bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of measurement system effects in ultrasonic scattering experiments
Authors: Waag Robert C. , Astheimer Jeffery P.
Published: October 2005

A general model is developed to characterize the effect of an ultrasonic measurement system on the experimental determination of ultrasonic scattering as a function of angle and frequency. The model includes arbitrary emitter beams and detector apertures as angular spectra of plane waves. Arbitrary emitted pulses and detector time gates are incorporated through frequency spectra of temporal harmonics. A transformation of variables is employed to express the spectrum of the measured pressure as a product in wave space of a system function and the Fourier transform of the medium variations. The mean-square value of the measured pressure spectrum is similarly expressed as a product of the squared magnitude of the system function and the power spectrum of the medium variations. The measured quantities are shown to become scaled values of intrinsic scattering characteristics when the system function weight is concentrated relative to the medium characteristics in wave space. The assumption of an indefinitely long detector gate is used to represent the system function as a product in which one factor is a beam function dependent on spatial frequency and the other factors are dependent on temporal frequency. Beam-function calculations as well as calculations of second moments and overall beam weight are made for identical Gaussian-shaped emitter and detector apertures to illustrate the blurring and weighting effects of measurement system beam patterns as a function of scattering angle. The moment calculations are shown to identify circumstances when the medium variation function can be factored out from under the integral and the measurement represented as a simple product of the medium properties and a measurement system weight. The results may be used to design scattering experiments in which degradations due to system effects are within acceptable limits.
Application of the method of multiple scales to linear waveguide boundary value problems
Authors: Anderson M. J. , Vaidya P. G.
Published: October 2005

The perturbation analysis method of multiple scales is applied to the problem of linear sound propagation in a rectangular waveguide with viscous and thermal dissipation effects at the boundary. In the past, the method of multiple scales has been applied to the corresponding problem of finite level fluctuations in a waveguide. The second-order solution (representing the first correction due to nonlinearity) cited in these investigations would however preclude the solution of the linear problem, as it grows without bound with the axial coordinate of the waveguide. In this investigation an alternate solution at second order is proposed, which is bounded throughout the spatial domain of the duct. This property of the alternate solution allows the linear problem to be solved, including the region arbitrarily close to the cutoff frequency for higher-order modes. In addition, the uniform solution may be directly applied to the analysis of finite level fluctuations, with consequences as yet unknown.
Regression equations for the transfer functions of ANSI S3.5-1969
Authors: Sherbecoe Robert L. , Studebaker Gerald A.
Published: October 2005

Regression equations for the transfer functions displayed in Fig. 15 of ANSI Standard S3.5-1969 are reported. Predicted values are within 2.15 percentage points of the expected values for most inputs.
Mode stretching and harmonic generation in the flute
Authors: Coltman John W.
Published: October 2005

Comparison of the resonance frequencies of modes in conical and cylindrical piccolos showed pronounced differences in the degree to which the octaves are stretched. Measurements for a note on a flute with only two modes showed that second harmonic generation and total radiated power were greatest when the modes were stretched 25 cents from an exact octave, supporting the idea that mode stretching may be beneficial in flutelike instruments.
Harmonic and melodic octave templates
Authors: Demany Laurent , Semal Catherine
Published: October 2005

For normal-hearing adult listeners, two simultaneous pure tones with a frequency ratio close to 2/1 may perceptually fuse into a single sound, which shows that such listeners are sensitive to ‘‘octave harmony.’’ Many adult listeners are also able to consistently adjust two successive pure tones ‘‘one octave apart,’’ which shows that they possess melodic octave templates. According to Terhardt [J. Acoust. Soc. Am. 55, 1061–1069 (1974)], melodic octave templates and the perception of octave harmony originate from a common learning process taking place in early life. In the two experiments reported here, subjects performed repeated octave adjustments for pairs of simultaneous and successive tone bursts. Both tones were presented monaurally, at 45 or 65 dB SPL. The frequency of the lower tone (fref) was an independent variable, while the frequency of the higher tone was adjustable within a 500-cent range. In some conditions, when the two tones were presented simultaneously, they were sinusoidally frequency modulated in a coherent manner, at a rate of 2 or 4 Hz; the aim of this frequency modulation was to force the subjects to adopt a synthetic listening strategy, i.e., to base their adjustments on perceived harmony. For fref values ranging from 270–2000 Hz, subjects performed consistent adjustments when the tones were presented successively: fref had little effect on the adjustments’ variability. However, in the same frequency range, the variability of the harmonic adjustments markedly increased with fref ; for the highest fref values, it was much greater than the variability of the melodic adjustments. The results suggest that, in adult listeners, the perception of octave harmony disappears at frequencies for which melodic octaves are still accurately perceived.
Transient wave estimation: A multichannel deconvolution application
Authors: Candy J. V. , Ziolkowski R. W. , Kent Lewis D.
Published: October 2005

