bluuebunny/crossref_metadata_2025 huggingface dataset:
The transient wave fields in the vicinity of the cuspoid caustics
Authors: Brown Michael G.
Published: October 2005

A general formalism is presented for the study of the transient wave fields in the vicinity of caustics of arbitrary complexity. The caustics are classified using catastrophe theory. In the present study, a general introduction to the subject is presented and explicit results (numerical and analytical) for the cuspoid family of catastrophes are given. Numerical results are presented for the fold, cusp, and swallowtail catastrophes which show the smooth variation of the acoustic field as the control parameters are independently varied. These results vividly demonstrate the phenomenon of ray focusing, showing the number of rays which converge at each catastrophe, the resulting phase shifts they undergo, as well as their decay in shadow regions. Analytical results are given which describe the time-dependent acoustic field on and at large distances away from each of the cuspoid catastrophes. Four sets of numbers are introduced which describe the behavior of the wave field in the vicinity of each catastrophe. These are: (1) an exponent which describes the temporal decay of the acoustic field on the most singular point of each catastrophe; (2) a number which describes the asymmetry of the time-dependent acoustic field on the most singular point of each catastrophe; (3) an exponent which describes the time separation as a function of control parameter between individual ray arrivals as each of the control parameters are independently varied; and (4) an exponent which describes the asymptotic decay as a function of control parameter of each constituent ray arrival. Sets (1) and (3) are shown to be simply related to the singularity and fringe indices previously introduced by Arnold [V. I. Arnold, Usp. Mat. Nauk. 30(5), 1–75 (1975)] and Berry [M. V. Berry, J. Phys. A10, 2061–2081 (1977)], respectively. It is argued that many features of the frequency domain representation of the acoustic field in the vicinity of the catastrophes are most easily understood by examining the time domain representation.
On the spectral theory of wave propagation in a weakly range-dependent environment
Authors: Chan Kuan-Kin
Published: October 2005

The spectral theory of wave propagation in a weakly range-dependent environment is deduced from the corresponding theory for a wedge-shaped structure. The solution obtained is compared to that derived previously, which suggests that some modifications are necessary in the previous formulation in order to bring the solution into a symmetric form.
Helmholtz integral formulation of the sonar equations
Authors: Schenck Harry A.
Published: October 2005

The sonar equations provide a convenient way to calculate the detection range of actual and proposed sonar systems. They are simple, but approximate, relationships between parameters that describe the effects of source, target, and acoustic medium independently. The purpose of this paper is to derive an exact form of the active sonar equation by using the Helmholtz integral formulation to solve the boundary-value problem with source and target both present in the medium. The resulting equation involves combinations of linear integral operators; however, it is suitable for solution by numerical techniques already developed for radiation from objects of arbitrary shape. Furthermore, it is shown that these integral operators reduce to multiplicative factors which represent general definitions of the source level, transmission loss, and target strength when the source-to-target distance is large. Thus this work establishes a basis for the sonar equations as the limiting form of an exact boundary-value problem and presents formulas for calculating the sonar parameters.
Discrimination of interaural temporal disparities by normal-hearing listeners and listeners with high-frequency sensorineural hearing loss
Authors: Smoski Walter J. , Trahiotis Constantine
Published: October 2005

Thresholds of ongoing interaural time difference (ITD) were obtained from normal-hearing and hearing-impaired listeners who had high-frequency, sensorineural hearing loss. Several stimuli (a 500-Hz sinusoid, a narrow-band noise centered at 500 Hz, a sinusoidally amplitude-modulated 4000-Hz tone, and a narrow-band noise centered at 4000 Hz) and two criteria [equal sound-pressure level (Eq SPL) and equal sensation level (Eq SL)] for determining the level of stimuli presented to each listener were employed. The ITD thresholds and slopes of the psychometric functions were elevated for hearing-impaired listeners for the two high-frequency stimuli in comparison to: (a) the listener’s own low-frequency thresholds; and (b) data obtained from normal-hearing listeners for stimuli presented with Eq SPL interaurally. The two groups of listeners required similar ITDs to reach threshold when stimuli were presented at Eq SLs to each ear. For low-frequency stimuli, the ITD thresholds of the hearing-impaired listener were generally slightly greater than those obtained from the normal-hearing listeners. Whether these stimuli were presented at either Eq SPL or Eq SL did not differentially affect the ITD thresholds across groups.
Performance in several binaural-interaction experiments
Authors: Koehnke Janet , Colburn H. Steven , Durlach Nathaniel I.
Published: October 2005

