bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of synthetic-aperture processing to towed-array data
Authors: Yen Nai-Chyuan , Carey William
Published: October 2005

A synthetic-aperture processing technique has been applied to towed-array hydrophone data and has demonstrated that significant increase in signal gain, improved angular resolution, and improved peak-to-sidelobe level ratios can be achieved. The synthetic aperture was formed by the coherent sum of subaperture beams at successive time intervals. When the signal spatial coherence was greater than the synthetic-aperture length and the signal stationary over the synthetic-aperture processing time, 85% of the achievable coherent processing gain was realized. This gain was described by (x−1)10 log(NTF), with x the coherent gain factor and NTF the number of sequential time samples. The coherent gain factor was found at 175 Hz to be 1.7±0.3 for synthetic-aperture lengths between 192 and 962 m, formed from subaperture lengths between 5 and 80 m over coherent processing times of less than 9 min. Beamwidths were found to be comparable to 58°, divided by the effective aperture length in wavelengths. Synthetic apertures, formed from subaperture lengths of 160 and 640 m, showed improvement when a tow-ship phase reference was employed and yielded x=1.4, compared to a maximum value of 2. The synthetic processing technique was also shown to function as a velocity filter sensitive to the relative velocity of the source and receiver. These results demonstrate that the formation of midfrequency synthetic-aperture arrays in the deep-ocean environment is feasible.
Narrow-band indoor measurement of the sound power of a complex mechanical noise source
Authors: Hickling Robert
Published: October 2005

There is a need to develop practical standard sound-power tests for manufactured products independent of the test location. That it is possible to develop such standards, for use in a normal work area, has been demonstrated in tests with six light vehicles. The sound power of each vehicle was measured for different engine speeds and loads using a semicircular array of sound-intensity probes rotated over a hypothetical, hemispherical surface enclosing the vehicle running on a dynamometer roll. The presence of the walls and ceiling of the work area appears to have a negligible effect on A-weighted sound-power measurement. Good agreement was obtained with the overall sound power of a standard reference source. Results for the six vehicles indicate that the peaks in the narrow-band sound-power spectra occur at frequencies corresponding to the orders of excitation of components of the vehicle power train. This has diagnostic value because it identifies noisy components and provides a quantitive measure of their contribution to the total sound power of the vehicle. It could also be used to detect malfunctioning and wear of components.
Detection of broadband signals in signal-dependent noise
Authors: Poor H. Vincent
Published: October 2005

The optimum choice of detection nonlinearities for generalized radiometric detection of broadband random signals in noise is considered for the situation in which the signals and noise are individually and mutually dependent random sequences. Explicit solutions to integral equations specifying the optimum nonlinearities are derived, and an analysis of the effects of ignoring dependence structure is provided
Estimation of eardrum acoustic pressure and of ear canal length from remote points in the canal
Authors: Chan Joseph C. K. , Geisler C. Daniel
Published: October 2005

Sound pressure distributions in the human ear canal, whether unoccluded or occluded with ear molds, were studied using a probe tube technique. On average, for frequencies below 6 kHz, the measuring probe tube had to be placed within 8 mm of the vertical plane containing the top of the eardrum (TOD), determined optically, in order to obtain sound pressure magnitudes within 6 dB of ‘‘eardrum pressure.’’ To obtain that accuracy in all of the eight subjects studied, the probe had to be within 6 mm of the TOD. Since probe location relative to the drum has to be known, a purely acoustic method was developed which can be conveniently used to localize the probe-tip position, utilizing the standing wave property of the sound pressure in the ear canal. The acoustically estimated ‘‘drum location’’ generally lay between the optically determined vertical planes containing the TOD and the umbo. On average, the ‘‘drum location’’ fell 1 mm medial to the TOD. Of the 32 estimates made acoustically in various occluded and unoccluded conditions in 14 subjects, 30 estimates lay within a ±2-mm range of this average.
Vocalic nomograms: Acoustic and articulatory considerations upon formant convergences
Authors: Badin Pierre , Perrier Pascal , Boë Louis-Jean , Abry Christian
Published: October 2005

Fant [G. Fant, Acoustic Theory of Speech Production (Mouton, The Hague, 1960)] has been the first to use the four-tube model of the vocal tract and to introduce vocalic nomograms to speech production studies. These nomograms proved to be an efficient tool for the study of articulatory–acoustic relationships. This paper deals with particular regions of these nomograms, referred to as focal points. These are points where formant convergences occur and where affiliations between formants and cavities are exchanged. A study of appropriate nonsense words has confirmed the existence of these points in natural speech. Generating nomograms with an articulatory model of the vocal tract allowed the location of these convergence regions along the vocal tract, and demonstrated that vowels [i,a,u,y] are located in the vicinity of focal points. The examination of the human speakers’ nomograms obtained by Ladefoged and Bladon from real speaker productions [P. Ladefoged and R. A. W. Bladon, Speech Commun. 1, 185–198 (1982)] shows the relevance of such a notion in determining formant values. The extreme cardinal vowels [i,a,u], the three most commonly encountered in the vocalic systems of the world, are focal points. Focal points may thus constitute important landmarks for the study of vocalic systems.
Tables of Zolotarev polynomial difference distributions for linear transducer arrays
Authors: McNamara Derek A.
Published: October 2005

