bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic imaging of large vibrating structures
Authors: Clark Joseph A. , Honke Paul M. , Ellis J. Michael
Published: October 2005

Large vessels, such as ships and submarines, present unique challenges to designers of acoustic imaging systems. The measurement environment is usually noisy and reverberent. Acoustic data must be collected rapidly over large areas. Data processing systems need to be small, fast, and portable. Displays of the processed data must be appropriate for easily answering structural acoustics questions such as: What is the distribution of vibrations on a hull? Are the vibrations localized or distributed over a large area? Are modes coupled? Do the modes radiate? What is the distribution of acoustic energy in frequency and wave number as well as position? A multichannel acoustic imaging system has been developed and used to investigate a variety of structural acoustics problems associated with large underwater structures during the past year. In this talk, the imaging system used in these investigations will be described, examples of structural acoustics problems where the system has been found to provide important information will be discussed, and some of the major limitations of currently available techniques for imaging vibrations on large structures will be identified.
Effects of attention on the interpretation of acoustic cues in phonologically natural forms
Authors: Eberhardt Jennifer L. , Gordon Peter C.
Published: October 2005

In previous studies, it was shown that the relative phonetic importance of acoustic cues shifts when listeners are not able to pay complete attention to the speech stimulus. The effect of attention has been studied by examining how listener's identification of speech sounds changes when they must perform a nonspeech distractor task while a speech stimulus is presented. These studies have shown that, under low-attention conditions, the contribution of weak phonetic cues increases relative to that of strong phonetic cues. This is the case for the (strong) VOT cue and (weak) F0 cue to the /ba/-/pa/ distinction and for the (strong) formant pattern cue and (weak) duration cue to the /i/-/l/ distinction. By using words as stimuli, the present research extends these findings to more phonologically natural speech sounds. [Work supported by AFOSR.]
Time-varying spectral properties of chaotic otoacoustic emissions
Authors: Keefe Douglas H. , Burns Edward M. , Ling Robert
Published: October 2005

The dynamics of some spontaneous and sinusoidally forced otoacoustic emissions (OAEs) are chaotic [Keefe et al., in Mechanics and Biophysics of Hearing, edited by Geisler et al. (Springer, New York, 1990)]. This suggests the possibility of complex interactions between the line-spectral components of such emissions. The amplitude envelopes of adjacent line-spectral components of some spontaneous OAEs have been shown to be negatively correlated, implying energy transfer between components [Wit, in Mechanics and Biophysics of Hearing, edited by Geisler et al. (Springer, New York, 1990)]. The correlation dimensions of acausally filtered OAEs were calculated to identify chaotic signals, and these signals were short-time Fourier analyzed. Preliminary analyses indicate that spontaneous, chaotic OAEs exhibit energy transfer between components; sinusoidally evoked, chaotic OAEs do not, although amplitude fluctuations at frequencies between line-spectral components may be present. [Research supported by NIH.]
Range-dependent acoustic propagation in a channel with ocean variability: A comparison of observations and modeled results
Authors: Potter J. R.
Published: October 2005

The skewness of the distribution of acoustic intensities due to multiple scattering [T. E. Ewart, J. Acoust. Soc. Am. 84, 1490–1498 (1989)] and the possible obliteration of fine detail diffraction effects by random phase modulation indicate that it may never be appropriate to decouple variability from calculations of a mean acoustic field. If so, this has serious implications for the (often used) approach of adding on (or even ignoring) variability to the mean-field results of deterministic modeling. In October 1989, an experiment was conducted in the North Sea by SACLANTCEN, Italy in collaboration with FWG, Germany to simultaneously observe the acoustic field and oceanographic condition in a weak acoustic surface channel. The channel exhibited volume variability and appreciable surface roughness. A 50-m depth source was towed away from a stationary 62-m vertical array, transmitting 40-ms cw pulses at 800, 1000, and 1500 Hz. Measurements were taken out to a range of 35 km and back. A simultaneous oceanographic survey was carried out with a towed thermistor chain and an oscillating CTD. Sparse oceanographic data from 5 CTD casts, such as might be used for deterministic predictions, have been used as input to propagation models. The modeled results are compared with observations from the acoustic array. While noise can account for some of the differences, it is clear that significant deviations from the deterministic modeled results are obtained.
Intensity fluctuations at close ranges with application to underwater vehicle radiated noise measurements
Authors: Stein Peter J. , Santos Gerald M. , Menoche Richard K.
Published: October 2005

