bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance of hearing-impaired listeners under various types of amplitude compression
Authors: Nábělek Igor V.
Published: October 2005

Speech perception by subjects with sensorineural hearing impairment was studied using various types of short-term (syllabic) amplitude compression. Average speech level was approximately constant. In quiet, a single-channel wideband compression (WBC) with compression ratio equal to 10, attack time 10 ms and release time 90 ms produced significantly higher scores than a three-channel multiband compression (MBC) or no compression when a nonsense syllable test (City University of New York) was used. The scores under MBC, WBC, or no compression were not significantly different when the modified rhyme test (MRT) was used. But when overshoots caused by compression were clipped, the MRT scores improved significantly. The influence of MBC on reverberant speech and of WBC on noisy speech were tested with the MRT. Reverberation reduced the scores, and this reduction was the same with compression as without. Noise added to speech before compression also reduced the scores, but the reduction was larger with compression than without. When noise was added after compression, an improvement was observed when WBC had a compression ratio of about 5, attack time 1 ms, and release time 30 ms. Other compression modes (e.g., with high-frequency pre-emphasis) did not show an improvement. The results indicate that WBC with a compression ratio around 5, attack time shorter than 3 ms, and release time between 30 and 90 ms can be beneficial if signal-to-noise ratio is large, or, if in a noisy or reverberant environment, the effects of noise or reverberation are eliminated by using listening systems.
Acoustically evoked radial current densities in scala tympani
Authors: Brownell W. E. , Manis P. B. , Zidanic M. , Spirou G. A.
Published: October 2005

We have developed a method for measuring current density within the fluid spaces of the cochlea and report the existence of stimulus evoked radial currents in scala tympani of the guinea pig cochlea. The spatial distribution of electrical potentials in scala tympani was measured along a radial path parallel to the basilar membrane. Click evoked potentials were recorded at successive points separated by a fixed increment as the electrode was either advanced from the spiral ligament or withdrawn from a position near the modiolus. Potential differences were found to exist between recording points and gradients were calculated from the evoked potential measurements. Evoked potential gradients are observed at the same position along the path of the electrode both on advancing and on withdrawing the electrode. The largest potential gradients are located beneath the organ of Corti. Condensation and rarefaction clicks produce radial currents in opposite directions at a given location along the electrode’s path. The magnitude and spatial distribution of radial currents is a function of stimulus intensity. Potential gradients of small magnitude are observed at locations other than below the organ of Corti in some penetrations. Control experiments suggest the smaller gradients are artifactual and may result from displacement of the spiral ligament by the recording electrode. The locations, magnitude, and direction of intracochlear ionic flow relate directly to the mechano-electrical transduction process in the organ of Corti.
Nearfield of a large acoustic transducer, Part II: Parametric radiation
Authors: Garrett Greer S. , Tjo/tta Jacqueline Naze , Tjo/tta Sigve
Published: October 2005

The transducer is the same as the one considered in an accompanying paper by the same authors [Part I, J. Acoust. Soc. Am. 72, 1056–1061 (1982)]. It has a diameter of 182 cm, and is composed of 364 elements, 4.8×6.4 cm each, which are distributed in 13 equally spaced rings. It is used to generate difference frequency sound at 0.5–5 kHz in water. Amplitude and phase of the generated sound are measured at various distances in the nearfield of the transducer. The results are compared with calculations based on the quasilinear approximation of the governing equations. Simplifications are obtained by utilizing the parabolic approximations [J. Naze Tjo/tta and S. Tjo/tta, J. Acoust. Soc. Am. 67, 484–490 (1980)]. This also makes it possible to use a realistic model for the primaries (see the accompanying paper) when evaluating the nonlinear source term, such that all effects of the nearfield oscillations in amplitude and phase are fully accounted for. The analytical results obtained also apply to the case of an amplitude and/or phase shaded source.
A new rigorous expansion for the velocity potential of a circular piston source
Authors: Hasegawa Takahi , Inoue Naoki , Matsuzawa Kiichiro
Published: October 2005

In the case of boundary value problems such as the sound scattering from a sphere placed in the nearfield of a plane piston source, it is sometimes essential to express the velocity potentials in terms of the orthogonal expansion. It is demonstrated in the present work that the Rayleigh surface integral, giving the velocity potential for a plane piston source surrounded by an infinite rigid flange, reduces to a rigorous expansion of the simplest form for a circular piston as series of spherical surface harmonics. The resulting equation is valid for any field points even on the piston surface. Sample calculations made with a microcomputer are presented with three-dimensional and contour plots.
Range ambiguity and pulse interval jitter in the bottlenose dolphin
Authors: Kadane J. , Penner R.
Published: October 2005

