bluuebunny/crossref_metadata_2025 huggingface dataset:
Sound scattering by randomly rough elongated objects. I. Means of scattered field
Authors: Stanton T. K.
Published: October 2005

By use of the recently published deformed cylinder formulation [T. K. Stanton, J. Acoust. Soc. Am. 86, 691–705 (1989)], the scattered field due to randomly rough elongated dense elastic objects is derived. The radius of the deformed cylinder is allowed to vary with respect to position along the lengthwise axis resulting in a one-dimensional roughness. Explicit expressions are derived describing both the mean and mean-square scattered field for the rough straight finite length cylinder for both ka ≪ 1 and ka ≫ 1 (k is the acoustic wavenumber and a is the radius), while only the mean is calculated for the prolate spheroid, uniformly bent finite cylinder, and infinitely long cylinder for ka ≫ 1. The modal-series-based solution is used in the ka ≪ 1 case and a recently published form of the Sommerfeld-Watson transformed solution is used in the ka ≫ 1 region where the coupling coefficients of the surface elastic wave components of the field are in simple approximate form [P. L. Marston, J. Acoust. Soc. Am. 83, 25–37 (1988)]. All ka ≫ 1 results in this work demonstrate attenuation of the “specular” (echo from front face) and Rayleigh surface elastic wave components of the scattered field due to the roughness. In addition, the attenuation of the Rayleigh wave depends on the number of times it has circumnavigated the object resulting in a loss of the higher “m” terms in excess to that due to radiation alone. The results are compared with the scattering by rough planar interfaces with distinct differences arising because of effects specific to volumetric scattering. [Work supported by ONR.]
Instability and chaos in acoustically driven flows
Authors: Chandra K. , Mehta V. , Mulpur A. , Thompson C.
Published: October 2005

A number of inquiries into the mechanisms responsible for the instabilities observed in time-periodic fluid motion have been made. However, only recently has it been theoretically shown that a fluid, driven by a time-periodic acoustic wave, can bifurcate from stability at a fixed acoustic particle velocity amplitude. This departure from stability is the result of the action of the gradient of the Reynolds stress. Hence, the parametric interaction of acoustically driven vorticity with external disturbances is important. This basic result will serve as the foundation material. Sensitivity of the acoustic instability mechanism to temporal and spatial modulations generated by harmonics resulting from shock formation will be examined. A theoretical model will be presented to describe the nonlinear evolution of unstable disturbances, such as burst-associated, Reynolds stress pulses near a rigid boundary wall. The relationship between unstable vortical disturbances and self-modulation to experimentally observed low-frequency noise will be discussed. Transient conditions for instability will be addressed.
A finite element solution of the inverse scattering problem for determining acoustic bubble spectra
Authors: Commander Kerry W. , McDonald Robert J.
Published: October 2005

The determination of acoustic bubble spectra in the ocean from multi-frequency attenuation measurements was improved by numerical solution of the inverse scattering problem [K. W. Commander and E. Mortiz, in Proceedings of IEEE Oceans '89, 1181–1185 (1989)]. Although this numerical solution offers an improvement over the resonance approximation (at small radii), it too suffers a loss of accuracy at the small radii end of the bubble spectrum. The numerical solution of this problem has been improved by replacing the Fourier series approximation to the unknown distribution by a piecewise linear polynomial constructed from a series of basis functions. The basis functions used were linear B-splines or “hat” functions. The resulting coefficient matrices are much less ill-conditioned than those from the previous method because of the local support of the basis functions. This improvement leads to a more accurate solution of the inverse scattering problem near the end points. Improvements in accuracy due to the finite element solution are quantified using calculated attenuations from several bubble distributions of interest. [Work supported by ONT.]
An experimental search for classical second sound in a system of nonlinear random waves
Authors: Larraza A. , Yarber R. K. , Garrett S. L. , Putterman Seth J.
Published: October 2005

A nonlinear medium driven far from equilibrium by the input of energy in the form of mechanical wave motion becomes wave turbulent. The steady state corresponds to a power spectrum with a low-frequency dependence that is characteristic of the particular system [A. Larraza and S. J. Putterman, in Irreversible Phenomena and Dynamical Systems Analysis in Geosciences (Reidel, Dordrecht, The Netherlands, 1987), p. 139]. It has been shown [A. Larraza and S. J. Putterman, Phys. Rev. Lett. 57, 2810 (1986)] that the wave turbulence can be elastic, so that its energy fluctuations, instead of diffusing, propagate as waves, in analogy to (thermal) second sound in superfluid helium. Experiments in a wind-driven wave tank will be described that are designed to measure the theoretical predicted second sound mode for a random field of short, deep-water gravity waves [Larraza et al., Phys. Rev. A (March 1990)], by use of dual-channel capacitive wave staff and a “probe wave” generated by a hydraulically actuated plunger. [Work supported by the NPS Direct Funded Research Program.]
Bifurcation phenomena in nonlinear clarinetlike systems
Authors: Brod Klaus
Published: October 2005