The relationship between interaural correlation discrimination and binaural detection was investigated using common experimental procedures and common subjects. Psychometric functions were obtained for four normal-hearing subjects at 500 and 4000 Hz using third-octave noise signals for the correlation discrimination experiment, and pure-tone signals and third-octave noise maskers for the detection experiment. Results from these two measurements, which were compared by expressing the signal-to-noise ratio as an equivalent change in interaural correlation, support the idea that interaural correlation discrimination and binaural detection are closely related. Since large intersubject differences in binaural performance were observed in these experiments, interaural-time, interaural-intensity, and monaural-intensity discrimination were measured in a second experiment. The results of the second experiment show large intersubject differences for the interaural tasks, but not for the monaural task.
Lateralization of low-frequency tones and narrow bands of noise
Authors: Schiano Jeffrey L. , Trahiotis Constantine , Bernstein Leslie R.
Published: October 2005

It is well known and universally accepted that people’s ability to use ongoing interaural temporal disparities conveyed via pure tones is limited to frequencies below 1600 Hz. We wish to determine if this limitation is the result of the constant amplitude and periodic axis-crossings which characterize pure tones. To this end, an acoustic pointing task was employed in which listeners varied the interaural intensitive difference of a 500-Hz narrow-band noise (the pointer) so that the position of its intracranial image matched that of a second, experimenter-controlled stimulus (the target). Targets were either pure tones or narrow bands of noise (50 or 100 Hz wide). The narrow bands of noise were delayed interaurally in two distinct manners: Either the entire waveform or only the carrier was delayed. In the latter case, the envelopes and phase-functions of the bands of noise were identical interaurally. This resulted in noises which resemble the pure-tone case in that the interaural delay is manifested as a constant phase-shift and resemble ordinary noises in that the envelope and phase are random functions of time. Surprisingly, it appears that all three targets were lateralized virtually identically regardless of frequency or bandwidth. Apparently, the dynamically changing envelopes and phases did not affect the listeners’ use of interaural temporal disparities in any discernible fashion.
K-space scattering formulation of the absorptive full fluid elastic scalar wave equation in the time domain
Authors: Compani-Tabrizi Behrooz
Published: October 2005

The absorptive full fluid elastic scalar wave equation is developed by deriving the full fluid elastic scalar wave equation from the first principles and adding an absorptive term to the result. The time domain solution to the initial value forward scattering problem is developed for this equation. The solution algorithm is an exact numerical solution and is useful in pressure wave modeling for media with spatially varying velocity, density, and attenuation profiles. The number of operations per time step is of the order of N log2 N, where N is the number of spatial points into which the model has been discretized.
Laboratory studies of diffuse waves in plates
Authors: Weaver Richard L.
Published: October 2005

Measurements were conducted on the reverberant diffuse elastodynamic field in a 30- ×30- ×1.21-cm aluminum plate, the disturbances being generated by simulated acoustic emission concentrated step loads. The acoustic response in the 50- to 500-kHz range was monitored over periods of 16 ms, long compared to the 100-μs acoustic transit time across the width or length of the plate. Accurate power spectra estimates were found to require the collection of large amounts of data and to require correction of this data for the effects of absorption, or internal friction. Comparison of the frequency, time, and spatially averaged power spectra with theoretical predictions shows substantial agreement.
Reconstruction of one-dimensional inhomogeneities in elastic modulus and density using acoustic dimensional resonances
Authors: Norton Stephen J. , Testardi Louis R.
Published: October 2005

A method is described for quantitatively reconstructing a spatial inhomogeneity along a one-dimensional structure from measurements of its resonant frequencies (fundamental and higher modes). A relationship between the shifts in the resonant frequencies of the structure due to a material inhomogeneity (computed relative to the frequencies of the homogeneous state) and the coefficients in a Fourier expansion of the inhomogeneity, which holds to the first order in the material perturbation, is derived. If a number of successive resonant frequencies are excited and measured, the unknown inhomogeneity may then be reconstructed by Fourier summation. The material inhomogeneity recovered by this technique is the sum of the fractional changes in elastic modulus and density. For simplicity, the analysis is carried out in one dimension in the absence of damping. Compared to pulse-echo methods, the advantages of the dimensional resonance method are that it can image slowly varying impedance variations, can utilize narrow bandwidth detection, has its signal enhanced by the resonant Q, and generally utilizes lower frequencies where problems of attenuation and scattering are less serious.
Diffractive corrections to the high-frequency Kirchhoff approximation
Authors: McDaniel Suzanne T.
Published: October 2005

Diffractive corrections to the physical optics solution for the scattering of high-frequency sound by a random rough pressure release surface are derived. The correction terms are obtained by applying the composite-roughness theory to an expansion of the scattering integral. Results are presented for a three-dimensional rough surface and are compared with those obtained using a conventional composite-roughness approach.
Application of a Neumann-series method to two problems in acoustic radiation theory that are formulated in terms of Green’s functions
Authors: Rudgers Anthony J.
Published: October 2005

