bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface waves and anomalous sound absorption
Authors: Kligman Ronald L.
Published: October 2005

A theoretical model of surface waves in equilibrium with acoustic waves at a fluid–fluid interface is developed. Modifications to the usual pressure and particle velocity boundary conditions lead to a dispersion relation for the waves of the coupled system. An expression for the total reflection coefficient is found which consists of the usual term and an additional one which depends on the interfacial surface tension, the surface wave frequency, and wavenumber. The ratio of acoustic energy absorbed due to reflection from the interface to the incident wave energy is calculated making use of the previously obtained reflection coefficient. This ratio is relatively constant except in a wavenumber regime which corresponds to a minimum in the total reflection coefficient, and itself exhibits ’’resonance transmission’’ behavior.
The amplitude of edgetone sound
Authors: Holger David K. , Wilson Theodore A. , Beavers Gordon S.
Published: October 2005

A model is proposed to predict the amplitude of sound generated by an edgetone. The edgetone configuration under consideration consists of a flat plate located in the medial plane of a fully developed two-dimensional jet. The flow is modeled as follows. A periodic disturbance at the jet origin leads to the formation of an asymmetric vortex street which propagates downstream with a fixed convection velocity and wavelength. The vortex strength, convection velocity, and wavelength are determined as functions of the Strouhal number by applying conservation laws and kinematic relationships. The farfield acoustic pressure is calculated from a potential flow estimate of the periodic force on the edge. Predicted sound pressures are compared with experimental results and found to be in reasonable agreement.
The reflection of ultrasonic pulses from surfaces
Authors: Haines N. F. , Langston D. B.
Published: October 2005

Ultrasonic pulse echo techniques have proven particularly valuable in locating discrete flaws, such as cracks or inclusions, in metal components. It has long been recognized that many factors influence the echo amplitude from a defect. Three factors of particular significance are the angle of incidence between pulse and defect, the shape and size of the defect, and the roughness of its surface. A diffraction model is developed which includes these parameters and successfully accounts for the experimentally observed reflections of ultrasonic pulses from a variety of surfaces. The equations describing reflection in the frequency domain essentially predict the complex frequency spectra of pulses reflected from surfaces of various geometries: by Fourier transforming them, expressions describing the actual pulse waveforms reflected from the surfaces have been obtained. The predicted effects of surface roughness, size, shape, and defect orientation on both the reflected pulse waveform and its frequency spectrum are confirmed by experiment. The converse problem of using the reflected pulse to infer information about the reflecting surface via a deconvolution technique is also demonstrated.
On the acoustical probing of the ocean surface for measuring the directional-frequency spectrum
Authors: Harper E. Y.
Published: October 2005

An acoustic source, in conjunction with an array of acoustic receivers in a nearby isovelocity region, can be used as a probe to measure the ocean surface. F. M. Labianca [J. Acoust. Soc. Am. 67, 1567–1577 (1980)] has developed a procedure for estimating the ocean-surface directional spectrum by this means. The problem he solves is typically called inverse scattering. This paper addresses the issue of what region of the ocean surface is being sampled in his procedure. It is desirable that the sampled region be sufficiently confined that the assumption of spatial homogeneity may be safely made, otherwise the directional spectrum has no meaning. It is proved in this paper that, for a given receiver, the region sampled by Labianca’s procedure is a small circle on the ocean surface, with center over the source and radius equal to the horizontal range between source and receiver. The proof is subject to a constraint on the wavelength of the source.
Multipath analysis of explosive source signals in the ocean
Authors: Mitchell S. K. , Bedford N. R. , Ellis G. E.
Published: October 2005

A computer-based system has been developed for the measurement of acoustic propagation loss in multipath arrivals of signals from explosive sources. The system involves both signal measurement operations and careful theoretical representations of the measured quantities. Initial applications have been for measurement of bottom-reflection losses using signals which reflect many times from the bottom. It has been found that the levels of arrival pulses can be strongly affected by predictable surface-reflection effects. Measurements demonstrate consistent bottom-reflection loss values across homogeneous basin areas.
Spectra of filtered click stimuli used to evoke acoustic brainstem responses
Authors: Teas D. C. , Kramer S. J.
Published: October 2005

Re-determination of the spectra for filtered click stimuli used by Klein and Teas [J. Acoust. Soc. Am. 63, 1887–1895 (1978)] and by Kramer and Teas [J. Acoust. Soc. Am. 66, 446–455 (1979)] with improved instrumentation showed minor differences from the previously published data. The differences are discussed briefly.
Schlieren optical filtering for sound-intensity measurements
Authors: Carpenedo L. , Ciuti P. , Iernetti G.
Published: October 2005

A method of filtering the light diffracted by an ultrasonic beam is presented. It allows sound field intensity measurements, in an extended range, from the optical density of the Schlieren photographs.
Measured noise levels for a laboratory fiber interferometric hydrophone
Authors: Cole J. H. , Bucaro J. A.
Published: October 2005