The Zolotarev polynomial linear array distribution is optimum for difference pattern synthesis in the same sense as the Dolph–Chebyshev distribution is for sum synthesis. In this paper, tables of numerical data that are not readily available elsewhere are given for the synthesis of such distributions.
Spatial processing for coherent noise reduction in ultrasonic imaging
Authors: Bilgutay Nihat M. , Murthy Rashmi , Bencharit Uthai , Saniie Jafar
Published: October 2005

When the target is received in the presence of coherent noise resulting from a large number of complex and randomly distributed scatterers inherent to the medium, the ability of the system to distinguish between the two types of signals often becomes the most crucial performance consideration. Conventional techniques that are capable of suppressing time-varying (incoherent) noise are generally not effective when the noise is time invariant (coherent). In recent years, diversity techniques have been developed that allow the decorrelation of the coherent noise term by altering either the transmitted frequency or the position of the transducer. Although the diversity techniques provide some noise suppression when used in conjunction with the conventional averaging algorithms, their potential benefits cannot be fully exploited by such linear techniques alone. In the work presented here, a nonlinear detection scheme based on the polarity of the spatially decorrelated signals is examined. The theoretical and experimental results indicate that the polarity-thresholding algorithm provides target enhancement that is far superior to the linear techniques previously used in spatial processing. Furthermore, the paper examines the spatial decorrelation properties of the experimental data to determine the desirable parameters for data acquisition and signal processing.
Coherence effects on the detection performance of quadratic array processors, with applications to large-array matched-field beamforming
Authors: Morgan Dennis R. , Smith Thomas M.
Published: October 2005

The effect of coherence on the detection performance of quadratic array processors is examined using an exponential-power-law model for the signal wave-front correlation in an uncorrelated noise field. Detection performance is quantified by the small-signal deflection criterion, which is first reviewed in the general setting of quadratic detectors, and then applied to matched-field and optimal quadratic beamformers. It is shown that the detection performance of matched-field beamforming is substantially degraded for large arrays and typical coherence lengths. The optimal quadratic processor reduces this coherence loss, however, at a cost of greatly increased processor complexity. Several suboptimal beamformers with reduced computational load are also developed, and their detection performance is compared to that of the matched-field and optimal beamformers. One suboptimal processor, the subarray beamformer, has proved outstanding for this application in three respects: It can realize within 1 dB of optimal performance, is robust over a class of correlation functions, and entails a computational burden no greater than full-array matched-field beamforming.
Minimum cross entropy seismic diffraction tomography
Authors: Lo Tien-when , Duckworth Gregory L. , Toksöz M. Nafi
Published: October 2005

One difficulty in applying seismic tomography is that seismic sources and detectors cannot be deployed so that the imaging area is probed from all directions. This paper develops two methods to alleviate this difficulty. These methods combine the minimum cross entropy estimation algorithm with two tomographic image reconstruction algorithms: the direct transform reconstruction algorithm and the backpropagation reconstruction algorithm. These two methods were tested by numerical and scaled model ultrasonic laboratory experiments simulating seismic cross-hole tomography. It was found that (1) the horizontal resolution, which is inherently poor for the cross-hole geometry, can be improved, and (2) artifacts caused by the sparse sampling and noise can be reduced. Both methods work better when the targets are isolated impulses surrounded by a uniform background medium.
Analysis, synthesis, and perception of voice quality variations among female and male talkers
Authors: Klatt Dennis H. , Klatt Laura C.
Published: October 2005

Voice quality variations include a set of voicing sound source modifications ranging from laryngealized to normal to breathy phonation. Analysis of reiterant imitations of two sentences by ten female and six male talkers has shown that the potential acoustic cues to this type of voice quality variation include: (1) increases to the relative amplitude of the fundamental frequency component as open quotient increases; (2) increases to the amount of aspiration noise that replaces higher frequency harmonics as the arytenoids become more separated; (3) increases to lower formant bandwidths; and (4) introduction of extra pole zeros in the vocal-tract transfer function associated with tracheal coupling. Perceptual validation of the relative importance of these cues for signaling a breathy voice quality has been accomplished using a new voicing source model for synthesis of more natural male and female voices. The new formant synthesizer, KLSYN88, is fully documented here. Results of the perception study indicate that, contrary to previous research which emphasizes the importance of increased amplitude of the fundamental component, aspiration noise is perceptually most important. Without its presence, increases to the fundamental component may induce the sensation of nasality in a high-pitched voice. Further results of the acoustic analysis include the observations that: (1) over the course of a sentence, the acoustic manifestations of breathiness vary considerably—tending to increase for unstressed syllables, in utterance-final syllables, and at the margins of voiceless consonants; (2) on average, females are more breathy than males, but there are very large differences between subjects within each gender; (3) many utterances appear to end in a ‘‘breathy-laryngealized’’ type of vibration; and (4) diplophonic irregularities in the timing of glottal periods occur frequently, especially at the end of an utterance. Diplophonia and other deviations from perfect periodicity may be important aspects of naturalness in synthesis.
Vowel-onset detection
Authors: Hermes Dik J.
Published: October 2005

