bluuebunny/crossref_metadata_2025 huggingface dataset:
Uncertainty bounds for energy of imperfectly characterized vibration fields
Authors: Guyader Jean-Louis
Published: October 2005

Uncertainty bounds of vibration energy for viscoelastic continuous media are given. They are related to a residual functional measuring the error of characterization associated with an approximate solution and a factor that can amplify or attenuate the uncertainty bounds, depending on the driving frequency. (That factor considerably amplifies the uncertainty when the structure is excited near resonances.) Assuming a statistical distribution of the error of characterization of the vibration field, over the modes of the structure, allows a considerable reduction of the energy uncertainty bounds. The case of Gaussian distribution is presented and analyzed for various mean values and standard deviations. The bounds can be used as a criterion of convergence of modal expansion. The case of the acoustical response of a room is presented, and the influence of the size and type, of the sets of modes taken into account in calculations, is analyzed.
Effects of intensity modulations on the power spectra of random processes
Authors: Mark William D.
Published: October 2005

An intensity-modulated random process {(x(t)} is defined as the product of a deterministic modulating function a σ(t) or modulating process {σ(t)} and a stationary-modulated process {z(t)} that is statistically independent of {σ(t)}. General expressions for the instantaneous power spectra of intensity-modulated processes are presented for various classes of modulating functions and processes. A series expansion of the instantaneous power spectrum of intensity-modulated processes is presented which has for its first term a well-known locally stationary spectrum approximation. This expansion is especially useful when the fluctuation scales Tσ of the modulating functions are large in comparison with the fluctuation scales Tz of the modulated processes. The expansion can be interpreted as an asymptotic series in the parameter Tσ/Tz. For given scales Tσ and Tz, it is shown that modulating processes {σ(t)} possessing no first derivative have a substantially larger effect on the power spectrum of modulated processes {z(t)} than modulating processes possessing a first derivative. Examples illustrating various aspects of the theory are provided.
The design, construction, and testing of a miniature shaker and force gauge
Authors: Davis H. , Watters B. , Graham T.
Published: October 2005

BBN has designed, fabricated, and tested a miniature combined shaker and force gauge for mechanical impedance testing of light structure (metal plating of the order of 0.030 in., for example). The design is basically a Wilcoxon miniature accelerometer to be driven electrically through the signal cables, modified with a heavier reaction mass and a substitution of PZT 4 for the original PZT 5A. The shaker is attached to a stinger wire that supports the gravity load of the shaker while isolating the test object from the rotary impedance of the shaker itself. The stinger wire is attached to a specially fabricated force gauge that is glued to the test object to minimize the mass below the force gauge. The force gauge is composed of two PZT 5A crystals mounted back to back. The shaker design will be described and results presented showing that the shaker can apply up to 150 mN force with a sensitivity of 1 mN/V. The force gauge sensitivity is 350 mV/N and the frequency range is 2.6–6.6 kHz. By starting out with an accelerometer design, BBN was able to produce a working miniature shaker in a minimum amount of time.
The statistics of scattered waves
Authors: Jakeman E.
Published: October 2005

The statistical properties of waves scattered by random media are a subject of long-standing interest both in the context of remote sensing and noise limtation of system performance. It is usually agreed that when many independent scattering centers contribute to the amplitude at the detector, then the statistics will be Gaussian as a consequence of the central limit theorem. There are many situations where this is not the case, however, and it is necessary to adopt non-Gaussian noise methods. In the past, these have often been chosen on the ad hoc basis of goodness of fit to limited data sets, rather than being well founded on physical insight and a clear understanding of the scattering mechanisms involved. More recently, it has been conjectured that hierarchical behavior within the scattering medium, which is often observed in nature, could give rise to rather characteristic non-Gaussian fluctuations. Supporting evidence from optical scattering experiments, from microwave sea echo data, and from certain exactly solvable configurations has encouraged the development of the K-distribution model. A general review of this area will be presented.
Detection of simple and complex changes of spectral shape
Authors: Bernstein Leslie R. , Green David M.
Published: October 2005

In most of the previous studies (see Green, 1987) concerning the detection of a change in spectral shape, or ‘‘profile analysis,’’ the listener’s task was to detect an increment to a single component of an otherwise equal-amplitude, multicomponent background. An important theoretical issue is whether listeners’ sensitivity to more complex spectral changes can be predicted from these results. In the present investigation, the sensitivity of a single group of listeners to a wide variety of simple and complex spectral changes was determined. After collecting the data, it was noted that almost all the thresholds could be predicted by a simple calculation scheme that assumed detection of a change in spectral shape occurs when the addition of the signal to the flat, multicomponent background produces a sufficient difference in level between only two regions of the spectrum. Unfortunately, this scheme, while successful for our limited set of data, fails to account for other ‘‘profile’’ data, namely, those obtained when the number of components is altered.
Auditory intensity discrimination in the chinchilla
Authors: Saunders Samuel S. , Shivapuja Bhagyalakshmi G. , Salvi R. J.
Published: October 2005

