bluuebunny/crossref_metadata_2025 huggingface dataset:
Issues in the development of virtual acoustic environments
Authors: Wenzel Elizabeth M.
Published: October 2005

This paper will review the nature of virtual acoustic displays, which attempt to simulate a spatial acoustic environment in real time (usually over headphones) such that a listener can dynamically interact with virtual sound sources that have apparently fixed locations in space and perceptual qualities that approximate real sound sources. They represent a new, multidisciplinary area in the study of audition, which encompasses both basic research in human perception as well as a very applied or engineering-oriented approach to system implementation. The common goal is to develop technology that is driven by human needs and requirements while resulting in useful, working systems for a variety of application areas including architectural acoustics, advanced human-computer interfaces, navigation aids for the visually impaired, telepresence and virtual reality, and as a test bed for psychoacoustical investigations of complex signals. Achieving this goal requires understanding of the nature of an acoustic object, including both spatial characteristics and nonspatial cues like the spectral and temporal properties that determine perceptual streaming. It also requires practical consideration of the means needed to realistically generate such environmental sounds in a real-time display system. Research issues in these areas will be outlined, the nature of current systems will be reviewed, and some directions for future research and development will be discussed.
Virtual-acoustics research at the Ruhr University of Bochum−with some remarks on the virtual-acoustics scene in Europe
Authors: Giron Franck , Lehnert Hilmar , Blauert Jens
Published: October 2005

Research in the field of virtual acoustics at the Ruhr University of Bochum, as well as in other places in Europe, has focused on binaural room simulation−a method used to accomplish listening into spaces that only exist in the form of computer models. Being based on a combination of traditional techniques for sound-field modeling and binaural technology, binaural room simulation can be used in all kind of areas where the creation of virtual auditory environment is required. Application possibilities include architectural acoustics, advanced man–machine interfaces, virtual reality, and many more. An overview on the development of binaural room simulation in Europe will be given and the current state of the research work in Bochum as well as in other labs will be described.
Neutral coding of virtual acoustic space
Authors: Brugge J. F. , Chan J. C. K. , Hind J. E. , Musicant A. D. , Poon P. W. F. , Reale R. A.
Published: October 2005

The spectrum of a free-field sound source is transformed by the head, pinna, and ear canal before reaching the eardrum. Prominent spectral features in the free-field to eardrum transfer function (FETF) vary systematically with changes in sound-source direction. Inner ear transduction mechanisms subsequently filter the transformed sound before the information is encoded in the discharge rates of auditory nerve fibers. This information may then be modified by neural interactions at all levels if the central auditory system. An earphone delivery system has been implemented that incorporates FETFs to reproduce the spectral properties of a free-field click. This simulation of sound sources in different directions creates an acoustic virtual space (AVS). Responses of auditory nerve fibers and primary auditory cortical neutrons of anesthetized cats were obtained to a set of clicks in AVS. The stimulus set was derived from a family of 3600 FETFs obtained as part of the related study [Musicant etal., J. Acoust. Soc. Am. 87, 757 (1990)]. For both the auditory nerve and cortex, vigorous neutronal responses were obtained to clicks from a restricted number of virtual space locations. An azimuth-versus-elevation map of evoked spike activity derived from responses to clicks in AVS is termed a ‘‘virtual space receptive field’’ (VSRF). The VSRF of a single auditory nerve fiber is well matched by the spatial pattern of sound pressure for frequencies near a fiber’s CF, reflecting the combined filtering action on free-field sound by both the cochlea and the external ear. Thus, the auditory nerve array transmits faithfully information about the spatial distribution of sound pressure over the full range of frequencies to which the animal is sensitive. This information is preserved by certain neurons at the level of the cortex. For these cells, monaural VSRFs are similar in shape to those of auditory nerve fibers having the same CF. The VSRF of most cortical neurons is modified by binaural interactions.
Holographic analysis of environmental and flow noise in a large cavitation channel
Authors: Clark Joseph A. , Sartori Michael A. , Honke Paul M.
Published: October 2005

In a large water cavitation channel, the ability to differentiate between environmental noise and flow noise was previously unavailable. Through the use of holographic processing of hydrophone array data, the direction of the environmental noise is revealed, and enhanced beam-focusing capabilities are provided. At various flow speeds in the channel, the pressure data are acquired from a planar array residing in a trough below the measurement cross section of the channel. The pressure data are filtered, amplified, digitized, and then processed with a holographic algorithm implemented in MATLAB. The holographic algorithm is able to predict pressures and pressure distributions in the channel at various distances above the array and at various flow speeds in the channel. In this presentation, the large cavitation channel and the method used to acquire the channel’s flow data will be described. The holographic algorithm utilized in the data processing and for the analysis of the channel will be explained. The channel’s features revealed by the holographic analysis at various channel flow speeds will be presented, and the environmental noise and the flow noise found through this study will be discussed. The theoretical and observed array gains achieved by the holographic processing will be compared, and their use in enhancing the beam-focusing capabilities of the planar array will be described. [Work supported by CD/NSWC.]
Holographic reconstruction of the acoustic intensity from measurements over a limited surface
Authors: Sarkissian Angie
Published: October 2005

