bluuebunny/crossref_metadata_2025 huggingface dataset:
The reduction of binaural interference by the temporal nonoverlap of components
Authors: Stellmack Mark A.
Published: October 2005

Threshold interaural delays were measured for a single interaurally delayed 753-Hz target component presented against a background of six diotic distractor components (453, 553, 653, 853, 953, and 1053 Hz). In one set of conditions, all components were gated on simultaneously, but 200-ms after their onset the distractors were turned off for 10, 25, 50, 100, or 200 ms, then turned on again for the remainder of the 500-ms listening interval. In a second set of conditions, the target component was present only during the temporal notch in the distractors for notch durations of 50, 100, and 200 ms. Threshold interaural delays were also measured for the target component in isolation at durations of 50, 100, 200, and 500 ms. In both sets of conditions in which the distractors were present, it was observed that a brief isolated presentation of the target reduced threshold interaural differences of time to nearly the level of thresholds for the target presented in total isolation, while thresholds were many times higher when the distractors had no temporal notch. Possible sources of binaural interference are discussed and the evidence supporting each is evaluated.
Relation between the growth of loudness and high-frequency excitation
Authors: Hellman Rhona P.
Published: October 2005

To test the conjecture that cochlear impairment and a masking noise in normal ears produce analogous effects on the growth of loudness, loudness was measured for 21 listeners, all with bilateral symmetrical high-frequency cochlear losses. Beyond the normal-hearing region, thresholds increased by 30–49 dB/octave for 10 listeners in group I and by 51–71+ dB/octave for 11 listeners in group II. Measured by absolute magnitude estimation and production at two frequencies where thresholds were normal, the dynamic range over which loudness grows was not altered by the adjacent hearing loss. This was not true however, for the slope. Whereas the overall shape and slope of the loudness functions were essentially the same for group I, the mid-to-high level slope for group II was noticeably flatter for a tone at the cutoff frequency than for a lower-frequency tone. In contrast, markedly steeper loudness functions, characteristic of loudness recruitment, were obtained for both groups at a frequency in the region of impaired hearing. The reduced rate of loudness growth observed in the region of normal hearing for listeners with steep low-pass losses, like the reduction usually found for a tone masked by an adjacent high-frequency noise, is ascribed to the tone’s restricted excitation pattern. These results indicate that high-frequency auditory cues are effectively eliminated by a steeply sloping high-frequency hearing loss just as they are eliminated by the addition of an external noise.
Frequency and frequency-ratio resolution by possessors of absolute and relative pitch: Examples of categorical perception?
Authors: Burns Edward M. , Campbell Shari L.
Published: October 2005

The methodology derived from the trace–context theory of intensity resolution (Durlach and Braida, 1969; Macmillan et al., 1988) was applied to resolution over an octave range along two continua: a sequential-frequency-ratio continuum for possessors of relative pitch (RP), and a pure-tone frequency continuum for possessors of absolute pitch (AP). The performance of both RP and AP possessors was exceptional in that total identification sensitivity along both continua was much greater than identification sensitivity along unidimensional psychophysical continua characterized by the 7±2 rule. In addition, the performance of RP possessors was exceptional in that, on average, total sensitivity for identification resolution was greater than sensitivity for resolution in discrimination. Finally, identification sensitivity between category prototypes (chromatic semits) along both continua was approximately the same as identification sensitivity between phonemic category prototypes along speech continua, despite the fact that both the discrimination ranges and the total number of categories are much larger for the two pitch continua.
Loudness level versus sound-pressure level: A comparison of musical instruments
Authors: Miśkiewicz Andrzej , Rakowski Andrzej
Published: October 2005

Loudness levels (LL) of musical scale segments played pianissimo and fortissimo were predicted for 11 orchestral instruments, using Zwicker’s and Stevens’ Mark VI procedures for loudness calculation. The results show that the dynamic LL range of musical instruments depends not only on the dynamic sound-pressure level range, but is also influenced by changes in the spectral envelope that accompany the dynamic gradations of sound. As the sound is played louder, its bandwidth extends to high frequencies, and the increase in sound-pressure level (SPL) is greater for the high partials than for the low ones. Due to spectral loudness summation, the changes in spectral envelope with playing level enhance the dynamic LL range of the sound. As a consequence, for most instruments the dynamic LL range in a given pitch register is larger than the dynamic SPL range in that register. The difference between the two ranges was found to be greatest for brass instruments and for the clarinet, and approached about 6 dB in certain pitch registers.
Comodulation masking release for single and multiple rates of envelope fluctuation
Authors: Eddins David A. , Wright Beverly A.
Published: October 2005

