bluuebunny/crossref_metadata_2025 huggingface dataset:
Impulse response estimation with underwater explosive charge acoustic signals
Authors: Dicus Ronald L.
Published: October 2005

A procedure is presented for estimating the impulse response of a linear system from noise contaminated measurements of random input and output signals. The estimation requires ensemble averaged estimates of input and output noise spectra and a priori assumed spectra of the system function and input signal. A minimum mean-square-error estimator is derived and its theoretical signal-to-noise ratio is shown to be a slowly increasing function of the measured signal-to-noise ratios. The procedure is applied to a set of measured underwater explosive charge acoustic signals. For this application additional techniques are presented for synthesizing source replica signals and for accurately determining bubble pulse periods. The result of the deconvolution is a single sharp spike with at least 20-dB bubble pulse suppression. With approximately 20-dB signal-to-noise ratio in the measured signals the processed signal-to-noise ratios range from 10 to 13 dB and are all within 1 dB of theoretical values. Peak-signal to rms-noise ratios are 41 and 38 dB before and after processing, respectively.
Interference of corner reflected and edge diffracted signals for a surface-breaking crack
Authors: Achenbach J. D. , Norris A. N.
Published: October 2005

Backscatter of time-harmonic longitudinal waves from a surface-breaking crack is investigated in the high-frequency range. It is assumed that the distance of the transducer to the crack is large as compared to the crack depth, and that the incident rays are normal to the crack edge. The crack length is assumed much greater than its depth. A two-dimensional model for the transducer is considered. In the time domain, the first and second received signals are the edge-diffracted signal and the corner-reflected signal, respectively. These signals are analyzed in the frequency domain, by using the uniform asymptotic theory of diffraction. The response of the transducer due to the interference of the two signals is calculated. It is shown that the transducer’s response is a sensitive function of its position.
An array model for transducers with flexing heads
Authors: Butler John L. , Brown Willie D.
Published: October 2005

The equations which govern the mutual radiation interaction for an array of transducers with simple head flexure are developed. It is shown that in this case although an additional matrix inversion is required the matrix size need be no greater than the size for an array of rigid head elements.
Effect of probe duration on psychoacoustical tuning curves obtained in forward masking
Authors: O’Loughlin B. J. , Moore B. C. J.
Published: October 2005

The duration of the probe affects the sharpness of tuning of psychoacoustical tuning curves obtained in forward masking. With probes of less than 30 ms, a major factor appears to be the increase in the frequency spread of spectral energy with decreasing duration. Even with low-level probes, the redistribution of energy within the mainlobe of the spectrum is considerable and increases off-frequency listening.
More on the diffraction theory of Schroeder diffusors
Authors: Strube Hans Werner
Published: October 2005

The diffraction theory for ’’well-array’’ sound diffusors as suggested by M. R. Schroeder has been previously derived by this author. Here, the equations are simplified so that one multiplication by a large complex matrix is saved. Further manipulation of the new equations clarifies the relationship to the equations for a locally reacting plane, which are obtained in the limit of zero well width. The equations are also extended to the case of nonzero thickness of the walls separating the wells.
The effect of occluded ear impedances on the eardrum SPL produced by hearing aids
Authors: Gilman Samuel , Dirks Donald D. , Stern Richard
Published: October 2005

The purpose of the investigation was to determine the effect of eardrum and earmold impedance on eardrum sound pressure level (SPL) produced by a hearing aid receiver. Acoustic interactions between receivers and ears occurring at receiver resonances were explored and analyzed. Results with ear simulators showed that the effect of simulator eardrum impedance was increased in regions where ear and receiver impedance approached each other during resonances. Earmold acoustics were also significant factors at frequencies where their impedances were comparable to ear impedances. Resonant frequency shifts of 540 Hz in the region between 800 and 1500 Hz were observed for the range of simulator eardrum and earmold impedances employed, with SPL changes of 10 dB occurring at some frequencies. Results were different for each of the five receivers tested confirming the effect of the receiver characteristics on the eardrum SPL. A subsequent test was performed using real ears with results that agreed substantially with those obtained with the simulators.
Lateral position of sinusoids presented with interaural intensive and temporal differences
Authors: Yost William A.
Published: October 2005

The lateral position of pulsed sinusoids presented with interaural intensive or temporal differences was determined for a variety of frequencies, overall intensities, and durations. The lateral position of stimuli presented with interaural temporal differences was linearly related to interaural phase for interaural phases between 0 ° and ±90 °. Beyond ±90 ° the images often appeared at more than one position, usually on opposite sides of the head. The lateral position of stimuli presented with interaural intensive differences was linearly related to interaural intensity up to ±15 dB. These results were largely unaffected by frequency, duration, and overall intensity, although some of the small dependencies are described and discussed. The results are consistent with the assumption that lateral position at any one frequency is determined by mechanisms similar to coincidence networks or cross correlators. However, a single cross-correlation mechanism cannot account for the results obtained across frequency.
Finite amplitude effects on the thresholds for lesion production in tissues by unfocused ultrasound
Authors: Carstensen E. L. , Becroft S. A. , Law W. K. , Barbee D. B.
Published: October 2005