An algorithm is presented that correctly detects the large majority of vowel onsets in fluent speech. The algorithm is based on the simple assumption that vowel onsets are characterized by the appearance of rapidly increasing resonance peaks in the amplitude spectrum. Application to carefully articulated, isolated words results in a high number of false alarms, predominantly before consonants that can function as vowels in a different context such as another language or as a syllabic consonant. After applying some modifications in the setting of some parameters, this number of false alarms for isolated words can be reduced significantly, without the risk of a large number of missed detections. The temporal accuracy of the algorithm is better than 20 ms. This accuracy is determined with respect to the perceptual moment of occurrence of a vowel onset as determined by a phonetician.
Ultrasonic spectroscopy in bovine serum albumin solutions
Authors: Choi P.-K. , Bae J.-R. , Takagi K.
Published: October 2005

Ultrasonic absorption and velocity spectra in bovine serum albumin (BSA) aqueous solutions have been measured at 20 °C over the broad frequency range 0.1–1600 MHz in the pH range 1.5–13.2. Five different techniques were used: the plano–concave resonator, plano–plano resonator, pulse–echo overlap, Bragg reflection, and high-resolution Bragg reflection methods. The absorption spectrum at neutral pH was well fitted to the relaxation curve assuming a distribution of relaxation frequency with a high-frequency cutoff and long low-frequency tail. The relaxation behavior was interpreted in terms of various degrees of hydration of BSA molecules. At acid pH’s, excess absorption over that at pH 7 was explained by double relaxation. The pH dependences of the relaxation frequency and maximum absorption per wavelength showed that the relaxation at about 200 kHz was related to the expansion of molecules and that at 2 MHz resulted from the proton transfer reaction of carboxyl group. At alkaline pH’s, the excess absorption was explained by triple relaxation. The relaxation at about 200 kHz was associated with a helix–coil transition, and the two relaxations at 2 and 15 MHz were attributed to the proton transfer reactions of phenolic and amino groups, respectively. The rate constants and volume changes associated with these processes were estimated.
Information in sonar echoes of fluttering insects available for echolocating bats
Authors: Kober Rudolf , Schnitzler Hans-Ulrich
Published: October 2005

Insects were mounted in the acoustical beam of an ultrasonic loudspeaker transmitting either an 80-kHz continuous constant frequency (CF) tone or a short frequency-modulated (FM) signal (82–18 kHz). The returning CF or FM echoes were recorded and analyzed. Short amplitude peaks or amplitude glints, which occur in the echo in the rhythm of the wing beat, are produced each time some part of the wing surface moves into a plane perpendicular to the impinging sound waves. The amplitude glints are represented in spectrograms of echoes as transitory spectral broadenings or frequency glints. In CF echoes, the composition of positive and negative frequency shifts associated with glints encode the attitude of the flying insect relative to the sound source independent of the insect species. Further information in CF echoes allows a classification of insects as to wing beat frequency, wing structure, wing beat type, wing length, and insect size. Only the wing beat rate of a fluttering insect could be decoded from FM echoes of sounds delivered at fixed duration and repetition rate toward a beetle. The information in the insect echoes described here explains much of the performance of bats concerning their ability to identify insects in behavioral experiments. Whether bats are able to classify insects in the field is discussed. The data from this study allow the computation of the maximum echo sound-pressure levels for insects.
Voyager flight crew hearing threshold levels resulting from 5- and 9-day continuous in-flight noise exposure
Authors: Stephenson Mark R. , Billings Bradley L. , Jutila George A.
Published: October 2005

The flight crew of the Voyager aircraft were continuously exposed to a broadband noise for nearly 5 days during a trial flight, and for over 9 days during their nonstop flight around the world. Evaluation of the threshold shifts resulting from these exposures represents a unique opportunity to study the effect of human exposure to intense continuous noise for long durations. Postflight audiometry demonstrated that the 9-day flight did not result in larger hearing threshold shifts than those following the 5-day flight. Neither crewmember incurred a permanent threshold shift from these exposures.
A comment on ‘‘Conical bores. Part I: Reflection functions associated with discontinuities’’ [J. Acoust. Soc. Am. 8
4, 1613–1619 (1988)] and ‘‘Alternatives to the impulse response h(t) to describe the acoustical behavior of conical ducts’’ [J. Acoust. Soc. Am. 8
4, 1606–1612 (1988)]
Authors: Agulló J. , Barjau A. , Martínez J.
Published: October 2005