For the next generation of quiet underwater vehicles, high-array gain noise measurements systems, with accuracy on the order of 1 dB, are necessary. The design of these systems requires evaluation of the propagation stability over the short ranges normally encountered during radiated noise trials. Intensity fluctuations were measured at AUTEC at frequencies 1 kHz<f<20 kHz, at ranges r<1 km, at source depths SD = 90 m, 240 m, and 580 m, and at several grazing angles 0° < θ < 40°. Measured TL often differed from spherical spreading by greater than 5 dB for f > 2 kHz, θ near 0°, and r > 200 m at all source depths. This difference, with a few exceptions, fell off rapidly to less than 1 dB for grazing angles greater than 4°. The mean and standard deviation of the TL difference from spherical spreading were estimated in 1° grazing angle bands. The standard deviation was lower at the deeper source depths and always fell off rapidly for θ > 4°. The mean value was not always lower at deeper source depths and, although it fell off rapidly for θ > 4° and f < 8 kHz, it did not always do so at the higher frequencies. These higher frequency and higher angle measurements, however, were associated with longer range measurements (r > 500 m). Theoretical predictions of the TL using a fine structure CTD measurement as input to the SAFARI propagation routine explain most of the results seen and suggest that the mean errors seen at higher grazing angles will go away for f < 500 m. All of these results indicate that intensity accuracy on the order of 1 dB can be achieved for f < 20 kHz and r < 500 m (or f < 8 kHz and r < 1 km) by making radiated noise measurements at θ > 4° or by restricting ranges to less than 200 m.
On the equation for reverberation time in acoustics
Authors: Stanzial Domenico
Published: October 2005

A new derivation for the reverberation time equation is here proposed. From the accurate analysis of a model describing the acoustics of enclosed spaces in terms of a feedback system, a surprisingly easy and deep insight of the complex phenomenon of reverberation is readily obtained without any loss of formal rigor. While the experimental consistency of the approach is pointed out by directly measuring the average absorption coefficient of the room, its theoretical consistency follows from the ability of the model to deduce the well-known Norris-Eyring formula for the reverberation time. Finally, starting from a new definition of reverberation time considering the phenomenon of reverberation essentially connected with the whole history of the sound field and not only with its transient parts (buildup or decay), a new equation for reverberation time is obtained.
Acoustics of the Chinese qing
Authors: Tsai Jianming , Rossing Thomas D.
Published: October 2005

The qing is a bowl-shaped musical instrument, commonly used in Buddhist religious ceremonies; it usually rests on a silk pillow and is struck at the rim with a wooden stick. The principal modes of vibration resemble those of a bell, have 2-m well-defined modes around the mouth of the bell. Mode frequencies have been measured in four small qing, having diameters of 18, 15, 12, and 10 cm, and mode shapes in the larger two have been determined by means of holographic interferometry. The pitch of the qing is determined by the frequency of the fundamental (2,0) mode, although the (4,0) partial typically has the largest amplitude. The mode frequencies are not harmonic, so no subjective strike note is heard.
Optimization of clarinet tone holes
Authors: Feng Ji Lu , Strong William J.
Published: October 2005

Intonation and stability of clarinet tones are influenced by the resonance frequencies of the instrument that are influenced in turn by the placement and size of its tone holes. Dimensions of an instrument of moderate quality were measured and served as the starting point for the optimization procedure. Input impedances were calculated for 47 different fingerings of the instrument. Minimization of the frequency differences between four resonance frequencies—modes 1 and 2 in the chalumeau register, mode 2 in the clarion register, and mode 3 in the altissimo register—and four reference frequencies served as the optimization criteria. The reference frequencies were arbitrarily chosen from an equal tempered chromatic scale tuned to A4 = 440 Hz. Tone-hole position, diameter, and height were the optimization parameters. In one method, these parameters were modified one at a time, while in a second method all three were modified together. Both methods produced similar results with average reductions in “frequency error” of 9 cents for chalumeau mode 1, 28 cents for chalumeau mode 2, and 16 cents for modes 2 and 3 of the combined clarion and altissimo registers. Optimization procedures and results will be discussed.
Acoustic aspects of acoustic charge transport devices
Authors: Hunt William D.
Published: October 2005

The Gallium Arsenide (GaAs) acoustic charge transport (ACT) device was first reported in 1982 [M. J. Hoskins and B. J. Hunsinger, 1982 IEEE Ultrasonics Symposium Proceedings, IEEE Catalog No. 82CH1823-4 (IEEE, New York, 1982), pp. 456–460] and has been subsequently developed for a variety of analog signal processing tasks. An ACT device is essentially a CCD for which the electrons are transported by the potential, which propagates with a surface acoustic wave (SAW) instead of being transported by the potential imposed by clock pulses applied to surface electrodes. Among these devices are convolvers, correlators filters, analog memories, and programmable tapped delay lines. Due to the sinusoidal transporting potential that propagates with the SAW, ACT devices exhibit concomitant bandwidth and transfer efficiency than is currently achievable with CCD devices. An overview of ACT technology will be presented and the importance of acoustics on the design of these devices will be underscored. The presentation will include a discussion of transducer design and SAW propagation through surface electronic structures. In addition, techniques to minimize acoustic reflections from gratings will be discussed and the acoustic properties of GaAs, AlGaAs, and GaAs/AlGaAs superlattices will be compared.
Frequency shift in spontaneous otoacoustic emission and threshold fine structure
Authors: He Ning-ji , Abbas Paul J. , Bentlet Ruth A.
Published: October 2005

