bluuebunny/crossref_metadata_2025 huggingface dataset:
The approximation of pressure waveforms of impact sound radiation from clamped circular plates of various thicknesses
Authors: Takahagi Toshio , Nakai Mikio
Published: October 2005

The purpose of this paper is to investigate the mechanism of impact noise generation, in order to reduce noise at its source. A fundamental model, the case of a ball striking a clamped circular plate, was studied. In the experiments, the effects of plate thickness and observation distance on sound pressure were observed. In the theoretical analysis, the rotary inertia of the plate, shear deformation, and the air reaction of the radiated sound were considered. The impact force history was assumed to be a triangular pulse, since it was determined by three parameters: the maximum impact force, the impact duration, and the rise time. The time when the maximum sound pressure occurred, the influence of the rise time on the sound pressure level, and the vibrational modes which contributed to the sound were obtained using this approximation.
A technique for measurement of structure-borne intensity in plates
Authors: Williams Earl G. , Dardy Henry D. , Fink Richard G.
Published: October 2005

A measurement technique to determine the structure-borne intensity (power flow) in a point-driven, fluid-loaded, homogeneous thin plate is demonstrated. This intensity is uniquely determined from a knowledge of the normal velocity of the surface of a sinusoidally driven plate. A noncontact method is presented which uses a scanning hydrophone to measure the pressure in a plane very close to the source. It is shown how this pressure measurement is sufficient to compute the two-dimensional structural intensity vector inside the plate. We call this technique SIMAP for Structural Intensity from the Measurement of Acoustic Pressure. Uses of the structural intensity vectors to compute the power injected into the plate from a point driver are shown. Independent measurement of injected mechanical power is shown to be in close agreement. SIMAP, which is an outgrowth of nearfield acoustical holography (NAH), also provides the normal acoustic intensity radiated into the medium from the same pressure measurement. A comparison of the structure-borne intensity with this normal acoustic intensity indicates that structural intensity is much more accurate in locating the real source than the acoustic intensity, the latter often failing completely. The examples given in this paper are for an underwater source, but the technique applies without modification to plate sources in air.
Nonlinear frequency shifts in quasispherical-cap shells: Pitch glide in Chinese gongs
Authors: Fletcher N. H.
Published: October 2005

The large-amplitude vibrational behavior of a shallow spherical-cap shell is investigated theoretically using simple arguments. The results of this approximate analysis are expressed in the form of appealingly simple nondimensional quantities. It is shown that the frequency of the fundamental mode of such a shell falls by as much as 50% as the vibration amplitude is increased to approximately the shell depth. For even larger amplitudes the frequency rises, and it exceeds the small-amplitude frequency when the amplitude is more than about twice the shell depth. The influence of shell thickness is considered and increasing thickness is shown to decrease the frequency shift. This analysis is shown to account for the pitch glide behavior of certain Chinese opera gongs.
The ultrasonic field of a Gaussian transducer
Authors: Du Gonghuan , Breazeale M. A.
Published: October 2005

A transducer is described which produces a Gaussian distribution of amplitudes along a radial dimension. The ultrasonic beam produced by this transducer is examined both experimentally and mathematically and is shown to have none of the zeros of amplitude in the Fresnel region, and none of the secondary maxima in the Fraunhofer region characteristic of the piston transducer. Applications both to verification of physical theories and to nondestructive evaluation situations are mentioned.
Investigation of lightning strikes to water surfaces
Authors: Hill R. D.
Published: October 2005

Recent experiments by Arnold et al. [J. Acoust. Soc. Am. 76, 320–322 (1984)] established that cloud-to-water lightning generates acoustic pulses in the ocean. In this paper, the connection of a lightning stroke with an ocean surface is analyzed, and a blow-off mechanism is proposed for the acoustic pulse generation process.
On the acoustic response of a deeply corrugated periodic surface— A hybrid T-matrix approach
Authors: Lakhtakia Akhlesh , Varadan Vijay K. , Varadan Vasundara V.
Published: October 2005

The extended boundary condition (EBC) method, as proposed by Waterman [J. Acoust. Soc. Am. 57, 791–802 (1975)], is hybridized with the point-matching technique in order to derive a T matrix for a periodically corrugated surface on which either the Dirichlet or the Neumann boundary condition is imposed. The limitations imposed by the Rayleigh hypothesis on Waterman’s T matrix are overcome by a correct choice of eigenfunctions for the surface field representation. Highly corrugated surfaces can now be considered. The numerical results are compared with the data computed by Holford [J. Acoust. Soc. Am. 70, 1116–1128 (1981)], using an integral equation method, as well as with the experimental results collected by Lacasce and Tamarkin [J. Appl. Phys. 27, 138–148 (1956)].
Measurements of the acoustic backscatter of manganese nodules
Authors: Weydert Marco M. P.
Published: October 2005

