bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite element approximation for low-frequency sound in a room with absorption
Authors: Geddes E. R. , Porter J. C.
Published: October 2005

The two-dimensional flow of acoustic energy is calculated in a room with parallel ceilings and floors and of a rectangular floor plan in the finite element approximation. The interior surfaces of the room are assumed to be reverberant, with the exception of a locally reactive vertical strip of impedance Z=0.7 ρc located on one of walls. Solutions are obtained for a vertically oriented acoustic line source with volumetric flow rate Q per unit length and frequency ω that intersects horizontal planes in the room at the point (x(s),y(s)). The frequency response is calculated by expanding the acoustic Green’s function as the direct product of the damped room eigenmodes, as approximated by the finite element analysis. This approach allows calculation of the room response for various frequencies and source locations in the post processing phase of the finite element solution.
Measurement distance, direct field bias, and critical frequency in the measurement of reverberant sound fields
Authors: Sepmeyer Ludwig W.
Published: October 2005

The determination of the sound power output of small sources in reverberation rooms and the transmission loss of building partitions require the measurement of space-averaged sound pressure squared. Such measurements are contaminated by a direct field bias error. This article reviews the underlying theory and presents a number of graphs for determining the direct field bias error as a function of measurement distance, source directivity factor, room volume, and reverberation time. Also, an in situ experimental method for determining the effective directivity factor of a source is presented in graphical form. Finally, the concepts of ‘‘modal overlap’’ and Schroeder frequency are explored in terms of an elementary electrical resonant circuit and the more descriptive term, number of modes per modal bandwidth, is proposed.
Sound transmission through single plates with absorptive facings
Authors: Takahashi D.
Published: October 2005

Sound transmission through single plates with absorptive facings is investigated theoretically. The effect of attached absorptive layers on the sound transmission is included by taking into account the mass and impedance variation due to the layer. A consistent theory is applied to the various surface conditions that include the case of absorptive treatments of the surface, attached layers on source and/or receiver side, and a surface with complete rigidity. An expression predicting the transmission loss explicitly as a function of both frequency and angle of incidence is obtained. The result has a very simple form. Numerical calculations carried out for the field-incidence-averaged transmission loss are compared with existing experimental data. The results are in good agreement at mid and high frequencies.
Closed-form approximations and series representations for partially saturated ocean acoustic processes
Authors: Perakis Anastassios N. , Nikolaidis Efstratios , Katzouros Emmanuel
Published: October 2005

An approximate, closed-form expression for the value of the integral encountered in the calculation of the probability density function (PDF) of the envelope of a partially saturated ocean acoustic process is obtained. Furthermore, an expression of this PDF as a series of modified Bessel functions is presented. The results may also be directly applied to the evaluation of the PDF encountered in the structural reliability analysis of rotating machinery components. Numerical applications show that the closed-form expression is always within 1%2% of the exact result. The required computational effort is substantially lower than that required by direct numerical integration.
Speech understanding and aging
Authors: Aging Working Group on Speech Understanding and
Published: October 2005

The increasing age of the population forecasts a corresponding increase in the number of people suffering from hearing loss and who therefore have difficulty with speech communication. This article, prepared by the Working Group on Speech Understanding and Aging for the Committee on Hearing, Bioacoustics, and Biomechanics, discusses a number of the factors that act on the elderly listener’s ability to understand speech, including physiological aging, changes in cognitive ability, noisy signals, and sensory aids. Both sensory and perceptual processes are considered.
Wave propagation in media with time-dependent spatial inhomogeneities
Authors: Abraham P. B.
Published: October 2005

The propagation of waves in a medium with time-dependent spatial inhomogeneities in its velocity profile is given a rigorous integral equation formulation for source and incident field descriptions. This is in the spirit of Rayleigh, whose aim was to bypass complications arising from boundary conditions. A perturbation expansion, correct to all orders, is then obtained with the aid of a simple identity, for the two cases: (i) weak scatterers and (ii) strong scatterers. It is shown that for case (i) a correction term has to be added to previous results already in second order—this seems to have been overlooked until now. For case (ii), the expansion obtained here is new—the reason for this gap in the existing literature is discussed. With these results, expressions are derived for the wavefunctions when the inhomogeneity in the medium is due to distributions of moving particulates. These new closed-form time-dependent approximations exhibit explicitly the appropriate Doppler behavior. The application of this formulation to other cases, such as media with random inhomogeneities, is discussed.
Transmission of guided precursor curvilinear waves in layered media
Authors: Ziv M.
Published: October 2005