The frequency coincidence between otoacoustic emissions and associated threshold fine structure has led to the hypothesis that the two phenomena may result from the same underlying mechanism. To test this hypothesis, the coincidence in frequency change between spontaneous otoacoustic emission (SOAE) and threshold fine structure were determined. Here, SOAEs were measured at different times over 2 days for a male subject and at different days during several weeks for four female subjects. The range of SOAE frequency change varied across subjects from 0.2% to 0.7% of the center frequency. Threshold fine structure was measured in the region surrounding a specific SOAE. The results showed that SOAE frequencies and the frequencies of threshold minima varied in a similar manner. A highly significant positive correlation (r > 0.9) between SOAE frequency shift and the frequency shift of the associated threshold minimum was obtained, estimated using a two-dimensional best-fit technique. Hypotheses regarding the underlying mechanism of these two phenomena will be discussed.
Repeated-measures ABRs in multiple sclerosis: Demonstration of a new tool for individual neurological assessment
Authors: Lauter Judith L. , Lord-Maes Janiece
Published: October 2005

This research using a simple measure of evoked-potential variability based on repeated-measures within-subject testing has demonstrated that (1) replicable patterns in relative variability both of latency and amplitude in peaks of the auditory brainstem response (ABR) may be observed in normal children and adults, and (2) these patterns are sensitive to individual differences, ear differences, and developmental changes persisting at least through age 12. Several individuals with multiple sclerosis have now been tested using our protocol, based on clinically standard procedures for data collection and analysis, with the single exception the repeated-measures design, comprising collection of four left ear, four right ear, and eight binaural waveforms in the same 1.5-h session. Results to date indicate that the array of dependent variables yielded by this method: (1) may distinguish MS patients from normals as well as from members of other groups such as Alzheimer's patients and substance abusers; and (2) makes it possible to order MS patients along a continuous scale from mild to severe, in a ranking which compares well with clinical ratings. These observations have currently been extended to include other progressive diseases such as Alzheimer's Disease and Parkinsonism, and pathologies involving arousal, such as addictive personality, hyperactivity, and coma. Indications promise new applications in differential diagnosis, disorder staging (acute status, progressive time course, cycles of remission, and exacerbation, etc.), and objective documentation of treatment efficacy. [Work supported by AFOSR.]
Surface waves and surface wave devices in atmospheric acoustics
Authors: Daigle G. A. , Embleton T. F. W.
Published: October 2005

Surface waves exist above porous grounds when the surface can influence the airborne particle velocity near the ground and reduce the phase velocity of sound waves in air at the surface, thereby trapping some of the energy to remain near the surface as the wave propagates. The experimental evidence for the existence of an acoustic surface wave has been recently reviewed [G. A. Daigle, J. Acoust. Soc. Am. Suppl. 1 85, S82 (1989)] and included a discussion of preliminary experiments using pulses above a comblike surface designed to optimize the expected reduced phase velocity and enhance the identification of a separate arriving surface wave from the direct pulse. Further experiments above this surface are described. The results reveal sound pressure levels 10 dB higher than levels expected from pressure doubling above a rigid surface. The model surface can be further modified to obtain a directional receiver device. Measurements of the directional response of the device under controlled conditions indicate gains of up to 20 dB. The characteristics of the receiver device are also studied outdoors under realistic conditions.
Comparison of a model for the dynamic response of the fish swimbladder with frequency responses measured in vivo
Authors: Hastings Mardi Cox
Published: October 2005

The displacement wave scattered by the swimbladder in bony fishes is believed to provide information to the inner ear that allows fish to determine the direction of an underwater sound source. Thus accurate modeling of the scattered field will aid in understanding mechanisms involved in directional hearing. In a model developed for the near-field acoustics of the swimbladder [J. C. de Munck and N. A. M. Schellart, J. Acoust. Soc. Am. 81, 556–560 (1987)], the volume behaves like a damped harmonic oscillator driven by the acoustic pressure of the source. The formulation, however, neglects the viscoelasticity of surrounding tissue, resulting in unrealistically low damping factors and resonance frequencies. Frequency responses predicted by the model are compared with those of swimbladders in goldfish measured in vivo using a noninvasive technique [M. Cox and P. H. Rogers, J. Vib. Acoust. Str. Rel. Des. 109, 55-59 (1987)]. Methods for incorporating the viscoelastic properties of surrounding tissue in the model are presented.
Linear systems theory and its relationship to ocean acoustics
Authors: Ziomek Lawrence J.
Published: October 2005

The purpose of this talk is to demonstrate the consistency and relationships between linear systems theory and the physics of propagation of small-amplitude acoustic signals in fluid media. Using the principles of linear, time-variant, space-variant filter theory and time-domain and spatial-domain Fourier transforms, derivations of the solutions of the linear, three-dimensional, inhomogeneous wave equation for (1) an unbounded isospeed fluid medium, (2) and unbounded fluid medium with speed of sound an arbitrary function of depth, and (3) a full-wave, pulse-propagation model for three-dimensional wave propagation in a Pekeris waveguide are presented. Characterizing a fluid medium as a linear filter is valid since this involves trying to solve the linear wave equation. Computer simulation results are presented. [Work supported by ONR, Code 11250A, and the Naval Postgraduate School.]
A predictive filter for active noise control in small spaces
Authors: Hendrix James E. , Harley T. R. , Shields F. Douglas
Published: October 2005

