bluuebunny/crossref_metadata_2025 huggingface dataset:
Layer stripping approaches to inverse scattering for inhomogeneous viscoelastic media
Authors: Yagle Andrew E.
Published: October 2005

Two different layer recursive algorithms for reconstructing an inhomogeneous viscoelastic medium are presented. A viscoelastic medium is one whose stress–strain relation is not instantaneous, in that the present stress depends on past strains. Hence, the inverse scattering problem for such media involves the reconstruction of functions varying in time as well as in space; thus it is much more difficult than the inverse problem for simple acoustic media. Both algorithms reconstruct an inhomogeneous viscoelastic medium whose wave speed c(z) and elastic modulus G(z,t) vary with position; variations in density ρ(z) can also be reconstructed using the first algorithm. The first algorithm requires as data the steady-state reflection response of the medium to a point harmonic source at a wide range of frequencies. The second algorithm requires as data only the reflection response to a normally incident plane wave, but applies only to layered media whose relaxation times are less than the two-way travel time through a layer. Several computer simulations illustrate the performance of the algorithm on synthetic data.
Detectability of words and nonwords in two kinds of noise
Authors: Repp Bruno H. , Frost Ram
Published: October 2005

Recent models of speech perception emphasize the possibility of interactions among different processing levels. There is evidence that the lexical status of an utterance (i.e., whether it is a meaningful word or not) may influence earlier stages of perceptual analysis. To test how far down such ‘‘top-down’’ influences might penetrate, an investigation was conducted to determine whether there is a difference in detectability of words and nonwords masked by amplitude-modulated or unmodulated broadband noise. The results were negative, suggesting either that the stages of perceptual analysis engaged in the detection task are impermeable to lexical top-down effects, or that the lexical level was not sufficiently activated to have any facilitative effect on perception.
The development of skill in producing word-final English stops: Kinematic parameters
Authors: Flege James Emil
Published: October 2005

It was hypothesized that native English adults would be more skillful in producing word-final English /p/ and /b/ than native English children who, in turn, would be more skillful in doing so than adult native speakers of a language (Mandarin Chinese) that does not possess word-final stops. A video tracking system was used to monitor lip and jaw movements. The subjects in all three groups made vowels significantly longer before /b/ than /p/, but the effect seen for the English subjects was three times as large as the Chinese subjects’ effect and depended less on differences in lip closing velocity for /b/ and /p/. The English subjects also showed a difference in duration between /a/ and /i/ that was twice as large as the difference seen for the Chinese subjects. Of the three groups, only the English adults showed significantly greater displacement and peak movement velocity for the final stop consonant of /bap/ than /bab/. This suggested that their central phonetic representations specified a more forceful constriction of the lips for /p/ than /b/. The English adults seemed to compensate more effectively for a bite block in producing the final stops in /bip/ and /bib/. The results obtained for the English children were intermediate to those obtained for the English and Chinese adults, which is consistent with the hypothesized experience-based differences in level of skill.
Acoustic analysis of compensatory articulation in children
Authors: Baum Shari R. , Katz William F.
Published: October 2005

A study was undertaken to explore the effects of fixing the mandible with a bite block on the formant frequencies of the vowels [i a u] produced by two groups of children aged 4 and 5 and 7 and 8 years. Vowels produced in both normal and bite-block conditions were submitted to LPC analysis with windows placed over the first glottal pulse and at the vowel midpoint. For both groups of children, no differences were found in the frequencies of either the first or second formant between the normal and bite-block conditions. Results are discussed in relation to theories of the acquisition of speech motor control.
Superposition of geometries of surface for desired directional reflections in a concert hall
Authors: Ando Yoichi , Sakamoto Masaru
Published: October 2005

In order to obtain desired directional reflections of boundary walls in a concert hall, which may greatly depend upon the frequency range of sound [Y. Ando and Y. Kurihara, J. Acoust. Soc. Am. 80, 833–836 (1986)], a method of superposing geometries of surface is proposed.
A method to account for acoustic microstreaming when predicting bubble growth rates produced by rectified diffusion
Authors: Church Charles C.
Published: October 2005

A reinterpretation of existing theory for rectified diffusion, the process by which bubbles in a sound field may grow in radius, is presented in order to quantitate the effect of acoustic microstreaming on bubble growth rates. The 1/t term in the growth rate equation is defined as the ‘‘decay term’’ and t as the ‘‘decay time,’’ the time required for the gas concentration in the liquid contacting the bubble to rise (or fall) from its initial to its final value. In the absence of microstreaming, t is the duration of sonification. In the presence of microstreaming, t may be calculated from the streaming velocity and the bubble radius. A comparison between theory and the experimental results of Eller [A. Eller, J. Acoust. Soc. Am. 46, 1246–1250 (1969)] and of Gould [R. K. Gould, J. Acoust. Soc. Am. 56, 1740–1746 (1974)] shows reasonable agreement in the low kHz range. Theoretical results in the frequency range of 1–10 MHz at 1 and 4 bar are also presented.
Shallow water acoustic studies using an air-suspended water waveguide model
Authors: Chamuel Jacques R. , Brooke Gary H.
Published: October 2005

