bluuebunny/crossref_metadata_2025 huggingface dataset:
Coupled perturbed modes
Authors: Higham Chris J. , Tindle Chris T. , O’Driscoll Lin M.
Published: July 2002

Conventional coupled modes are combined with perturbation theory to allow fast range-dependent normal mode calculations in deep water. The mode-coupling method follows R. B. Evan’s two-way coupled mode formulation [R. B. Evans, J. Acoust. Soc. Am. 74, 188–195 (1983)], where conservation of pressure and particle displacement along the z axis yields an algorithm to couple the modes as sound propagates in range. The conventional approach requires calculation of a complete set of normal modes at each step in range and is computationally intensive. Here perturbation theory is used to find the normal modes and wave numbers of each step in terms of linear combinations of the modes of the previous step. The process can be repeated for many steps and allows rapid calculation to long ranges. The method of coupled perturbed modes is applied to benchmark and canonical problems.
Computed horizontal time-reversing array retrofocusing in a dynamic shallow-water sound channel
Authors: Dungan Michael R. , Dowling David R.
Published: July 2002

A time-reversing array (TRA) can retrofocus acoustic energy to the location of its original source even when the acoustic environment is complex and unknown. Previous computational and experimental studies have utilized a vertical TRA to determine performance in shallow-water sound channels. However, other TRA deployment configuration possibilities exist. Here, results, based on narrow-band computations made with a parabolic equation code (ram by M.D. Collins), are presented for a horizontal array in various orientations with respect to the source. In addition to characterizing the influence of range, acoustic frequency, and horizontal-TRA orientation on the quality of the retrofocus, the sensitivity of horizontal-TRA retrofocusing to internal wave dynamics in the water column of a shallow-water sound channel is also shown. The internal wave model is based on a superposition of linear internal waves whose temporal spectrum has been matched to spectra measured during the SWARM ’95 experiment. Some performance differences are noted between end-fire and broadside array–source orientations. If time allows, results from fully 3D simulations will be shown. [Work supported by ONR, Ocean Acoustics.]
Dynamic coupling of primitive equation soliton models and acoustic propagation models via acoustic mode analysis
Authors: Chin-Bing Stanley A. , King David B. , Warn-Varnas Alex C. , Zingarelli Robert A.
Published: July 2002

Simulation studies of acoustic mode conversions resulting from underwater acoustic fields propagating through solitons in the Strait of Messina have indicated a novel way of coupling oceanographic models with ocean acoustic models using dynamic feedback from the acoustic analysis. A weakly nonhydrostatic primitive equation model was used to generate simulations of oceanographic soliton fields in the Strait of Messina. The soliton fields were used to study acoustic mode conversions as the acoustic field passed through the solitons and propagated upslope. Conversion into modes having higher bottom loss have shown resonance effects similar to that observed in the Yellow Sea. Oceanographic parameters were adjusted so that amplitude and phase of the first two wavelengths of the simulated soliton fields were in agreement with measured soliton data. However, identical acoustic signals propagated through the simulated and measured soliton fields produced different acoustic mode structures. Oceanographic parameter values were varied until the differences in acoustic predictions were minimized. Thus, a feedback approach was used to dynamically couple the oceanographic and acoustic models. Initial results and the suitability of a two-layer oceanographic model for detailed acoustic studies will be discussed. [Work supported by ONR/NRL and by a High Performance Computing DoD grant.]
Temporal resolution in birds: Discriminating temporal fine structure in harmonic complexes
Authors: Dooling Robert J. , Leek Marjorie R. , Gleich Otto , Dent Micheal L. , Cucina Jeff M.
Published: July 2002

Recent behavioral experiments on auditory masking and waveform discriminations using harmonic complexes as stimuli have shown significant differences in performance between birds and humans. In humans, but not in birds, Schroeder-phase harmonic complexes constructed with monotonically increasing (positive Schroeder) or decreasing (negative Schroeder) component phases are differentially effective as maskers, even though they have identical temporal envelopes and long-term spectra. The similarity in masking effectiveness of these harmonic complexes notwithstanding, birds can easily discriminate the fine-structure differences between the positive and negative Schroeder waveforms even with harmonic periods as short as 2 ms. By contrast, humans are unable to make these discriminations unless the periods are greater than about 5–6 ms. These behavioral discrimination and masking results have now been replicated by measuring evoked-potential responses in budgerigars. Amplitude and waveform shapes of the compound action potentials reflect the behavioral discriminations between the two Schroeder stimuli, but cochlear microphonics do not. The similarity in results between the behavioral and the electrophysiological studies, using the same stimuli, suggest differences in both temporal and spectral processing in avian versus mammalian cochleas. [Work supported by NIH R01 DC00198, DC00626, and NRSA DC00046.]
Parameter dependence of 20-MHz passive inertial cavitation detector output
Authors: Bonnoit Alyssa , Everbach E. Carr
Published: July 2002