The phenomenon of thermal lesion production in tissues by unfocused ultrasound has been modeled under the assumptions (1) that damage to the tissues is the result of a chemical rate process and (2) that the time–temperature exposure of the tissue results from a competition between the rate of heat generation by absorption of ultrasonic energy and thermal diffusion. The model was tested by observing thresholds for color change in samples of excised bovine liver at 6 cm from a 2.25-MHz, 1.27-cm-diam piston source and 11.5 cm from a 4.4-MHz, 1.27-cm source. The observations disagreed sharply with predictions of the linear model. However, after recognition of the fact that finite amplitude phenomena modify the effective absorption coefficients of the tissues, the model gives excellent predictions of observed thresholds simply by using intensity dependent values of the absorption coefficients in the numerical calculations. Thermoelectric and radiation force methods were used to demonstrate the nonlinear absorption phenomenon in excised liver. In contrast with the case of focused ultrasound, the thresholds for lesion formation by unfocused sources (1) occur at lower intensities, (2) are strongly dependent upon frequency, and (3) because acoustic saturation in the coupling medium imposes lower limits on tissue intensities for unfocused than for focused ultrasound, unfocused lesions are limited to relatively long exposure times.
Vowel height and the perception of consonantal nasality
Authors: Abramson Arthur S. , Nye Patrick W. , Henderson Janette B. , Marshall Charles W.
Published: October 2005

By means of an articulatory synthesizer, the preception of the oral–nasal distinction in consonants was explored experimentally. This distinction was chosen because it is achieved by a very simple articulatory maneuver and because it is phonologically relevant in virtually every language. Lowering the velum in equal increments provided continua of CV syllables varying in size of velopharyngeal port which were divided perceptually into /d/ and /n/ categories by American English listeners. To test the hypothesis that the coarticulation of these nasal consonants with lower (more open) vowels requires a larger area of velopharyngeal coupling to give a nasal consonant percept, three oral–nasal continua incorporating the vowels /i/, /Λ/, and /α/, respectively, were presented for identification. The results were compared with those of A. S. House and K. N. Stevens [J. Speech Hear. Disord. 21, 218–232 (1956)] and A. S. House [J. Speech Hear. Disord. 22, 190–204 (1957)] obtained with steady-state vowels and consonantal murmurs and with those of M. H. L. Hecker [J. Acoust. Soc. Am. 34, 179–188 (1962)]. Three conclusions emerged. First, the relationship between vowel height and the amount of velopharyngeal coupling needed for a nasal percept occurs in conditions where subjects are required to make linguistically relevant judgments. Second, the relationship can arise in conditions where vocalic coarticulation is present. Third, the relationship is not confined to vowels but can also be observed in the case of dynamically articulated consonants. One of the continua was also used for discrimation experiments, which yielded the classical pattern of high discriminability at the category boundary.
Discrimination of speech by nonhuman animals: Basic auditory sensitivities conducive to the perception of speech-sound categories
Authors: Kuhl Patricia K.
Published: October 2005

Chinchillas (Chinchilla laniger) were tested in a same–different task to determine the location of greatest sensitivity along a continuum of voice-onset-time (VOT). The procedure used was an up–down staircase technique which allowed the determination of the just-noticeable-difference in VOT (Δ VOT) for VOT’s on a continuum ranging from [dα] to [tα]. Results demonstrated that the animals were most sensitive to change (i.e., produced the smallest Δ VOT values) in the region of the phonetic boundary dividing voiceless-unaspirated and voiceless-aspirated sounds, in good agreement with the boundary value previously obtained in an identification task with this same species [Kuhl and Miller, J. Acoust. Soc. Am. 63, 905 (1978)]. The results support the notion that the mammalian auditory system provided a selective pressure on the choice of acoustic cues to represent the phonetic oppositions employed by the world’s languages. The data are discussed in terms of the original definition of categorical perception and current psychoacoustic explanations of the peak in sensitivity for two-component stimuli varying in onset time.
Cochlear model including three-dimensional fluid and four modes of partition flexibility
Authors: Taber Larry A. , Steele Charles R.
Published: October 2005

The WKB solution is developed for the analysis of a straight box cochlear model which includes four modes of partition displacement, simulating the motion of the bony shelf and arches of Corti, as well as the pectinate zone of the basilar membrane. The theory is similar to that previously used for the 1-mode model with scalar quantities now replaced by 4-vectors. Calculations are carried out for the guinea pig cochlea with stiffness computed mainly from the anatomy and assumed physiological values for the materials. Results show that the stiffness is such that the amplitude and phase of the basilar membrane response are not significantly altered from those given by the 1-mode model. For primates and some other mammals, the bony shelf is substantially weaker than in the guinea pig and causes a much more rapid accumulation of phase along the basilar membrane. Thus, with anatomically and physiologically consistent parameters, the model yields good correlation in phase and amplitude with the in vivo measurements which have been made in the squirrel monkey by Rhode [J. Acoust. Soc. Am. 64, 158–176 (1978)] as well as in the guinea pig by Wilson and Johnstone [J. Acoust. Soc. Am. 57, 705–723 (1975)] and Rhode [Basic Mechanisms in Hearing (Academic, New York, 1973), pp. 49–63].
Frequency spectra of cochlear acoustic emissions (’’Kemp-echoes’’)
Authors: Wit H. P. , Langevoort J. C. , Ritsma R. J.
Published: October 2005

