bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-frequency transmission loss in the Arctic SOFAR channel for shallow sources and receivers
Authors: Yang T. C.
Published: October 2005

It is demonstrated that low-frequency (<50 Hz) transmission loss (TL) in the Arctic SOFAR channel for shallow sources and receivers (depth<four wavelengths) is insensitive to the angular dependence of the ice-scattering loss. Existing data of shallow sources and receivers, therefore, cannot distinguish the various published ice-scattering models based solely on the predicted angular dependence of the ice-scattering loss. Specifically, it is shown, using the 17.75- and 47-Hz TL data of DiNapoli and Mellen [Low frequency attenuation in the Arctic Ocean,’’ in Ocean Seismo-Acoustics, edited by T. Akal and J. Berkson (Plenum, New York, 1986).] as constraints, that the TL for shallow sources and receivers is determined predominantly by the first mode attenuation and is insensitive to the higher mode attenuations associated with ice-scattering loss at higher angles. Measurements of the first mode attenuation coefficients at 17.75 and 47 Hz are presented in this article. It is found that transmission loss based on the measured first mode attenuation coefficients agrees well with the DiNapoli data independently determined in the same ocean basin. The magnitude of the first mode attenuation coefficient has significant experimental implications. It is found that a 1-km-long vertical array offers little chance of distinguishing the various angular dependence models at 17.75 Hz (based on range-averaged transmission loss data or incoherently summed modal amplitudes), whereas a 300-m-long vertical array may do so at 47 Hz based on long-range (>250 km) range-averaged propagation data. It is also found that transmission loss varies significantly with source depth; consequently, transmission loss curves determined from data for multiple source depths have an inherent (not experimentally related) uncertainty of several dB and thus cannot shed light on the angular dependence of ice-scattering loss.
Models of the additivity of masking
Authors: Humes Larry E. , Jesteadt Walt
Published: October 2005

Three models of masking additivity are reviewed, which are referred to as the high-compression model [M. J. Penner, J. Acoust. Soc. Am. 67, 608–616 (1980); M. J. Penner and R. M. Shiffrin, J. Acoust. Soc. Am. 67, 617–627 (1980)], the power-law model [R. A. Lutfi, J. Acoust. Soc. Am. 73, 262–267 (1983); 80, 422–428 (1986)], and the modified power-law model with compressed internal noise [Humes et al., J. Acoust. Soc. Am. 83, 188–202 (1988)]. While the high-compression model was derived from data for two or more nonsimultaneous maskers and the power-law model was derived from data for two or more simultaneous maskers, the modified power-law model can be applied to both cases. The modified power-law model assumes that the threshold in quiet is equivalent to a masked threshold resulting from an internal noise that is continually present. Additional assumptions concern the interaction of two maskers prior to the addition of the masking effects. Most of the data on the additivity of masking are well described by the modified power-law model, regardless of the nature of the maskers. Thus the model provides a good description of data for combined simultaneous maskers and combined nonsimultaneous maskers, a task heretofore requiring the use of at least two separate and independently developed models.
The cricothyroid muscle in voicing control
Authors: Löfqvist Anders , Baer Thomas , McGarr Nancy S. , Story Robin Seider
Published: October 2005

Initiation and maintenance of vibrations of the vocal folds require suitable conditions of adduction, longitudinal tension, and transglottal airflow. Thus manipulation of adduction/abduction, stiffening/slackening, or degree of transglottal flow may, in principle, be used to determine the voicing status of a speech segment. This study explores the control of voicing and voicelessness in speech with particular reference to the role of changes in the longitudinal tension of the vocal folds, as indicated by cricothyroid (CT) muscle activity. Electromyographic recordings were made from the CT muscle in two speakers of American English and one speaker of Dutch. The linguistic material consisted of reiterant speech made up of CV syllables where the consonants were voiced and voiceless stops, fricatives, and affricates. Comparison of CT activity associated with the voiced and voiceless consonants indicated a higher level for the voiceless consonants than for their voiced cognates. Measurements of the fundamental frequency (F0) at the beginning of a vowel following the consonant show the common pattern of higher F0 after voiceless consonants. For one subject, there was no difference in cricothyroid activity for voiced and voiceless affricates; in this case, the consonant-induced variations in the F0 of the following vowel were also less robust. Consideration of timing relationships between the EMG curves for voiced and voiceless consonants suggests that the differences most likely reflect control of vocal-fold tension for maintenance or suppression of phonatory vibrations. The same mechanism also seems to contribute to the well-known difference in F0 at the beginning of vowels following voiced and voiceless consonants.
An experimental study of oscillating flow through two orifices in series
Authors: Elger Donald F. , Adams Ronald L.
Published: October 2005

