Volume 105, Issue 3, March 1999
- acoustical news—usa
- reviews of acoustical patents
- selected research articles 
- general linear acoustics 
- nonlinear acoustics 
- underwater sound 
- ultrasonics, quantum acoustics, and physical effects of sound 
- transduction 
- structural acoustics and vibration 
- architectural acoustics 
- acoustical measurements and instrumentation 
- acoustic signal processing 
- physiological acoustics 
- psychological acoustics 
- speech production 
- speech perception 
- speech processing and communication systems 
- music and musical instruments 
- music and musical instruments 
- bioacoustics 
- letters to the editor
Index of content:
- REVIEWS OF ACOUSTICAL PATENTS
105(1999); http://dx.doi.org/10.1121/1.426749View Description Hide Description
The purpose of these acoustical patent reviews is to provide enough information for a Journal reader to decide whether to seek more information from the patent itself. Any opinions expressed here are those of the reviewers as individuals and are not legal opinions. Printed copies of United States Patents may be ordered at $3.00 each from the Commissioner of Patents and Trademarks, Washington, DC 20231. Patents are available via the Internet at http://www.uspto.gov.
- SELECTED RESEARCH ARTICLES 
105(1999); http://dx.doi.org/10.1121/1.426686View Description Hide Description
Changes in magnitude and variability of duration, fundamental frequency, formant frequencies, and spectral envelope of children’s speech are investigated as a function of age and gender using data obtained from 436 children, ages 5 to 17 years, and 56 adults. The results confirm that the reduction in magnitude and within-subject variability of both temporal and spectral acoustic parameters with age is a major trend associated with speech development in normal children. Between ages 9 and 12, both magnitude and variability of segmental durations decrease significantly and rapidly, converging to adult levels around age 12. Within-subject fundamental frequency and formant-frequency variability, however, may reach adult range about 2 or 3 years later. Differentiation of male and female fundamental frequency and formant frequency patterns begins at around age 11, becoming fully established around age 15. During that time period, changes in vowelformant frequencies of male speakers is approximately linear with age, while such a linear trend is less obvious for female speakers. These results support the hypothesis of uniform axial growth of the vocal tract for male speakers. The study also shows evidence for an apparent overshoot in acoustic parameter values, somewhere between ages 13 and 15, before converging to the canonical levels for adults. For instance, teenagers around age 14 differ from adults in that, on average, they show shorter segmental durations and exhibit less within-subject variability in durations, fundamental frequency, and spectral envelope measures.
Does music performance allude to locomotion? A model of final ritardandi derived from measurements of stopping runners105(1999); http://dx.doi.org/10.1121/1.426687View Description Hide Description
This investigation explores the common assumption that music and motion are closely related by comparing the stopping of running and the termination of a piece of music. Video recordings were made of professional dancers’ stopping from running under different deceleration conditions, and instant values of body velocity, step frequency, and step length were estimated. In decelerations that were highly rated for aesthetic quality by a panel of choreographers, the mean body velocity could be approximated by a square-root function of time, which is equivalent to a cubic-root function of position. This implies a linear relationship between kinetic energy and time, i.e., a constant braking power. The mean body velocity showed a striking similarity with the mean tempo pattern of final ritardandi in music performances. The constant braking power was used as the basis for a model describing both the changes of tempo in final ritardandi and the changes of velocity in runners’ decelerations. The translation of physical motion to musical tempo was realized by assuming that velocity and musical tempo are equivalent. Two parameters were added to the model to account for the variation observed in individual ritardandi and in individual decelerations: (1) the parameter q controlling the curvature, corresponding to the runners’ deceleration, and (2) the parameter for the final velocity and tempo value, respectively. A listening experiment was carried out presenting music examples with final ritardandi according to the model with different q values or to an alternative function. Highest ratings were obtained for the model with and Out of three functions, the model produced the best fit to individual measured ritardandi as well as to individual decelerations. A function previously used for modeling phrase-related tempo variations (interonset duration as a quadratic function of score position) produced the lowest ratings and the poorest fits to individual ritardandi. The results thus seem to substantiate the commonly assumed analogies between motion and music.
- GENERAL LINEAR ACOUSTICS 
105(1999); http://dx.doi.org/10.1121/1.426688View Description Hide Description
Babinet’s principle states that the diffracted fields from complementary screens are the negative of each other. In electromagnetics, Babinet’s principle for infinitely thin perfectly conducting complementary screens implies that the sum, beyond the screen plane, of the electric and the magnetic fields (adjusting physical dimensions) equals the incident (unscreened) electric field. A test of the principle for the elastodynamic case was made using numerical calculations, and the results demonstrate that Babinet’s principle holds quite well for complementary plane screens with contrasting boundary conditions; that is, the complementary screen of a stress-free screen is a rigid screen with openings where the original stress-free screen existed, and vice versa. The results are exact in an anisotropic SH case; for the P–SV case, the diffracted waves, PdP, SdS, PdS, and SdP satisfy the principle exactly, while the refracted waves, PdPrSc and SdPrSc, do not satisfy the principle at all (these waves are generally much smaller than the PdS and SdP waves). Diffractedsurface waves also do not satisfy the principle. The numerical method is based on a domain-decomposition technique that assigns a different mesh to each side of the screen plane. The effects of the screens on wave propagation are modeled through the boundary conditions, requiring a special boundary treatment based on characteristic variables. The algorithm solves the velocity/stress wave equations and is based on a Fourier/Chebyshev differential operator.
