bluuebunny/crossref_metadata_2025 huggingface dataset:
MFP geoacoustic inversion applied to the WORKSHOP97 data
Authors: Tolstoy A.
Published: July 2002

Application of the refined iterated grid search (RIGS) MFP inversion method to four of the WORKSHOP97 test cases (SD, AT, SO, and WA) has resulted in some surprisingly accurate estimates for some geoacoustic parameters, i.e., sediment densities and attenuations, source ranges and depths, and some sediment gradients. Another surprise was the sensitivity of the inversion to small errors in the KRAKEN propagation model. This paper will discuss recent efforts to understand the benefits and shortcomings of the RIGS method and to propose future directions.
Broadband mode inversion for oceanographic and geoacoustic parameters
Authors: Potty Gopu R. , Miller James H.
Published: July 2002

A genetic algorithm was used for the inversion of sound speed in the water column and sediment layers south of New England in the Middle Atlantic Bight. The experimental data were SUS charge explosions acquired on a vertical hydrophone array during the Shelf Break Primer Experiment conducted in August, 1996. A genetic algorithm was used to search for optimal parameters in a wide space; the EOF coefficients in the ocean and the compressional sound–speed values in the sediment layers. A range-independent normal-mode routine was used to construct the replica fields corresponding to the parameters. Comparison of group speeds for modes 1–4 and for a range of frequencies from 10–100 Hz was used to arrive at the best parameter fit. A linear perturbative inversion also was done on the same data as described by Rajan et al. [J. Acoust. Soc. Am. 82, 998–1017 (1987)]. This linear method also gives estimates of resolution and variance. Analysis was also done to compute the degree of convergence of each of the parameters. Group speeds for the inverted sound–speed fields provide an excellent match to the experimental data. An efficient hybrid optimization scheme using genetic and linear techniques is presented. [Work supported by ONR.]
Measuring near surface ocean features using upward facing ADCPs
Authors: Strong Brandon S. , Gordon R. Lee
Published: July 2002

This paper presents the results of acoustic measurements of the ocean surface and near-surface features using a conventional broadband acoustic Doppler current profiler (ADCP). An analysis of the trade offs and error sources associated with surface detection reveals how transducer beam geometry and signal processing can affect surface measurement. Configurations are considered for the measurement of mean-surface height, ambient sound, wind speed, wind direction, surface currents, directional wave spectra, tidal flow, and entrained air. Observations of the sea surface conditions at Scripps Pier are compared with acoustic data collected using upward facing ADCPs of different beam geometries and a pressure sensor. Comparisons are made with previous studies [Zedel, Deep ocean wave measurements using a vertically oriented sonar, J. Atmos. Oceanic Tech. 11, 182–191 (1994) and Terray et al., Measuring wave height and direction using upward-looking ADCPs, to be presented at Oceans ’97].
Comparison between a nonlinear equation and acoustic measurement in a laminate graphite-epoxy composite
Authors: Elmore P. A. , Breazeale M. A.
Published: July 2002

Measurements of longitudinal phase velocity and rate of harmonic generation (nonlinearity parameter) have been made in a laminate graphite-epoxy composite. Both quantities are observed to be frequency dependent between 3.5 and 8 MHz. The theoretical model of Van Den Abeele and Breazeale [J. Acoust. Soc. Am. 99, 1430–1437 (1996)] has been applied to the data. Including dispersion terms and their nonlinear counterparts improves agreement over that obtained with the theory used for single crystals. The origin of this difference probably is in scattering from laminate boundaries. Some inadequacies still exist, however. Their origin has not been established yet. a)Current address: Naval Res. Lab., Ocean Acoustics Branch, Stennis Space Center, MS 39529.
A vibro-acoustic method for measuring Young’s modulus of building materials
Authors: Chu Wing
Published: July 2002

The current ASTM standards for the measurements of Young’s modulus are designed specifically for ceramics, bricks, carbon and graphite materials, and concrete. The techniques used are based on the measurement of either sonic velocity or the resonant frequency in the flexural mode of vibration of the specimen. The latter method has been adapted for determining the Young’s modulus of building materials, such as wood, gypsum board, and oriented-strand-board (OSB), in the Acoustics Laboratory of IRC/NRC using modern digital-signal processing. This paper will discuss the method and provide results for a number of building materials tested.
Far-field acoustic holography onto cylindrical surfaces using pressure measured on semicircles
Authors: Norris Andrew
Published: July 2002