A positive reinforcement conditioning procedure was used to train chinchillas to respond to intensity differences between successively occurring tone bursts. Intensity difference limens were measured at 0.5, 1, 4, and 8 kHz at five intensities ranging from 10- to 55-dB sensation level. The intensity difference limen decreased from approximately 8 dB near threshold to approximately 3.5 dB at the highest level. The intensity difference limens for the chinchilla were considerably larger than those for humans as well as several other mammals; however, the results were similar to those obtained for the parakeet. The present results from intensity discrimination appeared to be related to previous data for the discrimination of amplitude modulated noise.
Monaural envelope correlation perception
Authors: Richards Virginia M.
Published: October 2005

The ability to discriminate between simultaneously presented 100-Hz-wide bands of noise with envelopes that were either similar or dissimilar was measured. The center frequencies of the noise bands, fL and fL+Δf Hz, were systematically varied. When the bands of noise were separated by an octave, Δf=fL, discriminations were at chance levels. For frequency separations less than an octave, Δf<fL, discrimination was best for fL=2500 and 4000 Hz, somewhat poorer for fL=1000 Hz, and impossible for fL=350 Hz. Listeners were also asked to discriminate between bands of noise with envelopes that were either perfectly or partially correlated, and bands with envelopes that were either uncorrelated or partially correlated. The data suggest that, when transformed to an equal-variance scale (Fisher’s z), equal changes in Fisher’s z lead to equal changes in detectability, regardless of the correlation of the envelopes of the reference signal.
Auditory localization in the vertical plane: Accuracy and constraint on bodily movement
Authors: Noble William
Published: October 2005

In two preliminary experiments, listeners were instructed to limit increasingly the movement of their heads and/or bodies while attempting to localize narrow bands of noise centered on 2.3 or 8.3 kHz. With increasing constraint on movement, the high-frequency band was incorrectly perceived as elevated above the horizon. The low-frequency band, when actually elevated above the horizon, was not so regularly perceived incorrectly as being below the horizon, a finding inconsistent with a previous report. A third experiment, which more closely replicated the task conditions and strategies of the previous study, did tend to reveal the anomalous low-frequency error. The error is explicable as a default response to which listeners whose sensitivity to the vertical dimension, in general, appears imperfect are prone. From various reports, it emerges that about 25% of presumed normally hearing people exhibit this insensitivity.
Acoustic transfer characteristics in human middle ears studied by a SQUID magnetometer method
Authors: Brenkman C. J. , Grote J. J. , Rutten W. L. C.
Published: October 2005

The middle-ear transfer characteristics for sound in 14 human temporal bones were determined using a SQUID magnetometer method. With this method, the cochlea and middle ear remain intact. Postmortem changes were studied using a guinea pig. The mass-loading effects of the applied magnets were determined and were found to be negligible. The mean umbo displacement was equal to the mean of six other studies. Lever ratios varied between the individual temporal bones and as a function of frequency.
Probe tone thresholds in the auditory nerve measured by two-interval forced-choice procedures
Authors: Relkin Evan M. , Pelli Denis G.
Published: October 2005

An important goal of auditory physiology is to relate the coding of signals in the auditory nerve to behavioral sensitivity. A useful step towards that goal is to measure physiological thresholds for the detection of tones in the neural spike train that are comparable to psychophysical thresholds. Detectability depends on the variability as well as the mean value of the response. A two-interval forced-choice task provides a criterion-free measure of detectability. On each trial of our experiments a probe tone was taken to be correctly detected if the number of spikes in response to the tone exceeded the number of spikes in an otherwise identical interval that did not contain the probe tone. (Analysis of the pulse-number distributions also allowed construction of ROC curves directly comparable to psychophysical ROC curves.) The proportion of trials that yielded correct detections was measured as a function of stimulus intensity to form a neurometric function, directly comparable to a psychophysical psychometric function. Threshold was defined as the intensity that produced a given proportion correct. The threshold intensity was also measured by an up–down procedure. Agreement between the two measures of threshold was excellent. Using the up–down procedure we could measure threshold in about 1 min, making it practical to measure the thresholds of a single neuron for many conditions. Comparisons of physiological and psychophysical ROC curves and neurometric and psychometric functions show systematic differences indicating that the animal makes its decisions inefficiently, perhaps by basing its decision on the maximum response among many neurons, rather than just the activity of the single most sensitive neuron.
Accurate determination of object–image distance for planar objects in uniform subsonic flow
Authors: Narasimhan M. S. , Jegannathan S.
Published: October 2005

In this article, a technique for processing the image data to determine the object distance from the image plane, when a planar object is illuminated by a plane acoustic wave and the medium is in uniform subsonic flow, is presented. Closed-form expressions for the range are developed in terms of the Fourier transform of the image data for three specific directions of the flow, i.e., (i) normal and away from the object, (ii) normal and towards the object, (iii) parallel to the object. The Mach number of the flow is also determined from the image data, in addition to the range, making the technique useful, especially in the nearfield of the object.
Why can a decrease in dB(A) produce an increase in loudness?
Authors: Hellman Rhona , Zwicker Eberhard
Published: October 2005

