bluuebunny/crossref_metadata_2025 huggingface dataset:
High-frequency reflection and scattering of sound by ellipsoidally embossed surfaces
Authors: Lucas R. J. , Twersky V.
Published: October 2005

Earlier results for coherent reflection and incoherent scattering by embossed rigid or free surfaces [V. Twersky, J. Acoust. Soc. Am. 29, 209–225 (1957); 73, 85–94 (1983)] are applied to ellipsoidal bosses with axes large compared to wavelength. The asymptotic procedures used originally for circular cylinders and spheres, and, subsequently, for elliptic cylinders [J. E. Burke and V. Twersky, J. Acoust. Soc. Am. 40, 883–895 (1966)], are generalized to triaxial ellipsoids, and results for the corresponding bosses are obtained by the image method. Illustrative curves for both isotropic and anisotropic surfaces exhibit the influences of boss shape and orientation on the coherent reflection coefficients and incoherent differential scattering cross sections per unit area with emphasis on forward-(specular) and backscattered effects.
Generalized Doppler effect: Coherent and incoherent spectra
Authors: Censor Dan , Newhouse Vernon L.
Published: October 2005

The generalized Doppler effect spectrum produced by particles moving on arbitrary trajectories is analyzed. Scattering by a single particle moving in the farfield of a transmitter and a receiver is considered. It is shown that the Doppler spectrum exciting the particle is due to two factors: The longitudinal (or radial) component of the motion produces a spectrum similar to the conventional Doppler effect, by affecting the phase of the excitation wave. In addition, spectral effects are produced by the particle moving transversely (or angularly) through the spatially modulated radiation pattern of the transmitter. By virtue of the reciprocity properties of transmitters and receivers, each spectral component of the excitation signal again gives rise to spectra induced by the longitudinal and the transversal components of the motion relative to the receiver. The combined Doppler spectrum observed at the receiving transducer or antenna output is a convolution of all four spectra. The behavior of an ensemble of scattering particles is analyzed. The statistics are found by defining the particle and/or the trajectory parameters as random variables. Presently, it is assumed that the particles are identical, their positions are uncorrelated, and multiple scattering is ignored. It is shown that the interference of scattered waves from various particles, manifested in the coherent radiation, gives rise to a spectrum that might be different from that of a single particle. In special cases, the combined spectrum degenerates into a single frequency, and when this is the transmitter’s frequency, the Doppler effect completely disappears. This explains the fact that when we have moving media, but the boundary surfaces are at rest, there is no Doppler effect. The results of the present analysis contribute to our understanding of Doppler velocimetry methods using ultrasound or laser radiation in medical and industrial instrumentation.
Wideband acoustic response of fluid-saturated porous rocks: Theory and preliminary results using waveguided samples
Authors: Schmidt Ehud J.
Published: October 2005

The complex dilatational (C*12) and shear (C*44) frequency-dependent elastic constants of nonporous and porous solids are measured in a frequency range 5kHz to 1 MHz. The measurements are performed in a continuous wave acoustic transmission bridge using cylindrical samples. Using samples with free external surfaces produces waveguided modes, enabling experiments to be conducted circumventing problems of diffraction and wavefront spreading, which are difficult to correct over broad frequency ranges. The theory of waveguided elastic wave propagation in isotropic media with complex elastic constants [generalization of the Pochammer–Cree solution, Pochammer, J. Math. (Crelle) 81, 324 (1876)] is presented. For solids with frequency-independent complex elastic constants (constant Q), solution of the resulting dispersion relations reveals the appearance of specific dissipation peaks associated with waveguide geometry. The dispersion relations are utilized in the inversion of torsional shear and extensional experimental results from nonporous and porous solids, thus obtaining their complex frequency-dependent effective elastic constants. A great variation in the elastic constants of Plexiglas with frequency is demonstrated. Evidence of the effects of pore scattering and the reduction of matrix moduli due to water adsorption is shown for porous glass. The effects of adsorption on the effective elastic moduli of porous solids are quantified utilizing the concept of surface elastic constants [M. E. Gurtin and I. A. Murdoch, Arch. Rat. Mech. Anal. 57, 291 (1975)]. The resulting equation reveals the importance of the surface to volume ratio in determining the effective elastic constants.
Prediction of the nonlinearity parameter of a liquid from the Percus–Yevick equation
Authors: Endo Harumi
Published: October 2005

Using the compressibility of the Percus–Yevick equation, where a liquid is regarded as a hard sphere molecule, a nonlinearity parameter B/A of the liquid was calculated. The ratio B/A is in fair agreement with the experimental value. The expression of B/A has revealed information on the importance of geometrical packing effect on B/A.
Controlled experiments of the diffraction of sound by a curved surface
Authors: Berry Alain , Daigle G. A.
Published: October 2005