A simple formula was recently proposed by Williams [J. Acoust. Soc. Am. 99, 2022–2032 (1996)] for imaging pressure and velocity on a vibrating circular cylindrical shell using the far-field pressure measured along a meridional semicircle. The method is discussed and some new results are presented. The procedure is generalized to handle cylindrical surfaces of a noncircular but convex cross section. It is demonstrated that Williams’ formula predicts a supersonic surface intensity, which gives the same meridional energy flux as the exact radiated far-field pressure. A modification of Williams’ formula is suggested, which uses pressure data from several neighboring semicircles, although complete spherical coverage is not required. The modified imaging formula is based upon the first two terms in an asymptotic expansion in the dimensionless wave number. The leading-order term yields the original formula, and the second term results in a boundary layer type of correction in the circumferential direction. Numerical examples compare the exact supersonic acoustic intensity on a cylinder with that from the original and the modified formula. These indicate that the circumferential on-surface resolution is significantly enhanced by combining data from neighboring semicircles, even when the total far-field spherical coverage is small. [Work supported by ONR.]
Mechanical and radiated power and radiation efficiency of point driven panels
Authors: Ertel J. , Dickey J. , Maidanik G.
Published: July 2002

The radiation and partial radiation efficiencies from point and line driven panels were previously defined and investigated by the authors [J. Acoust. Soc. Am. 98, 2888(A) (1995) and J. Sound Vib. 144, 71–86 (1991)]. In this paper, the mechanical power dissipated in a point driven fluid loaded panel is studied and compared to the radiated power. The interdependence of the mechanical and the radiated powers is investigated, and they are related as fractions of the total input power. The dependencies of the mechanical and radiated power on frequency, fluid loading, and mechanical loss are further studied. In the present paper, the mechanical power as well as the radiation efficiency is shown to increase with increased damping in a panel while the radiated power decreases, as it must. These results again show the fallibility of the conclusion that ‘‘a higher radiation efficiency necessarily implies more radiated power.’’ The results of computer experiments are cited in numerical examples.
An overview of interaction between friction and vibrations
Authors: Akay Adnan
Published: July 2002

Friction is a function of both the interface properties and dynamic response of a friction pair. The true contact area and thus the total time-dependent friction and normal forces change as a result of the relative motion of the surfaces with respect to each other. Friction in a dynamic system has the dual role of both exciting vibrations as well as dissipating vibratory energy. In this presentation, mechanisms by which friction induces vibrations in dynamic systems are reviewed and the fundamental issues involved in friction force modeling are discussed.
Underwater acoustics for seafloor geodesy
Authors: Spiess Fred Noel
Published: July 2002

Geodetic data, particularly using electronic distance measuring and space-based techniques, are central to terrestrial studies of crustal deformation. A decade ago, no comparable capabilities existed for use in the Earth’s extensive ocean-covered areas. It had been clear for some time, however, that underwater acoustics could play a key role, replacing or extending the electromagnetic methods used in nearly all terrestrial systems. Three classes of centimeter-capable systems have emerged. For short ranges, direct path measurements using high frequencies are preferred. At intermediate ranges (1–10 km) marker transponders can be interrogated from an intermediate vehicle and their relative positions calculated. Beyond about 10 km, inadequate knowledge of sound speed limits purely acoustic systems, but a combined GPS/acoustic method has been devised to cope with the need for data over important longer base lines. Since 1990, several systems have been implemented in the context of geologically relevant problems, particularly in the northeast Pacific. As operating experience has grown and real data are being analyzed, useful initial results are emerging in conjunction with insights into the problems that must be solved when moving toward future developments. [Work reported has been supported by NSF, NASA, NOAA, PGC, and USGS.]
Possible seismic evidence for fluid migration at the eastern Juan de Fuca Ridge flank
Authors: Zuehlsdorff L. , Spiess V. , Huebscher C.
Published: July 2002

Young and permeable crust along oceanic ridges is often characterized by large-scale fluid migration depending on permeability and heat distribution. The eastern flank of the Juan de Fuca Ridge off the west coast of North America is buried under an unusual thick sediment cover and is therefore suitable for detailed studies on fluid exchange processes. In autumn 1996 a high-resolution seismic survey was carried out in the vicinity of ODP Leg 168 drill sites to collect detailed information about sedimentary structures and acoustic anomalies in relation to basement morphology. The seismic equipment was optimized for high lateral and vertical resolution to identify small-scale features from the surface down to the basement as potential migration paths for fluids. The acquired seismic sections exhibit numerous vertical zones with reduced reflection amplitudes which may represent paths for fluid advection. The lateral amplitude changes are visible using seismic sources with different frequency content and are apparently related to basement topography. Observations on parallel profiles indicate a 2-D geometry. Theoretical studies suggest that local porosity changes may be the reason for the acoustic visibility of the proposed advection zones.
Speech intelligibility as a function of the number of channels of stimulation for signal processors using sine-wave and noise-band outputs
Authors: Dorman Michael F. , Loizou Philipos C. , Rainey Dawne
Published: July 2002