The evolution of new concepts in wave theory have led to proof-in-principle experiments aimed at validating the generation of a specified wave front. Not only have these concepts initiated research in transient wave theory, but they have also caused renewed effort in multichannel signal processing. In this paper, the development of a processor to deconvolve a transient acoustic wave from sensor array measurements is discussed. The design of the multichannel deconvolver coupled with model-based signal processing techniques using acoustic pressure field measurements is discussed. Here, it is shown that an efficient solution to this problem can be obtained using a vector form of the Levinson–Wiggins–Robinson (LWR) algorithm.
Transient waves: Reconstruction and processing
Authors: Candy J. V. , Ziolkowski R. W. , Lewis D. Kent
Published: October 2005

New solutions to the wave equation have been shown to exhibit enhanced localization and energy fluence characteristics. The transmission and reception of these localized waves create unique problems, since they are essentially transient wave fronts in both time and space. Nonetheless, the ability to transmit wave energy through space with these interesting properties has many potential applications in a variety of applications areas. To realize their potential, new methods must be developed to analyze and process these waves. In this paper, approaches to design receiving arrays to reconstruct these special transient waves from noisy measurement data are discussed.
Atmospheric absorption of sound: Update
Authors: Bass H. E. , Sutherland L. C. , Zuckerwar A. J.
Published: October 2005

Best current expressions for the vibrational relaxation times of oxygen and nitrogen in the atmosphere are used to compute total absorption. The resulting graphs of total absorption as a function of frequency for different humidities should be used in lieu of the graph published earlier by Evans et al. [J. Acoust. Soc. Am. 51, 1565–1575 (1972)].
Perception of amplitude envelope variations of pulsatile electrotactile stimuli
Authors: Blamey P. J. , Alcantara J. I. , Cowan R. S. C. , Galvin K. L. , Sarant J. Z. , Clark G. M.
Published: October 2005

Gross variations of the speech amplitude envelope, such as the duration of different segments and the gaps between them, carry information about prosody and some segmental features of vowels and consonants. The amplitude envelope is one parameter encoded by the Tickle Talker, an electrotactile speech processor for the hearing impaired which stimulates the digital nerve bundles with a pulsatile electric current. Psychophysical experiments measuring the duration discrimination and identification, gap detection, and integration times for pulsatile electrical stimulation are described and compared with similar auditory measures for normal and impaired hearing and electrical stimulation via a cochlear implant. The tactile duration limen of 15% for a 300-ms standard was similar to auditory measures. Tactile gap detection thresholds of 9 to 20 ms were larger than for normal-hearing but shorter than for some hearing-impaired listeners and cochlear implant users. The electrotactile integration time of about 250 ms was shorter than previously measured tactile values but longer than auditory integration times. The results indicate that the gross amplitude envelope variations should be conveyed well by the Tickle Talker. Short bursts of low amplitude are the features most likely to be poorly perceived.
Amplitude and frequency fluctuations of spontaneous otoacoustic emissions
Authors: van Dijk Pim , Wit Hero P.
Published: October 2005

Amplitude and frequency fluctuations of spontaneous otoacoustic emissions have been studied. Spontaneous otoacoustic emissions were recorded from eight human ears and two frog ears (Rana esculenta). Record length typically was 80 s. For a recorded emission signal, the amplitude signal A(t) (average A0) and time intervals T(ti) between successive positive-going zero crossings (i counts zero crossings) were determined. Emission amplitude and period both showed small fluctuations: δArms/A0 ranged from 0.7×10−2 to 6.3×10−2 for human emissions and was 24×10−2 for both frog emissions; δTrms ranged from 1.4 to 6.9×10−7 s for human emission and was 50.0 and 55.0×10−7 s for the two frog emissions. There was a positive correlation between δArms/A0 and δTrms as determined for different emissions (R=0.9). Spectra of A(t) and T(ti) revealed that amplitude and period were slowly fluctuating functions: cutoff frequency ΔfδA of the amplitude spectrum ranged from 3 to 18 Hz; ΔfδT ranged from 7 to 32 Hz. Results have been compared to amplitude and frequency fluctuations of a second-order oscillator, that interacts with a noise source. It has been concluded that an oscillator with linear stiffness (for example a Van der Pol oscillator) driven by white Gaussian noise, cannot account for all experimental results. Other possible oscillators (e.g., nonlinear stiffness) and noise sources (e.g., narrow-band noise), that may account for the observed phenomena, are discussed.
What type of force does the cochlear amplifier produce?
Authors: Kolston Paul J. , de Boer Egbert , Viergever Max A. , Smoorenburg Guido F.
Published: October 2005