Controlled measurements of the sound field from a point source above a curved surface are described. The measurements were made in the frequency range between 0.3 and 10 kHz, in the case of a rigid boundary and a surface of finite impedance. Receiver positions include all of the area within, and above, the shadow zone and for various source heights. Particular attention is given to the region across the shadow boundary. The measurements are compared to diffraction theory expressed in terms of a residue series, or creeping wave solution. The calculation is extended by removing restrictive approximations and by carrying the computation to higher-order terms. A numerical algorithm allows the extension to the general case of a finite impedance. Above the shadow boundary, the sound field is calculated using geometrical theory that accounts for reflections from a curved surface. Deep within the shadow, theory and measurements agree to, typically, 0.5 dB. The same agreement is obtained between measurements and the geometrical theory well above the shadow boundary. In the vicinity of the shadow boundary, both theories agree to within 0.5 dB but differ from the measured results by 2 to 5 dB. Finally, the theory is compared to measurements obtained outdoors above a grass covered curved ground with no refraction and above flat ground with refraction.
Numerical ray tracing in the atmospheric surface layer
Authors: Hallberg Bengt , Larsson Conny , Israelsson Sven
Published: October 2005

A numerical ray-tracing model, including calculation of the sound pressure, was developed. It is valid for propagation from a point source in a moving, stratified atmosphere. Numerical integration of the ray equations was performed, and all rays reaching a specific point were found. Several expressions for the height dependency of the wind speed and the temperature were used, e.g., Monin–Obukhov similarity theory functions, the parameters of which were determined by use of a least-squares method. Measurements of sound propagation from a point source over finite impedance ground were made. Meteorological parameters were monitored simultaneously, wind direction and relative humidity at a single height, wind speed and temperature at five elevations. Comparison with the model was made out to a distance of 150 m. The agreement between the model values and those measured was good. The influence of the directional characteristics of the source was studied, and found to be very important.
A generalized approach to acoustic intensity
Authors: Kelly Jeffrey J.
Published: October 2005

An approach to acoustic energy considerations by employing the general theory of mechanics of continua is the topic of this article. A description of power flow is developed from the first law of thermodynamics instead of utilizing combinations of the linearized governing equations describing a continuous medium. The main aim is the derivation of energy equations when a mean background flow is present. The actual energy flux in moving media is first considered. After this, the appropriate energy equations to consider in moving media are taken up. In the first case, an accurate interpretation of energy flux is essential to determine the power output and location of a sound source. For the second topic, acoustic energy equations can describe conservation principles. These, in turn, can be used to determine regions where dissipation is occurring.
Calculations pertaining to the dipole nature of the edgetone
Authors: Ohring Samuel
Published: October 2005

Calculations are performed to verify the dipole nature of the edgetone in which the flow consists of an incompressible two-dimensional jet issuing from a nozzle and impinging on a fixed rigid wedge-shaped body. The wedge body is abruptly removed from a previously computed, laboratory-verified, multifrequency edgetone flow at a Reynolds number of 450 and replaced by an oscillating dipole. The dipole strength is treated as unknown and part of the solution process but is such that the combination of the dipole flow and jet flow yields a transverse jet velocity time trace near the the dipole identical to that from the previously computed edgetone flow. The resultant flow field is numerically computed for a Reynolds number of 450 and, after initial start-up effects, the flow field for the latest cycle computed strongly resembles that of the previously computed edgetone flow. Results for the jet–dipole flow are given in the form of stream function and equivorticity contour plots and jet spectra. In addition, sound-pressure radiation due to a fluctuating pressure distribution at the surface of the wedge-shaped body is computed using data from the previously calculated edgetone flow. The moduli of the computed sound-pressure components corresponding to various time frequencies reveal on polar plots a figure eight pattern in the farfield with the largest component or tone associated with the frequency of jet impingement. According to theory, this is the farfield sound pattern due to a fluctuating dipole centered at the wedge tip with axis transverse to the wedge tip.
Random-bottom structural effects on shallow-water sound transmission using a modified ray theory
Authors: Ashley C. E. , Jacobson M. J. , Siegmann W. L.
Published: October 2005

A modified ray theory is used to study the effects on acoustic intensity of randomness in bottom structure. A shallow isospeed ocean channel with horizontal boundaries is assumed. The randomness is produced by stochastic variations in the bottom density and sound speed in the horizontal direction beneath the water–bottom interface. Beam and time displacements at the ocean bottom are incorporated into each acoustic ray. Ray geometry, spreading loss, and bottom loss are analyzed in order to obtain expressions for the mean and variance of intensity at a point receiver for a transmitted cw signal. Formulas are sufficiently general to permit their use with different bottom-acoustic models of sound reflection. In order to incorporate bottom attenuation simply, Mackenzie theory is employed here. The distinctive acoustic consequences of bottoms of different density mean and horizontal correlation are discussed. In addition, comparisons of results using the modified ray theory and standard ray theory are provided. Also, intensity moments are described for differing source–receiver range, water depth, and acoustic frequency.
Numerical computations of time-domain diffractions from wedges and reflections from facets
Authors: Clay C. S. , Kinney Wayne A.
Published: October 2005