Vowels, consonants, and sentences were processed through software emulations of cochlear-implant signal processors with 2–9 output channels. The signals were then presented, as either the sum of sine waves at the center of the channels or as the sum of noise bands the width of the channels, to normal-hearing listeners for identification. The results indicate, as previous investigations have suggested, that high levels of speech understanding can be obtained using signal processors with a small number of channels. The number of channels needed for high levels of performance varied with the nature of the test material. For the most difficult material—vowels produced by men, women, and girls—no statistically significant differences in performance were observed when the number of channels was increased beyond 8. For the least difficult material—sentences—no statistically significant differences in performance were observed when the number of channels was increased beyond 5. The nature of the output signal, noise bands or sine waves, made only a small difference in performance. The mechanism mediating the high levels of speech recognition achieved with only few channels of stimulation may be the same one that mediates the recognition of signals produced by speakers with a high fundamental frequency, i.e., the levels of adjacent channels are used to determine the frequency of the input signal. The results of an experiment in which frequency information was altered but temporal information was not altered indicates that vowel recognition is based on information in the frequency domain even when the number of channels of stimulation is small.
A computational model of the cochlear nucleus octopus cell
Authors: Levy Kenneth L. , Kipke Daryl R.
Published: July 2002

Cochlear nucleus octopus cells are characterized by a temporally precise response at the onset of tone bursts and other phasic stimuli. The objectives of this study were to develop a biologically plausible model of an octopus cell based on typical morphological and physiological properties, and to describe the model’s ability to simulate responses of octopus cells and onset units. The compartmental model represents the basic morphology of octopus cells with a single passive, equivalent dendrite and a lumped, active soma. Independent, excitatory synaptic inputs are distributed on the dendrite and soma to represent inputs from 60 or 120 auditory-nerve fibers. The computed model responses were evaluated using simulated current injections, short-duration tone bursts, and several other types of stimuli. With biologically plausible values for the model parameters, the representation of 60 auditory-nerve inputs yields responses consistent with an OL unit while the representation of 120 inputs yields responses consistent with an OI unit. This study demonstrates that responses typical of OL and OI units can be produced with a relatively simple model of an octopus cell. It also suggests that the numbers of independent auditory-nerve fiber inputs to the cell can affect the onset response.
An improved acoustic Fourier boundary element method formulation using fast Fourier transform integration
Authors: Kuijpers A. H. W. M. , Verbeek G. , Verheij J. W.
Published: July 2002

Effective use of the Fourier series boundary element method (FBEM) for everyday applications is hindered by the significant numerical problems that have to be overcome for its implementation. In the FBEM formulation for acoustics, some integrals over the angle of revolution arise, which need to be calculated for every Fourier term. These integrals were formerly treated for each Fourier term separately. In this paper a new method is proposed to calculate these integrals using fast Fourier transform techniques. The advantage of this integration method is that the integrals are simultaneously computed for all Fourier terms in the boundary element formulation. The improved efficiency of the method compared to a Gaussian quadrature based integration algorithm is illustrated by some example calculations. The proposed method is not only usable for acoustic problems in particular, but for Fourier BEM in general.
Determination of source data for a thermoacoustic prime mover by the multiload method
Authors: Zhao Bosen , Jebali Fathi , Francois Maurice X.
Published: July 2002

A thermoacoustic prime mover can be used as a sound source to drive thermoacoustic refrigerators. The nitrogen-filled prime mover studied is a quarter-wavelength resonator that produces sound at nominally 86 Hz for a temperature difference of ΔT≥430 K. The pressure and specific impedance at the mouth of the prime mover were measured as a function of the load realized by different reservoirs. These measurements allow one to determine the characteristics of the prime mover at operation states and therefore to predict the maximum acoustic power at a perfect match. Nonlinear losses in the prime mover are analyzed by estimating the measured impedance.
Heterogeneity of maple wood for musical instrument making
Authors: Rajčan Emil , Urgela Stanislav
Published: July 2002

Maple wood for back plates of bowed string instruments is more and more rare. The measuring of its properties is then, very topical. This paper is concerned with physicoacoustical characteristics such as density, Young’s modulus of elasticity, and the acoustic constant, and their distribution along the radial direction in the trunk of a tree. The study was performed with the nondestructive Chladni method on plates. A bending beam vibrational mode along the grain was visualized and the pictures indicate interesting shapes caused by the heterogeneity of the wood and internal stress. Then, the plates were cut to sticks and the same mode was visualized. Also here, the distortion of nodal lines, when compared with homogeneous material, has been shown. The elastic characteristics were calculated from the natural frequencies of the modes. Such testing has been proven as useful for the quality determination of maple wood as a material for musical instrument making. [Work supported by Slovak Grant Scientific Agency.]
Exploring mid-frequencies with a ‘‘hybrid statistical energy analysis’’ method
Authors: Bremner Paul G. , Langley Robin S.
Published: July 2002