Cochlear acoustic emissions were recorded with a sensitive microphone from within the ear canal of normal hearing subjects. Frequency spectra of these acoustic emissions were obtained with two different procedures: real-time recording or calculation of the spectrum of time-averaged emissions. The two procedures give different input–output curves for click-evoked acoustic emissions. A phase-locking mechanism is proposed to explain this difference. It is shown that the real-time spectrum recording procedure can be used to measure tuning curves or to study the distortion product 2f1–f2. Experimental results indicate that sharply tuned emission generators are present in the human cochlea.
Uniqueness and linear independence of steering vectors in array space
Authors: Godara Lal C. , Cantoni Antonio
Published: October 2005

The study of array processing often involves the manipulation of steering vectors defined in array space. The question of uniqueness and linear independence of steering vectors often arises in the analysis of array processing algorithms and in their formulation. The paper examines the effect of array geometry on the mapping between directions in three-dimensional space and steering vectors in array space. Conditions on array geometry for uniqueness and linear independence of steering vectors are established for linear, planar, and general arrays.
Diffuse wave fields in solid media
Authors: Egle Davis M.
Published: October 2005

The diffuse-field concept is applied to develop the power balance equations relating the time-averaged energy densities associated with longitudinal and transverse waves to the diffuse-field mode conversion coefficients and the power generated by sources in the medium. A solution for an impulsive source in a solid with stress-free surfaces shows that, regardless of the initial partition of energy, the transverse-wave energy density quickly increases to become the dominant energy form in the medium.
Transverse-vibration responses of nonuniform, internally damped cantilever beams. II
Authors: Kerlin R. L.
Published: October 2005

The Bernoulli–Euler theory of transverse beam vibration, suitably extended to take into account internal beam damping, is used to derive closed-form expressions for the mechanical driving-point impedance and force transmissibility of two types of nonuniform cantilever beams that are driven at their free ends by a sinusoidally varying point force. The two types of beams considered are ones: (1) truncated and of rectangular cross section with a linearly tapered depth and a breadth appropriately varied (hyperbolically) to maintain constant cross-sectional area, and (2) composed of three stages, each of which is uniform but may vary arbitrarily from the others in cross section and proportionate length. Representative computations of the frequency dependence of impedance and transmissibility are plotted for beams having the same length and mass as an equally long and equally massive uniform reference beam. Significant attenuation or amplification of force transmissibility is observed, depending on the proportions of the beams and on whether their depth diminishes towards their fixed or free end. The measured resonance frequencies of a set of nonuniform aluminum alloy (6061-T651) cantilever beams and the measured transmissibility of one other such beam agree closely with the predictions of theory.
Parabolic equation calculations versus North Pacific measurement data
Authors: Hanna J. S. , Rost P. V.
Published: October 2005

Calculations of transmission loss using a Parabolic Equation (PE) model are compared to measured transmission loss from a North Pacific propagation experiment. In the range-dependent environment various combinations of two source depths, three receiver depths, and three frequencies permitted a thorough examination of the influence of PE model input parameters. Sensitivity of calculated transmission loss to variations in the input parameters is discussed and some omissions in the measurements are found to be significant when evaluating the model. When known measurement uncertainties are used to vary the model’s input, changes in the model’s predicted transmission loss are of the same scale as the differences seen in model-to-data comparisons. Repeatability of the measurement was determined by two comparable measurement events. Data-to-data statistical comparisons of those two measurement events are no better than the model-to-data comparisons. The data-to-data comparisons showed mean differences up to 1.5 dB with standard deviations between 1 and 3.5 dB. Model-to-data comparisons yield comparable means and standard deviations. It is concluded that the PE model permits comparisons with the data at a level of detail which demands more information from measurements than is available from even this unusually comprehensive data set.
Influence of acoustical and linguistic factors on the SPIN test difference score
Authors: Owen Jeffrey H.
Published: October 2005

SPIN test difference scores, which are the numeric difference between items of high predictability and low predictability, were obtained from three groups of subjects to determine whether the subject’s language skills influenced the size of the difference score. For this purpose the relationship between the difference score and the following variables was determined: syntactic skills, semantic skills, IQ, age, hearing loss, and signal-to-noise ratio (S/N). Results indicated that the difference scores were significantly related to the subject’s hearing and the S/N ratio used in the administration of the SPIN sentences. Possible reasons for these results are discussed.
Additional solutions to the free bending waves of a fluid loaded thick plate
Authors: Pierucci Mauro
Published: October 2005

Different researchers over the last few years have presented results showing how the root loci of the free bending waves of a fluid loaded infinite plate vary as a function of frequency and fluid properties. The purpose of this paper is to present other possible solutions of this paper and to indicate how the different modes can, for few typical cases of interest, shift from one Riemann sheet to the other.
Radiation losses in resonant tubes
Authors: Zuckerwar Allan J. , Meredith Roger W.
Published: October 2005