Measurements of mininum detectable pressures for a laboratory fiber optic acoustic sensor have been made in the frequency range below 1 kHz. Near shot noise limited performance was observed.
Measurements of underwater signal phase stability using a moving source
Authors: Young H. J.
Published: October 2005

In an experiment using a cw source suspended from a drifting ship, the phase angles of the signals at four hydrophones laid on the bottom in a horizontal line were compared. The experimental technique used was a new one which canceled out the Doppler shift of the signal by using the combined outputs of all the hydrophones as a phase reference signal. This technique made it possible to compare the phase angles of signals arriving over multiple paths. The mean cosines of the phase differences were obtained as a function of separation for four pairs of hydrophones. An empirical expression was selected to fit the experimental results and permit interpolation to obtain values for other hydrophone spacings.
Method for solving vibration problems of a plate with arbitrary shape
Authors: Nagaya Kosuke
Published: October 2005

This paper is concerned with a method for solving vibration problems of a thin elastic plate with arbitrary shape. The exact solution of an equation of motion is utilized and the boundary conditions along both arbitrarily shaped curved and straight line boundaries are satisfied by means of the Fourier expansion method. Numerical calculations are carried out for the clamped or simply supported elliptical and parabolic plates.
Effects of noise on some autonomic system activities
Authors: Kryter Karl D. , Poza Fausto
Published: October 2005

Experiments were conducted on the effects of various expected noise conditions upon autonomic system activity in men during rest and work (bicycle ergometer). Skin temperature and heart rate were not appreciably, if at all, affected by any of the noises. Wide-band, predominantly low-frequency noise, at a level of 92 dB, A-weighted, generally caused a decrease in pulse amplitude (indicative of constriction of peripheral blood vessels) during either work or rest, whereas an equally intense one-third octave band of random noise, center frequency of 3150 Hz, had no appreciable effect on pulse amplitude. Repeated exposures to the wide-band noise showed some adaptation or habituation of the pulse amplitude response during conditions of either work or rest. The results were the same for fast rise time (impulsive) bursts of wide-band noise as for bursts with slow, gradual onsets. Rapid interruptions of wide-band noise caused less of a decrease in average pulse amplitude than did uninterrupted noise. It is suggested that constriction of peripheral blood vessels in response to expected intense low-frequency or wide-band noises is more related to auditory, reflexive protective mechanisms than to autonomic system responses generally considered to be stressful to the organism.
Acoustic propagation in rigid sharp bends and branches
Authors: El-Raheb Michael , Wagner Paul
Published: October 2005

The linear acoustic propagation in rigid planar sharp bends and bifurcation ducts is analyzed using a Green’s-function integral technique often known as the surface element method. The acoustic characteristics of the sharp bend differ substantially from those of a circular bend with identical turning angle, width, and centerline length. The acoustic loading resulting from a duct bifurcation is highly two dimensional beyond the first cutoff frequency.
Acoustic entrainment to randomly generated calls by the frog, H
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Authors: Lemon R. E. , Struger J.
Published: October 2005

A series of 30 randomly timed calls was played to free-living spring peepers (Hyla crucifer) calling at their breeding pond. The effect of each random call (RC) in the timing of the immediately following call of the frog was ascertained. The results showed that precise entrainment by delayed response or alternation occurs when the RC’s are placed after the refractory periods of the preceding calls of the frogs. However the frogs are sensitive also to RC’s heard in the refractory period. In such cases they advance the next call to an extent dependent on the position of the RC in the refractory period. The results are interpreted in relation to signal interactions of other animals and to models of pacemaker oscillators.
A theory of liquids with vapor bubbles
Authors: Drumheller Douglas S. , Bedford Anthony
Published: October 2005

In this paper, which consists of three major parts, the theory of bubbly liquids developed previously by the authors is extended to the case of a liquid containing spherical vapor bubbles. In the first part, the nonlinear equations of motion are derived by a variational procedure. The equations are then linearized. In the second part, a set of constitutive relations for vapor bubbles are developed which include the temperature distributions in both the spherical bubbles and in the surrounding liquid. Nonequilibrium evaporation and condensation processes are also included. In the third part, solutions for plane harmonic wave propagation are presented for water–steam and for liquid sodium–sodium vapor mixtures. The qualitative effects of condensation and evaporation on the propagation of waves through the mixture are discussed. It is found that the wave attenuation is greatly increased and the phase velocity is substantially decreased when phase transitions are included.
Acoustical research in the life sciences
Authors: Hirsh Ira J.
Published: October 2005

This paper briefly reviews research progress during the past 50 years in physiological and psychological acoustics. Special attention is paid to the physiology of the auditory system, sound conduction in the ear, cochlear mechanics, masking, auditory localization, psychoacoustic behavior in animals, speech perception, medical applications, coupling between psychophysics and physiology, temporal aspects of sensory attitudes, and ecological acoustics.
Applications of acoustical phenomena
Authors: Mason Warren P.
Published: October 2005

