bluuebunny/crossref_metadata_2025 huggingface dataset:
Impedance calculations for a refracting layer
Authors: Stickler D. C. , Ahluwalia D. S.
Published: October 2005

Calculations of the normal component of the specific acoustic impedance due to a point harmonic source suggest that a measurement of the impedance function may prove to be a useful tool for estimating some of the acoustic parameters in the sediments and crust. These calculations show that this impedance function depends not only on the parameters of the sediments and crust, but also on the geometry and frequency of the experiment. This suggests that this dependence be exploited in any attempt to determine these parameters. This paper also discusses some of the advantages and disadvantages in the implementation of this method.
Low-frequency broadband noise generated by a model rotor
Authors: Aravamudan Krishna S. , Harris Wesley L.
Published: October 2005

Low-frequency broadband noise generated by model rotors is attributed to the interaction of ingested turbulence with the rotor blades. The influence of free-stream turbulence in the low-frequency broadband noise radiation from model rotors has been experimentally investigated. The turbulence was generated in the M.I.T. anechoic wind tunnel facility with the aid of biplanar grids of various sizes. The spectra and the intensity of the low-frequency broadband noise have been studied as a function of parameters which characterize the turbulence and of helicopter performance parameters. The location of the peak intensity was observed to be strongly dependent on the rotor-tip velocity and on the longitudinal integral scale of turbulence. The size scale of turbulence had negligible effect on the intensity of low-frequency broadband noise. The experimental data show good agreement with an ad hoc model based on unsteady aerodynamics.
The real roots of the fluid-loaded plate
Authors: Strawderman Wayne A. , Ko Sung-Hwan , Nuttall Albert H.
Published: October 2005

The vibration of an infinite, thin plate, immersed in a fluid and excited by a time-harmonic line-force, is a classical problem in acoustics. The classical solution to the fluid-loaded plate argues that one pair of real roots, equal in magnitude and opposite in sign, exists to the equation defining the free wavenumber. However, recent papers by Stuart [J. Acoust. Soc. Am. 59, 1160–1169; 1170–1174 (1976)] and by Pierucci and Graham [J. Acoust. Soc. Am. 62, S84(A) (1977)] argue that, for certain plate-fluid combinations, three such pairs of real roots exist: the classical pair plus two additional pairs. This paper reexamines this problem to clarify the existence and physical significance of these multiple pairs of real roots. It is shown that only the classical pair of real roots (1) can exist when the radiation condition is satisfied, (2) characterizes the waves in a free plate, and (3) characterizes significant wavenumber contributions to the displacement of the line-force excited plate at large distances from the line excitation. The other two paris of real roots result only if the radiation condition is ignored, and therefore cannot characterize free waves in the plate. Further, these wavenumbers do not characterize any nondecaying contributions to the displacement of the line-force excited plate.
Postpartum survival of mice exposed i
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o to ultrasound
Authors: Edmonds P. D. , Stolzenberg S. J. , Torbit C. A. , Madan S. M. , Pratt D. E.
Published: October 2005

We found no credible enhancement of neonatal mortality in mice exposed in utero on Day 8 of gestation to ultrasound at 0.44 W/cm2 (±20%) spatial average intensity, 2 MHz, continuous wave, for 60–180 s in a 37 °C water bath. This result is compared with the adverse effect on neonatal survival reported by Curto [in Ultrasound in Medicine (Plenum, New York, 1976), Vol. 2, pp. 535–536] for exposure on Day 14 of gestation at about 0.125 to 0.5 W/cm2, 1 MHz, continuous wave, for 180 s in a 30 °C bath. It is concluded that a temporary reduction in fetal viability, lasting from 4 days to less than 10 days after exposure, could account for both sets of data. It is also evident from these data that improved methods of determining intensities within mammalian tissues are highly desirable.
Comments on the effects of overstimulation on microphonic sensitivity
Authors: Durrant John D.
Published: October 2005

Utilizing the differential recording technique, microphonic isopotential measurements were carried out before and after overstimulation. Recordings were made in the first and third turns of guinea pig cochleas. The exposure stimuli were pure tones of frequencies near the best frequency of the recording site. The results were suggestive of differences in the effects of overstimulation in different turns of the cochlea, at least as they are manifested electrophysiologically.
The acoustic reflex, aging, and the distortion product: A reply to Jerger [J. Acoust. Soc. Am. 66, 908 (1979)]
Authors: Silman Shlomo
Published: October 2005