A novel experimental technique is introduced that allows multimode interference and coupling due to boundary topography and to the presence of scatterers in shallow water acoustic waveguides to be studied in the absence of radiation and elastic bottom effects. The air-suspended water waveguide model consists of a water layer bounded above by air and below by a thin rubber membrane supported by pressurized air to counteract the weight of the water. Experimental data on the transmission of transient ultrasonic signals along the ‘‘perfect’’ waveguide are presented and compared with theory. Both experimental and numerical results are used to demonstrate that multiple nondispersed discrete pulses in a waveguide are equivalent to a summation of highly dispersed waveguide modes. Preliminary experimental results are also given demonstrating the propagation of transient acoustic waves in a free-fluid layer waveguide with sloped or periodic boundaries.
Measurements of upslope wave-front curvature in a sand-bottom wedge
Authors: Hobaek H. , Westwood Evan K.
Published: October 2005

The results of an experiment designed to measure the curvature of wave fronts traveling upslope in a water wedge having a sand bottom and an air surface are presented. In the experiment, a point source emits a narrow-band pulse in the deep end of the wedge, and the resulting waveforms are measured on a vertical line in the shallow end of the wedge. Analysis of the recorded waveforms indicates that the wave fronts upslope from the source are curved and that the probable center of the curvature is the apex of the wedge. These results are in agreement with theoretical predictions for a wedge with perfectly reflecting boundaries, where the normal modes are referenced to circular arcs around the apex.
Reply to ‘‘Comments on ‘On the measurement of glottal flow’ ’’ [J. Acoust. Soc. Am. 8
5, 2672–2673 (1989)]
Authors: Cranen B. , Boves L.
Published: October 2005

In this letter, the authors reply to comments written by R. S. McGowan [J. Acoust. Soc. Am. 85, xxx–xxx (1989)] on an earlier article by Cranen and Boves [J. Acoust. Soc. Am. 84, 888–900 (1988)]. [AIP]
Comment on ‘‘Transfer function method of measuring acoustic intensity in a duct system with flow’’ [J. Acoust. Soc. Am. 6
8, 1570–1577 (1980)]
Authors: Park Chan Surk , Kim J. W.
Published: October 2005

The authors have found a minor correction to the subscripts and the omission of a variable of integration in the subject publication. These may be typographical errors and are noted for information to users.
Unfolding axial caustics of glory scattering with harmonic angular perturbations of toroidal wave fronts
Authors: Arnott W. Patrick , Marston Philip L.
Published: October 2005

Axisymmetric toroidal wave fronts are pertinent to the near forward and backward scattering by objects that have rotational symmetry. For spheres, the wave field produced by such a wave front is known as glory scattering. As the wave front propagates, some porton of it becomes focused on an axis, forming a structurally unstable line caustic. A specific class of harmonic perturbations of the wave front shape is considered that leads to unfoldings of the axial caustic. When the wave front shape is perturbed to have two-fold rotational and mirror symmetry, the unfolded caustic is a four-cusped astroid curve. The three-fold symmetric perturbed wave front propagates to produce a hypocycloid caustic with three cusps. In general, perturbed wave fronts with p-fold rotational and mirror symmetry have caustics of cusped stars, with p cusps when p is odd, and 2p cusps when p is even. These wave front perturbations have applications to scattering from symmetric, slightly nonspherical, homogeneous objects such as spheroids. Wave fields are computed using a Fresnel approximation of the diffraction integral. The wave field patterns associated with astroid caustics are displayed. They have features similar to Pearcey patterns. Applications to backscattering from spheroids, distorted torii, and axicon reflectors are noted. Certain inverse problems are considered. An inequality is given for determining the magnitude of wave front perturbations needed to cause a significant change in the wave field from that of a spherical scatterer. The merging of rays as the observation direction moves across the caustic is discussed using concepts from catastrophe optics. A novel expression in polar coordinates is given for the Hessian associated with propagation.
Oblique acoustic wave propagation through a slotted waveguide
Authors: Lahlou Rochdi , Amram Maurice , Ostiguy Germain
Published: October 2005

The behavior of a wide rectangular slotted waveguide subjected to low-frequency spherical waves incident along its surface has been investigated theoretically and experimentally. A mathematical model, borrowed from the theory of electromagnetic surface waves, propagating across a slotted metallic surface at an oblique angle to the teeth, was adapted to acoustics by using an electrical mobility analogy. Expressions giving the amplitude and phase variation as functions of the frequency and the wave direction were derived. The analytical predictions match quite well the experimental results up to 400 Hz (within a maximum deviation of 20° for the phase and 1.5 dB for the amplitude). Above this frequency, there is a discrepancy due to the physical difference between the real waveguide (with a symmetrical half-part) and the mathematical model used for modeling the surface waves propagation (without the symmetrical half-part).
The asymptotics of evanescent fields in waveguides
Authors: Sen Rahul
Published: October 2005