Two experiments are presented that investigate the influence of envelope fluctuation rate upon the magnitude of comodulation masking release (CMR). In Experiment 1, thresholds were measured for a tonal signal centered in either one or five masker bands. The maskers were either narrow-band noises or 100% sinusoidally amplitude-modulated (SAM) tones. The five masker bands had either the same (coherent) or different (incoherent) envelopes. Envelope rate was varied by manipulating either the noise bandwidth (10–200 Hz) or the SAM rate (10–128 Hz). The CMR values were largest for slow envelope rates. In Experiment 2, envelope coherence was simultaneously manipulated at two rates by amplitude modulating (10 Hz) narrow-band noises (100 Hz). The modulation depth was 100%, 83%, or 50%. The CMR based on the coherence of the noise carriers was about 5 dB, regardless of the SAM coherence or the modulation depth. The CMR based on the SAM coherence decreased from about 19 to 2 dB as modulation depth decreased, regardless of the noise-carrier coherence. Thresholds were highest when the envelope fluctuations were incoherent at both rates and were lowest when the envelope fluctuations were coherent at both rates. These data suggest that the auditory system is able to make across-frequency envelope comparisons at both envelope rates simultaneously.
ASHRAE sound and vibration technical committee position statement on the use of fiberglass in HVAC systems
Authors: Cooper Russell A.
Published: October 2005

Fiberglass duct liner continues to be the most cost-effective solutions to noise control in most HVAC air duct systems. There has been a recent increase in the number of institutional, educational, and medical projects for which the use of fiberglass has been banned or severely limited. The decisions are based on concerns that the fibers may be carcinogenic and that the products may promote microbial growth. This paper will present the ASHRAE TC2.6 (Sound & Vibration) technical committee’s response to these developments, describe the state of the medical research and briefly outline alternatives and the consequences of duct lining removal from HVAC systems.
Nonfibrous air and gas flow silencers and sound absorbers
Authors: Hirschorn Martin , Ingard Uno
Published: October 2005

Post-WWII jet aviation, air conditioning, quieter working and living conditions, and OSHA legislation necessitated new noise control products largely based on fibrous sound absorptive materials. In June 1994 the U.S. Department of Health and Human Services announced that fiberglass is a material ‘‘reasonably anticipated to be a carcinogen.’’ Nonfibrous silencers, noise suppressors, and sound absorbers have already been developed, for reasons unrelated to this announcement, for over 40 years—longer when automobile mufflers, Maxim silencers, and Helmholtz resonators are considered. Nonfibrous aircraft ground jet engine noise suppressors provide superior acoustic performance and durability. Nonfibrous HVAC silencers and sound absorbers are used in medical operating rooms and others requiring a risk-free environment. The design of nonfibrous silencers, rooms, sound absorbers, and encapsulated fiber designs for various acoustical requirements will be discussed. Most sound absorptive materials lend themselves well to mathematical modeling. Absorption characteristics of a variety of future absorber configurations, including their nonlinear behavior in intense sound fields, will be presented. Such designs are often perfected by means of laboratory models tests, with airflow if applicable, before finalization. For certain nonfibrous duct liners, the possibility of negative insertion loss must be considered.
Effects of salinity on the acoustics of bubble plumes
Authors: Orris Gregory J. , Nicholas Michael
Published: October 2005

A previous paper [ 2826(A) (1993)] presented acoustic data collected near bubble plumes of various void fractions and sizes produced by varying the flow velocity of a water jet impinging normally on a water surface. Subsequent analysis has revealed that the data’s spectral content varies considerably between the two phases of the experiment—one involving fresh water in Lake Washington and the other involving salt water in Puget Sound. In the fresh-water portion of the experiment the spectra are completely dominated by modes corresponding roughly to the gross dimensions of the plume. In the salt-water portion of the experiment, the salts and other contaminants (which act as surfactants and lower the surface tension) dramatically reduce the mean bubble size with respect to that of fresh water. The acoustic data from the salt-water experiment are drastically different from that of the fresh water, and show little or no modal structure. For this particular physical situation it is suggested that the dominant acoustic generation process is likely to be turbulence. Furthermore, differences in the acoustic signatures of the experiment could be exploited to determine, amongst other things, the concentration of the salts and contaminants.
A semianalytical method for the noise emission of finite size objects in shallow water
Authors: Oguz Hasan N.
Published: October 2005

Point sources are commonly used in underwater ambient noise computations to model wave breaking noise. A semianalytical solution to sound emission by a finite size object in shallow water is developed. The coefficients of the normal modes obtained by this technique are compared with the coefficients given by the point source approximation for the case of a hemispherical bubble cloud. The comparison is only good when the size of the bubble cloud is much smaller than the acoustic wavelength. Substantial differences occur when the radiation pattern near the bubble cloud deviates from a circular shape associated with the point dipole emission. Accurate normal modes coefficients given by the current method could be coupled with shallow water propagation models used in ambient noise calculations. [Work supported by the Office of Naval Research.]
Using shear waves to predict the liquefaction potential of seafloor sediments
Authors: Pyrah James , Davis Angela
Published: October 2005