A common problem of pulse-mode sonar systems which utilize range gating is the range ambiguity caused by echoes from objects at multiple distances returning simultaneously. Research conducted at the Naval Ocean Systems Center, Oahu, Hawaii, investigating bottlenose dolphin echolocation indicate that there is adequate varying of consecutive interpulse intervals (jittering of the repetition rate) to eliminate range ambiguity and range-ambiguous interference in this biological sonar system.
Involvement of ultrasonically induced cavitation in the production of hind limb paralysis of the mouse neonate
Authors: Frizzell L. A. , Lee C. S. , Aschenbach P. D. , Borrelli M. J. , Morimoto R. S. , Dunn F.
Published: October 2005

The exposure conditions which produce hind limb paralysis in 10%, 50%, and 90% of mouse neonate specimens exposed to 1-MHz ultrasound at 10° C and at 1- and 16-atm hydrostatic pressure were determined for the intensity range 86–289 W/cm2. The change in the exposure duration for 50% of the specimens paralyzed resulting from pressurization to 16 atm was negligible at 86 and 144 W/cm2 but was almost a factor of 2 increase at 289 W/cm2. Pressurization suppressed the observed half-harmonic received signal at all intensities. These results suggest that cavitation may influence the production of the hind limb paralysis produced in the neonate at 1 atm and at 289 W/cm2.
High-resolution beamforming with oversampled arrays
Authors: Byrne C. L. , Fitzgerald R. M.
Published: October 2005

Interpreting plane-wave beamforming as wave-vector spectrum estimation, we show that the maximum entropy spectrum estimation technique (MEM) indicates the presence of false targets when used to beamform a spatially oversampled array. The source of this instability lies in the presence in the MEM technique of the prior estimate that the wave-vector spectrum is white over the Nyquist band. By the use of a new, adaptive, high-resolution spectral estimator, which includes MEM as a special case, the instability is removed. The results are of particular significance for short arrays operated at low frequencies.
An approximate maximum entropy method for a uniform line array with less than half-wavelength spacing
Authors: Hebbert R. S. , Barkakati Leha T.
Published: October 2005

The usual maximum entropy power estimate is obtained under the assumption that the uniform line array has sensors half a wavelength apart. In this paper an approximate method is presented for computing the maximum entropy power estimate when the sensor spacing is less than half a wavelength. Results of a simulation illustrate the effectiveness of the method.
Aperture diffraction theory applied to ultrasonic attenuation imaging
Authors: Chenevert T. L. , Meyer C. R. , Bland P. H. , Carson P. L.
Published: October 2005

Ultrasonic computed tomography (UCT) suffers significant quantitative errors when attempting attenuation imaging of refractive objects. The problem can be aggravated when a relatively large, single element, phase sensitive receiver is used. A method designed to maintain high resolution while minimizing refractive error is introduced. This technique (referred to as profile migration) utilizes an array receiver and an algorithm based on aperture diffraction theory. The profile migration and a more conventional migration approach are applied to data obtained from single projection scans of an object under refractive and nonrefractive conditions. Attenuation projections generated using two single-element receiver methods are also compared. Reconstructed images using projections produced via the profile migration method are compared to those using a technique currently employed on our UCT breast scanner. For both minimal and realistic refractive situations the profile migration method displays advantages over the other methods based on a qualitative assessment of the projections and images.
Resonant acoustic scattering from elastic cylindrical shells
Authors: Breitenbach Edward D. , Überall Herbert , Yoo Kwang-Bock
Published: October 2005

The normal mode solution of the scattered pressure due to a normally incident plane acoustic wave on an infinitely long, air-filled aluminum cylindrical shell in water is analyzed. Our study yields a physical interpretation of normal mode contributions to the backscattering function. The modes in the near-soft (thin-shell) region are compared to theoretical predictions and empirical observations. Transitions from Rayleigh-type surface waves to Lamb-type waves are found to take place for thin shells. A smooth transition of the first transverse wave on a thick shell to that of the first symmetric Lamb wave on a thin shell is shown to occur, and the inception of these thin-wall modes is investigated as a function of shell thickness. Also, the antisymmetric Lamb mode is shown to exist and its intermittent nature is examined.
A kinematic study of lingual coarticulation in VCV sequences
Authors: Parush Avraham , Ostry David J. , Munhall Kevin G.
Published: October 2005

Intra-articulator anticipatory and carryover coarticulation were assessed in both temporal and spatial terms. Three subjects produced VCV sequences with velar stop consonants and back vowels. Pulsed ultrasound was used to examine the vertical displacement, duration, and maximum velocity of the tongue dorsum raising (VC transition) and lowering (CV transition) gestures. Anticipatory coarticulation was primarily temporal for two subjects, with decreases in the duration of the VC transition accompanying increases in displacement for the CV transition. Carryover coarticulation was primarily spatial for all three subjects, with decreases in CV displacement and maximum velocity accompanying increases in VC displacement. It is suggested that these intra-articulator patterns can be accounted for in terms of an interaction between the raising gesture and a vowel-specific onset time of the lowering gesture towards the vowel. The implications of this kinematic characterization are discussed.
Perceptual cues to the onset of voiced excitation in aspirated initial stops
Authors: Darwin C. J. , Seton John
Published: October 2005