Evanescent fields produced by the scattering of an incident wave in a waveguide play a vital role in determining farfield amplitudes. Neglecting the interaction between evanescent and traveling modes can lead to a severe restriction on the dynamic range of a theory. This has been overlooked in asymptotic theories of scattering, mainly because evanescent modes decay rapidly in space. Some fundamental mathematical issues are involved in the asymptotics of evanescent modes. These are discussed, and a new asymptotic matching technique is developed. The technique is capable of treating, in a rational manner, asymptotic expansions that are not in Poincaré form. Using it as a basis, a general theory of scattering in variable-area waveguides is also developed. It is seen that in contrast to previous theories, wave fields must be described by singular expansions, so that evanescent fields may be included.
Calculations of turbulent boundary layer pressure fluctuations transmitted into a viscoelastic layer
Authors: Ko Sung H. , Schloemer Howard H.
Published: October 2005

The development of a model for calculating the turbulent boundary layer pressure fluctuations transmitted into a viscoelastic layer is presented. The transmitted flow noise received by a rectangular hydrophone embedded in the elastomer layer was calculated using the turbulent wall pressure spectrum developed by Corcos [J. Acoust. Soc. Am. 18, 353–378 (1964)]. Wave vector spectral densities of turbulent wall pressure models developed by Corcos and Chase [J. Sound Vib. 70, 29–67 (1980)] are discussed. A transfer function representing a layer of elastomer as a wave vector filter and spatial averaging over a rectangular hydrophone are also described.
Effects of liquid relaxation time on S
H surface waves liquid sensors
Authors: Josse Fabien , Shana Zack
Published: October 2005

Effects of liquid relaxation time on the propagation characteristics of shear horizontal (SH) surface waves at the interface between a piezoelectric crystal and a fluid medium are theoretically analyzed for liquid sensor applications. General closed-form expressions are derived for both velocity change and attenuation coefficient for a Maxwellian viscoelastic fluid that can be treated as a Newtonian fluid or as an amorphous solid, depending on the liquid shear relaxation time. It is shown that relaxation time becomes important as the liquid viscosity and/or the wave frequency increases. The result is a saturation level in the propagation loss and the device sensor frequency shift as the liquid relaxation time approaches the wave period. The effect of liquid relaxation is thus to set detection limits on the range of liquid vicosity that can be measured. However, it is also shown that in actual sensor applications, a trade-off can be performed between the maximum measurable viscosity and the SH surface wave device frequency of operation, and thus the device sensitivity.
Time- and frequency-domain characteristics of laser-generated ultrasonic surface waves
Authors: Scala C. M. , Doyle P. A.
Published: October 2005

The generation of elastic waves by illumination of a free metal surface with a laser pulse was studied to establish a quantitative basis for laser ultrasonics in nondestructive evaluation of surfaces. Experiments were carried out using a Q-switched Nd:YAG laser for generation and a wideband piezoelectric sensor for detection. A theoretical model for laser generation was developed for the thermoelastic energy regime. This model integrates over point source Green’s functions, suitably spread throughout the illuminated region. Good agreement was found between experiment and theory for characteristics in both time and frequency domains, for surface waves excited in the thermoelastic regime. For a given laser pulse energy, the highest Rayleigh wave peak frequency and bandwidth occurred when the Gaussian laser-beam half-width a was reduced just enough to begin surface damage. Once such damage commenced, further spot size reduction slightly lowered the peak frequency. Quantitative agreement with theory was found for the observed dependence, on both source–receiver distance and a, of the amplitudes for both the Rayleigh wave and the surface wave traveling at the bulk pressure wave speed (sP). In the nearfield, the sP wave overlapped the Rayleigh wave and made a greater contribution to the observed waveform than in the farfield.
Is it necessary to measure hearing protector attenuation at 3.15 and 6.3 kHz?
Authors: Berger E. H. , Rowland L. D.
Published: October 2005

The real-ear attenuation data for 81 different hearing protectors were analyzed with respect to the errors that would arise if, instead of averaging the 1/3-octave-band results at 3.15 and 4 kHz and 6.3 and 8 kHz, respectively, the octave-band attenuation at 4 and 8 kHz was estimated from only the 1/3-octave-band data at those two frequencies. Errors as large as 3–4 dB were found to occur in rare instances, but more typically were in the range of 0.5–1.5 dB. However, in terms of computation of an overall noise reduction rating such as the NRR, the effect of excluding the 3.15- and 6.3-kHz data led to errors that averaged only 0.1 dB and never exceeded 0.3 dB, except in one instance, where the error was 0.6 dB. It was concluded that there is little value in measuring real-ear attenuation in a diffuse sound field at the frequencies of 3.15 and 6.3 kHz for applications in which hearing protector attenuation data are normally utilized.
Prediction of the spectrum of atmospheric microburst noise in the range 2–20 Hz: Preliminary results
Authors: Hardin Jay C. , Pope D. Stuart
Published: October 2005