There is growing evidence to support the use of the seismic shear wave velocity as a predictor of seafloor sediment liquefaction potential. At the University College of North Wales laboratory experiments are being performed to determine the steady-state characteristics of a variety of noncohesive sediments. The conventional laboratory approach involves an investigation of void ratio/effective stress relationships, and provides an indication of the sediment’s likely behavior—contractive or dilative—when subjected to cyclic shear stresses such as those imposed by earthquake or water wave loading. In the tests currently being carried out at UCNW, the shear wave velocity is also being monitored to establish velocity/void ratio/effective stress relations which offers the possibility of extrapolating the laboratory findings to the field situation. Thus given a knowledge of the insitu shear wave velocity, grain characteristics, and static stress regime, it becomes possible to provide an estimate of the sediment’s stability under cyclic load conditions.
Determination of vertical correlation lengths in a channel using SWELLEX-1 thermistor data
Authors: Barnard T. , Beran M. J.
Published: October 2005

In order to properly determine the volume scattering in a channel, it is necessary to know the characteristic vertical and horizontal correlation lengths associated with the random index-of-refraction fluctuations. The results we have obtained for characteristic vertical correlation lengths using SWELLEX-1 vertical-array thermistor data are discussed. The data have been analyzed for day-time and night-time observations. In addition, the results are dependent upon averaging times and this effect is discussed. Graphs are given for the standard deviation and normalized cross correlations of the fluctuations, as a function of depth. [The vertical temperature data analyzed in this presentation were produced by NRL Code 7120 and NRAD Code 541 under ONR sponsorship. The data were supplied to us by B. Pasewark of NRL Code 7120. Our analysis was supported by ONR.]
Noise reduction of an experimental pulse combustion work station
Authors: Zimmer Jeffrey A. , Collier Robert D.
Published: October 2005

Pulse combustors are pulsating acoustical systems which radiate high-intensity radiated noise. The Forbes energy engineering experimental pulse combustor was operated in a ‘‘high pressure mode’’ at a fundamental frequency of 50 Hz and an output between 330 000 and 390 000 BTU/h. The noise levels of the baseline configuration, measured around the exhaust outlet, had an SPL over 110 dB at 50 Hz and a series of high intensity narrow-band components up to 2 kHz. The A-weighted broadband SPL in the range of 100 dB(A) exceeded damage/risk criterion by as much as 25 dB. The noise reduction goals corresponded to NC50 and SIL of 50 dB. The approach consisted of three parts: (1) A cowl silencer installed at the outlet vent for control of mid to high frequency broadband noise; (2) a custom designed tuned low-frequency muffler installed as part of the exhaust decoupler; and (3) thermoacoustic cladding applied to the structure. The silencer provided a reduction of 20 dB(A) in the mid-frequency range and the muffler resulted in narrow-band reductions of 25 to 40 dB at the lowest frequencies and 5 to 15 dB up to 2 kHz. The results, including sound intensity mapping, are discussed in terms of the goals, design modifications, and operational factors. [Work supported by The Gas Research Institute.]
Low-frequency underwater transducer modeling using the direct global stiffness method
Authors: Fricke J. Robert , Hayner Mark A.
Published: October 2005

The direct global stiffness matrix method (DGSM), described by Fricke and Hayner [direct global stiffness matrix method for 3-D Truss Dynamics, submitted to the ASME 15th Biennial Conference on Mechanical Vibration and Noise, 17–21 September 1995], provides an efficient method for analyzing two-dimensional and axisymmetric, low-frequency, underwater, transducer geometries. The DGSM method is a wave-type solution based on the Euler–Bernoulli beam element. The mechanical motion of the transducer element is modeled using a collection of beam elements welded together at joints. By imposing dynamic equilibrium conditions at these joints, a banded symmetric stiffness matrix is formed. The matrix is then solved using Gaussian elimination to find joint displacements and rotations with beam energies calculated on a post-processing basis. The radiation load due to the surrounding water is included using a compact source assumption. Thus fluid loading interaction effects, important for low quality factor transducers, are properly addressed. Analysis of a class IV flextensional transducer is offered as an example of the usefulness of this approach.
In-water modal analysis using a combined finite element/boundary element method
Authors: Siders Clementina M. , McCollum M. D.
Published: October 2005

A combined finite element/boundary element modeling technique can be used to analyze fluid-loaded transducers to compute the displacements of the structure at specified frequencies. The problem with this technique is that there is no way of knowing apriori the in-water resonance frequency corresponding to a given in-air mode. A common approach is to ‘‘guess’’ a frequency range that will encompass the in-water resonance frequency by using a coarse frequency step size. A fluid-loaded analysis is then performed in this frequency range. By examining the resulting displacements versus frequency, it can be determined whether the resonance has occurred in the frequency range. If the in-water resonance frequency is located, a finer frequency step can be used over a smaller frequency range to determine the resonance to a better resolution. This paper describes a method to determine the in-water resonance frequency of a finite element/boundary element model using an iterative eigenvalue solution, thus avoiding the lengthy convergence process of a harmonic solution. The time savings between this new in-water modal solution and the traditional harmonic solution can be phenomenal. Several example problems are also presented.
Variational principles derived for discontinuous electromagnetic fields
Authors: Altay G. Aşkar , Dökmeci M. Cengiz
Published: October 2005