The normal component of the acoustic intensity on the surface of a radiating structure is reconstructed from pressure values over a limited region of space. The small measurement surface that is located very close to the structure enables a high resolution reconstruction of the surface pressure and the surface normal velocity over a small region on the structure surface located just below the measurement surface, from which the normal component of the acoustic intensity is computed. The reconstructed intensity in the region below the measurement surface compares favorably to the intensity reconstructed from a measurement surface surrounding the entire structure. The algorithm is developed by applying the boundary-element method to compute operators relating the surface pressure and the measured pressure to the surface normal velocity with the latter operator inverted by applying singular value decomposition.
Improved determination of the relative strengths of resonances excited for plane waves scattered from elastic spheroids
Authors: Dean C. E. , Werby M. F.
Published: October 2005

In a previous paper [C. E. Dean and M. F. Werby, J. Acoust. Soc. Am. 91, 2469 (1992)] initial calculations for scattering from spheroids composed of six materials for aspect ratios of three and six were presented. Improved results for the same cases are now shown. The difference in resonance locations as a function of material properties is noted and explained in terms of the pseudo-Rayleigh type resonances described extensively in the literature for spheroids. There is also a marked difference between the amplitudes of the resonances. The relative amplitudes of the resonances is predicted as a function of material properties based on the Rayleigh wave interpretation of these resonances. A theory is developed based on the fact that Rayleigh type resonances can only be excited as a function of the appropriate grazing annular region. This region is determined as a function of the material property and geometry. Numerous results are presented.
Numerical simulation of modal ocean acoustic tomography
Authors: Shang E. C. , Wang Y. Y.
Published: October 2005

Numerical simulation of modal tomography has been conducted at low frequency (f=50 Hz) for the same vertical slices of the ‘‘sampled ocean model’’ for which ray tomography is simulated [by M. Jones and T. Georges, in this session]. Modal travel time perturbation data are synthesized using an adiabatic mode theory and also by the modal spectrum of the PE field (MOSPEF) to investigate mode coupling effects. The inversions given by the different methods are compared. [Work supported by NOAA.]
Issues important in modal tomography
Authors: Shang E. C. , Wang Y. Y. , Gao T. F.
Published: October 2005

Modal ocean acoustic tomography working at lower frequencies (lower than 100 Hz) is appropriate for basin scale ocean monitoring. One of the advantages of modal tomography is that it does not need to identify rays and measure the travel time by identified and resolved rays as in ray tomography. With a vertical receiving array, the modal features of each individual mode can be measured by mode filtering, or on the other hand, to measure the total field at each hydrophone for the matched-field processing (MFP). However, there are some important issues that need to be investigated and clarified. The following issues will be addressed in this talk: (1) The forward model (data) should be based on adiabatic or nonadiabatic mode? (2) The measured modal features (travel time perturbation, etc.) have a linear or nonlinear relationship with the sound-speed profile (SSP) perturbation? (3) How to solve the 2π ambiguity in modal phase tomography? [Work supported by NOAA.]
A tomographic view of mesoscale activity in the Gulf Stream southern recirculation gyre
Authors: Chester David , Malanotte-Rizzoli Paola
Published: October 2005

Variability of the mesoscale eddy field in a region just south of the Gulf Stream has been monitored via acoustic tomography. For 10 months (November 1988 through August 1989), a pentagonal array of tomographic transceivers was situated in a region centered at 38°N, 55°W. The tomographic array was part of the eastern array of the SYNOP (SYNoptic Ocean Prediction) experiment. This region is one rich in mesoscale energy, with the influence of local Gulf Stream meandering and cold core ring activity strikingly evident. The tomographic data set has been analyzed and a view of the temperature, current velocity, and vorticity fields has been revealed. The signature of cold core rings is clearly seen in these sections. Spectra are estimated from the tomographic time series, and are shown to be consistent with concurrent current meter data. Second-order statistics, such as heat and momentum fluxes, are also estimated. The integrating nature of the tomographic measurement has been exploited to shed some light on the radiation of eddy energy from the Gulf Stream.
The influence of a bubbly layer on near-surface acoustic propagation and surface loss modeling
Authors: Christian Raymond J.
Published: October 2005

The impact of refraction, attenuation, and scattering due to a near-surface bubbly layer on acoustic propagation modeling can be significant in appropriately sensitive surface duct and shallow water environments. Hall [J. Acoust. Soc. Am. 86, 1103–1117 (1989)] presents a semi-empirical acoustic model to determine the propagation affects of the bubbly layer on one-way horizontal transmission in a surface duct. Expressions for the depth-dependent complex sound speed and attenuation are used to extend the Hall model to the general near-surface acoustic interaction problem. The rough surface scattering at the air–sea interface and the propagation through the subsurface bubbly layer are treated independently in a simplified approach toward examining the impact of bubbles on modeled surface duct and shallow water transmission loss. The dependence of the ‘‘effective’’ surface loss on grazing angle and wind speed are analyzed in the frequency band of approximately 0.5–5 kHz.
Periodicity of maskers not targets determines ease of perceptual segregation using differences in fundamental frequency
Authors: Summerfield Quentin , Culling John F.
Published: October 2005