An engineering estimate of the spectrum of atmospheric microburst noise radiation in the range 2–20 Hz is developed. This prediction is obtained via a marriage of standard aeroacoustic theory with a numerical computation of the relevant fluid dynamics. The ‘‘computational aeroacoustics’’ technique applied here to the interpretation of atmospheric noise measurements is illustrative of a methodology that can now be employed in a wide class of problems.
Free vibrations of nonuniform beams with rotational and translational restraints and subjected to an axial force
Authors: Yeh F. H. , Liu W. H.
Published: October 2005

The analytical method and Galerkin’s method with beam functions are used to solve the uniform and nonuniform beams with restrained boundary conditions and carrying intermediate masses and are subjected to an axial tensile or compressive force. The effects due to the degree of rotational and translational constraints, variation of the beam depth, magnitude of intermediate mass and its location, and axial tensile or compressive force are examined in detail. Some of the results are compared with different methods, and agreement between them is obtained.
Comments on ‘‘Passive synthetic arrays’’ [J. Acoust. Soc. Am. 8
4, 592–598 (1988)]
Authors: Carey William M.
Published: October 2005

The purpose of this letter is to formally comment on the accuracy of the ‘‘Background and Introduction’’ and the ‘‘Conclusions’’ sections of the article ‘‘Passive synthetic arrays’’ [S. W. Autrey, J. Acoust. Soc. Am. 84, 592–598 (1988)].
Modification of matched filtering for finite-aperture holographic imaging systems
Authors: Lee Hua
Published: October 2005

In this letter, a modified version of the matched filter for holographic imaging with finite-aperture systems is provided. The purpose of the modification is to achieve uniform resolving capability over the entire source region. The modification is formulated in the spatial-frequency domain by utilizing the knowledge of the source region and aperture size. The modification is especially significant for imaging systems with detached apertures and scattered source distributions.
Holographic acoustic microscopy for quantitative velocity profile imaging
Authors: Lee Hua , Chiao Richard Y.
Published: October 2005

In this letter, a new approach is reported for the quantitative measurement of the acoustic velocity profile with the scanning laser acoustic microscope operating in the holographic mode. Due to the addition of a quadrature detector, the acoustic microscope is now capable of holographic recording of the complex wave field. As a result, it enables one to estimate the velocity profile with superior resolving capability directly from the wave field distribution instead of from the interferometry fringe patterns of the conventional methods.
A nonlinear matched-field processor for detection and localization of a quiet source in a noisy shallow-water environment
Authors: Smith G. B. , Feuillade C. , Del Balzo D. R. , Byrne C. L.
Published: October 2005

Matched-field processing is a technique that has been developed for the detection and localization of an acoustic source in an underwater environment. Conventional matched-field processing utilizes cross correlations between the complex acoustic pressures measured from the elements of a submerged array of hydrophones and theoretically predicted complex acoustic pressures obtained from an appropriate model of the environment with an assumed source location. Modal matched-field processing has been recently developed for the detection and localization of an acoustic source in a shallow-water waveguide environment, where modal propagation of acoustic energy dominates. Modal matched-field processing utilizes the cross correlations between predicted complex modal amplitudes and complex modal amplitudes calculated from the measured complex pressures. The ambient noise field in a shallow-water environment has a correlated component that propagates to the hydrophone array through the discrete, trapped modes of the waveguide. Cross correlations due to this modal noise compete with signal cross correlations in the cross-spectral matrix used in conventional matched-field processing. In this article, it is shown that modal noise coming from a large number of discrete, randomly distributed, farfield sources contributes insignificantly to the off-diagonal elements of the cross-spectral matrix used in modal matched-field processing. This is to be contrasted with signal cross correlations, which contribute significantly to these off-diagonal elements. This provides a separation of signal from noise that is not available with conventional matched-field processing. In this article, nonlinear (off-diagonal), modal matched-field processing algorithms are demonstrated that exploit this separation of signal and modal noise. The superiority of these off-diagonal algorithms over conventional matched-field processing in a low signal-to-noise situation is demonstrated using computer simulations of a shallow-water Pekeris waveguide.
Ultrasonic interferometric characterization of highly attenuative materials
Authors: Batra N. K. , Delsanto P. P.
Published: October 2005

Experimental techniques for the ultrasonic characterization of materials usually aim at the determination of either their ultrasonic velocity or their attenuation. In this article, a technique is presented that allows a simultaneous measurement of both. It provides, also, a method for a quantitative nondestructive evaluation of material irregularities. This technique is based on the propagation of ultrasonsic continuous waves through a slab of material, designed in the shape of a wedge, and on a correlation analysis between reference (incident) and received signals. Experiments performed on several specimens of various polymers confirm the efficiency and reliability of the method.
An acoustic head simulator for hearing protector evaluation. I: Design and construction
Authors: Kunov Hans , Giguère Christian
Published: October 2005