A unified procedure based on a general principle of physics (e.g., Hamilton’s principle) together with Legendre’s (or Friedrichs’s) transformation is proposed to systematically derive certain variational principles for discontinuous electromagnetic fields which are useful to treat electromagnetic waves and vibrations in dielectrics. The integral and differential types of variational principles generate Maxwell’s equations and the associated natural boundary and jump conditions as well as the initial conditions, as their Euler–Lagrange equations, for a regular finite and bounded dielectric region with or without a fixed, internal surface of discontinuity. Special cases of the variational principles, including a reciprocal one, are recorded which have those for time-harmonic motions and a dielectric region within a vacuum or a perfect conductor, and they are shown to agree with and to recover some of earlier variational principles [e.g., M. C. Dökmeci, IEEE Trans. UFFC UFFC-35, 775–787 (1988); UFFC-37, 369–385 (1990) and G. A. Aşkar, 3007 (1994) and references therein]. [Work supported in part by The Scientific and Technical Research Council of Turkey.]
An approach to matched field processing in correlated multipath environments
Authors: Zeskind Robert , Owen Mark
Published: October 2005

Matched field processing (MFP) is based on some type of comparison of actual received signal across the elements of an array to predicted array element response based on complicated propagation models for postulated source locations. It is well known that these techniques are very sensitive to model mismatch. Investigators have proposed modified MFP techniques of varying complexity to be more robust to mismatch. A simplified approach to MFP in a correlated multipath environment is to estimate the parameters of the path arrivals at the array based on an assumed wavefront model for each path. The parameters to be estimated are arrival angles, relative received level for each path, and the correlation coefficient between pair of paths. For spherical wavefronts, the distance traveled along each path is also estimated. It is assumed that there are only a few dominant paths and their number is known. The parameter estimation problem is posed as a well-known optimization problem. The solution to the optimization problem not only acts as a detector, but provides the set of estimated parameters to be used in a raytrace propagation model to back propagate the multipath to localize the detected target. An example is presented to illustrate the method.
Multiple-frequency robust adaptive matched-field processing (MFP) in shallow water
Authors: Lee Yung P.
Published: October 2005

Application of robust adaptive algorithms to multiple-frequency MFP in shallow water has been studied and the minimum-detectable-level (MDL) has been examined via simulations. The multiple-frequency MFP output is obtained by incoherently averaging the MFP outputs of the discrete narrow-band-components. Performance of three different averaging techniques (arithmetic-mean, geometric-mean, and harmonic-mean) have been compared. The arithmetic-mean averages the amplitudes, the geometric-mean averages the dBs, and the harmonic-mean averages the reciprocals of the amplitudes. These algorithms have been applied to shallow water data from the Hudson Canyon experiment and have demonstrated excellent source localization results. simulations show a 10- to 20-dB improvement in the MDL against the simulated near or distant surface noise.
Localizing a source buried in noise in an uncertain environment
Authors: Fialkowski Laurie T. , Collins Michael D.
Published: October 2005

A source in an uncertain environment may be localized using focalization, which involves a parameter space that includes both source and environmental parameters. A source buried in noise may be localized using noise-canceling techniques, which involve matching both signal and noise, or eigen-processing techniques, which are capable of extracting signals from noisy data. These techniques have been combined to solve localization problems involving a source buried in noise in an uncertain environment. Noise-canceling techniques requires knowledge of the noise. Since it may not be practical to model the noise as part of the parameter search, it is assumed that the noise covariance matrix is obtained from data taken when the source is not present (mismatch associated with temporal environmental variability is included in the simulations). Eigen-processing techniques are less effective than noise-canceling techniques at suppressing noise and require source motion when multiple sources are present. However, they have the advantage of not requiring apriori knowledge of the noise.
Matched-field replica model optimization and bottom property inversion using multitone signals in shallow water
Authors: Baxley Paul A. , Booth Newell O.
Published: October 2005

Matched-field replica models based on an inaccurate knowledge of geoacoustic parameters such as bottom attenuation, shear, and interfacial sound-speed discontinuities, can predict an incorrect number of propagating modes for a shallow-water channel. The resulting degradation in the matched-field ambiguity surface can be substantially reduced by optimizing over the modal-sum-limit used in the replica model. The use of this technique for multitone (70, 95, 145, and 195 Hz) source-tow data recorded near San Diego during the first shallow water evaluation cell experiment (SWellEX-1) significantly increased matched-field correlation levels for all narrow-band tones (and their average), with the maximum peak more frequently coinciding the correct source location than that observed with a previous nonoptimized model [Schey and Ryan, 2981A (1994)]. The predicted number of propagating modes was also reduced substantially. An inversion for bottom properties (attenuation, interfacial sound-speed discontinuities, no shear) provided sediment attenuation estimates which agree well with Hamilton’s models and were an order of magnitude greater than that used in the nonoptimized model, which accounts for the reduction in the number of modes. A simulated model decomposition using the new attenuation verifies the number of modes predicted by the modal-sum-limit optimization.
Broadband matched-field processing of low level signals in shallow water
Authors: Booth Newell , Schey Phil
Published: October 2005