A closed-form solution is obtained for the deformation along a guided impulsive precursor wave that propagates in layered media bounded, transversely, by a free surface. Specifically, this article deals with the diffraction of an ideal elastic longitudinal wave, generated by stress boundary conditions, as it impinges at grazing incidence on the free surface of an array of layers arranged at a right angle to the free surface. Two examples of boundary-value problems relevant to this configuration are solved. One concerns an impulsive load applied uniformly and radially to the entire cylindrical surface of an infinite cavity drilled into a half-space made of layers running in the radial direction. The other concerns an impulsive load applied uniformly to one of the two boundaries of a Cartesian quarter-space made of layers running at a right angle to the free boundary of the quarter-space. Basic concepts employed in the determination of the material response along the leading wave are based on geometrical strong discontinuity formulas for computational wave motions and multi-dimensional wave characteristics formulations for solids. Refraction, reflection, and diffraction phenomena associated with the curvilinear guided precursor wave as it interacts with the interfaces of the layers are revealed explicitly by the proposed method of solution. For the cases considered here, criteria are established in order to predict stress amplification or attenuation at an interface—the usual prediction criterion based on the uniaxial strain plane wave is not valid here. Mathematical avenues used in this article can be extended to materials with nonelastic and nonlinear behavior.
Validity of linear acoustics for prediction of waveforms caused by sonically moving laser beams
Authors: Pierce Allan D. , Berthelot Yves H.
Published: October 2005

The question is raised as to whether the analysis of the generation of sound by a laser beam moving over a water surface at the sound speed c for an interminable time period requires consideration of nonlinear effects. A principal consideration in this regard is whether the linear acoustics theory predicts a pressure waveform that is bounded in the asymptotic limit when the laser irradiation time is arbitrarily large. It is shown that a bounded asymptotic limit exists when the upper boundary condition corresponds (as is more nearly appropriate) to that of a pressure release surface, but not when it corresponds to that of a rigid surface. The asymptotic solution to the appropriate inhomogeneous wave equation is given exactly for the former case, and it is shown that the highest asymptotic amplitudes, given specified laser power and beam radius a, occur in the limit of a very small light absorption coefficient μ. In this limit, the peak amplitude is independent of μ and occurs at a depth of 0.88/μ. An approximate solution for the pressure waveform at intermediate times establishes that the characteristic time for buildup to the asymptotic limit is of the order of 2.5/(cμ2a). If this time is substantially shorter than the time that a plane-wave pulse with the asymptotic waveform would take to develop a shock wave, then accumulative nonlinear effects are of minor importance.
The input power of distributed sources
Authors: Smith Marian
Published: October 2005

An alternative to the conventional method of calculation of net power radiated by flux integration is presented. This method allows power radiated by distributed sources to be calculated by an integral only over the source region. Furthermore, the method is applicable to calculation of radiation from distributed sources in flow. Examples of power radiation, for the geometry of the finite cylinder, are given for both stationary and moving media. Analytic results are presented for the long wavelength approximation.
Hybrid (ray)-(parabolic equation) analysis of propagation in ocean acoustic guiding environments
Authors: Ishihara T. , Felsen L. B.
Published: October 2005

Acoustic ray theory provides an effective means for predicting propagation in general environments. Ray theory fails in the vicinity of caustics and must there be augmented by uniform asymptotic treatment. However, even such corrections are inadequate at long ranges in a ducting channel, where the caustics due to multiple reflected and/or refracted rays accumulate at locations near the duct axis. To repair this deficiency of ray acoustics, the caustic forming ray spectra have previously been replaced by guided modes in a self-consistent ray-mode scheme. It is now shown that the troublesome ray spectra at long ranges can be replaced as well by a narrow-angle parabolic equation (PE) approximation to the full pressure field. Taken together, the hybrid ray-PE form can be regarded either as correcting via PE the failure of ray acoustics near the guiding axis or as removing the narrow-angle restriction from PE by filling the wide angle spectra with rays. The theory is developed first for a range-independent surface duct, and then for a range-dependent guiding-to-antiguiding transition. Unlike the adiabatic modes, the numerical PE algorithm can accommodate changes from guiding to antiguiding. The analogous problem of propagation along a circular concave boundary and along a boundary with concave–convex transition is treated briefly in the Appendix.
Optical levitation of bubbles in water by the radiation pressure of a laser beam: An acoustically quiet levitator
Authors: Unger Bruce T. , Marston Philip L.
Published: October 2005

This article demonstrates the stable levitation of single small gas bubbles in water in a downward directed visible laser beam. The natural upward buoyancy of the bubbles was counteracted by the optical radiation pressure of the light beam, whose optical power ranged from 1–3.5 W. The sizes of the levitated bubbles ranged from 10–30 μm in radius. (The term ‘‘levitation’’ is synonymous to ‘‘trapping’’ even though the radiation force must be directed downward on the bubble.) For horizontal stability of the levitated bubble, the laser was operated in a mode giving an irradiance minimum at the center of the laser beam. An approximation is derived for the force on the bubble in the direction of the beam axis; it includes only the contribution to the radiation pressure due to the total-reflection region of the bubble’s surface (which appears to be the major contribution). The resulting estimate of the power required to levitate is consistent with observations. Optical levitation is a quiet alternative to acoustical levitation that could facilitate the measurement of weak acoustic emissions from isolated bubbles.
Experimental study of the Stoneley wave at a plane liquid–solid interface
Authors: Luppé Francine , Doucet Jacques
Published: October 2005