The physical processes leading to sound generation in reed instruments can be represented as an interaction between the linear sound propagation in the tube and the strongly nonlinear dependence between flow rate and pressure in the mouthpiece. Considering the model equations of this system as a function of the fraction ε = E/E0, E0 being the energy introduced into the tube and E being the energy reflected at the end of the tube, one finds bifurcational behavior for the sound pressure in the passive range (|ε| ⩽ 1). In the active range (|ε| > 1) the bifurcations continue, leading eventually to chaos. This behavior is also dependent on the shape of the reflection function; for very narrow ones the model equations simplify to a one-dimensional iterated map that can be treated rather easily. The types of bifurcations occurring here as well as typical quantities (Lyapunov exponents, etc.) will be analyzed; similarities and differences between this model and experiments carried out will be discussed.
Suppression of acoustic radiation from impulsively excited structures
Authors: Baumann William T. , Banach Antoni S. , Saunders William R. , Robertshaw Harry H.
Published: October 2005

The objective is to use active control to suppress the acoustic energy that is radiated to the farfield from a structure that has been excited by a short duration pulse. The problem is constrained by the assumption that the farfield pressure cannot be directly measured. Therefore, a method is developed for estimating the total radiated energy from measurements on the structure. Using this estimate as a cost function, a feedback controller is designed using linear quadratic regulator theory to minimize the cost. Computer simulations of a clamped-clamped beam show that there is appreciable difference in the total radiated energy between a system with a controller designed to suppress vibrations of the structure and a system with a controller that takes into account the coupling of these vibrations to the surrounding fluid. The results of this work provide a framework for a general, model-based method for actively suppressing acoustic radiation that can also be used to deal with steady, narrow or broadband disturbances. [Supported by DARPA/ONR and AFOSR.]
Lateral position and across-frequency envelope coherence
Authors: Heller Laurie M. , Richards Virginia M.
Published: October 2005

The relationship between across-frequency and across-ear (binaural) information was varied in an effort to determine the relative locus of the two processes. Interference effects might be expected if the output from one system influences the input to the other. In the first experiment, observers indicated whether the envelopes of 200-ms, 100-Hz-wide bands of noise, centered at 2000 and 5000 Hz, were identical or statistically independent. The lateral positions of the two bands of noise were either the same or varied independently via interaural intensity differences (IID). No difference was observed. The second experiment measured threshold IID values for a 100-Hz-wide band of noise centered at 2000 Hz that was presented either with or without a 100-Hz-wide distractor band centered at 5000 Hz. The distractor band had an envelope that was either identical to or independent of the envelope of the target band. Although adding a distractor band produced some increase in threshold, the threshold did not depend on envelope similarity. The lack of interference suggests that these two processes proceed independently. [Work supported by the National Institutes of Health.]
Lateralization and interaural correlation
Authors: Pollack Irwin
Published: October 2005

The lateralization of ongoing interaural delays for broadband noise is necessarily related to the interaural correlation of the noise. (Ongoing delays between independent noise sources cannot be defined. Thresholds for interaural delays may be obtained by simply manipulating the interaural correlation.) A possible interpretation of the poorer lateralization at long interaural delays is that the interaural correlation of the presented signal is reduced, perhaps as the result of greater internal noise associated with longer delays. A weak test of this interpretation is to examine the discrimination of interaural correlations at different interaural delays. The course of discrimination thresholds for interaural correlation closely follows the course of thresholds for longer interaural delays.
Effects of stimulus sensation level on binaural performance of normal-hearing and hearing-impaired listeners
Authors: Curliss P. , Koehnke J. , Colburn H. S.
Published: October 2005

Interaural time and intensity jnd's and NoSπ detection thresholds for normal-hearing and hearing-impaired subjects at levels from 0 to 90 dB SL are being measured. For hearing-impaired listeners, the range of sensation levels is limited due to their reduced dynamic range. Reference interaural intensity differences range from 0–24 dB. The stimuli are 1/3-oct noise bands centered at 500 and 4000 Hz, with a tonal target at the center frequency of the noise band in the detection experiment. Preliminary data for two normal-hearing listeners show that NoSπ thresholds and interaural jnd's decrease with increasing level, plateauing at approximately 50 dB SL. Thus far, data have been obtained for one hearing-impaired listener with a bilateral, flat, moderate-severe sensorineural hearing loss. This subject's performance, in contrast to the normal-hearing subject's plateaus at levels as low as 15 dB SL in some conditions. For this particular subject, binaural performance tends to plateau at slightly lower sensation levels for the 4000-Hz stimulus than the 500-Hz stimulus, and when a reference interaural intensity difference is present.
Minimum audible movement angle in the horizontal plane as a function of stimulus frequency and bandwidth, source azimuth and velocity, and number of ears
Authors: Chandler David W. , Grantham D. Wesley
Published: October 2005

