bluuebunny/crossref_metadata_2025 huggingface dataset:
Objective: Evaluation of violin tone quality
Authors: Pickering Norman C.
Published: October 2005

A method has been developed for comparing violins by computer processing of the long-term one-third octave spectrum obtained while bowing the instrument in a rigidly prescribed program. At the same time, the sound pressure level of each semitone for the lowest three octaves is recorded. All the data obtained are analyzed by a program which assigns a figure of merit, derived from correlation with subjective evaluation of many instruments over several years of data accumulation. Results will be shown for some old Italian instruments, nineteenth century French and German violins, and some contemporary work.
Air modes in the violin
Authors: Hutchins Carleen M.
Published: October 2005

In 1972 the higher air modes of the violin, which radiate very little through the f-holes, were explored by Erik Janson [E. V. Jansson, “On Higher Air Modes in the Violin,” Catgut Acoust. Soc. Newsletter ♯19 (May 1973)]. He studied the standing wave patterns of these modes in a violin shaped cavity with rigid walls, and then recorded the first (A1) air mode frequency for six normal violins. The present study extends this work to include the A1–A2 and A3 higher air modes in more than 50 violins of a wide variety of styles ranging from 1595 to the present. The test method will be described and mode frequencies reported with selected examples discussed in detail, particularly in relation to evidence of coupling between the wood and these higher air modes.
Bayesian weight estimation for adaptive arrays
Authors: Earp S. L. , Nolte L. W.
Published: October 2005

Adaptive arrays are used in many underwater sound applications. Although there are algorithms available for updating the adaptive weight vector, most of them are obtained by considering the heuristics of a given application. In this work, an algorithm derived from a formal optimization procedure is presented. The algorithm is a recursive realization of a Bayes estimate for the weighting vector, and is in this sense optimal. Initialization of the algorithm, governed by prior knowledge of the problem, is also shown. Performance for selected situations is obtained by computer simulation, and the behavior of the algorithm as a function of several adjustable parameters is discussed in detail. [Sponsored by ONR Code 411SP.]
Detection performance in non-Gaussian environments
Authors: Zeferjahn Karen , Nolte L. W.
Published: October 2005

The detection performance of optimal processors in non-Gaussian environments is examined. A numerical method for computing likelihood ratios and the corresponding processor performance is developed with minimal restrictions on the probability density of the independent noise. This enables one to obtain the ROC rapidly for a wide range of non-Gaussian noise types. Results are presented for two different impulsive noise environments: (1) the Middleton Class A narrow-band noise model, and (2) a mixture model of normal and Laplacian noise. In addtion to the ROCs the detector nonlinearities are presented. Finally, a suboptimal processor (cross correlator) is compared to the optimal processor. [Sponsored by ONR Code 411SP.]
Factors affecting descending binaural loudness balance
Authors: Young I. M. , Lowry L. D.
Published: October 2005

The control continuous tone (1000 Hz) was presented in one ear starting at an intensity of 100 dB SPL with an attenuation rate of 1 dB per second by descending manner. The balancing comparison continuous tone (1000 Hz) was presented in the opposite ear also starting at 100 dB SPL with an attenuation rate of 5 dB per second. Three trained subjects with normal hearing were instructed to release the Bekesy switch to increase the loudness and to push the switch to reduce the loudness of the comparison tone. While there were inter-subject variations, our data indicated that there was continuous decrease in the ratio of balanced loudness levels between tones with attenuation rates of 5 dB per second and 1 dB per second as the functions of time and decreasing intensity. This is considered a manifestation of normal adaptation. Present results were compared with our previous reports for the threshold differences produced by different attenuation rates at the suprathreshold starting intensities.
Intensity discrimination in chinchillas
Authors: Shivapuja Bhagyalakshmi G. , Saunders Samuel S. , Salvi Richard J.
Published: October 2005

Previous research using amplitude modulated noise has suggested that the intensity discrimination thresholds of the chinchilla would be larger than those of humans. Consequently, intensity discrimination thresholds (ΔI) were measured in the chinchilla using a positive reinforcement technique. Intensity discrimination thresholds were obtained at several different frequencies over a range of sensation levels. In general the intensity discrimination thresholds improved as the sensation level increased. The smallest intensity discrimination thresholds obtained were approximately two to three times larger than those for humans. Furthermore, the effect of sensation level on intensity discrimination threshold was more pronounced in the chinchilla than in man. Results and their implications will be discussed.
Features of infant vocalization at successive age levels
Authors: Stark Rachel E. , Bond Jennifer L. , Bernstein Lynne E. , Heinz John M.
Published: October 2005