Two problems in radiation theory are analyzed. In the first problem, two acoustic sources in a fluid interact via their radiated pressure field. Each source may have an arbitrary shape and an arbitrary nonuniform surface vibration. The two sources may be placed in the fluid in an arbitrary fashion, so that there is no preferred orientation of one with respect to the other. A Neumann-series method is used to simplify that term in the integral equation expressing the pressure field which describes the interactions taking place between the sources. By use of this method, the pressure field can be expressed in terms of the Green’s functions of the individual sources, rather than in terms of an abstract ad hoc Green’s function defined on the disjoint surface that comprises the surfaces of both sources. This field formulation is used to express the self and mutual radiation impedances of the sources. A physical description of the interactions taking place between the sources is given. This description is suggested by the form of the equation describing the pressure field that results when the Neumann-series method is used. In the second problem, the exterior Neumann and Dirichlet Green’s functions are analytically determined for a radiating acoustic source with an arbitrary shape and with an arbitrary nonuniform surface vibration. These Green’s functions are constructed by using a Neumann-series method to simplify that term in the integral equation expressing the pressure field which describes the interaction of the source with its own radiation. In principle, the exterior Green’s functions, which are expressed in terms of the geometry of the source and the free-space Green’s function for the Helmholtz equation, are calculable for any source by performing a series of elementary mathematical operations.
Scattering of elastic waves by a smooth rigid movable inclusion
Authors: Olsson Peter
Published: October 2005

The null-field approach is used for treating the problem of scattering by a smooth rigid movable inclusion of finite mass. The solution is obtained both directly and as a limit of the solution to the problem of scattering by a smooth elastic obstacle. The infinite mass limit for the smooth rigid movable inclusion is also investigated, and it is shown that while the immovable smooth spherical rigid body violates Rayleigh’s law, the movable inclusion does not. Numerical examples for spheres and spheroids are presented.
Directional dependence of ultrasonic propagation in textured polycrystals
Authors: Hirsekorn Sigrun
Published: October 2005

The theory of ultrasonic wave propagation in textured polycrystals presented previously [S. Hirsekorn, J. Acoust. Soc. Am. 77, 832–843 (1985)] for propagation and polarization parallel to symmetry axes of texture is generalized to calculate the directional-dependent scattering coefficients and phase and group velocities of plane waves with arbitrary propagation and polarization direction as a function of frequency. The analytical calculations are carried out for cubic polycrystals with orthorhombic texture symmetry. Numerical evaluation is done for an austenitic weld metal. The results are compared to those of the frequency-independent description of ultrasonic propagation.
Three-dimensional acoustic analysis of circular expansion chambers with a side inlet and a side outlet
Authors: Yi Sung-Il , Lee Byung-Ho
Published: October 2005

The effects of higher-order acoustic modes upon the performance of a circular expansion chamber with its inlet and outlet located on the cylinder wall are investigated. The sound distribution in the expansion chamber is obtained, theoretically, considering the influences of the diffracted sound pressure generated by the presence of end plates in the chamber. A theoretical method for the estimation of the transmission loss is suggested by using the derived four pole parameters, assuming that the chamber can be modeled as a piston-driven circular rigid cylinder. A series of experimental observations are taken for verification, and it is found that they are in good agreement with the theoretical results. The influences of those modes are studied for a variety of chamber lengths and combined inlet/outlet locations. As a result of this study, it is concluded that the diffracted sound pressure affects the performance of the expansion chamber considerably in the range above the cutoff frequency of the n=1, m=0 asymmetric mode, and that the plane-wave theory can hardly be adopted even in the low-frequency range where the fundamental mode prevails.
Transmission loss optimization in acoustic sandwich panels
Authors: Makris Spilios E. , Dym Clive L. , Smith J. MacGregor
Published: October 2005

Considering the sound transmission loss (TL) of a sandwich panel as the single objective, different optimization techniques are examined and a sophisticated computer program is used to find the optimum TL. Also, for one of the possible case studies such as core optimization, closed-form expressions are given between TL and the core-design variables for different sets of skins. The significance of these functional relationships lies in the fact that the panel designer can bypass the necessity of using a sophisticated software package in order to assess explicitly the dependence of the TL on core thickness and density.
Measurement of down-slope sound propagation from a shallow source to a deep ocean receiver
Authors: Carey William M.
Published: October 2005

An experiment has been performed to investigate the coupling of surface–ship noise to the deep ocean sound channel. These calibrated measurements of sound propagation from the 18-m, 135-Hz source were obtained at a deep ocean receiver while the source tow proceeded from deep water up the Sable Island Bank at ranges between 730 and 910 km. The sound propagation path was from the cold slope waters over the bank through the Gulf Stream and to the edge of the Sargasso Sea. The mean value of the transmission loss was 110 dB with a down-slope enhancement estimated to be 4 dB resulting from the combined effects of trapping in the strong shallow sound channel and reflections from the slope. Comparisons with calculated results using the parabolic equation method were good and demonstrate coupling to the deep ocean sound channel. The acoustic field, sampled by 16 transverse hydrophone groups with a 4.75-m center spacing over six consecutive (12.5 s, 0.08 Hz) samples, yielded a mean standard deviation of 1.7 dB (6≤S/N≤20 dB) corresponding to a coefficient of variation of 0.6. Coherent summation of slope-reflected and deep-refracted hydrophone signals yielded estimated mean values of the spatial coherence of 0.89 and an estimated spatial coherence length of 460 m, when multipath effects were not dominant; however, these estimates were found to range as low as 0.63 and 150 m. These results facilitate the interpretation of the spatial coherence of the ship-induced, ‘‘slope-enhanced’’ contribution to deep ocean ambient noise.
Sonically produced heat in a fluid with bulk viscosity and shear viscosity
Authors: Nyborg Wesley L.
Published: October 2005