The acoustic backscatter of eight well-curated ferromanganese nodules has been measured in 1 °C seawater at frequencies from 45 to 167 kHz. The nodules have diameters from 37 to 121 mm and are thought to be representative of the Cu–Ni–Co-rich nodules from the area around 14° 40′ N, 125° 25′ W (DOMES site C). They had been collected in box cores on the Echo 1 expedition and were kept refrigerated and water soaked in air-tight plastic bags. Acoustic backscatter variations of over 10 dB were observed while the nodule was rotated 10° to 30° about one of its principal axes. The complicated fine structure, as well as the target strength, makes it clear that nodules cannot be modeled as simple spheres.
The theoretical responses of vertical and horizontal line arrays to wind-induced noise in shallow water
Authors: Hamson Rachel M.
Published: October 2005

A wave theory model for the propagation of noise from a surface source layer has been used to investigate the directional response of vertical and horizontal arrays to wind noise in shallow water. The model assumes an infinite layer of sources radiating sound with pressure directionality of the form cosm α, where m >1 and α is an angle measured from the downward vertical. The field incident on the array is inhomogeneous in the vertical plane, and directional responses have been calculated from the appropriate spatial correlation matrix for various bottom types, sound-speed profiles, and values of m up to 3. Results show that both components of the noise field, the discrete normal modes and the continuous spectrum, can contribute significantly to the total noise level and to the array responses. The mode arrivals give rise to high vertical array responses near broadside and high horizontal array responses towards endfire. Thus considerably different forms of directional response pattern can be produced compared to those predicted by a simple model for ideal conditions. The extent of these differences is strongly dependent on bottom type and on the source directionality parameter m, and slightly dependent on sound-speed profile.
Acoustic scatter from a slightly rough boundary between a fluid and an elastic solid
Authors: Tolstoy I.
Published: October 2005

Smoothed boundary conditions have heretofore been used for describing acoustic scatter from hard (infinitely rigid) rough walls or from rough interfaces between fluids in the domain kb ≂ kh ≲ 1, where k is the wavenumber, b and h are, respectively, measures of the roughness height and spacing between roughness elements. The present paper extends the technique to the case of acoustic scatter in a fluid off the rough surface of an elastic solid. The boundary condition defining the perturbation of the displacement potential φs in the fluid is isomorphic to the equivalent condition for two fluids, the main difference residing in the calculation of the physical constants. These calculations are straightforward; with continuity of pressure (stress) at the boundary, one can solve the scatter problem for an acoustic source in the fluid. Of particular interest is the boundary wave problem, corresponding to modes with potential φ1 (in the fluid) and φ2, ψ2 (in the solid) falling off exponentially away from the interface. The characteristic equation here has always at least one solution—the Stoneley wave mode as affected by roughness (which makes it dispersive and introduces attenuation due to incoherent scatter). When the fluid sound velocity c1 is less than the shear velocity cs in the solid, there is, in addition, a surface roughness boundary mode solution—essentially the surface roughness boundary wave of the hard wall solution described elsewhere [I. Tolstoy, J. Acoust. Soc. Am. 66, 1135–1144 (1979)] and measured by Medwin [H. Medwin et al., J. Acoust. Soc. Am. 66, 1131–1134 (1979)], but modified by the elasticity of the solid. Stoneley wave attenuation due to incoherent scatter is greater than that of the surface roughness boundary mode. The boundary wave pressure field excited by a point source near the boundary will therefore have greater farfield amplitudes than the Stoneley mode (even though its nearfield amplitudes are less).
Intrinsic modes: Numerical implementation in a wedge-shaped ocean
Authors: Topuz E. , Felsen L. B.
Published: October 2005

Two recently developed related spectral theories [Kamel and Felsen, J. Acoust. Soc. Am. 73, 1120–2230 (1983); Arnold and Felsen, J. Acoust. Soc. Am. 73, 1105–1119 (1983)] have provided potentially new options for calculating source-excited sound fields in a weakly range dependent ocean environment. So far, these theories have been applied to a homogeneous two-dimensional ocean and bottom separated by a plane sloping interface. It has been recognized that their common building blocks are what have been referred to as ‘‘intrinsic modes’’ [Arnold and Felsen, J. Acoust. Soc. Am. 76, 850–860 (1984)]. Intrinsic modes have spectral integral representations that reduce in a lowest order approximation to adiabatic modes, where these can be defined, but which remain uniformly valid in their integral form through the cutoff transition in upslope propagation. An efficient numerical algorithm has now been developed for calculating the intrinsic modes and the Green’s function in the ocean and in the bottom. Numerical results are compared with those from the parabolic equation [Jensen and Kuperman, J. Acoust. Soc. Am. 67, 1564–1566 (1980)] and the augmented adiabatic mode theory [Pierce, J. Acoust. Soc. Am. 74, 1837–1847 (1983)]. Also discussed and compared are asymptotic approximations of the spectral integral, which are found to be accurate and computation intensive everywhere in the water and also at small depths in the bottom.
Hybrid representation of long-range sound pulse propagation in an underwater surface duct
Authors: Topuz E. , Felsen L. B.
Published: October 2005