The dynamical behavior of a complex structure at midfrequencies poses special analytical modeling challenges. Traditionally, finite-element analysis (FEA) has been viewed as an analysis method for low-frequency vibrations, while statistical energy analysis (SEA) has been used to analyze high-frequency vibrations. Ongoing work funded by the RESOUND Consortium is directed at bridging the gap between these two methods to produce an analysis technique which is applicable across the whole frequency range, including the problematic ‘‘midfrequency’’ region. A novel wave-number partitioning scheme has been developed under which the system dynamic response is represented as a combination of finite-element ‘‘global modes’’ and SEA subsystem ‘‘local modes.’’ It has been found that the interaction between these two sets of modes encompasses many of the features of ‘‘fuzzy structure theory,’’ an area of great current interest in structural dynamics. In many design situations a (relatively) course mesh finite-element model of a vehicle is developed to study static and low-frequency dynamical behavior. Such a model can be incorporated into the proposed method without the need for labor intensive remodeling. This paper will describe initial applications of the method that was introduced by the authors in a previous abstract [J. Acoust. Soc. Am. 100, 2754(A) (1996)]. In particular, it will present the results of some experimental validation of the method applied to midfrequency vibration response of a truss-frame structure.
Measurement and analysis of structural wave types on fluid-loaded shells
Authors: Feit David , Warwick David C.
Published: July 2002

The frequency-wave-number spectrum of the vibration field of force excited, fluid-loaded cylindrical shells is a significant determinant of the shells’ acoustic radiated field. This presentation discusses the procedures used and results obtained using accelerometer arrays to sample the vibrations on a number of different type shells. The arrays are formed by distributing accelerometers with uniform spacing, either along a longitudinal generator or around a circumference of the cylinder. Depending on the orientation of the accelerometers relative to the shell’s midsurface, the dispersion characteristics found allow for the identification of the various wave types that exist on fluid-loaded cylindrical shells. These are the quasi-flexural waves and in-plane membrane waves, both longitudinal and shear. In an early set of measurements, made in 1986, the shell structure could be considered as unstiffened, while the other results show the effects of stiffening ribs in the frequency-wave-number plots. These effects manifest themselves as aliased quasiflexural waves. The shapes of the dispersion curves are in good agreement with numerical results arising from analytical expressions.
Acoustic monitoring of flow through the Strait of Gibraltar
Authors: Worcester Peter F. , Send Uwe , Cornuelle Bruce D. , Tiemann Christopher O.
Published: July 2002

The Strait of Gibraltar Acoustic Monitoring Experiment was conducted during April–May 1996 to determine the feasibility of using acoustic methods to make routine, rapidly repeated, transport measurements in the Strait of Gibraltar, as well as to explore the acoustic scattering caused by the internal wave bores generated in the Strait. Three different approaches to monitoring the flow were explored: (i) high-frequency (2-kHz) reciprocal transmissions; (ii) high-frequency (2-kHz) horizontal arrival angle measurements of ray bending due to currents; and (iii) one-way transmissions from a low-frequency (250-Hz) source to a vertical receiving array on the opposite side of the Strait. Extensive independent measurements of the temperature, salinity, and velocity fields were also made. The deep-turning rays are stable and yield differential travel times that give reasonable values for the current components along the acoustic paths. Horizontal arrival angles (phase differences) are strongly correlated with rough estimates of the current perpendicular to the acoustic path made using current meter data, suggesting that this approach is feasible at ranges up to at least 15 km. Finally, the acoustic signals show the effects of the nonlinear internal waves present in the Strait. [Work supported by ONR.]
Endoscopic and acoustic evidence of the guttural natural class
Authors: Zawaydeh Bushra
Published: July 2002

While Arabic gutturals comprise of laryngeals, pharyngeals, uvulars, and emphatics, Salish gutturals do not include laryngeals. To see if the pharynx could be the articulator that unites gutturals, an endoscopic experiment was conducted on a native speaker of Arabic. The pharyneal movement was videotaped while the subject repeated nonwords that had a plain or a guttural sound in the context of ?aCa. The result is that there is a significant difference in the pharyngeal width between the plain sounds and the pharyngeal, emphatic, and uvular sounds. As for the laryngeals, they showed no constriction in the pharynx. This result could explain why Salish laryngeals do not pattern with other gutturals, but it does not explain why Arabic laryngeals pattern with the rest of the gutturals. Hence, an acoustic analysis of the voice of four native speakers of Arabic saying the same nonwords that were used above revealed that the midpoint steady state of the second low vowel has a higher F1 in all of the guttural sounds, including the laryngeals, than the F1 of the plain sounds. This means that in Arabic (unlike Salish), the guttural natural class is better explained acoustically than articulatorily.
Word–initial versus word–final consonant articulation
Authors: Keating Patricia A.
Published: July 2002