This paper briefly reviews progress in research on specific applications of acoustic radiation during the past 50 years. Among the topics discussed are the following: underwater ultrasonic detectors, the ultrasonic interferometer, use of ultrasonics in the nondestructive testing of metals, acoustics delay lines, improvements in the materials used in ultrasonic transducers, surface wave devices, acoustic emission, use of ultrasonics in the study of internal friction and fatigue in metals, and the ultrasonic microscope.
Acoustical measuring instruments over the years
Authors: Kundert Warren R.
Published: October 2005

Electronic technology has permitted many advances in acoustical measuring instruments over the years. Generally, size and weight have been reduced and speed and convenience greatly increased. The important technological advances are discussed and some examples are given of how coupling technologies with need has produced changes. The characteristics of some specific old and new instruments are contrasted and, finally, some ideas about future instruments are presented.
Wave-theory peaks in range-averaged channels of uniform sound velocity
Authors: Weston D. E.
Published: October 2005

Even in isovelocity water the wave or modal nature of the sound propagation causes special effects at four particular depths. Thus, the range-averaged level shows a zero at the free surface, a maximum at the source depth, and effects of uncertain sign at the bottom and near the source complementary depth. These peaks show further curious behavior, akin to interference, as source depth is varied. The present source depth peaking is a wave effect in isovelocity water, in contrast with the flux-theory infinities predicted for refracting conditions. For large numbers of modes, the present source depth peak is normally 50% above the average, and this anticipates a similar wave-theory result for refracting conditions.
Acoustical research in the physical sciences: Properties of gases, liquids, and solids
Authors: Greenspan Martin
Published: October 2005

This paper reviews research during the past 50 years on the relation between acoustical behavior, mainly velocity and attenuation of sound, and the properties of gases, liquids, and solids.
Acoustics and the Acoustical Society of America in historical perspective
Authors: Lindsay R. Bruce
Published: October 2005

The early workers in every science were in general animated by an urge to communicate their findings and thoughts to like-minded enthusiasts. Hence arose the desire to form scientific societies, an important aspect of the so-called scientific revolution of the 16th, 17th, and 18th centuries. No one can question the beneficial role the great scientific academies of Europe played in all branches of science in the stimulation of theoretical, observational, and experimental research and its practical applications. Our own time has seen an enormous proliferation of scientific societies, many of them dedicated, as has been said, to the encouragement of learning more and more about less and less. The founders of the Acoustical Society of America were very wise in insisting that the Society should encompass the whole body of the science of sound, a very old discipline that makes an impact on human experience more profound and varied than almost any other worthy of the name scientific. As the Society completes its first half-century, we can assert with some assurance and without undue smugness that it is successfully fulfilling the purpose laid down in its charter, namely, ’’to increase and diffuse the knowledge of acoustics and promote its practical applications.’’ The past is secure. The future cannot be otherwise than bright.
Sound source reconstructions using a microphone array
Authors: Williams Earl G. , Maynard J. D. , Skudrzyk Eugen
Published: October 2005

A square microphone array with 256 elements has been constructed along with interfacing electronics to study low-frequency (1–5 kHz) sound sources in air using the principles of acoustical holography. The array is used in the nearfield of a radiating object and the sound source structure of that object is reconstructed with an on-line minicomputer. Reconstruction of the source structure of a point source and an unbaffled, free rectangular plate point excited below its coincidence frequency are presented. The latter shows clear evidence of ’’corner’’ and ’’edge’’ modes in which the respective areas of the plate are the dominant radiating sources. A new imaging process which is not limited in resolution by the wavelength of the radiated sound is introduced.
Use of a microsphere probe for pressure field measurements in the megahertz frequency range
Authors: Edwards P. L. , Jarzynski J.
Published: October 2005

A procedure has been developed that may be used to measure the finestructure of acoustic fields at frequencies up to 10 MHz. It consists basically of locating a microsphere in the pressure field at the point of interest and measuring the amplitude of the scattered waves. Details of the system are discussed, and some examples of experimental data presented.
Reflection characteristics of torsional waves in a semi-infinite cylindrical rod connected to an elastic half-space
Authors: Wada Hiroshi
Published: October 2005

Reflection characteristics of torsional waves in a semi-infinite rod connected to an elastic half-space are analyzed under two specific incident pulse loads, applying Laplace transformations with respect to time and numerical inverse Laplace transformations. The time histories of the torsional stress and rotation of the semi-infinite rod at an arbitrary point are shown. The advantage of this method, i.e., applying the numerical inverse Laplace transformations, is that it is simpler than using Fourier analysis and synthesis, and applicable to any incident pulse load except where the rise time interval of the incident pulse load is too short. In the case of a step pulse load, the stress curves approach that of the fixed boundary condition and the rotation curves approach asymptotically the static rotation value of each given shear modulus ratio GR/G and velocity ratio K. In the case of a half-sine pulse load, the reflected stress peak values decrease and those of the rotation increase with an increase in GR/G and K. A cross−over effect occurs when GR/G≳1 and K≳1; it becomes pronounced as GR/G and K increase.
Airborne ultrasound characteristics of open-cell polyurethane foam layers
Authors: Matsuzawa Kiichiro , Ochi Masayuki
Published: October 2005