It has been suggested that speech motor abilities in infants emerge within an invariant sequence of levels. The present study was designed to describe the articulatory-acoustic features of infant vocalization and thus, to identify those that may be characteristic of infant utterances at different age levels or developmental levels. The vocalizations of five infants were studied on a limited longitudinal basis. The age ranges of these infants were 2–10, 12–23, 26–36, 40–55, and 72–88 weeks, respectively. Forty to 50 vocalizations were selected randomly from each infant's output at the first and at the last recording session for a total of ten recordings. These vocalizations were analyzed acoustically by means of computer-assisted spectral analyses. Measurements of duration and frequency were made from the resulting displays, which also provided information to listeners as they judged voicing and vocalic and consonantal features. Analyses of these preliminary data suggest that three classes of features may provide useful indices of development of infant speech motor abilities: namely, (1) pitch contour; (2) vocalic features; and (3) consonantal features. The relative importance of each will be discussed. [Work supported by Bureau of Community Health Services, Maternal and Child Health.]
A neuroethologic hypethesis of speech development
Authors: Bauer Harold R.
Published: October 2005

The relation between phonetic contrast and individual differences in infants was noninvasively measured to operationally state a hypothesis of speech development. Four 13-month-old infants were recorded interacting with their mothers at home. Continuous f0 and amplitude displays were used in analyses made by two observers from each 1-h, time coded session of all vocalizations. Acoustic-phonetic data were lumped into front, central, and back vocants and bilabial, apical, palatal, and velar closants to emphasize motor contrast. These seven categories of speech sounds were graphed by each minute in the Phonetic Record, and then multiplied within each minute sample to yield a Phonetic Product, as a production/contrast measure. Individual Phonetic Record and Phonetic Product populational differences in production and contrast were found in the temporal analyses that are hypothesized to be predictive of speech-language development. [Supported by NINCDS Grants NS 16763 and 5T32 NS 07147.]
Developmental speech perception of three acoustic cues associated with place of articulation
Authors: Sussman J. E. , Carney A. E.
Published: October 2005

In this experiment, 30 children and 10 adults participated in three speech perception tasks: discrimination, labeling, and adaptation. Stimuli were four sets of synthetic CV syllables, varying along a bilabial-to-alveolar, place-of-articulation continuum. The primary acoustic cue in each continuum was the change in slope of the F2–F3 transitions. The continua were constructed so that two had transition lengths of 45 ms, and two of 95 ms. Two continua contained a 5-ms burst, and two were burstless. The discrimination task was a change-no change procedure, in which subjects indicated whether a set of four stimuli remained the same or changed. Results indicated a complex developmental pattern. For discrimination, there was a progression in response strategy and sensitivity with increasing age. In contrast, labeling performance was similar for all subjects. Finally, only the adult subjects showed significant adaptation effects. Children's responses were essentially unchanged after adaptation. Further, transition length affected all three tasks, while the presence of a burst was nonsignificant. Results will be discussed with respect to implications for the study of children's speech perception.
Acquisition of the English voicing contrast by Arabic children
Authors: Fokes Joann , Bond Z. S. , Steinberg Marcy
Published: October 2005

Children are typically more proficient than adults in learning the phonetic detail of a second language. The purpose of this study was to investigate the acquisition of the English voicing contrast as cued by voice onset time in syllable-initial position comparing the performance of children whose native language is Arabic with that of American English speaking children and of adult speakers of Arabic learning English as a second language. Twelve children, 24 to 135 months in age, were recorded producing 11 minimal pairs differing in the voicing of the initial stop consonant, such as pea/bee and cab/gab. Voice onset time (VOT) was measured from spectrograms for labial, apical, and velar stops. Children were highly variable in their mastery of the voicing contrast; neither a child's age nor his experience with English could predict his phonetic proficiency.
Organization and timing of prephonatory movements in mild and severe stutterers
Authors: Watson Ben C. , Alfonso Peter J.
Published: October 2005

In a previous paper [J. Acoust. Soc. Am. Suppl. 1 73, S16 (1983)], we reported a composite foreperiod and stuttering severity effect on stutterers' acoustic laryngeal reaction time (LRT) values. That is, mild, but not severe, stutterers' LRT values approach nonstutterers' values as foreperiod increases. This observation lead to the formulation of the differential deficit hypothesis, which suggests that mild and severe stutterers execute qualitatively different prephonatory movements. In the study reported here, the differential deficit hypothesis was tested directly by examining movement and acoustic data obtained simultaneously from mild and severe stutterers and nonstutterers. The acoustic data replicated our previous results with respect to the composite foreperiod and stuttering severity effect on stutterers' LRT values. More importantly, movement data reveal that mild and severe stutterers can be differentiated on the basis of the organization, frequency of occurrence, and timing of prephonatory laryngeal and respiratory movements. That is, movement data both support the differential deficit hypothesis and account for the composite foreperiod and stuttering severity effect on stutterers' acoustic LRT values. [Work supported by NINCDS grant NS 13870 to Haskins Laboratories.]
Detecting and correcting mispronunciations: A note on methodology
Authors: Small Larry H. , Bond Z. S.
Published: October 2005