Meddis and Hewitt [J. Acoust. Soc. Am. 91, 233–245 (1992)] proposed a model of the use of differences in fundamental frequency to segregate competing sound sources. Key features of the model are: (i) a bank of bandpass filters, to simulate peripheral frequency analysis; (ii) autocorrelation, to determine the periodicities present in each channel; (iii) pooling of autocorrelation functions across channels, to determine the dominant periodicity. Evidence of the dominant source is found by grouping channels containing the dominant periodicity. Evidence of the nondominant source is found in the remaining channels. The model predicts that the periodicity of the dominant source, rather than the nondominant source, determines the ease of segregation. To test the prediction, thresholds for the identification of ‘‘target’’ vowels were measured in the presence of ‘‘masking’’ vowels. Targets and maskers were composed of sinusoids placed either harmonically or randomly in frequency. Masked thresholds were significantly lower when maskers were harmonic rather than random, but the harmonicity of the targets had little effect. Thus, the results are compatible with the predictions of Meddis and Hewitt’s model and are incompatible with models which attempt to compute the pitches of both sources prior to segregation.
The proportion-of-total variance (PTV) rule for the discrimination of auditory patterns
Authors: Lutfi Robert A.
Published: October 2005

Recently, Kidd and Watson [J. Acoust. Soc. Am. (to be published)] identified what appears to be a rule of auditory perception that governs the detectability of changes in components of unfamiliar tone sequences. According to the proportion-of-total-duration (PTD) rule, each individual component of a random sequence of tones is resolved with an accuracy that is a function of its proportion of the total duration of the sequence. In the present paper, the PTD rule is shown to be an incident of a more general phenomenon governing the perception of tone sequences previously reported by Lutfi [J. Acoust. Soc. Am. 91, 3391–3401 (1992)]. The general rule may be stated as follows: each component of a random sequence is resolved with an accuracy that is a function of its proportion of the total variance (PTV) in the sequence. The generality of the PTV rule is supported by three observations: the PTV rule predicts a PTD effect but the reverse is not true; the PTV rule predicts the effects of number and duration of targets in the data of Kidd and Watson where, in both cases, the PTD rule fails; and the PTV rule describes behavior consistent with a broad class of ideal detectors in auditory pattern discrimination tasks. It seems that the PTV rule reflects a general property of auditory analysis wherein the perception of an auditory pattern is dominated by it’s most variable features. [Work supported by NIDCD.]
Teaching speech acoustics: Periodic functions and the voice source
Authors: Rossing Thomas D.
Published: October 2005

To teach acoustical principles using only basic high school mathematics, acoustical phenomena should be emphasized rather than theory. Phenomena should be illustrated with simple demonstration experiments and with videotapes of phenomena that cannot be demonstrated live in the classroom. The voice source can be represented in the time domain by a waveform and in the frequency domain by a spectrum. Students should have early exposure to both representations and learn to appreciate their complementarity. Sound spectra and glottal waveforms resulting from different types of phonation are illustrated.
Resonant ultrasound spectroscopy of single crystals
Authors: Migliori A.
Published: October 2005

Electronics, transducer design, and computational procedures are described for the application of resonant ultrasound spectroscopy (RUS) to single crystal systems. The particular implementation of RUS described here can be used on samples without x-ray orientation of crystallographic axes and, because of the unique point-contact transducer design, works well from cryogenic temperatures to about 400 K. The power of the technique is illustrated with examples of studies on doped and stoichiometric single crystals and it is shown how the doped samples exhibit certain fundamental symmetry breaking effects only observable with RUS. [This work performed under the auspices of the U.S. Department of Energy.]
Application of resonant ultrasound spectroscopy to the study of small single crystal wafers
Authors: Spoor P. S. , McKenna M. J. , Maynard J. D.
Published: October 2005

The study of acoustic waves in a solid can reveal many of its fundamental properties, such as the Debye temperature, the second derivatives of the free energy, and the strength of the electron–phonon coupling−but only if a specimen can be considered a single crystal with a minimum of defects and impurities. Such specimens tend to be extremely small and fragile, especially for newly discovered materials. Often, as the case with the high-temperature copper oxide superconductors, the samples can only be grown as wafers, typically 200×200×40 μm in size. These extremely small sizes and the ‘‘plate’’ proportions complicate the resonant ultrasound technique because stress on the sample from the transducers is more of a concern; second, only the ‘‘plate’’ modes, which have no dependence on the thin dimension, can be excited, and the overtones are widely spaced in frequency, so frequency-dependent mechanisms have to be considered; for example, measurements of the attenuation are of particular interest in high Tc materials. Applications to high Tc and TiB2 crystals will be discussed. [Work supported by NSF Grant No. DMR-9000549 and by the Office of Naval Research.]
Resonances of a finite elastic cylinder with hemispherical endcaps
Authors: Décultot D. , Lecroq F. , Maze G. , Ripoche J. , Werby M. F. , Niemiec Jan , Bao X. L. , Überall H.
Published: October 2005