According to J. Martínez and J. Agulló [J. Acoust. Soc. Am. 84, 1613–1619 (1988)] and Agulló et al. [J. Acoust. Soc. Am. 84, 1606–1612 (1988)], reflection functions and modified impulse responses can always be obtained from the corresponding frequency-domain functions through a Fourier transform. The following letter is a revision of that conclusion.
Monte Carlo studies of multiple scattering of waves in one-dimensional random media
Authors: Romack George M. , Weaver Richard L.
Published: October 2005

A numerical study was undertaken for the ensemble average, or coherent, wave in a one-dimensional random medium composed of uncorrelated point scatterers. Average responses as constructed from numerical solutions of the wave equation were compared to the predictions of the quasicrystalline (QCA) and self-consistent theories. As anticipated, the QCA was found to fail whenever the Waterman and Truell criterion was not satisfied, and also in the case of high scatterer density and low scatterer strength where the attenuation was badly predicted by the QCA. The self-consistent coherent potential approximation failed only under extreme conditions of scatterer strength or density. Nonlocality in the self-energy had a recognizable effect on the average response only in the limiting case of infinite scatterer strength.
Experimental investigation of the wave propagation on a point-driven, submerged capped cylinder using K-space analysis
Authors: Williams Earl G. , Houston Brian H. , Bucaro Joseph A.
Published: October 2005

Classically, sparse accelerometer measurements are made on vibrating structures to help in deducing the physics of the vibration. However, the experimenter now has at his command more sophisticated measurement tools, such as nearfield acoustical holography or laser Doppler velocimetry, which provide much more data. Often complete mapping of the acceleration or displacements on the surface of these structures can be acquired. As a result, more sophisticated analysis tools must be developed. Such a tool useful for vibrating structures which are basically cylindrical or planar, is presented herein. The measured spatial velocity is decomposed at fixed temporal frequencies into its helical-wave spectrum, also known as the K-space spectrum. This decomposition contains a great deal of information about the physics of the vibrator. For example, it provides the dominant wavenumbers (the dispersion diagram) of free waves that exist on the shell. These free waves reach maximum amplitudes when close to a resonance frequency. The decomposition also provides an indication of the modal density of the shell. This technique is applied to experimental measurements on a shaker-driven, fluid-loaded, capped cylinder. The resulting helical wavenumber diagrams, plotted at a single frequency of excitation, show strong ‘‘figure 8’’ patterns. By comparison with helical-wave spectra computed from infinite-shell theory, it is shown that these patterns represent the wavenumber loci of the free waves that exist on the experimental shell. Excellent agreement between the measured helical-wave spectrum and predictions from infinite-shell theory are reported. The helical-wave spectra of the acoustic pressure, mapped on a cylindrical contour in the extreme nearfield of the capped cylinder, is also presented. From this spectra, the free waves on the structure can be identified and, in particular, how they participate in acoustic radiation. The frequency region was ka=0.5–2.0.
The angular and frequency characteristics of reflectivity from a solid layer embedded between two solids with imperfect boundary conditions
Authors: Pilarski A. , Rose J. L. , Balasubramaniam K.
Published: October 2005

In this paper, a comprehensive model of an isotropic, homogeneous, solid layer embedded in between two half-space solids with imperfect interfacial conditions is presented. The Thomson’s matrix technique for transfer of boundary conditions across a thin layer, based on recurrence formulas, coupled with separate normal and tangential rigidity representation for each interface was used. The reflection and transmission coefficients for oblique incidence of both longitudinal as well as transverse waves as a function of angle of incidence, incident frequency, interface condition, and material properties can be numerically computed through this model. Several studies of the reflection factors for a three-medium case is used to provide insight on the adhesively bonded structures. The ultrasonic quality evaluation of the commonly used aluminum–epoxy-resin–aluminum bond situation is dealt with here in detail.
Spectral reconstruction of uniformized wave fields from nonuniform ray or adiabatic mode forms for acoustic propagation and diffraction
Authors: Arnold J. M. , Felsen L. B.
Published: October 2005

Ray acoustic and adiabatic mode representations provide effective means for charting sound transmission in relatively complicated propagation and diffraction environments, under operating conditions that validate the use of such approximate waveforms. A principal limitation of these physically incisive and conveniently implemented algorithms is their failure in transition regions. For ray acoustics, transitions occur near caustics, foci, critical reflection angles, shadow boundaries, etc.; adiabatic modes undergo transitions when cutoff-inducing or other smooth environmental changes transform their initially well trapped into radiated (leaky) energy. Instead of constructing the uniformized spectral representations required in transitional domains by an independent, more general, analysis, it is shown here that the uniformized spectral forms for a large variety of propagation and diffraction phenomena can be synthesized directly from ray acoustic or adiabatic mode data. This feature should be helpful in generalizing existing acoustic ray or adiabatic mode algorithms to accommodate transitional wave processes. The theory is presented for two-dimensional configurations and fluid media, but the same considerations apply also in three dimensions and for multiwave effects due to elasticity or anisotropy.
The normal-mode theory of air-to-water sound transmission in the ocean
Authors: Chapman David M. F. , Ward Peter D.
Published: October 2005