At long ranges in an underwater duct, in a widening transition region around the transmitter depth, strong focusing effects due to a pileup of caustics occur which invalidate the use of ray acoustics even if the ray field is augmented with conventional caustic corrections. This deficiency can be repaired with a hybrid ray-mode representation, wherein the caustic forming troublesome rays are replaced by a group of surface ducted modes, while the troublefree rays are kept intact. Such a formulation is demonstrated here in a model duct environment, wherein a line source emits a high-frequency Gaussian pulse. Comparison of the hybrid solution with a reference solution obtained by summation of normal modes reveals the accuracy of the hybrid scheme and its numerical efficiency at high frequencies. The hybrid solution automatically and self-consistently blends the raylike behavior of the received waveform at early times with the modelike behavior at late times, thereby providing a physically incisive interpretation of the propagation process.
Sound generation by flow over relatively deep cylindrical cavities
Authors: Parthasarathy S. P. , Cho Y. I. , Back L. H.
Published: October 2005

An experimental investigation has been conducted into the production of high-intensity tones by deep cylindrical cavities in a flat surface at relatively low Mach numbers (i.e., 0.12–0.24). The application of such a mechanism is to the acoustic coding of moving objects containing drilled cylindrical cavities. The sound intensity and frequency have been determined as functions of flow velocity, diameter, and depth of the cavities resulting in correlations to be used for the design of a whistle in the range of f=5–17 kHz. As a practical matter, it is possible to produce a whistle producing 106 dB at a 30.5-cm distance from a cylindrical cavity of 0.508 cm in diameter and 1.32 cm in depth with an airflow of 57.7 m/s past the hole. An eddy-driven oscillator is represented by a one-dimensional oscillator with a forcing term dependent on a time-delayed displacement. This simple model shows how the natural frequencies of the shear layer are pulled to the acoustic frequencies at resonance, describes the shape of resonance, and shows how the natural frequencies of a pipe with no flow correspond to actual frequencies of the whistle which depend on the flow through the factor (1−M)−1.
A precise technique for the measurement of acoustic cavitation thresholds and some preliminary results
Authors: Roy R. A. , Atchley A. A. , Crum L. A. , Fowlkes J. B. , Reidy J. J.
Published: October 2005

A description is given of a precise technique for measuring the threshold for acoustic cavitation inception. The system, which is automated so as to remove operator involvement, utilizes a slow ramping of the acoustic pressure amplitude until cavitation occurs. The detection criterion is the generation of a sufficiently intense sonoluminescent signal. Measurements made in filtered water show a well-defined, reproducible, and stable cavitation threshold. Measurements of the dependence of the threshold on filter size, on time, and on the concentration of dissolved ions for various salts are also presented. Many of these results appear anomalous.
Extraction and enhancement of spectral structure by the cochlea
Authors: Horst J. Wiebe , Javel Eric , Farley Glenn R.
Published: October 2005

The intensity dependence of signal processing in the cat cochlea was studied in responses of single auditory-nerve fibers for harmonic complexes having various amplitude and phase spectra. Analyses were based on information present in temporal discharge cadences, and they consisted of assessing Fourier spectra of period histograms synchronized to the period of the waveform fundamental. At low intensities, response spectra resembled filtered versions of the stimulus spectrum, with the amounts of filtering being determined by fibers’ tuning curves. At high intensities, response spectra exhibited nonlinear behavior and could differ dramatically from spectra obtained at low intensities. The high-intensity response typically emphasized one or more aspects of the stimulus spectrum. When the stimulus possessed equal component amplitudes and phases, the features that were emphasized at high intensities were the high- and low-frequency edges of the spectrum, and when the component at fiber CF was changed in phase or amplitude relative to the others, fibers primarily signaled the presence of the phase- or amplitude-shifted component. Many of the intensity-dependent changes in response spectra are accounted for by considering the effects of the compressive input–output nonlinearity operating at or peripheral to the hair-cell level on the temporal waveform.
Simulation of nonlinear acoustic systems using bilinear transform and higher-order simulators
Authors: Bold Gary E. J.
Published: October 2005

A difference equation simulator for a linear physical system specified in terms of either a differential equation or a rational function of s can be derived by applying the bilinear transform. It is shown how the method may be extended to enable simulation of nonlinear systems. The same formal procedure can be used with higher-order (e.g., Runge–Kutta) integrators to give considerably enhanced accuracy for the same step size. Three simple examples are given illustrating the method.
Memories of Bruce Lindsay
Authors: Beyer Robert T. , Davis Hallowell , Mason Warren P. , Martin Daniel W. , White Frederick E. , Cook Richard K. , Rudnick Isadore , Greenspan Martin , Kirwan Donald F.
Published: October 2005

R. Bruce Lindsay, reknowned physicist, administrator, educator, and editor, is remembered by his friends and colleagues.
In-air analysis of piezoelectric Tonpilz transducers in a wide frequency band using a mixed finite element–plane wave method
Authors: Decarpigny J. N. , Debus J. C. , Tocquet B. , Boucher D.
Published: October 2005