The role of radiation losses in a resonant tube—the transfer of sound energy from the test gas through the confines of the tube to the ambient atmosphere—is investigated both theoretically and experimentally. It is concluded that losses of this sort make no noticeable contribution to the background losses, even at high gas pressures. Nevertheless, if an axial resonant frequency of the test gas closely matches a longitudinal resonant frequency of the tube wall, the internal sound pressure can excite tube displacements of disproportionate magnitude and thus cause excessive losses, not due to radiation but rather to frictional dissipation related to the motion of the tube structure. This mechanism is effective when the mode numbers of the gas and tube have opposite parity, and makes sound absorption measurements at the fundamental gas frequency particularly problematical. An experimental investigation confirms the existence of such additional losses when the parity condition is fulfilled.
Detection of binaural signals partially masked by a reproducible noise maker: The influence of the phase angle alpha
Authors: Dolan Terrence R. , Hirsh I. Richard , Yost William A.
Published: October 2005

The present experiment was an attempt to examine the detectability of partially masked tonal signals in a background of masking noise in both homophasic and antiphasic masking conditions as the angle of addition between the signal and masker was manipulated. In the present study, the masking noises were samples of reproducible (’’frozen’’) noise.
Series or parallel filtering in the cochlea?
Authors: Whitfield I. C.
Published: October 2005

It is suggested that a cochlear transduction system in which the ’’second filter’’ is in parallel, rather than in series with the classical mechanical transducer mechanism gives a performance that better fits observed data.
Hankel transform diffraction theory for circularly symmetric sources radiating into parabolically anisotropic (or isotropic) media
Authors: Szabo Thomas L.
Published: October 2005

A convenient form is presented for calculating acoustic diffraction of a circularly symmetric time harmonic beam radiating into a parabolically anisotropic (or isotropic) medium. The field amplitude is expressed as a spatial Hankel transform of the aperture source function. Closed form expressions for both the near- and farfield are obtained for the following types of sources: constant, Gaussian, and truncated Gaussian. Methods of numerical evaluation are discussed.
Wave theoretical approach to acoustic focusing
Authors: de Vries D. , Berkhout A. J.
Published: October 2005

From the acoustic wave theory, a set of synthetic focusing operators can be derived applying phase correction and amplitude weighting (apodization) to the data recorded within the aperture. The focusing quality in terms of axial and lateral resolution appears to be superior to that of conventional operators common in today’s focusing practice.
Frequency dependent refocusing in phase shift beamforming systems
Authors: Lynch James F. , Stokes Robert H.
Published: October 2005

It is shown that the focal point of a spatially focused phase shift beamforming system changes as one changes the operating frequency of the system. This change is small for linear arrays, but is quite large for curved arrays. The advantage of a system of this type is that it can be focused on any desired range simply by making a slight change in operating frequency. Theoretical predictions, computer simulation, and experimental results are presented, all showing good agreement.
Ultrasonic imaging through turbulent media using data selection processing
Authors: Sato Takuso , Linzer Melvin , Ikeda Osamu , Hirama Makoto
Published: October 2005

The concept of data selection during image formation is proposed to enhance ultrasonic images obtained by focusing through turbulent media. In this approach, a focused transducer array is used in transmit to concentrate the ultrasonic energy at a desired point in the object, and the reflected waves are detected by the array elements and focused through appropriate delay operations. Data selection is carried out by comparing the complex amplitudes of the delayed signals. Only the data which satisfy suitable criteria are used in synthesizing the image. The principles of data selection imaging are described in detail and several processing schemes are proposed. The basic features of the method are verified by computer simulation and demonstrated experimentally. The results show clearly the improvements obtained when imaging through turbulent media.
Fluctuations in underwater acoustic delay differences between orders of arrival
Authors: Broek H. W. , Lawlor J. E.
Published: October 2005

First-, second-, third-, and fourth-order downcoming arrivals of 400-Hz acoustic pulses transmitted over a 140-nmi range to five receivers were recorded concurrently. The source was ship-suspended at a depth of 1050 ft in 2400 fathoms of water; the receivers were bottomed on a slope at about 4500-ft depth, near Bermuda. The data were analyzed to display the fluctuations in inter-order delay differences between arrivals at a receiver. Data on the delay differences at two receivers for a given arrival order are also presented for downslope receiver separations of 247 and 904 ft.
Discussion of sea water sound-speed determinations
Authors: Mackenzie Kenneth V.
Published: October 2005

Available data on the speed of sound in sea water are examined to arrive at a basis for deriving simple equations suitable for most ocean areas. Extant laboratory data are compared. In situ measurements aboard deep submergence vehicles are presented, and convergence zone ranges discussed. Del Grosso and Mader [J. Acoust. Soc. Am. 52, 961–974 (1972)] equations appear superior, after numerous intercomparisons, to serve as a foundation for generating simple sound-speed equations.
Nine-term equation for sound speed in the oceans
Authors: Mackenzie Kenneth V.
Published: October 2005