A generalized modal impulse response and Fourier transform approach to investigate acoustic transient Bessel beams and Bessel bullets105(1999); http://dx.doi.org/10.1121/1.426689View Description Hide Description
A generalized modal space–time impulse response and Fourier transform approach is developed to investigate the general properties of transient Bessel beam (TBB) fields which are generated using planar circular apertures. The approach is based on a modal decomposition of the aperture source distributions which are required to generate the space–time TBB fields. Numerical results are presented to illustrate the general space–time properties of the modal impulse responses and the modal source functions. The on-axis far field for the finite aperture is shown to be simply related to the lowest order term in the modal expansion. The space–time properties of the acoustic field for a particular type of band-limited TBB field which is designated as an acoustic Bessel bullet (BB) are then investigated. Some numerical results are presented to illustrate the space–time properties of acoustic BB fields generated from an infinite aperture. Analogous on-axis harmonic results from a finite aperture are presented. These latter results clearly indicate that the higher-order modes exhibit spatial rates of decay which are greater than the inverse range decay for the lowest order mode.
105(1999); http://dx.doi.org/10.1121/1.426690View Description Hide Description
A new recording technique based on multichannel digital signal processing is suggested. The system uses a dummy-head that is modeled as a rigid sphere with two pairs of microphones mounted on opposite sides of the sphere in the horizontal plane. Reversals—front back confusion, is a well-known phenomenon when localizing virtual acoustic images produced by either headphones or loudspeakers. Reproduction with two loudspeakers to the front of the listener causes rear virtual acoustic images to be perceived primarily at “mirrored” angles in the frontal hemisphere. The problem is tackled here by using a multichannel signal processing technique rather than by mimicking accurately the acoustomechanical properties of a human head. The acoustic signals which are recorded at the microphones are filtered by a 4×4 matrix of digital filters before being transmitted via four loudspeakers. The performance of the system is investigated by means of computer simulations, objective measurements, and also by subjective experiments in an anechoic environment, where the listeners are asked to localize the perceived angle of the signals which were prerecorded with the sphere dummy-head. Successful discrimination of reversals is achieved primarily due to the dominant role of the interaural time delay (ITD) for localization at low frequencies, but the accuracy with which listeners can localize virtual acoustic images is reduced in comparison to a conventional two-ear dummy-head (e.g., KEMAR) with a two-loudspeaker arrangement. The system is robust with respect to head rotations—virtual acoustic images do not disappear and localization ability improves when listeners use small head rotations.
An advanced boundary element/fast Fourier transform axisymmetric formulation for acoustic radiation and wave scattering problems105(1999); http://dx.doi.org/10.1121/1.426691View Description Hide Description
An advanced boundary element/fast Fourier transform (BE/FFT) methodology for solving axisymmetric acoustic wave scattering and radiation problems with non-axisymmetric boundary conditions is reported. The boundary quantities of the problem are expanded in complex Fourier series with respect to the circumferencial direction. Each of the expanding coefficients satisfies a surface integral equation which, due to axisymmetry, is reduced to a line integral along the surface generator of the body and an integral over the angle of revolution. The first integral is evaluated through Gauss quadrature by employing a two-dimensional boundary element methodology. The integration over the circumferencial direction is performed simultaneously for all the Fourier coefficients through the FFT. The singular and hyper-singular integrals are computed directly by employing highly accurate three-dimensional integration techniques. The accuracy of the proposed boundary element methodology is demonstrated by means of representative numerical examples.
105(1999); http://dx.doi.org/10.1121/1.426692View Description Hide Description
Effective medium techniques have been developed by many authors to model the acoustic propagation through layers of visco-elastic materials which contain fluid-filled or elastic cavities. This paper extends such work to the case of materials containing air-filled microspheres whose thin glassy shell separates the interior air from the surrounding polymer. Such composites have been found particularly useful in conditions of high hydrostatic loading where the presence of the reinforcing shells delays the onset of the hole collapse and the consequent degradation in the acoustic performance of the composite. In the present paper, a model is presented which includes the effect of shell wall thickness variability but excludes the depth dependency—the latter will be presented in a sequel. Theoretical predictions are compared with experimentally measured values of transmission loss for both stiff and soft polymer substrates and, in each case, good agreement with experimental data is shown.