A detailed modal analysis of several axisymmetrical or fully three-dimensional Tonpilz transducers is carried out, both with a plane wave approach and with the finite element method. It allows identification and classification of the modes in a broad frequency range (longitudinal modes of the ceramic stack, flexural modes of the head mass, and longitudinal modes of the stress rod) and demonstrates that the motion of the ceramic part of the structure remains essentially of plane wave type. Following this conclusion, a mixed finite element–plane wave method is proposed and described, which gives fairly good results and uses the computational resources efficiently. Moreover, it is likely to be applied to other types of projectors.
Computer-steered microphone arrays for sound transduction in large rooms
Authors: Flanagan J. L. , Johnston J. D. , Zahn R. , Elko G. W.
Published: October 2005

The quality of sound pickup in large rooms—such as auditoriums, conference rooms, or classrooms—is impaired by reverberation and interfering noise sources. These degradations can be minimized by a transducer system that discriminates against sound arrivals from all directions except that of the desired source. A two-dimensional array of microphones can be electronically beam-steered to accomplish this directivity. This report gives the theory, design, and implementation of a microprocessor system for automatically steering a two-dimensional microphone array. The signal-seeking transducer system is implemented as a dual-beam ‘‘track-while-scan’’ array. It utilizes signal properties to distinguish between desired speech sources and interfering noise.
An examination of intra-articulator relative timing
Authors: Munhall Kevin G.
Published: October 2005

The relative timing of consonant and vowel related movements of the tongue dorsum across variations in stress patterns was examined in two subjects using a computerized pulsed ultrasound system. The patterns observed were similar to those reported by Tuller et al. [J. Exp. Psychol. H.P.P. 8, 460–472 (1982)] for interarticulator timing. Correlations between the duration of a ‘‘period,’’ defined as the interval between the onsets of movements associated with adjacent vowels, and the ‘‘latency,’’ defined as the interval between the beginning of the period and the point in the period at which movement associated with the intervocalic consonant begins, were positive and reliable. The source of this correlation pattern was examined and found not to be due to a scaling of an invariant phase relation but rather due to a main effect for stress on the vowel-to-vowel articulatory period combined with an artifactual part–whole correlation within each stress level.
Fundamental frequency correlates of stop consonant voicing and vowel quality in the speech of preadolescent children
Authors: Ohde Ralph N.
Published: October 2005

Fundamental frequency (F0) and voice onset time (VOT) were measured in utterances containing voiceless aspirated [ph, th, kh], voiceless unaspirated [sp, st, sk], and voiced [b, d, g] stop consonants produced in the context of [i, e, u, o, a] by 8- to 9-year-old subjects. The results revealed that VOT reliably differentiated voiceless aspirated from voiceless unaspirated and voiced stops, whereas F0 significantly contrasted voiced with voiceless aspirated and unaspirated stops, except for the first glottal period, where voiceless unaspirated stops contrasted with the other two categories. Fundamental frequency consistently differentiated vowel height in alveolar and velar stop consonant environments only. In comparing the results of these children and of adults, it was observed that the acoustic correlates of stop consonant voicing and vowel quality were different not only in absolute values, but also in terms of variability. Further analyses suggested that children were more variable in production due to inconsistency in achieving specific targets. The findings also suggest that, of the acoustic correlates of the voicing feature, the primary distinction of VOT is strongly developed by 8–9 years of age, whereas the secondary distinction of F0 is still in an emerging state.
The hearing aid feedback path: Mathematical simulations and experimental verification
Authors: Egolf David P. , Howell Henry C. , Weaver Kim A. , Barker D. Steven
Published: October 2005

Acoustic feedback in hearing aids has received little attention in the literature. Feedback occurs when stability conditions of the open-loop transfer function of an in situ hearing aid are violated. Solving the feedback problem will first require knowledge of the open-loop transfer function. Included in the open-loop transfer function is the acoustical path by which sound emanating from the earmold vent returns to the microphone (i.e., the feedback path). Reported herein are two different mathematical procedures for simulating transfer functions of the feedback path of an eyeglass-type hearing aid. In one procedure the vent exit was modeled as a point source of sound located on a flat plane, while it was treated as a point source on a sphere in the other. Results of laboratory experiments indicate that the mathematical models accurately predict those acoustic phenomena for which they were intended: point sources on plane and spherical baffles. Results of manikin experiments showed both models to be less accurate for simulating the feedback path around the human head. The maximum difference between experiment and theory was 6 dB at one frequency. Surprisingly, the flat-baffle model produced better agreement with experimental results than did the sphere model.
The spatial distribution of sound pressure within scaled replicas of the human ear canal
Authors: Stinson Michael R.
Published: October 2005

A theoretical model for calculating the variation of sound pressure within the ear canal is presented. The theory is an extension of the horn equation approach, and accounts for the variation of cross-sectional area and curvature of the ear canal along its length. Absorption of acoustic energy at the eardrum is included empirically through an effective eardum impedance that acts at a single location in the canal. For comparison, measurements of the distribution of sound pressure have been made in two replica ear canals. Both replicas have geometries that duplicate, as nearly as possible, that of a real human ear canal, except that they have been scaled up in size to increase the precision of measurements. One of the replicas explicitly contains a load impedance to provide acoustical absorption at a single eardrum position. Agreement between theory and experiment was good. It is clear that at higher frequencies (above about 6 kHz in human ear canals), this theoretical approach is preferable to the more usual ‘‘uniform cylinder’’ approximation for the ear canal. At higher frequencies, there is no unique eardrum pressure; rather, very large variations of sound pressure are found over the tympanic membrane surface.
Distortion product otoacoustic emissions in hearing-impaired mutant mice
Authors: Horner K. C. , Lenoir M. , Bock G. R.
Published: October 2005