A simple yet accurate nine-term, eight-variable equation for sound speed in the oceans, suitable for programmable pocket calculators, is presented. Ranges of validity encompass: temperature −2° to 30° C, salinity 30° to 40°/°°, and depth 0 to 8000 m. Good quality oceanographic data at 15 worldwide stations, including two in the Mediterranean, were utilized for the computations. The Del Grosso and Mader [J. Acoust. Soc. Am. 52, 961–974 (1972)] sound-speed equation was employed as ’’truth’’ after comparisons among Wilson [J. Acoust. Soc. Am. 32, 641–644. 1357 (1960)] and others. A precise method of computing pressure is detailed. Practical differences in critical depth, excess depth, conjugate depth, deep sound-speed gradients, and echo-sounder corrections are shown to be small between computations based on Wilson or Del Grosso and Mader sound-speed equations.
Acoustic propagation over ground having inhomogeneous surface impedance
Authors: Durnin James , Bertoni Henry L.
Published: October 2005

Previously it was found that when an acoustic source is located above a porous ground plane of infinite lateral extent, the acoustic fields contain both surface wave and ground wave components. Because of these components the acoustic fields exhibit attenuation differing from the 6 dB per doubling of distance found for propagation over a hard surface. In this paper we consider the excess attenuation that occurs in the mixed path case when a portion of the ground plane is acoustically hard and the rest is porous. Expressions are derived for the attenuation when source and receiver are at ground level and on opposite sides of the boundary line between the hard and porous surfaces. Two different approaches were used to approximate the acoustic fields, and were found to give good numerical agreement. The theoretical results were also found to agree with measurements made at 1 kHz over a concrete–grass path.
High-frequency sound propagation in a spatially varying mean flow
Authors: Cho Y. C. , Rice E. J.
Published: October 2005

An equation for acoustic ray paths in a spatially varying mean flow has been examined to determine some of the characteristics of the flow gradient effects on sound propagation. In a potential flow the acoustic rays are deflected in the direction of increasing mean flow, and the gradient of the mean flow speed is the dominant factor causing the ray deflection. In contrast, in a sheared mean flow, the vorticity is the dominant factor in deflection of the acoustic rays.
Piezoelectric transducers with ideal time limited impulse response
Authors: Hazony D.
Published: October 2005

Of interest is the performance of piezoelectric transducers where, in addition to transmission line effects, reactive effects are also present. Hence an ideal time-limited response is nearly impossible without severe electrical and mechanical damping. It will be seen that the problem has an ideal solution. A carefully designed linear network is inserted in the electrical circuit rendering the output time limited.
Ultrasonic absorption in deer blood
Authors: Shung K. K. , Rocco M. , Ballard J. O.
Published: October 2005

It has been shown that ultrasonic absorption of sickle cells obtained from human patients can be correlated with the aggregation state of sickle cell hemoglobin within the intact cells. We have extended this investigation to red blood cells obtained from white-tailed deer which also exhibit the sickling phenomenon. In contrast to the sickling phenomenon in humans, the sickling of deer erythrocytes occurs when the oxygen tension and pH of the blood are high. Nevertheless, remarkable similarities exist between the process of hemoglobin polymerization which produces sickling in both species. We have measured the ultrasonic absorption as a function of blood pH and oxygen tension and compare it with the morphological changes. High pH and oxygen tension which enhance sickling caused an increase in ultrasonic absorption. Low pH and low oxygen tension which retard sickling reduced ultrasonic absorption. The magnitude of the change in ultrasonic specific absorption coefficient under extreme conditions has been found to be more than two fold at a frequency of 15 MHz.
Developmental differences in identifying and discriminating CV syllables
Authors: Elliott Lois L. , Longinotti Cheryl , Meyer Dianne , Raz Israel , Zucker Karen
Published: October 2005

The purpose of this experiment was to determine whether age-related differences would be observed for identification and discrimination of synthesized, five-formant CV syllables among listeners who showed equal perfomance scores on a standard clinical test of speech understanding. A second question concerned the relations between performance on identification and discrimination tasks as a function of age. Two 13-item continua that varied in the place of articulation feature ([ba, da, ga]) were used; they differed primarily in the presence or absence of a 5-ms noise burst at the consonant onset. Digitized natural speech syllables were also employed in one experimental task. Strong age effects were obtained for the three tasks—identification of syllables, adaptive estimation of ba, da- and da, ga- boundaries, and discrimination. With the exception of one condition for six-year-olds, only adults showed significant differences between boundaries and just-noticeable differences. Minimal differences were obtained in responses to stimuli with and without initial bursts. Across ages there were no significant differences in the subjects’ ability to label the synthesized syllables as compared to the natural speech stimuli. Possible explanations for the observed developmental effects are discussed.
Discrimination of steady-state vowels by blackbirds and pigeons
Authors: Hienz R. D. , Sachs M. B. , Sinnott J. M.
Published: October 2005