Experiments on ultrasonic backscattering from submerged elastic cylinders with hemispherical endcaps have been carried out for solid steel cylinders at Catholic University, for solid tungsten carbide cylinders at the University of Le Havre, and for hollow air-filled steel cylindrical shells at DTRC and Le Havre. The experimental results will be presented, and will be theoretically interpreted by the method of phase matching, taking into account the dispersion of the wave speed of the surface waves propagating axially along the cylinder (guided waves). Use of these explicit dispersion formulas, rather than their high-frequency constant limits as they have been employed previously (thereby neglecting transverse curvature effects) is shown to be very important in the correct identification of the resonance peaks.
Design and performance of a high-power, low-frequency sound source
Authors: Sabatier James M. , Bass Henry E. , Bolen Lee N.
Published: October 2005

A well-controlled low-frequency, high-intensity sound source that is self-contained on a telescoping semi-trailer is described. The three major components of the sound source are: the air-supply system, the Wyle Laboratory air-stream modulator, and the acoustic horn. The modulator has been available for some 20 years and is capable of producing 30 000 acoustic watts of output power from 10 to 630 Hz. It has been modified to allow for CO2 cooling of the voice coil. The air-supply system consists of a rotary lobe blower driven by a 150 horsepower diesel engine. The acoustic horn is a true 10-Hz exponential horn, 17.1 m (56 ft) long. The mouth and throat diameters are 2.34 m (92 in.) and 0.01 m (4 in.). Measurements of the acoustic output and performance will be presented.
An improved-performance barrel-stave projector
Authors: Hughes Steven J.
Published: October 2005

Researchers at the Defence Research Establishment Atlantic (DREA) have been active since 1986 in the development of the barrel-stave flextensional projector. Intended primarily for use in sonar systems, the barrel-stave projector promises to be a small, light-weight projector with high power and low resonance frequency. This paper describes work in progress aimed at increasing the power output of the projector by nearly doubling the mass of ceramic in the drive element, and at improving operability at depth by implementing passive pressure compensation.
Two degree of freedom model for prosthetic devices for the middle ear
Authors: Brink W. Richard , Finch Robert D.
Published: October 2005

Current prosthetic devices for the human middle ear are essentially mechanical rods. This paper will first point out that such devices essentially conform to the old piston and lever model. Neither these devices nor any variation of the piston and lever model take into account the articulation of the joint between the malleus and the incus. The substantial evidence for the articulation of the malleoincudal joint is reviewed. In addition, in a normal ear the acoustic middle ear reflex seems to provide protection against harmful high-amplitude signals. The current models provide no such protection. A new model for a prosthetic device based on a two degree of freedom model will be proposed and compared with current models. Methods of limiting response at high amplitudes will also be proposed.
Noise normalization technique for beamformed towed array data
Authors: Stergiopoulos Stergios
Published: October 2005

Noise normalization techniques for beamformed towed array data attempt to remove the ambient and self-noise directionality characteristics associated with the measurements in order to enhance detection of weak signals. The problem of normalization in bearing space for broadband or narrow-band plane wave detection is similar to normalization for signal detection in frequency domain. As a result, noise normalization techniques for the spatial domain may be modified versions of those used in the frequency domain [i.e., Struzinski, J. Acoust. Soc. Am. 76, 1738–1742 (1984)]. The aim of this paper is to develop a new concept of noise normalization for beamformed towed array data. This concept has two sets of operations, the first applies low angular resolution beamforming to obtain stable noise background estimates that retain the directionality characteristics of the noise field while the second includes the estimation of the geometric mean over a number of time snapshots in order to remove any high-level signal from the beam-power towed array estimates. In situations where the above two steps are insufficient to remove a strong broadband signal’s influence from the noise background estimates, a third step may be applied for signal suppression. In principle, the above set of operations are similar to those used in frequency domain noise normalization techniques. Their numerical implementation, however, is fundamentally different. Performance analysis and comparison of the proposed normalization technique with the two pass split-window normalizer have been carried out by using synthetic and real data sets. Application results indicate similar performance for these two fundamentally different normalization schemes.
Acoustic measurements of suspended sediment in the STRESS experiment
Authors: Lynch J. F.
Published: October 2005