Recent experimental measurements suggest that the mechanical displacement of the basilar membrane (BM) near threshold in a viable mammalian cochlea is greater than 10−8 cm, for a stimulus sound-pressure level at the eardrum of 20 μPa. The associated response peak is very sensitive to the physiological condition of the cochlea. In the formulation of all recent cochlear models, it has been explicitly assumed that this peak is produced by the cochlear amplifier injecting a large amount of energy into the cochlea, thereby altering the real component of the BM impedance. In this paper, a new cochlear model is described which produces a realistic response by assuming that the cochlear amplifier force acts at a phase such that the main effect is to reduce the imaginary component of the BM impedance. In this new model, the magnitude of the cochlear amplifier force required to produce a realistic response is much smaller than in the previous models. It is suggested that future experimental investigations should attempt to determine both the magnitude and the phase of the forces associated with the cochlear amplifier.
Critical behavior of the ultrasonic attenuation and velocity and shear viscosity for the binary mixture of nitrobenzene-n-hexane
Authors: Abdelraziq Issam R. , Yun S. S. , Stumpf F. B.
Published: October 2005

Ultrasonic velocity and absorption as a function of temperature, concentration, and frequency (5–25 MHz) and shear viscosity as a function of concentration and temperature are reported for the binary mixture nitrobenzene-n-hexane in the homogeneous phase above Tc. For the observed absorption at critical concentration and critical temperature αc/f2 vs f−1.06 yields a straight line as predicted by the dynamic scaling theory of Ferrell and Bhattacharjee [Phys. Rev. A 24, 1643 (1981)]. Also, the critical amplitudes of the thermal expansion and specific heat have been calculated using the two-scale factor universality relation. The adiabatic coupling constant g is calculated and compared to the experimental value. In addition, the experimental values of α/αc (where α is the absorption at critical concentration above the critical temperature) for nitrobenzene-n-hexane are compared to the scaling function F(ω*) and show a good agreement with the theory. Finally, the velocity for the system at the critical concentration above the critical temperature appears to decrease linearly with increasing temperature.
Ultrasonic studies in aqueous solutions of rare earth nitrates
Authors: Tandon S. P. , Gambhir S.
Published: October 2005

Ultrasonic velocity at 3 MHz has been measured at 32 °C using a variable path interferometer in the aqueous solutions of nitrates of lanthanum, cerium, terbium, and dysprosium at various concentrations ranging from 0.01 to 1.0 mol/ℓ. The various acoustic parameters, namely, the molar sound velocity, adiabatic compressibility, specific acoustic impedance, and relative association for these solutions have been computed. The variation of these constants with concentration has been discussed. The dependence of these constants on other parameters like atomic weight and ionic radius of the cation has also been discussed. Ultrasonic velocity and other constants except adiabatic compressibility are found to increase with the concentration.
Low-frequency wind-generated ambient noise source levels
Authors: Kewley D. J. , Browning D. G. , Carey W. M.
Published: October 2005

Measurements of ambient noise (30–800 Hz) useful in characterizing the wind-generated component have been obtained in the low ship density Southern Hemisphere. Source levels that characterize the frequency and wind speed dependence of this noise have been obtained by Burgess and Kewley using vertical noise directionality data and had been implemented in a diagnostic computerized noise model. Northern Hemisphere vertical noise directionality data have been examined, processed for source level, and compared to these results. These data and other data summaries, when taking a two-mechanism viewpoint, are found to be consistent with respect to wind speed and frequency dependence. When a dipole source model, based on the possible physical mechanism of sound production, is used, a set of consistent source levels for wind-dependent noise are realized from the several data sets examined.
Influence of environmental conditions on acoustical properties of sea ice
Authors: Jezek K. C. , Stanton T. K. , Gow A. J. , Lange M. A.
Published: October 2005

Sonar echo amplitude data have been collected at carrier frequencies of 188 and 120 kHz from the underside of different sea ice types. Histograms of normal incidence echo amplitudes were formed from over 90 samples of each ice type. Experiments were conducted on saline ice grown in an outdoor pond under relatively controlled conditions at the USA Cold Regions Research and Engineering Laboratory (CRREL) and on the sea ice cover in the Fram Strait. Analysis shows marked variations (about a factor of 5) in the magnitude of the coherent reflection coefficients as congelation ice at the bottom of an ice sheet evolves from a growing dendritic interface to an ablating, thermally altered interface. Larger differences (about a factor of 10) are observed between growing congelation ice and slush ice, used to simulate frazil. These results indicate that important variations in acoustic regime exist in areas where different ice types are intermingled.
A novel method for the measurement of acoustic speed
Authors: Kuo I. Y. , Hete B. , Shung K. K.
Published: October 2005

Traditional methods for measuring acoustic speed require knowledge of either the specimen thickness or the distances between the transducers and the specimen. In general, the accuracy in measuring these quantities determines the accuracy of the experimental technique for measuring speed. This problem is particularly acute in measuring sound speed in biological specimens. A new method for measuring acoustic speed of materials, which eliminates the need for determining these quantities, has been developed. The technique, which necessitates the use of only one transducer, requires measurement of four times of flight of a sound pulse and the knowledge of the speed of sound in a reference fluid medium in which the specimen is placed. Ultrasonic speed in stainless steel and Plexiglas was measured using this method to verify its validity. Results on measurements on porcine liver, myocardium, and soft fat are also reported.
Some factors affecting the magnitude of comodulation masking release
Authors: Moore Brian C. J. , Hall Joseph W. , Grose John H. , Schooneveldt Gregory P.
Published: October 2005