A predictive filter was designed for controlling helium flow noise at up to 115 dB in diving helmets. The transducer configuration consists of an earphone with a single detecting microphone located near the opening of the ear canal. A high-speed digital signal processor implements the filter in such a way that communications from the surface can be passed into the ear without being cancelled. Frequencies up to 1000–1500 Hz are controlled by the filter and passive means are used beyond that point. The filter in question is not adaptive and was designed from the time domain perspective and so that its coefficients convey physical meaning. Adaptation can be applied to the filter coefficients with the detector microphone doubling as an error microphone.
Eigenray analysis of the acoustic power flowing in an annular duct
Authors: Martinez R.
Published: October 2005

This paper breaks up the sound field of a high-frequency source in a duct into a spectrum of eigenrays. The duct space is annular (i.e., there is an inner core), axially infinite, and is lined with ring patches of lossy material. The medium is still. Reported calculations include maps of the acoustic intensity normal to cross sections at chosen distances from the insonifying source, and predictions of the power left over to propagate past the arrangement of damped rings.
Acoustic forces and torques
Authors: Garrett S. L. , Rudnick I. , Rudnick J. A. , Rudnick Charles
Published: October 2005

In ordinary daily experience, the forces associated with sound waves are usually negligible. In a resonator, the sound levels can be much greater and hence the Bernoulli forces can create a variety of dramatic effects. This video will illustrate the pressure and velocity fields in a standing wave tube using a microphone and hot-wire anemometer. This standing wave field will then be used to demonstrate the “Maidenform effect” and acoustic levitation. Radiation pressure will be demonstrated using a Helmholtz resonator and then a pair of Helmholtz resonators will be used to make an acoustic radiometer. The standing wave field will then be extended from one to two dimensions to illustrate the torque on a Rayleigh disk and, finally, the controlled rotation of objects in a standing wave field whose particle motion is determined by the relative phasing of the degenerate modes. [Work supported in part by the Naval Postgraduate School Direct Funded Research Program.]
A video tutorial on modal analysis
Authors: Elder S. A.
Published: October 2005

A modal analysis system, consisting of a B&K digital spectrum analyzer and an IBM desktop computer with SMS modal analysis software, is used for measurements in junior- and senior-level physics courses in acoustics and sonar. In order to make this complex system accessible to students in a 2-h lab, a brief booklet together with a video tutorial has been developed which bypasses conventional manuals. The student is quickly guided through the maze of buttons and menu choices to perform a particular measurement, as the correct procedure is illustrated, step-by-step. The 12-h tape is divided into separate segments dealing with specific parts of the procedure, such as analyzer screen setup, hammer technique, defining model geometry, data acquisition, and analysis. The combination of the tape and hardcopy booklet makes it possible for students to perform an experiment with minimum direct assistance from the instructor, an important factor for labs sometimes assigned as out-of-class projects.
Demonstrations of undergraduate acoustic experiments
Authors: Korman Murray S. , Baker Leonyx G.
Published: October 2005

Physics majors at the U. S. Naval Academy enrolled in Acoustics (a senior-level elective) and seniors (with a wide variety of backgrounds) enrolled in Underwater Acoustics and Sonar will demonstrate some of the experiments they perfrom in the laboratory. Experiments in water include such topics as interference, refraction, reflection, transmission, and scattering. Measuring the target strength of a model submarine versus angle is very popular. Experiments in air involve sound tubes, the use of an anechoic chamber, and musical acoustics, to name a few. There is some flexibility over choosing and peforming an experiment. The seniors have put together a videotape to show some of the details of their recent experiments. [Work supported by the Naval Academy Research Council.]
A potpourri of videos
Authors: Rossing Thomas D. , Hanson Roger J.
Published: October 2005

Selected excerpts from a wide variety of acoustics videotapes and videodiscs will be shown. Some of these come from commercial distributors, some from television programs, and some from individuals. Some are from complete “stand-alone” lectures, and some are demonstration experiments to be used in the classroom or laboratory. Opportunities will be available later in the week to view complete videos of interest.
Measuring ocean surface velocities with sonar: Waves and the mixed layer
Authors: Smith Jerome A.
Published: October 2005