Some of the properties of the Stoneley wave at a plane liquid–solid interface are reviewed after having deduced them from the general ones of evanescent plane waves. A liquid wedge method of generation of this wave is presented, and the predicted properties are verified.
Dummy load backing of ultrasonic transducers for bandwidth enhancement
Authors: Gazalet M. G. , Houze M. , Logette P. , Bruneel C. , Torguet R.
Published: October 2005

A new method based on the electromechanical simulation of a mechanical backing medium by an electrically loaded piezoelectric element is reported. Among the advantages, one may state the size reduction, especially at lower frequencies, and the flexibility, the fast modification of the overall bandwidth and bandshape being possible. The main results of the theoretical study together with an experimental investigation are given, from which the feasibility of bandwidths greater than an octave is demonstrated.
Statistical expectation of the interval histograms from marginal time statistics of the Poisson process
Authors: Bi Qi , Brown John L. , Lachs Gerard
Published: October 2005

It is known that responses from auditory nerve fibers may be modeled by an inhomogeneous Poisson point process. Based on such a model, timing patterns from the responses of the auditory nerve can be described by the marginal time statistics of the Poisson process. In this letter, these marginal time statistics (the probability density functions for the nth arrival time and the nth interarrival time) are derived and then used to obtain the ensemble mean of the interval histograms constructed from the experiments. The results of this letter show that interval histograms contain both the intensity and the frequency information of the stimuli, whereas the phase information of the stimuli is lost.
A new index for evaluation of the turbulent noise in pathological voice
Authors: Fukazawa Tatsuya , El-Assuooty Ashraf , Honjo Iwao
Published: October 2005

The validity of the parameter Br index, which was designed as an indicator of the turbulent noise in breathy voice, was tested. The parameter was determined by the ratio between energy of the second derivative of the high-pass filtered wave and that of the nonderived high-pass filtered wave. The principle of this method is the utilization of the difference in the frequency range between the turbulent noise and other components present. The parameter was found to correlate with the perception of breathiness. Clinical applications of this index suggest the possibility of using it further as a detection tool for diseases that generate turbulent noises.
Design charts for sound absorber layers
Authors: Mechel F. P.
Published: October 2005

Based on the experience that the acoustic characteristic variables Γan, Zan of fibrous absorber materials can be expressed by one nondimensional variable E=fρ0/Ξ with sufficient accuracy for survey calculations, the sound absorption of absorber layers has been calculated and plotted in a way that permits at the same time the reconstruction of the frequency curve of sound absorption for individual absorbers, as well as quantitative answers on questions of general interest, which up to now have been discussed in literature mostly in qualitative manner only. The sound field was assumed to consist of plane waves, with either normal, oblique, or diffuse incidence. The absorber layers could be either locally reacting or bulk reacting. The same holds for air cavities that could exist between the absorber layer and the rigid wall. A general recurrence calculus for computation of the input impedance or the reflection factor and absorption of multilayer arrangements was presented. Some numerical examples of its application were shown, in conclusion.
Underwater noises: Statistical modeling, detection, and normalization
Authors: Bouvet Michel , Schwartz Stuart C.
Published: October 2005

Knowledge of the noise probability density function (PDF) is central in signal detection problems, not only for optimum receiver structures, but also for processing procedures such as power normalization. Unfortunately, the statistical knowledge must be acquired since the classical assumption of a Gaussian noise PDF is often not valid in underwater acoustics. In this article, statistical modeling is studied using a Gaussian–Gaussian mixture (GGM) for three different underwater noise data sets. It is shown that one of them can be adequately described by a Gaussian–Gaussian mixture, one is very close to a Gaussian model and is described by a mixture with a very small perturbating term, whereas the third one seems closer to a nonstationary version of the Middleton class-A model. The first noise sample is also studied with emphasis on the normalization needed in the receiver in order to achieve a constant false alarm probability and on the optimal receiver structure for the detection of a deterministic signal. It is also shown that the classical noise power estimate, calculating the L2 norm of the observation vector, is a good approximation of the square of the maximum likelihood estimator of the noise amplitude for the Gaussian–Gaussian mixture. The notion of noise alone reference is investigated and the performances of normalized test functions using different power estimates are studied. The principal result of our preliminary study is that the use of the receiver associated with the mixture model can lead to improvements with respect to the classical matched filter, this improvement being measured in terms of receiver operating characteristics (ROC) curves.
Broadband signal analysis with the smoothed pseudo-Wigner distribution
Authors: Allard Jean F. , Valiere Jean C. , Bourdier R.
Published: October 2005

Several nonstationary broadband signals, a voiced speech signal, and flute signals are studied with the short time Fourier transform (STFT) and the smoothed pseudo-Wigner distribution. The time frequency description of flute signals is more precise with the smoothed pseudo-Wigner distribution, and the instant of glottal closure can be reached with better precision in the voiced speech signal. The smoothed pseudo-Wigner distribution is more suitable for these signals than the STFT.
Detectability of tonal signals with changing interaural phase differences in noise
Authors: Grantham D. Wesley , Luethke Lynn E.
Published: October 2005

