bluuebunny/crossref_metadata_2025 huggingface dataset:
Speech coding in the auditory nerve: V. Vowels in background noise
Authors: Delgutte Bertrand , Kiang Nelson Y. S.
Published: October 2005

Responses of auditory-nerve fibers to steady-state, two-formant vowels in low-pass background noise (S/N=10 dB) were obtained in anesthetized cats. For fibers over a wide range of characteristic frequencies (CFs), the peaks in discharge rate at the onset of the vowel stimuli were nearly eliminated in the presence of noise. In contrast, strong effects of noise on fine time patterns of discharge were limited to CF regions that are far from the formant frequencies. One effect is a reduction in the amplitude of the response component at the fundamental frequency in the high-CF regions and for CFs between F1 and F2 when the formants are widely separated. A reduction in the amplitude of the response components at the formant frequencies, with concomittant increase in components near CF or low-frequency components occurs in CF regions where the signal-to-noise ratio is particularly low. The processing schemes that were effective for estimating the formant frequencies and fundamental frequency of vowels in quiet generally remain adequate in moderate-level background noise. Overall, the discharge patterns contain many cues for distinctions among the vowel stimuli, so that the central processor should be able to identify the different vowels, consistent with psychophysical performance at moderate signal-to-noise ratios.
Mandible movements during increasingly rapid articulations of single syllables: Preliminary observations
Authors: Nelson Winston L. , Perkell Joseph S. , Westbury John R.
Published: October 2005

A previous study of mandible movements in normal speech [W. L. Nelson, J. Acoust. Soc. Am. Suppl. 1 68, S32 (1980)] suggested that the speech motor control process resulted in a relationship between movement time, distance, and peak velocity which implied (1) some adaptation to the physical effort required for the movement, and (2) that the force limit effective during speech was considerably below that which the mandibular muscles are capable of producing. In the present study, mandible movements were measured during maximally rapid opening and closing tasks, and during increasingly rapid repetitions of a spoken syllable and a nonspeech ‘‘syllable.’’ The results indicate that (1) peak acceleration levels for the repeated mandible movements were less than half of those for the maximally rapid single mandible movements, and (2) a rather different mode of control is used for the repeated speech movements as compared to the nonspeech movements.
Precise measurement of phase difference and the amplitude ratio of two coherent sinusoidal signals
Authors: Wong George S. K.
Published: October 2005

This paper describes the theory of the interchange reference method for the precise assessment of phase difference θ and amplitude ratio R of two coherent sinusoidal signals. Systematic errors are analyzed in depth. For θ equal to 10°, the uncertainties in R and θ are of the order of 2 ppm and less than 0.01°, respectively. Experimental verification confirms the theory of the above method.
Response of an edge-supported circular membrane electret earphone. Part I—Theory
Authors: Busch-Vishniac Ilene J.
Published: October 2005

The behavior of an edge-supported circular membrane foil electret earphone is studied in a three-step analytical procedure. First, the static deflection is determined for a specified set of transducer parameters. The deflection is expressed as a power series in radial location. Second, the dynamic deflection, which depends on the static deflection, is found. It is also expressed as a power series in radial location. Third, the linear dynamic response is examined to determine a procedure for maximizing the sound pressure level which is generated in the ear. The results presented here indicate that with the choice of an optimum set of earphone parameters it is possible to construct an earphone with a sensitivity of 82 dB/V and a relative distortion level of about −40 dB.
Does sound propagation really have inversion symmetry?
Authors: Kittinger Erwin , Tichý Jan
Published: October 2005

The basic equation for plane elastic waves in crystals remains invariant under a reversal of the propagation direction. If the direction of the wave normal is rotated in a crystallographic plane containing an acoustic axis, a situation may arise under certain conditions which leads to an apparent violation of this inversion symmetry, namely, to a period of 360° for the angular dependence of phase velocity and displacement eigenvectors of both quasitransverse modes. A specific example for this is given and the general conditions for the occurrence of this situation are discussed.
Measurements of backscattered leaky Lamb waves in plates
Authors: de Billy Michel , Adler Laszlo , Quentin Gerard
Published: October 2005

We have reported earlier the observation of backscattered leaky Raleigh waves from a liquid–solid interface [J. Acoust. Soc. Am. 72, 1018–1020 (1982)]. Now we have carried out experiments to observe backscattered leaky Lamb waves from a plate immersed in liquid, using a single transducer in pulse echo modes. Sharp peaks were observed at angles corresponding to backward propagating symmetrical and antisymmetrical Lamb modes. These backward propagating Lamb waves leak back at both sides of the plate.
Thresholds of perception of vibration in recumbent men
Authors: Miwa Toshisuke , Yonekawa Yoshiharu , Kanada Kazuo
Published: October 2005