Over the last decade, Doppler sonar technology has proven useful in studying the waves and currents at the surface of the sea. Recent development of an “incoherent coding” technique has allowed a modest increase in resolution, while retaining the simplicity and robustness of the “averaged covariance” technique. To exploit this technology effectively, a system was designed and built for “scanning” the underside of the sea surface, with waves and mixed layer motions (Langmuir circulation, convection, etc.) specifically in mind. This system was deployed recently (February–March 1990) as part of the “Surface Wave Processes Program” (SWAPP). In addition to providing detailed directional-frequency spectra of the surface waves, the system provides a good “overview” of Langmuir cell activity, as the environmental conditions change. It is hoped that certain wave-current interactions can also be observed or inferred from the sonar data. [Work supported by ONR.]
Surface wave measurements with an acoustic Doppler current profiler (ADCP)
Authors: Lohrmann Atle
Published: October 2005

Data collected with an acoustic Doppler current profiler (ADCP) show that nonintrusive acoustic methods can be used to measure wave orbital velocities at and near the sea surface. Data sampled simultaneously at the surface, 4 m below the surface, and below the surface sidelobe layer are consistent with linear wave theory. It will be argued that this finding is in agreement with the operating principals of an ADCP. The accuracy of the measurements, as well as the frequency resolution, improves with increasing sea state. The directional spectrum of wave orbital velocities and of surface elevation can be calculated using acoustic Doppler data collected simultaneously along four narrow beams. Progress on finding the optimum beam geometry and the optimum spectral estimator will be reported.
Finescale velocity profile and turbulence measurements under surface gravity waves using a coherent bistatic acoustic Doppler profiler
Authors: Stanton Timothy P.
Published: October 2005

Finescale velocity profiles below surface gravity waves have been measured using an acoustic Doppler profiler that has been developed to measure turbulent processes in the upper ocean. Acoustic energy from scatterers ensonified by a single, narrow-beam, pulsed transitter is received by four fan beam response hydrophones placed radially around the transmitter transducer. This system was mounted on a 9-m-high platform approximately 5 m below the ocean surface during the SAXON experiment, which was staged from the Chesapeake Lighthouse tower. Concurrent measurements from a four-element pressure array provided wave height and directional wave spectra data, and the surface wind stress was measured by other participants during the 3-week deployment. The coherently sampled bistatic Doppler data have allowed three-component velocity profiles to be estimated every 8 cm to the wave surface at a 6-Hz sample rate, and adequate velocity range has been achieved by using a dual interpulse period coherent sampling technique. Methods to resolve remaining ambiguities in the vertical velocity components will be described. Examples of the near surface velocity field and derived Reynolds stress profiles under several wind conditions will be shown. Limitations imposed by the high orbital velocities of typical open ocean waves, injection, and surface reverberation will also be discussed.
Coupled volume and surface scattering
Authors: Ewart Terry E. , Ballard John W.
Published: October 2005

The oceanography of the near-surface zone of the temperate oceans is characterized by a mixed layer of varying depth and a sharp thermocline with large sound velocity gradients. Most studies of surface scattering have ignored the effect of the coupling between volume scattering and scattering from the rough surface. Recent Navy emphasis on ocean surface scattering measurements has also ignored the volume effects. The gradients at the bottom of a mixed layer can be large enough to cause wide variations in the transmission and reflection coefficients (including total internal reflection) for the shallow angles of long-range propagation. The wave packets that are found on the sharp thermocline can have large displacements and space-time scales near those of surface waves, but with differing dispersion relations. A wide-angle PE code has been used to scatter sound from an ocean surface with a Pierson-Moskowitz spectrum, and the effects of the randomness on the scattered field with and without thermocline waves have been studied. The PE code used was developed in a joint project with Eric Thorsos (APL-UW). The internal waves were generated to be similar in scale to observations with a towed chain (Marmorino et al., J. Geophys. Res. 92 C12, 13049–13062). The results indicate that volume scattering cannot be ignored when modeling shallow-angle surface scattering.
Weak localization in frequency domain
Authors: Fu Yaotian
Published: October 2005

Strong coherent multiple scatterings cause wave localization in a disordered medium. In a medium in which the localization is complete, the transmission is zero. Such a medium, however, is different from a mere perfect reflector, in that the phase shift of the reflected wave is a rapidly varying function of the frequency and contains valuable information about the medium. The propagation and reflection of a pulse signal in a weak localization medium are considered, generalizing the work in the strongly localized regime [White et al., Phys. Rev. Lett. 63, 2228–2231 (1989)]. It is possible to infer long wavelength properties of the medium from the spectrum function of the reflected wave. The analytical results obtained are supported by numerical simulations and summarized in terms of several simple interpolation formulas. The role of dissipation in causing delocalization and its consequence to statistical inversion are assessed. [Work supported by ONR.]
Multidimensional elastic scattering for inclusions buried in inhomogeneous media. Part II: The inverse problem
Authors: Aymé-Bellegarda Eveline J. , Habashy Tarek M.
Published: October 2005