Detectability of binaurally presented 400- and 800-Hz tonal signals was investigated in an adaptive, two-interval forced-choice experiment. A continuous 3150-Hz low-pass noise masker was presented either diotically (No), interaurally uncorrelated (NU), or interaurally phase- reversed (Nπ), at an overall level of 70 dB SPL. Signal duration was either 100 or 1000 ms. The interaural phase difference (IAPD) of the signal was either fixed (0°–180°) or time- varying (slightly different frequencies were presented to the two ears). The range of interaural phase variations was selected to yield the same varying interaural temporal differences that would be produced if real auditory targets moved through various arcs in the horizontal plane. In no case was a signal with varying IAPD any more (or less) detectable than would be expected from averaging subjects’ performance in the corresponding fixed-IAPD conditions through which the variation occurred. However, in detecting these signals, subjects placed relatively more weight on the temporal central portion than on either the onset or offset. It is proposed that this weighting effect is based on two factors: (1) the signal’s 20-ms rise–decay time (i.e., the onset and offset receive less binaural weight because of monaural attenuation); and (2) the very low-pass filtering effected by the binaural system, which results in some minimum time required for it to become ‘‘fully engaged.’’ Another finding was that signal detectability became gradually worse as the antiphasic moment in a varying-IAPD signal was moved from the temporal midpoint toward the onset. No evidence was found that a signal’s onset and offset were weighted differently in a binaural signal detection task.
Coarticulatory influences on the perceived height of nasal vowels
Authors: Krakow Rena A. , Beddor Patrice S. , Goldstein Louis M. , Fowler Carol A.
Published: October 2005

Certain of the complex spectral effects of vowel nasalization bear a resemblance to the effects of modifying the tongue or jaw position with which the vowel is produced. Perceptual evidence suggests that listener misperceptions of nasal vowel height arise as a result of this resemblance. Whereas previous studies examined isolated nasal vowels, this research focused on the role of phonetic context in shaping listeners’ judgments of nasal vowel height. Identification data obtained from native American English speakers indicated that nasal coupling does not necessarily lead to listener misperceptions of vowel quality when the vowel’s nasality is coarticulatory in nature. The perceived height of contextually nasalized vowels (in a [bṼnd] environment) did not differ from that of oral vowels (in a [bṼd] environment) produced with the same tongue–jaw configuration. In contrast, corresponding noncontextually nasalized vowels (in a [bṼd] environment) were perceived as lower in quality than vowels in the other two conditions. Presumably the listeners’ lack of experience with distinctive vowel nasalization prompted them to resolve the spectral effects of noncontextual nasalization in terms of tongue or jaw height, rather than velic height. The implications of these findings with respect to sound changes affecting nasal vowel height are also discussed.
Ultrasonic propagation properties (@100 MHz) in excessively fatty rat liver
Authors: O’Brien William D. , Erdman John W. , Hebner Tammy B.
Published: October 2005

The effects on the ultrasonic propagation properties of livers of the addition of 1% orotic acid to rat diets were examined. In rats, dietary orotic acid exerts several effects on lipid metabolism; its overall consequence is that excessively high hepatic fat concentrations are built up over a short period of time, thus making this an ideal model to study the ultrasonic propagation properties as a function of sequential development of fatty liver. Over a 16-day period on the orotic acid diet, the supplemented rat liver lipid concentrations increased from a normal range of 2–4% to the lower 20’s%; hepatic water concentration decreased from a normal value of approximately 70% to approximately 50%; total protein concentration decreased slightly from a normal range of 17%–20% to 11%–16%; and rat liver weight increased from approximately 11 g to around 20 g. Ultrasonic attenuation coefficient and speed were assessed in liver tissue with the scanning laser acoustic microscope at 100 MHz. As hepatic lipid increased, ultrasonic attenuation at 100 MHz increased temporally from a normal range of 12–14 dB/mm to a maximum of 54 dB/mm and ultrasonic speed decreased from a normal range of 1553–1584 m/s to a minimum of 1507 m/s. Multivariant linear regression was used in the analysis of covariance to fit the least-squares estimates to the linear regression model. Strong correlates of ultrasonic speed with both water concentration and fat concentration in the liver were observed.
The effect of laryngeal nerve stimulation on phonation: A glottographic study using an i
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Authors: Moore Dennis M. , Berke Gerald S.
Published: October 2005