The thresholds of perception of vibration by recumbent men are a significant index for the governmental agency concerned with regulation of vibration exposure. The thresholds of perception of continuous sinusoidal vibrations and single and multiple bursts of sinusoidal vibrations in the horizontal and vertical directions were investigated in recumbent men. We found that the threshold curves, as a function of the frequency, had different characteristics for vertical vibrations than for horizontal vibrations in the recumbent position. The threshold values for pulsed vibrations became smaller (easier to perceive) as the bursts were elongated until saturation occurred at 4 s duration. Threshold values for pulse durations longer than 4 s were the same as those for continuous vibration. This suggests the existence of temporal integration of sensation of vibrations as in psychoacoustics.
A sequential hypothesis testing, optimal stopping problem in underwater acoustic detection
Authors: Psaraftis Harilaos N. , Perakis Anastassios N.
Published: October 2005

A sequential hypothesis testing, optimal stopping problem in underwater acoustic detection is formulated and solved using dynamic programming. The problem calls for deciding whether acoustic signals being received over long ranges in the ocean are due to a source or to ambient noise alone, so as to minimize the expected value of a specified cost function over a given time horizon. The cost function incorporates a constant cost per observation as well as terminal costs for false acceptance of either hypothesis. According to previous work by the authors, and without loss of generality, modeling the acoustic signals assumes a two-state discrete-time Markov process for each of the two hypotheses, the state of the process depending on whether the intensity of the signal at the receiver is above a specified threshold or not. The decision process presented is based on observations of the signal’s ‘‘interarrival times,’’ that is, the time intervals between two successive detection events. The algorithm is then extended into more than two alternative hypotheses (several ‘‘false’’ targets) and results using both simulated and experimental acoustic data for the two and three hypotheses cases are presented. Computational issues in implementing the algorithms as well as possible extensions of this work are finally discussed.
Transverse stresses in plane and cylindrical Rayleigh waves
Authors: Lee D. A. , Crane R. L. , Stubbs D. A.
Published: October 2005

Plane and cylindrical Rayleigh waves are shown to involve tractions perpendicular to the propagation direction, on planes perpendicular to both the free surface and direction of propagation. Experiments show that backscatter from interruptions of these transverse tractions is sufficiently efficient to allow the observation of planar cracks the planes of which are perpendicular to the free surface and contain the propagation direction.
Rayleigh waves in a poroelastic half-space
Authors: Tajuddin M.
Published: October 2005

The propagation of Rayleigh waves in a poroelastic half-space is investigated for pervious and impervious surfaces. It is seen that the solutions presented by Jones for ‘‘Rayleigh waves in a porous elastic saturated solid’’ [J. Acoust. Soc. Am. 33, 959–962 (1961)] are incorrect. A plot of phase velocity versus Poisson’s ratio is presented.
Distortion and harmonic generation in the nearfield of a finite amplitude sound beam
Authors: Aanonsen Sigurd Ivar , Barkve Tor , Tjo/tta Jacqueline Naze , Tjo/tta Sigve
Published: October 2005

Distortion and harmonic generation in the nearfield of a finite amplitude sound beam are considered, assuming time-periodic but otherwise arbitrary on-source conditions. The basic equations of motion for a lossy fluid are simplified by utilizing the parabolic approximation, and the solution is derived by seeking a Fourier series expansion for the sound pressure. The harmonics are governed by an infinite set of coupled differential equations in the amplitudes, which are truncated and solved numerically. Amplitude and phase of the fundamental and the first few harmonics are calculated along the beam axis, and across the beam at various ranges from the source. Two cases for the source are considered and compared: one with a uniformly excited circular piston, and one with a Gaussian distribution. Various source levels are used, and the calculations are carried out into the shock region. The on-axis results for the fundamental amplitude are compared with results derived using the linearized solution modified with various taper functions. Apart from a nonlinear tapering of the amplitude along and near the axis, the results are found to be very close to the linearized solution for the fundamental, and for the second harmonic close to what is obtained from a quasilinear theory. The wave profile is calculated at various ranges. An energy equation for each harmonic is obtained, and shown to be equivalent within our approximation to the three-dimensional version of Westervelt’s energy equation. Recent works on one-dimensional propagation are reviewed and compared.
Ray directions, wave normals, and rigorous ray tracing
Authors: Floyd Edward R.
Published: October 2005

Herein some exact effective sound velocity profiles for rigorous ray tracing are developed numerically. The equations of motion for rigorous ray tracing are developed and it is shown that in general a ray is not normal to the wave surfaces of constant phase.
Sonar estimates of seafloor microroughness
Authors: Stanton T. K.
Published: October 2005