Silman [J. Acoust. Soc. Am. 66, 735–738 (1979)] reported data on the stapedius reflex thresholds for tonal and broadband noise (BBN) activating signals on young and elderly normal hearing subjects. His results indicated that, whereas the thresholds for tonal signals are the same in young and old subjects, the thresholds for BBN is significantly higher in the elderly than in young subjects. Silman’s data are not in agreement with the findings and the distortion hypothesis reported by Jerger et al. [Monogr. Contemp. Audiol. 1, 1–20 (1978)]. Jerger [J. Acoust. Soc. Am. 66, 908 (1979)], in a letter to the editor, attempted to refute Silman’s findings and interpretation relating to the effect of age on the stapedius reflex thresholds. He based his argument on differences in the experimental design used by Silman (1979); Jerger, Hayes, and Anthony [Arch. Otolaryngol. 104, 383 (1978)]; and Jerger et al. (1978). This letter refutes the points proposed in Jerger’s letter to the editor (Jerger, 1979).
Comparison of DT 48, TDH 49, and TDH 39 earphones
Authors: Fastl Hugo
Published: October 2005

The frequency responses of the earphones TDH 49, TDH 39, and DT 48 (the latter with and without free-field equalizer) were compared by means of measuring hearing threshold curves. While the TDH 39 and TDH 49 give almost identical results (average deviations 2 dB), the TDH 49 and DT 48 show moderate (5 dB) differences. In the most usual application mode, i.e., TDH 49 without and DT 48 with free-field equalizer, distinctly different threshold curves were found, indicating rather different real-ear frequency resonses. Accordingly, using the latter two earphone systems, psychoacoustic experiments with broadband stimuli may lead to somewhat different data.
Central denervation hypersensitivity in the auditory system of the cat
Authors: Gerken George M.
Published: October 2005

Data are reported for seven cats with a total of 29 electrodes permanently placed in or near the cochlear nucleus, the superior olivary complex, the nucleus of the inferior colliculus, and the medial geniculate body. Detection thresholds for pulsate electrical stimuli were measured using an operant behavioral procedure. Electrical stimulation thresholds were measured prior to and following bilateral destruction of the cochleas in all animals. In addition, four of the animals were tested using a site-of-stimulation discrimination prior to and following the cochlear lesion. Finally, hearing loss was evaluated in all cats after the completion of the experiments. Electrical stimulation thresholds showed a mean reduction of 7.9 dB throughout the brain stem auditory system after cochlear destruction. The ability of the animals to perform the site-of-stimulation discrimination was not permanently impaired by the cochlear lesion. The data indicated the presence of increased sensitivity to electrical stimulation in most regions of the subcortical auditory system, although a lesser effect was found at the thalamic level. It was concluded that stimulation threshold provides an index relevant to the state of auditory neurons proximal to the electrode tip.
Comments on ’’The effect of aging on the stapedius reflex thresholds’’ [J. Acoust. Soc. Am. 66, 735–738 (1979)]
Authors: Jerger James
Published: October 2005

It is suggested that it is inappropriate to compare the author’s results with those of Silman, since the age of the two experimental groups differ greatly.
An examination of the influence of the range dependence of the ocean bottom on the adiabatic approximation
Authors: Rutherford Steven R. , Hawker Kenneth E.
Published: October 2005

The effects of radial sediment sound-speed derivative and sloping water–sediment interface on the adiabatic approximation to the set of coupled radial equations of coupled-mode theory are examined. The investigation was carried out using the adiabatic criterion of Milder. This criterion requires that the coupling coefficient between adjacent modes be small compared to the mode-cycle distance. It is determined that sediments having large characteristic acoustic impedances can have larger radial sediment sound-speed gradients within the adiabatic approximation than can sediments with smaller characteristic impedances. It is also determined that this trend is reversed for the case of sloping water–sediment interface with sediments of small characteristic impedance being able to have more bottom slope within the adiabatic approximation than sediments of higher impedance.
Reciprocal acoustic transmission in a midocean environment: Fluctuations
Authors: Worcester Peter F.
Published: October 2005

The fluctuations in acoustic receptions from simultaneous transmission of broadband pulses in opposite directions between two points in midocean have been examined. A variety of measures of the observed fluctuations (pulse and CW) for two well-resolved paths are somewhat ambiguous due to the short time series analyzed, but in most cases are not inconsistent with the theoretical predictions based only on sound-speed perturbations due to vertical displacements. Particle velocities are found to have significant effects when differences between reciprocal transmissions are examined.
Spectral domain formulation for acoustic scattering
Authors: Murphy Joseph E.
Published: October 2005

The scattering amplitude for several types of acoustic scatterers is shown to satisfy an integral equation similar to the quantum mechanical Lippmann–Schwinger equation.
Application of the transition matrix to a ribbon-shaped scatterer
Authors: Weaver Richard L. , Pao Yih-Hsing
Published: October 2005

The transition matrix for scalar waves scattered by a ribbon-shaped obstacle with Neumann boundary conditions is derived using a basis set for the surface field expansion chosen to facilitate convergence. An analytic expression for the scattering amplitude in arbitrary directions exact to order (ak)6 is derived from the transition matrix. Comparisons with the results based on the geometrical theory of diffraction and solutions for the integral equation at low frequencies indicate that valid numerical results are obtained throughout the range of frequencies considered (0<ak<10).
Relationship between psychophysical tuning curves and ’’suppression’’
Authors: O’Malley Honor , Feth Lawrence L.
Published: October 2005