The normal-mode theory is presented for the transmission of sound from a stationary source in a homogeneous, stationary, air layer into an arbitrarily stratified ocean. Transmission loss calculations are performed for a Pekeris-type shallow-water environment consisting of an isospeed water layer over a uniform elastic solid seabed. Notable features of the results are: the sensitivity of transmission loss to bottom type, the weak dependence of incoherent transmission loss upon source height, and a 25 log r range dependence of average transmission loss in the mode-stripping region. Finally, some approximate intensity-range relations are proposed for shallow-water propagation.
A parabolic wave equation based on a rational-cubic approximation
Authors: Vefring Erlend H. , Mjo/lsnes Svein
Published: October 2005

A parabolic wave equation based on a rational-cubic approximation of the square root operator is presented. The equation yields accurate solutions in cases with angles of propagation up to about 89 deg. In the homogeneous case an analytic solution to the equation has been found.The correspondence between approximating the square root operator and the modal wavenumbers of the exact solution of the Helmholtz equation is shown. By using the analytic solution of the rational-cubic parabolic equation (PE), comparisons are made with the rational-quadratic PE and the Helmholtz equation.
Range and depth-averaged fields in ocean sound channels
Authors: Zhang Renhe , Wang Qin
Published: October 2005

By use of the generalized phase-integral approximation of the mode depth function and representing the square of the depth function as a sum of slow-varying and fast-varying components, a concise expression of the average intensity in an ocean channel is obtained by smooth averaging the intensities over range and depth. This expression is not divergent and will degenerate into the Brekhovskikh, Smith, and Weston one when the frequency approaches infinity. The caustic corrections in the vicinity of the source and its conjugate depths and the contributions of inhomogeneous waves are discussed and the numerical results for the linear, bilinear, and canonical channels are given.
Deconvolution applied to high-frequency echograms in sea bottoms
Authors: Cobo-Parra P. , Ranz-Guerra C.
Published: October 2005

The echo-sounding technique visualizes the marine subbottom by a cascade representation of consecutive traces resulting from the medium response to a normal-incidence sonar pulse train. The resolution, i.e., the possibility of resolving close targets, depends on the sonar pulse widths. Similar to seismics, this resolution can be remarkably increased by applying deconvolution techniques. This paper analyzes the design of spiking deconvolution filters in the frequency domain and its performance in improving the resolution of real echograms collected from Buendia reservoir, 45 m deep. The effects of bandpass filtering and stabilization in the deconvolution process are also considered.
The effect of fluid–structural coupling on sound waves in an enclosure—Theoretical part
Authors: Pan Jie , Bies David Alan
Published: October 2005

This paper presents a theoretical investigation into the effect of the interaction between a sound field and its boundaries upon the characteristics of the sound field in an enclosure. Recent experimental measurements have shown that the boundaries of the sound field in a reverberation room cannot be correctly described in terms of a locally reactive normal acoustical impedance. Fluid–structural coupling must be taken into account if the mechanism of sound decay in the reverberation room is to be understood. A solution based on modal coupling analysis is obtained for the decay of sound waves in a panel–cavity system. The vibration of the system is resolved into a number of acoustical modes (including fluid and structural vibrations). The reverberation times and the resonance frequencies of different modes are calculated as a function of the modal parameters of the uncoupled panel and cavity. The effect of the panel characteristics on the decay behavior of the cavity sound field is investigated. The interesting phenomena of maximum sound absorption and resonance frequency ‘‘jump’’ are identified and interpreted in terms of the coupling behavior of the panel and cavity modes.
Effects of fiber motion on the acoustic behavior of an anisotropic, flexible fibrous material
Authors: Dahl Milo D. , Rice Edward J. , Groesbeck Donald E.
Published: October 2005

The acoustic behavior of a flexible fibrous material was studied experimentally. The material consisted of cylindrically shaped fibers arranged in a batting with the fibers primarily aligned parallel to the face of the batting. This type of material was considered anisotropic, with the acoustic propagation constant depending on whether the direction of sound propagation was parallel or normal to the fiber arrangement. Normal-incidence sound-absorption measurements were taken for both fiber orientations over the frequency range 140–1500 Hz and with bulk densities ranging from 4.6–66.7 kg/m3. When the sound propagated in a direction normal to the fiber alignment, the measured sound absorption showed the occurrence of a resonance, which modified the absorption that was primarily attributed to viscous and thermal effects. When the sound propagated in a direction parallel to the fiber alignment, indications of resonances in the data were not present. From comparing these two sets of data and from considering the material structure, the resonance in the data for fibers normal to the direction of sound propagation was attributed to fiber motion. An analytical model for the acoustical behavior of the material displayed the same fiber-motion characteristics shown in the measurements.
Transient acoustic radiation from excited plates
Authors: Mackertich Seroj S. , Hayek Sabih I.
Published: October 2005