The position of a consonant within its prosodic word is known to have an effect on the degree, or strength, of its articulatory stricture: in stronger prosodic positions, the active articulator may be higher, making the oral opening smaller. This study examines the robustness of this asymmetry in consonant articulation. Electropalatography was used with five speakers to determine linguo–palatal contact for several English consonants in word–initial versus word–final position. The various experiments manipulated such factors as identity of the consonant, the test word’s lexical stress, its position in its sentence, and phrasal accent in the sentence. Results show that: (1) noncontinuant consonants generally have more contact in word–initial than word–final position, but sibilant fricatives do not; (2) intonational–phrase–final position is a strong position, so that word–final consonants /t d n/, which are also sentence final often show little word–final weakening (/l/ is an exception for some speakers); and (3) in contrast to this positional effect, lexical stress and phrasal accent never strengthen word–final consonants in this way, nor do these prosodic factors consistently strengthen word–initial consonants. [Work supported by NSF.]
Articulatory trade-offs reduce acoustic variability in American English /r/ productions
Authors: Guenther Frank H. , Espy-Wilson Carol Y. , Boyce Suzanne E. , Matthies Melanie L. , Zandipour Majid , Perkell Joseph S.
Published: July 2002

Acoustic and articulatory recordings indicate that speakers utilize trade-offs between different articulatory parameters to maintain acoustic stability during American English /r/ productions. Electromagnetic midsagittal articulometer data from seven subjects producing /r/ in five phonetic contexts were analyzed. Articulator configurations for /r/ in different contexts showed systematic trade-offs between constriction length, constriction area, and front cavity volume. The hypothesized effects of these three parameters on F3, derived from acoustic theory, were verified using a 51-tube model of the vocal tract derived from structural MRI scans of a speaker producing /r/. All seven subjects utilized a trade-off between front cavity volume and the length of the constriction formed by the tongue. Further analysis of acoustic and articulatory variabilities indicates that the net effect of these articulatory covariances is a considerable reduction in acoustic variability, thus allowing large contextual variations in vocal tract shape; these contextual variations in turn appear to reduce the total amount of articulatory movement required. These findings contrast with the view that speaking involves a target set of vocal tract constrictions for each phoneme and provide strong evidence for acoustic theories of speech production. [Work supported by NIDCD, NSF, and the Sloan Foundation.]
Perceptual interactions among voice onset time, second formant onset, voice, and place of articulation
Authors: Benkí José R.
Published: July 2002

The categorization of voicing in syllable-initial stops is dependent primarily on voice onset time (VOT), while the categorization of place of articulation (POA) in stops is dependent primarily on higher formant transitions. This study tested for perceptual interactions among these two orthogonal acoustic dimensions (VOT and higher-formant transitions) and the corresponding phonological contrasts of voice and POA. Fifteen subjects categorized initial stops in a /Ca/ context as /ba/, /pa/, /ga/, or /ka/. The initial stop of each token was from a synthetic two-dimensional continuum with acoustic dimensions of VOT (0–45 ms) and second formant (F2) onset frequency (1100–1700 Hz), so that the corners of the continuum were unambiguous /ba/, /pa/, /ga/, and /ka/. A model of POA and voicing categorization derived from logistic regression suggests that the VOT category boundary can change depending on the perceived POA. Tokens categorized as bilabial were more likely than those perceived as velars to be also categorized as voiced, regardless of the F2 onset. The change in perceptual VOT boundary is consistent with previous results [J. R. Benki, J. Acoust. Soc. Am. 100, 2691 (1996)], though the magnitude of the effect is not as large. [Work supported by NSF.]
Perception of long and short tones in Taiwanese speech
Authors: Jian Francine H.
Published: July 2002

Taiwanese, in common with other ancient Chinese dialects, has a more complex tonal structure than the well-known standard Peking Mandarin. One important feature is the notion of ‘‘long’’ and ‘‘short’’ tones. In order to build a successful computer-aided speech recognition system for Taiwanese speech, it is vital to understand this much overlooked phenomena. In a set of experiments, we set out to determine how subjects distinguish long versus short tones. A palette of long and short words was composed such that a long word would have a short counterpart and vice versa. Using a resynthesis tool, these words were gradually modified to resemble the opposite tone to study the boundaries of perception. Two main features were investigated, namely word duration and energy drop-off (or glottal stop). The experiments reveal that duration has an insignificant impact on the distinction between long and short tones, while the energy drop-off has a strong impact on the perception of long versus short tones. A word with a steep energy drop-off is more likely to be perceived as a short tone than a word with a gentle energy drop-off.
Virtual reality: The perils of synthesis that is almost correct
Authors: Hartmann William M.
Published: July 2002

The experimental method of Hartmann and Wittenberg [J. Acoust. Soc. Am. 99, 3678–3688 (1996)] is an approach to virtual reality with many limitations, but it is the most reliable technique for scientific purposes. Experiments using this method find that a precise VR synthesis is entirely convincing. Of interest are the perceptual consequences of perturbations on the precise synthesis. Large, random perturbations lead to diffuse and internalized images. Better controlled perturbations can lead to split images with perceived timbre differences and even pitch differences. Incorrect images overwhelmingly tend to be localized in the back, e.g., reversing interaural time differences while maintaining interaural intensity differences reverses the azimuth but also reflects the image in a front–back plane (when not internalized). Smaller perturbations produce images that are unitary, but not compact, and they are normally located at distances that are nearer than the true source. Perturbations of intermediate size can lead to extended but well-defined source images, such as gobs of sound extending from the back of the neck and running down the spine. Spatial effects like these can be disconcerting and illustrate the perils of synthesis, getting it almost right, but not entirely right. [Work supported by the NIDCD, DC00181.]
Perceptual validation of multimedia sound systems
Authors: Wightman Fred , Kistler Doris
Published: July 2002