Numerical computations of time-domain impulsive functions require a low-pass-filter operation to satisfy the Nyquist sampling rule. For example, the exact impulsive solutions for diffraction and reflection from a rigid wedge [M. A. Biot and I. Tolstoy, J. Acoust. Soc. Am. 29, 381–391 (1957)] both have singularities at their initial arrival times. These particular solutions can be approximated and low-pass filtered to satisfy the sampling rule in numerical computations. In evaluating specular reflection from a finite plane facet, a reinterpretation of the physical meanings of the terms resulting from the impulsive solution of the Fresnel–Kirchhoff integral is introduced [M. Born and E. Wolf, Principles of Optics (Pergamon, Oxford, 1965), Sec. A.9, and A. W. Trorey, Geophysics 35, 762–784 (1970)]. It is believed that the solution contains terms associated only with reflection, and that the interpretation of the Rubinowicz representation of the boundary terms as boundary diffraction waves is physically incorrect. As a consequence, for amplitude calculations of a specular facet reflection, a working hypothesis is proposed, namely that the reflected amplitude is proportional to the incident signal where the constant of proportionality is a function of the geometry, facet width, and the signal waveform. By numerical studies, the constant of proportionality g(v) can be expressed as a polynomial in v, where v=w(λAr)1/2, w is the facet width, λA is the wavelength corresponding to the peak frequency of the signal, and r is the distance from a colocated source and receiver to the facet. The function g(v) depends on the waveform of the signal (i.e., a boxcar, single cycle of a sinewave, etc.). As v tends to zero, the facet reflection tends to zero. For large v (>2 or 3), g(v) tends to one and the facet reflection is effectively that from a full plane.
Differences in fricative production between children and adults: Evidence from an acoustic analysis of /∫/ and /s/
Authors: McGowan Richard S. , Nittrouer Susan
Published: October 2005

Speech samples of 12 speakers (8 children and 4 adults) producing the fricatives /s/ and /∫/ followed by the vowels /i/ and /u/ were analyzed to locate the major spectral prominences. Results showed that the fricative low-frequency prominences for children’s samples differed from those of adults in three important ways: (1) They were generally higher in frequency; (2) they were greater in amplitude relative to higher frequency regions; and (3) they showed greater effects of vowel context. The first finding can be explained by a simple scaling of adult models of fricative production to accommodate children’s smaller vocal tracts. The other two findings suggest, however, that there are other anatomical and articulatory differences between children and adults affecting fricative production. The data presented here suggest that one important difference may be the relative sizes of the fricative constriction and the glottal opening.
Sentence reception in noise from one versus two sources: Effects of aging and hearing loss
Authors: Gelfand Stanley A. , Ross Leslie , Miller Sarah
Published: October 2005

Sentence reception thresholds (SRTs) and babble detection thresholds (BDTs) were measured for signals presented from loudspeakers located at 0 deg and 90 deg azimuth. In addition, the S/B ratios necessary to achieve SRT in the presence of a 12-talker babble were determined under three conditions in which the speech and babble were presented from the same or spatially separated loudspeakers. In the first experiment, normal-hearing subjects were tested on two occasions. The results were highly reliable, with standard errors of the test–retest differences of less than 1dB for all conditions. In the second experiment, SRTs, BDTs, and S/B ratios were measured for three normal-hearing groups (≤39, 40–54, and ≥55 years) and for a fourth group with presbycusis (≥55 years). Presbycusics had higher SRTs and BDTs than all other groups regardless of age, and the oldest normals had higher thresholds than younger subjects. Presbycusics required higher S/B ratios than any of the normal groups, and the oldest normal group needed a higher S/B ratio compared to the youngest group. All groups demonstrated a significant advantage in S/B ratio when the sentences and babble sources were spatially separated compared to when they were presented from the same loudspeaker. There was no significant difference in the magnitude of advantage due to spatial separation of speech and noise between the normal groups regardless of age, but the presbycusics had significantly smaller advantages than all normals. These findings suggest that aging alone does not impair the ability to take advantage of the spatial separation of speech and noise, and that the speech reception problems of aging individuals involve various components that depend upon the nature of the listening task.
Measurement of pitch by subharmonic summation
Authors: Hermes Dik J.
Published: October 2005

In order to account for the phenomenon of virtual pitch, various theories assume implicitly or explicitly that each spectral component introduces a series of subharmonics. The spectral-compression method for pitch determination can be viewed as a direct implementation of this principle. The widespread application of this principle in pitch determination is, however, impeded by numerical problems with respect to accuracy and computational efficiency. A modified algorithm is described that solves these problems. Its performance is tested for normal speech and ‘‘telephone’’ speech, i.e., speech high-pass filtered at 300 Hz. The algorithm outperforms the harmonic-sieve method for pitch determination, while its computational requirements are about the same. The algorithm is described in terms of nonlinear system theory, i.c., subharmonic summation. It is argued that the favorable performance of the subharmonic-summation algorithm stems from its corresponding more closely with current pitch-perception theories than does the harmonic sieve.
GTD for backscattering from elastic spheres and cylinders in water and the coupling of surface elastic waves with the acoustic field
Authors: Marston Philip L.
Published: October 2005