In a viscous fluid, sound produces heat in a spatial pattern which, in general, depends on the relative magnitudes of the shear viscosity coefficient η and the bulk viscosity coefficient B′. It is well known that when the particle velocity components ui relative to Cartesian coordinates xi are given for an arbitrary sound field, or any field of flow, the volume rate of heat production qv can be determined from a dissipation function in the form B′T1+ηT2. Here, T1 and T2 are quadratic functions involving derivatives of the type ∂ui/∂xj. In this paper, examples are discussed for continuous monofrequency sound fields, including crossed plane waves, as well as focused and unfocused fields. In these examples, spatial distributions of the time-averaged quantity 〈qv〉 for media in which the loss mechanism is primarily bulk viscosity are compared to those for media in which shear viscosity dominates.
Ultrasound fields in attenuating media
Authors: Lerch R. , Friedrich W.
Published: October 2005

For medical ultrasonic imaging and for nondestructive testing, the attenuation of pressure waves and the resulting shift in wave velocity are important features in commonly used transmission media such as biological tissue. An algorithm for the numerical evaluation of pressure field distributions generated by ultrasonic transducers is presented. The attenuation and dispersion of the sound transmission medium are taken into consideration. The sound fields are computed numerically for continuous wave as well as pulse excitation. The transducer has plane or gently curved geometry and is embedded in a plane rigid baffle. The numerically determined pressure fields are presented as 3D plots, as gray-scale images for a fixed time stamp (like a snapshot), or as isobars regarding the maximum values over time for each local point in the area under investigation. The algorithm described here can be utilized as a tool for design of ultrasound transducers, especially array antennas.
Jacobi sensor arrangement for maximum array directivity
Authors: Weston David E.
Published: October 2005

The problem is, given n sensors or sources, to find the arrangement, the weights, and the delays necessary to maximize the array directivity. The likely solution is a vanishingly short equispaced linear array with symmetrical weights and regular delay increments, intended for signals at endfire. For such an array it is proved that the necessary angular pattern is specified by a Jacobi polynomial, and that directivity is equal to n2. There is much discussion on the meaning of this result, including the differences on changing to two dimensions. The design methods for practical arrays are discussed.
Jacobi arrays and circle relationships
Authors: Weston David E.
Published: October 2005

The previously derived Jacobi array is a vanishingly short equispaced linear array which maximizes the directivity for one endfire beam. For n sensors the directivity is n2, and for small n there is little fall-off for practical designs. It is related to the Gegenbauer array which maximizes directivity with two symmetrical endfire beams; and to the Legendre array which minimizes radiated power under certain constraints. It is explained why the pattern of zeros, for these and for some other polynomial arrays, has to obey a circle relationship, and a more accurate circle relationship is presented.
On the location of frequencies of maximum acoustic-to-seismic coupling
Authors: Sabatier James M. , Bass Henry E. , Elliott Glenn R.
Published: October 2005

Measurements of the acoustic-to-seismic transfer function (ratio of the normal soil particle velocity at a depth d to the acoustic pressure at the surface) for outdoor ground surfaces quite typically reveal a series of maxima and minima. In a publication [Sabatier et al., J. Acoust. Soc. Am. 80, 646–649 (1986)], the location and magnitude of these maxima are measured and predicted for several outdoor ground surfaces using a layered poroelastic model of the ground surface. In this paper, the seismic transfer function for a desert site is compared to the seismic transfer function for holes dug in the desert floor which were filled with pumice (volcanic rock). The hole geometry was rectangular and the hole depths varied from 0.25–2.0 m. The p- and s-wave speeds, densities, porosities, and flow resistivities for the desert floor and pumice were all measured. By varying the hole depth and the fill material, the maxima in the seismic transfer function can be shifted in frequency and the locations of the maxima compare reasonably with that of a hard-backed layer calculation. The area or extent of the acoustic-to-seismic coupling for pumice was determined to be less than 1 m2.
Influence of the free modes of vibration on the acoustic scattering of a circular cylindrical shell
Authors: Izbicki J. L. , Maze G. , Ripoche J.
Published: October 2005