This study examined two-tone unmasking and auditory frequency selectivity about 3 kHz for the purpose of demonstrating a qualitative relationship between the two. An adaptive 2IFC forward-masking procedure was used to collect psychophysical tuning curves (PTC’s) and two-tone masking data under a quiet and noise condition for the same normal-hearing listeners. In the noise condition, a narrowband noise masker, centered one decade down from the probe, was gated on with the tonal masker(s). Kiang and Moxon [J. Acoust. Soc. Am. 55, 620–630 (1974)] have found that low-frequency narrowband noise serves to decrease the sharpness of electrophysiological tuning curves by affecting only the tip segments. The data for four highly practiced listeners indicate that the gated-noise masker was effective in broadening the PTC’s and in lessening the magnitude of two-tone unmasking. The mutually reflected changes in tuning curves and in two-tone unmasking indicate a close relationship between frequency selectivity and unmasking: the greater the magnitude of unmasking above the center frequency of the PTC, the sharper the tuning of the PTC.
Effects of wind and ground plane attenuation on sound propagation near the ground
Authors: Foss Rene N.
Published: October 2005

A series of measurements of outdoor sound transmission near the ground was conducted to determine the effects of wind shear and ground plane attenuation. At the lower frequencies (250–500 Hz), where surface and ground waves predominate, the results obtained in still air were in good agreement with current theoretical predictions of ground plane attenuation. The direction and velocity of the wind had little effect on the transmissions at these frequencies. At higher frequencies, however, the data showed considerably more attenuation than the theory predicts, and the effect of wind shear was pronounced.
The influence of a submerged duct on sound propagation in a surface duct
Authors: Hall Marshall
Published: October 2005

Acoustic intensities at receivers in a surface duct and in a deep submerged duct are calculated using a normal-mode theory. The sound source is in the surface duct, which is 60 m thick, and the calculations are repeated for thicknesses of the submerged duct ranging from 0 to 150 m, at frequencies from 160 to 400 Hz. Intensities in the surface duct at 400 Hz and above are not significantly affected by the submerged duct. As the frequency is lowered, the intensity decreases at a rate that varies inversely with the thickness of the submerged duct. The intensity in the submerged duct (in the shadow zone) is almost independent of frequency in the band between the cutoff frequencies of the two ducts; but decreases as the frequency is lowered past the smaller of the two cutoff frequencies.
Effects of tidally varying sound speed on acoustic propagation over a sloping ocean bottom
Authors: Hamilton K. G. , Siegmann W. L. , Jacobson M. J.
Published: October 2005

The influence of sound-speed fluctuations on propagation of a CW signal in an ocean with a uniformly sloping bottom and a horizontal surface is analyzed using ray theory. The mean sound-speed structure is modeled as bilinear, with bottomed source and receiver above and below the SOFAR axis, respectively. The horizontally independent fluctuations oscillate with a 12-h period in the upper ocean. An examination is made of possible types of rays for down-slope propagation that might exist, depending on bottom-slope angle and source–receiver separation. The total acoustic field is investigated for its dependence on these parameters and time. For certain conditions when up to three rays comprise the mean total field, three patterns of time evolution are described, each of which may have significant amplitude variations. Numerically computed examples of each type are presented. The linear relationships between phase variations of individual rays and the sound-speed fluctuations are derived. Then, formulas are developed to explain the most frequent behavior of the relative amplitude and phase of the multipath total field. Predictions from the formulas show very good agreement with the numerical calculations.
Analysis of acoustical effects of receiver and source motions at short ranges in a deep ocean
Authors: Kays J. L. , Jacobson M. J. , Siegmann W. L.
Published: October 2005

An analytical approach is used to determine general results on a CW signal transmitted through a deep ocean channel at short ranges. A bilinear sound-speed profile is used. The receiver and source are restricted to the surface, and only SRBR rays are relevant. Time-dependent expressions for the total-field amplitude and phase are developed for appropriately limited time intervals, and numerical results are presented. General analytical expressions for the total field are derived and demonstrated to approximate closely numerical results. These expressions provide the basis for a study of the acoustical effects of varying motion parameters and initial range. It is demonstrated that effects of differences in range on total-field phase rate and the time interval between amplitude maxima are significant at short ranges and diminish as range increases. Effects on total field due to receiver motion are shown to be both significant and widely varying, depending on receiver and source directions and speeds.
The scattered acoustic boundary wave generated by grazing incidence at a slightly rough rigid surface
Authors: Medwin H. , Bailie J. , Bremhorst J. , Savage B. J. , Tolstoy I.
Published: October 2005