Previous experiments on the perception of initial stops differing in voice-onset time have used sounds where the boundary between aspiration and voicing is clearly marked by a variety of acoustic events. In natural speech these events do not always occur at the same moment and there is disagreement among phoneticians as to which mark the onset of voicing. The three experiments described here examine how the phoneme boundary between syllable-initial, prestress /b/ and /p/ is influenced by the way in which voicing starts. In the first experiment the first 30 ms of buzz excitation is played at four different levels relative to the steady state of the vowel and with two different frequency distributions: In the F1-only conditions buzz is confined to the first formant, whereas in the F123 conditions all three formants are excited by buzz. The results reject the hypothesis that voicing is perceived to start when periodic excitation is present in the first formant. The results of the third experiment show also that buzz excitation confined to the fundamental frequency for 30 ms before the onset of full voicing (formant excitation) has little effect on the voicing boundary. The second experiment varies aspiration noise intensity and buzz onset intensity independently. Together with the first experiment it shows that: (1) at all buzz onset levels a change in aspiration intensity moves the boundary by about the 0.43 ms/dB found by Repp [Lang. Speech 27, 173–189 (1979)]; (2) when buzz onsets at levels greater than −15 dB relative to the final vowel level, changes in buzz onset level again move the /b/–/p/ boundary by the same amount; (3) when buzz onsets at levels less than −15 dB relative to the vowel, decreasing the buzz onset level gives more /p/- percepts than Repp’s ratio predicts. This last result, taken with the results of the first experiment, may reflect a decision based on overall intensity about when voicing has started.
Frequency patterns of TTS for different exposure intensities
Authors: McFadden Dennis , Plattsmier H. S.
Published: October 2005

Temporary threshold shift (TTS) was measured for several different test frequencies following exposure to a 2500-Hz tone.The intensity of the exposure tone was varied from 82 to 97 dB SPL; its duration was 5 or 10 min. In each post-exposure session, TTS was followed for four test frequencies using a method of adjustment. In all cases, the ‘‘center of balance’’ of the TTS pattern moved upward in frequency as exposure intensity increased. This outcome is consistent with the idea of a basalward migration of the traveling-wave envelope with increasing exposure intensity, but the evidence is not unequivocal.
Low-frequency attenuation in the Northeast Pacific Subarctic transition zone
Authors: Chow R. K. , Browning D. G.
Published: October 2005

A long-range sound propagation experiment conducted in the Subarctic transition zone (40°–50° N) in the Northeast Pacific Ocean has permitted the investigation of the anomalously large attenuation values previously reported. Our results, based on an experimental track with relatively uniform propagation conditions in the zone (parallel to the boundaries), support ‘‘normal’’ attenuation values. This suggests that the earlier anomalously high values may have been an artifact caused by rapidly changing propagation conditions along the path selected (traversing the zone).
Some practical aspects of absorption measurements in reverberation rooms
Authors: Warnock A. C. C.
Published: October 2005

This paper discusses the results of a series of computer controlled measurements of sound absorption coefficients in a single reverberation room. The effects of factors such as diffuser area, microphone position, and rotating diffusers on the measurements are discussed. Spatial variations of decay rate, curvature, and measured absorption coefficients determine the precision of the measurements. The practical procedures necessary to achieve satisfactory precision are compared with those allowed in standard test methods.
The uniform WKB modal approach to pulsed and broadband propagation
Authors: Henrick R. F. , Brannan J. R. , Warner D. B. , Forney G. P.
Published: October 2005

A uniform asymptotic approach is utilized to consider pulsed and broadband propagation. For a given frequency, the WKB approach with boundary layer corrections is used to approximate the normal modes of the sound channel. This approach is demonstrated to yield significant reductions in computer processing time and high accuracy when compared to a conventional code. It is shown that a substantial amount of the calculations in the uniform WKB approach required at each frequency is frequency-independent, and need be done only once in multiple frequency runs. Hence, further efficiencies in broadband or pulsed propagation result without any sacrifice in accuracy. Comparison of waveform predictions between uniform WKB and conventional techniques show excellent agreement in a complex propagation environment with use of the uniform WKB approach resulting in reductions of computer time by a factor of over 100.
Field of a finite-amplitude focusing source
Authors: Lucas Bernard G. , Muir Thomas G.
Published: October 2005

An analytical description for the field of a harmonic focusing source is derived. It is valid for spherically concave sources with small aperture angle and high ka, under conditions of quasilinear distortion (strong shocks precluded). The solution furnishes access to the phase and amplitude of second harmonic sound. Underwater experiments conducted with an f/2 lens coupled to a low-density source array are discussed. The results support the utility and validity of the analytical model for describing the amplitude and phase distribution of the second harmonic along the acoustic axis. It is shown that phase shifting in the focal region differs from that of linear radiations, and that both nonlinear propagation and diffractive effects are important in determining phase properties.
Eigenvalues of slender cavities and waves in slender tubes
Authors: Geer James F. , Keller Joseph B.
Published: October 2005