Transmission and reflection characteristics at normal incidence have been measured for 1-cm-thick foam layers of 98% porosity in the frequency range 10–200 kHz. The ’’boundary frequency’’ is determined from these measurements. Below this frequency, (1) the transmitted field has no irregularity, (2) the transmission loss is proportional to the square root of frequency, (3) the reflection is specular, and (4) the reflected wave consists of two components which are reflected from the front and back surfaces of the layer and interfere with each other. The boundary frequency is 60 to above 200 kHz, for the layers with cell densities of 14 to 50 cells/in. It is found that, for each cell density, the boundary frequency is almost equal to the frequency at which one-half a wavelength of sound is equal to the average diameter of cells.
Coherent acoustic scatter at a rough interface between two fluids
Authors: Tolstoy I.
Published: October 2005

Given a rough interface between two fluids of different densities but similar sound velocities, we assume that the mean dimensions d and spacing h of the roughness elements is small compared to an acoustical wavelength, i.e., kd<kh?1, where k is the wavenumber. If these elements are hemispheres based on a plane z=0, one may express the diffracted field of each element by Rayleigh’s approximation; the use of classical integral theorems then allows one to replace the summed effect of these contributions by a simple linear boundary condition applied at z=0. Minor heuristic corrections allow one next to extend the result to roughness elements of other shapes and, by averaging, to stochastically rough surfaces. This technique was first introduced by Biot in the context of a rigid boundary and is generalized here to a rough interface between two fluids, giving two boundary conditions. The first states the continuity of vertical fluid displacement along a fictitious smoothed surface z=0 with an added correction which is first order in a roughness parameter of order kd. The second condition is the continuity of pressure and is, to within second-order terms, identical with the usual smooth boundary condition; in a first-order theory, then, this condition is the usual continuity of pressure at z=0. Use of this pair of boundary conditions shows that the body (volume) acoustic modes behave as in the smooth interface case, with the addition of corrections of order kd. It also demonstrates the existence of a slightly dispersive boundary wave mode traveling along the interface, and of order kd. Both are intrinsically first-order effects of coherent multiple scatter by rough surfaces; both include the effects of steep-side roughness elements and are not obtained in other theories of rough surface scatter. Use of the normal coordinate technique enables one, furthermore, to obtain new closed-form solutions for the boundary wave and the body (volume) wave fields that are first order in kd. The boundary wave amplitude decreases with range r from the source like r−1/2, in contrast to the body waves which fall off like r−1 or faster; it may thus dominate for sufficiently large range. This phenomenon has, in fact, been verified experimentally for the case of a rigid rough boundary, by means of model work in an anechoic chamber, in earlier work by Medwin and collaborators. It suggests interesting posibilities in geoacoustics and in underwater sound in particular, e.g., the propagation, under suitable conditions, of substantial low-frequency energy into regions of acoustic shadow.
Physiological acoustics and health
Authors: Kryter Karl D.
Published: October 2005

This paper reviews work on the assessment of the damaging effect of noise on man’s auditory system, the degree to which the auditory system interacts directly with the autonomic system of the body, noise as the sole or contributory cause of general (nonauditory) physiological and psychological ill health in communities, and the effect of noise on general health in industry.
Coding of AM tones in the chinchilla auditory nerve: Implications for the pitch of complex tones
Authors: Javel Eric
Published: October 2005

Responses to sinusoidally amplitude modulated (AM) tones were recorded in single auditory nerve fibers of anesthetized chinchillas. The tones chosen were of a class which, in humans, gives rise to a percept of low subjective pitch. It was found that, for high-frequency stimuli, neurons tuned to high frequencies signaled waveform envolope periodicity when the stimulus was of sufficient intensity. Neurons tuned to low frequencies responded to low-frequency AM tones in an orderly manner which ranged, as overall intensity was raised, from signaling all frequency components to signaling only the component to which the neuron was most sensitive. This result was interpreted to indicate the presence of two-tone suppression. Variation of modulation frequency and modulation depth produced response patterns which were generally predictable based on the relative effectiveness of each of the component frequencies in eliciting discharges. Neurons tuned to low frequencies did not respond at low and moderate intensities to higher-frequency AM tones, even though the subjective pitch of the tones corresponded to frequencies to which the neuron was sensitive. At high intensities, distortion products locked in-phase to the frequency of the subjective pitch were observed. Responses to a single AM tone recorded from different neurons in the same animal displayed considerable diversity in their responses. Response diversity was correlated with neuronal tuning characteristics, stimulus intensity, and intrinsic factors such as suppression. Neurons retained stimulus finestructure information in the temporal patterns of their discharges as stimulus components were varied from a harmonic relationship to an inharmonic relationship. The data indicate that responses of auditory nerve fibers contain sufficient information for extraction of the subjective pitch of AM tones by a central auditory processor which operates on temporal features of the responses.
Acoustic loading in straight pipes
Authors: El-Raheb Michael
Published: October 2005