Passive acoustic monitoring of inertial cavitation emissions has been a useful tool to quantify cavitational activity in vivo and in vitro. In particular, the time-averaged root-mean-squared voltage of a narrow-band-filtered 20-MHz transducer output has correlated well with cellular bioeffects, when the insonifying transducer is in the low-megahertz range [E. C. Everbach et al., Ultrasound Med. Biol. 23(4), 619–624 (1997)]. A thorough study of parameters affecting this inertial detector output has not been undertaken, however. The results of such a study will be presented, showing time-averaged rms detector output as a function of insonifying frequency, pulse parameters, and other acoustic measures of inertial cavitation activity. Limitations of the method will be discussed.
Control of transient disruptions in cell membranes by acoustic cavitation at 500 kHz
Authors: Guzman Hector , Nguyen Daniel , Prausnitz Mark
Published: July 2002

Ultrasound-mediated drug targeting and delivery is a nonchemical, nonviral, and noninvasive alternative for the transport of drugs and genes into cells. Delivery of molecules is performed by using ultrasound to disrupt cell membranes by a mechanism believed to involve cavitation. To develop efficient drug and gene delivery methods based on ultrasound-mediated disruption of cell membranes, it is critical to understand the dependence of molecular uptake and cell viability on the acoustic parameters that govern the complex cavitation activity. This study examined these effects in cell suspensions using two model cell lines (aortic smooth muscle and DU145 prostate cancer cells) and two model compounds (calcein and bovine serum albumin) at 500-kHz ultrasound in the presence of Optison contrast agent. The acoustic parameters varied in this study were: pressure, pulse length, and total exposure time. Cell membrane disruption increased with both pressure and exposure time, but was not influenced by pulse length over the range examined. A window of useful operating conditions was determined for delivering large numbers of molecules into viable cells. Correlations between membrane disruption and the acoustic spectra of cavitation were observed to support the proposed cavitation mechanism. [Work supported by Whitaker Foundation, NIH, and NSF.]
Ultrasound-guided thermo therapy
Authors: Lemor Robert M. , Kleffner Bernhard V.
Published: July 2002

Thermal therapies for cancer treatment have achieved a high level of interest in the medical society, especially for treatment of liver metastases. Laser-induced thermo therapy (LITT) is one of the most promising techniques for minimally invasive destruction of tumors through coagulation. The precision and efficiency of this treatment could be markedly improved by noninvasive monitoring of either temperature distribution in the tissue or by direct demarcation of the destructed zone. The purpose of this report is to demonstrate that parametric ultrasound imaging provides an efficient method for localizing the coagulated area during the treatment. An on-line time-of-flight velocimetry for temperature mapping as well as a mapping of the structural changes through measurement of changes in the attenuation coefficient are presented. The coagulation of porcine liver in vitro and in vivo has been performed by Nd:YAG laser radiation while access to the radio-frequency signals of a conventional ultrasound system served for collection of acoustical parameters from the treated zone. The introduced system is capable of acquiring 12 B-scans/sec with a mean spatial resolution of 1 mm. Quantitative parameters for the control of LITT treatments are derived.
Ultrasound-induced transskull lesions using a large-area phased array
Authors: Clement Greg , Giesecke Tonia , Hynynen Kullervo
Published: July 2002

A transducer array for transskull focused ultrasound surgery is constructed and tested. The transducer design is motivated by numeric and experimental studies, resulting in a hemispherical array optimized in frequency and number of elements. The hemisphere shape is incorporated to maximize the penetration area on the skull surface, thus minimizing unwanted heating. It is determined from the studies that 64 elements are sufficient for correcting scattering and reflection caused by transskull propagation. A resonant frequency near 0.7 MHz is chosen for the array using numeric and experimental thermal gain measurements between the transducer focus and the skull surface. An air-backed PZT array is assembled and characterized. The array is then used to focus high-intensity ultrasound through an ex vivo human skull. Thermally induced lesions are produced through a human skull in fresh tissue placed at the ultrasound focus inside the skull.
Semantic properties of short musical stimuli and their physical correlates
Authors: Scheirer Eric D.
Published: July 2002

When human listeners are confronted with musical stimuli, they rapidly and automatically orient themselves in the sound and begin to make semantic judgments about it. This ability—which might be termed perception of the musical surface—includes the perception of features such as genre, emotional content, and high-level descriptions. There is relatively little known today about the exact perceptual properties that listeners associate with actual musical sounds, or about the physical correlates of these properties. A preliminary study examined the perceptions of 40 musician and nonmusician subjects in response to 150 complex musical stimuli, each 5 s long, taken directly from a popular Internet music database site. Each listener rated each stimulus on six semantic scales: simple–complex, loud–soft, fast–slow, soothing–annoying, interesting–boring, and familiar–unfamiliar. Experimental results indicate that these ratings are made consistently between listeners and between segments of the same song. A psychophysical model, based on a pattern-recognition framework applied to a subband periodicity representation (the autocorrelogram), was able to predict a significant amount of the variance in responses on the first four scales. The regression weights and the psychophysical model suggest possible physical correlates that may underlie these semantic judgments.
Automatic classification of musical instrument sounds
Authors: Kostek Bozena
Published: July 2002