The acoustic intermodulation distortion product (2f1–f2) was recorded in the ear canal of two different types of normally hearing mice and in four different types of hearing-impaired mutant mice. In the normally hearing animals, primary tones at levels of 60- to 100-dB SPL evoked distortion product emissions (DP’s) at 20–50 dB below the primary levels. In the hearing-impaired mutants the level was dependent on the particular type of auditory dysfunction associated with the mutation. In both the deafness and the viable dominant spotting mutants, where either the whole organ of Corti or the stria vascularis is affected by the mutation, no DP’s could be detected. The quivering mutant has a central auditory dysfunction associated with the nuclei of the superior olivary complex and the lateral lemniscus, with apparently normal cochlear function. DP’s at levels and thresholds similar to those in normally hearing animals were recorded in quivering mice. The Bronx Waltzer mutant has a full complement of outer hair cells but only about of 20%–25% inner hair cells. DP’s of small amplitude were recorded but the thresholds were raised by about 30 dB. The data suggest that the 2f1–f2 emission can be used as a noninvasive monitor of cochlear function.
Speech processing in the auditory system I: The representation of speech sounds in the responses of the auditory nerve
Authors: Shamma Shihab A.
Published: October 2005

In a previous paper the speech evoked spatio-temporal response patterns recorded in large populations of auditory-nerve fibers in the cat were examined [M. I. Miller and M. B. Sachs, J. Acoust. Soc. Am. 74, 502–517 (1983)]. The distribution of the relative phases of synchronized activity emerges as an important response feature reflecting the stimulus spectral parameters. Specifically, each strong low-order harmonic of the stimulus (≤1.5–2 kHz) dominates the synchrony of a relatively broad segment of fibers near its corresponding characteristic frequency (CF) location in a pattern which mirrors the underlying traveling wave component. Each such fiber segment can be roughly subdivided into two regions: (1) a region basal to the point of resonance of the harmonic where the fiber PST histograms accumulate only small delays (or phase shifts) relative to each other reflecting the fast speed of propagation of the traveling wave, and (2) a region at or very near the point of resonance where the responses exhibit drastic relative phase shifts owing to the sudden slow down of the traveling wave and the consequent rapid accumulation of phase shifts. These rapid phase shifts thus manifest themselves as steep and localized spatial discontinuities in an otherwise relatively uniform instantaneous pattern of activity across the fiber array, all occurring at the CF locations corresponding to the low-order harmonics of the stimulus.
A speech-to-noise ratio measurement algorithm
Authors: Sims J. T.
Published: October 2005

An algorithm to measure speech-to-noise ratios has been implemented on a minicomputer. The algorithm attributes the energy within each consecutive 20-ms frame of a speech-plus-noise waveform to either a speech or noise source. This discrimination process is based upon the known characteristics of frame energy histograms of such waveforms. In response to observed inaccuracies of this discrimination process in cases of low speech versus noise separation, a method of estimating the speech Vrms of the signal is incorporated which attempts to recover speech energy, ‘‘masked’’ by noise. The algorithm’s ability to track known speech-to-noise ratios on a decibel-for-decibel basis down to a ratio of approximately 5 dB has been demonstrated by experimentation.
Modal solutions, symmetry properties, and orthogonality conditions for elastic waves in cylinders
Authors: McKenna J. , Simpkins P. G.
Published: October 2005

Modal analysis is used to study the elastic wave motions in a rod of circular cross section. Two particular situations are considered: the semi-infinite rod with an arbitrary load applied at one end, and the finite length rod with arbitrary loads at each end. Interest in this problem was stimulated by experimental observations of flexural waves generated in high-strength optical fibers during tensile testing. The use of modal methods to examine pulse propagation in elastic cylinders has been limited by the complexity of the analysis. Here, a number of symmetry relationships are established which reduce the complexity and simplify the analysis. Orthogonality properties of the modes are derived and are used to obtain general solutions of the wave equation in the frequency domain. These solutions occur only when particular types of mixed boundary conditions are applied to the ends. It is believed that the solutions for the finite rod problem are new. The results generalize the Pochhammer–Chree theory.
Consonant recognition in quiet as a function of aging among normal hearing subjects
Authors: Gelfand Stanley A. , Piper Neil , Silman Shlomo
Published: October 2005