A new theory describing sound scatter from a low roughness rigid surface [I. Tolstoy, ’’The scattering of spherical pulses by slightly rough surfaces,’’ J. Acoust. Soc. Am. 66, 1135–1144 (1979)] has predicted that at near-grazing incidence a boundary wave will be formed in the fluid above the surface, and that at sufficient ranges the amplitude of this scattered boundary wave will exceed that of the direct wave. A model experiment has been conducted using a point source and receiver embedded in a rough plane surface constructed of close-packed rigid hemispherical bosses and the prediction of the amplitude of the boundary wave has been fully confirmed. In addition, the experiment has revealed that the coherent scattered boundary wave, which at lowest frequencies or ranges leads the incident wave by 90°, becomes more nearly in phase with the incident spherical wave as frequency or range are increased, thereby further strengthening the signal at the rough surface relative to smooth surface propagation.
The scattering of spherical pulses by slightly rough surfaces
Authors: Tolstoy I.
Published: October 2005

Using a ’’small roughness’’ boundary condition due to Biot, which incorporates the effects of multiple scatter, one can obtain simple, closed-form solutions for the coherent scattering of transient spherical waves. Combining this boundary condition with the normal coordinate technique leads to explicit solutions for impulsive or other point sources above or on a rough, rigid plane, i.e., for both finite and grazing angles of incidence. This approach distinguishes naturally between two types of arrival: body (or volume) waves and boundary waves; the latter incorporate the backscatter. The boundary wave dies off rapidly with distance from the surface. But, parallel to the boundary, in the absence of attenuation, its amplitude decreases only as r−1/2 so that for sufficiently large r, and for source and receiver at or near the surface, the boundary-wave will dominate the direct acoustic pulse arrivals. The methods and results of this paper can be extended to problems of scatter and diffraction of spherical pulses by rigid (or free) plane rough surfaces bounding stratified media or by rough objects of other shapes, e.g., spheres, cylinders, ellipsoids, etc. This theory, valid for wavelengths or pulsewidths long compared to the characteristic roughness dimensions, leads to results that are different from those of the usual perturbation techniques and have been verified experimentally by Medwin et al. in a companion paper.
A nearfield, underwater measurement system
Authors: Marciniak Robert D.
Published: October 2005

A nearfield acoustic measurement technique for accurately computing the farfield radiation characteristics of underwater sound transducers was developed, implemented, and evaluated. The analysis was based on evaluation of a form of the Helmholtz integral which utilizes a Green’s function that vanished over the surface of integration, thereby requiring only knowledge of the nearfield acoustic pressure for computing the farfield radiation. An experimental program was conducted to evaluate the technique. Details of the nearfield measurement instrumentation are presented. Comparisons between conventionally measured farfield properties of four different types of test transducers and the results obtained by using the nearfield technique are given. The results showed that excellent agreement was achieved for the radiation properties compared. For the directional responses, the nearfield technique matched the conventionally measured results over the minor lobe structure as well as over the major lobe structure of the pattern. The results also showed that absolute sound-pressure levels could be determined accurately and with relative ease.
Horizontal resonant frequencies of vibration pickup on soil surfaces
Authors: Omata Sadao , Morita Sakae
Published: October 2005

A vibration pickup set on a soil surface has a resonant frequency caused by the mass of the pickup and the contact compliance of a setting point. The resonant frequency produced in the measurement system causes the errors in measurement and places restrictions on the measurement frequency range. This paper gives the characteristics of the horizontal resonant frequency and also derives expressions for a coupled motion of the vibration pickup model set on an elastic half-space. It is shown graphically, by an example, that the height of the center of gravity and the contact areas of the pickup have considerable effects upon the horizontal resonant frequency. The derived solutions, which are approximately represented as the function of resonant frequency and the frequency of an exciting force, provide adequate accuracy for engineering analysis to the footings of little bodies.
On the mechanism of transduction in optical fiber hydrophones
Authors: Price H. L.
Published: October 2005

The receiving sensitivity of optical fiber hydrophones is determined in part by the rate of change in the optical path length of the sensing fiber with respect to changes in the external pressure on the fiber. These changes in the optical path length are a result of the induced changes in index of refraction of the fiber (photoelasticity) and changes in the physical length of the fiber (elasticity). These two properties are analyzed to determine their individual impacts on the hydrophone sensitivity. It is shown that both of these two effects act to increase the optical path length of the fiber as it is subjected to an increasing external pressure. Therefore, the two effects act in concert with one another, not against one another, in their effect on hydrophone sensitivity.
Auditory lateralization in monkeys: An examination of two cues serving directional hearing
Authors: Houben Dirk , Gourevitch George
Published: October 2005

In assigning binaural ongoing time differences (phase) as the cue for localization of low frequencies, and binaural intensity differences as the cue for localization of high frequencies, the duplex theory has successfully accounted for human directional hearing of tones. Sensitivity of monkeys to these cues was examined in two experiments. The dependencies on frequency of interaural intensity difference thresholds (lateralization experiment I) and time difference thresholds (lateralization experiment II) were determined behaviorally on three monkeys (M. nemestrina). The range of frequencies was from 125 Hz to 8 kHz in experiment I and from 250 Hz to 2 kHz in experiment II. The results indicate that the duplex theory is applicable to monkeys. However, monkeys are less sensitive than man to both binaural cues. The shortest time disparity monkeys discriminate is 42 μs at 1.5 kHz and the smallest intensity difference is 3.5 dB at 500 Hz. Good agreement between the present findings and localization measurements [C. H. Brown et al., J. Acoust. Soc. Am. 63, 1484–1492 (1978)] suggests: (a) that monkeys utilize time disparity cues through higher frequencies than man; and (b) that inaccurate localization by monkeys at high frequencies reflects decreasing sensitivity to interaural intensity cues.
Electroacoustic transducers using piezoelectric polyvinylidenefluoride films
Authors: Lerch Reinhard
Published: October 2005