Claims about the subjective performance of consumer audio products are rarely supported by psychophysical data. Advertising hype and anecdotal reports from product reviewers are typically used in place of scientific evidence. With 3-D audio products, however, research preceded product development, and existing psychophysical data address many issues related to potential product performance. These data suggest that integrating high-fidelity 3-D sound into multimedia systems is likely to be a formidable challenge. One problem is that the acoustics of the listening environment are intractable unless the listener is constrained in some way (e.g., forced to wear headphones). Another obstacle is that even if the acoustics are handled properly, large individual differences preclude generalizations about the costs/benefits of engineering compromises, such as the use of nonindividualized spatial processing. Perhaps most important, the data suggest that the perceptual errors likely to be produced in any less-than-perfect 3-D audio system are not subtle; sound images fail to externalize or are heard in the rear when they are intended for the front. These problems underscore the importance of using rigorous psychophysics to evaluate the perceptual adequacy of any multimedia sound system. [Work supported by NASA, ONR, NIH, and Rockwell Semiconductor Systems.]
Perceptual fidelity versus engineering compromises in virtual acoustic displays
Authors: Wenzel Elizabeth M.
Published: July 2002

Immersive, multisensory displays are increasingly a goal of advanced human–machine interfaces, and three-dimensional sound techniques are now practical enough to be applied to these displays. The goal of virtual acoustics is to simulate the complex acoustic field experienced by a listener freely moving within an environment. Of course, such complexity, freedom of movement, and interactivity is not always possible in a ‘‘true’’ virtual environment, much less in lower-fidelity multimedia systems. Many of the perceptual and engineering constraints (and frustrations) that researchers, engineers, and listeners have experienced in virtual audio are relevant to multimedia. In fact, some of the problems that have been studied will be even more of an issue for lower fidelity systems that address the requirements of a large, diverse, and ultimately unknown audience. Examples include individual differences in head-related transfer functions, a lack of real interactivity in many multimedia systems, and perceptual degradation due to low-sampling rates or compression. This paper discusses some of the engineering constraints and perceptual consequences faced during implementation of virtual acoustic displays for NASA applications such as aeronautics and shuttle launch communications. An attempt is also made to relate these issues to low-fidelity applications such as the Internet.
Adapting to discrepant information in multimedia displays
Authors: Shinn-Cunningham Barbara
Published: July 2002

The ultimate goal of multimedia displays is to generate a realistic and engaging display of visual, auditory, and/or proprioceptive information that creates a consistent view of the ‘‘rendered’’ world. Unfortunately, time delays and inaccuracies in the display system may cause events to be temporally or spatially misaligned across modalities. Even within a single modality, technological constraints may limit the accuracy of the display. If a system is for entertainment, such discrepancies will matter only when they are consciously perceived by the observer. If the display is for command and control applications (for instance, to convey information to an air traffic controller or to the operator of a remotely controlled vehicle), discrepancies matter whenever they decrease performance on the task of interest, especially if such decrements in performance cannot be overcome by training. A series of experiments investigating the degree to which subjects can adapt to discrepancies between normal experience and simulated auditory spatial information suggests that subjects can adapt to such discrepancies; however, the degree to which adaptation affects the ability of the subject to perform spatial tasks depends on the amount and type of spatial discrepancy present in the display. [This work supported by AFOSR.]
Acoustic challenges in underwater range systems
Authors: Janiesch Robert E.
Published: July 2002

Over the last decade, several changes both domestically and world-wide have caused a shift in the way underwater range systems need to be designed and developed. These changes include a decline in resources (funding) available for the systems, and a shift in the world military threat from a super power in the open ocean to a variety of threats in littoral environments. As a result of these changes, new challenges—many of them directly related to acoustic issues—are presented to the designers of underwater range systems that are utilized for both tactical training and T&E. This briefing will outline the requirements for the new range systems and present the challenges that need to be met along with the associated acoustic issues. This briefing will serve as a frame work for other presentations that will follow in this session.
Underwater impulsive acoustical generation from steam bubbles
Authors: Dea Jack Y.
Published: July 2002