A Stemme drop-on-demand ink-jet printer nozzle consists of two closely spaced orifices in series. To provide insight into the nozzle fluid dynamics, a study of impedance and flow distribution was conducted. Air was used as a working fluid, and orifices were fabricated in equal diameter plates attached to a piston-driven cylinder. The outer orifice and the space between the plates were open to ambient air. Hot-wire anemometry and a standing wave resonance method were used to measure air velocity and orifice impedance, respectively. Impedance data exhibited the nonlinear behavior characteristic of a single orifice. Velocity data showed that orifice plate spacing has the largest effect on fluid velocity through the outer orifice.
Near-boundary streaming around a small sphere due to two orthogonal standing waves
Authors: Lee Chun P. , Wang Taylor G.
Published: October 2005

This article studies the acoustic streaming pattern near a small sphere due to two orthogonal standing waves, which have the same frequency but, in general, are out of phase. The results indicate a new kind of acoustic streaming arising from the circular motion in the medium caused by the two waves.
An investigation of the modal characteristics of nonrectangular reverberation rooms
Authors: Milner Joseph R. , Bernhard Robert J.
Published: October 2005

The finite element method is used to study the modal characteristics of a class of reverberation rooms with parallel floors and ceilings. Special numerical procedures are developed to express acoustic finite element matrices as functions of room shape and to reduce the computational requirements for room evaluation. The modal distribution function proposed by Louden [M. M. Louden, Acustica 24, 101–104 (1971)] is used to evaluate room performance. Two studies of rooms with one nonparallel wall illustrate the typical influence of room shape on the modal distribution in the room. A global optimization is attempted for a room with five independent shape variables. A solution 40% better than the best rectangular reverberation room was found using approximately 450 000 room evaluations.
Modeling of sound propagation in fitted workshops using ray tracing
Authors: Ondet A. M. , Barbry J. L.
Published: October 2005

This article describes the rayscat computer model, for prediction of noise levels in empty or fitted rooms. The model is based on a ray-tracing technique and takes into account both the real geometry of the room and areas with different fittings (furniture, machines, storage, etc.). Experimental results obtained in a test room are presented, demonstrating the influence of the fitting distribution on noise levels. Finally, the experimental results are compared with those obtained by numerical simulation using the rayscat model. Predicted values agree closely with measured ones.
Use of random noise for on-line transducer modeling in an adaptive active attenuation system
Authors: Eriksson L. J. , Allie M. C.
Published: October 2005

Active sound attenuation systems may be described using a system identification framework in which an adaptive filter is used to model the performance of an unknown acoustical plant. An error signal may be obtained from a location following an acoustical summing junction where the undesired noise is combined with the output of a secondary sound source. For the model output to properly converge to a value that will minimize the error signal, it is frequently necessary to determine the transfer function of the secondary sound source and the path to the error signal measurement. Since these transfer functions are unknown and continuously changing in a real system, it is desirable to perform continuous on-line modeling of the output transducer and error path. In this article, the use of an auxiliary random noise generator for this modeling is described. Based on a Galois sequence, this technique is easy to implement, provides continuous on-line modeling, and has minimal effect on the final value of the error signal.
Detection and discrimination of spectral peaks and notches at 1 and 8 kHz
Authors: Moore Brian C. J. , Oldfield Simon R. , Dooley Gary J.
Published: October 2005

The ability of subjects to detect and discriminate spectral peaks and notches in noise stimuli was determined for center frequencies fc of 1 and 8 kHz. The signals were delivered using an insert earphone designed to produce a flat frequency response at the eardrum for frequencies up to 14 kHz. In experiment I, subjects were required to distinguish a broadband reference noise with a flat spectrum from a noise with either a peak or a notch at fc. The threshold peak height or notch depth was determined as a function of bandwidth of the peak or notch (0.125, 0.25, or 0.5 times fc). Thresholds increased with decreasing bandwidth, particularly for the notches. In experiment II, subjects were required to detect an increase in the height of a spectral peak or a decrease in the depth of a notch as a function of bandwidth. Performance was worse for notches than for peaks, particularly at narrow bandwidths. For both experiments I and II, randomizing (roving) the overall level of the stimuli had little effect at 1 kHz, but tended to impair performance at 8 kHz, particularly for notches. Experiments III–VI measured thresholds for detecting changes in center frequency of sinusoids, bands of noise, and spectral peaks or notches in a broadband background. Thresholds were lowest for the sinusoids and highest for the peaks and notches. The width of the bands, peaks, or notches had only a small effect on thresholds. For the notches at 8 kHz, thresholds for detecting glides in center frequency were lower than thresholds for detecting a difference in center frequency between two steady sounds. Randomizing the overall level of the stimuli made frequency discrimination of the sinusoids worse, but had little or no effect for the noise stimuli. In all six experiments, performance was generally worse at 8 kHz than at 1 kHz. The results are discussed in terms of their implications for the detectability of spectral cues introduced by the pinnae.
Categorical perception of conspecific communication sounds by Japanese macaques, M
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Authors: May Brad , Moody David B. , Stebbins William C.
Published: October 2005