This paper examines some of the factors that can affect the magnitude of comodulation masking release (CMR). In experiment I, psychometric functions were measured for the detection of a 1-kHz sinusoidal signal in a ‘‘multiplied’’ narrow-band noise centered at 1 kHz (reference condition) and the same noise with two comodulated flanking bands added. The functions were slightly steeper for the comodulated than for the reference masker. Thus CMRs measured at a high percent correct point were slightly (0.4 dB) larger than CMRs measured at a low percent correct point. Large individual differences were found for the reference masker but not for the comodulated masker. Experiment II compared CMRs obtained with narrow-band Gaussian noise and multiplied noise, using a single flanking band. For a flanking band remote from the signal frequency, the CMRs were smaller and more variable for the multiplied noise than for the Gaussian noise. This variability arose mainly from individual differences in the reference condition. Experiment III compared growth-of-masking functions for a signal centered in Gaussian noise and multiplied noise. Thresholds were lower for the multiplied than for the Gaussian noise, and the differences were greatest at high noise levels. The results are consistent with the idea that, for multiplied noise, some subjects can detect a change in the distribution of the envelope of the stimulus, when the signal is added to the masker. Such subjects have low thresholds in the reference condition, and give small CMRs. Other subjects are relatively insensitive to this cue. They have higher thresholds in the reference condition, and give larger CMRs. For Gaussian noise, thresholds for the reference condition are relatively stable across subjects and CMRs tend to be substantial, even for flanking-band frequencies remote from the signal frequency.
Hearing a mistuned harmonic in an otherwise periodic complex tone
Authors: Hartmann William Morris , McAdams Stephen , Smith Bennett K.
Published: October 2005

The ability of a listener to detect a mistuned harmonic in an otherwise periodic tone is representative of the capacity to segregate auditory entities on the basis of steady-state signal cues. By use of a task in which listeners matched the pitch of a mistuned harmonic, this ability has been studied, in order to find dependences on mistuned harmonic number, fundamental frequency, signal level, and signal duration. The results considerably augment the data previously obtained from discrimination experiments and from experiments in which listeners counted apparent sources. Although previous work has emphasized the role of spectral resolution in the segregation process, the present work suggests that neural synchrony is an important consideration; our data show that listeners lose the ability to segregate mistuned harmonics at high frequencies where synchronous neural firing vanishes. The functional form of this loss is insensitive to the spacing of the harmonics. The matching experiment also permits the measurement of the pitches of mistuned harmonics. The data exhibit shifts of a form that argues against models of pitch shifts that are based entirely upon partial masking.
Sound velocity and related physical properties of fine-grained abyssal sediments from the Brazil Basin (South Atlantic Ocean)
Authors: Orsi Thomas H. , Dunn Dean A.
Published: October 2005

Empirical relationships between compressional wave (sound) velocity and selected physical properties have been determined for fine-grained abyssal sediments from the east Brazilian continental margin and Pernambuco abyssal plain of the Brazil Basin (NW South Atlantic Ocean). Porosity and wet bulk density were found to be the best sedimentological indices to sound velocity. In agreement with numerous other studies, other sediment properties were lesser, but still very good, indices. In order of decreasing statistical significance, these properties include mean grain size and percent clay. Averaged values of sediment physical properties of the Brazil Basin were compared with the published results of Hamilton and Bachman [J. Acoust. Soc. Am. 72, 1891–1904 (1982)] and show good agreement. The observed differences between the two studies were insignificant and attributed to slight mineralogical differences that can be expected in light of the differing sedimentation processes of the Pacific and Atlantic Oceans. Velocities of the Brazil Basin study, converted to in situ conditions from laboratory measurements, were compared with those previously reported by Hamilton and Bachman, which were converted to in situ conditions using bottom water velocities of this study and their velocity ratios. A plot of the velocities showed good agreement, but those of the present study were about 20 m/s lower. This discrepancy is probably not mineralogical in origin, but instead results from a systematic difference in the sediment velocimeters used in the two studies. The exact cause of the discrepancy is not known, and a detailed system evaluation of the velocimeters is recommended.
Acoustic nonlinearity parameter B/A of aqueous solutions of some amino acids and proteins
Authors: Sarvazyan A. P. , Chalikian T. V. , Dunn F.
Published: October 2005

A precision ultrasonic velocimeter and a new differential method of calculation of specific concentration increments were employed to study the nonlinear acoustic properties of aqueous solutions of ten amino acids and six proteins. The greater precision of the velocity measurements allows much more dilute solutions to be treated, providing for a wider range of amino acids and proteins to be studied. The specific increment of B/A of amino acids was found to exhibit a significant sensitivity to change of position or replacement of a single atomic group of the solute molecule. A strong influence of the character of the solute–solvent interaction on the B/A value is revealed. It is shown that the specific increment of B/A of a solute could be much more sensitive to the molecular structural features than other parameters such as the specific increments of sound velocity and density.
Acoustic radiation force on a rigid sphere in the near field of a circular piston vibrator
Authors: Hasegawa Takahi , Kido Tohru , Takeda Shigeki , Inoue Naoki , Matsuzawa Kiichiro
Published: October 2005