During the winters of 1988–1989 and 1990–91 a long-term sediment transport experiment called STRESS (sediment transport events on shelves and slopes) was deployed in 50 to 150 m of water off the California coast. The experiment’s aims were to quantify sediment transport, both by measurements and modeling, in an area where both surface waves and currents combine (nonlinearly) to produce the bottom stress. A number of oceanographic sensors were deployed as part of this effort, including an acoustic backscatter system (ABSS), which measured near bottom sediment concentration profiles. This system allowed one to make measures of integrated transport, quantify the wave-current interaction, and (when compared to optical devices working in a much higher ka range) quantify the particle size distribution to some extent. The results from the STRESS deployments, their implications, and the directions of both ongoing and future research will be discussed. [Work supported by ONR.]
Acoustic imaging of naturally occurring underwater plumes
Authors: Palmer David R. , Rona Peter A.
Published: October 2005

Acoustic imaging provides opportunities for studying naturally occurring plumes in the ocean that are not available using any other measurement technique. An overview is presented of recent experiments that recorded images of naturally occurring plumes using high-frequency sonar systems. These experiments, which involve different types of plumes, different scattering mechanisms, and different ocean environments, illustrate the value of acoustic imaging and form the basis for the design of future experiments and the development of new plume-imaging sonar systems. The types of plumes considered include shallow submarine springs, plumes formed from hydrocarbon seepage, and those resulting from hydrothermal activity. The possible physical mechanisms responsible for the acoustic backscattering are considered. The advantages of computer-assisted construction of plume images during and after an experiment are also illustrated.
Observations on subsonic edge tones, continued
Authors: Mascarenhas Noel , Powell Alan
Published: October 2005

The included angle α of the (w)edge and the stream breadth influence the region of operation (RO) and the frequency characteristics of the classical edge tone (laminar jet, ≤50 m s−1) [Powell and Unfried (1964)]. This is also so for high-speed subsonic edge tones (turbulent jet, 48–315 m s−1, 0.14≤Mach number≤1). For α=8°, 135°, and 180°, the RO decreases while the frequencies for the first two continuous frequency stages are closely proportional to jet velocity and inversely proportional to nozzle-edge distance, but are 5% higher for 180°. For increasing nozzle breadth, 25, 43, and 60 mm (nozzle width 1 mm) the RO increases; frequencies remain the same but with changed jump positions. The sound pressure of the tone decreases with increasing wedge angle and increases proportionally (or more) with the nozzle breadth. The results are qualitatively much the same as for the classical case, except that there are multiple tones and there is very little hysteresis with the frequency jumps; surprisingly, there is apparently no effect dueto the exit velocity being sonic. [Work supported by the Texas Advanced Research Program.]
Phonemes and syllables as units of speech perception in newborns
Authors: Kaye Kelley L.
Published: October 2005

There is some controversy concerning what constitutes the perceptual unit of speech. Bertoncini and Mehler [Infant Behav. Dev. 4, 247–260 (1981)] have presented evidence from infants supporting the syllable over the phoneme. The present study investigated this issue with newborns. Twenty-four subjects were presented with lists of nonsense syllables (CVC’s) over earphones, using an operant choice preference sucking procedure. The lists varied in number of syllables (length) and also in number of phonemes (complexity). Two contradictory effects occurred: the number of sucks produced decreased as syllables were added, and the number of sucks increased as phonemes were added. Speech perception in newborns thus requires two processes: the multidimensional space of the utterances is defined in terms of distinctive features, requiring a large number of presentations. Subsequently, the infant operates on the units defined in that space, with processing largely occurring in memory whereby the increased memory load suppresses sucking. An experiment to test this interpretation has been carried out, and will also be discussed.
Perception of ethnic identity: The roles of speech sample, speaker, and listener variables
Authors: Hawkins Francine Dove , Yeni-Komshian Grace H.
Published: October 2005

This study was conducted to examine the influence of speaker, listener, vowel type, and speech sample length variations on ethnic identification. The speakers (equal number of black/white/male/female) provided test materials that consisted of isolated vowels, words, and sentences. The stimuli were also differentiated by vowel type: /ae/ and /i/. The listeners (n=180) were divided equally by ethnicity and gender. The results revealed that listeners identified speakers’ ethnicity with overall accuracy rates greater than chance (64% correct). Accuracy rates for /ae/ and /i/ stimuli were similar. In addition, listener variables, such as ethnicity, gender, and site of residence, did not consistently affect ethnic identification responses. Ethnic identification was most accurate for black male and white female speakers. For these two speaker groups only, accuracy rates increased consistently from vowel to word or sentence stimuli. An acoustic analysis of some of the speech samples was performed in which the fundamental frequency (F0) was measured. The findings of this analysis were consistent with the interpretation that listeners may be using the speaker’s F0 in the ethnic identification process.
Assimilative and contrast effects of speaking rate on speech perception
Authors: Newman Rochelle S. , Sawusch James R.
Published: October 2005