The geometrical theory of diffraction (GTD) has been extended to describe surface elastic wave (SEW) contributions to backscattering from spheres and cylinders in water at high frequencies. The coupling (described by a coefficient Gl ) of the lth class of SEW with the acoustic field and the resulting contribution fl to the form function for solid spheres were previously derived [K. L. Williams and P. L. Marston, J. Acoust. Soc. Am. 79, 1702–1708 (1986)] via a Sommerfeld–Watson transformation (SWT). That work gave a Fabry–Perot representation of fl . A similar representation was postulated by applying the principles of GTD to the Lamb wave contributions to backscattering from empty cylindrical shells [V. Borovikov and N. Veksler, Wave Motion 7, 143–152 (1985)]. In either case, ‖ fl ‖=‖Gl  exp[−2βl ×(π−θl )]/[1+j exp(−2πβl +i2πkac/cl )]‖ ,where j=1 for spheres and j=−1 for cylinders, each of radius a. The SEW phase velocity and attenuation coefficient are cl and βl , sin θl =c/cl , and c and k are the velocity and wavenumber in water. High-frequency resonances of the elastic response were shown to be described by the fl of the relevant SEW. The present work gives approximations for ‖Gl ‖ for spheres and cylinders in terms of βl , c/cl, and ka. These are confirmed by comparison with numerical data for ‖Gl ‖ from Borovikov et al. for cylinders and from SWT results for Rayleigh and whispering gallery waves on spheres. The ratio of the approximate ‖Gl ‖ is confirmed by geometric considerations. The analysis is applicable to other supersonic surface guided waves. The derivation uses results of resonance scattering theory and the identification of a nonresonant SEW ‘‘background.’’
Cochannel speech separation
Authors: Lee C. K. , Childers D. G.
Published: October 2005

The multisignal minimum-cross-entropy spectral analysis (multisignal MCESA) is applied to the problem of separating the speech signals of two talkers speaking simultaneously on a single channel, e.g., when two talkers use a single microphone. A new two-stage approach to the problem is proposed in which a spectral separator is followed by a spectral tailoring procedure. The spectral separator produces an initial estimate of the speech spectrum for each talker. Then the spectral tailoring procedure employs the multisignal MCESA technique to adjust the initial spectral estimates to account for the characteristics of the known cochannel composite speech signal. The research emphasis is placed on the implementation and evaluation of the spectral tailoring procedure, i.e., the use of the multisignal MCESA in the proposed scheme. Its usefulness is evaluated and validated by listening tests and by comparing the spectral distortions of the estimated voices before and after the multisignal MCESA processing.
Parameters of violin plates and their influence on the plate modes
Authors: Molin N. E. , Lindgren L-E. , Jansson Erik V.
Published: October 2005

Noncontact measuring methods and numerical calculations are used in a study of musical instruments. First, a simple method to determine the material parameters of a blank to a violin plate is presented. Eigenmodes of rectangular free–free violin wooden blanks are determined using optical nondestructive methods, Chladni patterns, or tapping. Assuming orthotropic material, the first three eigenmodes for such a blank are calculated using the finite element method (FEM). It is shown that the frequency of each eigenmode depends on separate elastic parameters. With this one variable dependence, it is a simple task to determine effective material parameters for quarter-cut standard wooden blanks when the frequencies and mass are known. Second, the violin maker’s problem with the influence of material and geometrical parameters on the vibration modes is investigated. Numerical models and corresponding real violin plates are made from the spruce and the maple blanks. Good agreement between calculated and experimentally obtained plate modes is found. Calculations with a 10% variation in each parameter are thereafter used to give information about the influence of overall plate thickness variation, of local thickness variations, of changes in arch-height, and of material parameters. Third, boundary conditions for the plates when glued to the ribs are examined in a pilot experiment.
The clarinet spectrum: Theory and experiment
Authors: Benade A. H. , Kouzoupis S. N.
Published: October 2005

While a great deal is known about the oscillation and radiation mechanisms of the clarinet, an overall account has not been provided of the manner in which the tones of a clarinet are generated and then transmitted into the listening room. This article presents such an account for the clarinet in general. Room-averaged spectra measurements are presented that are shown to be consistent with the implications of theory, with both measurement and theory showing a great deal of spectral regularity over the playing range. The fact that the tonehole lattice cuttoff frequency is essentially constant over the scale is of particular importance, making it possible to define a single semiempirical formula for the odd harmonics of all the notes in the scale and a closely related one for the even harmonics. Both of these formulas are fitted to the data by way of the same three adjustable parameters.
Dispersion of waves in piano strings
Authors: Podlesak Michael , Lee Anthony R.
Published: October 2005