Based on linear one-dimensional acoustics, a geometrically perfect elastic waveguide would respond to an oscillatory internal pressure only in the presence of path deflectors (elbows and branches). In practice, a significant elasto-acoustic interaction results even in straight conduits as a result of manufacturing tolerances. A theoretical model of the linear acoustic loading in straight pipes is developed that considers the acoustic wave distortion due to perimeter, axial, and wall thickness nonuniformities.
Scattering of acoustic waves by layered elastic and viscoelastic obstacles in water
Authors: Peterson B. , Varadan V. V. , Varadan V. K.
Published: October 2005

A T-matrix formalism is presented for a multilayered three-dimensional scatterer of arbitrary shape immersed in a fluid, to study the scattering of acoustic waves. The layers of the scatterer may be composed of elastic or viscoelastic material. Explicit expressions for the T-matrix of a two- and three-layered scatterers are presented. Frequency dependent numerical results have been obtained for two-layered prolate and oblate elastic and viscoelastic spheroidal obstacles where the inner layer is assumed to be a cavity. The differential, backscattering, absorption, and extinction cross sections have been obtained for both thin and thick layers. For purposes of comparison, results for the homogeneous scatterers are also presented. The scattering cross sections for a thick outer layer are found to be considerably different from those for a thin layer.
Species-specific coding in bird song
Authors: Sinnott Joan M.
Published: October 2005

Red-winged blackbirds and brown-headed cowbirds were trained with operant conditioning techniques and food reinforcement to categorize complex song themes from both their own (conspecific) and from the other (alien) species’ vocal repertoire. Following training, songs were separated into initial and terminal portions and birds were retested for identification of the isolated song elements. Results revealed no species differences in identifying the ’’introductory note’’ portions of redwing and cowbird song; however, redwings were superior to cowbirds in identifying terminal redwing ’’trills,’’ while cowbirds were superior in identifying terminal cowbird ’’whistles.’’
Some observations on the lateralization of complex waveforms
Authors: Henning Bruce
Published: October 2005

Consistent lateralization judgement can be obtained with interaural delays in the envelope but not in the carrier of high-frequency sinusoidal signals that are amplitude modulated. At low frequencies the situation is reversed and delays in the carrier, but not the envelope, can be detected. Delays in quasi-frequency-modulated or frequency-modulated waveforms allow lateralization by some observers but require much larger delays for performance as good as that obtained with amplitude-modulated signals. The implications of some of these observations for models of the envelope extraction process are discussed.
Electroacoustic equations for one-domain ferroelectric bodies
Authors: Maugin G. A. , Pouget J.
Published: October 2005

Based on a fully Galilean electrodynamics of dielectric deformable bodies, a completely deductive derivation of the coupled, dynamical, electromagnetic, electroacoustic, and energetic equations and constitutive equations for elastic, pyroelectric, ferroelectric dielectrics accommodating viscosity and dielectric-relaxation phenomena is presented. Of necessity the theory is first constructed in a fully nonlinear framework even though applications to signal processing are envisaged. Then a linearization is performed by Lagrangian variation about an initial ferroelectric state in which there exist no strains, but there are present both stresses and local electric field as well as an initial electric polarization. The latter provokes a breaking of the ideal symmetry of the material, so that finally linearized coupled electroacoustic and heat-propagation equations are deduced on which can be based the study of coupled acoustic-soft optic modes in ferroelectrics of the BaTiO3-type. No thermodynamical restriction other than the fulfillment of the second principle of thermodynamics is considered, so that dissipative processes such as viscosity and dielectric relaxation appear naturally on an equal footing with elasticity, piezoelectricity, thermoelasticity, and pyroelectricity.
Discrete frequency noise reduction modeling for application to fanjet engines
Authors: Fleeter Sanford
Published: October 2005

A model for the generation of discrete frequency noise due to rotor–stator interactions in a fanjet engine is examined to ascertain its relevance to noise reduction studies. Predictions are obtained for the noise reduction between a base fan stage and one redesigned to achieve reduced discrete frequency noise utilizing response functions corresponding to incompressible flow isolated airfoil transverse and longitudinal gust analyses as well as incompressible and compressible flat plate airfoil cascade transverse gust analyses. The correlation of the various predictions with the actual fan test results demonstrated that the viscous wake-generated noise model utilizing the compressible flow cascade response function was the one most appropriate for noise reduction studies of fanjet engines. The significant parameters and their relative importance were then identified by means of a parametric study of the base fan based on the compressible flow cascade response analysis. This study showed that the dominant parameter relevant to discrete frequency noise generation is the interblade phase angle, equal to the ratio of the number of upstream rotor blades to downstream stator vanes. Other parameters of importance included the Mach number, reduced frequency, and vane solidity.
Cavitation thresholds of a polyalkylene glycol and of castor oil
Authors: Moffett Mark B.
Published: October 2005