Matched-field processing analysis is presented for multitone signals from the shallow water evaluation cell experiment ♯3 (SWellEx-3) which was carried out in July 1994 west of Point Loma in 200 m water of complex bathymetry. The multitone test signal was transmitted from an acoustic source towed at various depths over tracks designed to test matched-field processing replica generation over complex propagation paths. The multitone signal consisted of 5 sets of 10 tones, each set spanned 50–200 Hz and was transmitted at various levels with 22-dB dynamic range. Using noise level estimates obtained at frequencies between the tones, the input signal + noise-to-noise ratio is estimated. Bartlett and minimum variance distortionless response (MVDR) adaptive matched-field processing results are presented from this data set over various paths for input signal to noise ratios spanning +12 to −10 dB.
Effects of ship trim and dynamic attitude on the relative noise level measured by a hull-mounted multibeam bathymetric sonar
Authors: de Moustier C.
Published: October 2005

Acoustic data recorded in various sea conditions with the hull-mounted multibeam swath bathymetry system SeaBeam 2000 aboard R. V. MELVILLE have been analyzed to quantify the relationship between the ship’s attitude and the relative noise levels observable in the data. The data consist of concurrent time series of echo magnitude and direction of arrival for each transmission cycle, and of the three attitude components roll, pitch, and heave. Although higher noise levels are usually associated with pitch, in these data heave has the greatest impact on noise level, presumably because of bubble syphoning from the areated surface layer. In addition, a slight change in the trim of the ship from horizontal to bow up results in an average relative noise increase of about 12 dB. [Research supported by ONR.]
Gradient-based receiver structures for detecting sound directions
Authors: Henderson Terry L. , Brudner Terry J.
Published: October 2005

The use of a pressure gradient microphone for detecting the source direction of an incident plane wave is well known. Furthermore, any receiving aperture that applies a specified apodization can be regarded as extracting a point-sample of a spatially filtered version of the incident wave. Our result is that when the gradient method is applied to the spatially filtered wave (which is also a plane wave), the answer can be expressed in terms modified apodizations, formed from the originally specified apodization function and its vector gradient, integrated over the original aperture and/or its boundary, together with simple temporal filters. Fortunately, this seemingly complicated structure collapses to a much simpler one in many cases of interest, and it is even possible to extend the method to the higher order case in which two or more wave directions are detected simultaneously. Alternatively, one wave direction can be measured while steering a broadband null in another specified direction, and the steered-null direction can be altered dynamically even after beamforming. Examples are given. Our results are especially applicable to transient sounds of arbitrary bandwidth. [Work supported by ARL:UT IR&D.]
Mirages in shallow water matched-field processing
Authors: D’Spain G. L. , Murray J. J. , Hodgkiss W. S. , Booth N. O.
Published: October 2005

Broadband (50–200 Hz) matched field processing was performed on vertical line array data from a recent shallow water experiment. Although the actual water depth steadily decreased from 200 to 100 m over the source tow track, the replica vectors were calculated assuming a range-independent environment of 200 m depth. Rather than breaking up due to the increasingly severe environmental mismatch, the broadband matched field output peak in range and depth behaved in a consistent way; both the predicted range and depth of the source became increasingly greater than its true range and depth as the true water depth decreased. A simple analytical model was developed to predict the behavior of these MFP mirages. The good agreement between model predictions and actual results suggests that the model can be used to quantify the impact of unknown water depth changes (e.g., ocean swell on synthetic aperture studies) and to ‘‘calibrate’’ water depth in a region using the sinking mirages of surface ships of opportunity. By use of the concept of ‘‘effective depth’’ developed by D. E. Weston etal., the model also can be applied to studies of ocean bottom geoacoustic parameter mismatch. [Work supported by ONR, code 321.]
Acoustic calibration of shallow underwater explosive charges
Authors: Cable Peter G. , Marshall William J.
Published: October 2005