Two different techniques were employed to investigate subjects' ability to detect mispronounced words in continuous speech. Twenty two-syllable words were mispronounced in each of three prose passages, changing either the stress pattern, the voicing of obstruents, or the frontback dimension of vowels. Each passage contained only one mispronunciation type; the mispronounced words were equated for predictability from context and for frequency of occurrence in English. Subjects were tested under two conditions. In the first, subjects indicated mispronounced words on a script while listening to the passages. In the second, subjects were instructed to stop the tape when they detected a mispronounced word and to say what the word was. The subjects' spoken responses were recorded on tape. The first condition provides information regarding subjects' ability to detect mispronunciations under optimal conditions. The second condition provides detection information as well as information about the subjects' ability to correct the mispronounced words and the location of the detection in the stream of speech. The subjects' responses to stress mispronunciations were different from those to the other two mispronunciation types, in both test conditions.
An investigation of sound pressure level predictions in large lecture halls
Authors: Kahn David W. , Tichy Jiri
Published: October 2005

Measurements of steady-state sound pressure levels above the audience in large lecture halls show that the classical equation for predicting the sound pressure level is not accurate. The direct field above the seats was studied on a 1:10 scale model of a large lecture hall using the removable audience from the scale model. It was found to be dependent on the incidence angle and direction of sound propagation across the audience. The reverberant field above the seats was studied by subtracting the direct field from the measured field in the model. It was found to be dependent on the magnitude and particularly on the placement of absorption in the room. The decrease of sound pressure level versus distance in the total field depends on the angle (controlled by absorption placement) at which the strong reflections are incident upon the audience area. Sound pressure level decreases at a fairly constant rate with distance from the sound source in both the direct and reverberant field, and the decrease rate strongly depends on the absorption placement. The lowest rate of decay occurs when the side walls are absorptive, and both the ceiling and rear wall are reflective. The consequences are discussed with respect to prediction of speech intelligibility, and modifications are suggested for three current speech intelligibility prediction schemes.
Image method predictive acoustic: Shortcuts to computational time and infinite summation accuracy
Authors: Lemire Gilles , Nicolas J.
Published: October 2005

The image method can be used to predict the noise levels within rectangular halls. One of the drawbacks of this method is the lengthy computational time involved to reach a reasonable accuracy. Although the commonly used Allen and Berkley algorithm [J. Acoust. Soc. Am. 65, 943–950 (1979)] is excellent, we thought that an algorithm which would permit us to evaluate the sound level produced by each of the sources order would be useful. So we derived one, and information on each order contribution showed that, at high enough orders, the contribution of each order is independent of receiver location and that it varies linearly with the order number. It will be explained how these two findings can be used to reduce the computational time and yet approach the infinite summation accuracy. [Work supported by the Institut de Recherche en Santé et Sécurité du Travail.]
Guidelines for noise exposure: An analysis of 100-dB vs 90-dB ambient levels
Authors: Erdreich John
Published: October 2005

Among the various techniques available to reduce noise exposure, personal protective devices may be used to reduce worker exposure from 100-dB TWA to 90-dB TWA. From an analysis of risk statistics for workers exposed between 80 and 100 dB the effect of relying on personal protection in this range rather than to require source reduction to 90 dBA is shown to be a 20% increase in attributable risk of hearing loss and a doubling of the odds that an exposed worker will suffer an occupationally produced hearing loss.
Intermittence and the equal-energy theory
Authors: Ward W. Dixon
Published: October 2005

The “equal-energy” theory of noise-induced damage to the auditory system caused by habitual daily exposure postulates that the degree of damage depends only on the total amount of energy absorbed by the ear during the workday, and not on the temporal pattern of the noise. To test this hypothesis, two groups of chinchillas were exposed to 700–2800-Hz noise at 102-dB SPL, Monday through Friday, for 9 weeks. One group received a single daily 48-min continuous exposure; the other was given 40 1.2-min exposures, one every 12 min. The intermittent exposure produced significantly less temporary threshold shift, permanent threshold shift, and histological damage. Comparison with other chinchilla data indicates that the degree of reduction in hair-cell destruction, for this pattern of intermittence, is consistent with the trading relation of 5 dB per halving of exposure duration still used in the USA for assessing daily exposure, rather than the 3 dB required by the equal-energy-based ISO recommended standard R-1999. [Work supported by NIH Grant NS 12125.]
Hyperthermia: Its role in the production of tissue damage induced by high intensity focused ultrasound
Authors: Borrelli Michael J. , Dunn Floyd
Published: October 2005