The aim of the present study is to show that the process of automatic classification of musical instrument sounds is possible on the basis of a limited number of parameters. However, due to the complexity as well as to the unrepeatable nature of musical sounds, both steady and transient states should be taken into account while creating feature vectors. For this purpose a database of musical instrument sounds was built containing various instrument sounds played with a different articulation. Then, this database was used in further experiments consisting of some stages, i.e., preprocessing, parametrization, and pattern recognition. The main subject of this study was the optimization of the set of parameters to be included in the feature vectors. Therefore, the quality of parameters with regard to automatic pattern recognition was analyzed both using statistical methods and learning algorithms.
Instability in a thermoacoustic prime-mover: A numerical approach
Authors: Delbende Ivan
Published: July 2002

A numerical model aimed at investigating the development of instability in a thermoacoustic prime-mover is presented. It is based on a discretization of the two-dimensional compressible Navier–Stokes equations, and does not rest on the plane pressure wave assumption. The computational domain is made of a single stack interplate space extended up to both resonator ends. The working gas is assumed to be initially at rest, and a longitudinal temperature gradient is enforced. The linear instability properties of the system are then given by the eigenmodes of the discretized evolution operator linearized in the vicinity of the above basic state. Temporal growth-rate and oscillation frequency are thus obtained for all thermoacoustic modes, and the prime-mover instability onset is determined as a function of the various parameters (mainly temperature gradient magnitude and mean pressure). As far as linear instability is concerned, this formulation is attractive, since it avoids any direct numerical simulation and any problem involved by the presence of two very different time scales.
Perceptual channel weights for level discrimination
Authors: Buus So/ren , Kortekaas Reinier , Florentine Mary
Published: July 2002

This study examines how listeners combine information for level discrimination (aka intensity discrimination) across auditory channels. Individual components’ contributions to listeners’ decisions were measured in a conditional-on-single-stimulus (COSS) paradigm. Stimuli were 7- and 15-tone complexes with components spaced one critical band apart around 1600 Hz. The mean component level was 60 dB SPL for the standard and was increased for the target to obtain 75%–80% correct responses. Results for four normal listeners show that the weights were highest for the two highest-frequency components when all components had equal level increments. Progressively increasing the level increment for components above the center generally had little effect on the weights. This indicates that listeners may be limited to using an optimal selection of channels for the decision. Adding 3-Bark-wide roving-level maskers above and below the complexes had little effect on the weights for the 7-tone complexes, but reduced the weights for the high components of the 15-tone complexes. The masker bands had near-zero weights. Altogether the results indicate that level discrimination depends on information across many auditory channels. Differences in component contributions are unlikely to reflect optimum weighting and are only partly explained by spread of excitation. [Work supported by NIH/NIDCD Grant No. R01DC00187.]
The effect of interval order and highpass filtering on the pitch strength of shuffled click-train regular interval stimuli
Authors: Mapes-Riordan Dan , Yost William A.
Published: July 2002

Regular interval stimuli (RIS) contain temporal regularities that are known to produce a pitch percept. Previous experiments [Mapes-Riordan and Yost, ARO MidWinter meeting proceedings (2000)] showed that shuffled, wide-band first-order ‘‘kxkx’’ click-train RIS have a stronger pitch strength than the original, unshuffled stimuli, where ‘‘k’’ is a fixed duration interval and ‘‘x’’ is a random interval. The primary difference between ordered and shuffled click-train sequences is that shuffled sequences contain multiple instances of regular ‘‘k’’ intervals. This result provides evidence for the importance of the short-term periodicity within RIS in determining its pitch strength. The current experiments investigated whether this phenomenon also occurred when the RIS were created from higher-order intervals and/or whose spectrum was limited to unresolved frequency channels. A set of trials was run in which listeners compared the pitch strength of an ordered click-train RIS and a shuffled version of the same sequence. Relative pitch strength judgments were made as a function of the regular interval duration, regular interval order, and highpass filter cutoff frequency. The results of these experiments revealed that second-order interval click-train RIS require resolved frequency components to generate a salient pitch percept. [Work supported by a NIDCD Program Project Grant.]
Discrimination of brief interaural temporal disparities embedded within diotic bursts of broadband noise
Authors: Akeroyd Michael A. , Bernstein Leslie R. , Trahiotis Constantine
Published: July 2002

Zurek (1980) measured listeners’ sensitivity to interaural disparities conveyed by a 5-ms segment of a 50-ms burst of otherwise diotic broadband noise [P. M. Zurek, J. Acoust. Soc. Am. 67, 952–964 (1980)]. He found that thresholds for interaural time delay (ITD) were markedly elevated when their onset was between 1 to 5 ms following the onset of the noise. Zurek postulated that the leading portion of the diotic burst of noise briefly inhibited sensitivity to subsequent binaural information and, in that manner, linked his findings to the ‘‘precedence effect.’’ In our view, one implication of that reasoning is that the trailing portion of the diotic burst should have little, if any, effect on threshold ITDs. In order to test this hypothesis, we employed Zurek’s general paradigm and included conditions in which we omitted either leading or trailing portions of the diotic burst of noise. We found that omitting either the leading or the trailing portion of the diotic noise greatly reduced the elevation in threshold ITDs observed in the original paradigm. Consequently, it appears that Zurek’s original data, although interesting and important, may reflect effects and mechanisms apart from those responsible for the ‘‘precedence effect.’’ [Work supported by NIH DC 04073.]
Experiments on radiated noise and vibration from a lifting surface at high Reynolds numbers
Authors: Dowling David R. , Bourgoyne Dwayne , Ceccio Steve , Mathews Thomas
Published: July 2002