The acoustic radiation time signature as radiated from an infinite elastic plate is obtained for transient forced excitation applied to a point on the plate. The forced excitations considered are those encountered in industrial and marine applications such as the sudden application of dead weight, an impact load, or a sinusoidal finite length pulse that could be generated by starting machinery. The solutions in these cases were idealized by use of a point force whose time history is a step function, a square pulse, or a cw pulse. The time signature for the radiated noise was obtained by convolving the approximate acoustic radiation impulse response solution for an impulsive force with the force time history.
Flow of endolymph in the inner spiral sulcus and the subtectorial space
Authors: Raftenberg Martin N.
Published: October 2005

Flows of endolymph within the inner spiral sulcus and the subtectorial space are studied analytically. These flows are driven by boundary displacements and scala media pressure, all prescribed in the form of traveling sine waves with uniform amplitude, wave speed, and wavelength. Prescribed boundary displacements have no axial components and are assumed ‘‘small.’’ In the subtectorial space, waves are further assumed ‘‘long,’’ and inner and outer hair cells’ stereocilia are represented by permeable barriers. Boundary motions of the subtectorial space are assumed to be associated with basilar membrane motion. The localized boundary motions that would presumably accompany independent outer hair cell motions are not admitted. The pressure drop across the barrier representing the inner hair cells’ stereocilia is evaluated for four specific input conditions. The results are used to assess its relative sensitivity to three types of boundary displacement and to examine the contribution of endolymph flow to the ‘‘second filter.’’ The model predicts the introduction of appreciable tuning (102.3 dB/octave) into the auditory signal between the stages of relative normal displacement of the boundaries of the subtectorial space and the generation of a pressure drop across the inner hair cells’ stereocilia. The outer barrier is removed from the model, and the pressure drop across the inner barrier is reevaluated for the same four cases to study its sensitivity to destruction of the outer hair cells’ stereocilia. These results are examined in light of data by Robertson and Johnstone [D. Robertson and B. M. Johnstone, J. Acoust. Soc. Am. 66, 466–469 (1979)].
Asynchronous neural activity recorded from the round window
Authors: Dolan David F. , Nuttall Alfred L. , Avinash Gopal
Published: October 2005

Voltage recorded from an electrode on the round window (RW) of guinea pig has characteristics that reflect the activity of auditory-nerve fibers in the absence of acoustic stimulation. Fast Fourier transformation (FFT) of the noise recorded from the RW electrode shows a broad spectral peak from 0.8–1.0 kHz. The magnitude of the biological noise is increased by high-frequency, bandlimited acoustic noise stimulation. Pure tones can suppress or enhance the spectral components around 0.8–1.0 kHz depending on frequency and intensity. Kainic acid applied to the intact RW membrane eliminates the biological noise (and the evoked cochlear whole-nerve responses) without alteration of the cochlear microphonic or the summating potential. The spectral characteristics of the biological noise seem to be related to the elemental waveform contributed by the individual auditory-nerve fibers to the voltage recorded at the RW electrode [Kiang et al., Electrocochleography, edited by R. J. Ruben, C. Elbering, and G. Solomon (University Park, Baltimore, 1976)].
Monaural envelope correlation perception, revisited: Effects of bandwidth, frequency separation, duration, and relative level of the noise bands
Authors: Moore Brian C. J. , Emmerich David S.
Published: October 2005

This article presents the results of two experiments investigating performance on a monaural envelope correlation discrimination task. Subjects were asked to discriminate pairs of noise bands that had identical envelopes (referred to as correlated stimuli) from pairs of noise bands that had envelopes which were independent (uncorrelated stimuli). In the first experiment, a number of stimulus parameters were varied: the center frequency of the lower frequency noise band in a pair, f1; the frequency separation between component noise bands; the duration of the stimuli; and the bandwidth of the component noise bands. For a long stimulus duration (500 ms) and a relatively wide bandwidth (100 Hz), subjects could easily discriminate correlated from uncorrelated stimuli for a wide range of frequency separations between the component noise bands. This was true both when f1 was 350 Hz, and when f1 was 2500 Hz. In each case, narrowing the bandwidth to 25 Hz, or shortening the duration to 100 ms, or both, made the task more difficult, but not impossible. In the second experiment, the level of the higher frequency noise band in a pair was varied. Performance did not decrease monotonically as the level of this band was decreased below the level of the other band, and only showed marked impairment when the level of the higher frequency band was at least 60 dB below that of the lower frequency band. The pattern of results in these two experiments is different from that which is obtained when the same stimulus parameters are varied in experiments investigating comodulation masking release (CMR). This suggests that the mechanisms underlying CMR and those underlying the discrimination of envelope correlation are not identical.
Reductions in overshoot during aspirin use
Authors: McFadden Dennis , Champlin Craig A.
Published: October 2005