Minimum audible movement angles (MAMAs) were measured in the horizontal plane for four adult subjects in a darkened anechoic chamber. On each trial, a single stimulus was presented, and the subject had to say whether it came from a stationary loudspeaker or from a loudspeaker that was moving at a constant angular velocity around him. Thresholds were established by adaptively varying stimulus duration. MAMAs were measured under both monaural and binaural listening conditions as a function of center frequency (500–5000 Hz), bandwidth (pure tone to 1 oct), velocity (10°–180°/s), azimuth (0°–90°), and direction of motion (left versus right). Preliminary data are consistent with previous observations for frequency and source velocity effects [D. R. Perrott and J. Tucker, J. Acoust. Soc. Am. 83, 1522–1526 (1988)]. Data will be compared to static measures of auditory spatial resolution (the minimum audible angle) obtained under the same stimulus conditions from the same subjects. Discussion will focus on whether specialized mechanisms in the auditory system are required to account for dynamic spatial resolution. [Work supported by NIH.]
Articulatory timing and prosodic modeling of French
Authors: Fletcher Janet , Vatikiotis-Bateson Eric
Published: October 2005

In an earlier paper, it was noted that shorter durations of opening lip/jaw movements in nonfinal syllables compared to final open syllables in French are largely the result of truncated or undershot movements. Final movements are longer because they are not cut short by the onset of a closing gesture belonging to a following syllable. This study looks at the unaccented/accented contrast and the closing phase of motion in the same corpus of reiterant French speech. Unlike the final/nonfinal contrast, the durational difference between accented and unaccented movements is localized in the acceleration phase, i.e., the time from movement onset to the point where maximum velocity is reached. While the magnitude of duration effects in closing movements is much smaller than in opening movements, there is some evidence that the onset of lip/jaw opening in final syllables occurs later in relation to the preceding closing gestures. Thus truncation is occurring in the closing as well as opening phase of syllable production. It also suggests a stress or accent anticipation effect possibly related to pretonic lengthening effects that have been noted in acoustic timing studies of French. [Work supported by the Ohio State University, NSF, and NIH.]
An acoustic study of the timing of contextual nasalization in English
Authors: Huffman Marie K.
Published: October 2005

The time course of contextual nasalization in English was investigated using acoustic data. DFT spectra were analyzed to identify spectral differences betwen contextually nasalized vowels (as in “bean”) and their oral counterparts (as in “bead”). Analysis by synthesis was performed to clarify the contributions of the first formant, the nasal formant, and the accompanying nasal zero, to the spectrum of the vowel. As in previous work, nasalization resulted in spectral changes in the first-formant region, and formants that are shifted relative to what is observed in oral vowels. In our data, the nasal pole falls in the 600- to 1000-Hz frequency range; the nasal zero is usually 200-300 Hz above it. The nasal pole appears 40–50 ms after onset of the vowel (occasionally earlier), and moves up slowly throughout the vowel. These results agree with physiological data in the literature, suggesting that noninvasive, acoustic measures may be useful for investigating the temporal properties of linguistic nasalization.
Onset-rhyme temporal structure of Mandarin syllables
Authors: Bell Alan , Liu Meichun
Published: October 2005

In order to determine whether rhymes of Mandarin Chinese syllables can be said to have the status of a temporal invariant in some sense, the durations of onsets, rhymes, and nasal codas were measured. The effects of different onsets and vowel qualities, as well as the presence or absence of high-vowel onglides or offglides or a final nasal consonant were considered. The syllables were spoken at normal and fast tempos in sentence frames by six speakers. The main result is that vowel + nasal rhymes and vowel + high offglide rhymes (e.g.,/ai/, /au/) are not appreciably longer than rhymes with simple vowels (confirming an earlier claim by Ou Yah, 1980), although a longer onset does in general make a syllable longer. Finer temporal compensations help further characterize the status of the rhyme as a quasiinvariant.
Design and characterization of a digital annular array scanner
Authors: Foster F. Stuart , Larson J. D. , Pittaro R. J. , Lum P. K.
Published: October 2005

Annular array transducers are playing an increasingly important role in diagnostic ultrasound imaging systems. The development of this equipment raises a number of questions concerning the role these systems will play in the clinic and how the annular array can best be implemented in a scanner. In this presentation, the development of a 12-element, 4.5-MHz, 30-mm aperture prototype annular array scanner is described. The factors that affect resolution and contrast in imaging—beamwidth, sidelobe levels, number of annuli, depth of field, and delay quantization—are discussed. The use of a novel digital beamformer is described. Preliminary clinical studies with the prototype scanner show that large aperture annular arrays can offer significant resolution improvement in some patients, while tissue velocity inhomogeneities limit its effectiveness in others. A first-order correction scheme for velocity inhomogeneities is described, and results for a study of 70 patients will be presented.
Effects of familiarity on serial recall for spoken word lists
Authors: Lightfoot Nancy
Published: October 2005