One of the main hydroacoustic noise sources from fully submerged lifting surfaces is the unsteady separated turbulent flow near the surface’s trailing edge that produces pressure fluctuations on the surface and induces vibratory motions of the lifting surface itself. However, the hydrodynamic forcing and subsequent structural response of lifting surfaces are largely undocumented at the high Reynolds numbers typical of many marine propulsion applications. This talk describes a new experimental effort to identify and experimentally document the turbulent flow, induced surface pressures, structural response, and radiated noise of a hydrofoil at chord-based Reynolds numbers up to 60 million. The experiments are conducted at the US Navy’s Large Cavitation Channel with a two-dimensional test-section-spanning hydrofoil (2.1-m chord, 3.0-m span) at flow speeds from 0.5 to 18 m/s. The foil section is a modified NACA 16 with a flat pressure side. At a zero angle of attack, the lift load on the foil approaches 700 kn. The results presented here cover the first phase of the experiments and illustrate flow-structure coupling phenomena that will be investigated in greater detail in the second phase of experiments planned for later this year. [Work sponsored by ONR, Code 333.]
A formulation for modeling the operating propellers of an aircraft as a noise source in an acoustic boundary element analysis
Authors: Vlahopoulos Nickolas , Liu Sandy
Published: July 2002

The propellers constitute a major noise source in turboprop/proprotor subsonic aircraft. In order to optimize the interior noise reduction, it is important to have accurate information about the excitation exerted on the fuselage by the exterior acoustic field. Technology is developed for simulating the operating propellers of an aircraft as boundary conditions in an acoustic boundary element analysis (BEA). The propeller modeling utility program developed is called xstream (eXterior STructual/Rotor Emission Acoustic Model). The geometry of the propeller and the operating conditions are utilized for generating the appropriate boundary conditions for the BEA computation. This approach fully accounts for scattering and diffraction effects due to the presence and the shape of the fuselage within the acoustic field created by the propellers. Detailed information about the acoustic loading over the entire structure is computed from the analysis. The developed formulation is implemented into computer software. The latter is utilized for simulating acoustic load exerted on the XV-15 tilt-rotor aircraft during flight. Numerical results for the acoustic pressure on the fuselage are compared successfully to test data for six flight conditions. Numerical results for the footprint of the aircraft are also compared successfully to test data for one flight condition. [Research supported by Rotorcraft Industry Technology Association.]
Current research with cochlear implants in adults and children
Authors: Dorman Michael F.
Published: July 2002

Much of the early work at Haskins Laboratories, under the direction of Frank Cooper, focused on the development and evaluation of prosthetic devices. Near the end of his life, Frank Cooper again evidenced an interest in a prosthetic device—the cochlear implant. Part of Frank’s interest stemmed from the fact that the most commonly used cochlear implant uses a scheme for stimulation which has a historical antecedent in the Peterson and Cooper (1957) peak-picking, vocoder (which, in turn, was based on the pattern playback). The other part of Frank’s interest grew out of the many inter-related studies at Haskins Laboratories on deafness, phonetic processing, memory, and reading. In our last conversation, Frank quizzed me at length on cochlear implants in children—were the children intelligible, did they understand speech, did they acquire oral language, and did they read at grade level? In this talk I will continue my conversation with Frank and summarize recent research with cochlear implants in adults and children.
Goals and targets in speech production
Authors: Lofqvist Anders
Published: July 2002

In a book chapter published in 1983, Franklin Cooper discussed past and current approaches to speech motor control [F. S. Cooper, ‘‘Some reflections on speech research,’’ in The Production of Speech, edited by P. MacNeilage (Springer, New York, 1983), pp. 275–290]. Since he had been involved in what might nowadays be called the gestural approach to speech production at Haskins, he contrasted this approach with another one based on acoustic and/or perceptual targets. These different approaches are still being pursued today, and the presentation will focus on some of the theoretical and experimental issues in deciding on the proper coordinate system for speech planning. A survey of published experiments suggests that those studying vowels often end up with an acoustic coordinate system, while those studying consonants tend to favor an articulatory coordinate system. The notion of target will be examined and evaluated. It is suggested that this notion is more complex than usually presented, often involving multiple dynamic targets in both acoustic and articulatory space. Given that the production and perception of speech have evolved together, it may be artificial to make a sharp distinction between them and exclusively favor one coordinate system rather than the other.
Performance results of noisy speech enhancement using undecimated wavelets and spectral peak enhancement
Authors: Koh Min-sung , Mortz Margaret , Vaughan Nancy
Published: July 2002