Field studies indicate that Japanese macaque (Macaca fuscata) communication signals vary with the social situation in which they occur [S. Green, ‘‘Variation of vocal pattern with social situation in the Japanese monkey (Macaca fuscata): A field study,’’ in Primate Behavior, edited by L. A. Rosenblum (Academic, New York, 1975), Vol. 4]. A significant acoustic property of the contact calls produced by these primates is the temporal position of a frequency peak within the vocalization, that is, an inflection from rising to falling frequency [ May et al., ‘‘Significant features of Japanese macaque communication sounds: A psychophysical study,’’ [Anim. Behav. 36, 1432–1444 1988)]. The experiments reported here are based on the hypothesis that Japanese macaques derive meaning from this temporally graded feature by parceling the acoustic variation inherent in natural contact calls into two functional categories, and thus exhibit behavior that is analogous to the categorical perception of speech sounds by humans. To test this hypothesis, Japanese macaques were trained to classify natural contact calls by performing operant responses that signified either an early or late frequency peak position. Then, the subjects were tested in a series of experiments that required them to generalize this behavior to synthetic calls representing a continuum of peak positions. Demonstration of the classical perceptual effects noted for human listeners suggests that categorical perception reflects a principle of auditory information processing that influences the perception of sounds in the communication systems not only of humans, but of animals as well.
Across-critical-band processing of amplitude-modulated tones
Authors: Yost William A. , Sheft Stanley
Published: October 2005

Two experiments using two-tone sinusoidally amplitude-modulated stimuli were conducted to assess cross-channel effects in processing low-frequency amplitude modulation. In experiment I, listeners were asked to discriminate between two sets of two-tone amplitude-modulated complexes. In one set, the modulation phase of the lower frequency carrier tone was different from that of the upper frequency carrier tone. In the other stimulus set, both amplitude-modulated carriers had the same modulator phase. The amount of phase shift required to discriminate between the two stimulus sets was determined as a function of the separation between the two carriers, modulation depth, and modulation frequency. Listeners could discriminate a 50°–60° phase shift between the modulated envelopes for tones separated by more than a critical band. In experiment II, the modulation depth required to detect modulation of a probe carrier was measured in the presence of an amplitude-modulated masker. The threshold for detecting probe modulation was determined as a function of the separation between the masker and probe carriers, the phase difference between the masker and probe modulators, and masker modulation depth (in all conditions, the rate of probe and masker modulation was 10 Hz). The threshold for detecting probe modulation was raised substantially when the masker tone was also modulated. The results are consistent with theories suggesting that amplitude modulation helps form auditory objects from complex sound fields.
Headphone simulation of free-field listening. I: Stimulus synthesis
Authors: Wightman Frederic L. , Kistler Doris J.
Published: October 2005

This article describes techniques used to synthesize headphone-presented stimuli that simulate the ear-canal waveforms produced by free-field sources. The stimulus synthesis techniques involve measurement of each subject’s free-field-to-eardrum transfer functions for sources at a large number of locations in free field, and measurement of headphone-to-eardrum transfer functions with the subject wearing headphones. Digital filters are then constructed from the transfer function measurements, and stimuli are passed through these digital filters. Transfer function data from ten subjects and 144 source positions are described in this article, along with estimates of the various sources of error in the measurements. The free-field-to-eardrum transfer function data are consistent with comparable data reported elsewhere in the literature. A comparison of ear-canal waveforms produced by free-field sources with ear-canal waveforms produced by headphone-presented simulations shows that the simulations duplicate free-field waveforms within a few dB of magnitude and a few degrees of phase at frequencies up to 14 kHz.
An interpretation of cortical maps in echolocating bats
Authors: Altes Richard A.
Published: October 2005

Target parameters such as reflectivity, range, velocity, and angular position are represented by ordered maps of tuned cortical neurons in insectivorous bats. It is suggested that the response of each neuron in such a map is determined by a hypothesis test conditioned on a particular value of the mapped parameter. The excitation of each neuron is then interpreted as a sample value of a conditional log-likelihood ratio or a log-likelihood function. Interpolation between the samples, which is needed to find the parameter that maximizes the mapped function (e.g., the maximum likelihood parameter estimate), can be accomplished with overlapped tuning curves. An attempt to portray a sharp peak by a weighted sum of relatively broad neuronal tuning curves or interpolation functions results in excitatory center/inhibitory surround behavior. Facilitation or antifacilitation of neurons that are likely to be excited by succeeding observations can be used for sequential detection and tracking. Interpolation and pulse-to-pulse data storage capability are required to explain range jitter sensitivity and to allow for moving target indication in bat sonar. If a cortical map represents an ordered array of hypothesis tests, then many such tests are implemented in parallel when target parameters are unknown. Detection performance is then degraded relative to the idealized situation in which all parameters are specified. Performance in noise may thus appear to be much worse than that of an ideal detector, even if each hypothesis test is optimally implemented.
Ubiquity of hyperacuity
Authors: Altes Richard A.
Published: October 2005