This paper presents an analysis of the effects of microroughness of the ocean bottom on a sonar signal. The results best apply to features where the roughness amplitude is less than one-quarter of an acoustic wavelength such as with ripples, beds of rocks, and nodules. The shape of the probability density function (PDF) of the echo envelope is examined in terms of the rms roughness and a new parameter, the correlation area of the bottom. The area is equal to the product of the x and y correlation distances along the floor. The PDF is shown to be extremely sensitive to small changes in the roughness. Furthermore by determining the rms roughness from standard coherent reflection measurements, the correlation area may be extracted directly from the PDF. Thus both vertical as well as lateral information is obtainable from sonar data. The technique can be used to discriminate between different types of bottoms that may have the same roughness but different correlation areas, for example a floor with ripples versus one with rocks or nodules. The analysis combines (1) a general statistical model employing the Rice PDF [S. O. Rice, in Selected Papers on Noise and Stochastic Processes, edited by N. Wax (Dover, New York, 1954), pp. 133–294], and (2) a theory originated by Eckart [C. Eckart, J. Acoust. Soc. Am. 25, 566–570 (1953)]. The analysis is applied to sonar data collected from the continental shelf near Cape Hatteras, North Carolina. The results are consistent with the known characteristics of the area.
Speech coding in the auditory nerve: III. Voiceless fricative consonants
Authors: Delgutte Bertrand , Kiang Nelson Y. S.
Published: October 2005

Responses of auditory-nerve fibers in anesthetized cats were recorded for synthetic voiceless fricative consonants. The four stimuli (/x/, /š/, /s/, and /f/) were presented at two levels corresponding to speech in which the levels of the vowels would be approximately 60 and 75 dB SPL, respectively. Discharge patterns were characterized in terms of PST histograms and their power spectra. For both stimulus levels, frequency regions in which the stimuli had considerable energy corresponded well with characteristic-frequency (CF) regions in which average discharge rates were the highest. At the higher level, the profiles of discharge rate against CF were more distinctive for the stimulus onset than for the central portion. Power spectra of PST histograms had large response components near fiber characteristic frequencies for CFs up to 3–4 kHz, as well as low-frequency components for all fibers. The relative amplitudes of these components varied for the different stimuli. In general, the formant frequencies of the fricatives did not correspond with the largest response components, except for formants below about 3 kHz. Processing schemes based on fine time patterns of discharge that were effective for vowel stimuli generally failed to extract the formant frequencies of fricatives.
Speech coding in the auditory nerve: IV. Sounds with consonant-like dynamic characteristics
Authors: Delgutte Bertrand , Kiang Nelson Y. S.
Published: October 2005

Discharge patterns of auditory-nerve fibers in anesthetized cats were obtained for two stimulus levels in response to synthetic stimuli with dynamic characteristics appropriate for selected consonants. A set of stimuli was constructed by preceding a signal that was identified as /da/ by another sound that was systematically manipulated so that the entire complex would sound like either /da/, /ada/, /na/, /σa/, /sa/, or others. Discharge rates of auditory-nerve fibers in response to the common /da/-like formant transitions depended on the preceding context. Average discharge rates during these transitions decreased most for fibers whose CFs were in frequency regions where the context had considerable energy. Some effect of the preceding context on fine time patterns of response to the transitions was also found, but the identity of the largest response components (which often corresponded to the formant frequencies) was in general unaffected. Thus the response patterns during the formant transitions contain cues about both the nature of the transitions and the preceding context. A second set of stimuli sounding like /σ/ and /C/ was obtained by varying the duration of the rise in amplitude at the onset of a filtered noise burst. At both 45 and 60 dB SPL, there were fibers which showed a more prominent peak in discharge rate at stimulus onset for /C/ than for /σ/, but the CF regions that reflected the clearest distinctions depended on stimulus level. The peaks in discharge rate that occur in response to rapid changes in amplitude or spectrum might be used by the central processor as pointers to portions of speech signals that are rich in phonetic information.
Nearfield effects in acoustic scattering
Authors: Hackman Roger H. , Werby M. F.
Published: October 2005

We investigate the scattering of the radiation from an acoustic point source by a solid, elastic prolate spheroid at a variety of transducer–scatterer separations. We find that the most important effect, when contrasted to the plane-wave limit, is an increase in scattering strength (with decreasing transducer–scatterer separation) associated with the 1/r variation of the incident field and the finite size of the scatterer. We use the results of this investigation to formulate a rough criterion for establishing the farfield region in scale model scattering experiments in the low-frequency region.
A fast and simple nonlinear technique for high-resolution beamforming and spectral analysis
Authors: Wagstaff Ronald A. , Berrou Jean-Louis
Published: October 2005

A simple and fast approximate technique is presented that can generate high-resolution spectra from the output of a conventional processor (i.e., beamformer or spectrum analyzer). The speed and simplicity of the algorithm results from two factors: the input data of the system are not used, only the conventional output data; the significant mathematical operations are simple additions and subtractions of log-transformed quantities, which make the technique nonlinear in power and avoids matrix inversions. As a result, the technique is extremely robust, being relatively insensitive to system and measurement errors. The algorithm is explained and results are presented for both modeled and measured data.
Diversity of adaptation patterns in responses of eighth nerve fibers in the bullfrog, R
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Authors: Megela Andrea L.
Published: October 2005