We have theoretically and experimentally analyzed microphones with cylindrical and spherical polyvinylidenefluoride diaphragms. In particular, the response of such microphones to airborne sound and to vibrations as a function of diaphragm geometry, acoustic impedance of the surrounding medium, coupling volume, and excitation was calculated. Most importantly, a relationship between the output voltage at low frequencies and the position of resonant frequencies was established. There is good agreement between calculated and measured frequency responses.
The effect of the reed resonance on woodwind tone production
Authors: Thompson Stephen C.
Published: October 2005

In normal woodwind tone production the nonlinear flow control properties of the reed transfer energy among the harmonics of the spectrum, and the favored playing frequency is one for which the air column input impedance is high at several harmonics. Above the middle of the second register, woodwinds have only one participating impedance peak; yet these notes can be played even without the use of a register hole, despite competing possibilities of low register intermode cooperation. Such notes are possible because enhancement of the reed’s transconductance A near its own resonance frequency can offset the small input impedance Z of the air column so that (ZA−1) ≳0, providing an additional means for energy production above cutoff. Spectral levels as a function of blowing pressure, air column impedance, and reed characteristics are derived. Experiments on the clarinet show that the player can adjust the reed resonance frequency from about 2 to 3 kHz. When the reed frequency is adjusted to match a harmonic component of the tone, the amplitude of that component is increased, and the oscillation is heard as being stabilized in loudness, pitch, and tone color.
On oscillation of vapor bubbles
Authors: Hsieh Din-Yu
Published: October 2005

A physical analysis of various mechanisms involved in the oscillation of a vapor bubble is presented. Approximate expressions for the second resonance frequency are obtained in agreement with the recent findings by Marston [J. Acoust. Soc. Am. 66, 1516–1521 (1979)].
Acoustic waves in a half-space with sinusoidal boundary
Authors: Nusayr Abdul-Majid
Published: October 2005

The method of straightforward expansion is applied to acoustic waves in a half-space with sinusoidal boundary. It is found that the expansion is uniform. Propagating waves show their dependence on the undulations of the surface in a proportional manner to the order of the terms. Moreover, it is found that for certain values of wavenumbers the propagating waves have terms that are body waves.
Optimal distribution of density and dilatation modulus in inhomogeneous layers
Authors: Scharnhorst K. P.
Published: October 2005

The extremals of the minimal layer thickness problem for reflectance modification, given monochromatic waves at normal incidence and real material parameters, are analyzed. The structures of sublayer sequences leading to minimal total layer thickness, when both the density and the dilatation modulus are allowed to vary independently are presented. It is found that there exist two different sublayer sequences. Both are periodic with unit cells of four layers. Minimal sequences for the corresponding one-parameter problems are obtained as limiting cases.
Binaural critical masking bands
Authors: Sever Joseph C. , Small Arnold M.
Published: October 2005

Current understanding of the relation between monaural estimates of the critical bandwidth for masking and those obtained in binaural listening situations is poor. The present study was designed to improve this situation by obtaining estimates of critical bandwidth when the signal and masker were presented: (1) monaurally (NmSm), (2) binaurally with both signal and masker in phase at the ears (NoSo), (3) binaurally with masker in phase and signals 180° out of phase (NoSπ). Threshold estimates were obtained in a two-interval forced-choice paradigm as a function of masker bandwidth for signal frequencies of 500 and 2000 Hz for the three conditions mentioned above. Maskers were computer-synthesized and had essentially infinite rejection slopes. For all conditions, as masker bandwidth was narrowed from wide band, threshold remained relatively constant until some critical bandwidth was reached. Further reductions in bandwidth were followed by progressive lowering of threshold, presumably due to removal of masker energy in the critical band. For both signal frequencies, the derived critical bandwidth estimates for the NmSm and NoSo conditions were similar and were smaller than the critical bandwidth estimates obtained in the NoSπ condition.
Temporal modulation transfer functions based upon modulation thresholds
Authors: Viemeister Neal F.
Published: October 2005