A decision as to whether two line segments are colinear, as on a vernier scale (—‖— vs—‖—), can be made with high sensitivity by the human visual system. Just-noticeable vernier displacement is much smaller than the separation required to resolve two parallel lines, i.e., to perceive them as two lines rather than one. Vernier acuity is thus also called ‘‘hyperacuity.’’ Similar effects have been discovered in bat echolocation, for discrimination of a range-jittered point target from a nonjittered target, in the jamming avoidance response (JAR) of electric fish, and in differential pitch sensitivity experiments with human subjects. Are jitter sensitivity in echolocation, JAR in electroreception, differential pitch sensitivity in audition, and vernier acuity in vision based on the same general principle? The results in this article indicate that such phenomena are indeed similar from the viewpoint of detection theory, and that experimental performance can be used to behaviorally estimate auditory parameters such as bandwidth, beamwidth, and temporal resolution, as well as to test different signal processing models without resort to masking. Applications of the hyperacuity effect to radar, sonar, and medical ultrasound are suggested.
Ultrasonic leaky waves in a solid plate separating a fluid and vacuum
Authors: Chimenti D. E. , Nayfeh Adnan H.
Published: October 2005

The reflection of a finite acoustic beam from a solid plate separating fluid and vacuum half-spaces has been measured and analyzed. Material viscous damping has been included in the reflection model and the finite beam has been approximated by an integral of the plane wave reflection coefficient times the spatial beam transform over the incident wave vector. The effects of viscosity and the finite beam on the reflected field are separately demonstrated, and generally good agreement is found between the model calculation and experiments on an aluminum plate with water chosen for the fluid. It is shown that the finite beam alone modified the plane-wave reflection coefficient substantially, whereas the introduction of viscosity exerts a smaller, but still important, influence.
Elastodynamic scattering by a surface-breaking void
Authors: Roberts R. A.
Published: October 2005

The boundary integral formulation is presented for the two-dimensional problem of elastodynamic scattering by a void that breaks the traction-free surface of an elastic half-space. Procedures for numerical evaluation of the resulting integral equation for the displacement of the void surface are described. Numerical results for scattering by a symmetric triangular groove contained in the surface of an elastic half-space are presented that demonstrate the effect of ‘‘opening up’’ a surface-breaking crack. All possible combinations of mode conversion (e.g., bulk-to-surface, surface-to-bulk, etc.) are examined for groove depth/groove width ratios of 1 and 10, and groove depth/Rayleigh wavelength ratios ranging from 0.0 to 1.5.
Influence of absorbing and scattering media on the propagation of ultrasound
Authors: Van den Aarssen M. , Verhoef W. A. , Thijssen J. M.
Published: October 2005

The preservation of the sound field produced by a single element ultrasound transducer was investigated for the assessment of the applicability of diffraction correction strategies. A variety of purely absorbing and absorbing plus scattering phantoms was employed. The acoustic parameters (velocity of sound, frequency-dependent attenuation coefficient, and differential backscattering coefficient) were estimated for these phantoms and compared to the parameters of human liver and skin specimens. The focal beam properties were estimated with a small diamond reflector positioned beyond the investigated media. The changes of the beam characteristics in the phantoms could be explained completely by the overall attenuation, i.e., either by absorption exclusively or by absorption plus scattering. In liver tissue, the averaged beam broadening could be explained by the attenuation, but great and irregular distortions of the sound beam were observed. The distortions by skin, subcutaneous fat, and muscle layers were even more severe. An important conclusion from the present study is, therefore, that diffraction correction strategies should be considered as a first-order approximation when applied to in vivo diagnostic procedures.
Method for solving eigenvalue problems of the Helmholtz equation with a circular outer and a number of eccentric circular inner boundaries
Authors: Nagaya Kosuke , Poltorak Krzystof
Published: October 2005

The eigenvalue problem of the Helmholtz equation is of importance because various physical phenomena are governed by this equation. This article presents a method for solving the boundary value problem governed by the Helmholtz equation with a circular outer boundary and a number of eccentric circular inner boundaries. In this problem, it is difficult to satisfy the multiconnected boundary conditions. The present analysis uses the point-matching approach for treating the inner boundary conditions and presents the expression for finding the eigenvalues. Numerical calculations have been carried out for the system having one, two, or four eccentric circular inner boundaries.
An exact one-dimensional analysis of the acoustic sensitivity of the antiturbulence probe tube in a duct
Authors: Munjal M. L. , Eriksson L. J.
Published: October 2005