Loudness measured by the method of absolute magnitude estimation is compared to loudness calculated in accordance with ISO 532 B [International Organization for Standardization, Geneva, 1966]. The measured and calculated loudness functions exhibit a similar pattern of loudness growth. Both measured and calculated loudness of a complex sound composed of a 1000-Hz tone and broadband noise is a nonmonotonic function of the overall SPL of the complex. The nonmonotonic loudness-growth pattern holds over a 30-dB range from 73.5 to 103.5. To facilitate understanding of the results, a single cycle of data is analyzed in detail. The analysis shows that loudness patterns produced in the auditory system by the tone–noise complex can account for the observed effects. Moreover, they show that the A-weighting and the loudness of the complex are negatively related. This inverse relation means that the A-weighted SPL is an inappropriate and misleading indicator of the loudness of sound combinations with heterogeneous spectral envelopes. Consequently, its suitability for noise control is diminished. A loudness meter that combines the spectral shapes of different sounds to produce an overall perceived magnitude offers greater promise.
Near-grazing propagation above a soft ground
Authors: Makarewicz Rufin
Published: October 2005

An expression for the A-weighted sound-pressure level of noise propagating above a locally reacting plane is derived. Atmospheric absorption is taken into account. Far away from the source, a 21-dB decrease per doubling distance has been found. For a source with an exponentially decreasing power spectrum, there is a category of ground that minimizes the A-weighted sound-pressure level.
Acoustic scattering from an arbitrarily rough surface
Authors: Kachoyan B. J. , Macaskill C.
Published: October 2005

A method is described for dealing with acoustic scattering from a time-independent pressure-release surface. As in work by previous authors, the problem is formulated as an integral equation on the surface. This formulation takes account of arbitrarily large surface roughness and multiple scattering phenomena at the surface. The problem may be considered naturally in two stages. The first part of the problem is to invert the integral equation to find the pressure gradient on the surface. The eigenfunction expansion method used by Holford [J. Acoust. Soc. Am. 70, 1116–1128 (1981)] for periodic surfaces is extended to deal with more general aperiodic surfaces. It is then shown that this approach is almost exactly equivalent to a direct collocation method. The second part of the problem is to evaluate the scattered pressure away from the surface. The method used here is to calculate the reflection coefficients from the Fourier transform of the pressure gradient on the surface. The reflection coefficients give a convenient representation of the distribution of scattered wave energy with angle and can be used to find the scattered pressure directly. Results are presented showing the growth of fluctuations in the nearfield of the surface and demonstrating the qualitative as well as quantitative differences between a surface with a Gaussian correlation function and a more realistic surface with a modified Pierson–Moskowitz spectrum. From a study of the cases dealt with here, it appears that the Kirchhoff approximation is more successful with randomly modulated surfaces than it is with simple periodic surfaces.
A technique for calculating bottom reflection loss from borehole data
Authors: Fisher Craig A. , Duennebier Frederick K.
Published: October 2005

Traditional methods of calculating bottom-reflection loss (BRL) cannot be applied to acoustic water-wave data from borehole receivers. A bottom transmission loss (BTL), incurred as acoustic energy passes through overlying bottom material, is present in these data. The BTL is a function of the grazing angle of acoustic arrivals. A versatile ‘‘self-calibrating’’ technique, called the grazing angle matching empirical (GAME) method, that can be used with these data, is presented. The GAME method employs bottom-interacting arrivals of several orders from different shots, all with similar grazing angles, to obtain BRL. The GAME method was applied to acoustic water-wave data obtained with a deep-ocean borehole receiver located in the Northwest Pacific Basin. The BRL values of 0 to 8 dB, with an uncertainty of ±2 dB, were obtained for grazing angles between 27 ° and 66 ° in two frequency bands, 9–18 and 21–29 Hz. The BTL values calculated from these data vary from 0 to 26 dB and have a similar spread in the same range of frequency and angle.
Comparison of target detection capabilities of the beluga and bottlenose dolphin
Authors: Turl Charles W. , Penner Ralph H. , Au Whitlow W. L.
Published: October 2005