The detectability of amplitude modulation in the absence of spectral cues provides a quantitative description of temporal resolution for steady-state signals with relatively small amplitude changes. Modulation thresholds for sinusoidally amplitude-modulated wideband noise were measured as a function of modulation frequency. The resulting ’’Temporal Modulation Transfer Function’’ (TMTF) shows a lowpass characteristic for modulation frequencies below about 800 Hz. The lowpass characteristic is extended up to approximately 2 kHz when the increment in average power produced by modulation is eliminated. The important parametric effects are summarized as follows: (1) TMTFs are independent of overall level, except at very low intensities; (2) the time constant indicated by the TMTF decreases as the center frequency of the band-limited, modulated noise is increased; (3) modulation thresholds generally decrease with increasing duration of modulation, particularly at low modulation frequencies; (4) when the carrier is gated for the duration of modulation, the TMTF shows a highpass segment at low modulation frequencies. Although the TMTFs are not directly consistent with the attenuation characteristic of a simple lowpass filter, a model which incorporates such a filter, with a time constant of 2.5 ms, describes the entire TMTF and also describes the modulation functions obtained with square-wave and pulse modulation. The wide bandwidth of initial filtering indicated by the model raises the important question of the role of peripheral filtering in determining the detectability of high-frequency modulation.
Representation of steady-state vowels in the temporal aspects of the discharge patterns of populations of auditory-nerve fibers
Authors: Young Eric D. , Sachs Murray B.
Published: October 2005

This paper is concerned with the representation of the spectra of synthesized steady-state vowels in the temporal aspects of the discharges of auditory-nerve fibers. The results are based on a study of the responses of large numbers of single auditory-nerve fibers in anesthetized cats. By presenting the same set of stimuli to all the fibers encountered in each cat, we can directly estimate the population response to those stimuli. Period histograms of the responses of each unit to the vowels were constructed. The temporal response of a fiber to each harmonic component of the stimulus is taken to be the amplitude of the corresponding component in the Fourier transform of the unit’s period histogram. At low sound levels, the temporal response to each stimulus component is maximal among units with CFs near the frequency of the component (i.e., near its place). Responses to formant components are larger than responses to other stimulus components. As sound level is increased, the responses to the formants, particularly the first formant, increase near their places and spread to adjacent regions, particularly toward higher CFs. Responses to nonformant components, except for harmonics and intermodulation products of the formants (2F1,2F2,F1+F2, etc.), are suppressed; at the highest sound levels used (approximately 80 dB SPL), temporal responses occur almost exclusively at the first two or three formants and their harmonics and intermodulation products. We describe a simple calculation which combines rate, place, and temporal information to provide a good representation of the vowels’ spectra, including a clear indication of at least the first two formant frequencies. This representation is stable with changes in sound level at least up to 80 dB SPL; its stability is in sharp contrast to the behavior of the representation of the vowels’ spectra in terms of discharge rate which degenerates at stimulus levels within the conversational range.
Estimation of differential Doppler shifts
Authors: Schultheiss Peter M. , Weinstein Ehud
Published: October 2005

If the acoustic signal radiated by a moving source is observed at two or more locations, the received signals exhibit differential Doppler shifts which provide information about source motion. This paper calculates minimum mean-square errors for the estimates of differential Doppler shifts, which can be obtained in a given observation interval. Both Gaussian and sinusoidal signals are considered. The noise is assumed to be Gaussian and independent from sensor to sensor. Dependence of the estimation errors on observation time, signal-to-noise ratio, and size of the receiving array are studied. The estimation of differential Dopplers is found to be uncoupled from the estimation of differential delays and from the estimation of signal parameters, such as center frequency and bandwidth. A comparison is made between two possible procedures of differential Doppler estimation: coherent processing of the signals received at two sensors and subtraction of separate frequency estimates obtained at each sensor. The two are equivalent for sinusoidal signals, but for large TW Gaussian signals the coherent procedure yields substantially smaller errors.
Predicting annoyance from detectability of low-level sounds
Authors: Fidell Sanford , Teffeteller Sherri , Horonjeff Richard , Green David M.
Published: October 2005

The relationship between the predicted detectability and judged annoyance of 24 low-level sounds heard in three noise backgrounds was investigated by an adaptive paired comparison procedure under free-field listening cojditions. The predicted detectability of the set of sounds acco nted for almost 90= per−cent)= of the variance in judgments of anjoyance made in the most commonplace (falling spectru ) background noise environment. Conventional methods of predicting annoyance did not yield significantly higher correlations than a detectability-based method in two other unusually shaped background noise environments.
Variation of the vertical directionality of noise with depth in the North Pacific
Authors: Anderson Victor C.
Published: October 2005

A vertical array of 20 vibration isolated hydrophones was suspended from the Research Platform FLIP at various depths from 713 to 4816 m. Preformed sets of beams were formed with a digital beamformer to observe the vertical noise distribution at several frequencies between 23 and 100 Hz. Directional spectra derived from 10-min samples of digital records are presented. Interpretation of the data set leads to a model for the vertical noise directional spectrum as a function of depth which indicates a reduction of a factor of 2 in the vertical extent of the noise window as depth increases from the sound channel axis to the critical depth. This reduction in width is accompanied by a reduction in the maximum level of about 4 dB. The effect is essentially independent of frequency over the observed range of 23 to 100 Hz. No horizontal null in the directional spectrum of the noise, as predicted by ray theory for a horizontally homogeneous ocean, was observed in the data.
Nonacoustic noise interference in measurements of infrasonic ambient noise
Authors: Strasberg M.
Published: October 2005