The antiturbulence probe tube used in the in-duct method for the measurement of acoustic power of ducted fans and in active noise control systems is analyzed for its acoustic sensitivity or frequency response by means of the distributed parameter approach wherein mutual interaction of the acoustic pressure fields in the probe tube and the annular duct are considered. This enables one, incidentally, to check the correctness of the one-way interaction implied in the available analytical methods. The analysis takes into account both the locations of the microphone, the mean flow convection, and the normal radiation condtions as well as anechoic termination used in the literature. Arising from the computed plots, some general criteria for the design of the windscreen probe tubes have been offered.
Digital holographic reconstruction of sources with arbitrarily shaped surfaces
Authors: Veronesi W. A. , Maynard J. D.
Published: October 2005

Nearfield acoustic holography has proven to be a useful tool for studying sound radiation. However, the analytic formulation and all current implementations of the technique require that the measurement and reconstruction surfaces be level surfaces of a separable coordinate system. In this article, a holographic process is presented based on numerical methods that work for source surfaces or measurement surfaces that may have an arbitrary shape.
The acoustic surface wave above a complex impedance ground surface
Authors: Raspet Richard , Baird Gordon E.
Published: October 2005

A surface wave like term arises in the analysis of spherical wave propagation above a complex impedance plane. Whether this wave is a true independently propagating surface wave, or a reaction to the incident air wave, has been the subject of discussion for a number of years. In this article, it is demonstrated that this term is a true surface wave that can exist independent of the body wave in air.
A numerical treatment of the fluid/elastic interface under range-dependent environments
Authors: Shang Er-Chang , Lee Ding
Published: October 2005

The technique introduced by McDaniel and Lee [J. Acoust. Soc. Am. 71, 855–858 (1982)] for the handling of the fluid/fluid interface boundary under range-dependent environments is extended to handle the horizontal fluid/elastic interface boundary. Representative wave equations of the parabolic type are considered in both fluid and elastic media. The required interface conditions, (1) continuity of vertical components of displacement, (2) continuity of vertical components of stress, and (3) that horizontal components of stress must vanish on the interface, are satisfied with this numerical treatment. A complete theoretical development is presented along with a test example to demonstrate its validity.
Scattering from hard and soft corrugated surfaces: Iterative corrections to the Kirchhoff approximation through the extinction theorem
Authors: Wirgin Armand
Published: October 2005

The extinction theorem (ET) is combined with an expansion of surface fields in terms of incoming plane waves to yield an infinite set of linear algebraic equations that can be solved, in an obvious manner, by an iteration technique. The zeroth-order iterate is shown to be equivalent to the Kirchhoff approximation (KA) and the extent to which higher-order iterates provide corrections to the KA is examined by numerical comparison with reference solutions. An ET-based iterate of low order is shown to greatly improve the KA solution in almost the entire low-to-medium wavenumber region provided: (a) the angle of incidence (with respect to the normal to the average plane of the corrugated surface, assumed to be a sinusoid in the computations) of the impinging plane wave is not too close, and, in any case, inferior to the shadowing angle, and (b) the amplitude of the corrugation does not exceed one tenth of the corrugation period. These improvements are obtained at the expense of a quite modest volume of computations.
Underwater noise due to rain—Open ocean measurements
Authors: Scrimger Joseph A. , Evans Donald J. , Yee Wayman
Published: October 2005

Measurements of underwater noise produced by rain over the open ocean were made at a site some 1 km off Ucluelet on the west coast of Vancouver Island, British Columbia, Canada. A hydrophone was placed near the bottom in 55 m of water in the path of the prevailing eastward moving Pacific storm systems. The spectral noise-level dependence on rain rate between zero and 20 mm/h was determined for various frequencies and sea states. A straight line, least-squares fit to the sample values of spectral level plotted against the log of rain rate was found to best represent the relationship. Representative rain noise spectra for various rain rates and sea states were derived.
Linear pressure waves in bubbly liquids: Comparison between theory and experiments
Authors: Commander Kerry W. , Prosperetti Andrea
Published: October 2005

Recent work has rendered possible the formulation of a rigorous model for the propagation of pressure waves in bubbly liquids. The derivation of this model is reviewed heuristically, and the predictions for the small-amplitude case are compared with the data sets of several investigators. The data concern the phase speed, attenuation, and transmission coefficient through a layer of bubbly liquid. It is found that the model works very well up to volume fractions of 1%–2% provided that bubble resonances play a negligible role. Such is the case in a mixture of many bubble sizes or, when only one or a few sizes are present, away from the resonant frequency regions for these sizes. In the presence of resonance effects, the accuracy of the model is severely impaired. Possible reasons for the failure of the model in this case are discussed.
Ultrasonic tomography of metals using noncontact transduction
Authors: Hutchins D. A. , Hu J. K. , Young R. P. , Stoner R. , Jansen D. , Zhang Q. L.
Published: October 2005