The echolocation detection capabilities of a beluga (Delphinapterus leucas) and an Atlantic bottlenose dolphin (Tursiops truncatus) were directly compared in a target detection experiment. Both animals were trained to detect targets in the presence of masking noise. Targets were stainless-steel, water-filled spheres 7.62 and 22.86 cm in diameter. Target ranges of 16.5 and 40 m were used with the 7.62-cm sphere and 80 m with the 22.86-cm sphere. Masking noise with a flat spectrum from 40–160 kHz was projected from a spherical transducer placed 4 or 5 m, depending on the target distance, from the animal hoop station in line with the target. Target detection performance was determined as a function of masking noise level at each target range. The echo-to-noise ratio (Ee/N0)max for the beluga at the 75% correct response threshold was approximatly 1.0 dB compared to about 10 dB for the dolphin. The differences of each animal’s detection performance across the threee ranges were consistent with target strength and transmission loss differences. It is speculated that the difference in performance between the two species may be due to differences in critical bandwidth, signal processing capability, or echolocation strategy.
Speech masking. I. Simultaneous and nonsimultaneous masking within stop /d/ and flap /J/ closures
Authors: Spiegel Murray F.
Published: October 2005

This article reports on investigations of the relative roles of simultaneous and nonsimultaneous masking on detection thresholds using natural speech utterances. Thresholds were obtained for 15−ms probe tones placed in the stop or flap closures of /ada/ and /idi/. Threshold elevations due to simultaneous and nonsimultaneous masking could be explained by the dynamics of neighboring speech spectra. Nonsimultaneous effects were related to spectra at least 30 ms around the probe tone. Although simultaneous masking is usually stronger than nonsimultaneous masking, the relative amplitude of adjacent speech segments in natural speech is sufficiently high near formant regions to cause noticeable effects of nonsimultaneous masking.
Optimum time domain signal transmission and source location in a waveguide: Experiments in an ideal wedge waveguide
Authors: Li S. , Clay C. S.
Published: October 2005

Source location experiments in a wedge waveguide were conducted to test a single-channel time domain technique for a known source. The laboratory measurements were made in the air wedge having rigid sheet rock boundaries. The wedge angle was 6.6°. The source transmitted a short oscillatory signal having a frequency band of 3–13 kHz. The distances of the source and receiver from the wedge apex were 1.85 and 3.13 m. The Biot–Tolstoy wedge solution was used to calculate the source-to-receiver impulse response. For the geometry, all of the arrivals are due to images. The waveguide matched filter was the time reverse of the theoretical impulse response. The output of the matched filter was cross correlated with the known input signal. Maps of possible source locations were made by (i) assuming a trial source location, (ii) computing a theoretical impulse response and the corresponding matched filter, (iii) filtering the signal, and (iv) mapping the peak absolute maximum of the matched filter output. The actual source location was correctly mapped. There were several lower amplitude maxima that gave false source locations. The Appendix includes a tutorial description of the Laplace generating function (z transforms) and their applications.
A simple procedure for tracking fast maneuvering aircraft using spatially distributed acoustic sensors
Authors: Dommermuth F. M.
Published: October 2005

Acoustical tracking of maneuvering aircraft based on bearing measurements from distributed sensors is not directly accessible to conventional techniques because of the retardation between emission and reception of sound. To overcome this complication, the following two-step strategy is proposed: (1) Estimate the aircraft location at an arbitrary time and repeat this procedure to obtain a sequence of position estimates; (2) combine these estimates by conventional filtering methods. Focusing on the first step, the localization problem is treated on the basis of at least two separated sensors that measure the direction of arrival of the incident sound wave. An assessment of the accuracy of the resulting position estimates is provided, as well. The procedure is illustrated both with simulated and real data.
Scattering by a planar three-dimensional crack
Authors: Lin W. , Keer L. M.
Published: October 2005

The scattering of a three-dimensional crack is formulated by the boundary integral equation method. A numerical scheme for solving the derived integral equations by using triangular boundary elements is described in detail. The computed results include the stress intensity factors and the scattered patterns for cracks having an elliptical shape.
Signal-to-noise enhancement by underwater intensity measurements
Authors: Lo Edmond Y. , Junger Miguel C.
Published: October 2005

Horizontal components of acoustic intensity of noise radiated by isotropic surface disturbances, e.g., rain, fluctuate around zero. Consequently, the ratio of the time averages of the horizontal intensity components of a stationary signal and of ambient noise increases with averaging time to a value limited by the imperfect isotropicity of the noise intensity component in horizontal planes. Unlike conventional techniques, time-averaged intensity measurements discriminate against noise whose spectrum and direction of incidence coincide with that of the signal. The technique is illustrated for a broadband signal whose spectrum coincides with that of ambient noise, a situation where filtering of pressure measurements does not enhance the signal.
Central to peripheral sound propagation in excised lung
Authors: Rice David A. , Rice Janet Carol
Published: October 2005