The firing patterns of eighth nerve fibers in the bullfrog, Rana catesbeiana, were analyzed for responses to long duration tone bursts at best excitatory frequency (BEF) and at frequencies along the upper and lower boundaries of the excitatory tuning curve of each fiber. These firing patterns were used as an index of the degree of short-term adaptation of each fiber. Amphibian papilla fibers (with BEFs 100–1000 Hz) exhibited marked diversity in their firing patterns to BEF tones, ranging from very flat or tonic (sustained responses throughout the duration of the stimulus) to very peaked or phasic (responding primarily or exclusively to stimulus onset). Moreover, the degree of short-term adaptation shown by an individual fiber varied with stimulating frequency. The firing patterns of amphibian papilla fibers tended to become more tonic as stimulus frequency was lowered below BEF; conversely, as stimulus frequency was increased above BEF, firing patterns either showed little change from that at BEF, or became more phasic. A similar frequency dependence of adaptation has not been reported in responses of mammalian eighth nerve fibers with comparable BEFs. The firing patterns of basilar papilla fibers (BEFs greater than 1000 Hz) remained similar in response to both BEF and non-BEF tones. These data reveal that the firing patterns and degrees of short-term adaptation of amphibian papilla fibers vary considerably across the tuning curve, whereas those of basilar papilla fibers remain relatively more constant with changes in stimulating frequency. These data also suggest that the amphibian papilla and the basilar papilla may play different roles in the use of physiological adaptation as a dimension for coding of information in sounds by the bullfrog.
Amplitude modulation thresholds in chinchillas with high-frequency hearing loss
Authors: Henderson Donald , Salvi Richard , Pavek Gary , Hamernik Roger
Published: October 2005

Estimates of auditory temporal resolution were obtained from normal chinchillas using sinusoidally amplitude modulated noise. Afterwards, the animals were exposed to noise whose bandwidth was progressively increased toward the low frequencies in octave steps. The first exposure was to an octave band of noise centered at 8 kHz. Three additional octave bands of noise were subsequently added to the original exposure in order to progressively increase the extent of the high-frequency hearing loss. The first exposure produced a temporary hearing loss of 50 to 60 dB near 8 kHz and elevated the amplitude modulation thresholds primarily at intermediate (128 Hz) modulation frequencies. Successive noise exposures extended the temporary hearing loss toward lower frequencies, but there was little further deterioration in the amplitude modulation function until the last exposure when the hearing loss spread to 1 kHz. The degradation in the amplitude modulation function observed after the last exposure, however, was due to a reduction in the sensation level of the test signal rather than to a decrease in the hearing bandwidth. The results of this study suggest that the high-frequency regions of the cochlea may be important for temporal resolution.
The influence of pinnae-based spectral cues on sound localization
Authors: Musicant Alan D. , Butler Robert A.
Published: October 2005

The role of pinnae-based spectral cues was investigated by requiring listeners to locate sound, binaurally, in the horizontal plane with and without partial occlusion of their external ears. The main finding was that the high frequencies were necessary for optimal performance. When the stimulus contained the higher audio frequencies, e.g., broadband and 4.0-kHz high-pass noise, localization accuracy was significantly superior to that recorded for stimuli consisting only of the lower frequencies (4.0- and 1.0-kHz low-pass noise). This finding was attributed to the influence of the spectral cues furnished by the pinnae, for when the stimulus composition included high frequencies, pinnae occlusion resulted in a marked decline in localization accuracy. Numerous front–rear reversals occurred. Moreover, the ability to distinguish among sounds originating within the same quadrant also suffered. Performance proficiency for the low-pass stimuli was not further degraded under conditions of pinnae occlusion. In locating the 4.0-kHz high-pass noise when both, neither, or only one ear was occluded, the data demonstrated unequivocally that the pinna-based cues of the ‘‘near’’ ear contributed powerfully toward localization accuracy.
The discrimination of vowel duration by infants
Authors: Eilers Rebecca E. , Bull Dale H. , Oller D. Kimbrough , Lewis Diana C.
Published: October 2005

Three groups of nine 5–11-month-old infants provided evidence of discrimination of speechlike stimuli differing only in vowel duration. Ease of discrimination was directly related to the magnitude of the ratio of the longer to shorter vowel. Group one infants discriminated three vowel duration contrasts (with ratios of 0.33, 0.67, and 1.0) embedded in a synthetic /mad/ syllable; group two discriminated these same duration contrasts within the bisyllable /samad/, and group three in the trisyllable /masamad/. In all cases, the contrasting durations were carried by the last vowel of the synthetic word. These same three infant groups failed to provide evidence of discrimination of a final position released stop consonant contrast (/mat/ versus /mad/) cued by voice excitation during closure of the /d/ and not the /t/. These results suggest that vowel duration may be a primary cue for infants’ perception of the voicing of final position stop consonants.
Fresnel diffraction: Some extensions of the theory
Authors: Hasegawa Takahi , Inoue Naoki , Matsuzawa Kiichiro
Published: October 2005