This paper presents a new speech enhancement algorithm based upon an undecimated discrete wavelet transform followed by spectral peak enhancement. Experimental data is presented which demonstrates improved automatic speech recognition scores in noisy speech. The new algorithm first removes noise by soft-thresholding in the undecimated wavelet domain. However, the noise reduction process leaves residual noise that impairs intelligibility. In the new algorithm, residual noise removal after the undecimated wavelet denoising scheme is achieved by a nonlinear modification of the Fourier spectrum to enhance the spectral peaks relative to the valleys. Using 30 sentences at each SNR, evaluation of the new algorithm was conducted with the Connected Speech Test (CST), a procedure that ensures that the speech sentences have equal difficulty. For additive white Gaussian noise, significant improvements are observed in the experiment results and it is shown that an effective speech enhancement is obtained by spectral peak enhancement with small decomposition level. The results were variable with babble noise and office noise. Performance results will be presented
On the invariance of intensity striation patterns: Effect of shallow-water internal waves
Authors: Rouseff Daniel
Published: July 2002

In the second edition of their book, Brekhovskikh and Lysanov [Fundamentals of Ocean Acoustics (Springer-Verlag, Berlin, 1991)] introduced the concept of intensity invariance to a larger audience. They showed how contour plots of acoustic intensity, mapped in range and frequency, would show definite striation patterns. A single scalar parameter called beta could characterize these patterns. Referencing a large body of Russian literature, they claimed that beta was invariant to the details of the environment, and that in shallow water it equaled one. The published Russian work was primarily analytical; consequently, it concentrated on relatively simple environments. In the present paper, the concept of intensity invariance is examined by numerical simulation for more complicated scenarios. Realizations of time-evolving shallow-water internal wave fields are generated. Acoustic propagation through the internal waves is simulated using the parabolic equation. Both random background internal waves and more eventlike solitary waves are considered. Beta is estimated from images of intensity using radon transforms and tracked as the internal wave field evolves. The effect of varying bottom attenuation is quantified. Receiver depths both above and below the thermocline are considered. [Work supported by ONR.]
Acoustic propagation experiment in the East China Sea
Authors: Li Ma , Tianfu Gao , Lan Wang , Tian Xiao , Wugang Xu
Published: July 2002

An acoustic propagation experiment has been conducted recently in the shallow water of the East China Sea. The water depth of the experiment area is about 50 m. A receiving vertical array of 20 equal spacing hydrophones spanning the whole water column was suspended from one ship. The broadband explosive sources (7 and 40 m) were deployed by another moving ship. The transmission losses along three directions are recorded and the propagation range is from 1 to 20 km measured by GPS. The temperature chain was used to obtain the sound-speed profile data at the receiving ship over the duration of the experiment time. The temperature data show clearly that there is a warm water mass around the mid-depth ∼25 m, and consequently caused a ‘‘double channel’’ in this shallow water. This warm water mass is likely related to the warm current of the Kuroshio. Significant impacts on acoustic propagation are observed: (1) a sound propagation shadow can be found in the mid-depth; (2) anomaly transmission loss can be found in a certain frequency band. Numerical simulation has been done by running PE with Pade approximation to make a comparison and to illustrate the impact.
Classroom acoustics: The effects of background noise and room-finish materials on speech intelligibility
Authors: Siebein Gary
Published: July 2002

This paper will review recent research conducted at the University of Florida defining conditions in actual school classrooms that contribute to speech intelligibility. Many classroom settings were observed to determine how communication paths among teachers and students occurred in modern classrooms. A survey of classrooms was conducted with measurements of background noise levels, STI, and reverberation time made in the rooms at locations corresponding to those found in actual rooms. A computer model and a physical model of a typical classroom were constructed to further study classroom acoustic situations. A second-order curve was found relating RASTI to background noise levels (as a result of air-conditioning system noise) and distance from the teacher. The effects of room-finish materials played a secondary role in increasing RASTI once background noise levels of NC 32 or less were achieved.
Dynamics of lithotripter shock-wave-induced bubble oscillation in constrained media
Authors: Zhong Pei , Zhou Yufeng , Zhu Songlin
Published: July 2002

Rupture of small blood vessels is often observed in vivo following shock wave lithotripsy (SWL), and cavitation has been implicated as a potential mechanism for the injury. To understand more precisely the underlying mechanical process of the injury, the dynamics of SWL-induced bubble oscillation in constrained media have been investigated. Silicone tubes (0.3–1.5-mm inner diameter), filled with circulating saline solution containing 0.1% Albunex contrast agent, were immersed in castor oil and placed in the acoustic field of a Dornier XL-1 lithotripter. Bubble dynamics induced inside the silicone tubes were characterized using high-speed shadowgraph and passive cavitation detection via a 20-MHz focused hydrophone. The result shows that the symmetric bubble oscillation, typical for SWL-induced cavitation in water, is largely disrupted due to the constraint of the silicone tube on bubble expansion, leading to an asymmetric elongation of the bubble along the tube axis. The subsequent collapse of the bubbles inside the silicone tube (or blood vessels) is therefore significantly weakened, and thus the potential to cause tissue injury. Additional experiments using hollow cellulose fibers suggest that the damage to small blood vessels may be caused by the rapid, large intraluminal expansion of the bubble. [Work supported by NIH.]
Combined sound-pressure and pressure-gradient hydrophone design
Authors: Aronov Boris , Reinhart Lawrence , Brown David A.
Published: July 2002