Broadband underwater acoustic measurements are often performed using explosive charges as sources. For moderate weight charges detonated at shallow depths the bubble pulse oscillation period can exceed the separation between direct and surface reflected arrivals for any source-to-receiver geometry. Because of the overlap of multipath arrivals with the time signature of the charge, a direct determination of free-field source levels and spectral characteristics for such a situation can be problematical. In order to perform acoustic calibrations of explosive charges in shallow water, a method has been developed that uses the multiple arrivals on a vertical receiving array of hydrophones separated from the source detonation by one or two water depths. The technique involves averaging the time series from the vertical array phones after time aligning the direct shock arrivals on all the phones. This focused beamforming method has been used to obtain source calibrations from data obtained during area characterization test II (ACT II) in water 50 fathoms deep using 4 lb Comp B charges detonated at 25 fathoms. High levels of consistency and repeatability were obtained from several sources detonated at different ranges from the array. The calibration technique will be described and illustrated, and the achievable precision of the method discussed. [Work supported by ARPA under the Adverse Environments Program.]
Nonlinear transformations for spatial matched filtering (detect-on-track)
Authors: Lee Yung P. , Shyu Haw-Jye
Published: October 2005

A detect-on-track algorithm based on the Hough transform has been applied to acoustic broadband correlograms for passive detection and localization. The Hough transform integrates (sums) the amplitudes along a set of delay curves of interest. The delay curves are calculated over a range of closest point of approach (CPA), speed, and heading of the targets. When normalized by the number of points, the Hough transform computes the arithmetic-mean along the track. This process is referred to as an arithmetic-sum (AS) transform. This AS transform optimally reduces the variance of the noise, but can also generate significant ambiguous sidelobes. To reduce the sidelobe, two nonlinear transforms are proposed: The logarithmic-sum (LS) transform and the harmonic-sum (HS) transform. The LS-transform sums dB’s while the HS-transform sums the reciprocal of the amplitudes along the track. When normalized by the number of points, the LS transform computes the geometric-mean and the HS transform computes the harmonic-mean along the track. Simulations show that the nonlinear transforms perform the same as the AS transform in noise-limited environments but outperform the AS transform in sidelobe-limited environments.
Shallow water source track localization using matched multipath correlations
Authors: Knobles D. P. , Westwood Evan K. , Focke K. C.
Published: October 2005

A method for localizing a broadband moving source using the signals received on a horizontal planar array is presented. The method involves finding the constant-velocity, straight-line source track that generates the least error between measured and modeled correlation traces over a period of time. Measured correlation traces are obtained by cross-correlating multiple pairs of received time series. Simulated correlation time delays are obtained using a ray model that includes the effects of refraction on the ray arrival times. A nonlinear optimization routine is used to obtain the best match in measured and simulated time delays over time and receiver pair. The main problem in shallow water is to identify which multipath pairs produce the correlation traces observed in the measured data. An approach for overcoming this problem that involves testing multiple hypotheses concerning the multipath pairs will be presented. An example application of the method to a shallow water dataset with three bottom-mounted receivers in a triangular configuration is presented. In order to validate the localization, the measured correlagram is compared with a correlagram produced by a broadband normal mode model using the derived source track. [Work supported by the Office of Naval Research (Code 322).]
Results on the sequential classification of spherical objects in shallow water
Authors: Dwyer Roger F.
Published: October 2005

Based on the theoretical results reported in [ 1460 (1993)] and the simulated results reported in [ 3312(A) (1994)] an experiment to determine the performance of sequential classifying spherical objects in shallow water has been carried out. The shallow water data were obtained from experiments off the East Coast of the United States in 1993. Five spherical objects of different composition were embedded in shallow water data and the performance of a sequential classifier to correctly identify the objects was obtained. The performance results of these tests using standard measures of effectiveness will be reported.
Masking and aging: II. Human behavioral and auditory brain-stem response thresholds
Authors: Dubno Judy R. , Mills John H. , Ahlstrom Jayne B. , Matthews Lois J.
Published: October 2005

Masked thresholds measured psychophysically are equivalent for young and aged human subjects with equal quiet thresholds. However, higher masked thresholds derived from auditory brain-stem responses (ABR) are observed for aged than for young gerbils, independent of quiet thresholds. The purpose of this exeriment was to characterize further age-related changes in masking by comparing masked thresholds measured electrophysiologically and psychophysically for young and aged humans with normal hearing. Signals were Gaussian 1.8-ms tone pips at 1.0, 2.0, and 4.0 kHz; the masker was a 1.0 kHz, low-pass-filtered noise. Using identical signals, ABR and behavioral thresholds were measured in quiet and in maskers with overall levels of 74, 82, and 90 dB SPL. Thresholds measured psychophysically are equivalent for young and aged subjects in both on- and off-frequency masking conditions, consistent with previous findings. However, quiet and masked ABR thresholds are higher for aged than for young subjects, and masking functions are shallower. Thus, whereas ABR thresholds of aged humans are higher than their behavioral thresholds, they are consistent with elevated ABR thresholds observed in aged gerbils. More direct comparisons of the characteristics of human and gerbil ABRs are contained in a companion poster. [Work supported by NIDCD.]
Rate of rise sensitivity of medial geniculate neurons in the squirrel monkey
Authors: Olsen John F.
Published: October 2005