An asymptotic method is used to find the eigenvalues and eigenfunctions of the reduced wave equation in slender cavities, and to find the modes of propagation in slender tubes. The results for the eigenvalues of prolate spheroids are found to be in good agreement with those computed numerically by Chang.
Effects of acoustic trauma on the cochlear potentials
Authors: Gans Donald P.
Published: October 2005

The cochlear microphonic, summating potential, and action potential were recorded from all three turns of the gerbil cochlea prior to and following a 1-h exposure to a high-intensity pure tone. Results proved that the depression in the cochlear microphonic was greater when recorded from the upper two turns of the cochlea. The losses for the summating potential were not dependent on recording location. Although the cochlear microphonic and to some extent, the negative summating potential, reflected locally generated activity from the hair cells, the positive summating potential appeared to be dependent on distant electrical activity.
A survey of community attitudes towards noise near a general aviation airport
Authors: Schomer Paul D.
Published: October 2005

This paper describes a community attitudinal noise survey performed in the vicinity of the Decatur, Illinois Airport. Two hundred thiry-one respondents were drawn from four distinct noise zones in populated areas near the airport. The day/night average sound levels (DNL) ranged from 44–66 dB. The area is otherwise quiet, residential with large (l/2 acre) lots. The primary analysis arrayed the percent of respondents highly annoyed versus DNL. Good agreement was found between the results of this survey and the general relation developed by Schultz from surveys worldwide, primarily in the vicinity of large commercial airports and highways. In addition, reasonable comparisons were found between respondent estimates of the number of aircraft operations and actual traffic counts. It was also found that respondents who were highly annoyed by aircraft noise were three to four times as likely to be highly annoyed by some other noise than were other respondents.
New ultrasonic resonator method using optical diffraction for liquids
Authors: Choi P.-K. , Naito Y. , Takagi K.
Published: October 2005

A new resonator method has been developed for measuring ultrasonic absorption in liquids in the frequency range 0.3–10 MHz. This method utilizes Raman–Nath light diffraction to detect a resonance spectrum of standing waves in a cylindrical cavity. Comparison with the spectrum obtained by conventional resonator method demonstrates that distortion of plane-wave peaks by higher modes can be avoided with the present method. The use of a concave reflector is found to reduce a cavity loss considerably, enabling us to measure absorption down to a few hundred kHz. Results for water obtained using three types of reflectors with curvature radius 100–400 mm are shown.
Dispersion of extensional waves in fluid-saturated porous cylinders at ultrasonic frequencies
Authors: Berryman James G.
Published: October 2005

Ultrasonic dispersion of extensional waves in fluid-saturated porous cylinders is studied by analyzing generalized Pochhammer equations derived using Biot’s theory. Cases with open-pore surface and closed-pore surface boundary conditions are considered. For both cases, the dispersion of the fast extensional wave does not differ much qualitatively from the dispersion expected for extensional waves in isotropic elastic cylinders. A slow extensional wave propagates in the case with a closed-pore surface but not in the case with an open-pore surface. The propagating slow wave has very weak dispersion and its speed is always lower than, but close to, the bulk slow wave speed.
A wide-angle split-step algorithm for the parabolic equation
Authors: Thomson D. J. , Chapman N. R.
Published: October 2005

In this paper we describe a new wide-angle parabolic equation based on an operator-splitting that permits the use of a marching-type Fourier transform solution method. The equation was first presented by Feit and Fleck [Appl. Opt. 17, 3990–3998 (1978)] for studying propagation within optical fibers. Existing computer codes which numerically solve the standard parabolic equation of ocean acoustics by the split-step algorithm of Tappert and Hardin are easily modified to accommodate the wide-angle capability of the new equation. In addition, since the new wide-angle equation is less sensitive to the value of the reference wavenumber, the effects of phase errors are greatly reduced. The results of a simple error analysis indicate that improved accuracy can be achieved by the new wide-angle equation for propagation conditions typical of deep ocean environments. This is supported by our numerical experience, a summary of which is presented in the paper. For test cases, where the variation of the acoustic index of refraction was large, the new wide-angle equation gave results superior to those of the standard parabolic equation. Moreover, even for conditions which support long range, low-angle propagation in the deep ocean, the predictions based on the new equation are a significant improvement over those obtained with the standard equation.
Sounddrops...?
Authors: Leonard C. M. L. , Mirabelli Andre
Published: October 2005

We consider the question: Does sound fall under gravity?
Frequency discrimination and signal detection in band-reject noise
Authors: Emmerich David S. , Brown William S. , Fantini Deborah A. , Navarro Nicholas C.
Published: October 2005