Tissue damage resulting from irradiation of adult cat brain with varying exposure of focused 1-MHz, 300-W/cm2 intensity ultrasound was examined with electron and light microscopy, and thermocouples were used to record the ultrasonically induced temperature changes. Identical exposures produced both more tissue damage and a higher peak temperature in white than gray matter. Cultured BHK cells were heated at temperatures corresponding to the peak temperatures recorded by the tissue-embedded thermocouples. Electron microscope observations of the heated cells revealed that for temperatures less than 57°C, the heating time required to elicit morphological changes was significantly longer than the ultrasonic exposure times which produced an identical peak temperature yet induced tissue damage within the cat brain. These results suggest that tissue damage resulting from the ultrasonic exposures shorter than 3–4 s was not strictly the result of the ultrasonic hyperthermia. The degree of hyperthermia apparently does, however, influence the degree of tissue damage, as evidenced by the differences observed between the damage in identically irradiated white and gray matter. [Supported in part by NSF and NIH.]
Assessment of vibrational effects by ultrasound on biological targets at low temperatures
Authors: Himberger Douglas E. , Malinin George L. , Mayer Walter G.
Published: October 2005

Biomedical applications of ultrasound are generally regarded to be reasonably safe. However, under certain conditions, the functional and structural integrity of biological targets can be severely impaired by ultrasound. Tissue damage by insonication can be brought about concurrently by thermal and by vibration-induced mechanisms. Whereas thermal effects have been characterized extensively, virtually nothing is known about vibration-induced damage. The problem is compounded by practical impossibility of separating the two effects at ambient temperatures. In order to assess only vibrational effects of ultrasound we have developed and tested a system for insonication of biological targets at 77°K in liquid nitrogen. Isolated human erythrocyte membranes (ghosts) frozen in the presence of 10% dimethysulfoxide (DMSO) in phosphate buffered saline (PBS) were irradiated with ultrasound ranging in frequency from 3 to 7 MHz and intensities between 2 and 24 mW/cm2. Thawed control and insonicated ghosts were then analyzed by sodium dodecylsulfate (SDS)-polyacrylamide gel electrophoresis for changes of membrane protein components. Preliminary results are presented. [Work supported in part by the Office of Naval Research, U.S. Navy.]
Progress in our understanding of forward acoustic scattering
Authors: Ewart T. E. , Uscinski B. J.
Published: October 2005

Recent solutions of the parabolic fourth moment equations, pioneered by Shishov have led to good predictions of the power spectral density of temporal intensty fluctuations as meaured in the Cobb71 and MATE experiments for a wide range of scattering parameters. Comparison of Monte-Carlo solutions of the parabolic wave equation with the above predictions for the vertical spatial fluctuations of intensity produces excellent agreement between simulations and theory. The discrepancies between experiment and theory which remain appear to be due to our lack of understanding of the index of refraction field itself. The intensity moments mq, q > 2 of a propagating wavefield in a random medium exhibit log-normal behavior at short ranges when observed as a function of m2; subsequently they rise to a maximum in the second moment and then drop back at long ranges to the exponential moments. The shape of the moment curves and their point of departure from log-normal are dependent on the specific correlation function of the index of refraction. Prediction of the higher moments using a model which spans the regime between log-normal and exponential, and is based on the m2 and m3 moments as parameters, has proved quite successful at explaining the Cobb71, MATE, AFAR, and SW Bermuda results. Thus, if a theoretical prediction of m3 can be obtained, the probability distribution and the spectral decomposition of the lower moments of intensity fluctuations due to forward scattering should be predictable in the parabolic approximation. The development of the theory-experiment comparisons will be presented and so will the authors views on what else needs to be measured for a complete test of the current theories.
Two-scale solutions for intensity fluctuations in strong scattering
Authors: Frankenthal Shimshon , Whitman Alan M. , Beran Mark J.
Published: October 2005

An exact integrodifferential equation is derived for a certain transform of the 4-point coherence function, using a two-scale embedding procedure. The solution is expanded in an asymptotic series in the inverse strong scattering parameter, whose terms are solutions of a hierarchy of simple first-order partial differential equations. Further approximations simplify the retransformation, and display the 4-point coherence in a useful, numerically convenient form. Results compare favorably with existing numerical computations of the scintillation index and the covariance in two-dimensional plane-wave propagation. Results for three-dimensional plane-wave propagation are also presented.
High-frequency acoustic scattering from stratified turbulence
Authors: Lintz Andrew , Dube C. M.
Published: October 2005

A laboratory study of high-frequency acoustic scattering from stratified turbulence was performed in order to test the theories and techniques used for the prediction of acoustic scattering. Scattering predictions were made with a computer simulation code which incorporates Lane's hydrodynamic model of stratified turbulence with the relevant aspects of linear scattering theory. Laboratory acoustic measurements were made for a range of acoustic system parameters, including forward scatter in the vertical and horizontal planes, and vertical backscatter. Hydrodynamic characterization of the sound speed spectrum was made with traversing conductivity probe arrays and with quantitative optical shadowgraphs; the data were then used to define the turbulence model parameters. The analytical techniques used to extract the hydrodynamic model parameters from both conductivity and shadowgraph data gave consistent results, and verified the Lane model as a valid descriptor of stratified turbulence. Theoretical acoustic scattering level predictions made with the simulation code are in good agreement with the laboratory acoustic measurements. These results verify the laboratory measurement techniques and validate our implementation of linear scattering theory and Lane's turbulence model for predicting acoustic scattering from stratified tubulence. [Work supported by Navy SSPO and Dynamics Technology internal R&D funding.]
High-frequency propagation through a turbulent thermal plume
Authors: Posey Joe W. , Levenson Coleman
Published: October 2005