Three potential nonacoustic noise sources which can interfere with low-frequency measurements of underwater ambient noise are examined. All of them are flow induced and require relative motion between the hydrophone and the water around it. Two of them result from the response of the hydrophone to different types of nonacoustic pressure fluctuations developed on the hydrophone surface by the flow. The third noise source results from the incidental sensitivity of the hydrophone to temperature inhomogeneities normally existing in the sea. It is shown that both types of flow-induced pressure fluctuations can be significant under conditions encountered in the open sea, whereas interference due to temperature fluctuations will be negligible except under unusual circumstances.
Very low frequency (VLF) wind-generated noise produced by turbulent pressure fluctuations in the atmosphere near the ocean surface
Authors: Wilson James H.
Published: October 2005

Measurements of ambient noise for very low frequencies (VLF) from 5 to 50 Hz indicate that wind-generated noise is a significant source of the total ambient noise field during high-wind/sea-state conditions. Determining dominant physical mechanism(s) for transfer of energy from the wind field into the underwater acoustic field is very important in modeling the wind-generated noise field at very low frequencies. Frequency dependence, wind speed dependence, directivity characteristics, and dependence on oceanographic parameters of the wind-generated noise source can be established only after the physical mechanism is understood. The objective of this paper is to extend the development of the theory of turbulent pressure fluctuations initiated by Isakovich and Kur’yanov. In their original paper, Isakovich and Kur’yanov established a very good basic theoretical approach to describe the energy transfer from the wind field into the underwater acoustic field as a result of turbulent pressure fluctuations in the atmosphere near the ocean surface. However, in developing their approach, they made errors in algebra, mistakes in integration, and unsubstantiated assumptions. In this paper, these mistakes are corrected and their theory is revised accordingly. In addition, the wave height spectra of Mitsuyasu and Honda is incorporated into the theory, since this is the accepted wave height spectra in the VLF acoustic region. (These wave height data were not available to Isakovich and Kur’yanov at the time of publication of their original theory.) The wind speed and frequency dependence of the resulting source spectrum level agrees well with data measured in the northeastern Pacific Ocean under low distant and local shipping noise conditions.
Severing the corpus callosum in rats using ultrasound: Theoretical and experimental correlations
Authors: Lee A. J. , Taberner P. V. , Halliwell M.
Published: October 2005

A single, focused, ultrasound beam of 3.5 W total acoustic output for 2 s at 3.3 MHz was used to create a series of overlapping lesions to sever the corpus callosum of the rat on the midline. A theoretical and experimental determination of the ultrasound field is described and histological evidence of the lesions is provided. Good correlation occurred between the theoretical and experimental results only for the intensity contour lines examined. The experimentally derived focal intensity of 162 W cm−2 (at 25 °C) was 24% of the intensity predicted from theoretical calculations. A difference of 2 mm was found for the axial position of maximal intensity, thermocouple plotting showing the focal region to be nearer the transducer than expected from the theory. Histological results indicated that, under certain conditions, from a single dose of ultrasound two lesions could be obtained corresponding to both the theoretically and experimentally derived locations. At lower intensities it was possible to ulitize the upper location to sever the corpus callosum, the lower intensity site then being subthreshold for the rat brain. The trackless localized damage caused by ultrasound makes this method of obtaining split-brain rats suitable for behavioral and biochemical studies, where any nonspecific damage may have undesirable effects.
Auditory discrimination of rise and decay times in tone and noise bursts
Authors: van Heuven V. J. J. P. , van den Broecke M. P. R.
Published: October 2005

There are indications in the literature on speech perception that differences in rise and decay times of the amplitude envelope are relevant physical correlates in phonemic contrasts. Yet, little is known about the perception of rise and decay times as such. In the present study we have attempted to establish JND’s for both rise and decay times of 1000-Hz sine waves as well as white noise bursts by means of an adjustment method. The rise and decay of stimulus amplitude were synthesized to be linear functions of time. Results show that the JND for a change in rise/decay time is generally about 25% of the duration of the rise/decay time. This Weber fraction is a minimum at rise/decay times of about 80 ms and increases significantly for rise/decay times below 20 ms. Of the four signal conditions (rise versus decay, sine wave versus noise), discriminations of decay time in noise bursts were performed with the greatest accuracy (at moderate rise/decay times), while changes in onset time of sine waves were discriminated best at very short rise times (where energy splatter may have contributed an additional cue).
Speech-reception threshold for sentences as a function of age and noise level
Authors: Plomp R. , Mimpen A. M.
Published: October 2005