The time it takes audible sound to travel from the trachea to the pleura in five intact, excised horse lungs and one dog lung inflated with several gases was measured. Regression estimates of sound speed at total lung capacity (TLC) using straight line distance from the carina to the pleura are: helium, 775±60.5 m/s (x̄±95% confidence limits); air, 282±23.5; carbon dioxide, 219±25.5; sulfur hexafluoride, 142±43.5. With the exception of sulfur hexafluoride, these speeds are 15%–20% less than the free-field speed of sound in each gas. Total airway length did not predict time delay any better or worse than straight line distance, but the high correlation between these two predictors (r=0.94) prevents showing either to be the more predictive. In one lung, airway length was partitioned according to airway diameter. A regression using partitioned airway lengths significantly improved time delay prediction (p<0.001) over an unpartitioned model. Sound speed in the trachea equals free-field sound speed. Sound speed in air-filled airways 1 to 25 mm in diameter equals 268±44 m/s. We conclude that the first sound to reach the surface travels in the airways for at least 90% of the distance, spending at least 87% of the total travel time there.
Prediction of speech intelligibility for normal-hearing and cochlearly hearing-impaired listeners
Authors: Ludvigsen Carl
Published: October 2005

The word recognition ability of 4 normal-hearing and 13 cochlearly hearing-impaired listeners was evaluated. Filtered and unfiltered speech in quiet and in noise were presented monaurally through headphones. The noise varied over listening situations with regard to spectrum, level, and temporal envelope. Articulation index theory was applied to predict the results. Two calculation methods were used, both based on the ANSI, S3.5-1969 20-band method [S3.5-1969 (American National Standards Institute, New York)]. Method I was almost identical to the ANSI method. Method II included a level- and hearing-loss-dependent calculation of masking of stationary and on–off gated noise signals and of self-masking of speech. Method II provided the best prediction capability, and it is concluded that speech intelligibility of cochlearly hearing-impaired listeners may also, to a first approximation, be predicted from articulation index theory.
Two-mass models of the vocal cords for natural sounding voice synthesis
Authors: Koizumi Takuya , Taniguchi Shuji , Hiromitsu Seijiro
Published: October 2005

Three new two-mass models of the vocal cords are treated. First, the features, structure, and differential equations of motion are described for each of the new models and compared with those of previous models. Second, performances of the models are discussed in terms of glottal volume flow, glottal area, radiated sound pressure, trajectories of mass movement, running spectra of the output sound pressure, and perceptual naturalness of the output sound. Finally, the major effects of glottal source–vocal tract interaction including skewing, truncation, and superposition are investigated, using one of the simplest types of two-mass models and two types of load representing the vocal tract.
Auditory temporal processing: Two-tone flutter fusion and a model of temporal integration
Authors: Robin Donald A. , Royer Fred L.
Published: October 2005

Auditory temporal processing was examined using a flutter-fusion paradigm in which two tones were separated by a silent interval. The listener’s task was to judge when the two tones, presented in a background noise, fused perceptually. The fusion point was studied in a series of six experiments. In the first five experiments, the duration of the first stimulus (T1) was the dependent variable. In the last experiment, the duration of the second stimulus (T2) was the dependent variable. An inverse relationship was found between T1 duration and the interstimulus interval (ISI) such that, when ISI was decreased, T1 duration had to be increased to maintain fusion. When ISI was plotted as a function of T1 duration, the data were represented by a negative exponential equation. Increasing the level of the tones, increasing the bandwidth of the background noise, or presenting the stimuli dichotically lowered the duration of T1 necessary for fusion. Changing the frequency of the tones had no effect on fusion. Decreasing the duration of T2 and holding T1 constant also resulted in fusion. A neurophysiological model implicating ON and OFF neural response interactions is postulated to account for the data.
Effect of periodic rest on hearing loss and cochlear damage following exposure to noise
Authors: Clark W. W. , Bohne B. A. , Boettcher F. A.
Published: October 2005

Changes in hearing sensitivity and cochlear damage were determined in two groups of chinchillas exposed to an octave band of noise (OBN) centered at 0.5 kHz, 95 dB SPL on two different schedules: 6 h per day for 36 days, or 15 min/h for 144 days. Hearing sensitivity was measured behaviorally at 1/4 -oct frequency intervals from 0.125 to 16.0 kHz before, during, and for a period of 1 to 2 months after the exposure, at which time the animals’ cochleas were fixed and prepared for microscopic examination. Cochlear damage was determined by counts of missing sensory cells. Both exposures produced an initial shift of thresholds of 35–45 dB; however, after a few days of exposure, thresholds began to decline and eventually recovered to within 10–15 dB of original baseline values even though the exposure continued. Measures of recovery made after completion of the exposures indicated minimal permanent threshold shifts in all animals. The behavioral and anatomical data indicated that these intermittent exposures produced less temporary and permanent hearing loss and less cochlear damage than continuous exposures of equal energy.
On the insertion losses produced by plane acoustic lagging structures
Authors: Au Angus C. K. , Byrne Kerry P.
Published: October 2005