The overshoot effect was measured before, during, and after the administration of a moderate dose of aspirin. Prior to the drug, detectability of the 6-ms, 3550-Hz signal was 5–11 dB worse when presented 2 ms after the onset of the 200-ms wideband masking noise than when presented 190 ms after masker onset. Following 4 days of aspirin use, detectability in the long-delay condition was unchanged from the predrug value, but (for four of the five subjects) detectability in the short-delay condition was improved by about 4–8 dB. Thus the overshoot effect was markedly reduced by aspirin because the drug partially counteracted the normally poor detectability for signals presented soon after masker onset. This paradoxical improvement in detectability was accompanied by an aspirin-induced loss in detectability of 5–16 dB for a 200-ms sample of that same signal presented in the quiet. Similar paradoxical effects have previously been obtained by inducing a temporary hearing loss with exposure to intense sound. It is presumed that the same basic mechanisms underlie the parallel outcomes. The so-called cochlear amplifier is discussed in this regard, and also the possibility that the known differences in those primary auditory fibers having high and low spontaneous rates may be involved. A supplementary experiment demonstrated that shifting audibility with either a wideband or a narrow-band background noise does not affect the overshoot effect in the same way as does aspirin or exposure to intense sound, further suggesting that the cochlear amplifier must be altered in order for overshoot to be diminished.
Plosive/fricative distinction: The voiceless case
Authors: Weigelt LaDeana F. , Sadoff Steven J. , Miller James D.
Published: October 2005

Using only three measures of the waveform, the zero-crossing rate, the logarithm of the root-mean-square (rms) energy, and the derivative of the log rms energy with respect to time [termed rate of rise (ROR)], voiceless plosives (including affricates) can be distinguished from voiceless fricatives in word-initial, medial, and final positions. Peaks in the ROR contour are considered for significance to the plosive/fricative distinction by examining the log rms energy and zero-crossing rate. Then, the magnitude of the first significant peak in the ROR contour is used as the primary classifier. The algorithm was tested on 1364 tokens (720 word-initial tokens produced by four female and four male speakers; 360 word-medial tokens produced by two males and two females; 320 word-final tokens produced by two males and two females). Data from two male and two female speakers (360 word-initial tokens) were used as a training set, and the remaining data were used as a test set. The overall rate of correct classification was 96.8%. Implications of this result are discussed.
Scattering of elastic waves by localized anisotropic inclusions
Authors: Ben-Menahem Ari , Gibson Richard L.
Published: October 2005

The existence of Rayleigh scattering of elastic plane waves by anisotropic homogeneous inclusions is theoretically demonstrated. The case of transverse isotropy is studied in detail. It is shown that a scattered longitudinal wave creates radial-longitudinal (P), collatitudinal-shear (SV), and azimuthal shear waves (SH). Likewise, scattered SV and SH waves, each generate radial P waves and SV and SH shear waves. All scattered amplitudes are proportional to the square of the frequency and have radiation pattern signatures as those of equivalent dipoles, center of compression, and double couples. It is shown that observations of spatial patterns of scattered amplitudes can yield, through inversion, the elastic constants of the anisotropic inclusion. The results obtained can serve as a theoretical basis for the observed short-period SH and SV waves from underground explosions at teleseismic distances.
Resonant interaction of a sound wave with a cylindrical vortex
Authors: Sozou C.
Published: October 2005

The interaction of a plane sound wave with a compressible fluid rotating about an axis in the form of a Rankine vortex is considered for the case of small Mach numbers. It is shown that when the frequency of the sound wave is close to that of the rotating core of the vortex, resonance is generated in the vortex core. Resonance is also possible when the frequency of the sound wave is a multiple of the frequency of the rotating core. The amplitude of the scattered wave is reexamined and it is shown that in some limiting cases the details of some published material are inaccurate.
Inverse scattering of the three-dimensional elastic wave equation for three parameters
Authors: Zhu Wen-Hau
Published: October 2005

In this paper, a method for simultaneously reconstructing three-dimensional variations in the density and the two Lamé coefficients characterizing an inhomogeneous elastic material is presented. The method requires two single wideband point-source experiments, each with a separate compressional and rotational excitation. The scattered data of the two types of insonification for each experiment are collected on a surface surrounding the inhomogeneous volume. The work in this paper is an extension of the previous inverse scattering of the scalar wave equation with one or two parameters to the case of an elastic vector wave equation with three parameters.
Absorbing boundary conditions for a spherical monopole in a set of two-dimensional acoustics equations
Authors: Sparrow Victor W. , Raspet Richard
Published: October 2005

The numerical solution of the two-dimensional (2-D) acoustic equations as a hyperbolic system by the use of the finite-difference method has been investigated. For efficient computation, the numerical domain must be truncated by an absorbing boundary condition. Deriving nearly reflectionless conditions that are both accurate and stable for spherical waves is nontrivial. In this paper, absorbing boundary conditions are developed for the case of an acoustic pulse radiated from a spherical monopole source. Numerical results are presented comparing conditions based on a characteristic variable formulation to conditions based on the Bayliss–Turkel B1 condition. It was found that the best conditions were those employing the Bayliss–Turkel B1 condition on the acoustic density deviation (or equivalently the acoustic pressure) and a particular condition on the particle velocity component normal to the absorbing boundary.
Exact solution for a density contrast shallow-water wedge using normal coordinates
Authors: Chu Dezhang
Published: October 2005