A recent survey of piano acoustics literature revealed an apparent lack of attention to various aspects of dispersion in piano strings, apart from some information on its effect on inharmonicity of piano tone partials. In this article, it will be shown how group velocity of transverse waves in piano strings can be measured as a function of frequency with the aid of a short-time spectral analysis method. Examples of group velocity measurements appear to be essentially in agreement with the theoretical predictions based on a model of a flexurally stiff string. In addition, the relationship between the group and phase velocity, as a function of frequency, is also illustrated, indicating correspondence between theoretical predictions and experimental results. A short-time spectral analysis of transverse string displacement as a function of time, monitored near the bridge, has revealed a quasiperiodic succession of frequency glides. This effect is due to dispersion and is particularly prominent in the lowest bass strings. However, the same type of analysis applied to the sound-pressure signal of the corresponding radiated sound yielded somewhat different results. While frequency glides similar to those found in the string displacement spectra were partly evident in the sound-pressure spectra, strong precursive components of longitudinal string vibration origin were found to dominate the higher frequency portion of the attack transient of the radiated sound.
Arterial stenosis murmurs: An analysis of flow and pressure fields
Authors: Abdallah Sanaa A. , Hwang Ned H. C.
Published: October 2005

The flow field distal to an arterial stenosis is simulated by a confined turbulent jet with moderate Reynolds numbers. The wall pressure fluctuations are related to the momentum fluctuations of the jet by the Poisson equation. A Green’s function was derived to satisfy the boundary conditions on a cylindrical surface. This allows the solution of the Poisson’s equation to include only a volume integral of the fluctuating momentum, weighed by the relative distance between the source and the sensor. The velocity fluctuations on the jet centerline and at the middle of the shear layer were measured using a laser Doppler anemometer. The wall pressure fluctuations were detected simultaneously by an array of nine wall-mounted pressure transducers along the axial direction. Cross correlation performed between the velocity and pressure fluctuations reveals that the pressure fluctuations were mostly imposed by the passage of turbulent eddies with a convective velocity that is a function of the jet exit velocity. The Strouhal number, defined by the frequency of the passing large-scale structure, is a function of the initial conditions only very close to the jet exit. Further downstream, where the effect of the initial conditions is lost, the Strouhal number approaches a constant irrespect of the jet Reynolds number. The contribution of a source near the jet exit to wall pressure fluctuation near the reattachment is rather weak due to the rapidly decaying weighting function in the axial direction. However, for sources located within one nozzle diameter from the sensor, the cross-spectral density function has a high magnitude with maximum coherence where the pressure spectral changes its slope.
Waveguide characterization and source localization in shallow water waveguides using the Prony method
Authors: Shang E. C. , Wang H. P. , Huang Z. Y.
Published: October 2005

Horizontal samples of a point source in a shallow water waveguide are processed by the Prony method. First, when the source position is known, a high resolution estimation of the normal mode parameter Km (the horizontal component of mode wavenumber) can be obtained. Owing to the weak damping process, βm, the modal attenuation coefficient, can be obtained by using a modified Prony method. In this article, an ‘‘interval average and iterative’’ approach is proposed. Numerical examples illustrate that a 10−4 resolution of Km (150-Hz frequency) is provided by a 500-m data length, roughly an order of magnitude smaller than the data length required by the linear spectrum analysis technique. Second, when the source position is unknown but the waveguide characters (Km, βm) are known, the same procedure can be used for source position estimation. Some numerical examples in typical shallow water are presented.
Ultrasonic losses at cryogenic temperatures in a Roraima (Venezuela) tuff
Authors: Nava R. , Londoño G.
Published: October 2005

Measurements in a local tuff of the attenuation of ultrasonic waves in the range from 10–60 MHz are reported as a function of temperature from 4–365 K. The relative attenuation in the material is low corresponding to Q’s in excess of 1000 and, except for negligible scattering losses below 150 K, it displays temperature- and frequency-dependent contributions that are sensitive to vacuum outgassing at moderate and high temperatures. Stress relaxations at low temperatures attributed to viscous losses in adsorbed supercooled water films produce an attenuation peak centered around 250 K. A fast rising loss above room temperature is analyzed in terms of thermally activated motions of physisorbed fluid molecules.
The eigenvalue problem for −Δu=λu with Dirichlet boundary conditions for two-dimensional regions. II. T-shaped, cross-shaped, and H-shaped regions
Authors: Hashimoto Kazuo
Published: October 2005

This article deals with the calculation of the eigenvalues and eigenfunctions of the two-dimensional Laplacian with Dirichlet boundary condition for T-shaped, cross-shaped, and H-shaped regions. The method used is the Weinstein method (the intermediate method). The suitable base problem can be obtained through dividing the given region into rectangles and replacing Dirichlet boundary conditions by Neumann boundary conditions on a part of the boundaries. The intermediate problems can be determined by appropriate trial functions, and by the eigenvalues and eigenfunctions for each decomposed rectangle. The numerical results are considered to be reasonably precise. Special attention is paid to the dependence of the eigenvalues and eigenfunctions on parameters of the region. Some consideration is also given to the curve-veering phenomena observed frequently in the numerical results.
Vowel processing by a model of the auditory periphery: A comparison to eighth-nerve responses
Authors: Payton Karen L.
Published: October 2005