High-frequency acoustic signals were propagated in a large water tank over a fixed range which included a turbulent thermal plume of variable thickness. The signals were 1-ms cw pulses in the frequency range 0.8 to 2.0 MHz. The repetition rate was one pulse per second, and the propagation range was 10.4 m. The thermal plume was created by activating all or part of an array of heating elements wheh ran the full length of the propagation path about 1.5 m below it. Five different heating configurations were investigated by energizing portions of the heat array: (1) the one third nearest the projector, (2) the one third nearest the receiver, (3) the two thirds nearest the projector, (4) the two thirds nearest the receiver, and (5) the entire array. It was found that the incoherent energy fraction of the received signals (measured over 2-min intervals) did not depend upon the position of the plume along the propagation path. Furthermore, observed fluctuations are in good agreement with the Wenzel theory if the length of the propagation path through the plume is used as the range.
Volume scattering: Echo peak PDF
Authors: Stanton T. K.
Published: October 2005

The probability density function (PDF) of the maximum echo value achieved in a depth gate has been analytically derived, computer simulated, and measured in the field—all in cases where clouds of scatterers are involved. The clouds of interest are plankton, nekton, bubbles, etc. or a combination and are sufficiently dense so that echoes from the individual scatterers overlap. We show that this echo peak PDF is quite different than the Rayleigh PDF of the envelope, even for gate lengths smaller than one transmission pulse length. We have employed measured PDFs by (1) estimating the abundance of occasional large scatterers that are within the clouds (for example large fish feeding on plankton) since their occurrence is differentiable from the rest of the cloud in the PDF, and (2) clearly differentiating between conditions where the echoes overlap and do not overlap. Once it is determined whether or not they overlap, lower or upper bounds in scatterer density (number per unit volume) may be calculated. We have utilized both of these techniques in situ at the Gulf Stream Boundary near Cape Hatteras, NC where we observed continuous distributions of plankton and nekton. [Work supported by the ONR.]
Acoustic surveys for marine mammals using a towed hydrophone array
Authors: Thomas Jeanette A. , Fisher Sheldon R. , Ferm Lisa M.
Published: October 2005

For the purposes of identifying and locating marine mammals by their sounds, we designed a broadband linear array of hydrophones that is towed from a survey vessel. This array is a modification of the low-frequency arrays currently used by the military and the geophysical industry. The array has been used during four studies: one offshore California, two in the eastern tropical Pacific, and one on a circumnavigation of Antarctica. Comparisons of visual and acoustic detections of marine mammals will be discussed. During one cruise as many as 32% of the marine mammals encountered were detected by the array, but not by observers. Factors affecting reception and detection of marine mammals will be discussed. We conclude that combining visual and acoustic surveys may produce more accurate species identifications and estimates of abundance for marine mammals.
Autoregressive modeling of pulse-to-pulse incoherent Doppler sonar data
Authors: Hansen D. Scott
Published: October 2005

An innovative approach to modeling the range evolving spectral structure of pulse-to-pulse incoherent Doppler sonar data is presented. This approach is demonstrated on a unique multifrequency, parallel beam oceanic data set. The approach is motivated by the desire to determine the parameters of the oceanic velocity field. Under a set of assumptions the mean frequency of the Doppler spectrum can be used to infer the velocity field of the oceanic water mass on a range evolving basis. If the Doppler spectrum is symmetric and unimodal, this mean freqency may well characterize the Doppler shift from which the relative radial velocity between the sonar platform and a dense “cloud” of scatterers may be derived. However, the Doppler spectrum may be multipeaked and/or asymmetric due to the nonhomogeneous nature of the reverberation process, instrumental effects, or beam pattern structure. In this case the mean frequency may have little relation to the Doppler shift associated with the true scaterer-platform velocity. To aid in interpretation, the data are modeled spectrally on closely spaced range intervals via autoregressive (AR) techniques. Interpretation of these AR spectra may lead to a determination of the velocity field and/or to the causative mechanism of anomalous spectral structure. In the case anomalous spectral structure is found, careful interpretation of the spectra is necessary to determine the velocity field. Two regions of the multifrequency, parallel beam data set are analyzed to demonstrate the relationship between the mean frequency and AR techniques. The first of these regions is shown to possess a unimodal, symmetric spectral structure on a range evolving basis. In this region the mean frequency profiles are shown to agree closely. In the second region, which is shown to possess an asymmetric spectral structure, the mean frequency velocity profiles are shown to agree poorly. Interpretation of the spectra leads to closer agreement between the velocity field as seen by the two parallel beam sonars.
Coherent acoustic Doppler measurement of estuarine internal waves
Authors: Clarke T. L. , Craynock J. F. , Proni J. R.
Published: October 2005