An experiment was conducted in order to compare the importance of information from frequency regions remote from the nominal signal frequencies for frequency discrimination and signal detection. In both tasks, signals were presented within the ‘‘notch’’ of band-reject noise, and different notch widths were employed. The results indicate that information is integrated over a wider range in frequency discrimination than in signal detection. Further, experiments in which a noise floor was present as well as band-reject noise, indicate that disrupting the information from regions remote from the nominal signal frequencies impairs frequency discrimination even in the absence of any significant impairment of signal detection performance.
A comparison between basilar membrane and inner hair cell receptor potential input–output functions in the guinea pig cochlea
Authors: Patuzzi R. , Sellick P. M.
Published: October 2005

Intracellular recordings were made from inner hair cells and basilar membrane motion was measured at a similar place, but in different preparations, in the first turn of the guinea pig cochlea. Potential recordings were made using glass microelectrodes and mechanical measurements were made using the Mössbauer technique. Intensity functions of DC receptor potential and basilar membrane velocity in animals with good and poor thresholds are presented. In animals with good thresholds, stimuli at and above the characteristic frequency produce similarly compressive input–output functions for both inner hair cell receptor potentials and basilar membrane motion. However, for frequencies lower than the characteristic frequency, receptor potential input–output functions obtained from animals in good and poor condition show saturation at high stimulus intensities at which basilar membrane motion is linear. This discrepancy is believed to be due to a nonlinear inner hair cell transduction mechanism. We propose that nonlinearity observed in receptor potential input–output functions is a consequence of the simple cascading of a frequency-dependent nonlinear mechanical input and a frequency-independent nonlinear transduction process.
Diffraction of waves and singular stresses in a soft ferromagnetic elastic solid with two coplanar Griffith cracks
Authors: Shindo Y.
Published: October 2005

Magnetoelastodynamic stress intensity factors are computed for diffraction of normally incident longitudinal waves by two coplanar Griffith cracks in a soft ferromagnetic elastic solid. The solid is permeated by a uniform magnetostatic field normal to the crack surface. The problem is formulated by means of integral transforms, and reduced to the solution of a singular integral equation of the first kind. Numerical calculations are carried out and stress intensity factors are obtained for several values of frequency, magnetic field, and geometrical parameter.
An analytical model for noise generated by axial oscillations of unbaffled cylindrical elements
Authors: Perreira N. Duke , Dawe Daniel
Published: October 2005

A simple method to predict the noise generated by cylindrical-shaped machine elements in axial vibration is presented. An approximation of the Helmholtz integral equation valid when the receiver–source distance is much greater than either the cylinder’s diameter or length is used to determine the acoustic pressure generated by axial oscillations of cylinders at any aspect ratio or frequency. The results are used in developing free-field and reverberent field design contours. Experimental evidence points to the validity of the prediction model. Included are two design problems and solutions that show the method can be used to reduce noise generated by cylindrical shaped bodies.
Acoustic streaming in a waveguide with slowly varying height
Authors: Thompson Charles
Published: October 2005

An analysis of acoustic streaming in a two-dimensional waveguide having slowly varying height is presented. Special attention is paid to waveguides with cross sections that are small compared to the acoustic and/or wall wavelengths. It is shown that the dynamic behavior of the enclosed fluid can be parameterized by the values of three small parameters, ε, 1/S, and 1/R, where ε is the ratio of the typical duct height H0 to the wall wavelength L0, 1/S is the ratio of the typical oscillatory particle displacement U0/ω to the typical duct height H0 and 1/R is the ratio of the oscillatory boundary layer thickness lν to the typical duct height H0. An analytical solution describing the streaming flow in the duct is given in terms of a regular perturbation sequence in ε. It is shown that the oscillatory pressure must satisfy the lossy Webster horn equation to O(ε2) if the no slip boundary condition is to be satisfied. Outside the boundary layer it is shown that the time averaged slip velocity is the sum of two terms. The first term is proportional to the product of the incident and reflected wave amplitudes. The second term is proportional to the difference between the incident and reflected acoustic intensity of the wave. For small values of 1/S, 1/R, and ε the streaming solution given is shown to be valid until εR/S2 becomes of O(1).
Resolution enhancement of a sector-scan image using a homomorphic transform and deconvolution
Authors: Sato Takuso , Nakamura Yukito , Ikeda Osamu , Hirama Makoto
Published: October 2005

A method of resolution enhancement is presented for the case of sector-scan ultrasonic imaging. In this method, a homomorphic transform, in which image reconstruction is carried out on the polar coordinates through the space−variant selection of the received data depending on each reconstruction point, is used so that an image convolved with a space-invariant 2-D point-spread function is obtained. Then, the conventional deconvolution process is applied to get an image with uniformly improved resolution.
Smoothed boundary conditions, coherent low-frequency scatter, and boundary modes
Authors: Tolstoy I.
Published: October 2005