In this study neural sensitivity to rate of rise was measured. The responses of 32 medial geniculate neurons to linear increments of a broadband noise from a defined baseline level were recorded extracellularly. Step rise time (3–96 ms), step amplitude (6–24 dB), and baseline level (0–73 dB SPL) were varied independently. A typical response to the step consisted of a transient burst of 1–8 spikes. Response probability increased as a function of the step’s rate of rise (amplitude/rise time), such that increases in rise time could be traded for proportional increases in step amplitude to obtain a criterion response. Increases in baseline level decreased the slope of the probability versus rate of rise function and increased the threshold rate of rise. Response probability was independent of peak level (=baseline level+step amplitude). The results show that the response of a common type of medial geniculate neuron is determined by the rate at which stimulus amplitude increases from a defined background level, indicating a possible role for these neurons in the perceptual segregation of auditory events [A. S. Bregman, P. A. Ahad, and J. Kim, 2694–2703 (1994)].
Phase-space processing of scattering from a submerged elastic layer
Authors: Nagem Raymond J. , Felsen Leopold B. , Collins Brian J.
Published: October 2005

In scattering from an insonified submerged elastic layer, whose surface is perturbed with periodic or quasiperiodic variations, the resulting Bragg modes are expected to couple to the leaky modes that can be radiated by the unperturbed smooth layer. If these two distinct but coupled phenomenologies can be separately identified and extracted from acoustic scattering data by ‘‘wave-oriented’’ processing, one may gain discriminants for imaging the properties of the elastic layer and of its surface topology. A simple two-dimensional model—a finite array of filamentary scatterers on the insonified face of a fluid layer—has been investigated previously [T. Hsu, L. B. Felsen, and L. Carin, to appear in IEEE Trans. Antennas Propag.]. It has been shown that windowed-transform processing of data observed along a track parallel to the layer extracts space-wave-number phase space distributions in which the leaky mode and Bragg mode footprints are clearly separated; these features are poorly resolved in the unprocessed data. The present paper explores these phenomenologies and the corresponding phase-space processing when the fluid layer is replaced by an elastic layer with its far richer variety of layer-guided modes. Parametric studies show how the space-wave-number distributions are affected by the processing window size, the physical parameters of the layer, and the size and spacing of the filament array.
Variable phase coupling coefficient for leaky waves from resonance scattering theory and physical aspects of background contributions
Authors: Marston Philip L.
Published: October 2005

Approximations are examined for the coupling coefficient Gl for the launching and detachment of leaky waves having application to situations where thin shell theory is not applicable. The approach is based on a comparison of ray and resonance scattering theory (RST) formulations which includes effects on the phase of Gl of higher-order Debye approximations of Hankel functions and derivatives [P. L. Marston, Wave Motion (accepted for publication)]. The comparison includes a frequency dependent transition (between soft and rigid limits) for the RST background factor in the product expansion of the S function. The transition is formulated such as to not affect ‖Gl‖. The high frequency phase of Gl for limiting background cases previously examined [P. L. Marston and K. L. Williams, J. Acoust. Soc. Am. Suppl. 1 83, S94 (1988)] S94 (1988)] is recovered. A variable phase term depending on the background transition function corresponds to a term given by the convolution formulation of variable curvature scattering [P. L. Marston, 34–41 (1995)] when applied to thin circular cylindrical shells. Other correlations with shell theory are evident. Diffractive and inertial aspects of the background contribution are also examined. [Work supported by the Office of Naval Research.]
A theory for predicting the scattered signals from elastic spheroidal shells near smooth absorbing interfaces
Authors: Werby M. F. , Sidorovskaia N. A.
Published: October 2005

A new formulation that allows one to describe backscattered echoes from elastic shells near absorbing plane interfaces is presented. This formulation is always consistent even at low frequencies and large distances from the interfaces and allows the rapid reproduction of backscattered echoes over frequency ranges of practical interest. This novel formulation is developed and is shown to be consistent with that reflecting interfaces. The method has been implemented and numerical results for both pulse and continuous wave signals are carried out. [Work sponsored by NRL and the Office of Naval Research.]
Scattering from a fluid-loaded cylindrical shell with axially periodic circumferential constraints using analytical numerical matching
Authors: Loftman Rickard C. , Bliss Donald B.
Published: October 2005

Acoustic scattering from an infinitely long, thin elastic cylindrical shell with axially periodic circumferential constraints leads to the excitation of flexural, longitudinal, and shear waves on the shell. Of interest is the interaction of these structural waves with the discontinuous constraints, and the effect of this interaction on the resultant scattered sound field. This three-dimensional, fully coupled, structural acoustic problem is solved with the aid of a new method called analytical/numerical matching (ANM). The method combines high-resolution local analytical solutions and low-resolution global numerical solutions to more efficiently model structural discontinuities. ANM local solutions have been developed to efficiently capture the rapid variation in system response across the discontinuous constraint. The local solutions are combined with a smooth global solution, modeled by modal methods, to form an accurate, uniformly valid composite solution. The ANM composite solution is more accurate and converges more rapidly than the traditional modal approach. An important observation is that this scattering problem exhibits considerable sensitivity to modeling accuracy and convergence of structural response in the region of the discontinuities. Errors in these regions have an overall effect on the structure and the associated scattered field. [Work supported by ONR.]
Acoustical scattering by a penetrable wedge
Authors: Davis Anthony M. J.
Published: October 2005