Redwing blackbirds, brown-headed cowbirds, and pigeons were trained with operant conditioning techniques to discriminate the steady-state vowels /ε/, /ae/, /a/, and /sa/ from each other. A pulsed train of one of these vowels comprised the background stimulus. Birds were trained to peck on one response key to produce occasional alternations from this standard vowel to one of the three remaining comparison vowels, and to peck on a second response key during these alternations to produce a grain reward. All birds discriminated all combinations of vowel pairs employed when only one comparison vowel occurred during a session. Differences in discriminability emerged when three comparison vowels occurred within each session. For pigeons, increased discriminability (indicated by shorter response latencies and higher rates of correct detections) was directly related to the size of the first or second formant frequency shifts between standard and comparison vowels. For blackbirds, this was only true if the first or second formants shifted to higher frequencies when going from the standard to the comparison vowel. Comparison vowels producing downward formant shifts were not discriminated very easily, and in some cases not discriminated at all by blackbirds.
Space-ensemble average of reverberation decay curves
Authors: Kawakami F. , Yamaguchi K.
Published: October 2005

In the space-ensemble average of reverberation decay curves, {〈S2(t)〉}, based upon the decay process of total sound energy in an enclosure, the irregularities and the spatial variation inherent in the spatial average {S2(t)} and the ensemble average 〈S2(t)〉 are both effectively eliminated. Moreover, synchronized averaging incorporated with {〈S2(t)〉} minimizes the distortion due to time-varying background noise and extends the dynamic range of the resultant curve {〈S2(t)〉}NO which, as the number of averaging samples H increases, converges to a smooth linear decay with a slope peculiar to the enclosure. Identity exists between reverberation time (RT60) evaluated on {〈S2(t)〉}NO and arithmetic mean of RT60′s on the individual spatial sample curves 〈S2(t)〉NO′s. The {〈S2(t)〉}NO could also yield the spatial average of parameters for early reflections such as Definition D(%) proposed by R. Thiele, which are less influenced by the coincidence phenomenon of reflections and better reflect the true nature of the space. The {〈S2(t)〉}NO is elegantly measured by a newly developed technique called CDS which basically allows the real-time computation of 〈S2(t)〉 on portable equipment for field measurements, and will be conveniently used for absorption coefficient measurements as well as for the examination of sound diffusion. This paper mainly refers to: (1) basic characteristics of {〈S2(t)〉}, (2) associated synchronized averaging to give {〈S2(t)〉}NO and (3) CDS for 〈S2(t)〉NO and {〈S2(t)〉}NO measurements.
Effect of the sound field structure on array signal gain in a multipath environment
Authors: Neubert J. A.
Published: October 2005

A wide-aperture, horizontal line array receiving a low-frequency, long-range signal is considered. It is shown that the sound field structure as manifested by amplitude nonhomogeneity and the wave-front corrugation can reduce the performance of a conventional linear beamformer. Beamformer expressions that explicitly show the effects of amplitude nonhomogeneity and wave-front corrugation in a multipath environment are given. The limitations of some array algorithms that are inappropriate for a multipath environment are indicated. Array signal gain and side-lobe suppression relations for an ocean multipath environment are generalized from similar relations that are not valid in an ocean multipath environment.
Poroelasticity equations derived from microstructure
Authors: Burridge Robert , Keller Joseph B.
Published: October 2005

Equations are derived which govern the linear macroscopic mechanical behavior of a porous elastic solid saturated with a compressible viscous fluid. The derivation is based on the equations of linear elasticity in the solid, the linearized Navier–Stokes equations in the fluid, and appropriate conditions at the solid–fluid boundary. The scale of the pores is assumed to be small compared to the macroscopic scale, so that the two-space method of homogenization can be used to deduce the macroscopic equations. When the dimensionless viscosity of the fluid is small, the resulting equations are those of Biot, who obtained them by hypothesizing the form of the macroscopic constitutive relations. The present derivation verifies those relations, and shows how the coefficients in them can be calculated, in principle, from the microstructure. When the dimensionless viscosity is of order one, a different equation is obtained, which is that of a viscoelastic solid.
Rate-versus-intensity functions and related AP responses in normal and pathological guinea pig and human cochleas
Authors: Harrison Robert V.
Published: October 2005

Cochlear fiber discharge rate-versus-intensity functions, across frequency, have been measured in pathological guinea pig cochleas (ototoxic antibiotic poisoning) and compared with the normal animal. The frequency dependence of the slopes of these functions is reduced in cochlear pathology which results in minimum threshold elevations of more than 50 dB, i.e., there is a reduction in this frequency dependent nonlinearity. The rate functions at characteristic frequency (CF) become abnormally steep (e.g., 4–5 spikes/s/dB compared with a normal 1–2 spikes/s/dB), and comparable to those of the low-frequency tail region of normal cochlear fibers. The CF dynamic range is reduced from 30–40 to 10–15 dB in cochlear pathology. The fiber study has been confirmed by (and has confirmed) a method of indirect measurement of rate functions from AP suppression-versus-intensity functions using a pure-tone forward masking paradigm [Abbas and Gorga, J. Acoust. Soc. Am. 69, 492–499 (1981)]. This method has been used in normal and pathological guinea pigs, and the results parallel the single fiber study. In addition, AP suppression functions, across frequency, have been obtained in human subjects with (near) normal hearing thresholds, and in patients with sensorineural hearing loss of cochlear origin, during transtympanic electrocochleography. The AP suppression curves in pathology indicate, as for the animal studies, a loss of the frequency dependency of the rate function slopes, and predict steep rate functions at CF (and thus reduced dynamic range) in cochlear deafness. The findings are related to loudness recruitment.
Second formants in fricatives: Acoustic consequences of fricative-vowel coarticulation
Authors: Soli Sigfrid D.
Published: October 2005