A common design of a sound-pressure hydrophone relies on two bimorph piezoelectric circular plates symmetrically attached to a common base in the form of a ring or cylinder. This may be considered as having two inertially coupled partial systems vibrating in symmetrical and antisymmetrical modes. The symmetrical mode corresponds to the in-phase electrical connection of plates (hydrophone) and provides an output proportional to the omnidirectional sound pressure. The antisymmetrical mode corresponds to antiphase electrical connection of the plates and provides the figure-eight output proportional to the gradient of the pressure field. In order to make the electromechanical frequency responses of partial systems identical, the coupling between these systems must be made as small as possible. This can be achieved by proper design of the common base and achieving immunity to unwanted actions. The sound-pressure hydrophone should be insensitive to acceleration caused by the pressure gradient and the pressure-gradient hydrophone should be insensitive to sound pressure. The properties of a combined hydrophone and the procedure of plate equalizing are investigated. The experimental data obtained are in a good agreement with theoretical expectations.
Frequent criticisms of submitted manuscripts
Authors: Bacon Sid P.
Published: July 2002

Few manuscripts submitted to the Journal for consideration sail through without some critical comments by the reviewers and/or the associate editor. The manuscripts that the present editor sees are in the area of psychological acoustics, and many of the types of criticisms are undoubtedly similar to those made for manuscripts in other areas. A brief list (with sanitized examples) is given of the more common types of criticisms, and a discussion is given as to which of these lead to rejection of the article and as to which can be overcome by a revision. It is advised that authors view criticisms dispassionately and try to understand the substance of each criticism. In some cases, the criticisms are unjustified and the authors should endeavor to give a persuasive rebuttal rather than merely placating the reviewers. A good strategy for a successful author who desires rapid publication is to anticipate possible criticisms and to write the paper so that they will be avoided.
Extending modal analysis techniques: Representing the sound field
Authors: Hansen Uwe J. , Bork Ingolf
Published: July 2002

Modal analysis enables a visual representation of structural normal-mode vibrations. This is accomplished by obtaining a series of transfer functions over a predetermined point grid on the structure, and fitting them to a model of coupled harmonic oscillators. These data can subsequently be visualized in slow-motion animation on the computer screen, representing the motion of the structure at the normal-mode frequencies. The key element in this procedure is the phase coherence between the excitation and the response signal. The technique can be extended to represent a sound field by retaining the phase coherence between a drive signal and a response signal detected by a microphone placed successively at points on a spatial grid in the sound field. The moving displacement on the computer screen represents pressure variations in their phase relation to the source oscillations. The technique will be illustrated with measurements in the air column of a flute, and the sound field above and below the sound board of a grand piano, as well as in a plane in front of the instrument.
Forward and inverse modeling in porous media
Authors: Lingevitch Joseph F. , Collins Michael D. , Fredricks Andrew J. , Siegmann William L.
Published: July 2002

Techniques for solving forward and inverse wave propagation problems involving poroelastic layers will be discussed. Parabolic equation techniques are efficient for solving problems in laterally varying media. A parabolic equation for poroelastic media has been developed and applied to problems in ocean acoustics [J. Acoust. Soc. Am. 98, 1645–1656 (1995)]. This approach has been generalized to the anisotropic case. The smallness of shear speeds in many ocean sediments has motivated the study of poroacoustic media [J. Acoust. Soc. Am. 104, 783–790 (1998)], which is a limiting case of Biot theory in which the rigidity vanishes. Although parabolic equation techniques have not been fully generalized from acoustics to poroelasticity, studying the intermediate case of poroacoustics has helped to bridge the gap. The parabolic equation techniques have been used as tools for solving inverse problems. This approach is presently being applied to field data. One of the issues that arises in solving the inverse problem is the mapping between the coefficients of the wave equation and the wave speeds. The inverse of this mapping can be used to define problems in terms of natural parameters rather than moduli. [Work supported by ONR.]
Inverse scattering of three-dimensional obstacles
Authors: Ghosh-Roy Dilip N. , Couchman Luise S. , Warner Jeremy A.
Published: July 2002

The results of three-dimensional reconstructions of obstacles in an infinite, homogeneous ambience from the far-field scattering of plane acoustic waves in a resonance frequency region are presented. The reconstructions include penetrable and impenetrable objects. Also discussed are reconstructions of orientations (that is, Euler angles), surfaces, and interiors of penetrable axisymmetric scatter. In addition, inverse obstacle scattering using a highly restricted angular aperture in monostatic and quasimonostatic data collection configurations is also discussed.
Multiple scattering attenuation and anisotropy of ultrasonic surface waves
Authors: Scales John A. , Van Wijk Kasper
Published: July 2002