Ultrasonic images of the internal structure of metallic cylinders have been produced using noncontact ultrasonic transducers and tomographic reconstruction. Electromagnetic acoustic transducers (EMATs) were used as the detector with generation by either another EMAT or a pulsed laser. Reconstruction using both shear and longitudinal waves has been achieved for samples containing artificial defects.
The effect of traffic noise on sleep of young adults in their homes
Authors: Stevenson D. C. , McKellar N. R.
Published: October 2005

The disturbance of sleep by traffic noise is a major problem area in noise pollution. Extensive laboratory tests using multichannel electroencephalograms (EEG) have been carried out by many workers to determine the general response of people when exposed to noise during sleep. An experimental technique for obtaining results in people’s homes has been developed using a simplified one-channel EEG. The responses of six people in the age range 19–24 were measured. A significant correlation was found between sleep disturbance and traffic noise when the noise is expressed in EPNdB. In the home experiments the subjects appeared to be approximately 10 dB less sensitive to noises than laboratory subjects for similar noise exposure. There also appeared to be some adaptation to the noise exposure; however, only one subject was tested for a period of 20 days and was insufficient to give definite results on adaptation.
Phase and travel-time variability of adiabatic acoustic normal modes due to scattering from a rough sea surface, with applications to propagation in shallow-water and high-latitude regions
Authors: Lynch James F. , Miller James H. , Chiu Ching Sang
Published: October 2005

Simple theoretical expressions are generated for the phase and travel-time variations (specifically wander and bias) of normal modes due to scattering by a rough ocean surface. These expressions are explicitly demonstrated for two canonical waveguide examples, the hard-bottom (shallow water) waveguide and the n2-linear (high latitude) waveguide. Numerical examples of the scattering statistics generated for both waveguides are given, and the implications of the examples for shallow-water acoustics, high-latitude acoustics, and ocean acoustic tomography are discussed. An application of the theory developed to the cross coherence of modes measured in an Arctic waveguide during FRAM IV is also shown.
Some effects of talker variability on spoken word recognition
Authors: Mullennix John W. , Pisoni David B. , Martin Christopher S.
Published: October 2005

The perceptual consequences of trial-to-trial changes in the voice of the talker on spoken word recognition were examined. The results from a series of experiments using perceptual identification and naming tasks demonstrated that perceptual performance decreases when the voice of the talker changes from trial to trial compared to performance when the voice on each trial remains the same. In addition, the effects of talker variability on word recognition appeared to be more robust and less dependent on task than the effects of word frequency and lexical structure. Possible hypotheses regarding the nature of the processes giving rise to these effects are discussed, with particular attention to the idea that the processing of information about the talker’s voice is intimately related to early perceptual processes that extract acoustic–phonetic information from the speech signal.
Acoustic properties and perception of stop consonant release transients
Authors: Repp Bruno H. , Lin Hwei-Bing
Published: October 2005

This study focuses on the initial component of the stop consonant release burst, the release transient. In theory, the transient, because of its impulselike source, should contain much information about the vocal tract configuration at release, but it is usually weak in intensity and difficult to isolate from the accompanying frication in natural speech. For this investigation, a human talker produced isolated release transients of /b,d,g/ in nine vocalic contexts by whispering these syllables very quietly. He also produced the corresponding CV syllables with regular phonation for comparison. Spectral analyses showed the isolated transients to have a clearly defined formant structure, which was not seen in natural release bursts, whose spectra were dominated by the frication noise. The formant frequencies varied systematically with both consonant place of articulation and vocalic context. Perceptual experiments showed that listeners can identify both consonants and vowels from isolated transients, though not very accurately. Knowing one of the two segments in advance did not help, but when the transients were followed by a compatible synthetic, steady-state vowel, consonant identification improved somewhat. On the whole, isolated transients, despite their clear formant structure, provided only partial information for consonant identification, but no less so, it seems, than excerpted natural release bursts. The information conveyed by artificially isolated transients and by natural (frication-dominated) release bursts appears to be perceptually equivalent.
Estimates of wave front distortion from measurements of scattering by model random media and calf liver
Authors: Waag Robert C. , Dalecki Diane , Smith Wallace A.
Published: October 2005

An expression based on a perturbation method is employed to estimate the correlation of path length difference in a plane normal to the direction of wave propagation from measurements of ultrasonic scattering by model random media and calf liver. The expression gives the correlation function of path length difference in terms of an integral of the correlation function of the medium variations or an equivalent integral of the power spectrum of medium variations, both for a scattering angle of zero degrees. Power spectra derived from measurements of average differential scattering cross section over a spatial-frequency window are used to fit analytic functions that extend over all spatial frequencies. The results for the windowed and unwindowed data yield correlation functions and corresponding power spectra that are used to estimate the correlation function of path length difference. The results suggest that the correlation length in calf liver is less than 100 μm and that a root-mean-square path length variation of about 20 μm results from propagation through a 100-mm calf liver path.
On line, real-time densimeter—Theory and optimization
Authors: Kim Jin O. , Bau Haim H.
Published: October 2005