The acoustic radiation force exerted on a rigid sphere whose time-averaged center is at any specified point on the axis of a circular piston vibrator was investigated theoretically including points in the near zone of the radiation with a view to applying it to the absolute measurement of ultrasonic intensity. The velocity potential of incident waves in the near field was expressed in the form of an infinite series of spherical surface harmonics, thereby allowing the use of the conventional scattering theory to calculate the radiation force. The theoretical framework has the advantages that it includes neither approximations nor numerical integrations, and that it is applicable to elastic or compressible sphere cases with slight modifications of the boundary conditions.
Direct and inverse scattering of acoustic waves by low-speed free shear layers
Authors: Ahluwalia Daljit S. , Kriegsmann Gregory A. , Reiss Edward L.
Published: October 2005

In this paper, a direct method and a simple inverse method, which can be used to determine the velocity profile of a shear layer, are presented. Specifically, an infinite acoustic medium, with constant density and sound speed, containing a free shear layer of infinite extent, is considered. The free shear layer is probed with a two-dimensional plane wave, incident on the layer from outside, and it is assumed that the maximum Mach numbers for the flows in the shear layers are small, e.g., M=10−3 to 10−4 are typical values for oceanic shear layers. Then, the method of matched asymptotic expansions is employed to obtain an asymptotic expansion of the solution of the direct scattering problem as M→0 that is uniformly valid in the dimensionless wave number k and the angle α of the incident plane wave. It is found that the reflection coefficient of the scattered wave is proportional to the Fourier transform of the velocity profile of the free shear layer. This transform is inverted to obtain an asymptotic approximation of the solution of the inverse scattering problem. That is, given an incident plane wave and measurements of the reflected wave for a sequence of frequencies, approximations of the thickness and flow velocity distribution of the layer are determined. These results may be useful for studies that use acoustic exploration methods to determine oceanographic properties.
Relationship between leaky Lamb modes and reflection coefficient zeroes for a fluid-coupled elastic layer
Authors: Chimenti D. E. , Rokhlin S. I.
Published: October 2005

It is shown in this article how the zeroes of the plane-wave reflection coefficient for a fluid-coupled elastic layer are modified under fluid loading, throughout the entire range of fluid density. Transformation and exchange behavior of branches of the reflection coefficient zero spectrum with increasing fluid density has been found and discussed. This study extends an earlier investigation of the complex mode spectrum (reflection coefficient poles). The behavior of the zeroes of the reflection coefficient is compared with that of the poles as a function of the fluid density. In addition, we derive an analytical expression for the intersection of the fluid-modified fundamental zero branches and the Rayleigh wave speed. This number can be useful as a measure of the sensitivity of a solid material to fluid loading. More significantly, the results of the current study have immediate relevance for an important class of advanced materials: polymer-matrix composites. It is demonstrated that the spectral modifications similar to those induced in the reflection coefficient of aluminum at high fluid density occur below the density of water, if the solid plate is a polymer-matrix composite.
The solution of coupled interior/exterior acoustic problems using the boundary element method
Authors: Seybert A. F. , Cheng C. Y. R. , Wu T. W.
Published: October 2005

The boundary element method (BEM) is used to solve a class of problems in which an interior domain and an exterior domain are coupled by an interface surface, such as when sound propagates along a duct and radiates from the open end into the surrounding space. In the current approach, integral equations for the interior and exterior domains are coupled using continuity conditions at the interface surface between the two domains. The integral equations are reduced to numerical form using second-order boundary elements. The coupled interior/exterior boundary element method presented here overcomes numerical error and excess computer time problems present when traditional boundary element formulations are applied to this class of problems. The current approach is illustrated using several examples including: the radiation of sound from an open duct, the radiation of sound from a source within a partial enclosure, and the acoustical response of a slotted cavity due to an incident plane wave.
Active reduction of a one-dimensional enclosed sound field: An experimental investigation of three control strategies
Authors: Curtis A. R. D. , Nelson P. A. , Elliott S. J.
Published: October 2005

Three control strategies for the active reduction of an enclosed sound field are experimentally implemented and compared. A strategy of energy minimization successfully reduces the sound field at both resonant and antiresonant frequencies, whereas strategies developed for the control of propagating sound in ducts do not perform well.
Comments on ‘‘The rheology of an anelastic medium studied by means of the observation of the splitting of its eigenfrequencies’’ [J. Acoust. Soc. Am. 8
6, 1984–1987 (1989)]
Authors: Weaver R. L.
Published: October 2005

It is shown that the eigenfrequencies of a linear viscoelastic medium are not split.
Influences of structural factors of biological media on the acoustic nonlinearity parameter B/A
Authors: Zhang Jian , Kuhlenschmidt Mark S. , Dunn Floyd
Published: October 2005