One of the most common techniques to generate impulsive sound underwater is through the use of sparkers. The sound is generated through high-voltage arcing across two electrodes. Research at NCCOSC, RDT&E division has shown that modest sound levels can be produced from electrodes operated at nonarcing voltages. In this mode the main products in the electrode spacing are steam bubbles. The expansion and subsequent collapse of a single steam bubble is what generates the underwater sound. The advantages to the use of nonarcing electrodes are longer electrode life, greater reproduciblity, and the use of light-weight components. The disadvantages include lower electroacoustical conversion efficiency and lower electrical power input. The electroacoustical conversion efficiencies measured reached 0.7%. Extrapolation of efficiency data show that 1% or better efficiency may be achievable. A high-speed imaging was developed to capture the history of events in the electrode spacing. Images of various bubble events are shown and interpreted. [Work supported by ONR.]
Characteristics of low-frequency ambient sound in the surf zone
Authors: Kolaini Ali R. , Nystuen Jeffrey A.
Published: July 2002

An experiment was conducted along the Scripps Institution of Oceanography Pier to study the characteristics of the ambient sound in the surf zone. The role of the single large bubble oscillations versus the collective oscillations of bubble clouds as possible mechanisms of generation of the low-frequency sound, especially the relatively broadband peak that appears around 20 Hz in the sound spectrum, are discussed. The frequency band at which ambient sound from breakers in the surf leaks out is identified. The acoustic attenuation, which makes the surf zone extremely quiet above 2 kHz, and a possible method to use ambient sound to infer bubble size distribution in shallow water near the surf zone are discussed. [Work supported by ONR.]
Where the ‘‘Acoustic Daylight’’ analogy breaks down
Authors: Makris Nicholas C.
Published: July 2002

To make a scientific analogy between imaging with ocean-acoustic ambient noise and imaging with daylight, one must preserve the ratios of relevant physical scales. For example, the roughly meter-scale objects to be imaged by the ‘‘Acoustic Daylight Ocean Monitoring System’’ of Buckingham et al. [Sci. Am. (February 1996)] are millions of wavelengths across optically, but only tens to hundreds of wavelengths across in underwater sound even at up to 100 kHz. People commonly see meter-scale objects in normal diffuse daylight. When imaged with underwater sound, however, meter-scale objects behave as airborne dust particles behave in real daylight. This is because the dust particles are tens to hundreds of wavelengths across optically. Everyday, experience teaches us that dust particles are invisible in normal diffuse daylight and only become visible in special cases where they are cross illuminated by highly directional light beams. This is due to the heightened effect of diffraction and forward scattering for objects with diameters so close to the wavelength. The ‘‘acoustic daylight’’ analogy also breaks down because the signal-to-noise or mean-to-standard-deviation ratio, which sets image stability, is millions of times larger for typical optical systems in natural light than that possible in any ocean-acoustic ambient-noise imaging system.
Matched-field localization for Arctic ice-ridging events
Authors: Dosso Stan E. , Greening Michael V. , Zakarauskas Pierre
Published: July 2002

This paper describes an inversion of ambient noise fields measured in the Arctic in an attempt to determine the spatial distribution of ice-ridge building events in the polar ice pack. To this end, a matched-field algorithm is developed to localize multiple broadband sources in a range- and azimuth-dependent environment where the bathymetry is poorly known. Both the source locations and unknown bathymetric parameters are included as variables in a simulated annealing inversion that searches for the best match between the measured and modeled fields. A number of aspects of this problem are considered in a synthetic study including the importance of simultaneous inversion, the effect of bathymetry errors, and the problem of determining the number of sources present. The inversion accurately localizes multiple synthetic sources. The method is also applied to a set of ambient noise measurements recorded in the Lincoln Sea in the Canadian high Arctic. The results indicate that a small number of ice-ridging events is sufficient to accurately model the measured fields. Estimates of the number of sources and source bearings are unambiguous; however, source ranges could not be estimated unambiguously.
Calculations of the elastic compliance and piezoelectric constants of PVDF and P(VDF-TrFE) crystals using molecular mechanics
Authors: Robinson Harold C. , Kavarnos George J. , Holman Robert W.
Published: July 2002

The selection and/or design of projector materials for ultrasonic transducers requires knowledge of their elastic, piezoelectric, and dielectric properties. These properties can be measured directly; however, in order to minimize the fabrication and measurement of many different materials, it would be useful to compute these properties from the chemical composition and structure of the material. In molecular mechanics, a force field is used to describe short- and long-range interactions between atoms in a crystal. The most favored state occurs when the total energy, i.e., the sum of the interaction energies, is minimized. This paper presents calculated compliance and piezoelectric constants for β-phase crystals of polyvinylidene fluoride (PVDF) and its copolymer with trifluoroethylene, P(VDF/TrFE). The constants were derived by minimizing the energy of the unit cell while varying the stress. The model was validated using experimental and theoretical values for the properties of PVDF. The behavior of the compliance and piezoelectric constants of P(VDF/TrFE) are examined as a function of the molecular percentage of VDF. It was found that an optimum value for d33 exists between 55 and 65 mol % VDF. The implications of these results for the use of P(VDF/TrFE) copolymer in ultrasonic projectors will be discussed.
Audio application of the parametric array
Authors: Blackstock David T.
Published: July 2002