Measurements were made of the cavitation thresholds for a polyalkylene glycol and for castor oil in a cylindrical resonator at approximately 17 kHz. The threshold for degassed castor oil was in agreement with the measurements of Briggs, Johnson, and Mason [J. Acoust. Soc. Am. 19, 664–677 (1947)]. The degassed polyalkylene glycol exhibited wide variability in threshold, with an initial value higher than that of castor oil, dropping quickly to values much lower than for castor oil. Partial restoration to higher thresholds could be attained after a rest period of several hours.
Effects of finite aperture in a parametric acoustic array
Authors: Tjo/tta Jacqueline Naze , Tjo/tta Sigve
Published: October 2005

Theoretical results are given for a parametric acoustic array formed by nonlinear interaction of two coaxial sound beams in their nearfield regions. The results are obtained from a parabolic approximation of the inhomogeneous Helmholtz wave equation governing the generation of difference frequency sound in the quasilinear aproximation. In the case of the plane sound beams, a generalized aperture factor is derived using a previously obtained integral representation for the solution of the parabolic equation [J. Naze Tjo/tta and S. Tjo/tta, J. Acoust. Soc. Am. 68, 334–339 (1980)]. This is valid at shorter ranges than those where the results were based on the Born approximation [J. Naze Tjo/tta and S. Tjo/tta, J. Acoust. Soc. Am. 37, 174–175 (1965)], and leads to a focusing effect of the generated sound. The validity of using a Gaussian shaped function for the directivity of the primary beams is also discussed.
Comments on ’’Multiple-obstacle acoustic scattering in the simple source formulation with accuracy checks’’ [J. Acoust. Soc. Am. 66, 1536–1541 (1979)]
Authors: Radlinski Ronald P.
Published: October 2005

Sorensen implies that in scattering from multiple objects, no failure of the simple source integral method occurs at the characteristic wavenumbers. Comparisons of the simple source integral method with a multiple body eigenfunction expansion solution indicates numerical difficulty with the integral solution near a characteristic wavenumber of one of the objects. Calculations which differ from the results in Sorensen’s paper at a high wavenumber are presented.
Intensity perception XI. Experimental results on the relation of intensity resolution to loudness matching
Authors: Houtsma A. J. M. , Durlach N. I. , Braida L. D.
Published: October 2005

According to a recent extension of our theory of intensity perception [Lim et al., J. Acoust. Soc. Am. 62, 1256–1267 (1977)], two stimuli are matched in loudness if and only if their intensities divide the respective dynamic ranges proportionally in terms of just noticeable differences. This study reports results of intensity discrimination and loudness matching experiments designed to test this prediction. Data were obtained over most of the dynamic range for three different types of sounds: a 1000-Hz tone in quiet, a 1000-Hz tone partially masked by a 2-octave band of noise, and spectrally flat wide-band noise. Of the five subjects tested, three produced results that had sufficient internal consistency to be useful for testing the predictions. For these subjects, the data and the theory were found to be reasonably consistent. Comparison with other studies, however, reveals that loudness matching results vary with matching paradigm by an amount that is significant with respect to the task of evaluating the theory. Hence, a rigorous test of the theory requires an improved understanding of the effects of matching paradigm.
Processing of speech by the auditory nervous system
Authors: Kiang Nelson Y. S.
Published: October 2005

Recordings from auditory-nerve fibers indicate that several factors are necessary to characterize the response of a single fiber to speech sounds. These are the spectrogram and level of the stimulus, the characteristic frequency and threshold of the fiber. The responses of single fibers to tones are seen as changes in the instantaneous discharge rate which can be measured in various ways. Two measures, average rate and synchronization index, have been defined for tone stimuli and have been shown to behave differently under a variety of conditions. The work with tones can lead to simplified displays of activity in model neurons, which can be used to formulate general ideas on speech coding at the nerve level.
Statistical properties of energy spectral response as a function of direct-to-reverberant energy ratio
Authors: Chu W. T.
Published: October 2005

Analytical expressions for statistical properties of the spectral response curve in a reverberation room have been derived as a function of direct-to-reverberant energy ratio. Comparison with results obtained by other numerical methods is given.
Experimental study of a saturated parametric array in air
Authors: Trenchard Stephen E. , Coppens Alan B.
Published: October 2005

Study of the acoustical behavior of a 20-element rectangular array of electrodynamic horn loudspeakers used to generate a parametric array in air resulted in good agreement between the experimentally determined secondary source levels and beam patterns and theory for saturation-limited performance. The feasibility of splitting an array into two interlaced subarrays, each excited separately by one of the primary frequencies, is demonstrated.
Level dependence of psychophysical frequency resolution and auditory filter shape
Authors: Pick Graham F.
Published: October 2005