A procedure for calculating the insertion losses produced by a wide variety of plane acoustic lagging structures is described. Such lagging structures are commonly used in industry to inhibit the transmission of the sound radiated from vibrating surfaces such as those of ducts and machines. The procedure is based on the successive application of expressions that relate surface or wave impedances and acoustic pressures across the elements that make up an acoustic lagging structure. The elements considered are impervious barriers that can support bending waves (for example, metal cladding sheets), and flow resistive porous layers (for example, fiberglass blankets) and air spaces. The insertion losses produced by lagging structures applied to acoustically excited structures, such as duct walls, are found by determining the diffuse field sound transmission losses for the wall with and without the lagging structure applied. A comparison is made between the predicted and measured insertion losses for some simple lagging structures. The results of a study to show the effects of varying the parameters of a lagging structure are also presented.
The effect of intermittent noise on vigilance performance
Authors: Carter Norman L. , Beh Helen C.
Published: October 2005

An experiment was conducted to determine the effect of the level of predictability of intermittent noise on performance on a visual vigilance task. Under a quiet condition and three intermittent noise conditions, subjects (Ss) carried out a 55-min task where they were required to detect a change in the brightness of one element of a visual display. The results indicated that Ss were less sensitive, less accurate, and more prone to response failures during intermittent noise, although responses were faster under noise conditions. Measures of response bias and response certainty were not significantly affected by the presentation of noise. Variation in the level of predictability of the noise affected only the accuracy of response measure during the final quarter of the vigilance task, with the group receiving the least predictable noise performing significantly worse than the other three groups. The results are discussed in relation to theories of noise and performance.
Light aircraft sound transmission studies: Noise reduction model
Authors: Atwal Mahabir S. , Heitman Karen E. , Crocker Malcolm J.
Published: October 2005

Experimental tests conducted on the fuselage of a single-engine Piper Cherokee light aircraft suggest that the cabin interior noise can be reduced by increasing the transmission loss of the dominant sound transmission paths and/or by increasing the cabin interior sound absorption. The validity of using a simple room equation model to predict the cabin interior sound-pressure level for different fuselage and exterior sound field conditions is also presented. The room equation model is based on the sound power flow balance for the cabin space and utilizes the measured transmitted sound intensity data. The room equation model predictions were considered good enough to be used for preliminary acoustical design studies.
Gaussian beam tracing for computing ocean acoustic fields
Authors: Porter Michael B. , Bucker Homer P.
Published: October 2005

The method of Gaussian beam tracing has recently received a great deal of attention in the seismological community. In comparison to standard ray tracing, the method has the advantage of being free of certain ray-tracing artifacts such as perfect shadows and infinitely high energy at caustics. It also obviates the need for eigenray computations. The technique is especially attractive for high-frequency, range-dependent problems where normal mode, FFP, or parabolic models are not practical alternatives. The Gaussian beam method associates with each ray a beam with a Gaussian intensity profile normal to the ray. The beamwidth and curvature are governed by an additional pair of differential equations, which are integrated along with the usual ray equations to compute the beam field in the vicinity of the central ray of the beam. We have adapted the beam-tracing method to the typical ocean acoustic problem of a point source in a cylindrically symmetric waveguide with depth-dependent sound speed. We present an overview of the method and a comparison of results obtained by conventional ray-tracing, beam-tracing, and full-wave theories. These results suggest that beam tracing is markedly superior to conventional ray tracing.
Inversion of ultrasonic scattering data for red blood cell suspensions under different flow conditions
Authors: Lucas R. J. , Twersky V.
Published: October 2005

Recent results for low-frequency scattering by correlated random distributions of nonspherical particles averaged over orientation are applied to invert ultrasonic data for red blood cell suspensions under different flow conditions. The inversion procedure isolates a correlation parameter (c) representing a process in which the volume fraction (w) of particles increases linearly, and also a cell population parameter P. Reduced data records of scattering versus hematocrit are compared with S(c;w)P, where the generalized fluctuation function S is proportional to the variance in particle number, and P is proportional to the backscattering cross section of an isolated particle. The peak scattering for the different flow processes occurs at values of w ranging from about 0.15 for the most uniform to 0.25 for the least, corresponding to c values of about 2.1 to 0.4, as compared with w≊0.13 and c=3 for hard (repulsive at contact) spheres or aligned ellipsoids. The lower values of c suggest weaker repulsion between the deformable cells and effective interparticle attraction (aggregative trends), and c≊2 may also involve flow alignment of the discoids.
Volume estimation of symmetrical branching structures by resonance mode analysis
Authors: Raphael David T. , Epstein M. A. Farrell
Published: October 2005

An exact resonance condition is derived for rigid symmetric second-order bifurcating structures. In the low-frequency range, the resonance condition can be reduced into forms that facilitate volume estimation of bifurcating structures. Two such volume approximation techniques are presented: (1) a fundamental frequency method, in which the lowest resonant frequency is inversely proportional to the structure volume, and (2) an equivalent-length method, in which an equivalent length of two daughter branches is calculated for all branches distal to the first bifurcation. An experimental study to determine the resonance modes of seven bifurcating glass structures was performed. The volume estimates obtained by either method were in very close agreement with the true volumes.
A model for directional and distance hearing in swimbladder-bearing fish based on the displacement orbits of the hair cells
Authors: Schellart Nico A. M. , de Munck Jan C.
Published: October 2005