The scattering of an acoustic wave by an elastic circular cylindrical shell immersed in water depends on the natural modes of the target. Two groups of natural modes may be considered. The first group is related to circumferential waves which propagate around the tube. These resonances are provided by the resonance scattering theory. The second group is related to waves whose direction of propagation is parallel to the axis of the tube. The calculation of the natural modes and the experimental data obtained by the ‘‘method of isolation and identification of the resonances’’ agree very well.
Comment on ‘‘Linear inviscid wave propagation in a waveguide having a single boundary discontinuity: Part II: Application’’ [J. Acoust. Soc. Am. 7
5, 356–362 (1984)]
Authors: Bruggeman Jan C. , van de Wetering Theodorus F. H.
Published: October 2005

Some remarks are presented on the transmission of long wavelength acoustic waves in a waveguide with a right angle bend as treated by Thompson [J. Acoust. Soc. Am. 75, 356–362 (1984)]. A corrected expression for the acoustic pressure across the bend is compared with measurements by Lippert [Acustica 4, 313–319 (1954)].
Response to ‘‘Comment on ‘Linear inviscid wave propagation in a waveguide having a single boundary discontinuity: Part II: Application [J. Acoust. Soc. Am. 7
5, 356–362 (1984)]’ ’’
Authors: Thompson Charles
Published: October 2005

This paper addresses the comments of Dr. Bruggeman and Dr. van de Wetering. The source of the error present in the paper entitled ‘‘Linear inviscid wave propagation in a waveguide having a single boundary discontinuity: Part II: Application’’ is addressed. A rational fraction approximation for the transmission coefficient is presented.
Measurement of bow motion and bow force in violin playing
Authors: Askenfelt Anders
Published: October 2005

A simple piece of equipment which makes it possible to simultaneously register the motion of the violin bow and the downward force on the string (‘‘bow pressure’’) under normal playing conditions is described. Registrations of various bowing gestures in violin playing obtained with the equipment are presented and discussed.
The stop–glide distinction: Acoustic analysis and perceptual effect of variation in syllable amplitude envelope for initial /b/ and /w/
Authors: Nittrouer Susan , Studdert-Kennedy Michael
Published: October 2005

Amplitude change at consonantal release has been proposed as an invariant acoustic property distinguishing between the classes of stops and glides [Mack and Blumstein, J. Acoust. Soc. Am. 73, 1739–1750 (1983)]. Following procedures of Mack and Blumstein, we measured the amplitude change in the vicinity of the consonantal release for two speakers. The results for one speaker matched those of Mack and Blumstein, while those for the second speaker showed some differences. In a subsequent experiment, we tested the hypothesis that a difference in amplitude change serves as an invariant perceptual cue for distinguishing between continuants and noncontinuants, and more specifically, as a critical cue for identifying stops and glides [Shinn and Blumstein, J. Acoust. Soc. Am. 75, 1243–1252 (1984)]. Interchanging the amplitude envelopes of natural /bV/ and /wV/ syllables containing the same vowel had little effect on perception: 97% of all syllables were identified as originally produced. Thus, although amplitude change in the vicinity of consonantal release may distinguish acoustically between stops and glides with some consistency, the change is not fully invariant, and certainly does not seem to be a critical perceptual cue in natural speech.
Speech identification under simulated hearing-aid frequency response characteristics in relation to sensitivity, frequency resolution, and temporal resolution
Authors: Lutman Mark E. , Clark Julia
Published: October 2005

Word identification in noise was measured adaptively under flat and rising frequency response conditions to represent basic alternatives for a hearing-aid characteristic. The speech test results were compared with measures of sensitivity, loudness tolerance, frequency resolution, and temporal resolution in 23 hearing-aid users with mild or moderate sensorineural hearing losses. Subjects also rated the two frequency responses for preference and subjective quality. A paradoxical relationship was found whereby superior speech performance under the flat condition was associated with preference for the rising condition, and vice versa. No combinations of psychoacoustic variables satisfactorily explained either relative performance or preference, although high-frequency sensitivity and upward spread of masking were implicated. Absolute speech performance was related to sensitivity at 2 kHz, age, and sex, but not to frequency resolution once other factors were partialed. Temporal resolution was also a factor, but this was due largely to the influence of extreme values in two subjects. It is concluded that, for moderate degrees of hearing loss, speech identification in noise can be predicted from age, sex, and sensitivity with little advantage from recourse to measurement of frequency or temporal resolution.
Pitch identification of simultaneous dichotic two-tone complexes
Authors: Beerends John G. , Houtsma Adrianus J. M.
Published: October 2005

The optimum processor theory of Goldstein can, in principle, account for pitch perception phenomena involving simultaneous dichotic complex tones. The frequency-coding noise function, which is the only free parameter of the model, was estimated with pitch identification data of two simultaneous two-tone complexes presented to different ears. This ‘‘sigma’’ function was found to have a shape similar to that of the function derived from data on identification performance for single pitches. The sigmas in the simultaneous pitch identification experiment are larger by an amount that differs from subject to subject. By using different methods of data analysis it was found that the pitch estimation processes for the two tones are independent for most subjects. This allows a simple extension of Goldstein’s optimum processor theory.
Constrained-layer model investigation based on exact elasticity theory
Authors: Dubbelday Pieter S.
Published: October 2005