The rigorous expansion developed by the present authors for the velocity potential of a circular piston source [J. Acoust. Soc. Am. 74, 1044–1047 (1983)] is extended to include the space average pressure in the nearfield and the Fresnel diffraction of incident plane waves by an infinitely thin rigid disk. The present theoretical framework has the remarkable advantage that it includes neither approximations nor numerical integrations.
New ultrasonic modeling findings on Rayleigh wave propagation and their implications
Authors: Chamuel Jacques R.
Published: October 2005

The presence of unexplained large attenuation of low-frequency components and inverted dispersion of Rayleigh waves crossing the ocean-continent margin, the Tibetan Plateau, and the Iranian Plateau are examples of complex unsolved problems on Rayleigh wave propagation across vertical seismic boundaries. New ultrasonic modeling findings on Rayleigh wave propagation across step changes in elevation using two- and three-dimensional models are described explaining the previously mentioned phenomena. Laboratory seismic ultrasonic modeling results on Tibet are presented matching actual field data. Physical insights into the cause of the inverted dispersion and attenuation are obtained from the experimental results. Implications of the new findings indicate the need to reconsider the current ocean-continent margin, the Tibetan Plateau, and the Iranian Plateau crustal structure models. Contrary to the current belief of the presence of a deep low velocity layer (possibly partially molten) at 30 km below the surface of the Tibetan Plateau, the new reported findings support the author’s concept of a low attenuation solid crustal structure with monotonically increasing velocity with depth.
Vibration of a plate with arbitrary shape in contact with a fluid
Authors: Nagaya Kosuke , Takeuchi Jun
Published: October 2005

This paper is concerned with a method for solving vibration problems of arbitrarily shaped plates in contact with a fluid. Expressions of natural frequencies, displacements, and pressures for arbitrary plates in contact with a fluid are obtained with consideration of viscosity of fluid. The analysis applies the exact solution of the equations of motion and the Fourier expansion collocation method for satisfying the boundary conditions. Numerical calculations have been carried out for elliptical plates and rectangular plates with round corners in contact with a fluid.
Statistical distribution of free pathlengths in the acoustics of enclosures
Authors: Benedetto Giuliana , Spagnolo Renato
Published: October 2005

In the acoustics of enclosures it is often necessary to know the probability density function of free pathlengths. Some applications are reported of Coleman’s formula for the exact computation of the distribution and moments in ergodic regular enclosures. The results are compared with those obtained by computer ray-tracing simulation in the case of the specular reflection law. It is shown that the distribution is strictly connected to the shape of the enclosure.
Expanding sound created by a time-varying acoustic source in an arbitrarily oriented subsonic passage above a finite impedance reflecting ground surface
Authors: Chee-Seng Lim
Published: October 2005

An arbitrarily time-varying concentrated real source travels above a finite impedance (nonrigid) ground surface in an arbitrary direction. Sound transmission commences at zero instant. The impedance-modified reflected sound field is posed as a derivative of an intermediary field induced by the acoustic potential of an ‘‘underground’’ traveling image source. A general solution is then established in closed form for a subsonic source passage. The known impedance-independent acoustic potential of the image source together with an impedance-dependent transform of the temporal source factor constitute the reflected field. Superposed reflected and direct sounds expand inside a growing reflected front which, for an aerial source position at zero instant, trails above-ground behind a growing radiated front. The latter advances into a receding expanse of silence. Only direct sound evolves between both fronts. The reflected front must overtake the subsonic source; this, in turn, lags permanently behind the radiated front. Explicit results are deduced for time-invariant transmission. The sound field of a vertically ascending time-varying source is next investigated; it turns out to be axisymmetric. A large-time approximation discloses, for a time-invariant stationary source, an impedance supported transient superposed upon an impedance independent static field which ultimately survives in the steady state. Finally, if the traveling source emits a sequence of singular impulses, then reflection produces a sequential nonconcentric expansion of reflected fronts, each (i) conveying a singular but temporally attenuated distinct echo that is partially impedance influenced and (ii) enclosing an impedance-sustained nonsingular elongated reflected sound.
PERUSE: A numerical treatment of rough surface scattering for the parabolic wave equation
Authors: Dozier Lewis B.
Published: October 2005

Scattering of underwater acoustic signals from real ocean surfaces often does not fit into any of the classical theoretical approaches to the problem. Thus the need for a numerical approach is clear. A novel method is presented that uses a sequence of conformal mappings to locally flatten successive segments of the surface, which is assumed piecewise linear and frozen in time. Each conformal mapping preserves the elliptic form of the reduced wave equation, so that in each transformed space the parabolic approximation can be made and the solution advanced one range step using the split-step Fourier algorithm. This PERUSE (PE RoUgh SurfacE) numerical method is validated by exhibiting classically predicted Bragg angle peaks for single scatter of a plane wave from a sinusoidal surface. For multiple rough surface scattering in surface ducts, PERUSE results are analyzed by resolution in depth into the virtual modes of Labianca [J. Acoust. Soc. Am. 53, 1137–1147 (1973)]. The resulting modal intensities are then plotted as functions of range, and decay rates are estimated for each mode. Comparison with a classical ray-based scattering theory shows no obvious correlation; it appears that there is significant mode coupling due to the rough surface.
Application of two-variable Taylor series to the ray theory of propagation in an unbound medium
Authors: Hall Marshall
Published: October 2005