It is known that teleosts, without Weberian ossicles but with a swimbladder, can detect the direction of and, under appropriate conditions, the distance to a sound source [e.g., Schuijf and Hawkins, Nature 302, 143–144 (1983)]. It is hypothesized here that the underlying mechanism is the analysis of the parameters of the elliptical movement of the hair cells with respect to the otoliths. This movement results from the displacement wave impinging directly upon the labyrinth and the response displacement wave reradiated by the swimbladder. For a given swimbladder geometry, given the positions of the maculae of both labyrinths with respect to the swimbladder and the damping of the swimbladder, the displacement orbits of the maculae can be calculated [de Munck and Schellart, J. Acoust. Soc. Am. 81, 556–560 (1987)]. These calculations were made for the cod and the trout with the frequency, direction, and distance between the fish and the sound source as parameters with the source within the same horizontal plane as the fish. The orbit model predicts that the utriculus has the most strategic position to detect direction and distance of such a sound source. Moreover, the model predicts that this could basically be done monaurally. A hypothesis is proposed to describe how the utricular system analyzes the orbit parameters. The model is evaluated in relation to the results of behavioral experiments described in the literature.
Speaking rate of adventitiously deaf male cochlear implant candidates
Authors: Leder Steven B. , Spitzer Jaclyn B. , Kirchner J. Cameron , Flevaris-Phillips Carole , Milner Paul , Richardson Frederick
Published: October 2005

No objective group data on speaking rate or speaking duration have been reported on the speech of adventitiously profoundly hearing-impaired adults. Results of the present study showed that speaking rate, i.e., number of syllables per second, was significantly slower and speaking duration was significantly longer for 25 adventitiously profoundly hearing-impaired adult male cochlear implant candidates than for 10 normal-hearing control subjects. The factors of length of time since onset of profound hearing loss and hearing aid use did not significantly affect speaking rate. Based on these objective data, a rationale and method are presented for aural rehabilitation of the profoundly hearing-impaired who exhibit speaking rate abnormalities.
Frequency discrimination of complex signals, frequency selectivity, and speech perception in hearing-impaired subjects
Authors: Horst J. Wiebe
Published: October 2005

Frequency discrimination of spectral envelopes of complex stimuli, frequency selectivity measured with psychophysical tuning curves, and speech perception were determined in hearing-impaired subjects each having a relatively flat, sensory-neural loss. Both the frequency discrimination and speech perception measures were obtained in quiet and noise. Most of these subjects showed abnormal susceptibility to ambient noise with regard to speech perception. Frequency discrimination in quiet and frequency selectivity did not correlate significantly. At low signal-to-noise ratios, frequency discrimination correlated significantly with frequency selectivity. Speech perception in noise correlated significantly with frequency selectivity and with frequency discrimination at low signal-to-noise ratios. The frequency discrimination data are discussed in terms of an excitation-pattern model. However, they neither support nor refute the model.
Infants’ localization of sounds in the median sagittal plane: Effects of signal frequency
Authors: Morrongiello Barbara A.
Published: October 2005

The purpose of this research was to determine if infants, like adults, show differential localization performance in the median sagittal plane (MSP) as a function of the spectrum of the signal. Infants 6–18 months of age were seated in a dark room facing an array of nine loudspeakers, with one loudspeaker positioned at ear level, 0°, and four each positioned above and below ear level at 4°, 8°, 12°, and 16°. A two-alternative, forced-choice procedure was used in which a sequence of noise bursts was presented at 0° and then shifted vertically, above or below 0°, and continued to be presented until the infant made a directional head and/or eye movement; correct responses were visually reinforced. For each of three bandpass noise conditions (<4 kHz, 4–8 kHz, 8–12 kHz), minimum audible angle (MAA) for each listener, i.e., the smallest of the four angular shifts in vertical sound location that the listener could reliably detect, was estimated. Results indicated that MAA systematically decreased with increasing age, revealing an increasingly finer partitioning of auditory space. Moreover, performance at each age revealed the importance of high frequencies for localization in the MSP. Infants did not reliably localize the low-pass signal (<4 kHz) and showed the best performance to the signal comprising the highest frequencies (8–12 kHz). These findings reveal systematic age-related improvements in sound localization abilities during infancy, and suggest that spectral cues similar to those for adults operate for infants in vertical localization.
The role of tactile aids in providing information about acoustic stimuli
Authors: Weisenberger Janet M. , Miller James D.
Published: October 2005