105(1999); http://dx.doi.org/10.1121/1.426693View Description Hide Description
The acoustic eigenfrequencies in a spheroidal cavity containing a concentric penetrable sphere are determined analytically, for both Dirichlet and Neumann conditions in the spheroidal boundary. Two different methods are used for the evaluation. In the first, the pressure field is expressed in terms of both spherical and spheroidal wave functions, connected with one another by well-known expansion formulas. In the second, a shape perturbation method, this field is expressed in terms of spherical wave functions only, while the equation of the spheroidal boundary is given in spherical coordinates. The analytical determination of the eigenfrequencies is possible when the solution is specialized to small values of with d the interfocal distance of the spheroidal boundary and the length of its rotation axis. In this case exact, closed-form expressions are obtained for the expansion coefficients and in the resulting relation Analogous expressions are obtained with the use of the parameter with the length of the other axis of the spheroidal boundary. Numerical results are given for various values of the parameters.
105(1999); http://dx.doi.org/10.1121/1.426694View Description Hide Description
A quasi-one-dimensional approach is presented to analyze three-pass mufflers with perforated elements using numerical decoupling. The approach is further developed to include mufflers with ducts extended into the end cavities. Theoretical predictions are compared with experiments for three different muffler configurations, one fabricated and two commercially available mufflers, and shown to agree reasonably well. The effect of porosity, length of the end cavities, and expansion chamber diameter are studied. Also, the effect of ducts extending into the end cavities are investigated.
105(1999); http://dx.doi.org/10.1121/1.426695View Description Hide Description
Fourier–Bessel theory is used to derive a closed-form solution for the spatially averaged velocity-potential impulse response associated with one-way diffraction from an unfocused piston transducer of radius a. The derivation provides additional insight into the problem of diffraction from an unfocused piston transducer.
105(1999); http://dx.doi.org/10.1121/1.426696View Description Hide Description
The resonanceproperties of a prefractal cavity are studied in an acoustical transmission experiment. Resonance frequencies and quality factors are measured and compared to theory. All the delocalized modes are detected, and their measured eigenfrequencies closely fit numerical predictions. Most of the localized modes appear to be missing in the experimental spectra because of their weak coupling with the acoustic excitation and detection. The measurement of the quality factor of the acoustic resonances confirms the existence of increased damping due to the irregular shape of the cavity. This constitutes the first experimental evidence for the damping power of fractal structures.
- NONLINEAR ACOUSTICS 
105(1999); http://dx.doi.org/10.1121/1.426697View Description Hide Description
A numerical model of nonlinear propagation is used to investigate two cases of monochromatic ultrasonic beams interacting at small angles in a nonlinear medium. Two finite Young’s slits are seen to produce fringes at harmonic frequencies of the source in places where the source frequency is absent, which can be seen as a combination of harmonic generation near the source, and in the beam. Two intersecting beams with shaded edges are seen to produce similar fringes in the near field, with an oscillatory structure. Algebraic solutions to a simplified model, using the weak-field Khokhlov–Zabolotskaya equation, are invoked to illustrate the origin of the oscillations, and of the far-field directivity, providing an alternative view of the fringes due to Young’s slits. It is seen that two weakly interacting beams can produce fringes of second harmonic where the source frequency has low amplitude, if the beams coincide at the point of observation, or if a boundary condition is imposed on the second harmonic where the beams coincide.
105(1999); http://dx.doi.org/10.1121/1.426698View Description Hide Description
The nonlinear interaction of noncollinear acoustical waves is considered. Conditions of the resonantbackscattering of one wave from the lattice produced by the other two are formulated in analogy with the four-wave mixing known in optics. The efficiency of the phase-matchedinteraction of acoustical waves is calculated in the resonant approximation for a gas media. Such approximation is constructed on the basis of the expansion of the sound equations preserving up to cubic terms. The amplitude of the backscatteredwave is expressed as the product of the efficiency, the amplitudes of three waves, the wave number of the backscatteredwave, and the size of the region of interaction. Such backscattering is proposed as an acoustical remote probe. The distance to the interaction region and the amplitude of initial waves are limited by nonlinear degradation of waves due to the second-order nonlinearity. For acoustical waves with wave number 10 m−1, sources of size 1 m, and about 100 m to the interaction region, the amplitude of the backscatteredwave can be about of the atmospheric pressure. At the detection with a signal-to-noise ratio about of 10, the resolution of such method on the wind velocity may be about 1 m/s.
- UNDERWATER SOUND 
105(1999); http://dx.doi.org/10.1121/1.426699View Description Hide Description
Acoustic propagation along the Hawaiian–Aleutian path at low frequency (65 Hz) for the acoustic thermometry of ocean climate (ATOC) has been simulated using the implicit finite difference parabolic equation (IFD-PE). This simulation is based upon the Semtner–Chervin model with one-half-degree resolution. The adiabaticity has been assessed, and it was found that significant mode coupling takes place at the sub-arctic front area (44.8 ° N). Due to the range-dependent double channel, two characteristic ranges were identified in this area: (i) the modal degeneration range and (ii) the modal scattering range At range mode m and mode n (usually, are degenerated, the modal wave numbers of mode m and mode n become equal, and mode n then takes the shape of mode m. Therefore, there is no real repopulation (modal scattering), but a modal name change takes place at this range. The modal name change can cause a miscalculation of the adiabatic travel time. At range however, real repopulation does take place. Numerical simulations illustrate that and are separated by about 10 km at lower modes and are merged at higher modes.