The Taylor series method is applied to the ray theory solution for the acoustic field near the initial caustic of the first convergence zone. This field is formed by a pair of rays that are heading downward at the source and upward at the receiver. The ray parameter (namely the phase velocity) of each ray is expressed as a two-variable Taylor series in horizontal range and depth relative to a fixed expansion point. The terms of the series are calculated for derivatives up to fifth order. The method is applied to a typical oceanic example modeled by a bilinear sound-speed profile in which the caustic of the rays passes the expansion point at vertical distances of 15–60 m and at horizontal distances of 200–1200 m, respectively. The Taylor-series phase velocities are inserted into the usual ray theory expressions for relative energy and travel time. It is found in some cases that satisfactory accuracy is obtained over a region of the ocean that is sufficiently large for sonar application. The advantage of this new approach is that, to calculate the sound field at a grid of points within a region, the (relatively expensive) iterative method of determining ray parameters need be applied to only one expansion point.
Basic and applied research on tactile aids for deaf people: Progress and prospects
Authors: Sherrick Carl E.
Published: October 2005

A brief introduction describes the alternative methods for replacement of the sense of hearing, including the educational procedures of sign language and lipreading, the medical procedure of cochlear implants, and the sensory substitution procedures of visual or tactual displays. For the tactual displays, which are most commonly electronically activated, a listing of desirable objectives is discussed in some detail. Among these are a better understanding of the processing capabilities of the skin, the form an efficient transducer may take, and what features of the speech stream may most profitably be extracted for processing and display to the sense of touch. Because the technology for device design and production in this area is seriously retarded, a great amount of space is devoted to the precise specification of a transducer for the tactile display; included is a discussion of direct electrocutaneous stimulation as a realistic alternative. A number of multichannel displays exist, and several of these may be workable systems if their transducer elements can be kept small and use little energy. What is of current, even urgent, importance is the early and widespread deployment of a single-channel tactile aid to permit the general assessment of the effectiveness of a simple sensory adjuvant for a deaf person who has lipreading skills.
Reflection of finite acoustic beams from loaded and stiffened half-spaces
Authors: Nayfeh A. H. , Chimenti D. E.
Published: October 2005

Results of theoretical calculations and experimental measurements on the reflection of finite acoustic beams from a fluid–solid interace in the presence of a loading or stiffening layer on the solid are presented. Measurements with Gaussian-profile acoustic beams are reported on wave-speed dispersion and reflected-beam amplitude distribution for stiffening layers of chromium on either brass or stainless steel. Good agreement is generally observed. Detailed results of calculations of the reflection coefficient to delineate the behavior of cutoff modes for both stiffened and loaded half-spaces are given. A straightforward method for deducing the complex Rayleigh wavenumber directly from the reflection coefficient is discussed. Comparisons between direct numerical integration of the reflected beam distribution and results of an extended analytical model demonstrate decreasing accuracy of the latter as one nears a mode cutoff.
Diffraction on locally reacting surface—Schroeder’s diffusor
Authors: Qian Z. W.
Published: October 2005

In the process of sound scattering, we treat the scattering surface as a radiating source yielding the scattered sound wave. On the basis of this idea, the scattering problems of a locally reacting surface (the one- and two-dimensional Schroeder’s diffusor) are investigated when the incident wave is a plane wave or a pulse signal. A Schroeder’s diffusor with complex impedance is suggested.
Combined effect of two suppressors
Authors: Weber Daniel L.
Published: October 2005

Threshold for a 10-ms sinusoidal signal was measured as a function of signal frequency (0.65 to 1.40 kHz) in several forward-masking conditions. For signal frequencies near 1.0 kHz, the forward masking produced by a 395-ms, 100-Hz-wide noise centered at 1.0 kHz (total power 60 dB) could be reduced by the addition of a sinusoid to the noise. The effects of four sinusoidal suppressors (frequencies of 0.70, 0.85, 1.15, and 1.40 kHz, all at 75 dB SPL) were examined individually and in the six possible pairwise combinations. In general, the threshold reduction produced by two suppressors together was no greater than the larger of the reductions produced by the suppressors individually. It appears that suppression produced by different stimuli does not combine to yield significantly larger effects. Instead, the amount of suppression appears to be restricted to a specific range and it is not possible to exceed this limit.
The influence of temporal cues on the strength of periodicity pitches
Authors: Lundeen Conrad , Small Arnold M.
Published: October 2005