Low-frequency coherent scatter from a rough surface may be conveniently investigated using a linear boundary condition applied to a smoothed surface, of the form ∂φs/∂z=ηφ, where φ, φs are solutions of the wave equation representing, respectively, the total and scattered field potentials. The validity of the theories discussed here is restricted to kh≲1, where k is the wavenumber and h the mean spacing between roughness elements. The constant η is a function of frequency, angle of incidence, and type of roughness; in the general case of scatterers distributed isotropically over an interface between two fluids it is sensitive to eight physical parameters. Methods of calculating η for various types of rough boundary are discussed, and comparisons are made—notably between the boss and the stochastic perturbation models. Also examined are interesting implications of the smoothed boundary conditions; e.g., the boundary wave which is a true propagating mode corresponding to energy trapped in the vicinity of a rough surface, and which is only generated by a source near this surface (it thus differs fundamentally from the evanescent modes of a diffraction grating which may be excited by plane waves and are therefore not true boundary modes). For source and receiver near the boundary, and for negligible incoherent scatter, the farfield amplitude of the boundary wave may exceed that of the direct (normal) acoustic arrival—a fact which has been verified experimentally in model work. Incoherent scatter introduces an attenuation factor exp(−δr), where r is the source–receiver distance and δ is proportional to the sixth power of the frequency.
Input impedance of brass musical instruments—Comparison between experiment and numerical models
Authors: Caussé René , Kergomard J. , Lurton X.
Published: October 2005

We present a sequence of measured and calculated input impedance curves for tubes of increasing complexity, culminating in curves for a trombone and for a tuba. Measurements were made by the indirect method in a manner which afforded unprecedented accuracy. Calculations were done with a one-dimensional model, including visco-thermal losses, by a method of discretization, employing truncated cones. The correspondence between theory and experiment is sufficiently good that one can use model calculations to predict with some confidence the changes in input impedance caused by modifications to real instruments.
Receiving beam patterns and directivity indices of the Atlantic bottlenose dolphin T
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Authors: Au Whitlow W. L. , Moore Patrick W. B.
Published: October 2005

The receiving beam patterns of an Atlantic bottlenose dolphin was measured in both the vertical and horizontal planes for frequencies of 30, 60, and 120 kHz. Measurements in the vertical plane were performed by training the dolphin to rotate on its side and station on a vertically oriented biteplate device. A signal source was positioned 3.5 m directly in front of the animal on an arc while the position of a broadband noise source was varied in azimuth along the arc, with the animal stationed at the origin of the arc. Using a go/no-go response procedure, the masked threshold of the dolphin was determined by varying the intensity of the noise source via a tracking method of stimulus presentation, for different azimuth’s of the noise source. Measurements in the horizontal plane were obtained with the dolphin stationing on a horizontal biteplate. Two masking noise sources, projecting equal levels of uncorrelated noise, were located at ±20° on either side of the arc midpoint. The levels of the noise source were held constant and the masked thresholds determined by varying the level of the signal source while positioned at different azimuths along the arc. Results indicated that maximum sensitivity in the vertical plane (the major axis of the beam) occurred between 5° and 10° above the midline of the animal’s mouth and that the beam patterns were not symmetrical about the major axis. The sensitivity dropped off more quickly with increasing angle above the head than below. The beam patterns in the horizontal plane were directed forward and were fairly symmetrical about the midline of the animal’s body. The beam patterns in both planes became narrower as the frequency increased. Using the beam patterns measured in both planes, the receiving directivity index was calculated to be approximately 10, 15, and 21 dB for frequencies of 30, 60, and 120 kHz, respectively. A two-element rectangular array was used to model the dolphin’s directivity index with each aperture having a cross-sectional area of 8.1 cm2. The frequency dependency of the dolphin’s directivity index was found to be very similar to that of the model. Results also indicate that the receiving beam pattern at 120 kHz was slightly broader than the transmitting beam pattern for echolocation clicks with peak frequencies between 110 and 120 kHz.
Acoustic streaming due to an oscillatory source near a plate
Authors: Wang C.-Y.
Published: October 2005

High-frequency oscillations of a source cause an oscillatory flow near a flat plate. In addition, a nonlinear steady flow is also generated by viscous interactions. The problem is solved by matched asymptotic expansions. It is shown that a strong steady toroidal recirculation cell exist around the unsteady source.
The coherent Green’s function for acoustic propagation in a random ocean
Authors: Palmer David R.
Published: October 2005