Relatively few studies have dealt with the interaction between linguistic information and talker cues in speech perception and word recognition. The present study examines the effects of talker familiarity on serial recall for spoken word lists. Compared to lists of words produced by a single talker, lists produced by multiple talkers lead to decreased accuracy of serial recall in the primary portion of the recall curve at fast presentation rates. This pattern of recall for multiple- and single-talker stimuli reverses at slow presentation rates. Explanations for these differences in recall for single- and multiple-talker word lists have suggested that processing multiple-talker stimuli either increases rehearsal demands during transfer to long-term memory or increases difficulty of perceptual encoding. The present experiment examines these competing explanations for differential serial recall in multiple- versus single-talker word lists using voices that subjects have been trained to identify. As listeners become familiar with a talker's voice, it is possible either that mandatory rehearsal will encompass richer recall cues, including talker-specific information, or that perceptual normalization will become more automatic. Results provide support for the proposal that rehearsal of enriched cues leads to the differences in recall for multiple- and single-talker lists. Using familiar voices increases serial recall for multiple-talker lists over single-talker lists in the primacy portion of the recall curve, but does not appear to facilitate perceptual encoding. [Work supported by NIH Grant DC-0111-14 to Indiana Univ.]
Effects of category knowledge and syllable truncation during auditory training on Americans' discrimination of Hindi retroflex-dental contrasts
Authors: Pruitt John S. , Strange Winifred , Polka Linda , Aguilar Manuela C.
Published: October 2005

Previous research has shown that the Hindi retroflex-dental contrast among stop consonants is not easily differentiated by English speakers even after some training. In the present study, subjects were given four days of training (768 trials) in a categorial AX discrimination task on full (unmodified) or truncated tokens of naturally produced breathy-voiced [důha] vs [důha]. Truncation involved removing the vowel from the syllables. Half the subjects were given category knowledge during training (i.e., response forms listed the identity of the first token of each pair). Truncation of the stimuli resulted in better performance during training, but the advantage did not transfer to post tests with the full syllables. Category knowledge resulted in greater improvement during training on both truncated and full syllables. It also led to better performance on the post test of full syllables only for subjects trained on full syllables. Large individual differences found in each training condition suggest that subjects' strategies may be more important than stimulus and task variables in predicting success in perceptual differentiation of non-native contrasts.
Discrimination of syllable duration in English and French short sentences
Authors: Nishinuma Yukihiro
Published: October 2005

Two experiments were conducted in order to study the perceptual discrimination of syllable duration within sentences. Two natural French sentences and one English sentence, each consisting of eight syllables were resynthesized with 15% increases and decreases in syllable duration up to ± 60%. The modified, then randomized, stimuli were presented once to 20 subjects whose task was to judge how natural they sounded (experiment I). The same stimuli were then used to determine whether the modifications in duration were perceptible (experiment II). The results provide evidence of the fact that judgment of the rhythmic quality of sentences (a psycholinguistic task) and temporal discrimination (a psychoacoustic task) both have the same functional basis. The differential limen found in two experiments for both languages is remarkably similar and its estimated value is approximately 25% for an average syllable duration.
The perception of speech sounds recorded within the uterus of pregnant sheep
Authors: Brown W. S. , Sawallis Thomas R. , Gerhardt Kenneth J. , Abrams Robert
Published: October 2005

An experiment was designed to estimate the perceptual characteristics of speech sounds entering the fetal environment. A hydrophone in the amnion of a pregnant sheep and an air microphone near the flank were used to record speech stimuli delivered through a loudspeaker two meters from the ewe. The speech sample consisted of the carrier phrase “say the word___,” with the blank filled with three lists of 50 CVC token words and 14 VCV nonsense words. The lists were presented at three sound pressure levels (65, 75, and 85 dB). A perceptual tape was constructed utilizing rhyming minimal contrasts with the token words. A large group of listeners judged the intelligibility of the utterances associated with the hydrophone and air microphone. Preliminary analysis indicated that the perceptual scores were generally better for the air microphone and for the higher intensities. Discussion will address the effect transmission from the external environment to the fetal environment may have on the intelligibility of speech sounds.
A field study of acoustic scattering by marine organisms at the Gulf Stream boundary and the need for better scattering models
Authors: Stanton T. K.
Published: October 2005

The results of an earlier analysis are first reviewed where 70-kHz acoustic backscatter data and trawl data collected a! the Gulf Stream boundary near Cape Hatteras, North Carolina are compared [T. K. Stanton et al., IEEE J. Ocean Eng. 12(2), 339–348 (1987)]. The marine organisms caught at the boundary spanned a wide variety of species and in order to facilitate the scattering calculations, the animals were sorted into four groups of gross anatomical features [elongated shelled or shrimplike, fish, cephalopod (squid), and soft body]. There was great variability in the comparisons between observed volume scattering strength and predictions of scattering strength based on the trawl catch. The variability is attributed to (1) trawl avoidance, where some of the larger animals detected by the sonar may have swum around the trawl, and (2) inadequate scattering models (many animals were treated as “equivalent fluid spheres” where in contrast they may actually have been elongated, covered by an elastic shell, and whose shape and orientation change with time). Because of the variability, the author began a study to develop realistic scattering models where the shape (elongated, finite length, and deformed) and material composition (axially and radially varying such as an elastic-shelled object with an axially varying fluidlike interior) can be taken into account [see, for example, T. K. Stanton, J. Acoust. Soc. Am. 86, 691–705 (1989)]. These models, currently under development, which include random roughness of the outer boundaries of the organisms, and more sophisticated models (for example to include end effects) that need to be developed, will be discussed. [Work supported by ONR.]
Detection of peripheral sensory nerve dysfunction: A preliminary comparison of nerve conduction and mechanoreceptor-specific vibrotactile thresholds
Authors: Brammer A. J. , Piercy J. E. , Van Netten C. , Brubaker R. L. , Nakamura H.
Published: October 2005