Spectral analyses of the sibilant fricatives, [s, z, ℱ, z], as spoken in isolation and in initial position before the vowels [a, i, u], were performed for a corpus of 80 utterances. The mean LPC spectra for five utterances of each fricative produced in each vowel context revealed reliable anticipatory vowel coarticulation effects present at least 30–60 ms before vowel onset in the form of spectral peaks affiliated with the second formant of the vowel. Peak frequencies were between 1.5 and 2 kHz and were approximately 100–300 Hz higher before the front vowel [i] than before the back vowels [a, u]. The presence of these peaks in the fricative spectra indicate that during the latter part of the fricative the constriction begins to open in anticipation of the vowel, and, as a consequence, second formant resonances are excited. The acoustic characteristics of these fricative formants varied as a function of vowel context due to differences in the anticipatory coarticulation of the vowel. Fricative place of constriction was assimilated to the high vowels [i, u], resulting in different fricative formant frequencies, while overlap of fricative and vowel articulatory gestures produced additional acoustic differences. These effects were least in the [a] context because the opposing gestures required to produce the constricted fricative and the relatively open low vowel are presumably performed in sequence with minimal assimilation or overlap. The present acoustic evidence and related articulatory considerations are congruent with the results from a companion perceptual study [G. H. Yeni–Komshian and S. D. Soli, J. Acoust. Soc. Am. 70, 966–975 (1981)] showing that the high vowels [i, u] but not the low vowel [a], can be identified in fricatives excised from fricative–vowel syllables. These objective links between articulatory, acoustic, and perceptual aspects of coarticulation are discussed.
Elementary source-type solutions of the reduced wave equation
Authors: Holford R. L.
Published: October 2005

A class of exact and elementary solutions of the reduced wave equation exhibiting source-type behavior is obtained which considerably enlarges the catalogue of known elementary solutions for layered media, and which provides the first such example known for a medium possessing variability both in range (x) and depth (y). The medium, in general, is an unbounded one in which the square of the refractive index (n) is specified as an arbitrary biquadratic form in x and y. We are then able to obtain an elementary solution for a line source extending at right angles to the x–y plane. When n is independent of x (layered medium), we show that the solution for point-source excitation can be obtained in a similar form. We treat in some detail the cases: (i) n2 = 1−y2, corresponding to a sound-channel profile, which provides an example of cusped-caustic formation in the ray interpretation; and (ii) n2 = 1+y2, corresponding to a sound-barrier profile, which provides an example of the phenomenon known as ’’tunneling.’’ The latter can be analyzed in terms of Keller’s ’’complex rays.’’
Effective dynamic properties of composite viscoelastic materials
Authors: Kligman Ronald L. , Madigosky Walter M. , Barlow John R.
Published: October 2005

General expressions for the dilatation modulus and density of composite viscoelastic materials are derived within the framework of a theory that is an extension of the self-consistent field approach. The dynamic dependence of these parameters is found up to values of wavenumber in the host medium times void radius equal to two. For various void concentrations and damping constants, the effective modulus shows regions of high stiffness and resonant compliance. The effective density shows single-peaked behavior for various concentrations and damping constants. In the long wavelength limit the effective modulus and density agree with the results of other investigators.
Space–time dependence of acoustic waves in a borehole
Authors: Schoenberg Michael , Marzetta T. , Aron J. , Porter R. P.
Published: October 2005

A combined theoretical and experimental study, using a scale laboratory model with a cylindrical borehole, has been performed to study the space–time dependence of modal propagation. Wave analysis has been expanded to include cased hole as well as the more usual situation of open hole propagation. A general formalism for cylindrically layered media is presented. Experimental results include 40 waveforms with transmitter–receiver spacings in increments of 12.7 mm which is sufficient to avoid significant spatial aliasing. Wavenumber-frequency spectral estimation is used to resolve trapped modes in the data set. Good agreement between theory and experiment has been obtained for both modal dispersion and mode cutoff frequencies.
Response characteristics of a finite aperture, phase insensitive ultrasonic receiver based upon the acoustoelectric effect
Authors: Busse L.J. , Miller J.G.
Published: October 2005