From gated tone thresholds measured in the presence of ’’comb-filtered’’ (sinusoidal energy spectrum) noise maskers, the shape of the ’’auditory filter’’ was estimated in five frequency regions, 0.5, 1, 2, 4, and 8 kHz, at a number of masker levels. The auditory filter shape became wider, asymmetrical, and shifted towards lower frequencies as the level increased, for filters with center frequencies in excess of 1 kHz. The assumptions inherent in the derivation of the filter functions are discussed, and it is concluded that the likely deviation from these assumptions (in particular, as a result of the generation of nonlinear distortion products) leads to only small errors in the shapes of the derived filter functions.
Two-tone masking in normal hearing listeners
Authors: Rabinowitz W. M. , Bilger R. C. , Trahiotis C. , Nuetzel J.
Published: October 2005

Psychophysical measurements of two-tone masking [E. Zwicker, Acustica 4, 415–420 (1954)] were made at 0.25, 0.5, 1, 2, and 4 kHz utilizing a masker level of 62 dB SPL/tone. Fifty-eight ’’untrained’’ subjects were tested using a single run of a 4IFC adaptive procedure for each condition. Individual data were highly variable. Average data were systematic; they were analyzed using a two-line-regression procedure and the obtained critical-bandwidth estimates approximated normative values. Analysis of the literature revealed that a substantial increase of estimated critical bandwidth versus masker level occurs in two-tone masking. A portion of this increase appears artificial and stems from the relative ineffectiveness of the higher frequency masker tone at high masker levels. An alternative masker-frequency spacing is suggested to reduce level effects. Implications for an underlying critical-band mechanism are discussed.
Low-frequency underwater transducer—Introduction
Authors: Groves I. D.
Published: October 2005

An introduction to three oral papers on low-frequency transducers presented to the 97th meeting of the Acoustical Society of America in session WW on 15 June 1980 in Cambridge, Massachusetts.
Speech recognition in the Soviet Union
Authors: Makhoul John
Published: October 2005

Between 29 May and 11 June 1978, an NSF-sponsored US delegation visited the Soviet Union as part of a US–USSR scientific exchange program in the area of natural language and speech processing. Laboratories in four cities—Moscow, Novosibirsk, Leningrad, and Kiev—were visited. This paper describes those activities relating to speech processing, especially speech recognition.
Long-range target detection in open waters by an echolocating Atlantic Bottlenose dolphin (T
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Authors: Au Whitlow W. L. , Snyder Kathlyn J.
Published: October 2005

The long-range echolocation detection capability of an Atlantic Bottlenose dolphin, Tursiops truncatus, in a noise-limited environment was determined using a 7.62-cm diam water-filled sphere as the target. The 50% target detection threshold range was found to be 113 m. Using the transient form of the sonar equation, it was found that the results obtained with the 7.62-cm sphere matched previous results obtained with a 2.54-cm solid sphere and the same animal, to within 1.5 dB in terms of signal levels or within 5.4% in terms of ranges. The sonar equation was also used to obtain an estimate of the animal’s detection threshold, which was determined to be between 3.8–5.3 dB. The animal was found to perform like a Neyman–Pearson detector, limiting his false alarm rate to 23% and below.
Cross-sensor processing for a U-shaped array
Authors: Bucker Homer P.
Published: October 2005

This paper examines cross-sensor processing for a U-shaped array and for a horizontal line array. Attention is given to accounting for crossterms in the cross-sensor field (cross-spectral matrix) caused by doublet (i.e., two multi-paths) arrivals from the same source. For the arrays considered, the line array did not have sufficient aperture to resolve the doublets. Thus, its response to a doublet was the response to the single wave whose amplitude is the coherent sum of the multi-path arrivals. The U-shaped array did have sufficient vertical aperture to resolve the doublets. This requires a somewhat complicated procedure to account for the crossterms. Using these algorithms, a detection list was generated for the U-shaped array that contains accurate level, bearing, and elevation parameters. The detection list for the line array contains more signals; however, the spatial information about the signals is inherently limited to conical angles.
Improved numerical efficiency in a frequency tracker
Authors: Grube G. W. , Tom C.
Published: October 2005

In the course of applying the Kalman filter approach to estimating the frequency modulation of a single-frequency signal, a numerically efficient finite difference scheme was derived for implementing the filter. Digitized field data were processed faster than 300 times real time on an IBM 370. The numerical approach described here is generally applicable to frequency trackers utilizing Kalman filters.
The trapping of acoustical energy by a conical membrane and its implications for loudspeaker cones
Authors: van der Pauw Leo J.
Published: October 2005

The mechanical driving-point admittance of a truncated conical membrane has been investigated. It is shown that in a relatively wide frequency range, typically from 2–10 kHz, the driving-point admittance has a nonvanishing real part, even in the complete absence of mechanical damping of the cone material. It appears that the supplied energy is accumulated and trapped in the cone in a ring-shaped area with frequency-dependent radius. The implication for the design of loudspeaker cones is that it is of advantage to use a cone material of sufficient mechanical damping in order to dissipate the trapped power and so avoid nonlinear effects or permanent damage. Numerical results obtained from the lossless membrane model are found to be in good agreement with those obtained by Frankort from a model having small bending stiffness and small mechanical damping.
Comparison of the experimental and theoretical pressure fields in the nearfield of ultrasonic transducer-lens systems
Authors: Edwards P. L. , Cook Bill D. , Dardy Henry D.
Published: October 2005

