bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of traffic noise abatement strategies
Authors: Cermak Gregory W. , von Buseck Calvin R. , Cervenak John G. , Blanchard Robert D.
Published: October 2005

Computer simulations of traffic sound levels were performed to evaluate the probable effectiveness of several hypothetical noise abatement strategies in reducing residential exposure to traffic sound. These simulations were performed for 28 actual census tracts in six cities which were chosen to be representative of the urban United States. Results showed that limits on noise levels during acceleration for new automobiles would have only a small effect on traffic noise exposure, while limits on truck-acceleration noise levels would have a greater effect. Nonresidential zoning along arterials was calculated to have a greater effect than automobile-noise limits, but a smaller effect than truck-noise limits. A hypothetical vehicle fleet including large proportions of four-cylinder and diesel-powered automobiles was calculated to produce slightly greater residential noise exposure than at present.
An iterative calculation of auditorium reverberation
Authors: Gilbert E. N.
Published: October 2005

Formulas for reverberation time have always been derived assuming a constant distribution function for sound intensity throughout the auditorium. The true distribution is known to satisfy an integral equation, first derived by Kuttruff, which has not found much application because it contains the unknown reverberation time itself as a parameter. Here energy considerations supply another relationship which, together with the integral equation, form the basis of an iteration procedure. The intensity distribution and the reverberation time are both corrected on each iteration. The new procedure is tested on hemispherical auditoria. The hemispherical dome reflects specularly with loss parameter β. The plane floor reflects diffusely with loss parameter α. These auditoria exhibit a whispering gallery effect that makes a severe test of the iteration procedure.
Unified asymptotic theory of asymmetrical planar waveguides
Authors: Arnold J. M.
Published: October 2005

An asymptotic method is described for the analysis of modal propagation in planar inhomogeneous waveguides under conditions appropriate to underwater and geophysical guiding structures. This theory takes full account of caustics, interfaces with exterior homogeneous media, and possible interactions between them. It is capable of generating asymptotic representations for modal eigenfunctions to any desired order, anywhere within the discrete part of the spectrum, even close to the cutoff edge of the spectrum. This work is an extension of an analysis of symmetrical waveguides to more realistic asymmetrical environments.
Pitch and timbre in a two-tone dichotic auditory illusion
Authors: McClurkin Robert H. , Hall Joseph W.
Published: October 2005

The Deutsch paradigm that produces an auditory illusion with dichotic alternating 400 and 800 Hz tones [D. Deutsch, J. Acoust. Soc. Am. 55, 518–519, (1974a)] was modified to clarify aspects of pitch and timbre. The 400-Hz sinusoid was replaced by a high-frequency complex tone (1000–1200–1400 Hz) whose residue pitch was perceived as the low stimulus. Significant results based on the responses of 21 subjects indicated that the illusion is pitch-, and not frequency-, based. The effect of timbre was found to be negligible.
Relationship between collagen and ultrasonic backscatter in myocardial tissue
Authors: O’Donnell M. , Mimbs J. W. , Miller J. G.
Published: October 2005

The relationship between ultrasonic backscatter and collagen concentration estimated on the basis of hydroxyproline concentration was examined in hearts from normal dogs and in hearts from dogs subjected to ischemic injury by coronary occlusion as an approach toward elucidating the physical mechanisms underlying the scattering of ultrasound by soft tissue. Ultrasonic backscatter was found to increase significantly in regions of ischemic injury studied 5–17 weeks following occlusion. The average backscatter coefficient was six times larger in regions of infarct studied 8–10 weeks after occlusion than that in regions of infarct studied 5–6 weeks after occlusion. In contrast, the average hydroxyproline concentration, a quantitative index of molecular collagen content, for regions of infarct was only about 25% larger at 8–10 weeks compared with that at 5–6 weeks after occlusion. These results may suggest that the magnitude of ultrasonic scattering in regions of remote myocardial infarct is sensitive not only to the concentration of molecular collagen but also to the organizational state of this structural protein. In addition, the results of this study may indicate that scattering represents a small fraction of the total attenuation coefficient in a biological system exhibiting either low collagen concentration (normal myocardium) or significant collagen concentration (scarred myocardium).
Relation between pitch shifts and MMF shifts in forward masking
Authors: Moore Brian C. J.
Published: October 2005

Thresholds for brief sinusoidal signals were determined as a function of signal frequency for fixed sinusoidal maskers in a forward masking task. In some cases the frequency at which maximum masking occurred (MMF) was slightly above or below the masker frequency. In a second experiment subjects were required to adjust the frequency of the signal so that its pitch matched that of the ’’masker.’’ It was found that the frequency required for equal pitch corresponded closely to the MMF. A possible explanation is that differences in quality between signal and masker (such as pitch differences) provide a cue for detection in forward masking which is not available when the signal and masker are very similar in quality. Thus maximum masking occurs when the signal and masker are most similar in quality.
Vocal register ’’shift’’ identification in a modified breathing atmosphere
Authors: McGlone Robert E. , Brown W. S.
Published: October 2005