As an alternative to subjective methods, an acoustic head simulator was constructed for hearing protector evaluation. The primary purpose of the device is for hearing protector testing and research under high-level steady-state and impulse noise environments. The design is based on the KEMAR manikin and therefore approximates the physical dimensions and the acoustical eardrum impedance of the median human adult. The head simulator includes a mechanical reproduction of the human circumaural and intraaural tissues with a silicone rubber material. A compliant head–neck system was constructed to approximate the vibrational characteristics of the human head in a sound field in order to simulate the inertia effect of earmuffs. The bone-conducted sounds are not mechanically reproduced in the design. Applications for the device are reported in a companion article [C. Giguère and H. Kunov, J. Acoust. Soc. Am. 85, 1197–1205 (1989)].
Localization of multiple broadband targets via frequency domain adaptive beamforming for planar arrays
Authors: Ziomek Lawrence J. , Behrle Charles D.
Published: October 2005

Computer simulation studies of a frequency domain adaptive beamforming algorithm for planar arrays are presented. The algorithm, which can localize multiple broadband targets, is a modified complex least-mean-square (LMS) adaptive algorithm, and can process an arbitrary number of harmonics. The algorithm provides estimates of both the depression and bearing angles of incident plane-wave fields. Computer simulation results are presented comparing the average depression and bearing angle estimation errors as a function of the input signal-to-noise ratio (SNR) at a single element in the array, sampling rate, and harmonic number. The ‘‘full angular coverage’’ capability of the algorithm was also tested.
Detection thresholds for sinusoidal frequency modulation
Authors: Demany Laurent , Semal Catherine
Published: October 2005

An adaptive forced-choice procedure was used to measure, in four normal-hearing subjects, detection thresholds for sinusoidal frequency modulation as a function of carrier frequency ( fc, from 250 to 4000 Hz) and modulation frequency ( fmod, from 1 to 64 Hz). The results show that, for a wide range of fmod values, fc and fmod have almost independent effects on the thresholds when the thresholds are expressed as just-noticeable frequency swings and plotted on a log scale. In two subjects, the effect of fc on the thresholds was compared to the effect of standard frequency on the frequency just noticeable differences (jnd’s) of successive and steady tones. In agreement with previous data [(H. Fastl, J. Acoust. Soc. Am. 63, 275–277 (1978)], it was found that the two effects are significantly different if the frequency jnd’s are measured with long-duration tones. However, it was also found that the two effects are similar if the frequency jnd’s are measured with 25-ms tones. These results support the idea that, at least for low fmod values, the detection of continuous and periodic frequency modulations is mediated by a pitch-sampling process using a temporal window of about 25 ms.
Frequency difference limens in normal and sensorineural hearing impaired chinchillas
Authors: Prosen Cynthia A. , Halpern D. Lynn , Dallos Peter
Published: October 2005

This study assessed normal frequency discrimination ability in the chinchilla and determined how this ability changes as a function of an experimentally induced sensorineural hearing loss. Four chinchillas were trained by the methods of positive reinforcement to report absolute thresholds and frequency difference limens (FDLs). Subjects were then treated with the aminoglycosidic antibiotic amikacin until a 30-dB hearing loss was measured at 10.0 kHz. Absolute and frequency difference thresholds were determined during and after drug treatment. When post-drug thresholds had stabilized, subjects were sacrificed and their cochleas stained, embedded in plastic, microdissected, and viewed with phase contrast microscopy to permit examination of the cochlear tissue. Post-drug data suggest that frequency discrimination at a high frequency is unaffected by a 40- to 45-dB sensorineural hearing loss, considerable hair cell damage, and the resultant disruption of the cochlear micromechanics. The data, in concert with previously published reports, suggest that FDLs may be less affected by a high-frequency sensorineural hearing loss than by a low-frequency sensorineural hearing loss.
Performance characterization of human pitch control system: An acoustic approach
Authors: Jafari Mehdi , Wong Kwok-Hung , Behbehani Khosrow , Kondraske George V.
Published: October 2005

The performance of the human pitch control system was characterized by measurement of the speed of pitch shift and pitch shift response speed (inverse of reaction time) at various initial pitch and loudness levels. Data from three nonsinger adult male subjects and one professional singer suggest a strong inverse correlation (r>0.78) between initial pitch and rate of pitch rise. This study showed no significant relation between initial loudness and rate of pitch rise. Also, vocal response speed showed no significant relation with either initial pitch or loudness. However, it is suggested that pitch shift response speed might be related to the second formant frequency of the target vowel. A composite index of pitch control performance capacity was defined as the product of response speed and vocal fold contractile velocity. From experimental data, the composite index was able to reflect a distinct 74% superior performance by the professional singer (relative to the average maximum performance capacity of nonsingers). It is suggested that the product-based composite index of performance capacity can serve as a sensitive means for vocal proficiency determination.
On the origin of increased backward radiation from a liquid–solid interface at the Rayleigh angle
Authors: Nagy Peter B. , Adler Laszlo
Published: October 2005