Consider the two-dimensional scattering of a time-harmonic sound wave generated by a line source and incident upon a penetrable wedge. The wave speeds in the interior and exterior of the wedge are distinct and the radiation condition of only outgoing waves at infinity is applied in all directions. At the boundary of the wedge there is a pair of transmission conditions which ensure continuity of the acoustic pressure and normal velocity. By using suitably modified Green’s functions and considering separately the symmetric and antisymmetric parts of the pressure field with respect to the center plane of the wedge, a pair of disjoint integral equations of the first kind can be obtained for the two parts of the normal velocity on just one face of the wedge. Transformation to equations of the second kind is then achieved by using a technique for solving integral equations with Hankel function kernels [D. Porter, IMA, J. Appl. Math. 33, 211–228 (1983)]. The new kernels are bounded but defined on the interval (0, ∞). A numerical solution must describe the far field which, at the wedge boundary, will exhibit some mixture of the two wave speeds.
Acoustic and flexural wave scattering from a three member junction
Authors: Rebinsky Douglas A. , Norris Andrew N.
Published: October 2005

A three member junction is formed by a pair of semi-infinite plates in contact with fluid on one side and a mechanical structure on the other. The latter is described by an impedance matrix and the plates are modeled by the classical theory of flexure. The scattering problem for oblique incidence is solved using the impedance matrix for the plate junction without the attachment. This is accomplished using the Wiener–Hopf technique to solve the dual integral equations for the unknown pressure on the plates. Explicit formulae are obtained for the pressure transform, and corresponding explicit and relatively simple expressions are given for the various diffraction coefficients associated with the fluid/structure interaction. Numerical results for the redistribution of energy from flexural to flexural plus acoustic at a thickness discontinuity will be discussed in detail with respect to frequency and angle of incidence including the effect of various critical angles. It is verified that the general solution reduces to that for a pair of plates with clamped and welded junction conditions as limiting cases when the frame impedance is zero and infinite. [Work supported by ONR.]
Effects of listener expectation on eye movement behavior during audiovisual perception
Authors: Eigsti Inge-Marie , Vatikiotis-Bateson Eric , Yano Sumio , Munhall Kevin G.
Published: October 2005

In previous work [Vatikiotis-Bateson etal., Proc. ICSLP-94 2, 527–530 (1994)], listener eye movements were examined during audiovisual perception. Clear effects of masking noise level were observed in the stability and location of the listener’s gaze. At higher noise levels, listeners fixated primarily on the mouth and very little on the eyes. Listeners were implicitly directed to focus on phonetic detail in the stimuli, by means of questions used to determine intelligibility of the stimulus; however, attention to phonetic detail is only part of what goes on during audiovisual communication. In the current study, different patterns of eye movement were elicited from 10 English listeners by biasing the listener’s focus of attention. Two listener biases were tested—one toward phonetic discriminations, as previously studied, and the other toward practic information, e.g., having to do with perceived characteristics of the speaker. If visual cues during audiovisual perception are only partly phonetic, then differences in the listener’s interpretation of the experimental goals may evince different patterns of eye movement. For example, the perceived goal of the experiment may affect the relative proportion of gaze fixations on the eyes and the mouth.
The McGurk effect in infants
Authors: Johnson Jennifer A. , Rosenblum Lawrence D. , Schmuckler Mark A.
Published: October 2005

In the McGurk effect, auditory speech syllables are influenced by simultaneous presentation of discrepant visible speech syllables [McGurk and McDonald, Nature 264, 746–748 (1976)]. The effect is known to be stronger for native English than native Japanese-speaking subjects [Sekiyama and Tokhura, J. Acoust. Soc. Am. 90 (1991)]. It is unknown whether the strength of the effect is something lost or gained through developmental exposure to a given language. To explore this issue, two experiments tested for the McGurk effect in 5-month-old English-exposed infants. Infants were first gaze-habituated to an audiovisual /va/. They were then presented three different audiovisual combinations: audio /va/–visual /va/; audio /ba/–visual /va/ (perceived by adults as /va/); and audio /da/–visual /va/ (perceived by adults as /da/). The infants habituated to the tokens with audio /ba/ and /va/ components at the same rate, but habituated more slowly to the token with audio /da/. Further tests with a neutral static face and changing auditory syllables revealed that these habituation differences were not due to the auditory similarity of /ba/ to /va/ relative to /da/. This suggests that the infants were visually influenced in the same way as English-speaking adults.