The model for constrained-layer damping proposed by Kerwin [J. Acoust. Soc. Am. 31, 952–962 (1959)] provides a direct insight into the effect of the various physical and geometric parameters on the attenuation. It does not account for extensional-wave damping and is limited to lower frequencies since the analysis is based on thin-plate theory. Kerwin’s model is extended to improve upon these points. To check the extended model, a new hybrid model is developed that uses exact elasticity theory to describe the base plate, while the damping and constraining layers are treated analogous to Kerwin’s analysis. It is shown that for flexural waves the extended Kerwin model gives a good approximation to the hybrid constrained-layer model when the phase speed is computed according to either exact elasticity or thick-plate theory.
Speech intelligibility studies in classrooms
Authors: Bradley J. S.
Published: October 2005

Speech intelligibility tests and acoustical measurements were made in ten occupied classrooms. Octave-band measurements of background noise levels, early decay times, and reverberation times, as well as various early/late sound ratios, and the center time were obtained. Various octave-band useful/detrimental ratios were calculated along with the speech transmission index. The interrelationships of these measures were considered to evaluate which were most appropriate in classrooms, and the best predictors of speech intelligibility scores were identified. From these results ideal design goals for acoustical conditions for classrooms were determined either in terms of the 50-ms useful/detrimental ratios or from combinations of the reverberation time and background noise level.
Laboratory and marine measurements on the acoustic detection of sediment transport
Authors: Thorne Peter D.
Published: October 2005

This paper describes a series of measurements taken both in the laboratory and at sea, to examine the feasibility of monitoring marine gravel transport, by measuring the acoustic self-generated noise (SGN) produced by the interparticle collisions of bedload material. This study is a continuation of work previously reported on the SGN of agitated artificial sediments. Laboratory measurements are presented on the relationship between the SGN spectrum and particle size for naturally occurring gravels undergoing interparticle collisions. The dependence of the acoustic intensity level upon the mass of agitated material is also studied. Attempts are made to utilize the acoustic spectrum to obtain information on the particle size distribution for poorly sorted gravel samples. Using the laboratory results, a marine system was developed consisting of two hydrophones to monitor the SGN, an underwater TV camera to independently assess bedload transport, and electromagnetic current meters to obtain information on the flow condition. The instrumentation package was deployed on a seabed composed of mobile gravels. The results of an intercomparison between the acoustic and visual data are presented. Also, some discussion on the relationship between flow conditions and gravel movement is pursued. Attempts are also made to obtain the size distribution of the mobile material by an examination of the SGN spectrum taken at sea.
On the use of symmetrized dot patterns for the visual characterization of speech waveforms and other sampled data
Authors: Pickover Clifford A.
Published: October 2005

While the spectrogram (and related graphic analyses) have been invaluable in showing the general frequency content of an input signal, sometimes it is difficult for trained and untrained users to see on the spectrogram differences which are perceptible to the ear. In this paper, several demonstrations of a novel representation are presented which, in some cases, can make subtle differences in input signals obvious to the human analyst. The representation, a ‘‘symmetrized dot pattern’’ (SDP), provides a stimulus in which local visual correlations are integrated to form a global percept and can potentially be applied to the detection and characterization of significant features of any sampled data.
Reply to ‘‘Comments on ‘On the acoustic response of a deeply corrugated periodic surface—a hybrid T-matrix approach’ ’’ [J. Acoust. Soc. Am. 7
8, 2100–2104 (1985)]
Authors: Lakhtakia Akhlesh , Varadan Vijay K. , Varadan Vasundara V.
Published: October 2005

The authors respond to the comments of A. Wirgin [J. Acoust. Soc. Am. 80, 963–964].
Attenuation measurement uncertainties caused by speckle statistics
Authors: Parker Kevin J.
Published: October 2005

Attenuation measurements can be derived from the decay of backscattered signal with depth in an inhomogeneous material. In cases such as liver tissue, where many small inhomogeneities are likely to be included in sample volumes defined by pulse and beam widths, Rayleigh statistics describe the random nature of the magnitude of backscattered pressure. The statistics of speckle underlie the uncertainties in estimates of attenuation at discrete frequencies, and of the magnitude and frequency dependence of attenuation over a bandwidth. This paper derives expressions for the standard deviations of attenuation magnitude and frequency dependence in terms of parameters such as the dimensions of the region of interest, and the bandwidth of the ultrasonic system. Practical examples are given using published data, and comparisons to other techniques which measure ‘‘attenuation slope’’ are made. The analysis yields insights into trade-offs among variables such as the dimensions and shape of regions of interest, and the segmenting of data in time and frequency domain.
Sounds, source levels, and associated behavior of humpback whales, Southeast Alaska
Authors: Thompson Paul O. , Cummings William C. , Ha Samuel J.
Published: October 2005