We have derived an algorithm for calculating the coherent Green’s function of an acoustic wave propagating in an ocean possessing index-of-refraction fluctuations. This function is related to the so-called strength parameter which can be used to characterize the statistics obeyed by the acoustic field. Since we are interested in a wave solution we do not make the geometric optics approximation. Consequently, it is necessary to generalize the usual form of the Markov approximation. This is done in analogy with Dashen’s investigations. Our analysis accounts for the ocean boundaries and the depth dependence of the mean index of refraction. It is, however, restricted to convergence zone propagation. The phenomenological model of internal waves introduced by Garrett and Munk is used to describe the random fluctuations in the index of refraction. The analysis is based on the use of a Feynman path integral. The path integral formalism is particulary well suited to the approximations we consider. The algorithm consists of solving the parabolic equation using the split-step Fourier algorithm technique with an effective index of refraction term. The presence of the internal wave fluctuations are reflected in this term through an imaginary piece which attenuates the coherent Green’s function.
The spatial coherence of sound scattered from a wind-driven surface: Comparison between experiment, Eckart theory, and the facet-ensemble method
Authors: Kinney Wayne A. , Clay C. S.
Published: October 2005

Clay and Medwin [J. Acoust. Soc. Am. 47, 1419–1429 (1970)] performed an experiment in which they measured the spatial coherence of signals scattered from a wind-driven surface in a water tank. The coherence values were obtained by cross-correlating signals received at two hydrophones and were presented as a function of receiver separation. In this paper, a comparison is provided between these measured values and values predicted using (1) a technique based on Eckart theory [C. S. Clay, J. Geophys. Res. 71, 2037–2046 (1966)] and (2) the facet- ensemble method [W. A. Kinney et al., J. Acoust. Soc. Am. 73, 183–194 (1983)]. The former technique is presented by way of a review and provides an approximate single-valued estimate of coherence independent of receiver separation. The facet-ensemble method, on the other hand, provides precise estimates that are fully dependent on geometry. Agreement between the method and the experiment is good.
Response of elastic cylinders to convective flow noise I. Homogeneous, layered cylinders
Authors: Francis S. H. , Slazak M. , Berryman J. G.
Published: October 2005

One of the noise mechanisms experienced by passive towed sonar arrays is that of convective flow noise due to boundary layer turbulence generated as the array moves through the water at a fixed tow speed. The purpose of the present work is to arrive at quantitative predictions of the effects of convective flow noise using relatively simple model calculations. Line arrays are modeled as homogeneous, layered cylinders while turbulent eddies are modeled as random pressure fluctuations traveling at the convective speed of the eddies (about 80%) of the tow speed. The qualitative difference between solid and liquid fills is explained with this analysis. Solid-filled arrays are more susceptible to convective flow noise than are liquid-filled arrays because the noise-carrying shear waves are highly attenuated in the liquid. The detailed analysis is presented both for homogeneous cylinders and for cylinders with multiple homogeneous layers. Examples are presented to illustrate the analysis and the numerical methods employed in the calculations.
Vibrations of a lightly loaded tapered circular beam
Authors: Gottlieb H. P. W.
Published: October 2005

Analytical expressions for the free vibration frequencies of a lightly loaded tapered circular beam are determined by utilizing mathematical properties of Bessel functions. To first order, the proportional change in frequency parameter is independent of mode frequency and depends only on the mass ratio. Explicit formulas for second-order corrections to the unloaded case, accurate for small mass ratios up to about 0.1, are presented.
Horizontal spatial coherence of ocean reverberation
Authors: Jackson D. R. , Moravan K. Y.
Published: October 2005

Reverberation from the ocean surface, bottom, and volume is discussed in the context of the point scatterer model, with uniform spatial distributions. It is shown that, for sufficiently narrow beamwidths or bandwidths, the covariance factors into a product of spatial and temporal covariances. The spatial covariance is shown to vanish for separations larger than the horizontal width of the transmitting array. This prediction is found to be in reasonable agreement with the experimental results of Wilson and Frazer and with our own sea surface reverberation data reported here.
The effect of numbers of noise events on people’s reactions to noise: An analysis of existing survey data
Authors: Fields James M.
Published: October 2005

The effect of the number of noise events on noise annoyance has been examined in an analysis of data from large-scale social surveys. The relative impact of noise level and number on human reactions is measured by the decibel equivalent number effect (𝓀) expressed as the number of decibels which have an effect equivalent to that of a tenfold increase in number of events. Values of 𝓀 differ between surveys but none is significantly greater ( p>0.05) than the value of 𝓀=10 which is implicit in Leq or Ldn. The mean of the existing data provide a best estimate of 𝓀=5. Although there are some surveys in which annoyance decreases as numbers of events increase above about 150 a day, the available evidence is not strong enough to reject the conventional assumption that reactions are related to the logarithm of the number of events. The conventional assumption that the effects of number and peak noise level are additive cannot be rejected with these data. Differences between the surveys’ estimates of the effect of number of events remained large even when equivalent questionnaire items and definitions of noise events could be used. The most likely explanations for inconsistent estimates are (1) errors in specifying the values of noise parameters, (2) the effects of unmeasured acoustical and area characteristics which are correlated with noise level or number, and (3) large sampling errors which are due to community differences in response to noise. Multipoint annoyance scales give more reliable estimates than do dichotomous ‘‘very annoyed’’ measures. It is concluded that significant improvements in the knowledge about the effects of numbers of noise events will only occur if surveys include large numbers of study areas, a requirement which can only be met if economical noise measurement techniques are developed which have known levels of precision.
Scattering of sound from hard and soft eggcrate surfaces
Authors: Wirgin Armand
Published: October 2005