Devices that convert sound patterns into patterns of vibrotactile stimulation have been shown in laboratory and clinical studies to enable persons to appreciate many aspects of the acoustic environment, and thus are of potential benefit to deaf persons. In the present article, a framework is outlined for describing normal listening situations as a hierarchy of tasks requiring increasingly complex analysis of the acoustic waveform, including sound detection, environmental sound identification, syllable rhythm and stress categorization, phoneme and word identification, and comprehension of connected speech. The types of benefits provided by tactile aids in each of these tasks are exemplified using data from studies of single-channel commercially available devices and multichannel tactile vocoders in our own and other laboratories. The discussion of these data addresses such issues as the features of the acoustic environment that can or should be transmitted through a tactile aid, the differences in the information transmitted by commercially available versus experimental laboratory devices, the comparison of tactile aids and cochlear implants, and the technical problems that remain to be overcome in the design and evaluation of improved vibrotactile aids.
Parametric instability of elastically restrained circular plates
Authors: Sasaki M. , Chonan S.
Published: October 2005

This article is concerned with the parametric instability of circular plates elastically restrained against translation and rotation at concentric intermediate circles as well as along the periphery. The plate is subjected to a horizontal or tangential periodic radial load at the periphery. The instability regions of the plate both for the simple resonance and for the combination resonances of sum and difference types are determined analytically from the coupled Mathieu equations that are derived by applying the Galerkin method to the governing equations. The influences on the stability of the plate of the direction of periodic load and the stiffness of elastic supports are studied in detail for the plate with peripheral and one intermediate supports.
Prediction of the incidence of motion sickness from the magnitude, frequency, and duration of vertical oscillation
Authors: Lawther Anthony , Griffin Michael J.
Published: October 2005

A method is proposed by which the incidence of motion sickness may be predicted from measurement of the motion exposure. The method is based on data from both field and laboratory studies involving large numbers of people and is applicable to marine and other environments where vertical oscillation occurs at frequencies below 0.5 Hz. The dependence of motion sickness on the frequency of oscillation requires the use of a weighting function between 0.1 and 0.5 Hz. The dependence of sickness on the duration of exposure is incorporated by the use of a cumulative measure of motion dose based on the product of root-mean-square (rms) acceleration magnitude and the square root of stimulus duration. The influence of population variables such as sex, age, and motion experience is discussed. The method enables separate predictions to be made of vomiting incidence and of feelings of illness. The prediction procedure, while not seeking to explain the underlying mechanisms of motion sickness occurrence, provides a generally applicable method which is simple to use and has an accuracy consistent with the experimental data on which it is based.
Path-integral treatment of intensity behavior for rays in a sound channel
Authors: Flatté Stanley M. , Reynolds Stephen A. , Dashen Roger
Published: October 2005

The intensity coherence function (ICF) of the acoustic wavefunction from a point source is derived by the path-integral technique for transmission through internal waves in the presence of a sound channel. Separations in time are emphasized, although separations in transverse horizontal position, vertical position, and acoustic frequency are discussed. Approximate intensity coherence times, lengths, and bandwidths due to internal-wave fluctuations are derived. Analytic approximations suitable for computer coding are presented for the micropath focusing parameter γ, which controls the deviation of higher intensity moments from the Rayleigh-distribution values.
AFAR measurements of intensity and intensity moments
Authors: Flatté Stanley M. , Reynolds Stephen A. , Dashen Roger , Buehler Barry , Maciejewski Pat
Published: October 2005

In an acoustic-oceanographic experiment (AFAR) performed near the Azores in 1975, frequencies from 400–4670 Hz were transmitted over a 35-km wholly refracted path. In addition, a separate data set was gathered over a 3-km path in 1973. Measurements of the intensity coherence function of time and frequency, intensity moments, and the probability distribution of intensity are presented and compared with predictions of fluctuations due to internal waves.
Perturbative inversion methods for obtaining bottom geoacoustic parameters in shallow water
Authors: Rajan Subramaniam D. , Lynch James F. , Frisk George V.
Published: October 2005

Three perturbative inverse methods for obtaining bottom geoacoustic parameters as a function of depth in shallow water are described. The required input data are the trapped mode eigenvalues for one or more frequencies, the group velocity dispersion curves for one or more modes, or the cw pressure field versus range. In each case, a Fredholm integral equation arises that can be solved using linear inverse theory, and for which resolution and variance estimates of the solution can be readily made. Attention is focused primarily on the modal eigenvalue inverse problem for which the theory for determining the compressional wave speed, compressional wave attenuation, and density is developed in detail. Properties of this technique are studied using synthetic data and include investigations of the dependence of the results on acoustic frequency, number of modes excited, and partial a priori knowledge of the bottom. The method is demonstrated on experimental data obtained in Nantucket Sound at 140 and 220 Hz. Directions of future research on these techniques are indicated.
Vector calibration of ultrasonic and acoustic emission transducers
Authors: Simmons John A. , Turner Christian D. , Wadley Haydn N. G.
Published: October 2005

The independent transient responses of a transducer to displacements polarized in each of the three orthogonal directions have been determined using a new method that assumes only linearity and no angular impingement dependence of the transducer response. The modeling of the transducer response is thus converted from a vector problem to three much more tractable scalar problems, thereby forming the basis for vector calibration of acoustic emission and ultrasonic transducers as receivers.