This letter describes a simple experimental technique to identify the physical source of increased backward radiation from a liquid–solid interface at the Rayleigh angle. Extensive spatial averaging is used to distinguish between the two principal mechanisms, namely back reflection as a finite beam effect and backscattering due to inherent material inhomogeneities. In all cases considered, the increased backward radiation was found to be caused exclusively by backscattering, and no appreciable back reflection was detected.
Spectral statistics in elastodynamics
Authors: Weaver R. L.
Published: October 2005

The fundamentals of acoustic modal statistics are investigated with a view toward applications in understanding fluctuation phenomena in room acoustics, statistical energy analysis, and diffuse field ultrasonics. It is conjectured that the spectral fluctuations of a linearly elastic body, like those of large nuclei, will fall into the universality class described by the Gaussian orthogonal ensemble of random matrices. This conjecture is strongly confirmed by a laboratory study of the higher eigenfrequencies of small aluminum blocks. Level repulsions and spectral rigidities are observed to conform to the predictions of random matrix theory.
Acoustical properties of drill strings
Authors: Drumheller Douglas S.
Published: October 2005

The recovery of petrochemical and geothermal resources requires extensive drilling of wells to increasingly greater depths. Real-time collection and telemetry of data about the drilling process while it occurs thousands of feet below the surface is an effective way of improving the efficiency of drilling operations. Unfortunately, due to hostile down-hole environments, telemetry of this data is an extremely difficult problem. Currently, commercial systems transmit data to the surface by producing pressure pulses within the portion of the drilling mud enclosed in the hollow steel drill string. Transmission rates are between 2 and 4 data bits per second. Any system capable of raising data rates without increasing the complexity of the drilling process will have significant economic impact. One alternative system is based upon acoustical carrier waves generated within the drill string itself. If developed, this method would accommodate data rates up to 100 bits per second. Unfortunately, the drill string is a periodic structure of pipe and threaded tool joints, the transmission characteristics are very complex and exhibit a banded and dispersive structure. Over the past 40 years, attempts to field systems based upon this transmission method have resulted in little success. This article examines this acoustical transmission problem in great detail. The basic principles of acoustic wave propagation in the periodic structure of the drill string are examined through theory, laboratory experiment, and field test. The results indicate the existence of frequency bands that are virtually free of attenuation and suitable for data transmission at high bit rates.
The shadow zone in a stratified medium
Authors: Makarewicz Rufin
Published: October 2005

Assuming that the variations of wind speed and sound speed are significantly less than the speed of sound close to the ground, the first and the second approximations of ray equations have been derived. The first approach yields the parabolic shape of a ray when the linear dependence of wind speed and sound speed upon height is assumed. In the instance of nonlinear dependence, the generalization of Ingard’s formulas, which determines the slant distance between the source and shadow boundary, is given. Both cases of linear and nonlinear shadow boundaries are defined by grazing rays when specific conditions are met.
A simple estimate of propagation loss fluctuations due to modal interference
Authors: Chapman David M. F.
Published: October 2005

A simple estimate of propagation loss fluctuations due to deterministic modal interference has been devised for use with normal mode computer codes. It is based upon the relative mode amplitudes, and is easy to compute along with the incoherent mode sum that is used to estimate average propagation loss. The estimated levels of propagation loss fluctuation compare favorably with those computed from the coherent mode sum for shallow water environments.
A nearfield asymptotic analysis for underwater acoustics
Authors: Collins Michael D.
Published: October 2005

The method of stationary phase is used to show that the homogeneous half-space field projects properly onto the normal modes near a point source. The half-space field is useful for initializing the parabolic equation (PE) in both the time domain and the frequency domain and in both two and three spatial dimensions. It is shown to be more accurate for wide-angle propagation than the Gaussian PE starter. A Gaussian time-domain PE starter is derived and compared with the half-space starter. Application of the approach to scattering problems is discussed. The half-space field is the inner solution of a matched asymptotics solution. A simple approach for speeding up PE calculations and an efficient ray-tracing model for source localization are motivated by the matching.
Headphone simulation of free-field listening. II: Psychophysical validation
Authors: Wightman Frederic L. , Kistler Doris J.
Published: October 2005

Listeners reported the apparent spatial positions of wideband noise bursts that were presented either by loudspeakers in free field or by headphones. The headphone stimuli were digitally processed with the aim of duplicating, at a listener’s eardrums, the waveforms that were produced by the free-field stimuli. The processing algorithms were based on each subject’s free-field-to-eardrum transfer functions that had been measured at 144 free-field source locations. The headphone stimuli were localized by eight subjects in virtually the same positions as the corresponding free-field stimuli. However, with headphone stimuli, there were more front–back confusions, and source elevation seemed slightly less well defined. One subject’s difficulty with elevation judgments, which was observed both with free-field and with headphone stimuli, was traced to distorted features of the free-field-to-eardrum transfer function.
High-frequency audiometry: Test reliability and procedural considerations
Authors: Stelmachowicz Patricia G. , Beauchaine Kathryn A. , Kalberer Ann , Kelly William J. , Jesteadt Walt
Published: October 2005