An attempt was made to determine whether listeners’ perception of vocal register ’’shift’’ was related to speaker fundamental frequency or to supralaryngeal resonance. The method was to have speakers phonate tones while breathing air and, alternatively, a helium–oxygen mixture which influences resonance but not fundamental frequency. Recordings were made of these phonations and played to judges who were required to identify between which tones the register shift occurred. Results showed that judges had more difficulty identifying the shift point when speakers were phonating in air than with the HeO2 mixture. Comparison also was made between the speaker’s self-judgment of shift and that of the listeners. Under the helium condition the speakers and listeners were in nearly complete agreement, with the greatest variability occurring between the groups for the air breathing condition. These results indicate that register change is related to modification of laryngeal function.
Elastic wave propagation in fluid-saturated porous media
Authors: Berryman James G.
Published: October 2005

A new identification of the coefficients in the strain energy functional for Biot’s theory is presented. Two types of porous media are distinguished: (1) With the granular constituents fully consolidated so the porous frame acts as a cohesive unit, and (2) with the granular constituents only partially consolidated so a fraction of the solid particles compose the porous frame while the remaining particles are (essentially) suspended in the saturating fluid. For complete consolidation, an exact identification of the coefficients is found. This identification differs from the standard identification of Geertsma [Trans. AIME 210, 331 (1957)] and of Biot and Willis [J. Appl. Mech. 24, 594 (1957)] for frames whose effective elastic moduli are not related to the grain moduli by the Voigt average. For partial consolidation, an exact identification of the coefficients is not known, but the standard identification is a good approximation. A method from the theory of composites is used to estimate the frame moduli and a theoretical model of the frame inertia in a fluid environment is developed. The predictions of the resulting model are compared to Plona’s [Appl. Phys. Lett. 36, 259 (1980)] recent measurements on a water-saturated porous structure of sintered glass beads. Good agreement between the theory for a fully consolidated frame and the experiment is found. Measured fast and slow compressional wave speeds agree with the theoretical predictions within experimental error (3%) in all cases.
New formulation for ray theory range derivatives
Authors: White D.
Published: October 2005

Ray theory range derivatives (with respect to ray parameter) are needed in the evaluation of acoustic pressure and corrections for ray theory caustics. A new general formulation for the nth derivative is developed which is recursive in nature, i.e., involves a summation over previous derivatives plus a remainder term. This remainder term is expressed as an integral but can often be determined recursively. Summation over multilayered profiles are simplified with the new method. Specific examples are presented for four commonly used mathematical models of the sound speed profile.
Hybrid ray-mode fields in inhomogeneous waveguides and ducts
Authors: Felsen L. B.
Published: October 2005

High-frequency fields radiated by sources in transversely inhomogeneous waveguides or ducts are conventionally analyzed by ray or normal-mode techniques. When the duct width is very large, the excessive number of relevant rays or modes introduces computational difficulties. An alternative approach is provided by a hybrid representation that involves ray fields and modal fields in well-defined combinations: With respect to the angular domain centered at the source point, the modes fill those angular intervals left vacant by rays, and vice versa, the mode angles being defined as the angles of the upgoing and downgoing modal ray congruences as seen from the source. The hybrid mix is dependent on the position of the observer, and an additional remainder field assures the smooth transition from one hybrid combination to another. The analytical formulation, involving partial Poisson summation of the formal ray series, is applied to various ducting environments that cause wave trapping by refraction, reflection from boundaries, or both. For the special case of monotonically varying refractive index in a parallel-plane waveguide, the results from the asymptotic method are verified by rigorous Green’s function methods. Special examples, supported by numerical comparisons with exact reference solutions, are presented to demonstrate the validity and utility of the hybrid scheme.
Diffraction of a spherical wave by a thin infinite plate
Authors: Saadat H. , Filippi P.
Published: October 2005

A thin elastic plate extending to infinity is immersed in a perfect gas. The response of this system to a spherical harmonic sound source is studied, and an exact representation of the solution is developed. From this result, a series representation useful to calculate the farfield is established; expressions for the various mean powers are given.
Laser speckle method for the analysis of steady state vibration of plates
Authors: Lin C. J. , Chiang F. P.
Published: October 2005

A laser speckle method is described whereby time-average slope contours are obtained from vibrating plates. It has an advantage over deflection contouring methods in that only first-order differentiation of experimental data is needed for stress calculations.
Pitch for nonsimultaneous successive harmonics in quiet and noise
Authors: Hall Joseph W. , Peters Robert W.
Published: October 2005