A model of peripheral auditory processing that incorporates processing steps describing the conversion from the acoustic pressure-wave signal at the eardrum to the time course activity in auditory neurons has been developed. It can process arbitrary time domain waveforms and yield the probability of neural firing. The model consists of a concatenation of modules, one for each anatomical section of the periphery. All modules are based on published algorithms and current experimental data, except that the basilar membrane is assumed to be linear. The responses of this model to vowels alone and vowels in noise are compared to neural population responses, as determined by the temporal and average rate response measures of Sachs and Young [J. Acoust. Soc. Am. 66, 470–479, (1979)] and Young and Sachs [J. Acoust. Soc. Am. 66, 1381–1403, (1979)]. Despite the exclusion of nonlinear membrane mechanics, the model accurately predicts the vowel formant representations in the average localized synchronized rate (ALSR) responses and the saturating characteristics of the normalized average rate responses in quiet. When vowels are presented in background noise, the modeled ALSR responses are less robust than the neural data.
A liquid-metal magnetohydrodynamic acoustic transducer
Authors: Swift G. W.
Published: October 2005

The properties of a liquid-metal magnetohydrodynamic acoustic power transducer have been both calculated and measured. The calculations are based on linearized Navier–Stokes and Maxwell’s equations, and include Ohmic and viscous dissipation in the liquid metal. The measurements were made with liquid sodium at frequencies of about 1 kHz in a channel much larger than the viscous penetration depth but comparable in size to the electromagnetic skin depth. Calculated and measured quantities are in good agreement, indicating a quantitative understanding of this transducer. It converts acoustic power to electric power with 45% efficiency; substantially higher efficiencies appear possible with a slightly modified design.
The saxophone spectrum
Authors: Benade A. H. , Lutgen S. J.
Published: October 2005

The geometrical nature of the saxophone air column is outlined, along with a sketch of the theory of sound production and radiation of saxophones. The discussion is based upon a similar but somewhat more detailed discussion of the clarinet and its spectrum published recently by Benade and Kouzoupis [J. Acoust. Soc. Am. 83, 292–304 (1988)]. Room-averaged spectra were measured for essentially all notes in the low and second registers of a B-flat tenor and an E-flat alto saxophone played at a mezzoforte level (so that the reed was beating steadily). It is shown that the observed spectra have a great regularity of pattern that is in good agreement with theoretical expectation. All amplitudes of spectral components of all notes fit the same spectrum envelope function, E(x)=[Nx/(1+x7)]1/2. Here, N is a normalizing constant and x=f/fb, where fb is a break frequency characteristic of the instrument. This break frequency is closely related to the instrument’s tonehole lattice cutoff frequency fc. In addition to the f1/2 (3-dB/oct) spectral rise below fb and the 1/f3 fall (18 dB/oct) above fb, we find one or more ‘‘spectral notches’’ in the envelope. These are associated with the fact that the reed is beating, and they may lie almost anywhere in the upper part of the spectrum. The values of fb for the tenor and the alto saxophones are 618 and 837 Hz. These lie about a semitone below the break frequencies that would be calculated for such transposing instruments on the basis of the 1500-Hz fc that belongs to essentially all of the nontransposing soprano instruments. The systematic behavior of the spectrum when the instruments are played at a stronger or weaker dynamic level is also outlined and explained.
On the estimation of acoustic attenuation coefficient from peaks of echo envelope
Authors: He Ping
Published: October 2005

A noticeable problem in estimating the acoustic attenuation coefficient (the slope of the attenuation versus frequency, a parameter denoted by β) of soft tissue using current frequency-domain methods is the large variance of the estimate. As a consequence, the reliability of the measurement of the value of β as a method of tissue characterization is reduced. This variance of the β estimate can be much decreased by using a newly developed time-domain method—the envelope peak (EP) method. When the value of β is estimated from the same rf samples of one A line based on the maximum-likelihood principle, theoretical analysis indicates that in comparison with the frequency methods, the EP method produces more independent data points for least-squares fitting, each data point having a smaller variance. The results of these two effects is a reduction of nearly 50 times in the variance of the β estimate under typical scan conditions. Preliminary results from phantom experiments and in vivo liver scan supported the above analysis.
The acoustic features of vervet monkey alarm calls
Authors: Owren Michael J. , Bernacki Robert H.
Published: October 2005

Vervet monkeys routinely produce semantic alarm calls upon detection of various predators encountered in their natural environment. Two of these calls, snake and eagle alarms, were analyzed using digital signal processing techniques in order to identify potentially distinctive acoustic cues. Distinctive cues were sought in the periodicity of the source waveform associated with each call type, the probable vocal tract filtering functions, and in temporal patterning. Results were equivocal with respect to source periodicity, but a variety of distinguishing features were found in both supralaryngeal filtering and timing. These data provide a basis for psychoacoustic perceptual testing with vervets as subjects.
Tone ringer using polyvinylidene fluoride (PVDF) piezoelectric film
Authors: Garner Geoffrey M. , Holden Anthony J.
Published: October 2005