This study compared the reliability of a recently developed high-frequency audiometer (HFA) [Stevens et al., J. Acoust. Soc. Am. 81, 470–484 (1987)] with a less complicated system that uses supraaural earphones (Koss system). The new approach permits calibration on an individual basis, making it possible to express thresholds at high frequencies in dB SPL. Data obtained from 50 normal-hearing subjects, ranging in age from 10–60 years, were used to evaluate the effects on reliability of threshold variance, earpiece/earphone fitting variance, and the variance associated with the HFA calibration process. Without earpiece/earphone replacement, the reliability of thresholds for the two systems is similar. With replacement, the HFA showed poorer reliability than the Koss system above 11 kHz, largely due to errors in estimating the calibration function. HFA reliability is greater for subjects with valid calibration functions over the entire frequency range. When average correction factors are applied to the Koss data in an effort to convert threshold estimates to dB SPL, individual transfer functions are not represented accurately. Thus the benefit of being able to express thresholds at high frequencies in dB SPL must be weighed against the additional source of variability introduced by the HFA calibration process.
On the relation between subglottal pressure and fundamental frequency in phonation
Authors: Titze Ingo R.
Published: October 2005

The change in fundamental frequency with subglottal pressure in phonation is quantified on the basis of the ratio between vibrational amplitude and vocal fold length. This ratio is typically very small in stringed instruments, but becomes quite appreciable in vocal fold vibration. Tension in vocal fold tissues is, therefore, not constant over the vibratory cycle, and a dynamic tension gives rise to amplitude–frequency dependence. It is shown that the typical 2–6 Hz/cm H2O rise in fundamental frequency with subglottal pressure observed in human and canine larynges is a direct and predictable consequence of this amplitude–frequency dependence. Results are presently limited to phonation in the chest register.
Acoustic–phonetic characteristics of speech produced in noise and while wearing an oxygen mask
Authors: Bond Z. S. , Moore Thomas J. , Gable Beverley
Published: October 2005

The present study investigated changes in the prosodic and acoustic–phonetic features of isolated words by four male talkers speaking in quiet and in pink noise at a level of 95 dB SPL. Speech samples were collected both with and without an oxygen mask. Changes in duration, fundamental frequency, total energy, and formant center frequency were analyzed. In addition to the expected changes of increased pitch and amplitude associated with speaking in noise without an oxygen mask, significant effects were found (particularly in the formant center frequencies) as a result of using the oxygen mask. When the oxygen mask was employed, no further significant changes were caused by adding noise to the speaking situation.
In-plane flexural vibrations of nonuniform circular rings embedded in Winkler-type foundations
Authors: Filipich C. P. , Rosales M. B. , Laura P. A. A. , Rossi R. E.
Published: October 2005

Two approximate analytical solutions are obtained for the problem being considered by means of the Ritz method in the case of nonhomogeneous Winkler-type embedment of the ring. One solution makes use of polynomial coordinate functions that contain an exponential optimization parameter ‘‘γ,’’ which allows for minimization of the eigenvalues, while the other solution consists in approximating the ring response by means of sinusoidal functions. An independent numerical solution is also obtained using the finite element method.
Nonlinear scattering of crossed ultrasonic beams in the presence of turbulence in water. II: Theory
Authors: Korman Murray S. , Beyer Robert T.
Published: October 2005

A theoretical investigation is reported on the scattered (and radiated) sum frequency signals, generated nonlinearly from two finite-amplitude, mutually perpendicular ultrasonic beams intersecting (and interacting) in the presence of turbulence. This article forms a complement to experimental study of such interactions, previously published and referred to as Part I [M. S. Korman and R. T. Beyer, J. Acoust. Soc. Am. 84, 339–349 (1988)]. An investigation of the scattering to lowest order is from the cubic quadrupole source term in the Lighthill wave equation (the Reynolds stress tensor ρuiuj). This theory, combined with results by Kraichnan [J. Acoust. Soc. Am. 25, 1096–1104 (1953)] and Ishimaru [Wave Propagation and Scattering in Random Medium (Academic, New York, 1978), Vol. 2, Chap. 16], explains much of the experimental scattering phenomenon discussed in Part I.
Nonlinear acoustic phenomena due to bubble drift in a gas–liquid mixture
Authors: Kobelev Yu. A. , Ostrovsky L. A.
Published: October 2005

Nonlinear acoustic effects associated with collective dynamics of bubbles in a liquid are considered in this article. The mechanism of nonlinearity is caused by the variation of the bubble concentration in space due to bubble drift under the effect of radiation pressure and hydrodynamic (Bjerknes) forces (the latter may result in bubble coalescence). First, the individual behavior of a bubble or a pair of bubbles in an acoustic field is considered. Second, kinetic equations for the bubble distribution function in an acoustic field are derived, and, third, different effects of sound propagation are discussed. They include some steady-state and transient ‘‘envelope waves’’ propagating together with ‘‘concentration waves.’’ A simple model of ‘‘nonlinear transparency’’ in acoustics, which is in qualitative agreement with experimental results, is touched upon. A harmonic wave in a medium with homogeneous bubble distribution is shown to be unstable, and may possibly result in such effects as wave front conjugation, self-focusing of sound, and, probably, the formation of bubble groups.
Wave propagation in a thin cylinder that includes point masses
Authors: El-Raheb Michael , Wagner Paul
Published: October 2005