Pitch perception was studied with respect to nonsimultaneous successive harmonics of fundamentals in quiet and noise. Stimuli consisted of three nonoverlapping sine waves each of 40-msec duration. Pitch perception, examined by discrimination and matching, was found to correspond to spectral frequency in quiet and fundamental frequency in noise. The results suggest a pitch processor that integrates over time (synthetic mode) in noise and analyzes spectral components (analytic mode) in quiet. The findings are discussed with respect to current theories of pitch perception and auditory integrative functions. The findings are thought to be particularly relevant to analytic and synthetic modes of pitch perception.
Multiple features analysis of intervocalic English plosives
Authors: Edwards Thomas J.
Published: October 2005

A controlled study involving a multi-feature acoustic analysis of intervocalic English plosives has been conducted for the purpose of evaluating acoustic stop features for automatic stop recognition. Both time-domain and frequency-domain features were measured via computer interaction. The resulting discrete density functions allowed for a comparative evaluation of individual (and in some instances conditional or combined) feature contributions to stop identification. This evaluation consisted of the maximum a posteriori probability of a correct identification of either the voicing mode (voiced or voiceless) or the place of articulation (labial, alveolar, or palato-velar) of a stop independent of the talker or of a limited phonetic context. These features included variations on ten acoustic features for voicing mode identification and seven for place-of-articulation identification. The data base for this study consisted of five male and five female talkers producing all permutations of the stops C - /p,t,k,b,d,g/ and vowels V - /i,e,a,u/ in the sentence frame ’’please say /h◊′CVt/ again.’’ While the results indicate that the acoustic features of burst/formant-onset frequency and voice onset time (VOT) are the two single most salient features for stop identification, several additional features are also shown to provide important redundancy for identification. The often overlooked time-domain features of ’’double-burst release’’ and ’’voicing during stop closure’’ were found to be particularly useful in providing such redundancy.
Reply to ’’Comments on ’Multiple-obstacle acoustic scattering in the simple source formulation with accuracy checks’ ’’
Authors: Sorensen Lawrence
Published: October 2005

Statements made regarding the failure of the simple source formulation at characteristic wavenumbers are clarified, and numerical results obtained from this particular implementation of the simple source formulation are presented. A possible explanation is offered regarding the discrepancies in results at high wavenumbers.
The metacepstrum
Authors: Hirsch P.
Published: October 2005

The metacepstrum is a modification of the cepstrum, in which the logarithmic compressor is replaced by an equalizer (automatic gain control). It has performance and computational advantages over the cepstrum.
Performance degradation in a quadrature receiver for cw signals corrupted by multipath
Authors: Higgins Robert C.
Published: October 2005

In active sonar applications, a quadrature receiver can be employed to detect the presence of an underwater reflector. This well-known receiver performs optimally when the input waveform is a coherent signal (i.e., constant but unknown amplitude and phase) embedded in white, Gaussian, zero-mean noise. Unfortunately, when an attempt is made to detect a distributed highlight reflector in a multipath environment by using a sinusoidal transmit signal, the various multipath returns may overlap, producing a nonresolvable multipath situation and causing the amplitude and phase of the signal to become random functions of time. Under these circumstances, the detection performance of the quadrature receiver is degraded compared to its performance with a coherent signal. It is the intent of this paper to theoretically determine the degradation in the receiver’s output signal-to-noise ratio (SNR) when the input waveform consists of a narrowband Gaussian signal embedded in white Gaussian noise. The output SNR’s dependence on the correlation characteristics of the input signal is clearly shown.
Frequency–wavenumber array processing
Authors: Hinich Melvin J.
Published: October 2005

Most array signal processing systems use delay-and-sum beamforming to estimate source bearings. This paper demonstrates the close relationship between beamforming and frequency–wavenumber spectrum analysis. The latter approach has computational advantages over beamforming when the noise is spatially correlated. The wavenumber approach is used to derive the array response of a general linear or planar array to plane wave signals. The statistical properties of the maximum-likelihood estimators of source bearing and amplitude are presented for an array with many elements. Optimal array design is also discussed.
Physiological (waves I and V) and psychophysical tuning curves in human subjects
Authors: Klein Alan J. , Mills John H.
Published: October 2005

Tuning curves obtained on wave I (VIII nerve) and wave V of the auditory brainstem response were recorded simultaneously with ear-canal and forehead electrodes. On these same human subjects using the same acoustic stimuli psychophysical tuning curves were also measured. For each subject the three tuning curves were qualitatively similar; however, both intra- and inter-subject quantitative differences were present. The best agreement was between the psychophysical and the wave V tuning curves. The wave I tuning curve differed from the other two mainly on the high-frequency side by showing a wider response area. The main difference between both physiological tuning curves and the psychophysical tuning curve occurred near center frequency of the probe signal: Physiological tuning curves had deeper tips in comparison to the psychophysical tuning curves which had shallow rounded tips. This might be due to energy splatter of the short-duration signal which can significantly effect psychophysical judgments while minimally contributing to the physiological responses. A precise measure of sharpness of tuning was difficult to obtain; however, the response area of wave I appears to be more biased towards high-frequency cochlear neurons than either wave V or psychophysical judgments. Tuning curves are shown to be a viable method of relating physiological to psychophysical measurements in human subjects.
A neural-counting model incorporating refractoriness and spread of excitation. II. Application to loudness estimation
Authors: Lachs Gerard , Teich Malvin Carl
Published: October 2005