The speed of a torsional stress wave transmitted in a solid waveguide, which has a noncircular cross section and is submerged in a liquid, is inversely proportional to the density of the liquid. Thus, by measuring the speed of the torsional stress wave, information can be obtained about the density of the liquid or density-related characteristics such as liquid level and the mass composition of biphase mixtures. A predictive theory is developed to correlate the speed of the wave with the density of the liquid and the shape of the waveguide’s cross section. The theory is used to optimize the waveguide’s geometry so as to increase sensor sensitivity. The theoretical results are compared and found to favorably agree with experimental observations.
Simulating the open-loop transfer function as a means for understanding acoustic feedback in hearing aids
Authors: Egolf David P. , Haley Brett T. , Howell Henry C. , Legowski Stanislaw , Larson Vernon D.
Published: October 2005

Suppressing unstable acoustic feedback in hearing aids will first require knowledge of the open-loop transfer functions of such systems. Reported herein is a mathematical technique for simulating the open-loop transfer function of an in situ eyeglass-type hearing aid. In particular, a computer program was developed that characterized the hearing aid as a serial connection of two-port blocks, each representing one individual component of a hearing aid. Included, for example, were two-port blocks representing the microphone, amplifier, receiver, sound tubes leading to the eardrum (including the ear canal itself), earmold vent, and external pathway from the vent outlet back to the microphone. The computer program was validated by replicating laboratory data derived from an experiment involving a nonstandard manikin fitted with a nonstandard artificial ear. Next, the open-loop transfer function of an eyeglass-type hearing aid in situ on the manikin was simulated via the computer program. Unfortunately, those computer-generated data were not replicated in the laboratory due to the difficulty encountered in actually measuring the open-loop transfer function. Nevertheless, investigators were able to utilize those data to predict, within ±25 Hz, the ‘‘squeal’’ frequency of unstable acoustic feedback.
A subminiature condenser microphone with silicon nitride membrane and silicon back plate
Authors: Hohm Dietmar , Hess Gisela
Published: October 2005

The fabrication process and the properties of a capacitive silicon sensor for the detection of airborne sound are described. The device consists of two chips; one chip carries a 150-nm-thick silicon nitride membrane of 0.8×0.8 mm2 , and the second chip represents a complete back plate including the back electrode and the air gap spacer. Both chips are produced by means of an orientation-dependent etching procedure. The overall dimensions of the transducer are 1.7×2×0.6 mm3 . Measurements of the acoustic properties yield sensitivities between −60 and −90 dB re: 1 V/Pa, depending on the tension of the diaphragm. The most sensitive microphones have a frequency response extending up to 2 kHz, while the less sensitive transducers have higher cutoff frequencies.
Efficiency of a transonically moving thermoacoustic source
Authors: Chandrasekhar Rao , Busch-Vishniac Ilene J.
Published: October 2005

Experimental work on the sound generated from a moving thermoacoustic source has indicated that there is a significant boost in the pressure amplitude for sources moving transonically. This boost is not predicted by linear theories. This article examines possible causes of the anomaly. In particular, the effect of temperature variations on the properties of the medium, the dependence of the acoustic efficiency on the sound pressure present at the excitation location, and the validity of superposition of signals generated at different locations of the source path are examined. Results indicate that none of the proposed mechanisms can explain the discrepancy between theory and experiment.
Effects of a ‘‘soft’’ half-screen on the reception by a nearby sensor distribution
Authors: Martinez Rudolph , Stokes Ann
Published: October 2005

Spatial distributions of sensors must often function in the neighborhood of diffracting and reflecting surfaces. These, in turn, represent virtual passive sources that add to the incoming signal. The result is a computed wavenumber spectrum contaminated by the presence of spurious nearfields that shift the sought-after angular position of the true field source. This undesirable effect is demonstrated here analytically by positioning a continuous receiver of finite length near a field-canceling half-screen, taken either as a colinear surface or a perpendicular backstop to an incident plane wave. Exact and asymptotic expressions are derived for the perceived strengths of virtual screen sources and for the angular distortions they cause.
The Blake threshold of a cavitation nucleus having a radius-dependent surface tension
Authors: Atchley Anthony A.
Published: October 2005