This study focuses on the inverse scattering of a 2-D object buried in an inhomogeneous background medium composed of layers with markedly dissimilar elastic properties. The medium is probed by an ultrasonic point source and the scattered field is recorded at a finite number of receiver locations. The goal is to image and quantitatively characterize the object from the observed scattered field. As in the previous paper, the problem is modeled in terms of an integral equation elastic scattering framework. Here, the main difficulties arise from the nonlinearity and ill-posedness of the inverse scattering problem, which are addressed by (i) linearizing the problem within the Born approximation, and (ii) applying regularization in a way consistent with the observed data and any a priori knowledge about the object. The effectiveness of the method is illustrated in the case of an object buried in a layered structure insonified by a point force. Multiple ultrasonic frequency simulations are performed to gather enough scattering data to accurately reconstruct a 2-D density distribution. The algorithm is found to perform satisfactorily, both to locate the object and to determine its geometrical and physical properties.
Numerical studies of multiple scattering of waves in two-dimensional random media
Authors: Romack George M. , Weaver Richard L.
Published: October 2005

Numerical studies of the ensemble average, or coherent, wave in a two-dimensional random medium have been undertaken for both the steady-state and transient cases. The medium consisted of a tensioned mesh with a uniform distribution of point masses and an uncorrelated random distribution of springs attached at the mesh points. The effects of scatterer density and strength were both investigated by varying the number of springs in a mesh and the stiffness of the springs, respectively. For the steady-state case, the average responses as determined by a Monte Carlo method are compared to the predictions of the quasicrystalline and self-consistent theories. For the transient case, the spatial averages from the numerical experiments are compared to the theoretical ensemble averages for wave number and group and phase velocities. [Work supported by NSF.]
Rules for the combination of excitation patterns
Authors: Humes Larry E. , Lee Lidia W.
Published: October 2005

Excitation patterns derived from masking patterns measured for single-component maskers have been used frequently to estimate the excitation patterns for multicomponent stimuli, such as vowels. In doing so, one essentially derives excitation patterns for each component of the multicomponent stimulus and then combines the separate patterns using linear power summation. Thus, if the excitation patterns for two adjacent components of a multicomponent stimulus produce the same amount of excitation at a given location, then the combined excitation would be 3 dB greater. Recent modeling of masking additivity [L. E. Humes and W. Jesteadt, J. Acoust. Soc. Am. 85, 1285–1294 (1989)], however, suggests that such a linear combination rule is inappropriate and will underestimate the excitation for multicomponent stimuli. To evaluate this possibility, masking patterns were obtained for noise low-pass filtered at 1400 Hz, bandpass filtered from 2500–2800 Hz, and high-pass filtered at 4000 Hz. Masking patterns were obtained for each masker separately, for each possible two-masker combination, and for the three-musket stimulus. Results are discussed in terms of the rules used to combine excitation patterns. [Work supported by NIH.]
Verbal organization of vowel sequences: Effects of repetition rate and stimulus complexity
Authors: Richer Keri R. , Warren Richard M.
Published: October 2005

Recycling sequences of brief steady-state vowels cannot be heard as a succesion of vowels, but instead are transformed into syllables and words [R. M. Warren et al., Percept. Psychophys. 47, 423–432 (1990)]. With continued listening, perceptual reorganization occurs and new verbal forms are reported. The present study examined the effect of repetition frequency (vowel durations) and stimulus complexity (number of vowels) upon the rate and nature of perceptual reorganization. Separate groups listened to five-item sequences repeating at rates of 240, 120, or 80/min (vowel durations of 50, 100, and 150 ms). Across rates, equal numbers of stimulus repetitions produced equal numbers of changes and forms. When five- and ten-item sequences (vowel durations of 100 and 50 ms) were each presented at 120 repetitions per minute, the ten-item sequences evoked fewer changes and forms. Of the total of 4039 forms, all but three followed the rules for English syllabification. It would appear that the organization of phonetic sequences occurs at the syllabic level. [Work supported by NIH and AFOSR.]
Further studies of the critical band's role in learning vowel categories
Authors: Weitzman Raymond S.
Published: October 2005

In a previously reported set of concept formation experiments [J. Acoust. Soc. Am. Suppl. 1 87, S159 (1990)], it was found that vowel categorization seemed to be greatly facilitated when F2 of the stimuli for each category differed by at least 1 Bark, suggesting that the critical band plays an important role in such categorizations. However, because the average formant values for English /ʌ/ were used as the base stimulus, the category boundaries that subjects had previously learned as speakers of English might have influenced their judgments. Therefore, the real factor of discrimination might not have been just the differences in critical band. Here, the results of a similar series of experiments in which /φ/, a non-English vowel, was made the base stimulus will be reported. These experiments not only involved having subjects try to learn absolute discriminations of vowel sets that differed in F2 but also sets of vowels that differed in F1.
An x-ray microbeam study of the effect of lexical stress position and speech rate on word-medial stop consonants in American English
Authors: Turk Alice
Published: October 2005