In a previous paper [Teich and Lachs, J. Acoust. Soc. Am. 66, 1738–1749 (1979)] we demonstrated that an energy-based neural counting model incorporating refractoriness and spread of excitation satisfactorily described the results of pure-tone intensity discrimination experiments. In this paper, we show that the identical linear filter refractoriness model (LFRM) also provides proper results for pure-tone loudness estimation experiments at all stimulus levels. In particular, as the stimulus intensity increases from very low to moderate values, the model predicts that the slope of the intensity discrimination curve will climb from 1/2 toward 1, whereas the slope of the loudness function will gradually decline below 1 in this same region. For sufficiently high values of the stimulus intensity, the slopes calculated from a simplified (crude saturation) version of the model are found to be 1−1/4N for the intensity discrimination curve and 1/2N for the loudness function. The quantity N is the number of poles associated with the tuned-filter characteristic of the individual neural channels; it is the only important free parameter in the model. Appropriate values for N appear to lie between 2 and 4, providing an asymptotic slope for the intensity discrimination curve bounded by 7/8 and 15/16 (the near miss to Weber’s Law), and an asymptotic slope for the loudness function bounded by 1/4 and 1/8. The results follow from the assumption that the neural concomitant of loudness is the number of impulses observed on a collection of parallel neural channels during a fixed observation time. Our calculations are supported by Hellman and Zwislocki’s [J. Acoust. Soc. Am. 33, 687–694 (1961)] observation of unit slope for the loudness function at low intensities and provide a theoretical foundation, based on spread of excitation, for Stevens’ power law at high intensities.
Discussion of the pressure-source aerosonic theory and of Doak’s criticism
Authors: Meecham W. C.
Published: October 2005

The pressure-source theory is reviewed and simply derived, assuming that the source flow has a small fluctuation-Mach number. One prominent criticism of such theories is shown to be based upon a fundamental fluid mechanics error.
Compressional-shear wave coupling induced by velocity gradients in marine sediments
Authors: Fryer Gerard J.
Published: October 2005

The very high compressional and shear velocity gradients of marine sediments may result in continuous interconversion between P (compressional) and S (shear) types of motion at low frequencies. Since the ray theories commonly used in modeling acoustic interaction with the ocean bottom implicitly assume that P and S are decoupled, the importance of such phenomena must be assessed. The problem is investigated here through theoretical studies of the reflectivity function for representative models of the ocean bottom. The only practical approach for including all such wave phenomena in a determination of reflectivities involves numerical solution of the wave equation. For a depth-varying structure, the most efficient numerical scheme is the classical approximation by homogeneous layers. This procedure can be readily modified to isolate the effects of gradient-induced coupling by forcing the P- and S-wave potentials to be independent and studying the effects of this on the reflectivity. Unfortunately, the results of this analysis, being in frequency-wavenumber space, are so difficult to interpret that the physics of the coupling process is obscured. Some insight can be gained by transforming the frequency dependence of the reflectivity function to a time dependence. The resulting function (the plane-wave response) is more amenable to physical interpretation and shows clearly that the principal consequence of coupling is the conversion of shear to compressional motion. As a result, coupling reduces the amplitude of shear arrivals and draws out the tails of compressional arrivals. Above 1 Hz, however, the effects of this coupling are extremely small, so for most marine acoustics applications, the phenomenon can be ignored.
Frequency stability of a cw signal transmitted over a long underwater path
Authors: Robertson G. H.
Published: October 2005

A cw signal of 270 Hz derived from a very stable crystal oscillator was transmitted from a fixed projector at Eleuthera through 700 nautical miles (nmi) of deep water to fixed receivers at Bermuda. Samples of the received signal 40 s long were cross correlated with an equally stable reference signal of the same frequency for delay times of 0 to 18 s. Increased sensitivity of measurement was obtained by means of a heterodyning process in the correlation operation. The standard deviation of the frequency difference was calculated from data gathered over several days. In spite of multipath fading, the deviation was found to be only of the order of 0.001 Hz. For less than 5% of the time, the cross-correlation pattern could not be easily distinguished. The relationship between these results and previous measurements of signal coherence over the same path is discussed.
Differential sensitivity to pitch distance, particularly in speech
Authors: ’t Hart Johan
Published: October 2005