Three different waveforms were generated from the same component frequencies by setting the phase of the components so they were either homophasic (all component sinusoids start at 0°), diphasic (sinusoids alternate between −45° and + 45°), or heterophasic (starting phase randomly selected). Listeners were asked to rate the saliency of all periodicity pitches they could detect in stimuli which contained 12 or more components at frequencies above the region where pitches were perceived. A major finding was that the highest ratings of fundamental frequency ( f1) pitch ‘‘strength’’ were always obtained for homophasic waveforms, which among the test stimuli have the most abrupt envelope fluctuations. In contrast, diphasic and heterophasic waveforms, which have smoother envelopes, yielded lower pitch strength estimates at f1 and higher ratings two octaves above the fundamental. These data indicate that information concerning the stimulus waveform envelope influences the relative prominence of competing pitches evoked by periodicity pitch stimuli. However, no one-to-one correspondence between pitch and waveform periodicity is apparent.
An evaluation of some assumptions underlying the articulation index
Authors: Pavlovic Chaslav V. , Studebaker Gerald A.
Published: October 2005

The purposes of this investigation were to derive measurement and calculation procedures for the articulation index (AI) that were as precise and accurate as possible, and to evaluate the significance of the differences in assumptions made by early investigators. A nonsense syllable test specifically designed for this application was recorded. The implications of various assumptions utilized in different approaches to predicting speech sound identification were tested using 13 different conditions which differed with respect to filtering, level of interfering noise, or level of the speech signal. The listeners were three normal hearing individuals. A set of preferred assumptions was chosen based on a post hoc evaluation of the data. Predictions of speech sound identification were good, both for the average listener and for individual listeners.
The acoustic features of vervet monkey grunts
Authors: Seyfarth Robert M. , Cheney Dorothy L.
Published: October 2005

East African vervet monkeys give short (125 ms), harsh-sounding grunts to each other in a variety of social situations: when approaching a dominant or subordinate member of their group, when moving into a new area of their range, or upon seeing another group. Although all these vocalizations sound similar to humans, field playback experiments have shown that the monkeys distinguish at least four different calls. Acoustic analysis reveals that grunts have an aperiodic F0, at roughly 240 Hz. Most grunts exhibit a spectral peak close to this irregular F0. Grunts may also contain a second, rising or falling frequency peak, between 550 and 900 Hz. The location and changes in these two frequency peaks are the cues most likely to be used by vervets when distinguishing different grunt types.
Multiphase backing materials for piezoelectric broadband transducers
Authors: Bar-Cohen Y. , Stubbs D. A. , Hoppe W. C.
Published: October 2005

A multiphase, high-impedance damper to be used as a backing material for broadband piezoelectric transducers is described. The use of three or more phases, including a high-impedance alloy matrix, allows dampers to be made reproducibly which have acoustical impedances in the range of 20–45×105 g/(cm2⋅s). A simple model based upon the elastic properties of the constituents is described which was developed to predict the impedance of multiphase mixtures. This model was experimentally verified for two- and three-phase mixtures. Using this model a combination of tungsten, copper, and an indium–lead alloy was chosen as an optimum transducer backing. A backing made from these constituents was pressed onto a 10-MHz, PZT-5A blank, and the results of the pulse–echo response are presented.
Enhanced sound power from a recurved flute
Authors: Coltman John W.
Published: October 2005

A Boehm flute with a recurved headjoint that folds part of the column back on itself exhibits an increase in sound power of 2–3 dB at the lower frequencies, and similar reductions in output at some higher frequencies. The effect is due to shortening the separation between the two sound sources of the instrument.
Acoustoelasticity in transversely isotropic materials
Authors: Johnson George C. , Mase G. Thomas
Published: October 2005

The acoustoelastic response of a transversely isotropic body loaded in plane stress is computed for arbitrarily severe anisotropy. Relations for the propagation speeds of longitudinal and shear waves propagating normal to the plane of stress are given as functions of the stress. The shear wave results are combined to obtain expressions for the polarization direction, which in general differs from the principal directions of stress or strain, and the magnitude of the ultrasonic birefringence as given by the difference in transit time per unit length of the two shear waves. Similar expressions derived previously for slightly anisotropic bodies are recalled and are compared to the present results. It is shown that the earlier results are special cases of the more general model discussed here and a numerical investigation of the acoustoelastic response of several materials indicates that the assumptions leading to these more restricted models may not be valid, even in materials which at first glance appear to be slightly anisotropic.
Thin shell theories and acoustic wave scattering by infinitely long cylindrical shells of arbitrary cross section
Authors: Baskar S. , Varadan V. V. , Varadan V. K.
Published: October 2005

The scattering of acoustic waves by an infinitely long cylindrical shell immersed in a fluid is analyzed. A new approach has been proposed using thin shell theory incorporating the impedance of the shell in the T-matrix formulation. Numerical results are presented for the farfield backscattering amplitude as a function of frequency. Calculations were made for infinitely long circular and elliptic cylindrical shells immersed in water for various shell thicknesses for waves incident at an arbitrary angle in the plane normal to the axis of the cylinder. The impedance resulting from the use of various shell theory approximations for circular cylindrical shells is presented. Love–Timoshenko and Flügge–Byrne–Lurye theories for circular cylindrical shells have been compared with the full elasticity solution using the separation of variables approach. Comments have been made regarding the range of applicability of various shell theories.
Generation of acoustic waves by an impulsive point source in a fluid/solid configuration with a plane boundary
Authors: de Hoop Adrianus T. , van der Hijden J. H. M. T.
Published: October 2005