Consonant recognition in quiet using the Nonsense Syllable Test (NST) [Resnick et al., J. Acoust. Soc. Am. Suppl. 1 58, S114 (1975)] was investigated in 62 normal hearing subjects 20 to 65 years of age at their most comfortable listening levels (MCLs) and at 8 dB above and below MCL. Although overall consonant recognition performance was high (as expected for normal listeners), the effects of age decade, relative presentation level, and NST subsets were all significant, as was the interaction of age × level. The interactions of age × NST subset, and age × subset ×level were nonsignificant. These findings suggest that consonant recognition decreases with normal aging, particularly below MCL. However, the relative perceptual difficulty of the seven subtests is the same across age groups. Confusion matrices were similar across levels and age groups. Percent information transmitted for several consonant features was calculated from the confusion matrices. Older subjects showed decrements in performance primarily for the features recognized relatively less accurately by the younger subjects. The results suggest that normal hearing older individuals listening in quiet have decreased consonant recognition ability, but that their confusions are similar to those of younger persons.
The temporal course of simultaneous tone-on-tone masking
Authors: Bacon Sid P. , Viemeister Neal F.
Published: October 2005

Threshold for a 20-ms, 1-kHz signal was measured as a function of its temporal position within a longer duration gated masker; masker frequencies were below, at, and above 1 kHz. For a masker frequency above the signal frequency, there is a sizable temporal effect: As the onset of the signal is delayed, threshold decreases rapidly but then increases again as the signal approaches masker offset. Similar results can be observed for a masker frequency below the signal frequency, but that temporal effect is due to the detection of the cubic difference tone. The implication of this frequency-dependent temporal effect for measuring psychophysical tuning curves is discussed.
Relations between psychophysical data and speech perception for hearing-impaired subjects. II
Authors: Dreschler Wouter A. , Plomp Reinier
Published: October 2005

Twenty-one sensorineurally hearing-impaired adolescents were studied with an extensive battery of tone-perception, phoneme-perception, and speech-perception tests. Tests on loudness perception, frequency selectivity, and temporal resolution at the test frequencies of 500, 1000, and 2000 Hz were included. The mean values and the gradient across frequencies were used in further analysis. Phoneme-perception data were gathered by means of similarity judgments and phonemic confusions. Speech-reception thresholds were determined in quiet and in noise for unfiltered speech material, and with additional low-pass and high-pass filtering in noise. The results show that hearing loss for speech is related to both the frequency resolving power and temporal processing by the ear. Phoneme-perception parameters proved to be more related to the filtered-speech thresholds than to the thresholds for unfiltered speech. This finding may indicate that phoneme-perception parameters play only a secondary role, and for that reason their bridging function between tone perception and speech perception is only limited.
Track segment association with a distributed field of sensors
Authors: Mucci R. , Arnold J. , Bar-Shalom Y.
Published: October 2005

A performance prediction procedure is developed for geographical localization of targets traversing through a distributed field of sensors. The analysis is based on a tracking scheme where targets are detected and tracked locally by as few as two sensors. Target estimates from adjacent sensor sets are extrapolated to an estimated time of intersection, and the hypothesis is made that the two segments have a common origin (i.e., that the two tracks have emanated from a single target). Through a statistical test based on a maximum likelihood ratio, this hypothesis is either accepted or rejected. It is then shown that associated target track segments can be reestimated using the combined set of measurements. The theoretical results have been corroborated by applying a maximum likelihood tracking algorithm to simulated data and observing the results for a series of Monte Carlo simulations. The actual and expected statistics on the probability of correctly associating target segments, along with the localization ellipses, are displayed.
Investigation of the amplitude distribution of AT-cut quartz crystals
Authors: Hertl S. , Wimmer L. , Benes E.
Published: October 2005

The three-dimensional equations of linear piezoelectricity are used to compute the mechanical vibration amplitude distributions, as well as the resonance frequencies of plano-convex circular AT-cut quartz crystal resonators. These computations are compared with vibration amplitude measurements employing a new technique that utilizes the speckle effect. Very good agreement has been found between the measured and the computed vibration amplitude distributions.
Acoustic normal mode propagation through a three-dimensional internal wave field
Authors: Penland Cecile
Published: October 2005

In describing the effects of internal waves on acoustic normal modes excited by a time-harmonic point source, all previous descriptions have neglected the existence of azimuthal fluctuations in the acoustic field. This study compares this azimuthally symmetric case with the case where azimuthal fluctuations in the acoustic field are taken into account. Although azimuthal variations can enhance the randomization of interference effects so that different depth modes decorrelate more quickly in range, this enchancement is generally small. The autocorrelation functions of the depth modes approach equipartition at long ranges as in the azimuthally symmetric case, as long as each range function is interpreted as a sum of all the azimuthal modes. The mean energy flux vector 〈j〉 becomes radial at long ranges. Integral expressions for the scattering coefficients and interference terms have been derived so that these quantities can be calculated without having to perform an infinite sum.
Direct acoustic scattering for one-dimensional lossy media
Authors: Bai Jing , Rorres Chris , Pedersen Peder C. , Tretiak Oleh J.
Published: October 2005