The fundamental frequency in speech shows many rapid variations, part of which determine the perceived shape of the pitch contour. This implies that the accuracy with which listeners perceive changes of F0 is more relevant to understanding the perception of intonation than the traditional just noticeable difference of F0 in speech. This study examines the sensitivity to differences in the amount of change of F0, upward (Experiment Ia) and downward (Experiment Ib). Subjects, 74 and 104, respectively, with widely different musical ability can be divided into three categories: (1) Quite a number of them were not able to discriminate differences of less than 4 semitones (nondiscriminators); (2) other subjects wrongly tried to base their judgments on a simple comparison of the final pitches of a stimulus pair (final pitch discriminators); (3) the remaining subjects (pitch distance discriminators) yielded average jnd’s of about 1.5 to 2 semitones. Since the issue is associated with musical interval sense, similar experiments were carried out using piano tones. The results were essentially the same as with the speech stimuli. The outcome suggests that only differences of more than 3 semitones play a part in communicative situations.
Determining individual loudness scales from binary comparisons of loudness intervals
Authors: Schneider Bruce
Published: October 2005

A method is described in which individual loudness scales can be derived without resorting to numerical judgments on the part of the subject. Loudness scales constructed via this method differed significantly from subject to subject. Since a non-numerical scaling procedure was employed, the individual differences could not be attributed to biases in the way in which observers use numbers or numerical concepts to describe the loudnesses of tones.
Acoustic resonances and the determination of the material parameters of a viscous fluid layer
Authors: Fiorito Ralph , Madigosky Walter , Überall Herbert
Published: October 2005

In previous publications [J. Acoust. Soc. Am. 65, 9 (1979), J. Acoust. Soc. Am. 66, 1857 (1979)] we have shown that the acoustic transmission (T) and reflection coefficient (R) of a fluid layer and of an elastic layer imbedded in another fluid can be written in the form of a sum of resonance terms. Our resonance formalism provides an explicit determination of the position, width, and strength of each individual resonance contribution. In the work presented here we have extended the resonance theory of a fluid layer to include viscous effects, by the introduction of a complex phase velocity of sound in the layer, the imaginary part of which is written in terms of an absorption loss factor. Viscosity manifests itself in a second-order shift of the resonance positions as compared to those of the nonviscous layer, and in a first-order broadening and frequency dependence of the resonance widths. These effects can be used to determine the material parameters and the loss factor of a fluid layer at all incidence angles, and for a viscoelastic layer at normal incidence.
Resonance phenomena of Lamb waves scattering by a finite crack in a solid layer
Authors: Rokhlin S. I.
Published: October 2005

The paper is concerned with diffraction of Lamb waves by a finite crack, parallel to surfaces, in an elastic layer. The solution is constructed by the method of multiple diffractions at the edges of the crack. It is shown that the solution is identical with the solution obtained previously by the generalized Wiener–Hopf method. The resonance phenomena associated with the diffraction of Lamb waves by a finite crack are analyzed. The contribution of the different Lamb waves, generated in the crack zone, to the transmitted and reflected fields, is considered. An approximation of the solution, associated with incorporation of a finite number of Lamb waves, excited in the region of the layer occupied by the crack is discussed. Simple approximate equations are presented for resonance frequencies.
Uniformly accurate description of finite amplitude sound radiation from a harmonically vibrating planar boundary
Authors: Ginsberg Jerry H.
Published: October 2005

The velocity potential for the two-dimensional, finite amplitude acoustic waves induced by harmonic excitation on a region in an infinite baffle was obtained by the author (1980). That analysis, which represented the response in terms of a continuous spectrum of wavenumbers parallel to the boundary, was valid only for limited distances from the boundary. The current analysis employs the perturbation method of renormalization to derive expressions for the pressure and particle velocity that are uniformly accurate up to the location where a shock forms. The response consists of radiative and evanescent waves, with nonlinearity being significant only for the former. The solution is described as inversions of Fourier cosine transforms which feature a straining transformation of the space–time coordinates. A quantitative example for the case of an intense high-frequency excitation is shown to lead to a sound beam in which the nonlinear distortion is asymmetrical between the compression and rarefaction phases.
Indirect measurement of the mean acoustic backscattering cross section of fish
Authors: Ehrenberg J. E. , Carlson T. J. , Traynor J. J. , Williamson N. J.
Published: October 2005

A technique is described for indirectly determining the average backscattering cross section of individual fish from the measured probability distribution function for the amplitudes of the envelopes of single fish echoes. The technique is based on the assumption that the on-axis echo envelope is Rayleigh distributed. The validity of the Rayleigh assumption was tested by making controlled measurements of the envelope amplitude statistics of single fish echoes for two acoustic frequencies and four different fish lengths. These tests showed that the echo envelope data most closely fit the Rayleigh model when the ratio of fish length to wavelength was large. The indirect measurement technique described has been used to analyze some single fish-echo amplitude data for Bering Sea walleye pollock. These results are compared with some measurements made using a dual beam, direct, target strength measurement system. Expressions for the bias and variance of the indirect estimation technique are derived in an Appendix.
Generation of acoustic waves by harmonic electric current sheets in the sea
Authors: Harker K. J. , Fraser–Smith A. C.
Published: October 2005