A bottom-mounted 200-kHz narrow beam coherent acoustic Doppler system was used to observe profiles of vertical water velocity in Chesapeake Bay (17-m water depth) near the mouth of the Patuxent river in August 1982. Internal wave induced vertical water motion was up to 2 m as shown by observation of biological scattering layers. Coherent Doppler measurements gave vertical water velocities of several centimeters per second. The scattering layer motion and the velocity were in phase quadrature and the amplitudes were consistent with propagating internal waves. Of several types of internal waves seen, the most common were simple interfacial waves on the pycnocline, but some instances of higher mode waves were observed: Soliton wave packets were also seen. Problems of signal processing and of removing the aliasing resulting from the use of pulse-to-pulse coherent Doppler processing are also discussed. Fairly simple modifications to standard scientific echo sounders make it possible to extract vertical velocity profiles from recorded signals using coherent signal processing.
Doppler spread and temporal coherence of high-frequency volume reverberation
Authors: Tappert F. D.
Published: October 2005

The wave kinetic technique of radiation transport theory has been used to derive a theoretical expression for frequency spread, and hence temporal coherence, of high-frequency volume reverberation from particulate matter entrained by oceanic turbulence. The following effects are taken into account: intrinsic Doppler spread due to turbulent motion, Doppler due to platform motion, transit-time broadening due to transmitter and receiver beam patterns in both nearfield and farfield, and broadening due to finite transmitted pulse length. With additional simplifying assumptions (Gaussian beam patterns, Gaussian velocity distribution, etc.), explicit results are obtained for estimating temporal coherence of volume reverberation.
A point-scatterer model for the spatial-temporal covariance of reverberation
Authors: Wilson Gary R.
Published: October 2005

A point-scatterer model of reverberation was developed to predict the spatial and temporal covariance of surface reverberation for both horizontal and vertical receiver separations. The point scatterers are modeled as perfect point reflectors with no frequency spreading. The distribution of scatterers was chosen to be representative of a sub-surface bubble layer, which is appropriate for high-frequency scattering at high wind speeds. Comparison to experimental measurements of reverberation covariance at 80 kHz indicates that projector (and receiver) beamwidths are the primary factors determining the horizontal spatial coherence, and not waveheights or sub-surface bubbles. However, it was found that to adequately model the vertical spatial covariance the bubble layer distribution was required, suggesting that the dominant scattering mechanism was sub-surface bubbles rather than the air-water interface, at least at the high wind speeds associated with the vertical covariance measurements. The temporal covariance was also predicted and found to be in excellent agreement with the measured temporal covariance for the short pulse lengths used in the experiments. The pulse length and transfer functions of the projector and receivers were found to be the dominant factors affecting the temporal covariance for short pulse lengths.
Scattering of Rayleigh waves by an arbitrarily oriented sub-surface crack
Authors: van der Hijden J. H. M. T. , Neerhoff F. L.
Published: October 2005

The diffraction of acoustic waves by a crack in an unbounded elastic medium has been extensively discussed in the literature. For practical purposes the problem in a semi-infinite solid is a more realistic one. A rigorous theory of the diffraction of time-harmonic elastic waves by an arbitrarily oriented, cylindrical, stress-free crack of finite width embedded in a semi-infinite elastic medium has been developed. The incident wave is taken to be either a P wave, an SV wave, or a Rayleigh wave. The resulting boundary-value problems for the unknown jump in the particle displacement across the crack are solved by employing the integral-equation method in combination with the Galerkin method. Numerical results are presented in the form of normalized power scattering characteristics, dynamic stress intensity factors, and Rayleigh-wave transmission and reflection coefficients, for a range of geometricai parameters. The most striking feature in the scattering characteristics are the sharp peaks that occur for scattered shear waves, for which an explanation will be given.
The transition matrix in prolate spheroidal coordinates
Authors: Hackman Roger H.
Published: October 2005

At the 105th meeting of the Acoustical Society of America, a preliminary calculation of the acoustic scattering from a solid elastic prolate spheroid in water was presented. This calculation, which was based on a separation of variables technique in prolate spheroidal coordinates, can now be shown to be incorrect. In a recent paper [Hackman, J. Acoust. Soc. Am. 75, 35–45 (1984)], Betti's third identity was used to establish a spheroidal coordinate based transition matrix. This approach succeeds where the earlier work failed. Since this latter work is a true T-matrix approach, scattering by arbitrarily shaped bodies can be described. This work possesses a distinct advantage over the standard spherical coordinate based T matrix in that the formalism can be explicitly tailored to the aspect ratio requirements of the scatterer. Calculations are presented by the two T-matrix approaches and their rates of convergence are compared. The reasons for the failure of the earlier work is also discussed.
A comparison of acoustical scattering from fluid loaded elastic shells and sound soft objects
Authors: Werby Michael F. , Green Larry H.
Published: October 2005