Using the method described previously, mechanoreceptor-specific vibrotactile perception thresholds have been determined at the fingertips (digits 3 and 5) of a series of 24 chain saw operators, 83% of whom reported symptoms of intermittent or persistent numbness, and/or episodic white fingers. Motor and sensory nerve conduction velocities were then recorded from the median and ulnar nerves in each hand and arm, as well as motor distal latencies, following conventional procedures. If the results are compared with normative values from nonvibration exposed, symptom-free, manual workers (and the limit of normality is taken to be two standard deviations from the mean value), 71% and 29% of sawyers reported symptoms are found to possess abnormal vibrotactile thresholds and sensory nerve conduction velocities, respectively. Of the workers at present not reporting symptoms, 50% and 89% are found to possess normal vibrotactile thresholds and sensory velocities, respectively. Performance measures of the two objective tests will be discussed that attempt to account for the subjective nature of symptom reporting.
Aerodynamic noise generated by a centrifugal pump impeller
Authors: Mongeau Luc G. , Thompson Donald E. , Mclaughlin Dennis K.
Published: October 2005

The aerodynamic sound generated by a centrifugal pump impeller rotating in air with no casing or diffuser was measured. An inlet duct with variable density screening provided a quiet, uniform inflow to the impeller and enabled adjustment of the impeller operating condition. Measurements covered the entire impeller operating range from stall to free delivery. Sound spectra in the inlet duct and in the free field around the impeller were reduced and interpreted using acoustic similarity laws developed by Neise and Barsikow [Am. Soc. Mech. Eng. Paper WA/NCA-1 (1982)]. Implementation of the technique allowed the achievement of a high resolution in the Strouhal domain for the frequency spectrum source strength. The source strength spectrum is dominated by low-frequency spectral humps that vary substantially with the operating condition. These humps can be interpreted as Strouhal effects related to the convection of turbulent flows past the trailing edge of the blades. This hypothesis is substantiated by the analysis of the phase-averaged velocity measured at the discharge of the impeller with a cross hot wire anenometer. The ratio of velocity scales and integral length scales of the discharge flow in the impeller reference frame is compared with the mean frequency of the spectral humps.
Optimal uses of feedforward type and feedback type adaptive control algorithms in active noise control
Authors: Swanson David C.
Published: October 2005

One-dimensional active noise control problems such as canceling noise propagating down a duct or longitudal vibration within a structural vibration mount are considered, in general, to be well suited for active noise control. However (through the use of feedback control), active noise control can also be successful in applications where there are many sources of noise and low coherence between possible sensor locations. Feedback control requires only an error sensor and an actuator to minimize the noise at the error sensor. There is no question that if all the noise components at a sensor location can be observed before the noise propagates to the actuator and error sensor, then the best choice of controller involves a feedforward algorithm. However, if the noise propagates faster than the actuator can respond (a good example is high-frequency bending waves), random impacts or spectrally white noise cannot be canceled and complexity can be reduced by using feedback control to obtain the same theoretical performance. Feedback control also allows multiple periodic noise sources to be controlled using a single control loop.
Nearfield intensity and pressure distributions of actively controlled panel-radiated sound
Authors: Fuller Chris R. , Snyder Scott D. , Hansen Colin H.
Published: October 2005

Previous work has demonstrated the high potential for actively controlling sound radiation from vibrating panels using piezoceramic actuators. It has been shown that global reduction of farfield radiated pressure can be achieved with a low number of control transducers. However, little is known about the characteristics of the nearfield intensity and pressure distribution over the panel surface when control is applied. In this paper experimental work is reported in which these variables are measured using a microphone probe traversed near the surface of a vibrating baffled rectangular panel located in an anechoic chamber. Two different thicknesses of panel were considered in order to give a range of test frequencies relative to plate size. Control was applied by a single piezoceramic actuator bonded to the panel surface while error information was taken from a microphone located in the farfield. Results are presented for various modes of vibration, and are related to the distribution of the modal amplitudes of the panel. The influence of the location of the noise input and error sensor on the intensity and pressure distributions is studied. The work has lead to an increased understanding of the mechanisms of control inherent in the technique. [Work supported by NASA Langley Research Center and the Australian Electrical Board.]
Synchronous active noise cancellation with LPC noise synthesizer
Authors: Kuo Sen M. , Chen Liang , Lee Bob
Published: October 2005