Previously, results were presented showing that varying the duration of a distal vowel can produce assimilatory, rather than contrastive effects on perception. In a /shwas/–/chwas/ series, a longer vowel yielded more /sh/ responses rather than more /ch/ responses. Varying /w/ duration produced the standard contrast effect. The assimilative effect may reflect a chaining of contrast effects: the long /a/ made the /w/ seem shorter, and the ‘‘shorter’’ /w/ made the initial segment seem longer. Alternatively, the lack of a distinct acoustic boundary between /w/ and /a/ may have produced these results, in which case results should be very different for a voiceless stop followed by a vowel. In new experiments, a similar series was made ranging from /chkas/ to /shkas/, and the /k/ and /a/ durations were varied separately. The /k/ produced the usual contrast effect while the nonadjacent /a/ had no effect. These results and their implications for the understanding of rate normalization will be discussed. [Work supported by NIDCD Grant No. DC00219 to SUNY at Buffalo and an NSF Graduate Fellowship to the first author.]
Estimation versus word recognition of monosyllabic words
Authors: DePaolis Rory A. , Frank Tom
Published: October 2005

The relation between word recognition and the estimate of the percentage of words understood was examined for monosyllabic words. Six-hundred and sixteen words were presented to 30 subjects in four signal-to-noise ratios (SNR) under five high pass, five low pass, and in the unfiltered condition. In each condition the subjects listened to 14 words with the carrier phrase ‘‘you will write’’ preceding each word. Subjects were instructed to write down each word, and at the end of each set of 14 words, to estimate the percentage of words that they understood in 7.5% increments. The subjects were not able to reliably estimate the words that they correctly understood based upon their identification of the words. Confusion matrices for 10 of the 30 subjects show the filter conditions and phonemic classifications that subjects consistently misjudged as having correctly understood.
Binaural performance in children with a history of otitis media
Authors: Besing Joan , Koehnke Janet , Goulet Christine , Allard Marla
Published: October 2005

Binaural performance was measured for children ages 7 to 12 with and without a history of otitis media on three tests: binaural detection, localization, and speech intelligibility. NoSo and NoSπ thresholds were measured for pure-tone and 1/3-octave noise targets in narrow and wideband noise maskers as a function of frequency. Localization in the horizontal plane (nine locations from −90° to +90°) was measured using short phrases. Intelligibility of monosyllabic words was assessed with the speech at 0° in quiet and in noise. Localization and speech intelligibility were measured in anechoic and reverberant environments. Results of the detection tests show smaller masking-level differences (MLDs) for children with a history of otitis media than children with no history. Localization and speech intelligibility are also generally poorer for the children with a history of otitis media. Localization for all children is independent of environment, but speech intelligibility is better in the anechoic environment. Performance for all three tests also appears to improve as a function of age. Overall, good binaural detection tends to be associated with good localization and speech intelligibility, and children with a history of otitis media have more difficulty with tasks requiring binaural interaction. [Work supported by UCRF and Sertoma Club of Baton Rouge.]
Electrostatic actuator method for calibration of high- temperature fiber-optic microphones
Authors: Nguyen Trung D. , Gonzales Oscar , Zuckerwar Allan J.
Published: October 2005

A fiber-optic lever microphone has been developed for high-temperature applications. The sensitivity of the microphone is determined from a pistonphone calibration at room temperature. The electrostatic actuator method is used for the frequency response calibration of the microphone at room temperature and 1000 °F. The microphone is placed inside an oven, and is excited by the electrostatic force between the actuator electrode and the microphone membrane. The frequency response of the microphone, along with the background noise, is analyzed on an FFT analyzer. For a 0.072 in. diameter of the membrane, the typical sensitivity of the microphone is 1.3 μV/Pa, and the typical bandwidth is 47 kHz. The background noise includes contributions from the microphone and the photodetector, in which the shot noise is the dominant source of noise.
Laser generation of Rayleigh and Lamb waves for ultrasonic testing
Authors: Costley R. Daniel , Berthelot Yves H.
Published: October 2005

The thermoelastic generation of surface waves by a Q-switched ruby laser is investigated both experimentally and analytically. The motivation is to improve the amplitude and to control the frequency content of the ultrasonic signal by taking advantage of the tremendous flexibility that one has in controlling the size and the shape of the thermoelastic source. Waveforms have been recorded for several source geometries at the surface of an aluminum block: spot source, line source, periodic array of spot sources, and periodic array of line sources. Also, focusing effects have been measured with a periodic array of curved line sources obtained with a Fresnel lens. In all cases, the waveforms are reasonably well predicted by a simple and efficient convolution technique. Waveforms have also been generated in a 1-mm-thick aluminum plate and recorded over a distance of 50 mm at increments of 0.5 mm. Processing of these waveforms in the frequency–wave-number domain allows for the extraction of the dispersion curve and the various modes propagating in the plate. [Work supported by NSF.]
An investigation using an optical probe to study ultrasonic pulses
Authors: Hays-Stang Jo , Cook Bill D.
Published: October 2005

With care and working within well-defined constraints, it has been previously demonstrated that a laser beam and a fast responding light detector could be made to behave as a linear line receiver of low megahertz sinusoidal ultrasonic waves. It is a sufficiently good line receiver so that the principles of tomography can be used to unfold the sound field. Many of the constraints are frequency dependent and the question arises as to whether a laser beam could be used to investigate a pulse of moderate bandwidth. The studies show that major features of the signal from the line detector can be accounted for when the sound field is produced by a commercial NDE transducer driven with a known Gaussian time pulse.
Flexural vibration analysis of a loaded double-tapered circular beam with a linearly varying wall thickness
Authors: Lee Wei , Chao Hsicheng
Published: October 2005