The scattering of acoustic waves by inhomogeneities within a one-dimensional lossy medium is investigated. The inhomogeneities may be spatial variations in the attenuation coefficient of the lossy medium and/or variations in its density and wave velocity. The frequency dependence of the attenuation coefficient is modeled after loss mechanisms governed by viscosity, heat conduction, and single and multiple relaxation processes. Two methods previously developed for lossless media—the transmission matrix method and the forward scattering or impediography method—are extended to treat the determination of the reflection and transmission coefficients of an inhomogeneous lossy medium. These scattering coefficients are numerically determined for several one-dimensional media with varying density and attenuation profiles.
PVF2 velocity hydrophones
Authors: Josserand Michel A. , Maerfeld Charles
Published: October 2005

In underwater acoustical low-frequency applications a hydrophone with intrinsic directivity is often needed. Poled polyvinylidene fluoride (PVF2) bimorphs are suitable for design of velocity hydrophones. Because of its softness and mechanical flexibility, a PVF2 bimorph associated with an inertial structure follows water particle movement, and so the output current from the hydrophone is proportional to the particle velocity of the incident wave. Moreover, the PVF2 bimorphs manufactured in our laboratories (whose thickness may be greater than 1 mm), make possible a compromise between the opposite requirements that a high sensitivity demands a thick polymer and for a high mechanical flexibility of the membrane (to obtain the lowest possible resonance frequency) a thin bimorph is needed. The study of a low-frequency particle velocity calibration system made possible the achievement of small lightweight PVF2 velocity hydrophones showing an intrinsic directivity below 100 Hz. The same hydrophone can be connected so as to be also pressure sensitive: Intensity measurements might become possible with only one sensor.
Sound velocity in lipids, oils, waxes, and their mixtures using an acoustic levitation technique
Authors: Apfel R. E. , Young R. E. , Varanasi U. , Maloney J. R. , Malins D. C.
Published: October 2005

An acoustic levitation technique has been used to measure acoustical properties of single drops of a number of pure oils, some of which are found in the porpoise dome. Some of the data may be useful in elucidating the relation between lipid composition and sound transmission in porpoise head.
Effects of frequency modulation on absolute, masked, and reflex thresholds
Authors: Resnick Steffi B. , Pillion Joseph P. , Heinz John M.
Published: October 2005

Behavioral and acoustic reflex thresholds were determined for five normal-hearing subjects in response to carrier signals of 500 and 2000 Hz which were unmodulated or modulated sinusoidally at rates of 2, 20, and 200 times per second with frequency deviations (Δ f) of 30, 100, and 300 Hz. Behavioral (absolute and masked) thresholds were determined using an adaptive two-alternative forced-choice procedure. Acoustic reflex thresholds were determined by visual inspection of stored reflex waveforms. Frequency modulation was not found to exert a systematic effect at absolute threshold. Frequency modulation did affect threshold estimates systematically, but differentially, at masked threshold and acoustic reflex threshold. Increasing the frequency deviation of the modulation was associated with an increase in masked threshold and with a decrease in acoustic reflex threshold at both test frequencies. The findings are discussed in terms of critical band phenomena.
The effect of improper normalization on the performance of an automated energy detector
Authors: Struzinski William A. , Lowe Edward D.
Published: October 2005

This paper presents the results of a simulation experiment to determine the effect of improper normalization on the performance of an automated energy detector. The normalization algorithms investigated are the two-pass mean, the split two-pass mean, the split three-pass mean, the split average exclude average, and the order truncate average normalizers.
Low-frequency absorption of sound in air
Authors: Zuckerwar Allan J. , Meredith Roger W.
Published: October 2005

An extensive series of sound absorption measurements were taken in air over a range of frequencies from 10–2500 Hz, of temperature from 10°–50 °C, and of relative humidity from 0.3%–92%, all at a pressure of 1 atm. The N2 and O2 vibrational absorption components were extracted from a relatively large background absorption by means of a differential technique using a background gas, 89.5% N2–10.5% Ar, which matches the sound speed of air but has no molecular absorption over the range of experimental frequencies. The measurements reveal: (1) The humidity dependence of the relaxation frequency of N2 in air exceeds that in binary N2–H2O mixtures, possibly because the vibrational modes of CO2 provide a competing relaxation path for V–V exchange between N2 and H2O molecules; (2) the temperature dependence of the relaxation frequency of humid N2 is nearly the same in air as in binary mixtures; and (3) at very low humidities the relaxation frequency of O2 appears to approach a limiting value much lower than that determined from a prior study. The present experimental results, together with those of an earlier study at high frequencies, provide a substantial data base leading to revised formulas for standard values of the relaxation frequencies of N2 and O2.
Penetration of sound from a point source into a rigid porous medium
Authors: Richards Trevor L. , Attenborough Keith , Heap Nicholas W. , Watson Andrew P.
Published: October 2005