‘‘HyperSonic Sound’’ is American Technology Corporation’s commercial application of the parametric array to produce broadband audio sound (Business Week, 12-2-96 issue, pp. 108–109). E. G. Norris demonstrated the device at the Penn State ASA Meeting [J. Acoust. Soc. Am. 101, 3072(A) (1997)], but gave few technical details. An analysis of the device demonstrated is provided here. The primary fields are produced by sixty 40-kHz elements mounted on a ring, 4-cm i.d., 7-cm o.d., which produce an axial sound-pressure level of 140 dB at 30 cm. The values given imply a Rayleigh distance of about 1.2 m and a (primary) beamwidth of about 3°. Estimated by the absorption length for the primaries, the interaction region is about 9 m. Those who witnessed Norris’s demonstration can attest to the narrowness of the secondary sound (a synthesized musical melody) and apparent absence of sidelobes. However, the melody heard also exhibited distortion. Distortion may be predicted by recalling that when the primary wave is a modulated carrier, the secondary sound is (asymptotically) the second derivative of the modulation envelope squared. Prospects for reducing the distortion are discussed [see Yoneyama et al., J. Acoust. Soc. Am. 73, 1532–1536 (1983)].
Impact excitation of piano string vibration
Authors: Hall Donald E.
Published: July 2002

Piano strings are well described by linear partial differential equations, even when stiffness is included. But compressed-felt piano hammers have a distinctly nonlinear force–compression relation, so it is challenging to model the hammer–string interaction correctly. In recent years it has been practical with personal computers to carry out numerical integration of the nonlinear equations for specific examples, though hammer/string mass ratio, hammer compliance, hammer resistive loss, string stiffness, striking point, and striking velocity present a large parameter space to explore. Examples of such integrations, showing calculated string motions and spectra, will be presented on videotape. Related investigations have been carried out by several authors, and are of interest both for offering an understanding of energy transfer to the strings in acoustic pianos and for suggesting digital algorithms for synthesizing sounds that represent a generalization of the piano family.
Utilizing a modified surface roughness parameter for describing rough surfaces with an equivalent impedance
Authors: Chambers James P. , Sabatier James M.
Published: July 2002

Previous experimental and field work has shown that rough surfaces may be modeled acoustically as though they were smooth surfaces with a modified surface impedance. In these works the roughness length scale used was a single parameter equal to 1/2 of the average height of the surface roughness elements. Recent experiments have suggested that this simple form for the roughness parameter may yield incorrect results for certain conditions such as grazing incidence over impermeable surfaces or sparsely scattered roughness elements. Modifications to this roughness parameter will be investigated. Specifically, the influence of the slope of the roughness elements, which is quantified using the standard deviation in height and the correlation length, will be investigated. [Work supported by the USDA ARS National Sedimentation Laboratory.]
Overview of the numerical models for the vibroacoustics of multilayer panels with porous materials
Authors: Panneton Raymond
Published: July 2002

The vibration and noise control of mechanical and architectural structures often involves the use of multilayer panels containing sound absorbing materials. For these applications, different types of absorbing materials may be used in different types of multilayer configurations, which will be suitable to reach the manufacturer’s goals. Depending upon the type of multilayer configurations and materials to be used in a final product, the engineer has to use proper modeling tools to predict its vibroacoustic response. Commercially available codes offer the possibility of modeling sound absorbing materials in simple or complex configurations using different types of mathematical formulations. In this case, the engineer has to define what type of formulations is the best suited for his analysis. These formulations are often prohibitive whether in terms of computer time, memory requirement, or geometrical configurations. The engineer must be aware of the limitations related to each formulation. This paper presents an overview of the recent numerical models for porous media that are available for the analysis of multilayer panels. A brief description of the models and their limitations will be discussed. Also, comparisons between some of the models and experimental results will be presented.
Individual differences in the effects of stimulus variability and lexical difficulty in older adults
Authors: Sommers Mitchell S.
Published: July 2002

Sommers [M. S. Sommers, J. Acoust. Soc. Am. 101, 2278–2288 (1997)] has recently demonstrated significant declines in both talker normalization and lexical discrimination in older listeners and suggested that these deficits contribute significantly to age-related impairments in speech perception. The present set of investigations were designed to: (1) determine whether individual differences in talker normalization and lexical discrimination are related to the speech perception abilities of older adults assessed under a variety of listening conditions; and (2) examine whether age changes in the two abilities are related to deficits in more general cognitive capacities. Results to date suggest that individual differences in talker normalization and lexical discrimination account for a significant percentage of the variance in speech perception scores among older listeners. In contrast, performance on tests of working memory, general intelligence, and selective attention were largely unrelated to either of the two abilities. The overall patterns of findings suggests that talker normalization and lexical discrimination are independent components of the speech perception system that exhibit considerable individual variation in the extent to which they are preserved in older adults. [Work supported by the Brookdale Foundation.]