The acoustoelectric effect (i.e., the interaction of ultrasound with conduction electrons in a piezoelectric semiconductor) provides the basis for the construction of a finite aperture, phase insensitive receiver using a single crystal of cadmium sulfide. In this paper we present a formalism describing the operation of such a receiver. Criteria for the optimization of the device in terms of ultrasonic bandwidth, response time, sensitivity, and electrical and mechanical loading are presented. In an accompanying paper [J. Acoust. Soc. Am. 70, 1377–1386 (1981)], we discuss and demonstrate the merits of using a phase insensitive receiver when measurements of a phase distorted (spatially noncoherent) ultrasonic radiation must be made.
Sound propagation in shallow water: A detailed description of the acoustic field close to surface and bottom
Authors: Jensen Finn B.
Published: October 2005

Experimental data are compared with normal-mode predictions for an isovelocity shallow-water propagation channel overlying a complicated layered bottom. Measurements were made close to both the sea surface and the sea floor with a vertical hydrophone spacing of 1 m. Excellent agreement between theory and experiment is obtained over the frequency range 50–3200 Hz and for ranges up to 30 km. Some problems associated with deterministic modeling are also discussed and appropriate solutions are indicated.
Scattering of acoustic waves by a finite elastic cylinder immersed in water
Authors: Numrich S. K. , Varadan Vasundara V. , Varadan Vijay K.
Published: October 2005

The scattering of acoustic waves by a finite elastic cylinder immersed in water has been explored theoretically using the T-matrix method. Numerical results were obtained for an aluminum circular cylinder with hemispherical end caps. Cylinders of this type were immersed in water and subjected to detailed acoustic backscattering measurements as a means of verifying the numerical computations. Comparisons between theory and experiment were made at several angles of incidence. The frequency range covered was sufficient to include major, identifiable resonances at each of these angles. In all cases, the numerical results accurately delineated the observed resonances and compared favorably with the off-resonance, backscattered form function.
Piezopolymer transducers with point-supported membranes
Authors: Lerch R.
Published: October 2005

Theoretical and experimental studies of electroacoustic transducers using a piezoelectric foil membrane supported in its center by a rigid support are reported. The static as well as the dynamic deflections are described by the solutions of differential equations. In the case of microphones, a simplified calculation based on a superposition of the static and dynamic deflections of a ring-shaped membrane is described which represents a good approximation to the exact solution. For headphones, however, only the exact mathematical description of the mechanical system leads to useful results. While the sensitivities of such microphones are in the range −55 to −60 dB V per N/m2, the electroacoustic transmission factors of headphones with sizes suitable for telephone applications are in the range of 70 to 90 dB SPL re 1 V input voltage.
Interaural time discrimination in noise
Authors: Cohen Marion F.
Published: October 2005

Interaural time jnds were measured for a 250-Hz tone-burst signal as a function of signal level and interaural phase relations of a background white noise. Results indicate that midline interaural time jnds for a sinusoid of constant SPL become larger as the background noise changes from diotic to statistically independent to interaurally phase reversed. That background noise which favors signal detection impedes interaural time discrimination.
Velocity of propagation of bone-conducted sound in a human head
Authors: Tonndorf J. , Jahn A. F.
Published: October 2005

A psychophysical cancellation method after Zwislocki [J. Acoust. Soc. Am. 25, 752–759 (1953)] was used to measure the propagation velocity of bone-conducted sound across the head of an observer. The result, 330 m/s, compares quite well with Zwislocki’s earlier value of 260 m/s and Franke’s of 300 m/s. Since in all three experiments the velocity was frequency-independent at f≳2000 Hz, it is suggested that vibratory energy travels along the flat bones of the cranial vault in the form of plate waves and as distortional waves through its base. [As defined by Cremer and Heckl, K?rperschall (Springer, Berlin, 1967), plate waves are but a simpler form of distortional waves.] Quantitatively, the present result appears quite reasonable in the light of the material constants involved and by comparison with other materials.
Direct measurement of basilar membrane stiffness in the guinea pig
Authors: Gummer Anthony W. , Johnstone Brian M. , Armstrong Nigel J.
Published: October 2005

Measurements of basilar membrane stiffness were made in the 0.8–2.3-mm region of the guinea pig cochlea, within 1-h post mortem. A tungsten wire probe glued to a piezoelectric crystal was used to statically displace the scala tympani side of the basilar membrane. The extirpated temporal bone was fixed to a barium titanate crystal and vibrated at 40 Hz with a displacement of 10 nm (rms). The filtered signal from the piezoelectric crystal was analyzed with a lock-in amplifier and the stiffness calculated as a function of static displacement. The resulting curve was flat for a displacement of 1–3 μm, whereupon it increased, exhibiting two distinct sections, until piercing occurred at 50–60 μm. For measurements made at the membrane center the plateau value of the stiffness decreased exponentially with distance from the stapes with a space constant of 1.7±0.8 mm, in agreement with theory. The radial flexural rigidity and the effective membrane thickness were estimated from the first 10 μm of these curves; the values were 6.2±0.6×10−10N⋅m and 6.7±1.4 μm, respectively. A kanamycin treated animal gave similar results to the control group, implying that the basilar membrane is the principal contributor to the stiffness of the cochlear partition. Finally, curves measured from fixed cochleae not only suggested stiffnesses which were an order of magnitude greater than those from fresh cochleae, but also indicated an inability of a fixed basilar membrane to vibrate linearly.