signals with center frequencies of 3.5 and 4 MHz were transmitted through a cloud of bubbles and the level of the subharmonic component was measured as a function of the level of the exciting signal. No sharp threshold, as expected from theory, is found. The amplitude of the subharmonic response increases, however, approximately as the cube of the driving pressure when the driving pressure is in the region of 50–100 kPa.
Angle of arrival estimation of plane waves propagating in random media
Authors: Song Bong-Gee , Ritcey James A.
Published: October 2005

The well-studied problem of estimating the angle of arrival of plane waves in ocean acoustics is revisited. While beamforming is the classical technique, the most recent methods use parametric models of the signals, and maximum likelihood estimation (MLE). Yet, in all cases, fluctuations in the required signals due to medium perturbations have been neglected. In this paper, the advantages of using the correct second moment for waves propagating in random media (WPRM) to model the fluctuations of the arriving signals are investigated. In this way, the physics of WPRM is incorporated in this parametric model of the observations. This model is then used as the basis for the MLE. Finally, the Cramer–Rao lower bound versus fluctuation strength, angle of arrival, and the noise power is provided. Also developed are iterative ML algorithms based on the Newton–Raphson method for a single source and extended to multiple sources. The method is applicable for plane wave arrivals at any known array geometry with arbitrary medium autocorrelation function. Simulation results show a dramatic improvement in the precision of the estimated angle of arrival.
Propagation and analysis issues in the prediction of long-range reverberation
Authors: Smith Kevin B. , Hodgkiss William S. , Tappert Frederick D.
Published: October 2005

Data collected from the Office of Naval Research-special research program (ONR-SRP) bottom reverberation research cruises consist of various environmental measurements (sound-speed profiles, bottom properties, etc.), extensive bathymetric mapping of the 300 km×150 km natural laboratory, and high-quality acoustic reverberation data recorded in both monostatic and bistatic geometries.

The analysis of the acoustic data and the effects of propagation are investigated. Accurate GPS tracking of the participating research vessels provided the precision necessary to attempt to correlate ‘‘spiky’’ reverberation events with bathymetric features. Understanding the limitations of our ability to resolve such features—due to imperfect signal processing, environmental variability, and complex multipath structures—is the main objective of this work. Using a simplified time-to-range conversion, the measured reverberation data can be displayed over the local bathymetry. This process shows good correlation between large-scale [O(km)] high-level returns and bathymetric ridge structures. Employing a PE propagation model in a quasi-cw manner, many of the large-scale reverberation features can be shown to correlate well with predicted high-level ensonification of the total field [low transmission loss (TL)]. Extending the model predictions to include time domain broadband pulse propagation, it can be shown for ranges greater than ∼20 km that multipaths and forward scatter produce complex ensonification patterns which are unresolvable in time and/or range. The effect of this on the ability to correlate finer scale returns and bathymetric features will be discussed. Preliminary analysis of data from a bottom mounted vertical array in the vicinity of 1/2 CZ exhibits strong evidence for the existence of these predicted multipaths and provides a means of confirming the relative intensities predicted by propagation models.
A note on scattering by a stack of rough interfaces
Authors: Tang Dajun
Published: October 2005

Scattering by a stack of random rough interfaces is studied. Such interfaces are common in both shallow water and deep ocean sediments due to the natural sedimentation processes. When the roughness of each interface is small, first-order perturbation theory of Bass and Fuks [Wave Scattering from Statistically Rough Surfaces (Pergamon, New York, 1979)] is employed to formulate the scattered field due to such an interface. If the distances between interfaces are small compared to the acoustic wavelength and the variations of sediment properties are small, it is found that the collective scattered field due to a stack of random interfaces can be related to that due to a weak scattering volume where sound speed and density are randomly varying. Thus low-frequency subbottom scattering due to either weak volume inhomogeneities or a stack of rough interfaces can be formulated in a unified fashion.
Numerical solution of the fourth moment equation for acoustic intensity correlations and comparison with the mid-ocean acoustic transmission experiment
Authors: Macaskill C. , Ewart T. E.
Published: October 2005

In this paper numerical results for the solution of the fourth moment equation describing intensity fluctuations in the ocean are described. The work of previous authors who used adaptive grid methods to deal with the propagation of scalar waves through idealized random media with simple correlation functions is followed. Similar methods are applied to the analysis and prediction of the acoustic intensities measured in the mid-ocean acoustic transmission experiment (MATE). Here extensive measurements provide the parameters needed to define the statistical ocean medium completely, using existing models for internal waves and fine structure that are well-documented in the literature. When such models are used in the numerical solution of the fourth moment equation it is found that there are some discrepancies when comparisons are made with acoustic measurements of intensity fluctuations. However, if the fine structure model is modified in a simple way, then very good agreement is obtained with the experimental data. Most results are presented for the acoustic fluctuations of a propagating acoustic signal of fixed frequency, but some predictions for the cross correlation between two signals of different frequencies are also given.
Identification of parametric models for ultrasonic double transmission experiments on viscoelastic plates
Authors: Zhou D. , Peirlinckx L. , Van Biesen L.
Published: October 2005

In this paper, an identification method is proposed for the determination of the acoustic properties of viscoelastic plates based on an immersion pulse-echo technique. A double transmission (DT) configuration is used for the experiments, which facilitates the calibration of the measurement setup. With the DT configuration, parametric models are established for the ultrasonic plane-wave propagation through a viscoelastic plate at both normal and oblique incidence. The effects of beam spreading due to the finite aperture size of the ultrasonic transducer are taken into account by introducing a diffraction correction factor into the plane-wave models. A maximum likelihood estimator, which takes into account the measurement noise on both the input and the output signals, is constructed for the estimation of the parameters of the DT models. From the estimated model parameters, the absorption and dispersion properties and velocities for both shear and longitudinal waves, as well as the density and the thickness of the plate, are obtained simultaneously. Using the estimated parameters, the prediction of the DT measurement can be made at different angles of incidence. The predicted and measured transfer functions are then compared to validate the estimates. Experiments performed on a Plexiglas plate confirm the efficiency and reliability of the method.
A two-port analogous circuit and SPICE model for Salmon’s family of acoustic horns
Authors: Marshall Leach W.
Published: October 2005

A two-port electroacoustic analogous circuit model for finite-length acoustic horns belonging to Salmon’s family of horns is described. The circuit is useful for simulation of horn-loaded electroacoustic systems with electric circuit simulator software such as SPICE (simulation program with integrated circuit emphasis). An implementation of the circuit model for use with the PSpice simulator software is given. Example simulations are presented which illustrate applications of the model.