A theory has been developed that describes the dynamic operation of thin piezoelectric plastic domes of polyvinylidene fluoride formed by deflecting planar sheets of the film with compliant plastic foam. The theory describes the behavior of a novel double-dome structure designed as a telephone tone ringer transducer that will produce 80 dB SPL at 1 m at frequencies around 1 kHz when driven at 30-V rms.
A computer simulation of hearing aid response and the effects of ear canal size
Authors: Kates James M.
Published: October 2005

The response of a hearing aid is affected by many factors which include the head and outer ear, the microphone, amplifier, and receiver used in the hearing aid, the properties of the ear canal and the eardrum, and acoustic feedback through the vent. This article presents a computer simulation of an in-the-ear (ITE) hearing aid that includes all of the above factors. The simulation predicts the pressure at the eardrum for a frontal free-field sound source. The computer model was then used to determine the effects on the hearing aid response due to variations in the size of the ear canal. The simulation indicates that, for an unvented hearing aid, changes in the size of the ear canal shift the overall sound-pressure level at the eardrum but have only small effects on the shape of the frequency response. The situation is more complicated when a vent is present, however, since changes in the size of the ear canal that cause apparently small perturbations in the acoustic feedback signal may, nonetheless, have large effects on the overall system response.
The effect of masker interaural phase on the detection of a monaural signal
Authors: Hall Joseph W. , Helfer Karen
Published: October 2005

The masking-level difference (MLD) for a 500-Hz monaural pure-tone signal was examined as a function of the interaural phase shift of a 100-Hz-wide noise band centered on 500 Hz. Results indicated that the MLD decreased in magnitude as the interaural phase shift of the masker increased. In a second experiment, the 100-Hz-wide noise band was used as both the masker and the signal in order to examine the detection cues of interaural time difference and interaural level difference separately. Again, the interaural phase of the masker was varied, and an Sm signal was presented. Results indicated that the MLD decreased as a function of increasing masker interaural temporal difference for the time cue, but that the MLD did not change systematically for the level cue. The deterioration of binaural detection as a function of increasing masker interaural phase difference was not as great as that which has been reported in localization and lateralization experiments.
Long-range scattering in a deep oceanic waveguide
Authors: Hackman Roger H. , Sammelmann Gary S.
Published: October 2005

A general formalism is developed for the scattering from an arbitrarily shaped elastic shell in a range-independent, inhomogeneous-layered waveguide with an arbitrary sound-speed profile. This formalism is exact and valid through all orders of multiple scattering between the scatterer and the waveguide. The waveguide is terminated with a rigid bottom to avoid the branch cut associated with an infinite half-space, however there is sufficient flexibility to include multilayered, bottom sediment structure. This formalism is applied to the long-range, low-frequency acoustic scattering of a broadband acoustic pulse by an elastic spherical shell in a range-independent, deep ocean waveguide.
Discrimination of interaural differences of level as a function of frequency
Authors: Yost William A. , Dye Raymond H.
Published: October 2005

Discrimination of interaural differences of level (IDLs) was measured for pure tones as a function of frequency and as a function of the interaural difference of phase or level of a standard. Varying the interaural difference of the standard was assumed to change the lateral position of its intracranial image. Threshold IDLs were approximately constant over a frequency range from 200–5000 Hz, except in a region near 1000 Hz where they were slightly elevated. Thresholds increased as the value of the standard interaural differences of phase or level increased, implying that interaural resolution declines as the lateral image moves away from midline. The results are generally consistent with the predictions of current models of lateralization, but additions to these models are required in order for them to account for the slight frequency dependence of threshold IDLs.
Articulatory correlates of stress and speaking rate in Swedish VCV utterances
Authors: Engstrand Olle
Published: October 2005

Articulatory activity underlying changes in stress and speaking rate was studied by means of x-ray cinefilm and acoustic speech records. Two Swedish subjects produced vowel–consonant–vowel (VCV) utterances under controlled rate–stress conditions. The vowels were tense /i a u/, and the consonants were the voiceless stops, notably /p/. The spectral characteristics of the vowels were not significantly influenced by changes in the speaking rate. They were, however, significantly emphasized under stress. At the articulatory level, stressed vowels displayed narrower oral tract constrictions than unstressed vowels at the two speaking rates studied. At the faster speaking rate, vowel- and consonant-related gestures were coproduced to a greater extent than at the slower rate. The data, failing to produce evidence for an ‘‘undershoot’’ mechanism, support the view that dialect-specific correlates of stress are actively safeguarded by means of articulatory reorganization.
Acoustic observations in young children’s non-cry vocalizations
Authors: Robb Michael P. , Saxman John H.
Published: October 2005

A corpus of 1200 non-cry vocalization samples produced by 14 normal children between the ages of 11–25 months was examined retrospectively. Six percent of the samples yielded instances of either harmonic doubling (HD), fundamental frequency (F0) shift, or biphonation (Bp). These spectrographic features relate to short duration changes in F0, reflecting alterations in vocal fold state characteristics. The HD and Bp segments were perceptually judged to be harsh, while F0 shift closely reflected pitch breaks. The frequency of occurrence of the three acoustic features suggests that they are normally occurring phonatory events in normal children’s vocal patterns.
Perception of the [m]–[n] distinction in VC syllables
Authors: Repp Bruno H. , Svastikula Katyanee
Published: October 2005