The generation of acoustic waves by a harmonic electric current sheet in a conducting medium permeated by a weak static magnetic field is investigated. For a current sheet of 1 A/m, a time-averaged acoustic power flow per unit area normal to the direction of travel of the wave of 2×10−16 W/m2 is generated in seawater. A possible source of these current-generated acoustic signals is lightning. Because of the very large peak currents involved (∠20 kA), lightning striking the sea appears likely to be a strong source of transient acoustic signals in the lower ELF range (5–50 Hz).
Infrasonic ambient ocean noise measurements: Eleuthera
Authors: Nichols R. H.
Published: October 2005

Measurements of ambient ocean noise in the frequency range 0.02 to 20 Hz were made with three hydrophones bottomed off Eleuthera Island, at depths of 13, 300, and 1200 m, respectively, over a period of about six weeks in June, July, and August. The results are compared with reported results of other experimenters and with results of some published theories of infrasonic noise generation in the ocean. Comparisons with published data in the frequency range from 0.1 to 20 Hz show reasonable agreement. There do not appear to be published data in the region below 0.1 Hz for comparison. Comparisons with theories do not allow conclusive identification of generating mechanisms, but it appears that nonlinear interaction of surface waves and/or ocean turbulence are likely candidates in the frequency range 0.1 to 10 Hz. Below 0.1 Hz no specific mechanism is postulated to account for the steep rise in noise level with decreasing frequency observed in the Eleuthera data.
Interaction of sound with noise in water II
Authors: Stanton T. K. , Beyer R. T.
Published: October 2005

The prediction of the scattered intensity due to the nonlinear interaction between underwater sound and noise requires measurement of the complex intensity of the noise field. Such an experiment is made possible by use of the complex wattmeter. This paper describes an experiment in which the device is used to select the 2.8-kHz component from a stable noise field and process the signal to produce a value for the component’s complex intensity. The resultant value is inserted into Westervelt’s interaction equation to yield a value for the scattered intensity due to the interaction between the noise and a 2.7-MHz plane wave. The predicted intensity is within 1 dB of the measured figure.
The optical grating hydrophone
Authors: Tietjen Byron W.
Published: October 2005

An optical hydrophone has been developed having an output which is a direct intensity modulated representation of an incident acoustic field. The principle of operation involves the relative displacement induced by an acoustic field of two optical gratings which lie between a constant optical source and an optical receiver. The received light intensity is a function of the relative displacement of the two optical gratings. The optical source may be coherent or incoherent light, and a simple pin-photodiode detector affords adequate receiver sensitivity. Large, multimode optical fibers can be used to carry the light to and from the hydrophone. Since the device is photon-noise limited, arbitrarily high sensitivities can be obtained by increasing the optical power, and/or increasing the spatial frequency of the optical gratings. The direct intensity-modulated output eliminates the need for more sophisticated detection techniques that are often applied to phase modulating optical hydrophones. However, comparable sensitivities can be realized with the optical grating approach. Fabrication of the device is straightforward, without any advanced optical techniques required. Several prototypes have been built and have already demonstrated dynamic ranges as high as 160 dB, with the ability to detect acoustically induced displacements of less than 0.01Å.
Effect of sensorineural hearing loss on the stapedius reflex growth function in the elderly
Authors: Silman Shlomo , Gelfand Stanley A.
Published: October 2005

The effect of sensorineural hearing loss upon stapedius reflex growth functions was studied in the elderly. The reflex activators were pure tones (500, 1000, and 2000 Hz) and broadband noise; reflex magnitude was expressed in decibels relative to static acoustic impedance. When expressed in decibels relative to reflex threshold, the mean growth functions of the elderly were reduced compared to previous data for young subjects [Silman, Popelka, and Gelfand, J. Acoust. Soc. Am. 64, 1406–1411 (1978)] and the noise functions differed in terms of both shape and magnitude. When expressed in SPL, the mean growth functions of the normal hearing elderly demonstrated saturation at high activator levels, whereas saturation was not observed in the mean growth functions of the hearing loss subjects. In the normal elderly, saturation was found to be frequency dependent. The saturation effect is discussed in terms of energy integration of the reflex response in the aging ear.
Low-frequency ambient noise in the deep sound channel—The missing component
Authors: Wagstaff R. A.
Published: October 2005

There is an important component of the undersea ambient noise which has generally been overlooked or ignored. It is the noise which arrives at a sensor, located in a deep sound channel, by way of ducted sound propagation. It is generated at the surface and becomes channeled as a result of a gradually sloping sound channel axis and through repeated reflections from a sloping bottom. It can be of sufficient level to dominate the local measurement. Examples are given in which neglecting it leads to incorrect interpretation of results and erroneous conclusions, including agreement between modeling and measurement.
Evaluation of shadow-zone fields by uniform asymptotics and complex rays
Authors: White De Wayne , Pedersen Melvin A.
Published: October 2005