Multiple scattering of waves induces bulk effects such as attenuation and anisotropy that are important in seismology, optics, medical imaging, and other fields involving propagation in disordered media. Measurements are reported of ultrasonic surface wave propagation in a strong-scattering, quasiperiodic medium consisting of a grooved surface of aluminum. Using noncontacting optical methods we have tracked the evolution of surface wave pulses within the scattering medium. Waves propagating parallel to the grooves propagate nearly attenuation and dispersion free, whereas waves propagating normal to the grooves are dispersed and exponentially attenuated with distance as energy is transferred from the direct pulse into the multiple-scattering coda. We measure this attenuation length and show that there is, in addition, a scattering induced anisotropy in the phase velocity. [This work was partially supported by the U.S. Army Research Office under Grant No. DAAG55-98-1-0070.]
Localization of ripple-spectrum noise
Authors: Macpherson Ewan A.
Published: July 2002

Ripple-spectrum stimuli were used to investigate the level of spectral detail important for use of spectral cues for vertical-plane localization. Free-field localization judgments were obtained for 250-ms, 0.5–16 kHz noise bursts with various log-ripple spectra. Ripple density was varied between 0.25 and 8 cycle/octave at a depth of ±20 dB. Depth was varied between ±5 and ±20 dB at a density of 1 cycle/oct. Multiple ripple phases were employed at each combination of density and depth. ±20-dB rippled spectra substantially increased errors in vertical-plane localization in the range 0.5–2 cycle/oct. When systematic errors occurred, judgments were biased toward the location at which the listener’s directional transfer function (DTF) best matched the rippled source spectrum filtered by the target-location DTF. At 1 cycle/oct, localization accuracy was degraded only for ripple depths at or above ±15 dB. Although the upper limit for ripple discrimination is 10 cycle/oct [Supin et al., J. Acoust. Soc. Am. 106, 2800–2804 (1999)], these results indicate that detail finer than 2 ripples/oct does not strongly influence spectral cue processing. This has significance for localization modeling and for virtual-stimulus synthesis. [Work supported by NIH Grants R01DC00420 and T32DC00011.]
The use of off-frequency information in a high-frequency binaural discrimination task
Authors: van de Par Steven , Trahiotis Constantine , Bernstein Leslie R.
Published: July 2002

The ability of listeners to discriminate between N0Sπ and N0S0 stimuli was measured as a function of signal-to-noise ratio. Three types of Gaussian-noise maskers were employed: (1) broadband (300 to 6000 Hz) (2) high-frequency (2900 to 6000 Hz), or (3) low-frequency (300 to 3100 Hz). The signal was a 3-kHz sinusoid. The overall patterning of the data supports the hypothesis that listeners can and do utilize ‘‘off-frequency’’ information to enhance binaural performance. The data also suggest that the off-frequency information within auditory filters centered above the frequency of the signal is especially salient.
Head-slaved tracking of an acoustic target by human listeners
Authors: Bolia Robert S. , Nelson W. Todd
Published: July 2002

Numerous researchers have investigated the extent to which humans are able to track a visual target simply by following its motion with corresponding motions of the head. The results of these investigations have many practical applications, including vehicle guidance and the tracking and designation of moving targets. In spite of the amount of work done in this area, few, if any, studies have addressed the question of how well humans are able to track an acoustic target. This is surprising, given that, in addition to its potential advantages for multi-sensory tracking displays, head-slaved tracking of acoustic targets might prove utile as a means of navigation for the visually impaired. In the present study, listeners performed a head-slaved tracking task of an acoustic target the motion of which was constrained to the horizontal plane, under factorial combinations of field-of-regard (± 30, 45, or 90 degrees), spatial resolution of the audio display (3, 7, or 10 degrees), and the presence or absence of visual feedback (a color change in the visual display). Results will be discussed in terms of potential applications, and compared with performance on visual tracking tasks. [Work supported by the Air Force Office of Scientific Research.]
Velocity DLs for a simulated sound source: Effect of intensity
Authors: Hassett Sarah , Feth Lawrence
Published: July 2002

The Doppler effect refers to the frequency change observed for a moving sound source. The listener will observe a higher than emitted frequency as the moving source approaches, and a lower frequency as it recedes. Previous work [J. Acous. Soc. Am. 106, 2209 (1999)] determined the difference limen (DL) for the velocity of a computer-simulated moving sound source. The simulated source moved along a straight path that passed within 5 m of the listener. Subjects were tested at 500, 1000, and 4000 Hz for reference velocities of 1, 2, 4, and 8 m/s. Signal duration was 500 ms. A 2Q,2AFC adaptive procedure determined the listener’s velocity DL. The results indicated that DLs for both velocity and inferred frequency increase as reference velocity decreased, indicating that Weber’s law does not hold for either parameter. The influence of source intensity variations for the 5-m path were minimal, thus the current experiment repeated the conditions of the prior experiment except that the path passed 0.5 m from the location of the observer. The effects of simultaneous frequency and intensity changes were investigated and compared with model predictions. [Work supported by a grant from the Ohio State University College of Social and Behavioral Sciences.]
Extraction of modal amplitudes for the analysis of two- and three-dimensional underwater sound propagation
Authors: Riley Joseph M. , Glegg Stewart A. L.
Published: July 2002