Humpback whales in Southeast Alaskan waters produced five categories of sounds: moans, grunts, pulse trains, blowhole-associated sounds, and surface impacts. Frequencies (Hz) of moans and grunts were 20–1900. Major energy in low-frequency pulse trains was in a band of 25–80 Hz with pulse duration of 300–400 ms. Blowhole-associated sounds, recorded as transiting whales encountered one another, were of two types: shrieks, 555–2000 Hz, and trumpetlike horn blasts with fundamental at 414 Hz (median). Pulses and spread spectrum noise were associated with gas bubble formation and explosive bursts, respectively, in connection with spiral feeding maneuvers. Surface impacts resulted from fluke or flipper slaps in sequences of 3–21 sounds. Source levels ranged from 162 (low-frequency pulse trains) to 192 dB (surface impacts), re: 1 μPa, 1 m. Songs, commonly heard on winter breeding grounds, were absent from our recordings. Feeding and perhaps certain other whale activities can be monitored based on sound production.
Testing a model of intonation in a tone language
Authors: Lindau Mona
Published: October 2005

Schematic fundamental frequency curves of simple statements and questions are generated for Hausa, a two-tone language of Nigeria, using a modified version of an intonational model developed by Gårding and Bruce [Nordic Prosody II, edited by T. Fretheim (Tapir, Trondheim, 1981), pp. 33–39]. In this model, rules for intonation and tones are separated. Intonation is represented as sloping grids of (near) parallel lines, inside which tones are placed. The tones are associated with turning points of the fundamental frequency contour. Local rules may also modify the exact placement of a tone within the grid. The continuous fundamental frequency contour is modeled by concatenating the tonal points using polynomial equations. Thus the final pitch contour is modeled as an interaction between global and local factors. The slope of the intonational grid lines depends at least on sentence type (statement or question), sentence length, and tone pattern. The model is tested by reference to data from nine speakers of Kano Hausa.
Auditory filter shapes in the chinchilla
Authors: Halpern D. Lynn , Dallos Peter
Published: October 2005

Auditory filter shapes were determined for the chinchilla using the notched-noise technique [R. D. Patterson, J. Acoust. Soc. Am. 59, 640–654 (1976)]. Here, the derivative of the curve relating threshold to masker gap width outlines the shape of the auditory filter. Three chinchillas were trained, using positive reinforcement techniques, to provide forward masked thresholds at 1.0 and 10.0 kHz, at three masker spectrum levels. Unexpectedly, the threshold curves contained inflection points and regions of constant or nonmonotonic changes in threshold, so that the derived filters contained dips in their central passbands. Nonmonotonic variations in threshold may be discerned in human threshold versus notch width functions of previously published studies, suggesting that the two types of data are qualitatively similar. The filters computed from the chinchilla data widened with increasing masker level and were more broadly tuned than those obtained in humans. The physiological response to each frequency component of any stimulus is likely a combination of excitation and suppression. Hence, one cannot predict masked threshold from the acoustic spectra of the maskers used here since they differ from their internal representations. Thus the threshold versus notch width function probably reflects the operation of both an auditory filter and a nonlinearity.
An investigation of the sound field above the audience in large lecture halls with a scale model
Authors: Kahn David W. , Tichy Jiri
Published: October 2005

Measurements of steady-state sound pressure levels above the audience in large lecture halls show that the classical equation for predicting the sound pressure level is not accurate. The direct field above the seats was measured on a 1:10 scale model and was found to be dependent on the incidence angle and direction of sound propagation across the audience. The reverberant field above the seats in the model was calculated by subtracting the direct field from the measured total field and was found to be dependent on the magnitude and particularly on the placement of absorption. The decrease of sound pressure level versus distance in the total field depends on the angle (controlled by absorption placement) at which the strong reflections are incident upon the audience area. Sound pressure level decreases at a fairly constant rate with distance from the sound source in both the direct and reverberant field, and the decrease rate depends strongly on the absorption placement. The lowest rate of decay occurs when the side walls are absorptive, and both the ceiling and rear wall are reflective. These consequences are discussed with respect to prediction of speech intelligibility.
Consequences of conductive auditory impairment for binaural hearing
Authors: Zurek P. M.
Published: October 2005

Studies of persons with conductive hearing loss have revealed substantial degradations in binaural hearing abilities. Described here is a model based on the hypothesis that this degradation is due to high levels of bone-conducted signals relative to air-conducted signals. The model makes quantitative predictions for the effects of conductive impairment on measurements of interaural discrimination. Qualitative predictions for binaural advantages in detection and speech intelligibility are also made by employing auxiliary models. Generally, available data are consistent with the models, although strong tests have not yet been performed.
The use of acoustical test fixtures for the measurement of hearing protector attenuation. Part II: Modeling the external ear, simulating bone conduction, and comparing test fixture and real-ear data
Authors: Schroeter Juergen , Poesselt Christoph
Published: October 2005