This article presents the theory and numerical results of a new method for evaluating fields in ray-theory shadow zones. The travel time and pressure of ray theory are computed using complex ray parameters. With the use of these quantities, the amplitude and phase of the field, associated with each ray-theory caustic, are evaluated by uniform asymptotics. The complex conjugate properties of shadow-zone rays allow uniform asymptotics to be expressed in terms of only one ray arrival. At large distances into the shadow zone the uniform asymptotics has been reduced to geometric acoustics. The complex ray theory is developed utilizing the analytic continuation of the two real rays which form the caustic boundary of the shadow zone. Explicit steps for numerical calculations are given. Numerical calculations are presented for a bilinear sound speed model of the deep ocean. Results agree well with those obtained by other methods. For some receivers the entire shadow zone has been bridged with a continuous solution connecting the two caustic structures which bound the zone. Various properties of the shadow- zone fields are illustrated by the examples. Among the most surprising is the existence of a ray solution with the real parameter in the middle of the shadow zone. Another example is a ray solution with real travel time within the shadow zone, where the uniform asymptotic formulation for a two-ray system diverges.
Shadowing by finite noise barriers
Authors: Medwin H.
Published: October 2005

A technique is described for calculating the acoustical shadowing due to finite barriers. The method is an extension of the Biot–Tolstoy rigorous closed-form impulse solution for diffraction of point-source radiation by an infinite rigid wedge. By discrete Fourier transformation, spectral predictions are obtained which are closer to experimental results than previous schemes for infinite barriers. Furthermore, the limitations of the Kirchhoff Assumption are avoided, so that accurate predictions can be made for complicated finite barriers. Comparisons of theory and experiment are shown.
Hardware dynamic beamforming
Authors: Hodgkiss W. S. , Anderson V. C.
Published: October 2005

The hardware architecture of a programmable, time domain, digital beamformer built by the Marine Physical Laboratory is discussed. The Dynamic Beamformer permits the incorporation of slow changes in element positions and/or beam steering directions while carrying out the real-time formation of 1300 beams from 32 input sensors. The sensors are distributed in an arbitrary but known manner over a maximum aperture of 2 s in time delay, or 800 l at the uppermost operating frequency of 400 Hz. Oversampling the sensor signals by a factor of 2.5 above the Nyquist rate is shown to permit the use of a simple, two-point linear interpolation filter to achieve the time-delay quantization intervals required. Element-(as opposed to beam-) level recording of the original sensor data provides a flexible and compact mechanism for postexperiment data analysis.
Auditory tract asymmetry in brainstem electrical responses during binaural stimulation
Authors: Decker T. Newell , Howe Susan W.
Published: October 2005

A recently developed technique to demonstrate binaural interaction in brainstem auditory electrical responses was systematically investigated. From analysis of the BSERs of eight normal hearing adults, it was found that variations in binaural interaction difference traces are related to an artificial relationship created by this technique between the true binaural and summed monaural waveforms. The present investigation employed a refinement of the binaural interaction technique whereby left and right monaural waveforms were subtracted individually from the binaural waveform to produce a difference trace. Analysis revealed that variations in the difference trace morphology are related to dependence of binaural latencies on left or right auditory tract preference in the brainstem auditory pathways. Within the subject population, 50% demonstrated an auditory tract preference for binaural latencies while 50% showed no preference. It was concluded that the difference trace is mathematically predictable from the morphological differences between the binaural and monaural waveforms and that a more accurate representation of binaural interaction can be obtained from a comparison of individual monaural waveforms with the binaural trace.
Primary auditory neurons: Nonlinear responses altered without changes in sharp tuning
Authors: Robertson Donald , Johnstone Brian M.
Published: October 2005

Two-tone suppression as well as distortion product responses in mammalian auditory neurons were altered by exposure to short, high intensity tones in the frequency region of the suppressing or primary tones. These changes occurred without significant alteration of the single neurons’ tuning curves. The findings support the notion that two-tone suppression and distortion product responses are a function of the integrity of cochlear regions remote from the final transduction site.
Discrimination of interaural delays in complex waveforms: Spectral effects
Authors: Nuetzel John M. , Hafter Ervin R.
Published: October 2005

Sensitivity to interaural delays in high-frequency waveforms was examined using amplitude-modulated signals. Carrier frequencies ranged from 2 to 6 kHz, and modulation was varied from 50 to 550 Hz. The signals’ components were not harmonically related. Findings include: (a) As carriers exceed 3 kHz, a broad region appears (from 150 to 350 Hz of modulation) over which there is little change in sensitivity to interaural time differences in the modulation envelope. (b) Signals with interaurally-discrepant carriers are more difficult to lateralize, but for carriers at and above 4 kHz, a region of constant performance can also be found as the interaural frequency difference is increased from zero. (c) Variations in modulation depth are useful in approximating the sideband attenuation that may occur as wideband signals are filtered by the auditory system. Such a technique allows an assessment of the importance of critical bands in these phenomena.
Analysis of the acoustic response of circular electret condenser microphones
Authors: Zahn Rolf
Published: October 2005