The problem of scattering of a plane sonic wave from hard and soft eggcrate surfaces, composed of tridimensional protuberances distributed periodically on a plane along two orthogonal directions, is examined by means of the Rayleigh plane wave expansion method, numerically implemented by Fourier base projection of the boundary conditions. The Kirchhoff approximation solution, which predicts that the intensity specularly reflected from a surface of the form x3=f(x1)+f(x2) is the square of the intensity specularly reflected from a simple periodic surface of the form x3=f(x1), is shown, by means of the Rayleigh solutions, to be well-verified for surfaces with small-amplitude irregularities.
Linear inviscid wave propagation in a waveguide having a single boundary discontinuity: Part I: Theory
Authors: Thompson Charles
Published: October 2005

An examination of wave propagation in waveguides of rectangular cross section having a single boundary discontinuity is presented. Special attention is paid to waveguides with heights that are small compared to an acoustic wavelength. It is shown that the dynamic behavior of the enclosed fluid can be parametrized by the value of a single small parameter ε, where ε is the ratio of the typical duct height H0 to the wall wavelength L0. The influence of planar discontinuities of zero and small but finite thickness on wave propagation is determined using the method of matched asymptotic expansions. Junction conditions, impedance across the junction, and uniformly valid composite expansions for the pressure in the duct are presented.
Comparison of auditory filter shapes derived with three different maskers
Authors: Glasberg Brian R. , Moore Brian C. J. , Nimmo-Smith Ian
Published: October 2005

Auditory filter shapes were derived for three different masker types, by measuring threshold for a 1-kHz sinusoidal signal masked by: (a) a noise with a spectral notch of variable width; (b) two tones with variable frequency separation; and (c) a noise with a sinusoidally rippled spectrum with variable ripple density. In each case the masker spectrum was symmetric about the signal frequency, the signal level was fixed, and the masker level was varied to determine threshold using an adaptive, two-alternative, forced-choice procedure. Both simultaneous and forward masking were used. The auditory filter shapes derived from the data were broader in simultaneous masking than in forward masking for all three masker types. In simultaneous masking the derived filters were similar for the three masker types, although there was a tendency for the filters derived from the rippled-noise data to be broader than those for the other maskers. In forward masking the auditory filters derived from the data for three masker types differed considerably in bandwidth and the slope of the filter skirts, and in that a portion of the rippled-noise filter was negative valued. The results are consistent with the idea that suppression has the effect of enhancing frequency selectivity, and that this effect is revealed in forward but not in simultaneous masking. However, the degree and nature of the enhancement differs for different masker types.
Comparison of copper and tungsten carbide calibration spheres
Authors: Foote Kenneth G. , MacLennan David N.
Published: October 2005

The properties of calibration spheres made from electrical-grade copper, denoted Cu, and tungsten carbide with 6% cobalt binder, denoted WC, are examined theoretically. Effects of variations in material, medium, and equipment parameters are determined for spheres intended to calibrate 38-kHz echo sounders when a target strength of order −41.5 dB is required. The derived 30.4-mm-diam Cu sphere and selected 38.1-mm-diam WC ball bearing show different dependences on the varied parameters. Changes in the material and equipment parameters within wide ranges will not upset a precision calibration with expected ±0.1-dB accuracy. Adjustment of the calibration value of  backscattering cross section with changing temperature is generally necessary for elastic spheres. This is the case for the present WC sphere, but not for the Cu sphere by virtue of its optimization with respect to temperature. Greater hardness is found to be insufficient for choosing between the two; the particular application must be considered. Pragmatic criteria for sphere selection are discussed.
Acoustic propagation in a shallow sound channel in the Northeast Pacific Ocean
Authors: Dosso S. E. , Chapman N. R.
Published: October 2005

An experiment was carried out off the west coast of Canada to investigate the effects of a shallow sound channel on propagation for the frequency range from 20–4000 Hz. Using small explosive charges deployed in the shallow channel, the propagation loss was measured at receivers located in both the shallow and deep sound channels. The shallow channel behaved like an acoustic waveguide with an optimum duct propagation frequency of 800 Hz. At the optimum frequency, the propagation loss closely approached that due to cylindrical spreading, while at frequencies lesser or greater than the optimum the loss increased by up to 20–30 dB. The sound channel propagation was strongly dependent on changes in the environment with range, therefore the parabolic equation was used to model the experimental results. The parabolic equation model correctly predicts the range and frequency-dependent trends observed in the measured data.