Comparisons are presented for acoustical scattering from fluid loaded prolate spheroidal sound soft scatterers and elastic shells of the same shape ranging in thickness from 0.1% to 2.5% of the semi-major axis. The Ka region being studied varies from 3–12 where K is the wavenumber of the incident wave and a is one-half the length of the major axis. Exact theoretical calculations are performed using a modified T-matrix approach which allows one for the first time, to perform calculations on very thin nonspherical elastical shells. The calculations show that with the exception of the very thin shell, one does not observe a sound soft background. Furthermore, resonances for these objects are very broad and tend to dominate the form function plots. Of particular interest is the fact that by the time one reaches a thickness of 2.5% the background begins to appear rigid with a shift in resonance nulls which is related to the fact that rigid scattering is out of phase with sound soft scattering by 180°.
An orthonormalization method for solving the time harmonic acoustic scattering from finite, smooth, solid, elastic bodies
Authors: Dallas Alan , Gaumond C. F.
Published: October 2005

The null field integral equations [P. C. Waterman, J. Acoust. Soc. Am. 45, 1417–1429 (1969); A. Bostrom, J. Acoust. Soc. Am. 67, 390–398 (1980)] are solved using orthonormalization in the appropriate Hilbert Space. An interior limiting amplitude principle is developed to identify the unique interior elastic field in the long time limit. The result is an algorithm for computing the scattered acoustic and interior elastic field which requires no matrix inversions.
Complex eigenfrequencies of rigid and soft spheroids
Authors: D'Archangelo J. M. , Savage P. , Überall H. , Yoo K. B. , Brown S. H. , Dickey J. W.
Published: October 2005

The complex eigenfrequencies of impenetrable or penetrable target objects form a pattern which is characteristic for a given target, as far as its shape and/or composition is concerned. They manifest themselves as poles (resonances) in the amplitude of waves scattered from the object. We here obtain the eigenfrequency patterns of acoustically rigid and soft prolate spheroids in the complex frequency plane, and study their displacement when the eccentricity of the spheroids is varied. The eigenfrequencies were obtained numerically by subjecting spheroidal wavefunctions to the Neumann or Dirichlet boundary condition, respectively. Poles of both m = 0 (axial vibrations) and m ≠ 0 (vibrations with azimuthal components) were obtained, and axes ratios of 1:1 (sphere), 1.33:1, 2:1, 3:1, 5:1, and 10:1 were considered. Increasing axes ratios lead to increasing splittings between poles with different m values. [Supported in part by the David W. Taylor Naval Ship R&D Center, Annapolis, MD 21402.]
A solution of multiple scattering problem by method of spatial stochastic systems. I. Discrete scatterers with arbitrary shape. II. Discrete scatterers and random interface. III. Two random irregular interfaces
Authors: Liu K. C. , Varadan V. K. , Varadan V. V.
Published: October 2005

This paper is an application of the “Spatial stochastic system theory” [K. C. Liu, J. Sound Vib. 79(3), 321–339 (1979); 80(4), 473–498 (1982)] to the problem of multiple scattering. It consists of three parts: (1) multiple scattering of randomly distributed discrete scatterers with arbitrary shape, (2) multiple scattering between discrete scatterers and a random irregular interface, and (3) multiple scattering between two random irregular interfaces. For these cases, a general expression for the space correlation function and intensity of the multiple scattered field is derived under very weak constraints. By means of these expressions, the space correlation functions and intensities of the multiple scattered fields caused by any kind (plane or spherical or others) of monochromatic incident wave can be calculated as long as the scattering property of each scatterer (for the first case) or each scatterer and the random interface (for the second case) under plane monochromatic incident wave and the density function and the probability distribution of orientation of the scatterers are given. This calculation consists of only a single integration, a single summation, and some convolution operation. Some examples are considered and results will be presented for a uniform distribution of spherical particles in the presence of random irregular interfaces.
Iterative approaches in overcoming the instabilities of the T-matrix method for scattering by nonspherical objects
Authors: Lakhtakia Akhlesh , Varadan Vijay K. , Varadan Vasundara V.
Published: October 2005

The T-matrix method, although very popular to examine single-particle scattering, becomes very unstable for highly nonspherical objects and/or at high frequencies. In this paper we show how two different iterative schemes can be used to reduce these instabilities significantly. The first scheme is suitable for nondissipative objects and utilizes a priori the properties of the T-matrix and orthogonalization procedures to generate a stable T matrix for the computation of the scattered field. In the second scheme an initial “aproximate” solution is used to reduce the size of the resulting matrices and the field on the object surface is computed iteratively until it stabilizes. Numerical results pertaining to acoustic, electromagnetic, and elastic scattering phenomena are presented to illustrate the strengths of these two schemes.
Fundamental relationships for the active and reactive acoustic intensity and their relationship with the acoustic energy density
Authors: Tichy Jiri , Elko G. W.
Published: October 2005