An analysis of the average membrane deflection, sensitivity, and phase response of circular electret condenser microphones is presented. The analysis includes the influence of several parameters on the acoustic response, such as hole dimensions or air gap thickness, radiation impedance of the transducer, and viscous flow of the air in the gap and in the holes connecting the gap with the backchamber. Proper choice of the microphone parameters allows one to construct microphones for special applications.
Addendum to ’’Hybrid ray-mode formulation in inhomogeneous waveguides and ducts’’ [J. Acoust. Soc. Am. 69, 352–361 (1981)]
Authors: Felsen L. B.
Published: October 2005

This addenum is intended as a supplement to the article published in the February 1981 issue of the Journal.
Ultrasonic determination of the nonlinearity parameter B/A for biological media
Authors: Law W. K. , Frizzell L. A. , Dunn F.
Published: October 2005

The nonlinearity parameter B/A has been determined for solutions of bovine serum albumin, of dextrans, of sucrose, of hemoglobin extracted from blood, and for fresh whole blood. The value of B/A for solutions of bovine serum albumin has been observed to increase nearly linearly with concentration. Further, B/A appears to exhibit no dependence upon the molecular weight of dextrose and dextrans over the molecular weight range from 102 to 106.
Some effects of auditory stimulation on perioral motor unit discharge and their implications for speech production
Authors: McClean Michael D. , Sapir Shimon
Published: October 2005

The objective of this investigation was to describe the electrophysiological properties of short-latency reflexive pathways existing between the auditory system and the motoneurons involved in the control of lower lip movements for speech. The general procedure involved binaural presentation of auditory clicks (60–75 dB SL) at constant rates while subjects maintained a steady firing rate in a perioral motor unit. Post-stimulus time histograms were used to assess the effects of stimulation on the probability of firing of individual motor units. Data collected on 33 motor units in four subjects revealed a significant short-latency change in the probability of firing of 16 of these units. The mean latency of this effect was 20.4 ms. There was some indication that the direction and latency of the initial response to stimulation was dependent on the location and function of individual motor units. The likely neural pathways mediating these effects and their potential role in speech production are discussed.
Some notes on the clavichord
Authors: Thwaites Suszanne , Fletcher N. H.
Published: October 2005

Various acoustical features of the fretted clavichord, in some ways the simplest of keyboard instruments, are investigated experimentally and theoretically. The unusual excitation mechanism, in which a metal blade strikes the string and holds it deflected, yields an excitation force spectrum level with a smooth slope of 6 dB/oct, though the radiated spectrum depends greatly on the properties of the soundboard. Energy loss from the paired strings occurs primarily through the bridge to the soundboard, interaction between the strings giving a two-stage decay as described by Weinreich [J. Acoust. Soc. Am. 62, 1474–1484(1977)]. The uncomplicated soundboard configuration allows its measured response from 50 to 1000 Hz to be well accounted for theoretically. In this important range, a series of couplings between normal modes of the soundboard and of the enclosed air cavity considerably modifies the system response. The sound pressure level and sound decay time to inaudibility across the compass of the instrument are consistent with the string and soundboard behavior.
Computer-generated pulse signal applied for sound measurement
Authors: Aoshima Nobuharu
Published: October 2005

A computer-generated pulse signal for sound measurement is discussed. A pulse signal whose power spectrum is flat is generated by inverse Fourier transformation. The generation of a time-stretched pulse and its compression method are also discussed. Computer-controlled measurements enable time averaging and the elimination of reflected sound is made in the computer memory by the operator’s instruction monitoring acquired waveform on CRT.
Impedance measurement source and microphone proximity effects
Authors: Keefe D. H. , Benade A. H.
Published: October 2005

The input impedance Zin as normally defined is the air column pressure response to a unit plane-wave flow excitation. The experimental measurement of Zin for an arbitrary air column is affected by the nearfield interactions between an excitory source (capillary, annulus, membrane, etc.) and microphone. In addition to the plane-wave component, the source produces a local disturbance (due to the evanescent modes) at the microphone. The net microphone pressure pm can be written in terms of the source strength us, the wave impedance R0 and radius a of the air column entryway, and wavenumber k: pm = usR0[(Zin/ R0)+jkaℰ]. The evanescent mode factor ℰ is real and independent of frequency for ka<1. Its value depends on the source and microphone geometry. Measured values agree with detailed calculation. Placement of one transducer along the center axis of the air column, with the other at R = 0.6a from the center eliminates all azimuthal mode coupling (Jm Bessel functions, m≳0), and minimizes the coupling to the lowest order J0 evanescent mode. If neither transducer can be placed at the center, 90° azimuthal separation will eliminate all J1 modes. Placing one or both at R = 0.6a from the center then minimizes J0 effects. These configurations make the ℰ contribution to pm negligible for ‖zin/R0‖≳2, but experimental study near Zin minima (i.e., input admittance maxima) still poses special problems whose reduction is discussed.