The influence of structural factors of biological media on the acoustic nonlinearity parameter B/A have been studied at the tissue, cellular, and molecular levels, using the thermodynamic and finite amplitude methods. B/A was determined as the structural factors of the media were altered physically and biochemically, while chemical composition was maintained unchanged. Significant structural dependencies of B/A were observed at all three levels; 26% of the dry weight contribution to the total B/A (the B/A value with water contribution subtracted) is due to the cell–cell adhesive force in liver tissue, 20% is due to the hepatocyte cellular structure, and 15% is due to secondary and tertiary protein structure.
The propagation of plane sound waves in narrow and wide circular tubes, and generalization to uniform tubes of arbitrary cross-sectional shape
Authors: Stinson Michael R.
Published: October 2005

The general Kirchhoff theory of sound propagation in a circular tube is shown to take a considerably simpler form in a regime that includes both narrow and wide tubes. For tube radii greater than rw=10−3 cm and sound frequencies f such that rwf3/2<106 cm s−3/2, the Kirchhoff solution reduces to the approximate solution suggested by Zwikker and Kosten. In this regime, viscosity and thermal conductivity effects are treated separately, within complex density and complex compressibility functions. The sound pressure is essentially constant through each cross section, and the excess density and sound pressure (when scaled by the equilibrium density and pressure of air, respectively) are comparable in magnitude. These last two observations are assumed to apply to uniform tubes having arbitrary cross-sectional shape, and a generalized theory of sound propagation in narrow and wide tubes is derived. The two-dimensional wave equation that results can be used to describe the variation of either particle velocity or excess temperature over a cross section. Complex density and compressibility functions, propagation constants, and characteristic impedances may then be calculated. As an example, this procedure has been used to determine the propagation characteristics for a tube of rectangular cross section.
Signal pressure received by a hydrophone placed on a plate backed by a compliant baffle
Authors: Ko Sung H. , Schloemer Howard H.
Published: October 2005

An investigation is made of the signal reception of a hydrophone placed in front of an elastic plate backed by a compliant baffle layer. The baffle layer is the compliant tube array modeled by Junger [J. Acoust. Soc. Am. 78, 1010 (1985)] to represent a homogeneous, dispersive fluid layer. Noise reduction baffles such as compliant tubes are acoustically soft and thus tend to degrade the signal received. This paper describes the development of a theoretical model for evaluating the signal reception, and a comparison of theoretical results with experimental data is presented.
Echoes from vertically striated subresonant bubble clouds: A model for ocean surface reverberation
Authors: McDonald B. Edward
Published: October 2005

A surface reverberation model for acoustic frequencies below several kHz is proposed based on weak scatter from inhomogeneities whose geometry is descriptive of recent ocean observation [e.g., Farmer and Vagle, J. Acoust. Soc. Am. 86, 1897 (1989)]. Scatterers in this model are vertical cylinders of elliptical cross section representing either filamentary- or sheetlike subresonant microbubble clouds whose population decreases exponentially with depth. This geometry approximates intermediate-aged fossils of breaking waves and/or convective processes. Born approximation (weak scatter) results from this model show substantial agreement with observed surface backscatter cross sections as a function of wind speed, grazing angle, and acoustic frequency in the range 0.2–20 kHz. It is demonstrated that almost all the high-frequency weak backscatter in the model is specular reflection from surfaces of volume scatterers. Some preliminary speculations involving Langmuir circulation are offered for the application of this model to surface reverberation at frequencies below a few hundred Hz, where data are scarce.
Acoustic propagation through baffles with rectangular compliant tubes
Authors: Moore J. A.
Published: October 2005

Compliant tube baffles have been designed as effective barriers for acoustic propagation underwater over wide bands of frequencies. Acoustic energy reflection occurs due to compliant cross-sectional resonances in the tubes that exhibit significant volume deformation. Additional bandwidth is achieved with multiple layers of compliant tubes tuned to different frequencies. The design challenge is to provide sufficient baffle insertion loss levels and bandwidth while limiting adverse transmission peaks associated with interactions between noncompliant tube resonances and, tube and fluid layer system resonances. This paper discusses the acoustic performance of baffles with compliant tubes of rectangular cross section as opposed to the conventional designs with elliptical cross section. The tubes consist of flat face plates held apart along their edges by spacers. The knifelike edge support constitutes a simple support boundary condition for bending deformation of the face plate. This compliant tube configuration allows added design flexibility and degrees of freedom in minimizing the adverse effects of transmission peaks in a baffle’s insertion loss. Unequal face plate thicknesses and varied mass of the edge spacer have been effectively utilized in this regard.
Simulation of the propagation of an acoustic wave through a turbulent velocity field: A study of phase variance
Authors: Karweit M. , Blanc-Benon Ph. , Juvé D. , Comte-Bellot G.
Published: October 2005