Experimental measurements have been conducted over a laboratory scale model of the Santa Lucia Escarpment for the purpose of analyzing two- and three-dimensional underwater sound propagation. Transmission loss (TL) was measured as a function of depth at a series of ranges in the downslope direction of the model (referred to as depth profile measurements) and TL was also measured over a finite area in the horizontal plane for fixed source and receiver depths (referred to as two-dimensional surveys). The two-dimensional surveys show across slope interference, which may be indicative of bathymetric refraction, and the modal structure of the depth profile measurements appears to change as a function of downslope range (a result which may be caused by mode coupling). In order to investigate the interference observed in the two-dimensional surveys and also determine if the range-dependent variation in the depth profile measurements is being caused by mode coupling, an inversion algorithm was applied to measurements of the complex pressure field for the purpose of extracting the modal amplitudes. Analysis of the experimentally extracted modal amplitudes indicates that mode coupling and bathymetric refraction contributed significantly to the acoustic pressure field. [Work supported by ONR.]
Improving existing classroom sound isolation for advance media capabilities
Authors: Hougland Dana
Published: July 2002

A series of tests was conducted to assess the incremental improvement of the noise reduction and sound transmission loss between adjacent classrooms with various impovements to the demising construction. Classrooms were originally constructed without full height walls. Tests were conducted before modifications were implemented and after each modification was completed. The investigation was conducted as part of a larger classroom improvement project design to bring advanced media capabilities into 60 college classrooms campus wide. The results of the testing program are presented.
Breaking surf noise signatures: A comparison of plunging and spilling breakers
Authors: Means Steven L. , Heitmeyer Richard M.
Published: July 2002

Range-time-frequency distributions of surf-generated noise were measured within the surf zone during the SandyDuck’97 experiment at Duck, NC. A 24-phone, 138-m, bottom-mounted, linear array located along a line perpendicular to the shore at a depth of 1 to 3 m recorded the surf-generated noise. Concurrent video measurements of the location, size, and time evolution of the individual breaking waves directly above the array were made from a nearby 43-m tower. The present paper presents time-averaged source level spectra per unit wavefront length and range-time signatures for both plunging and spilling breakers. The source level spectra are obtained by using a modified fast-field program to account for water column and geoacoustic propagation from the distributed source region to an individual hydrophone. The length and location of the leading edge of breakers are tracked in time from rectified video images. It is observed that the source levels from large spilling breakers are lower (∼5–6 dB) than those produced by large plunging breakers that occurred during the same general time period. Distinguishing characteristics be- tween the range-time signatures of spilling and plunging breakers are also observed. [Work supported by ONR.]
Characteristics of choral and solo singing, illustrated using singing-voice synthesis
Authors: Ternstrom Sten
Published: July 2002

Solo and choral voices typically differ acoustically in several ways. Some of these differences are motivated by the differences in the vocal tasks, i.e., ‘‘be heard’’ as opposed to ‘‘blend,’’ while some are due more to differences in vocal training. Solo and choir singers vary in their control strategies for sound level, fundamental frequency (pitch), formant frequencies (timbre), and voice-source properties (phonatory behavior). These differences are discussed and illustrated using recent real-time voice-synthesis techniques. The topics of the acoustical nature of the ‘‘chorus effect’’ and of child singing voice are also visited. [Work supported by the Swedish Natural Science Research Council, the Swedish Research Council for Engineering Sciences, and the Bank of Sweden Tercentenary Foundation.]
High-resolution longitudinal and shear wave spectroscopy for analysis of complex colloids
Authors: Smyth Cormac , Kudryashov Evgeny , Buckin Vitaly
Published: July 2002

In the present paper we describe the applications of the high-resolution ultrasonic longitudinal and shear wave resonator techniques for food and bio-colloids. Our longitudinal wave technique allows us to measure the velocity and attenuation of ultrasonic waves with a resolution of 0.0001% for ultrasonic velocity and 0.1% for the ultrasonic attenuation in small volumes (0.1 to 1 ml) in the frequency range 4–20 MHz. The shear wave technique provides information on viscoelastic parameters of liquids and gels in the frequency range 4–25 MHz. Both techniques allow continuous, temperature ramp and automatic titration measurements for analysis of various processes in complex colloids. Examples of the application of both techniques for studying heat-induced milk coagulation, phase transitions in milk fats, acid milk gelation, and the detection of food pathogens are described. Combination of both techniques shows a high sensitivity to various processes, e.g., pregelation and gelation, in food colloids and provides the unique ability to evaluate simultaneously the changes in volume and shear viscoelastic moduli. Overall our ultrasonic measurements demonstrate their high potential for nondestructive analysis of complex food and bio-colloids.