The present study considers the small-amplitude, undamped transverse vibration of a double-tapered circular beam with a linearly varying wall thickness attached to a central mass. The natural frequencies and modeshapes for free vibration of the beam system are determined for various values of the ratio of central mass to beam mass. The steady-state vibration produced by a harmonic force applied to the central mass is developed to investigate the vibration absorption capabilities of the composite beam.
Asymmetrical discrimination of narrow-band stimuli
Authors: Elliott Lois L. , Hammer Michael A. , Carrell Thomas
Published: October 2005

A three-interval, forced-choice procedure that obtained complete psychometric functions was used to study frequency discrimination for 13-item continua of impulse-generated, narrow-band, buzz-like, steady-state sounds. For all subjects and durations, discrimination relative to the highest center frequency (1060 Hz) stimuli was better than discrimination relative to the lowest center frequency (940 Hz). This result is not in consonance with traditional reports of pure tone frequency discrimination and is not readily explained. However, additional experiments with similar stimuli replicated these findings.
Detection of temporal gaps in sinusoids by elderly subjects with and without hearing loss
Authors: Moore Brian C. J. , Peters Robert W. , Glasberg Brian R.
Published: October 2005

Thresholds for the detection of temporal gaps in sinusoidal signals were measured as a function of frequency (100–2000 Hz) and level in 15 elderly hearing-impaired subjects and 11 elderly subjects with near-normal hearing at frequencies below 2000 Hz. The sinusoids were presented in a background noise intended to mask spectral splatter associated with the gap. In a separate experiment, auditory filter shapes and detection efficiency were estimated for the same subjects using the notched-noise method, at center frequencies of 100, 200, 400, and 800 Hz. The gap thresholds at higher signal levels were similar for the two groups of subjects at all center frequencies tested. The mean gap thresholds were slightly higher than those obtained previously from young normally hearing subjects, but this was mainly due to the results of a few subjects with large gap thresholds; the majority of the elderly subjects had gap thresholds within the normal range. Thus reduced temporal resolution does not seem to be an inevitable consequence of aging. Gap thresholds at low center frequencies tended to be positively correlated with the equivalent rectangular bandwidth (ERB) of the auditory filter, the opposite of what would be expected if the auditory filter played a role in limiting gap detection. Detection efficiency, as estimated from the notched-noise experiment, was poorer for both groups of elderly subjects than for young normal listeners, but detection efficiency was not significantly correlated with gap thresholds.
A self-starter for the parabolic equation method
Authors: Collins Michael D.
Published: October 2005

An efficient method is developed for generating accurate starting fields for the parabolic equation (PE) method for both fluid and solid media. The self-starter, which is constructed by solving a one-dimensional boundary-value problem (BVP) involving the PE operator, is more efficient than the normal-mode starter, which requires the solution of a large number of similar BVPs. The self-starter depends on the depth-dependent properties of the medium and satisfies all interface and boundary conditions. Since the self-starter is based on higher-order parabolic approximations, it is accurate for problems involving wide propagation angles, large depth variations in the properties of the medium, low frequencies, interface waves, and the continuous spectrum.
Small-slope approximation for monostatic scattering
Authors: Berman David H.
Published: October 2005

By using a variational principle for scattering by rough interfaces, the functional derivative of the scattered part of an acoustic field originating from a point source is derived directly in the time domain. This general result is specialized to the case of scattering by surfaces on which fields satisfy Dirichlet boundary conditions. It is shown that when the small-slope approximation is used for surface fields, a simple result can be obtained for monostatic scattering.
Response of a beam to a moving mass
Authors: Mackertich Seroj
Published: October 2005

This paper presents the dynamic response of a simply supported beam excited by a moving mass based on the Timoshenko beam theory with corrections for the shear deformation and rotatory inertia effects. Numerical results for various velocities of a moving mass are given, and results are compared with response of a Bernoulli–Euler beam theory.
Near-field pressure, intensity, and wave-number distributions for active structural acoustic control of plate radiation: Theoretical analysis
Authors: Wang Bor-Tsuen , Fuller Chris R.
Published: October 2005

This paper presents a theoretical analysis of near-field time-averaged intensity and pressure distributions of actively controlled plate-radiated sound. A harmonic point force was considered as a noise source, and a piezoelectric element bonded to the plate was applied as control actuator. A single microphone that measures sound pressures in the radiated acoustic far field serves as an error sensor. The optimal input voltage to the piezoelectric actuator is obtained by minimizing a quadratic cost function, defined as the mean square of the error sensor signal. The influence of the location of the error microphone on near-field pressure and normal intensity was studied. Fourier transforms in the wave-number domain are also used to study the mechanisms of control. This work provides a better understanding of the behavior inherent in controlling structurally radiated sound using piezoelectric actuators. In particular, an understanding of the near-field behavior under closed loop control is inherent in the design of sensor arrays located near or on the plate surface.
Acoustic and elastic scattering from seamounts in three dimensions—A numerical modeling study
Authors: Burns Daniel R.
Published: October 2005