Experimental measurements of acoustic pressure fields near the focal points of ultrasonic transducer-lens systems are compared to calculations of a recently developed analytic technique. This method incorporates the Fresnel approximation to expand the field in terms of Gaussian–Laguerre functions to calculate the acoustic field for arbitrary placement of a lens in the nearfield of a circular transducer. The predicted field pattern symmetries near the focal region with a lens located either at one focal distance or at the transducer face are confirmed by experimental measurements made with a microsphere probe.
Infrapitch echo
Authors: Warren Richard M. , Bashford James A. , Wrightson John M.
Published: October 2005

A noise mixed with its repetition after a delay of t sec can produce a pitch corresponding to 1/t. The accepted range of this echo pitch is about 50 through 2000 Hz (t from 0.02 through 5×10−4 sec). Evidence is presented suggesting that temporal analysis should permit detection of echo repetition well below the pitch limit of t=0.02 sec. In keeping with predictions, we found that listeners could detect the delay of echo repetition for noise down to at least t=0.5 sec (periodicity of 2 Hz). While polarity inversion of the echo alters apparent frequency at delays producing pitch, such inversion has no effect on apparent frequency of infrapitch echo. It is suggested that echo detection within the pitch range involves both a neural place analysis of the rippled power spectrum and a concurrent neural temporal analysis insensitive to polarity inversion; echo detection in the infrapitch range cannot employ neural place cues and is based solely upon a polarity-insensitive temporal analysis. Infrapitch repetition is discussed as a tool for investigating temporal domain analysis free from concurrent frequency domain analysis.
Magnitude squared coherence for a unichannel pure tone
Authors: Grace O. D.
Published: October 2005

The probability density function of the magnitude squared coherence estimator is determined for the case of a pure tone in one channel and Gaussian noise in the other channel. It is found to be the same probability density function as for the case of Gaussian noise in both channels. It follows that the detection thresholds for both cases are the same and that no ad hoc threshold adjustment is required.
Near-bottom seismic profiling: High lateral variability, anomalous amplitudes, and estimates of attenuation
Authors: Tyce R. C. , Mayer L. A. , Spiess F. N.
Published: October 2005

For almost a decade the Marine Physical Laboratory of Scripps Institution of Oceanography has been conducting near-bottom geophysical surveys involving quantitative seismic profiling. Operating initially at 4 kHz and more recently at 6 kHz, this system has provided a wealth of fine scale quantitative data on the acoustic properties of ocean sediments. Over lateral distances of a few meters, 7-dB changes in overall reflected energy as well as 10-dB changes from individual reflectors have been observed. Anomalously high amplitudes from deep reflectors have been commonly observed, suggesting that multilayer interference is prevalent in records from such pulsed cw profilers. This conclusion is supported by results from sediment core physical property work and related convolution modeling, as well as by the significant differences observed between 4- and 6-kHz profiles. In general, however, lateral consistency has been adequate in most areas surveyed to permit good estimates of acoustic attenuation from returns from dipping reflectors and sediment wedges.
Measurements of coherence of sound reflected from ocean sediments
Authors: Berkson Jonathan M.
Published: October 2005

Spatial coherence of sound reflected from the ocean floor at grazing angles 50 °–70 ° was determined from sound received by a hydrophone array suspended at midocean depths. An explosive source and the sensor geometry allowed isolation of the bottom reflections from other paths. A coherence function was calculated as a function of frequency 20–250 Hz and vertical hydrophone separation up to 280 m. Generally coherence decreases with increasing frequency and increasing sensor separation. The rms roughness of the sea floor was estimated from the coherence data to be about 0.5 m for the Tufts Abyssal Plain and 0.5 m for the Cascadian Plain. Differences between measured coherence spectra and theoretical coherence spectra for rough surface scattering might be due to effects of subbottom arrivals and/or changes in effective scattering area with frequency.
The dependence of bottom reflection loss on the geoacoustic parameters of deep sea (solid) sediments
Authors: Vidmar Paul J.
Published: October 2005

Parameter studies are interpreted to determine the dependence of bottom reflection loss (RL) from the ocean floor on subbottom parameters. The emphasis is on examining thin sediment layers for which sediment shear (S) wave excitation is important. RL is obtained from a numerical model which includes sediment S wave propagation. The subbottom structure investigated has a single, horizontally stratified (solid) sediment layer with parameters typical of a high porosity, deep sea sediment overlying a semiinfinite homogeneous (solid) substrate. Subbottom parameter variations are constrained by available geophysical estimates. Homogeneous layers and layers with constant gradients are also investigated. The relationship between subbottom parameter accuracy and the uncertainty in calculated RL is addressed by making variations about a typical parameter set.