The present investigation was designed to examine the effect of change in vocal fold mass and stiffness on vocal fold vibration. To do this, the effect of variation in superior laryngeal nerve stimulation (SLNS) and recurrent laryngeal nerve stimulation (RLNS) was studied. Photoglottography (PGG), electroglottography (EGG), and subglottic pressure (Psub) were measured in seven mongrel dogs using an in vivo canine model of phonation. The PGG, EGG, and Psub signals were examined at three frequencies (100, 130, and 160 Hz) for SLNS and RLNS, using a constant rate of air flow. Increasing SLNS, which caused a contraction of the cricothyroid muscle, produced a marked increase in F0, little change in Psub, an increase in open quotient (OQ), and a decrease in the closed quotient (CQ) of the glottal cycle. Increasing RLNS, which caused activation of the intrinsic laryngeal muscles, produced a modest increase in F0, a marked increase in Psub, no change in the OQ, and an increase in CQ. Phase quotient (Qp), which describes the interval between opening of the lower and upper fold margins, decreased with increasing RLNS and did not change significantly with increasing SLNS. Based upon changes in F0, Psub, OQ, CQ, and Qp, SLNS provides a physiologic correlate of the tension parameter Q, and RLNS provides a physiologic correlate of the parameter Psub in the Ishizaka and Flanagan two-mass model.
Measuring the rate of change of voice fundamental frequency in fluent speech during mental depression
Authors: Nilsonne Åsa , Sundberg Johan , Ternström Sten , Askenfelt Anders
Published: October 2005

A method of measuring the rate of change of fundamental frequency has been developed in an effort to find acoustic voice parameters that could be useful in psychiatric research. A minicomputer program was used to extract seven parameters from the fundamental frequency contour of tape-recorded speech samples: (1) the average rate of change of the fundamental frequency and (2) its standard deviation, (3) the absolute rate of fundamental frequency change, (4) the total reading time, (5) the percent pause time of the total reading time, (6) the mean, and (7) the standard deviation of the fundamental frequency distribution. The method is demonstrated on (a) a material consisting of synthetic speech and (b) voice recordings of depressed patients who were examined during depression and after improvement.
Intraspeaker variability in fundamental frequency stability: An age-related phenomenon?
Authors: Linville Sue Ellen
Published: October 2005

The purpose of this investigation was to gather information on the extent to which intraspeaker variability on measures of jitter (%) and fundamental frequency standard deviation (F0 s.d.) is age related in women. Fifteen repeat productions of the vowels /i/, /a/, and /u/ from 22 young women (18–22 years) were analyzed for F0 s.d. and jitter. Findings for these young speakers were compared with those for elderly speakers tested previously (Linville and Korabic, 1987). Results indicate that the aging process brings about increases in the variability individual women demonstrate on measures of F0 stability when producing sustained vowels as steadily as possible. Further, young speakers differed markedly from elderly speakers in the pattern of frequency instability variations observed across the three vowels tested.
Model for piano hammers: Experimental determination and digital simulation
Authors: Boutillon Xavier
Published: October 2005

To explain the clearly nonlinear character of the interaction between a piano hammer and the strings it hits, a model for the hammer is proposed consisting of a point mass and a nonlinear, hysteretic spring that describes the action of the felt. Experimental determinations of force are fitted with an expression of generic form F=a(Δy)α, where α takes values such as 2.1, 3.5, and 5. Numerical simulations of hammer and string motions based on this model are found to be in good agreement with experimental measurements.
Anisotropy of the ultrasonic backscatter of myocardial tissue: I. Theory and measurements i
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Authors: Mottley Jack G. , Miller J. G.
Published: October 2005

This research addresses the variations in the ultrasonic backscatter from specimens consisting of a suspension of approximately aligned cylindrical scatterers in a fluid medium as a function of the angle of propagation in the sample. Predictions of the angular dependence of backscatter based on the time-domain Born approximation described by Rose and Richardson [J. H. Rose and J. M. Richardson, J. Nondestr. Eval. 3, 45–53 (1982)] were compared with experimental measurements of the backscatter from both tissue-mimicking phantoms consisting of graphite fibers suspended in gelatin and from canine myocardial tissue. The angular dependence of the backscatter was predicted and measured to be maximum for propagation perpendicular to the cylinder axes and minimum for propagation parallel to the axes. Maximum to minimum (i.e., perpendicular to parallel) changes in the integrated backscatter were predicted to be between 5 and 10 dB in the phantom. The corresponding quantity measured in both the phantom and in canine myocardial tissue was approximately 6 dB.
Accurate acoustic power measurements with a high-intensity driver
Authors: Hofler T.
Published: October 2005

The design, construction, and calibration of a high-intensity acoustic driver apparatus with instrumentation for accurate measurements of dynamic pressure, volume velocity, and their relative phase are discussed. The acoustic power supplied by the driver can be determined from these measurements. The apparatus is capable of driving closed systems containing various gases at mean pressures ranging from 1–10 bar, at frequencies ranging from 400–700 Hz. Maximum acoustic powers attained are in excess of 13 W for systems with appropriate impedance. The accuracy of the power measurement is ±3% and the accuracy of the relative phase measurement is better than ±1°. The design of this apparatus can be simply optimized for other acoustic load impedances and frequencies.
Heterodyne interferometer for submicroscopic vibration measurements in the inner ear
Authors: Willemin Jean-François , Dändliker René , Khanna Shyam M.
Published: October 2005