A three-dimensional (3-D) finite difference elastic wave propagation numerical model is used to study the acoustic scattering in the water column and the elastic scattering in the subbottom from seamounts (conical hills) located on the ocean floor. Two models are investigated: scattering from a single seamount located on a flat seafloor, and scattering from two seamounts on an otherwise flat seafloor. In both cases a point source of acoustic energy is introduced in the water column, and particular attention is paid to the backscattered acoustic energy that emanates from the seamount features. The results indicate that in addition to the expected scattering off the front and back faces of the seamount, additional energy is radiated onto the water column from reverberations inside the seamount and the related interface energy that propagates around the circumference of the seamount. Comparison of the single seamount and two seamount models suggests that the effect of multiple features is an increase in the overall level of backscattered acoustic energy. A comparison between the 3-D single seamount model and a two-dimensional (2-D) simplification is also presented. The 3-D model results in a more complicated backscattered wave field due to the effects of the seamount resonant and circumferential modes which are lost in 2-D representations. Elastic scattering in the subbottom due to seamount features is also illustrated.
Unsupervised neural networks that use a continuity constraint to track articulators
Authors: Hogden John , Saltzman Elliot , Rubin Philip
Published: October 2005

A recent study [Hogden etal., J. Acoust. Soc. Am. 91, 2443 (A) (1992)] showed that articulatory speech synthesizer parameters describing tongue positions can be recovered from synthesized acoustic signals using continuitymapping. Previous results are extended to two neural network implementations of continuity mapping. Both networks are tested on a two-dimensional spatial analog of the articulator tracking problem. The network’s inputs (analogous to acoustic signals in the previous study) are the distances between a randomly moving robot (analogous to the tongue) and its nearest obstacles. The network’s outputs encode the robot’s position. The first implementation uses a frequency-sensitive, competitive learning network (FSCLN) to vector quantize the inputs, followed by a linear layer with one output unit for each degree of freedom of the robot. At each time t the delta rule is used to teach the network to produce an output, O(t), that is similar to O(t−1). The second implementation follows the FSCLN with a Kohonen-like neural layer. The relationship between these simulations and the acoustic-to-articulatory mapping problem in speech will be discussed.
Technical summary of the Naval Air Warfare Center (NAWC)−Open Water Facility (OWF)
Authors: Furlong David M.
Published: October 2005

The NAWC-OWF is a Navy-owned facility dedicated to the development and measurement of sonobuoy transducers. It is located at a flooded quarry in Pennsylvania about 30 mi north of Philadelphia. Measurements are performed from a laboratory barge where the water depth is 60 ft and the nearest wall is 180 ft away. Acoustic and mechanical measurements consist of: (a) transmitting and receiving responses, (b) directivity patterns, (c) impedance and admittance, (d) hydrostatic simulation up to 8000 psig, (e) flow simulation from 0.1 to 1.0 kn using a 100-ft I beam rail, (f) first-order sea-state simulations up to sea state five, and (g) lift and drag with 18 data channels. Data are obtained via hard wire or rf link. The low-frequency cutoff is 200 Hz for pulse measurements and 3 Hz for continuous wave (CW) measurements. Instrumentation is controlled with menu-driven software and data outputs are real time in paper, disk, or tape format. The facility weight limits, in water, are 500 lbs for acoustic data and 100 lbs for mechanical data. The facility has phone and FAX service and a photo copy machine.
Experimental estimation of the longitudinal-wave backscatter coefficients for ultrasonic interrogation of weak scattering materials
Authors: Russell Mark D. , Neal Steven P. , Boote Evan J.
Published: October 2005

The starting point for solving inverse scattering problems in acoustics is an estimate of the target’s scattering function. A typical procedure for estimating a scattering function is to apply an inverse filter to the Fourier transform of the backscattered signal from the target. The inverse filter is based on an estimate of the measurement system response function that includes electronic, transducer, and wave propagation related effects. In this paper, we address the problem of estimating the backscatter coefficient for scattering from a large number of randomly distributed scatterers. A method is presented for estimating the backscatter coefficient for weak scattering polycrystalline metals for the case in which the backscatter coefficient is independent of depth into the material. Measurement system response function estimates were based on volume integrations over velocity fields calculated using Gauss–Hermite polynomials. Ultrasonic measurements were made for direct backscatter in an immersion mode at normal incidence using both planar and focused probes operated broadband. Results are presented that show close agreement between the frequency dependence of the backscatter coefficient estimates and the frequency dependence of the classically estimated attenuation coefficient. The backscatter coefficient estimates are shown to be reasonably independent of the system configuration and depth into the material.