This paper investigates two main features of the human head which influence the measured attenuation of circumaural and intraaural hearing protection devices (HPDs): the external ear and the different pathways of bone conduction. A theoretical model for the external ear shows that its influence on the insertion loss of HPDs, on the sensitivity level of headphones or earphones, and on the insertion gain of hearing aids, all can be described by one equation. While it is not necessary to simulate the eardrum impedance in order to measure the insertion loss of earmuffs and the sensitivity level of headphones with acoustical test fixtures (ATFs), the required accuracy of an ear simulator is more stringent when the same measurements are performed on intraaural devices. For the evaluation of HPDs, bone conduction plays an important role. We have developed a model to estimate HPD-dependent bone conduction effects. The model includes two bone conduction sources: one in the external ear and one in the middle ear. The model explains, for example, the occlusion effect of HPDs and the masking error at low frequencies due to physiological noise that arises when real-ear attenuation at threshold (REAT) measurements are made. Consequently, objectively measured insertion loss can now be used to predict REAT with improved accuracy. ATF and REAT data are compared using nine earmuffs and nine earplugs. In the majority of cases, the two sets of data agree well. Discrepancies are discussed.
Acoustic estimation of size distribution and abundance of zooplankton
Authors: Kristensen Åge , Dalen John
Published: October 2005

A series of investigations were undertaken to observe and describe the sound backscattering process from larger zooplankton (euphausiids). The target strength versus frequency, size, and aspect angle of the organism was measured. The target strength is highly dependent on the density and sound speed contrasts between the target and the medium, and both these parameters were measured. From the target strength observations it was concluded that the fluid sphere model was insufficient as a scattering model for krill. Observations of the tilt angle distribution of krill at natural field conditions showed that they were distributed over a large region of tilt angles. The deficiencies of the fluid sphere models required the development of a new scattering model based on experimental data. This model predicts a decreasing target strength versus frequency in the geometric scattering region. The backscattering spectra of euphausiids were better described by our empirical model than by the fluid sphere models. Applying the empirical model to estimate size distribution and biomass of krill, we found strong correlation between the acoustically estimated distributions and those from net catches.
A top-down philosophy for accurate numerical ray tracing
Authors: Bold Gary E. J. , Birdsall Theodore G.
Published: October 2005

Several examples of the ease of application and accuracy of ray tracing resulting from the top-down approach are given to demonstrate the results obtainable with today’s small computers. One example of a more traditional approach is given to demonstrate how easy it is to lose computational accuracy to mixing instead of isolating the steps in the solution. The current level of commonly available computing power means that it is important for the ordinary researcher to be aware of powerful integration subroutines. Their extraordinary accuracy makes the payoff worth the effort expended in understanding their use.
The scattering of ultrasound by cylinders: Implications for diffraction tomography
Authors: Robinson Brent S. , Greenleaf James F.
Published: October 2005

The validity of wave equations employed as system models in acoustical diffraction tomography is investigated using simulations and measurements of the scattering of plane ultrasound waves by cylinders. It is demonstrated by simulation and experiment that it can be appropriate to neglect density fluctuations and shear waves, implying that the commonly used form of the wave equation suitably describes scattering by fluctuations of acoustic speed and absorption. Diffraction tomographic reconstructions of simulated data reveal the importance of absorption, the behavior of the real and imaginary parts of the reconstructed refractive index, and the relative advantages and limitations of the Born and Rytov approximate transformations.
Towards a model for discrimination of broadband signals
Authors: Durlach Nathaniel I. , Braida Louis D. , Ito Yoshiko
Published: October 2005

The conventional model for broadband discrimination assumes that resolution is limited by peripheral internal noise that is statistically independent across channels. In this paper, we extend this model in a number of directions. In particular, we compute, compare, and discuss the effects of interchannel correlation and central noise on the sensitivity index d′, for discrimination of overall level and discrimination of spectral shape.
Creeping wave analysis of impulse propagation through a shadow boundary
Authors: Don C. G. , Cramond A. J.
Published: October 2005

Previous measurements have shown that there is a marked change in the attenuation of an acoustic impulse above grassland as it propagates into a meteorological shadow zone. This paper extends the theoretical calculations by considering penetration of the boundary by creeping waves. Calculated pulse waveforms for various ground impedance models are compared with the experimental results. Discrepancies between the pulse shapes and overprediction of the excess attenuation may be caused by the restrictive approximations used in applying the theory or imply that other mechanisms contribute to the sound penetration.
Reflection characteristics of an elastic slab containing a periodic array of elastic cylinders: S
H wave analysis
Authors: Lakhtakia Akhlesh , Varadan Vasundara V. , Varadan Vijay K.
Published: October 2005

The reflection and transmission characteristics of a grating of elastic cylinders arranged periodically in an elastic slab are examined. A simple approach synthesized from Fourier–Bessel expansions and the T-matrix method has been used for analysis of a two-dimensional problem involving SH waves only. It is observed that the nonspecular modes are generally very weak for such gratings in contrast with those for gratings made of periodic bimaterial interfaces.