Conditions in the inner ear for interferometric measurements are quite different from those encountered in other mechanical systems: (i) The inner ear is not mechanically stable, due to blood pulsations and breathing artifacts; (ii) access to the inner ear is limited by anatomical constraints that make it difficult to visualize the structures of interest; (iii) vibration amplitudes to be measured in the inner ear are very low; (iv) the structures in the inner ear are nearly transparent; therefore, the reflectivity is low and attempts to change this reflectivity artificially usually alter the response characteristics; (v) cells are subject to light damage if the incident light intensity is too high, which limits the laser power that can be utilized in the interferometer. A heterodyne interferometer specially designed to measure vibrations in the living inner ear is described. Theoretical and experimental characteristics of this instrument are discussed in detail. In contrast to the homodyne system, the measurement accuracy of this interferometer is not affected by the low-frequency animal movements. This system does not require attachment of a reference mirror to the animal, thereby providing an unobstructed view of the structure to be measured. It has a high linearity and dynamic range. Its vibration sensitivity is high (2.8×10−13 m for 1-Hz bandwidth) even under the condition of low light reflectivity (0.02%), with 0.5-mW incident laser power.
Numerical predictions of atmospheric sound-pressure levels in shadow zones
Authors: Franke Steven J. , Raspet Richard , Liu C. H.
Published: October 2005

This letter is a study of some practical considerations that must be addressed when using modern numerical methods to predict atmospheric sound-pressure levels in upward refracting environments. Conventional formulations of the shadow zone problem usually assume that the sound speed decreases indefinitely with height above the ground. A version of the fast field program (FFP) was used, which was formulated for a linear sound-speed profile to illustrate the effect of ‘‘capping’’ the linear sound-speed decrease with a homogeneous layer. This is found to give significantly increased sound-pressure levels in the ‘‘shadow zone’’ when the height of the homogeneous layer becomes comparable to the thickness of the creeping wave region defined in the theory for an indefinitely decreasing profile. Also considered was the accuracy of the homogeneous layer approximation when used to represent the sound-speed profile for noise propagation into a shadow zone. This approximation was used in a recent formulation of the fast field program (FFP) for the atmospheric propagation problem. The approximation is studied for some realistic examples of long-distance propagation of low-frequency (<500 Hz) acoustic signals. To assess the accuracy of the homogeneous layer approximation, a comparison of numerical calculations of sound-pressure levels computed using the FFP introduced by Lee et al. [J. Acoust. Soc. Am. 79, 628–634 (1986)] with the FFP formulated for the linear speed profile must be made. A realistic ground impedance model (Delaney–Bazley–Chessel) M. E. Delaney and E. N. Bazley [J. Sound Vib. 16, 315–322 (1971); C. I. Chessel, J. Acoust. Soc. Am. 62, 825–834 (1977)] is used so that this study will apply to the case of sound propagation over a typical grass covered surface.
A method for measuring acoustic wave attenuation in the laboratory
Authors: Tang X. M. , Toksöz M. N. , Tarif P. , Wilkens R. H.
Published: October 2005

The measurement of attenuation is performed by directly determining the attenuation operator (or the impulse response of the medium) in the time domain. In this way, it is possible to separate the attenuation operator from other nonattenuation effects, e.g., reflections. The Wiener filtering technique, or the damped least squares, is used to calculate the attenuation operator. For the damped least squares, we have corrected for the effect due to the addition of the damping constant using a perturbation method. Numerical tests are carried out to illustrate the technique. The geometric beam spreading of ultrasonic waves generated by a source of finite size can strongly affect the result of attenuation measurements. Corrections are made by equating the received signal to the average pressure over the receiver surface. The technique is used to measure ultrasonic attenuation in water, glycerol, and mud. The measurement in water offers a test of the corrections made for the geometric beam spreading. The measurement in glycerol and mud shows that, in the frequency range of 0.2–1.5 MHz, the attenuation of glycerol increases rapidly with frequency, whereas the attenuation of mud is proportional to frequency, exhibiting a constant Q behavior. The measurements show that the technique used here is an effective approach to the measurement of attenuation.
Viscous fluid effects on guided wave propagation in a borehole
Authors: Burns D. R.
Published: October 2005

In order to investigate the effect of borehole fluid viscosity on the attenuation and dispersion of the guided waves present in full waveform acoustic logs, the problem of wave propagation in a borehole containing a viscoelastic fluid surrounded by an infinite elastic formation is solved using boundary layer theory. The results indicate that the losses due to viscous drag along the borehole wall are a small component of the overall guided wave attenuation for the frequencies of interest in full waveform acoustic logging (2–15 kHz) and for reasonable viscosity values (1–1000 cP). These losses, however, can be significant at low frequencies. In addition, the variations in viscosity have a negligible effect on the guided wave dispersion for this range of frequency and viscosity. These findings indicate that friction between grains in fluid suspension may be the dominant attenuation mechanism in the drilling fluids present in boreholes.
A high-powered siren for stable acoustic levitation of dense materials in the Earth’s gravity
Authors: Gammel Paul M. , Croonquist Arvid P. , Wang Taylor G.
Published: October 2005