This paper will discuss the physical meaning of the active and reactive components of the acoustic intensity and the mathematical relationship with other sound field quantities, mainly, potential and kinetic energy. Examples of intensity fields for simple and complex sources will be presented and the interpretation and applications on some radiation and propagation problems will be shown.
Measurement of the complex acoustic intensity, the kinetic energy, and the potential energy in a reflective environment
Authors: Elko G. W. , Tichy Jiri
Published: October 2005

A four microphone intensity probe array has been designed and used to measure two components of the active and reactive acoustic intensity vector. The probe is also used to measure two components of the kinetic energy and the potential energy. Measurements of a point source above a reflecting plane and near the edge of two large reflecting planes were made. These results will be presented and the effects of sensor spacing, probe rotation, proximity of probe to source and boundary, and sensor phase error will be shown and the results will be compared to theoretically predicted values.
A review of the in-duct method for measuring acoustic intensity and acoustic properties of materials and systems
Authors: Seybert A. F.
Published: October 2005

The decomposition theory [Seybert and Ross, J. Acoust. Soc. Am. 61, 1362–1370 (1977)] is reviewed and some new results applicable to problems in measuring acoustic intensity and acoustic properties in plane-wave ducts are presented. Specifically, it is shown that formulations for the net acoustic intensity and for the so-called transfer function approach of measuring acoustical impedance proceed directly from the general decomposition theory. Potential sources of signal processing and instrument errors are discussed, as are methods for instrumentation phase calibration. Experimental data showing the application of the decomposition technique to acoustic intensity and property measurement are presented.
Applications and experience with a portable microcomputer system controller and programmable sound level meter/frequency analyzer
Authors: Hessler George F.
Published: October 2005

Today's availability and affordability of small truly portable, transportable, and desktop model microcomputers, with the power of recent minicomputers, make them ideal system controllers. The fundamental advantage of such a system is the ability to acquire massive amounts of measured data, perform complex and custom analysis, and format and present useful engineering results, all in near real time. A typical data acquisition and analysis system for sound level applications would consist of a computer controller interfaced with a programmable sound level meter and optional printers/plotters/noise sources, etc. This paper discusses experience and applications with a system comprised of a Hewlett-Packard transportable computer model HP 85 interfaced with a Larson-Davis laboratories model 800 programmable type 1 precision and sound level meter and 1/3–1/1 oct analyzer. Areas discussed are interface types and basic programming language routines for setting up the measurement and acquiring data on command. Application examples are routine steady-state and time varying sound level data acquisition, individual and cumulative aircraft flyover recording, and measurement of transmission loss and noise reduction in building wall structures.
Sound transmission through honeycomb stiffened panels
Authors: Grosveld Ferdinand W. , Mixson John S.
Published: October 2005

If the fundamental vibrational modes of the sidewall fuselage panels of a propeller driven aircraft coincide with highest excitation levels (at the propeller blade passage frequency and its harmonics), interior noise levels are adversely affected. To investigate experimentally how the increase in stiffness relates to the change in resonance frequency, various configurations of honeycomb stiffened panels have been tested in the NASA Langley Transmission Loss Apparatus. From the test results the effects of core thickness and the thickness of the facing material could be established. The change in resonance frequency was accurately determined by a modal analysis employing an impulse hammer and an accelerometer. The test results indicate that stiffening a panel with honeycomb material can shift the fundamental panel resonance frequency such that it no longer coincides with the frequencies of highest excitation. At low frequencies, this provides a potential noise control technique for propeller driven aircraft with a smaller weight penalty than encountered with conventional noise control methods.
Transition from simultaneous to forward masking
Authors: Weber Daniel L.
Published: October 2005

A stimulus condition in which the signal presentation partially overlaps the end of the masker presentation is intermediate between a simultaneous masking condition (complete overlap) and a forward masking condition (no overlap). The question is, “What process underlies signal detection in this condition?” To answer this question, this experiment examines the masked threshold for a 20-ms, 1-kHz sinusoidal signal (20-ms cosine-squared ramps with no steady state) as a function of the temporal position of the signal with respect to a 400-ms, 1-kHz, 70-dB SPL sinusoidal masker (quadrature phase, 0-ms ramps). These thresholds are compared to those obtained for the portion of each signal which occurred after the masker; these “partial” signals had 1-ms onset ramps which rose during the final 1 ms of the masker; the beginning portion of the 20-ms signal (the portion which overlapped the masker) was eliminated. When the threshold for the whole signal equals the threshold for the partial signal (which necessarily is determined by the process of forward masking), one may easily argue that the “simultaneous” portion of the signal did not measurably influence signal detection. The data show that signal thresholds in transition conditions are determined by forward masking for stimulus overlaps as great as 90%. [Research supported by NSF and NIH.]