This study complements earlier experiments on the perception of the [m]–[n] distinction in CV syllables [B. H. Repp, J. Acoust. Soc. Am. 79, 1987–1999 (1986); B. H. Repp, J. Acoust. Soc. Am. 82, 1525–1538 (1987)]. Six talkers produced VC syllables consisting of [m] or [n] preceded by [i,a,u]. In listening experiments, these syllables were truncated from the beginning and/or from the end, or waveform portions surrounding the point of closure were replaced with noise, so as to map out the distribution of the place of articulation information for consonant perception. These manipulations revealed that the vocalic formant transitions alone conveyed about as much place of articulation information as did the nasal murmur alone, and both signal portions were about as informative in VC as in CV syllables. Nevertheless, full VC syllables were less accurately identified than full CV syllables, especially in female speech. The reason for this was hypothesized to be the relative absence of a salient spectral change between the vowel and the murmur in VC syllables. This hypothesis was supported by the relative ineffectiveness of two additional manipulations meant to disrupt the perception of relational spectral information (channel separation or temporal separation of vowel and murmur) and by subjects’ poor identification scores for brief excerpts including the point of maximal spectral change. While, in CV syllables, the abrupt spectral change from the murmur to the vowel provides important additional place of articulation information, for VC syllables it seems as if the formant transitions in the vowel and the murmur spectrum functioned as independent cues.
Absence of overshoot in a dichotic masking condition
Authors: McFadden Dennis
Published: October 2005

Brief tonal signals presented soon after the onset of a masking noise are known to be less detectable than signals delayed by several hundred milliseconds. This difference in detectability is known as the ‘‘overshoot.’’ Signals of two sorts were studied here—either interaurally in phase (So) or interaurally out of phase by 180°(Sπ). When So signals of 750 Hz and about 14 ms in duration were presented 4 ms after the onset of a diotic, broadband masking noise (No), detectability was about 6 dB worse than when the signal was presented 325 ms after onset. By contrast, there was no such overshoot when Sπ signals were presented at varying times after masker onset; detectability was about the same for all values of signal delay. Accordingly, the difference in performance between NoSo and NoSπ—the masking-level difference or MLD— was large (about 16 dB) with the shortest delays used and diminished (to about 9 dB) as the delay was increased. This absence of overshoot with the Sπ signals is in accord with the well-established view that detectability in the dichotic masking conditions is based upon different stimulus information from that used in the diotic masking conditions. Specifically, the evidence confirms the common view that detectability in the diotic conditions is based more or less directly on neural firing rate, whereas, in the dichotic conditions, it is based upon interaural time differences encoded in the periodicity of neural firings.
Acoustic scattering by baffled cavity-backed membranes
Authors: Baker William P. , Kriegsmann Gregory A. , Reiss Edward L.
Published: October 2005

A flexible membrane backed by a rigid cavity is set into an infinite plane baffle. The upper half-space contains an acoustic fluid, and the cavity which lies in the lower half-space, contains another acoustic fluid. A time harmonic wave in the upper half-space is incident on the plane. When the frequency of the incident wave is bounded away from the resonant (natural) frequencies of the membrane, and of the acoustic fluid in the cavity, the reaction of the fluid on the cavity-backed membrane (CBM) is small. However, near a resonant frequency, the fluid–CBM coupling is significant. The method of matched asymptotic expansions is employed to obtain an asymptotic expansion of the scattered field as ε→0 that is uniformly valid in the frequency of the incident wave. Here, ε≪1 is the ratio of the upper half-space fluid and membrane densities. Simple and double resonant frequencies are analyzed; but the method is applicable to higher-order resonant frequencies. The method is applied to the normal incidence of a plane wave on a baffled circular membrane that is backed by a circular cylindrical cavity. It is found that the CBM is a more ‘‘susceptible’’ scatterer than the vacuum-backed membrane (VBM). In addition, the signature of the CBM differs from the signature of the VBM. For example, the scattered amplitude for the CBM has peaks with bandwidths of O(ε2), in addition to the peaks with bandwidths of O(ε) corresponding to the membrane resonant frequencies. Moreover, the CBM can have resonant ‘‘packets’’ that are of total bandwidth (ε)1/2.
High-frequency attenuation measurements using an acoustic microscope
Authors: Gracewski Sheryl M. , Waag Robert C. , Schenk Eric A.
Published: October 2005

An acoustic microscope was used to measure excess attenuation of aqueous solutions of sugars and proteins at 1.0 GHz. Interference pattern spacing and peak amplitude reduction of V(z) curves, obtained with these solutions as the acoustic microscope coupling liquid, were related to the solution wavespeed and attenuation, respectively. Consistent with published results for lower frequencies, solutions with molecular weight greater than 10 000 had a higher specific absorption than those with a molecular weight less than 1000 and within these two molecular weight ranges specific absorption was independent of concentration.