Levitation of large dense samples (e.g., 1-cm diameter steel balls) has been performed in a 1-g environment. A siren was used to study the effects of reflector geometry and variable-frequency operation in order to attain stable acoustic positioning. The harmonic content and spatial distribution of the acoustic field have been investigated. The best stability was obtained with an open reflector system, using a flat lower reflector and a slightly concave upper reflector while operating at a frequency slightly below resonance.
Dimensional analysis of windscreen noise
Authors: Strasberg M.
Published: October 2005

It is shown that data on wind noise in spherical and cylindrical windscreens may be represented by a single universal curve if the data are plotted in nondimensional form. Appropriate dimensionless variables are a dimensionless frequency ( fD/V) plotted against a sound pressure coefficient (p̃1/3/ρV2) or a dimensionless spectral density  fS/ρ2V4), where f is frequency, D is screen diameter, V is wind speed, p̃1/3 is sound pressure of the wind noise in a 1/3-octave band, ρ is fluid density, and S is spectral density of the wind noise at frequency f. Data obtained from various disparate sources form a single curve with surprisingly small scatter for values of dimensionless frequency ( fD/V) up to 5.
Matched field processing: Source localization in correlated noise as an optimum parameter estimation problem
Authors: Baggeroer A. B. , Kuperman W. A. , Schmidt Henrik
Published: October 2005

Matched field processing is a parameter estimation technique for localizing the range, depth, and bearing of a point source from the signal field propagating in an acoustic waveguide. The signal is observed at an array in the presence of additive, spatially correlated noise that also propagates in the same ocean environment as the signal. In a weak signal-to-noise situation this parameter estimation requires the maximum exploitation of the physics of both the signal and noise structure which then must be coupled to optimum methods for the signal processing. We study the physics of this processing by modeling the ocean environment as a waveguide that is horizontally stratified with an arbitrary sound-speed profile in the vertical. Thus, the wave equation describes the underlying structure of the signal and noise, and the signal processing via the generation of the replica fields. Two methods of array processing are examined: (i) the linear cross correlator (Bartlett) and (ii) the maximum likelihood method (MLM) for the parameter estimation procedure. The optimum potential resolution is evaluated using a generalized Cramer–Rao bound. The two processing methods and the lower bound demonstrate that the ability to reject ambiguities is determined not only by the signal-to-noise ratio but also by the relative spatial structures of the signal and noise. Simulations of both the array processing methods and the bounds for shallow water and Arctic environments using full wave modeling of the signal and noise fields illustrate the coupling of the ocean environment to the localization performance.
Analysis of multipath sound propagation in the ocean near 49° N, 128° W
Authors: Sen Mrinal K. , Frazer L. N. , Mallick S. , Chapman N. R.
Published: October 2005

Downslope sound propagation data collected off the west coast of Vancouver Island, British Columbia for a shallow source and a deep receiver are examined. The approach used in our analysis was, first, to identify ray paths from the source to the receiver and then to model the variation in measured pressure amplitude with range. The bottom interacting rays, bottom penetrating rays, and channel rays with bottom interaction were identified by the travel time differences between different bottom-bounce paths. Travel times were computed by ray tracing with an algorithm in which the time step along the ray is the independent parameter. Different propagation paths could be identified in different bathymetric regions viz., continental shelf, continental slope, and deep ocean. A ridge at a range of 79 km shadowed some of the propagating rays; ray tracing from the apex of the ridge was used to calculate travel time curves for some of the diffracted arrivals; however, these diffracted arrivals were difficult to identify in the data. Data collected in the range of 1–52 km were modeled by computing synthetic sonograms using a reflectivity technique modified to remove phase from the vertical wavefunctions. These synthetics were used to constrain the velocity, velocity gradient, sediment thickness, and the absorption coefficient in the upper part of the sediment.
Comparison of electrophonic and auditory-nerve electroneural responses
Authors: Lusted Hugh S. , Simmons F. Blair
Published: October 2005

Electrophonic and auditory-nerve electroneural responses were recorded from the inferior colliculus of the cat. The electrophonic response appeared at a latency 1.0–1.5 ms later than the electroneural response, due to the time requirements for cochlear transduction. The electrophonic response also demonstrated very slow growth of response amplitude with increasing stimulus current as compared to the electroneural response. Aminoglycoside perfusion of the cochlea eliminated the electrophonic component from the evoked response record and left the electroneural component relatively unchanged, indicating that the electrophonic is an acoustic stimulus that requires an intact auditory end organ for transduction.
Comodulation masking release for multicomponent signals
Authors: Hall Joseph W. , Grose John H. , Haggard Mark P.
Published: October 2005