The Blake threshold is encompassed in most theoretical models of transient acoustic cavitation. Previously, this threshold has been calculated for a bubble having constant surface tension. However, such a bubble is unstable against dissolution and is not a realistic model for a cavitation nucleus. In this article, the Blake threshold is calculated for a more realistic nucleus—a bubble having a radius-dependent surface tension. An expression is derived for the dependence of the surface tension on radius for a surfactant-stabilized cavitation nucleus. Two cases, appropriate for charged and polar surfactants, are examined. The Blake threshold for the former case exceeds that of the standard (constant surface tension) case by approximately 1% to 20% for radii ranging from 3.0 μm down to 0.01 μm. In the latter case, the Blake threshold exceeds that of the standard case by approximately 2% to 38% over the same range of radii. It is concluded that, for the sizes important for cavitation processes, both unstabilized and surfactant-stabilized bubbles become mechanically unstable under essentially the same acoustic conditions. Thus the use of the simpler, albeit unrealistic, nucleus in theoretical models results in no serious error.
Physiological responses to the pulsation threshold paradigm. II: Representations of high-pass noise in average rate measures of auditory-nerve fiber discharge
Authors: Hellstrom Lisa I. , Young Eric D.
Published: October 2005

In a companion article [L. I. Hellstrom, J. Acoust. Soc. Am. 84, 230–242 (1988)], it was shown that psychophysical pulsation threshold masking patterns (PTPs) for high-pass noise maskers are not a simple transformation of the profile of activity evoked in the auditory nerve by the masker. In this article, PTPs are compared with neural representations in which interactions of masker and probe are considered. It is hypothesized that, at pulsation threshold, some criterion value of rate change occurs when the stimulus switches from masker to probe. The iso-rate probe level, defined for single auditory-nerve fibers, is the probe level at which this rate change is zero. Iso-rate probe levels are lowest when probe frequency equals best frequency (BF) of the fiber. Profiles of iso-rate probe level versus BF (equal to probe frequency) are qualitatively similar to PTPs but differ quantitatively, e.g., in the rate of growth of probe level with masker level (1.2 dB/dB for PTPs, 0.54 dB/dB for iso-rate profiles). Quantitative differences can be further reduced by requiring a positive rate criterion. These results suggest that PTPs are not solely a reflection of the internal representation of the masker, but reflect responses to the probe tone as well.
Articulatory dynamics of loud and normal speech
Authors: Schulman Richard
Published: October 2005

A comparison was made between normal and loud productions of bilabial stops and stressed vowels. Simultaneous recordings of lip and jaw movement and the accompanying audio signal were made for four native speakers of Swedish. The stimuli consisted of 12 Swedish vowels appearing in an /i′b _b/ frame and were produced with both normal and increased vocal effort. The displacement, velocity, and relative timing associated with the individual articulators as well as their coarticulatory interactions were studied together with changes in acoustic segmental duration. It is shown that the production of loud as compared with normal speech is characterized by amplification of normal movement patterns that are predictable for the above articulatory parameters. In addition, it was observed that the acoustic durations of bilabial stops were shortened, whereas stressed vowels were lengthened during loud speech production. Two interpretations of the data are offered, viewing loud articulatory behavior as a response to production demands and perceptual constraints, respectively.
Sound propagation in the ear canal and coupling to the eardrum, with measurements on model systems
Authors: Stinson Michael R. , Khanna Shyam M.
Published: October 2005

A theoretical model of sound propagation in the ear canal is described, which takes into account both the complicated geometry of real ear canals and the distributed acoustical load presented by the eardrum. The geometry of the ear canal enters the theory in the form of a cross-sectional area function relative to a curved axis that follows the center of the ear canal. The tympanic membrane forms part of the ear canal wall and absorbs acoustical energy over its surface. Its motion leads to a driving term that must be added to the horn equation describing the pressure distribution in the ear canal. The sound field within the canal is assumed to be effectively one dimensional, depending only on longitudinal position along the canal. Experiments using model ear canals of uniform cross section were performed to test the ability of the theory to handle distributed loads. Sound-pressure distributions within each model canal were measured using a probe microphone. The behavior of the eardrum was simulated using either a distributed, locally reacting impedance or a mechanically driven piston. The agreement between theory and experiment is good up to a nominal upper frequency limit at which the ratio of canal width to wavelength is 0.25. It is estimated that the theory is applicable in ear canals of cats for frequencies at least as high as 25 kHz and in human ear canals to at least 15 kHz.
Specification of the geometry of the human ear canal for the prediction of sound-pressure level distribution
Authors: Stinson Michael R. , Lawton B. W.
Published: October 2005

The geometry of 15 human ear canals has been studied. Silicone rubber molds were made of the ear canals of human cadavers, and a mechanical probe system was used to obtain approximately 1000 coordinate points over the surface of each mold. The data points were accurate to about 0.03 mm in each of the three space directions, allowing ample resolution of surface detail. The measurements have been summarized as individual ear canal area functions, the area of cross-sectional slices normal to a curved central axis following the bends of the canal. Large intersubject differences were found, but several overall trends were evident in the area functions. Accurate specification of the canal geometry has lead to improved predictions of the sound-pressure distribution along the human ear canal at frequencies greater than 8 kHz. Such predictions are relevant to the development of high-frequency audiometric methods, high-fidelity hearing aids, and to the interpretation of experiments in physiological and psychological acoustics.