In the previous work, the exact impulse solution for an isovelocity wedge (ρ≠ρ′, v=v′) was obtained [D. Chu, J. Acoust. Soc. Am. 86, 1883–1896 (1989)]. In the present paper, the same method (normal coordinates) is used but the boundary conditions are modified to satisfy the present problem. Although isovelocity is still a highly idealized situation, it is a better approximation to an actual case than a free/rigid boundary model. The reflections and diffractions are well separated in the time domain. The former can be described accurately by images. When velocity contrast is closed to 1, in the absence of diffracted wave, the total field in a general penetrable wedge may be approximated by the image solution for an isovelocity shallow-water wedge plus the total reflections.
The leaky Rayleigh wave and Scholte wave at the interface between water and porous sea ice
Authors: Weng Xiaowei , Yew Ching H.
Published: October 2005

This paper extends the study on reflection and refraction of waves at the interface of water and porous sea ice by Yew and Weng [J. Acoust. Soc. Am. 82, 342–353 (1987)]. The behavior of leaky Rayleigh waves and Scholte waves generated by a line cylindrical wave source at a distance below the interface is analyzed. It is demonstrated that a wave receiver in the water would pick up a direct wave from the source, a specularly reflected wave from the interface, a leaky Rayleigh wave, and, if the source and receiver are close to the interface and to each other, a Scholte wave. The effects of porosity and frequency on the behavior of these surface and interface waves are also studied. PACS numbers: 43.30.Ma
Cavitation noise measurement using a fiber-optic hydrophone
Authors: Takahashi Sumio , Kikuchi Toshiaki , Hasegawa Akio , Murakami Yasunori
Published: October 2005

Dependence of the noise spectrum of acoustically induced cavitation on the vibrational level of a radiation surface was investigated in a range of vibrational displacement from 0.1 to 24 μm; a heterodyne fiber-optic hydrophone was used to detect cavitation noise. As vibrational level is increased beyond cavitation threshold, the fundamental component and the second and third harmonics cease to increase and n/2- and n/4-order subharmonics (n: integer) start to increase. At a vibrational level where n/2-order subharmonics become maximum, n/4-order subharmonics make a dip in their spectral level. At high vibrational levels, subharmonics of n/4 order become dominant.
A stable data-adaptive method for matched-field array processing in acoustic waveguides
Authors: Byrne Charles L. , Brent Ronald T. , Feuillade Christopher , DelBalzo Donald R.
Published: October 2005

Capon’s maximum likelihood (ML) method has been used with some success in matched field processing for source range and depth estimation. One reason for the interest in the ML is that it is data adaptive; that is, it adapts to the actual noise field present rather than requiring an a priori estimate of the noise component for prewhitening. When modal noise is present the ML can become sensitive to any deviations from the unperturbed case (i.e., from the model) as would be introduced by phase errors or model parameter errors. Using a dimensionality-reduction procedure a more stable data adaptive method, the ‘‘reduced’’ ML (RML), is obtained. The RML is compared here with the ML on simulated data from a 21-sensor array in a Pekeris waveguide supporting eight normal modes. Under modal noise conditions the RML provides a significant improvement over ML when phase errors occur. Although the deviation from the model considered here is that caused by phase errors, the nature of the perturbation is not important since the sensitivity of ML is not to any special type of perturbation.
Surface wave, internal wave, and source motion effects on matched field processing in a shallow water waveguide
Authors: Daugherty John R. , Lynch James F.
Published: October 2005

Given well-known environmental conditions, matched field processing has been shown to be a promising signal processing technique for the localization of acoustic sources. However, when environmental data are incomplete or inaccurate, a ‘‘mismatch’’ occurs between the measured and model fields that can lead to a severe degradation of the localization estimator. The possible mismatch effects of surface and internal waves on matched field processing in a shallow water waveguide were investigated. A modified ray theory was utilized, based on the work of Tindle [J. Acoust. Soc. Am. 70, 813–819 (1981); 73, 1581–1586 (1983)], to calculate the acoustic pressure field. Thus it was possible to simply incorporate range-dependent environmental conditions as well as to generalize this work to deeper waveguides. In general, the conventional (Bartlett) matched field beamformer does not provide sufficient resolution to unambiguously locate a source, even in a perfectly matched environment. The maximum likelihood method matched field beamformer has much better resolution, but is extremely susceptible to mismatch. The mismatch due to surface roughness can result in a large reduction of the estimator peak. Part, but not all, of the peak can be regained by (1) using a model that includes incomplete reflection at the surface based on actual sea surface statistics and (2) short-time averaging of the measured signal, with times on the order of the period of the surface waves. Mismatch due to internal waves can also result in a large degradation of the estimator. Averaging over the same time period as surface waves provides little improvement and leads one to surmise that internal waves may be a limiting constraint on matched field processing. Finally, the surface and internal wave fields were combined with a slowly moving source. This example highlights the necessity for the development of a beamformer that has a broader mainlobe while maintaining adequate sidelobe suppression. This issue is addressed by looking at two such beamformers.