The space–time acoustic wave motion generated by an impulsive monopole point source in a fluid/solid configuration with a plane boundary is calculated with the aid of the modified Cagniard technique. The source is located in the fluid, and numerical results are presented for the reflected-wave acoustic pressure, especially in those regions of space where head-wave contributions occur. There is a marked difference in time response in the different regimes that exist for the wave speed in the fluid in relation to the different wave speeds (compressional, shear, Rayleigh) in the solid. These differences are of importance to the situation where the reflected wave in the fluid is used to determine experimentally the elastic properties of the solid.
Rough surface scattering via the smoothing method
Authors: Watson John G. , Keller Joseph B.
Published: October 2005

The smoothing method is used to find the first two moments, i.e., the mean and the two-point two-time correlation function, of the field scattered by a rough surface. The results are expressed in terms of a reflection coefficient and a differential scattering coefficient. They are compared with those found by several other methods.
The impulse response of a focused source with an arbitrary axisymmetric surface velocity distribution
Authors: Verhoef W. A. , Cloostermans M. J. T. M. , Thijssen J. M.
Published: October 2005

An analytical expression for the impulse response of a focused transducer with an axisymmetric nonuniform surface velocity distribution is derived using a finite polynomial expansion of the velocity distribution function. A computing scheme is presented for the numerical calculation of the transient pressure at an observation point in front of the transducer. The effect of various nonuniform velocity distributions on the characteristics of the pressure field of a medium focused transducer is shown with grey-scale pictures of calculated continuous-wave and pulsed pressure distributions.
High-temperature acoustic bond compatible with fluoride fluorites. II. Transverse ultrasonic measurements in barium fluoride
Authors: Manasreh M. O. , Pederson D. O.
Published: October 2005

The ultrasonic pulse-echo technique method has been used to measure high-temperature acoustic wave velocities and ultrasonic attenuation in [110] oriented, single-crystal, barium fluoride. DuPont 9770 silver–platinum paste was used as an effective acoustic bond for transverse ultrasonic velocities for the first time. The velocity measurements for two different shear wave polarization directions have been made over a temperature range of 300 °K to approximately 1200 °K allowing calculations of the elastic constants C44 and (C11–C12) to be made. Ultrasonic attenuation measurements for one polarization were also made. Both (C11–C12) and the attenuation measurements begin anomalous behavior just below the diffuse solid electrolyte transition in barium fluoride at 1235 °K.
Reflection characteristics of longitudinal waves in a semi-infinite cylindrical rod connected to an infinite elastic stratum
Authors: Wada Hiroshi
Published: October 2005

Reflection characteristics of longitudinal strain waves in a semi-infinite cylindrical rod connected to an infinite elastic stratum are investigated analytically. Applying three-dimensional elasticity theory to the stratum and making use of Laplace transformations with respect to time and numerical inverse Laplace transformations, the time histories for the longitudinal strain at an arbitrary point of the rod are presented. Numerical results obtained from three-dimensional elasticity theory are compared with numerical results obtained from Mindlin plate theory, classical plate theory, and experimental results. When the stratum is stiff compared with the rod, the reflected waves from the interface between the stratum and the rod, which are obtained from the three theories, i.e., three-dimensional elasticity theory, Mindlin plate theory, and classical plate theory, are nearly coincident with one another. On the contrary, when the stratum is flexible compared with the rod, they are different from one another. The stratum may be considered as a half-space for a stratum thickness ratio (stratum thickness/rod radius) κ≥8.0 in the case of the stiff stratum, while it may be considered as a half-space for κ≥15.0 in the case of the flexible stratum.
The functional analysis of auditory discrimination
Authors: Harrison J. M.
Published: October 2005

Mammals have evolved the ability to acquire auditory discriminations. The characteristics of this discriminative ability presumably fit the natural conditions under which discriminations are normally acquired. The purpose of this paper is to review experiments which were directed at showing that auditory discriminations are most rapidly acquired when natural features are incorporated into the experiments. The experiments were also directed at discovering the underlying characteristics of the discriminative ability. When animals were trained to discriminate the position of a sound source in which natural features were incorporated into the experiment, the discrimination was acquired in one trial. Manipulation of the natural features suggested that one trial acquisition depends upon the following. (1) Stimulus novelty; the effect of reinforcement is stronger in the presence of novel than familiar stimuli. (2) Specific behavioral effect of reinforcement; the effect of reinforcing a response in the presence of a novel auditory stimulus is to increase the strength of approaching and manipulating the sound source.