A numerical technique for simulating the behavior of an acoustic wave propagating through a turbulent medium is introduced. The technique involves two elements: the generation of 3-D, random, hypothetical, isotropic velocity fields in terms of a collection of discrete Fourier velocity modes; and the integration of the ray-trace equations to describe the trajectories of points tagging an acoustic wave front. The propagation times for these points to travel fixed distances through each of an ensemble of random velocity fields are recorded, and the variance of travel time (or acoustic phase) over the ensemble is calculated. In numerical ray-trace experiments through fields having average perturbation indices ≊0.01, acoustic travel-time variances are obtained that have a higher-order dependence on travel distance R than the classical Chernov prediction—a linear increase with R. The Chernov result is obtained, however, when the rays are confined to axial trajectories. Additional numerical experiments integrating the stochastic Helmholtz equation and its parabolic approximation yield time-variance estimates consistent with the ray-trace results. Predictions from these simulations are then applied to the laboratory experiments of Blanc-Benon and found to be in qualitative agreement. Finally, a set of 2-D travel-time experiments are presented to identify differences between source–receiver eigenray propagation and preassigned initial direction ray propagation.
Segregation of concurrent sounds. II: Effects of spectral envelope tracing, frequency modulation coherence, and frequency modulation width
Authors: Marin Cécile M. H. , McAdams Stephen
Published: October 2005

The research presented here concerns the simultaneous grouping of the components of a vocal sound source. McAdams [J. Acoust. Soc. Am. 86, 2148–2159 (1989)] found that when three simultaneous vowels at different pitches were presented with subaudio frequency modulation, subjects judged them as being more prominent that when no vibrato was present. In a normal voice, when the harmonics of a vowel undergo frequency modulation they also undergo an amplitude modulation that traces the spectral envelope. Hypothetically, this spectral tracing could be one of the criteria used by the ear to group components of each vowel, which may help explain the lack of effect of frequency modulation coherence among different vowels in the previous study. In this experiment, two types of vowel synthesis were used in which the component amplitudes of each vowel either remained constant with frequency modulation or traced the spectral envelope. The stimuli for the experiment were chords of three different vowels at pitch intervals of five semitones (ratio 1.33). All the vowels of a given stimulus were produced by the same synthesis method. The subjects’ task involved rating the prominence of each vowel in the stimulus. It was assumed that subjects would judge this prominence to be lower when they were not able to distinguish the vowel from the background sound. Also included as stimulus parameters were the different permutations of the three vowels at three pitches and a number of modulation conditions in which vowels were unmodulated, modulated alone, and modulated either coherently with, or independently of, the other vowels. Spectral tracing did not result in increased ratings of vowel prominence compared to stimuli where no spectral tracing was present. It would therefore seem that it has no effect on grouping components of sound sources. Modulated vowels received higher prominence ratings than unmodulated vowels. Vowels modulated alone were judged to be more prominent than vowels modulated with other vowels. There was,however, no significant difference between coherent and independent modulation of the three vowels. Differences among modulation conditions were more marked when the modulation width was 6% than when it was 3%.
Detection of tones in reproducible narrow-band noise
Authors: Isabelle Scott K. , Colburn H. Steven
Published: October 2005

Hit and false-alarm rates were measured for detection of a 500-Hz tone target in each of ten reproducible samples of (1)/(3) -oct bandwidth noise centered at 500 Hz for both NoSπ and NoSo conditions. The effects on hit rates of the starting phase of the target relative to individual noise samples were investigated with two target phase angles for three subjects. The major results are: (1) performance varies significantly over masker waveforms; (2) for NoSπ conditions, the effect of target-to-masker phase angle on hit rates is not significant for these narrow-band maskers; (3) for NoSo conditions, the target-to-masker phase angle has a large effect; (4) no significant correlation between NoSo performance and NoSπ performance is seen across masker waveforms. These results are generally consistent with previously reported results for wideband maskers [R. H. Gilkey, D. E. Robinson, and T. E. Hanna, ‘‘Effects of masker waveform and signal-to-masker phase relation on diotic and dichotic masking by reproducible noise,’’ J. Acoust. Soc. Am. 78, 1207–1219 (1985)] with an important exception. Specifically, in the wideband experiment, significant correlation between NoSo and NoSπ performance across noise samples was found. In addition, in the wideband experiment, a small yet statistically significant effect of target-to-masker phase was observed in the NoSπ condition.
Perception of multiple electrode stimulus patterns: Implications for design of an electrotactile speech processor
Authors: Cowan R. S. C. , Blamey P. J. , Sarant J. Z. , Galvin K. L. , Clark G. M.
Published: October 2005