A new active noise cancellation scheme has been developed for the purpose of engine noise cancellation. The major difference between the new approach and the conventional two-microphone adaptive noise cancellation methods is that the new approach does not require the reference signal. Therefore, the problem of acoustical feedback from the canceling speaker to the reference channel is eliminated. In this new scheme, a linear predictive coding (LPC) technique is employed to synthesize an “engine noise,” which is used as a reference signal, and this synthesized noise is processed by an LMS adaptive filter. Simulation results using a set of digitized engine noise data show that the adaptive filter has a faster convergence rate and more than 10-dB mean-squared error improvement by using an LPC noise synthesizer in comparison with using an impulse train as input only. In the case that engine speed is varying or the engine rpm is not available, a multipulse excitation synthesizer has been used to generate the synthesized engine noise. The multipulse excitation method has also provided an improvement of 10 dB in mean-squared error.
High-frequency under-ice reflection losses and spatial coherence
Authors: Wilson Marcia A. , Meredith Roger W.
Published: October 2005

Propagation of high-frequency acoustic signals under a multiyear pack ice results in a scattered acoustic field of fluctuating amplitude and coherence. High-frequency scattering from under-ice surfaces is complicated by out-of-plane and multiple scattering because acoustic wavelengths may be many orders of magnitude smaller than ice relief. In addition, the transition layer between water and ice, ice inhomogeneities, and ice anisotropy become important scattering sources. Measurements are presented of horizontal spatial coherence at 24 and 42 kHz from linear FM slide pulses of 800-Hz bandwidth and 100-ms duration. Measurements were made with a linear array of 16 hydrophones distributed over a 16-m aperture and deployed 61 m below the ice surface. The data presented here were taken at a nominal range of 1000 m and results from array bearings at endfire, broadside, and 45° are compared. Results are presented for a fixed source at depths of 30, 61, and 91 m. Deconvolution of the source waveform is used to separate direct and reflected arrivals. Relative amplitudes of these arrivals are compared with what would be expected for a perfect reflector. The amplitude differences may be as high as 30 dB and the ice reflected coherence may increase slightly with range. In addition to hydrophone spacing, frequency, and source depth, the reflected arrival coherence is found to be sensitive to the physical location of the hydrophone in the aperture. This sensitivity is due to multipath interference from the scattering region. [Work supported by the Office of Naval Technology.]
Random-boundary structural and topographical effects on acoustic transmission in an ice-covered channel
Authors: Ashley Charles E.
Published: October 2005

The relative effects of the upper and lower boundaries of an ocean channel on the intensity of an acoustic signal in the channel were investigated. The upper surface of this channel was assumed to be covered by an ice layer whose density and sound speed were taken to be random variables. In addition, the ice-water interface was taken to consist of large-scale two-dimensional facets. Each facet was assumed to possess small random depth deviation, slope, and curvature. The lower water-sediment interface of this channel is modeled in a similar manner. Ray theory was then used to study the effects of these boundaries on the intensity at a point receiver for an acoustic signal. Expressions were derived for the mean and variance of the acoustic intensity in terms of the statistics of the two boundaries. Relative effects of structure and topography were compared along with the relative effects of the ice and sediment boundaries. The distinctive acoustic consequences of boundaries whose properties have different means, variances, and horizontal correlations were examined.
Methods of computer-aided analysis of non-Gaussian noise and application to robust adaptive detection
Authors: Kirsteins Ivars P. , Tufts Donald W.
Published: October 2005

A methodology is presented for the modeling of certain nonstationary and non-Gaussian Arctic acoustic noise data. Some components of the noise, which give it its non-Gaussian characteristics, can be individually modeled, synthesized, and subtracted to provide a Gaussian residual. Further, it is shown that this process can also be carried out when signals are present. Our motivation comes from the problem of the detection of weak signals in such noise. The methodology is a combination of adaptive differential quantization and adaptive signal estimation algorithms based on singular-value decomposition of a data matrix that has been developed. The combination of adaptive differential quantization with low-rank approximation to data matrices or estimated covariance matrices is believed to be a new and effective method for multivariable, robust, adaptive detection.
Directivity of an acoustic monopole in a floating ice plate and implications to Arctic ambient noise
Authors: Stein Peter J. , Euerle Steven E. , Lewis James K.
Published: October 2005