Detection of signals composed of one, two, or three pure-tone components was examined in comodulated and noncomodulated masking noises. The masking noise was either a single 30-Hz-wide narrow band of noise, two narrow bands of noise, or three narrow bands of noise. Comodulation masking release (CMR) was greatest when (1) the signal was a single pure tone; (2) the masker was composed of three noise bands (as opposed to two); and (3) at least one flanking band was lower in frequency than the signal. Substantial CMRs did occur, however, for two- and three-component signals presented in two- and three-component maskers, respectively. The results of the present experiments did not support a ‘‘dip listening’’ hypothesis, nor models based strictly on across-frequency differences in stimulus envelope pattern or correlation. The results were more consistent with a model of CMR in which across-frequency envelope difference is coded by subtracting the envelope at the signal frequency from the envelope at a flanking frequency.
High-frequency scattering from rigid prolate spheroids
Authors: Sammelmann Gary S. , Trivett D. H. , Hackman Roger H.
Published: October 2005

The scattering of an acoustic plane wave by a rigid, immovable prolate spheroid is investigated over a broad frequency range (0<kL/2≤300). An unexpectedly large, off-axis radiation lobe dominates the bistatic beam pattern for axial incidence and aspect ratios larger than unity, over the entire frequency range considered. This lobe is found to be due to an amplitude-modulated creeping wave. A new asymptotic expansion of the spheroidal radial functions is introduced that gives an improved estimate of the functions for moderate values of the azimuthal index at high frequency.
Sound scattering by cylinders of finite length. I. Fluid cylinders
Authors: Stanton T. K.
Published: October 2005

There are many different finite length scatterers in the ocean such as marine biota in the water column and protuberances (or ‘‘bosses’’) on the seafloor, sea surface, and underside of sea ice. Since it is impossible to describe scattering from the exact shape of most objects, one must use simple geometrical objects such as spheres, spheroids, or finite cylinders as the approximate shape. In this article, the scattering of an incident plane wave by a fluid finite circular cylinder is described for all frequencies. By neglecting end effects, the volume flow per unit length of the scattered field of the finite cylinder is approximated by that of the infinite cylinder. The solution is obtained by integrating this volume flow along the length of the cylinder. This approximation restricts the solution to geometries where the incident waves are normal or near normal to the axis of the cylinder. The solution is adapted to describe the scattering of sound by shrimp, which are elongated fluid-saturated marine organisms. There was excellent agreement between the adapted solution and shrimp backscatter data.
Reflection and transmission by an infinite array of randomly oriented cracks
Authors: Mikata Y. , Achenbach J. D.
Published: October 2005

Reflection and transmission of an antiplane shear wave by an infinite array of randomly oriented cracks in an isotropic elastic medium are investigated. The problem has been formulated for an averaged scattered field, and a ‘‘periodization’’ technique has been developed to derive the governing singular integral equation for the conditionally averaged crack-opening displacement. The singular integral equation has been solved by splitting the kernel into a singular and a regular part. A point scatterer approximation was introduced for the part containing the regular kernel. The approximation has been checked by comparison with exact results for a deterministic periodic system. By using this approximation, the coherent part of the averaged reflection and transmission coefficients of zeroth order has been calculated for normal incidence, a completely random crack orientation, and various values of the wavenumber and the ratio of crack length and crack-center spacing. The problem was formulated in the context of antiplane shear waves. The results are, however, also applicable to reflection and transmission of acoustic or electromagnetic waves by an array of screens.
Subjective acceptability of various regular twelve-tone tuning systems in two-part musical fragments
Authors: Vos Joos
Published: October 2005

Musically trained subjects rated the overall acceptability of the performance of two-part musical fragments. With the help of a computer these fragments were produced with intonations according to various regular 12-tone tuning systems: Pythagorean tuning (tempering T of the fifths equal to 0.0 cent), equal temperament (T=−2.0 cents), Silbermann (T=−3.9 cents), mean-tone (T=−5.4 cents), and Salinas tuning (T=−7.2 cents). In experiment 1, two systems in which T=2.0 or T=−10.0 cents were also included. In both the lower and the higher parts of the fragments we used complex tones with a spectral-envelope slope of −6 dB/oct. Mean acceptability ratings were about the same for −5.4≤T≤0.0 cent, whereas for T>0.0 and T<−5.4 cents the ratings strongly decreased. This effect of tuning system was also found when acceptability was determined by means of the method of paired comparisons. The specific effect of tuning system was not affected by the tempo of the fragments. The perception of beats in the harmonic intervals was manipulated in experiment 2 by varying the spectral content of the tones. The condition in which the interference of the nearly coinciding harmonics was canceled resulted in higher acceptability. The effect of tuning system was the same as in experiment 1. In both experiments overall acceptability could be accurately predicted from a linear combination of the purity ratings of the isolated harmonic fifths and major thirds. It is not precluded, however, that for T>0.0 and T<−5.4 cents, the subjects based their acceptability ratings partly on the subjective purity of the melodic intervals.
Is the structure of bat echolocation calls an adaptation to the mammalian hearing system?
Authors: Menne Dieter
Published: October 2005

A common feature of most bat echolocation calls is their hyperbolalike frequency modulation. It is proposed that these calls evolved as an adaptation to the filters in the peripheral hearing system. From an analysis of 420 echolocation sounds of Eptesicus fuscus, the bandwidths of filters giving a minimal error of time-delay estimation are predicted; these could be compared to neurophysiological findings.