Previous research indicates that total durations of work-medial stop consonants in all places of articulation (except /g/) are significantly shorter (p < 0.05) preceding an unstressed syllable than when preceding a stressed syllable [A. Turk, J. Acoust. Soc. Am. Suppl. 1 85, S136 (1989)]. The extremely short duration of American English flaps is a well-documented instantiation of this more general timing phenomenon. In this study, the articulatory patterns underlying the observed durational differences are explored in different stress environments: before a stressed vowel, immediately following a stressed vowel, and between two unstressed vowels at two rates of speech. The test words are of the form locále, lócal, and fóllicle. Velocities and displacements of the primary articulators involved in the production of each consonant will be compared across these conditions to see whether greater duration is a result of greater displacement or of holding the articulation longer. The effect of stress and rate on the phasing of consonant gestures with respect to vowel gestures will also be reported. [Work supported by Sigma Xi grants in aid of research.]
An articulatory analysis of formant asymmetries in symmetric CVC sequences
Authors: Johnson Keith
Published: October 2005

Symmetric CVC sequences (e.g., dVd, bVb, etc.) do not have symmetric formant trajectories. This paper reports a study of this phenomenon using articulatory data and vocal tract modeling. The x-ray microbeam system at the University of Wisconsin tracked the locations of seven gold pellets affixed to the tongue, lips, and mandible of five midwestern English speakers. The speakers read sentences containing symmetric sequences composed of the consonants /d/, /b/, and /s/ and ten vowels in English. Five events in the trajectores most closely associated with the consonant gesture (tongue tip for /d/ and /s/, and lower lip for /b/) were identified: initial and final consonant closure, maximum vowel displacement and maximum velocity during the opening and closing consonant gestures. The data suggest that symmetric CVC sequences are temporally symmetric, with the maximum vowel displacement occurring about half-way between the two consonant closures. Tense and lax vowels differ in the locations of maximum closing and opening velocity (which were also temporally symmetric), with maximum velocities occurring nearer the consonant closures in tense vowels. While the time course of the gestures was symmetric, the locations of the articulators was not. Consonant release and closure generally involved vertical displacement of the tongue before horizontal displacement, giving rise to a circular pattern of movement. There was evidence for this circular pattern of tongue movement for both alveolar and labial consonants. Preliminary vocal tract modeling using the microbeam data to specify the parameters of a vocal tract analog synthesizer has indicated that the pattern of results described above (temporal symmetry, spatial asymmetry) results in formant asymmetries similar to those shown in previous research.
Application of the canonical eigenvalue method to an underwater acoustic double duct
Authors: Pedersen I. M. A. , Gordon D. F. , Hosmer F.
Published: October 2005

This paper applies a new analysis method to double duct propagation. The term “canonical” arises because the solutions apply to an entire class of sound-speed profiles and apply to underwater acoustics or any equivalent problem in air acoustics, electromagnetics, seismology, or quantum mechanics. The canonical eigenvalue equation for an n-layer profile contains two dimensionless variables and 2(n −1) dimensionless profile parameters. The class of profile addressed here consists of all two-layer profiles bounded above by a free surface and below by a rigid bottom. Numerical results are presented for the eigenvalues and three other canonical functions related to the frequency, group velocity, and the normalization of eigenfunctions. Advantages of the canonical over conventional approaches are demonstrated. These include the reduction of the problem to its mathematical essence by the elimination of four superfluous physical parameters in the conventional approach, a relative ease in the determination of eigenvalues, and the application to a class of environments rather than to a single environment.
Rigorous ray tracing for frequency-dependent, stratified media
Authors: Floyd Edward R.
Published: October 2005

The equations of motion for rigorous ray tracing for a frequency-dependent, horizontally stratified media are the same as those for simply a horizontally stratified media. In the Hamilton-Jacobi representation, both time and range are still cyclic variables. The behavior of the motion of cyclic variables can be determined by Routh's procedure, and so the trajectory of the ray path in the vertical plane is described by the equations of motion of rigorous ray tracing. The concept of “group velocity” may be shown in a Hamilton-Jacobi representation to be an application of Routh's procedure where the velocity is explicitly dependent upon the momentum conjugate to time (i.e., frequency). As a by-product, since the effective velocity of rigorous ray tracing is dependent upon the momentum conjugate to horizontal range, the relationship between rigorous ray tracing and classical ray tracing is analogous to the relationship between “group velocity” and “phase velocity.”
Passive localization of calling animals using acoustic tomography
Authors: Spiesberger John L. , Bowlin James
Published: October 2005

The temporal and spatial patterns in the distribution of animals are poorly understood primarily because of inadequate observation techniques. A new passive localization technique (acoustic tomography) is demonstrated that automatically localizes the positions of calling animals with rms errors of a few centimeters from measurements of the call's travel-time difference at several pairs of microphones [J. L. Spiesberger and K. M. Fristrup, Am. Naturalist 135, 107'153 (1990)]. Tomographic localization is significantly more precise (by factors from about 2 to 100) than passive acoustic techniques used previously because tomography accounts for and estimates the sound speed and wind fields as well as the positions of the microphones all of which significantly modify the travel-time differences. Computers are now fast and inexpensive enough for automatic localization of calling animals in large regions of forests and other terrestrial environments.
20-Hz pulses and other vocalizations of fin whales, Balaenoptera physalus, in the Gulf of California, Mexico
Authors: Thompson Paul O. , Findley Lloyd T. , Vidal Omar
Published: October 2005