Predictions were made of the directivity of higher-frequency (1-kHz) acoustic radiation into the water from a monopole source located in a floating ice plate (2.4 m thick). Theoretical calculations were conducted using the SAFARI propagation routine [H. Schmidt and J. Glattetre, J. Acoust. Soc. Am. 78, 2105–2114 (1985)] and by the method of steepest descents (P. J. Stein, “Monopole Source in a Floating Ice Plate,” MIT/WHOI Ph.D. thesis, 1986). The models show close agreement with each other and predict a strong downward directivity with most of the energy radiated at grazing angles greater than 70°. This implies that (1) higher-frequency impulsive ice noises detected at an omnidirectional hydrophone are likely radiated from a relatively small area of ice directly above the receiver (the area increasing with receiver depth) and (2) the nonimpulsive (background) ambient noise at higher frequencies is dominated by radiation from ice events located within a horizontal range radius equal to roughly one water depth. Modeling also shows that nulls can occur for some radiation angles for particular source depths within the ice. Also, only small effects of a more realistic ice strength vertical profile over a uniform profile are seen. [Work supported by ONR.]
Extraction of the seabed critical angle using ice cracking noise as a signal source
Authors: Zakarauskas Pierre , Verrall Ronald I. , Greening Michael V.
Published: October 2005

A technique is described for measuring the reflection coefficient of the Arctic seabed with a single vertical array of hydrophones. Naturally occurring ice cracks were used as the acoustic sources. This method circumvents the difficulties and expense of introducing artificial sound sources through the thick Arctic pack ice. The measurements were made in April with a 22-element array suspended from the ice in 420 m of water. The range of the source is first determined using the direct arrival and multiple reflections from the seabed and under-ice surface. Then the directivity index is determined using the direct arrival path only. A plot of the reflection coefficient versus grazing angle clearly indicates the value of the critical angle. The sound speed of the sea bottom corresponding to this critical angle agrees well with that measured from a bottom grab sample taken during the field trip. Finally, an interesting phenomenon was an anomalous increase of power at a grazing angle of 60°. This is associated with a leaky plate wave radiating at the ice-water interface.
Ultrasonic propagation in electrorheological suspensions
Authors: Roy Ronald A. , Richardson Joseph
Published: October 2005

Electrorheological fluids are colloidal suspensions that exhibit dramatic and reversible increases in shear viscosity upon the application of an electric field. These fluids generally consist of hydrated, hydrophilic particles suspended in a hydrophobic and electrically insulating base liquid. In addition to viscosity changes, induced fibration, increases in local particle concentration, and changes in the fluid dielectric properties are observed. Since the suspended particles are hydrated, the application of an intense electric field likely results in the generation of induced dipoles. The mechanism for the ER effect is believed, by some, to be the chainlike linkage of these dipoles. A report is given on the measured changes in acoustical parameters exhibited by a model electrorheological fluid (cornstarch and peanut oil) in the presence of electric fields of order 1 kV/mm. Relative changes in compressional-wave sound speed and attenuation, both parallel and perpendicular to the applied electric field, were measured for frequencies ranging from 500 to 5 MHz. The data were taken at various field strengths and suspension concentrations to observe the effect that these parameters have on the acoustic properties of the suspension. Results exhibit qualitative agreement with previously published results [Korobko and Chernobai, Trans. Inhenerno Fizi. Zh. 48, 219 (1985)]. [Work supported by ONR.]
Do “adaptive frequency response” (AFR) hearing aids reduce upward spread of masking?
Authors: Fabry David A. , Leek Marjorie R. , Walden Brian E.
Published: October 2005

Speech recognition scores in noise are improved for some subjects wearing hearing aids that reduce low-frequency noise with an adjustable high-pass filter circuit. Fabry and Van Tasell (1989) argued that because speech-to-noise ratios are not altered by AFR hearing aids, improvements in speech recognition may be related to a reduction in upward spread of masking experienced by the listener [D. Fabry and D. Van Tasell, J. Acoust. Soc. Am. Suppl. I 85, S25 (1989)]. To evaluate this hypothesis, pure-tone masking patterns for a low-frequency bandpass noise were measured in normal and hearing-impaired subjects. The noise skirt of the masker was very steep, with attenuation above the 1000-Hz cutoff greater than 100 dB/oct. Masking patterns for the same noise were also obtained in the presence of a high-pass filter that simulated the effects of an AFR hearing aid. Differences in the masking patterns can be taken as a measure of upward spread of masking. Subjects with high-frequency hearing loss tended to demonstrate greater amounts of upward spread of masking than did normal-hearing listeners. Further, monosyllabic speech recognition in noise testing indicated improvements in performance of the hearing-impaired subjects related to the decrease of upward spread of masking in the high-pass filtering conditions.
Speech levels at the ear of a talker and their implication for a hearing-impaired person taking part in a discussion
Authors: Festen J. M.
Published: October 2005

Speech levels at the ear of a talker and corresponding levels at a listener's ear were measured near the ear-canal entrance. Eight subjects, each serving both as listener and as talker, were tested two by two in an anechoic room at a distance of 1.5 m. Below 1000 Hz, levels at the talker's ear appear to be about 15 dB higher than at the distant listener's ear. Above roughly 1000 Hz, the head progressively shields the talker's ear and the level differences between talker's and listener's ear diminish at a rate of about 6 dB/oct. Weighted according to the articulation index, speech is a 9 dB more efficient masker at the talker's ear than at the ear of a listener at 1.5-m distance. A voice interrupting at the same level as the primary voice is still intelligible for a normal-hearing talker (speech-reception threshold about −12 dB), but a hearing-impaired talker is forced to choose between talking and listening. With a compression hearing aid, the chance of understanding an interrupting voice is even less, because the compression system will strongly act upon the listener's own voice.
Compensatory articulation in normal and phonologically disordered children
Authors: Edwards Jan
Published: October 2005