A method of steepest-descents integration suitable for use when a pole may approach near to one of the saddle points in the complex plane of integration is applied to the problem of predicting the field resulting from a point source near to the interface between two semi-infinite media. It has been shown that it is possible to obtain asymptotic approximations for the field above or below the interface to any desired degree of accuracy in a way that is more straightforward and less algebraically cumbersome than that which is employed when using the subtraction of the pole technique. Approximation for the case where the receiving medium has a high refractive index produces the expected result whereby the field below the interface is related to that incident on the interface according to Snell’s law. Measurements are made of the phase and amplitude of the sound field below the surface of a 0.5-m-thick layer of glass fiber material, relative to those of the field at the surface due to the point source close to the surface. Experiments are reported using continuous, swept-tone burst and spark-discharge sources. The measured data are compared with theoretical predictions. The predictions require knowledge of the complex propagation constant within the material. Use of an empirical formula together with measured flow resistivity is found to produce overestimates of attenuation, whereas use of a theory for propagation in a rigid porous medium based upon a classical capillary-pore approach is found to enable tolerable agreement with measured data. This confirms directly the locally reacting nature of the boundary over the frequency range of the measurement.
Wave–wave interactions, microseisms, and infrasonic ambient noise in the ocean
Authors: Kibblewhite A. C. , Ewans K. C.
Published: October 2005

Underwater ambient noise is known to be wind dependent. Several mechanisms have been proposed to explain the nature of the transfer of energy from the wind to the acoustic noise field. Examples include wind and wave turbulence and nonlinear interactions between surface waves. This study examines these wind-related mechanisms at the low end of the acoustic spectrum. Data from a long-term investigation of ocean waves and the associated microseism response recorded ashore have provided evidence helpful in identifying the active processes. It is concluded that the noise field below 5 Hz is controlled by nonlinear wave–wave interactions and that existing theories account adequately for the effects observed.
Impulse propagation over grassland in the presence of temperature and wind gradients
Authors: Cramond A. J. , Don C. G.
Published: October 2005

Measurements are presented of the acoustic waveforms obtained over grassland at distances out to 300 m from an impulsive source. When propagating downwind, the pulses exhibit only slight attenuation over that predicted by geometric and atmospheric absorption effects. However, in the presence of a dominant temperature gradient and when propagating into a wind, a marked excess attenuation commences at a region corresponding to a shadow boundary. Inside the meteorological shadow zone, the recorded impulses have quite a different shape, being almost symmetric with a duration increasing with distance from the source. Attempts to fit the pulse behavior by using only the ground wave term were partially successful. A more promising approach is to model the shadow boundary as a frequency filter whose characteristics depend on the temperature and wind gradients.
Measurements of meteorological effects on long-range sound propagation using m-sequence correlation
Authors: Hallberg Bengt , Larsson Conny , Israelsson Sven
Published: October 2005

An m-sequence correlation method was used for measuring sound levels 1-km distant from a point source 1.25 m above the ground, a crop field and a snow-covered ground, respectively. Meteorological parameters were monitored simultaneously. Wind speed and temperature were measured at several elevations, together with wind direction, relative humidity, and atmospheric pressure at a single height. The effect of refraction on the sound level variation is interpreted in terms of the curvature for near-horizontal sound rays. It is found that the sound level increases as the curvature goes from negative to positive values. Comparisons with other investigations were made, and qualitative agreement is found. Calculations with acoustic theory were made, the results of which show large discrepancies with those measured.
An application of the spheroidal-coordinate-based transition matrix: The acoustic scattering from high aspect ratio solids
Authors: Hackman Roger H. , Todoroff Douglas G.
Published: October 2005

In a previous paper [Roger H. Hackman, J. Acoust. Soc. Am. 75, 35–45 (1984)], a spheroidal-coordinate-based transition matrix formalism was established for acoustic and elastic wave scattering. In this paper, the acoustic scattering by a solid elastic cylinder with hemispherical endcaps and a length-to-diameter ratio of 10 is considered. Numerical results are presented for the backscattered form function as a function of frequency for various angles of incidence. These results are compared with experimental measurements taken at the Naval Coastal Systems Center and given a physical interpretation.
A new approach to the derivation of the impulse response of a rectangular piston
Authors: Scarano G. , Denisenko N. , Matteucci M. , Pappalardo M.
Published: October 2005

In this work, a ‘‘spatial convolution’’ approach is employed to derive an exact solution for the impulse response of the uniformly vibrating rectangular piston. While in the classical approach, proposed by Stepanishen [J. Acoust. Soc. Am. 49, 1629–1638 (1971)], the impulse response is regarded as a function of time for a fixed field point location, here the impulse response is regarded as a function of the spatial coordinates, for a fixed time instant. The introduction of ‘‘line masses,’’ and the use of their integral properties, allow a simple derivation of the analytical expression of the impulse response. Computational results show a complete agreement with previously reported data for the same source geometry and field point locations. The diffraction analysis is also extended to the nonuniformly vibrating rectangular piston.
Transformation of sound-pressure level from the free field to the eardrum presented in numerical form
Authors: Shaw E. A. G. , Vaillancourt M. M.
Published: October 2005

In an earlier work [E. A. G. Shaw, J. Acoust. Soc. Am. 56, 1848–1861 (1974)], self-consistent families of curves which best fitted the experimental data from 12 studies were presented to show the average sound-pressure transformation from the free field to the human eardrum in the horizontal plane. Tabulated values of azimuthal dependence at 15-deg intervals in azimuth and transformation to the eardrum at 0° azimuth are given at 43 selected frequencies between 0.2 and 12 kHz. These values are self-consistent within 0.1 dB.