Identification of multiple-electrode stimulus patterns was evaluated in nine adult subjects, to assess the feasibility of providing additional speech information through the tactual display of an electrotactile speech processor. Absolute identification scores decreased from 97.8% for single electrodes, to 61.9% for electrode pairs, and, to 31.8% for electrode triplets. Although input information increased with paired- and triple-electrode stimuli, information transmission scores were not significantly increased for either electrode pairs (2.99 bits) or triplets (2.84 bits) as compared with single electrodes (2.84 bits). These results suggest that speech coding strategies using stimulus patterns of electrode pairs or triplets would provide little improvement beyond that found for the present single-electrode scheme. However, higher absolute identification scores (73.6%), and an increase in information transmission to 3.88 bits, were recorded for test stimuli containing all combinations of paired and single electrodes. Based on this finding, two stimulus sets using a restricted number of combinations of paired and single electrodes were evaluated. The two stimulus sets simulated the spatial patterns of paired and single electrodes arising from use of alternative speech coding schemes to increase consonant voicing information. Results for the two stimulus sets showed higher electrode identification scores (79.7% and 90.4%), as compared with paired-electrode stimuli. Although electrode identification score was not as high as for single electrodes, information transmission was increased to 3.31 bits for the VF2 stimulus set. Analysis of the responses also showed that scores for identification of simulated voicing information conveyed by the two stimulus sets were 99.4 and 90.4% correct. If similar performances are achieved with speech stimuli, use of either of these two speech coding schemes would significantly enhance perception of consonant voicing, with resultant improvements in speech perception for users of the electrotactile speech processor.
Observation of perturbations in a lumped-element model of the vocal folds with application to some pathological cases
Authors: Wong Darrell , Ito Mabo R. , Cox Neil B. , Titze Ingo R.
Published: October 2005

In this paper a mass–spring model is developed that is a hybrid of the two-mass and the longitudinal string models, proposed by Ishizaka and Flanagan [Bell Sys. Tech. J. 51, 1233–1268 (1972)] and Titze [Phonetica 28, 129–170 (1973)], respectively. The model is used to simulate the vibratory motion of both the normal and asymmetric vocal folds. Mouth-output pressure, lateral tissue displacement, phase plots, and energy diagrams are presented to demonstrate the interaction between vocal fold tissue and the aerodynamic flow between the folds. The results of the study suggest that this interaction is necessary for sustained large amplitude oscillation because the flow supplies the energy lost by the tissue damping. Tissue mass and stiffness were varied locally or uniformly. Decreased stress in the longitudinal string tension produced subharmonic and chaotic vibrations in the displacement, velocity and acceleration phase diagrams. Similar vibratory characteristics also appeared in pathological speech data analyzed using time domain jitter and shimmer measures and a harmonics-to-noise ratio metric. The subharmonics create an effect that has been perceptually described as diplophonia.
Calculation of a constant Q spectral transform
Authors: Brown Judith C.
Published: October 2005

The frequencies that have been chosen to make up the scale of Western music are geometrically spaced. Thus the discrete Fourier transform (DFT), although extremely efficient in the fast Fourier transform implementation, yields components which do not map efficiently to musical frequencies. This is because the frequency components calculated with the DFT are separated by a constant frequency difference and with a constant resolution. A calculation similar to a discrete Fourier transform but with a constant ratio of center frequency to resolution has been made; this is a constant Q transform and is equivalent to a 1/24-oct filter bank. Thus there are two frequency components for each musical note so that two adjacent notes in the musical scale played simultaneously can be resolved anywhere in the musical frequency range. This transform against log (frequency) to obtain a constant pattern in the frequency domain for sounds with harmonic frequency components has been plotted. This is compared to the conventional DFT that yields a constant spacing between frequency components. In addition to advantages for resolution, representation with a constant pattern has the advantage that note identification (‘‘note identification’’ rather than the term ‘‘pitch tracking,’’ which is widely used in the signal processing community, is being used since the editor has correctly pointed out that ‘‘pitch’’ should be reserved for a perceptual context), instrument recognition, and signal separation can be done elegantly by a straightforward pattern recognition algorithm.
Automatic measurement of descriptive features of Hector’s dolphin vocalizations
Authors: Thorpe C. William , Dawson Stephen M.
Published: October 2005

The reliable and accurate measurement of descriptive features to enable accurate description and statistical comparison of animal sounds has presented one of the major difficulties in bioacoustics. To facilitate a quantitative analysis of the acoustic repertoire of Hector’s dolphins (Cephalorhynchus hectori), a computer-based measurement system in a signal processing language (SIGPROC) has been developed. This automated system allowed us to easily measure descriptive features from 7661 dolphin clicks. The reliability of the measurement system was confirmed by reconstructing some of the clicks from their measured features. The measurement and reconstruction techniques are described. Analyses of the measured data showed that most Hector’s dolphin vocalizations are simple, high-frequency, narrow-band ‘‘clicks.’’ A few examples of wideband clicks were found, as was a sound comprising two frequency components.
Failure of a reported exterior overdetermination technique to resolve acoustic boundary element method (BEM) critical frequencies
Authors: Fyfe K. R. , Ismail F. , Sas P.
Published: October 2005

Many techniques have been proposed to overcome the non-uniqueness problem associated with calculating exterior acoustic radiation response when using various forms of the boundary element method. Each of the procedures have their relative merits. However a particular method, known as the exterior over-determination technique which is iterative in nature, has been tested and does not converge as reported. The author of the proposed method has been contacted and it has been acknowledged that the method does not work as reported.