Many researchers have found that adults can compensate for the effect of bite block and produce acoustically normal vowels, even on the first glottal pulse. Do normal and phonologically disordered children demonstrate similar evidence of motor equivalence during speech? Eight normal and four phonologically disordered preschool children said the words “heat,” “hit,” and “hat” in three conditions: control, with a 10-mm custom-fitted bite block, and with clenched teeth. The frequency of the first and second formants for /æ/ and the second formant for /i/ and /ɪ/ were measured. Acoustic effects of the fixed jaw positions were observed for all of the children. Adult listeners were also asked to identify the children's productions of the words and to rate vowel “typically” using a three-point equal interval scale. Perceptual effects for the fixed-jaw position vowels were observed. These results are consistent with the results of other studies, which suggests that motor equivalence for speech develops gradually. Three of the four phonologically disordered children differed from the normal children in displaying more idiosyncratic patterns of noncompensation.
Observations on disordered articulations
Authors: Bunnell H. Timothy , Polikoff James
Published: October 2005

An adequate characterization of dysarthric speech requires both a description of the nature of the motor impairment and a description of the articulatory compensation strategies talkers employ in attempting to minimize the consequences of their motor impairment. As a preliminary step in developing such a characterization of dysarthric speech, data from a single dysarthric talker and similar data from two normal talkers have been examined. Acoustic and articulatory recordings were obtained from the University of Wisconsin x-ray microbeam facility. Pellets for x-ray tracking were attached to the lips, mandible, tongue tip, tongue blade, and tongue dorsum. Due to technical difficulties, only pellets on the lips and tongue dorsum of the dysarthric talker were consistently tracked. In several speech production tasks, talkers repeated the syllables /ka/ and /pa/ with both constant and alternating stress; sustained the vowel /i/ and abruptly (in response to a click) switched to the vowel /a/; and repeated extended dipthongal gestures starting in a high front vowel position, moving through a low back vowel, and ending in a high back vowel at both slow and fast rates. Comparison of the articulatory data for the dysarthric talker versus the normal talkers shows, among other effects, (a) the presence of some articulator tremor for the dysarthric talker, (b) some rate restrictions in the dysarthric speech, and (c) an apparent attempt on the part of the dysarthric talker to reduce articulatory degrees of freedom by restricting tongue motion to primarily either front-back variation or high-low variation for a given production task. [Work supported by the Nemours Foundation and by NIDCD.]
Asymptotic modal analysis and coupled component systems
Authors: Dowell Earl H.
Published: October 2005

Asymptotic modal analysis (AMA) has been developed to provide a means for understanding the response of linear dynamical systems under random excitation in the limit as the number of modes excited in a frequency bandwidth tends to infinity. Single component systems, both structural (beams, plates, etc. ) and fluid (acoustic cavities), have been studied extensively and the results compared to those obtained from classical modal analysis (CMA) and statistical energy analysis (SEA). The understanding of the advantages and limitations of AMA, CMA, and SEA, both conceptual and computational, has thereby been enhanced. The outstanding open question for AMA and SEA remains that of how to treat coupled (connected) component systems when each component and its behavior are well understood. In this presentation, such systems will be discussed and recent, as well as earlier results, summarized with a view to suggesting fruitful directions for future work. [Work supported by NASA and NSF.]
Coupling rod energy models using local energy density
Authors: Cho Phillip E. , Bernhard Robert J.
Published: October 2005

To couple medium- and high-frequency models of rod vibration in terms of energy density and intensity, relationships that enforce continuity of power flow and compatibility of energy density are required at the joint. The continuity relationship for local power flow at a joint between two rods is straightforward. However, for joints of rods with different properties, there is a jump discontinuity of local energy density at the joint. An exact relationship for the power flow can be found using the receptance method. A good frequency-averaged approximation of the power flow can be found using the so-called wave transmission method commonly used in statistical energy analysis. In this investigation, a relationship for the jump discontinuity of the local energy density, which uses the ratio of the local kinetic energy density to the total density, is examined. The technique is capable of deterministic or statistical prediction of energy in the coupled rods. [This investigation was supported by the NASA Langley Research Center.]
A statistical approach for the scattering of sound from elastic objects
Authors: Photiadis Douglas
Published: October 2005

The scattering cross section of an extended elastic body is usually a very irregular function of frequency. This is partly due to the vibrational characteristics of the body and partly due to interference effects. The related problem of predicting the response of a body to localized excitation or a reverberent field has been analyzed using the statistical energy analysis and the mean value method with some success. In this paper, statistical methods are employed to predict aspects of the acoustic cross section of some relatively simple, extended objects.