The propagation of elastic waves of the type induced by impact are studied for a special class of cylinders. In this class are thin finite cylinders, for which Mindlin’s equations are appropriate, on which point masses are attached. An approximation is derived valid for frequencies below cutoff of the lowest shear mode. An eigenfunction expansion is used to compute the transient response of the coupled system.
Nondisturbing acoustical measurement of flow fields—New developments and applications
Authors: Engler Rolf H. , Schmidt Dieter W. , Wagner Wolfgang J.
Published: October 2005

Among the diverse demands on useful methods of flow measurement, there is often a requirement for not disturbing the flow under test, especially in cases of flows near a limit of stability. An acoustic method based on the measurement of flow-induced variations of the travel time of sonic pulses or, equivalently, of the phase of continuous sound waves has been developed that fulfills this requirement perfectly. Moreover, it offers further valuable advantages including much shorter measuring times and higher accuracy than several other methods of measurement commonly in use. The apparatus is relatively inexpensive, with no calibration needed. It has now been applied to a number of investigations made possible by these capabilities. This article presents a survey of a variety of cases where the acoustic method has proven valuable for flow research.
Predictors of subsyllabic durations in speech motor control
Authors: Keller Eric
Published: October 2005

Speech motor control timing was examined by means of a multiple correlational analysis involving interarticulatory delay and speech rate as predictor variables, and four subsyllabic time segments of the syllable [ka] as dependent variables. The hypothesis was that the two putative temporal constraints have differential predictive capacity for various segments of the syllable. Results from 11 subjects were in support of the hypothesis. Syllable onset duration was reliably predicted by the linear addition of interarticulatory delay and speech rate, while the duration of the midportion of the syllable was nearly exclusively predicted by the overall speech rate. This model was found to be applicable to all conditions of normal and clenched teeth, context-free and contextual, normally paced and rapid speech production, with minor differences in predictive capacity for different conditions.
Stop-consonant recognition for normal-hearing listeners and listeners with high-frequency hearing loss. I: The contribution of selected frequency regions
Authors: Dubno Judy R. , Dirks Donald D. , Ellison David E.
Published: October 2005

The purpose of this study is to specify the contribution of certain frequency regions to consonant place perception for normal-hearing listeners and listeners with high-frequency hearing loss, and to characterize the differences in stop-consonant place perception among these listeners. Stop-consonant recognition and error patterns were examined at various speech-presentation levels and under conditions of low- and high-pass filtering. Subjects included 18 normal-hearing listeners and a homogeneous group of 10 young, hearing-impaired individuals with high-frequency sensorineural hearing loss. Differential filtering effects on consonant place perception were consistent with the spectral composition of acoustic cues. Differences in consonant recognition and error patterns between normal-hearing and hearing-impaired listeners were observed when the stimulus bandwidth included regions of threshold elevation for the hearing-impaired listeners. Thus place-perception differences among listeners are, for the most part, associated with stimulus bandwidths corresponding to regions of hearing loss.
A two-channel laser Doppler vibrometer technique for characterizing the dynamic properties of elastomeric materials
Authors: McDevitt Timothy E. , Stuart Alan D.
Published: October 2005

An optical technique is described for obtaining the dynamic loss factor and Young’s modulus of elastomeric materials. The technique involves a two-channel laser Doppler vibrometer for measuring the relative amplitude and phase at two points on a longitudinally excited material sample. Replacing the two accelerometers ordinarily used in this materials characterization technique with nonintrusive laser probes offers numerous advantages. The primary advantage is the simplification of the mathematical procedure for obtaining the material properties, since end mass (accelerometer) effects can be discarded. Results from a test conducted to compare optical and accelerometer data show very good agreement except at frequencies where the sample and/or test apparatus exhibit a high degree of flexural motion. The lack of agreement in these cases is explained. In such cases, it is recommended that the optics be rotated in order to detect these flexural modes so that they can be avoided, if warranted, when evaluating the longitudinal response of the sample.
Pseudo-three-dimensional reconstruction of ultrasonic images of the tongue
Authors: Watkin Kenneth L. , Rubin Jonathan M.
Published: October 2005

The purpose of the present investigation was to develop a method for the three-dimensional reconstruction of the surface of the tongue using serial ultrasonic images gathered during the production of the sustained fricative /s/. Using a phased linear array ultrasonic monitoring system, transducer position, subject position, and ultrasonic scan data were recorded simultaneously on composite video for off-line analysis. Reconstruction of a series of ultrasound images was completed using a microcomputer programmed to transform the ultrasonic image contours into three-dimensional space. Additional transformations converting the three-dimensional tongue contours into two dimensions for screen plotting were also developed. Results are discussed in light of previously reported models of the tongue surface.