Low-frequency vocalizations were recorded from fin whales, Balaenoptera physalus, in the Gulf of California, Mexico (mainly the Sonoran coast) during three cruises in March 1985, and February and August 1987. The predominant sounds were patterned 20-Hz pulses. In March 1985, they were in sequences characterized by regular interpulse intervals of 9 s, whereas in August 1987, they were mainly in sequences of doublets in alternating 5- and 17-s interpulse intervals. In February 1987, no patterned pulse sequences were detected. The 20-Hz pulses were about 0.5-s duration, typically sweeping from 42 to 20 Hz. Other fin whale vocalizations were of similar duration and typically modulated downward in frequency, averaging 82, 56, and 68 Hz, respectively, for the three cruises. Gulf pulses differed from those elsewhere in terms of frequency sweep, sound level, and time interval patterns. This uniqueness points out the possibility that fin whales in the Gulf of California may represent a regional stock based on their sound characteristics.
A differential dynamical solution for acoustic wave propagation in the ocean from chaos theory
Authors: Akers Geoffrey R.
Published: October 2005

Initially, begin with the vector equations describing nonlinear propagation of acoustic waves in the ocean that have been derived in earlier investigations. Through the use of the methods of chaotic dynamics the nonlinear equations are converted into a system of first-order differential equations and the evolution of this propagation system is modeled in this autonomous form. The dynamics determined by the inhomogenenus vector field have much of their origin in the generalized loss field L. The equations are linearized in the neighborhood of the fixed points of the system to provide insight into the acoustic velocity field.
Intelligibility testing: Consultant experiences
Authors: Orfield Steven J. , Pierson Richard G.
Published: October 2005

Many competing intelligibility theories are available for the interesting practitioner of intelligibility testing. These include AI, STI, RASTI, ALcons objective tests and subjective tests, such as the PB Word and the Modified Rhyme Test. It is important to understand the most appropriate method for selecting which test to employ in a particular circumstance. Orfield Associates has used all of these tests and owns test systems for their performance. Testing experiences and views will be shared, along with current conclusions regarding these tests and intelligibility theory.
Back muscle response of seated individuals to single and superimposed sinusoidal, vertical vibration
Authors: Wilder David G. , Kaigle Allison , Beliveau Jean-Guy , Huston Dryver , Fenwick James , Tranowski James , Pope Malcolm
Published: October 2005

Data exist on the erector spinae muscle activity during steady state and random vibration. The purpose of this study was to determine how the muscles responded to vibration between those limits. This was achieved by measuring the surface electromyographic (EMG) muscle response to single and superimposed vibration signals. Subjects were tested at the following single and combined frequencies: 2, 3,…, 10, 2 + 4, 3 + 6, 4 + 8, 5 + 10, 2 + 4 + 6, 3 + 6 + 9, (All) 2 + 3 + … + 10. The EMG activity for the combined signals was evaluated at each single frequency and the ensemble averaged peak-to-peak predicted torques computed [Seroussi et al., J. Biomechanics 22(3), 219–229 (1989)]. For the superimposed signals, the torque was significantly greatest at the following frequency evaluation windows (signals used): 4 Hz (2 + 4, 2 + 4 + 6, All); 6 Hz (3 + 6, 3 + 6 + 9); 8 Hz (4 + 8); and 5 Hz = 10 Hz (5 + 10). The natural frequency of the seated subject has been reported in the 4.5- to 6-Hz range. The maximum EMG response for all but two of the seven superimposed signals occurred at a frequency within this range. The results show that the spinal system is frequency sensitive. Thus vibration attenuation may need to accommodate frequencies outside the natural frequency range of the seated driver. [Work supported by NIDRR, McClure Musculoskeletal Res. Ctr., Burlington, VT.]
Threshold limit values (TLVs) for exposure of the hand to vibration: A subject revisited
Authors: Brammer Anthony J.
Published: October 2005

Threshold limit values (TLVs) designed to restrict the severity of the vascular component of the hand-arm vibration syndrome (HAVS) have been proposed by the American Conference of Governmental Industrial Hygienists. A proposed revision to the TLVs would employ the same frequency-weighted accelerations measured according to ISO 5349 (1986), and daily exposure durations, but would associate the mild signs of stage 1 in the Stockholm workshop classification (SWS) with these exposure conditions, rather than, as previously, the severe signs of stage 3 [Anon. Appl. Occup. Environ. Hygiene 5, 464–470 (1990)]. Recent epidemiological data from populations of power tool operators experiencing exposure conditions close to those described in the TLVs reveal that prevalences of stage 2 + stage 3 white fingers of up to 20% have commonly occurred. It thus appears the claim of the revised TLVs, namely, to “represent conditions under which it is believed that nearly all workers may be exposed repeatedly without progressing beyond stage 1,” cannot be supported by epidemiological data.