For 140 male subjects (20 per decade between the ages 20 and 89) and 72 female subjects (20 per decade between 60 and 89, and 12 for the age interval 90–96), the monaural speech-reception threshold (SRT) for sentences was investigated in quiet and at four noise levels (22.5, 37.5, 52.5, and 67.5 dBA noise with long-term average speech spectra). The median SRT as well as the quartiles are given as a function of age. The data are described in terms of a model published earlier [ J. Acoust. Soc. Am. 63, 533–549 (1978)]. According to this model every hearing loss for speech (SHL) is interpreted as the sum of a loss class A (attenuation), characterized by a reduction of the levels of both speech signal and noise, and a loss class D (distortion), comparable with a decrease in signal-to-noise ratio. Both SHLA+D (hearing loss in quiet) and SHLD (hearing loss at high noise levels) increase progressively above the age of 50 (reaching typical values of 30 and 6 dB, respectively, at age 85). The spread of SHLD as a function of SHLA+D for the individual ears is so large (σ=2.7 dB) that subjects with the same hearing loss for speech in quiet may differ considerably in their ability to understand speech in noise. The data confirm that the hearing handicap of many elderly subjects manifests itself primarily in a noisy environment. Acceptable noise levels in rooms used by the aged must be 5 to 10 dB lower than those for normal-hearing subjects.
A plane-wave reflection loss model including sediment rigidity
Authors: Vidmar Paul J. , Foreman Terry L.
Published: October 2005

A method is presented for computation of the complex plane-wave reflection coefficient of an acoustic wave impinging upon a horizontally stratified ocean bottom consisting of a single inhomogeneous (fluid or solid) sediment layer overlying a semi-infinite homogeneous (fluid or solid) substrate. Within the sediment layer the density, the compressional wave speed and attenuation, and the shear wave speed and attenuation are permitted to vary arbitrarily and independently. A matrix formulation is used in which the depth-separated wave equations are replaced by the ’’propagator’’ matrix. The elements of the propagator are calculated by numerical integration of the Helmholtz equations with depth-dependent wavenumbers.
Forward masking with equal-energy maskers
Authors: Penner M. J.
Published: October 2005

Temporal masking of clicks by noise was investigated using a forward-masking paradigm. The temporal separation ΔT between the click and the noise ranged from 0.3 to 100 msec. The duration of the noise varied from 3 to 500 msec while its energy remained fixed. For fixed ΔT (ΔT≳3msec), the masking effect may actually increase for the longer, less intense noises despite the fact that, for long maskers, there is less masker energy near the signal in time. These results are interpreted in terms of the modified version of the running-average hypothesis [M. J. Penner, J. Acoust. Soc. Am. 63, 195–201 (1978)] in which it is argued that the auditory system compresses the intensity of the stimulus prior to integrating it. If the temporal integrator depends on stimulus intensity, then these results may be easily predicted. As an alternative explanation we show that compression may reduce the effective intensity of short maskers to such an extent that they do less masking than the longer ones. Such reduction in masking effectiveness will occur if the time between the masker and the signal is long enough so that the effects of compression and integrator shape do not counterbalance each other.
Discrimination of symmetric time-intensity traded binaural stimuli
Authors: Ruotolo B. Robert , Stern Richard M. , Colburn H. Steven
Published: October 2005

Experiments were conducted to determine the extent to which listeners can discriminate between different combinations of interaural time and intensity for binaural stimulus configurations which eliminate loudness, lateralization, and image-diffuseness cues. A two-interval forced choice paradigm was used, and the task of the subject was to determine the order of two stimuli, each of which was a slowly gated 500-Hz tone with a combination of interaural time and intensity differences that resulted in a centered primary spatial image. The two stimuli to be discriminated were symmetric in that they differed only in the polarity of their interaural differences. Also, in order to reduce artifacts introduced by variations in the coupling of the earphones to the head, acoustic monitoring and compensation was performed both before and after each experimental run. The performance of the two most highly trained subjects is consistent with previous experimental results that indicate an incomplete trading of interaural time and intensity information. The subjective perceptions of these observers are not consistent with previous studies that describe a ’’time image’’ and a ’’time-intensity traded’’ spatial image.
Measurements of binaural echo suppression
Authors: Zurek P. M.
Published: October 2005

The notion of binaural echo suppression that has persisted through the years states that when listening binaurally, the effects of reverberation (spectral modulation or coloration) are less noticeable than when listening with one ear only. This idea was tested in the present study by measuring thresholds for detection of an echo of a diotic noise masker with the echo presented with either a zero or a 500-μsec interaural delay. With echo delays less than 5–10 msec, thresholds for the diotic echo were about 10 dB lower than for the dichotic signal, a finding opposite that of the usual binaural masking-level difference but consistent with the notion of binaural echo suppression. Additional echo-threshold measurements were made with echoes of interaurally reversed polarity, producing out-of-phase spectral modulations. The 10–15 dB increase in thresholds for the reverse-polarity echo, over those for the same-polarity echo, indicated that the apparent ’’hollowness’’ associated with spectral modulations can be partially canceled centrally. Overall, the results of this study are consistent with a model in which: (1) the monaural representations of spectral magnitude are nonlinearly compressed prior to being combined centrally; and (2) neither monaural channel can be isolated in order to perform the detection task.