bluuebunny/crossref_metadata_2025 huggingface dataset:
Loudspeaker parameter measurement in reverberant environments
Authors: Kahrs Mark , Rabinkin Daniel V.
Published: October 2005

Loudspeaker driver small-signal parameter measurement is required to design and quantitatively measure loudspeaker enclosures. Such measurements are conventionally performed in an anechoic chamber with the intent of eliminating the acoustic response of the room from influencing the measurement. A novel procedure is proposed to perform the measurements in arbitrary untreated enclosures using a standard sound card. Aoshima’s optimal time stretched pulse [Aoshima, J. Acoust. Soc. Am. (1981)] [Suzuki et al., J. Acoust. Soc. Am. (1995)] is used to excite the loudspeaker. The response is captured by a high-quality flat response microphone. Knowledge of the minimum first reflection time of the enclosure is used to filter out the effects of room response without affecting the measurement of loudspeaker response. A sliding window is used to remove reverberent effects similar to time delay spectrometry (TDS) [Heyser, J. Audio Eng. Soc. (1967)]. The filtered signal is fit against a complex rational polynomial transfer function, inspired by the method described by Leach et al. [IEEE Trans. ASSP Dec. (1979)] and Jain et al. [IEEE Trans. ASSP Feb. (1983)]. The fit is performed by a nonlinear least-squares method written in AMPL [Fourer et al., 1993], a language for mathematical programming.
Sound field reproduction using wavefront synthesis based on the four microphones measurements
Authors: Yamasaki Yoshio , Kudo Shuji , Oikawa Yasuhiro
Published: October 2005

Reverberation time, distribution of sound pressure, intelligibility, and/or other parameters are used in sound room evaluation. But characteristics of room acoustics are complex, and often quite different impressions are received from rooms that have nearly the same parameters. These differences might come from the difference of spatial information, especially in early reflection periods. Thus a four-microphone method is proposed to measure spatial information of the room. Here, the sound field reproduction using the wavefront synthesis [A. J. Berkhout, J. Acoust. Soc. Am. 93(5) (1993) and Y. Yamasaki, J. Acoust. Soc. Jpn. 10(2) (1989)] based on the four-point measurement is discussed.
Ray chaos and two-dimensional wave fields
Authors: Fujisaka Yoh-ichi , Tohyama Mikio , Sugimura Akira
Published: October 2005

In a two-dimensional wave field under irregular shape boundary conditions, the trajectory of a sound ray is unstable because of chaotic motion [M. V. Berry, Eur. J. Phys. 2, 91 (1981)]. For wave theory, the spacing distribution of the neighboring eigenvalues is not degenerated in irregular systems because of the repulsion effects, but follows a Wigner distribution. [S. W. McDonald and A. N. Kaufman, Phys. Rev. Lett.42 , 1189 (1979); R. H. Lyon, J. Acoust. Soc. Am. 45, 545 (1969)]. This article discusses the sound fields in 2-D irregularly shaped boundaries, using both ray and wave theories. In ray theory, the reflection processes of billiard problems are considered to be like mapping processes on a logistic map, and the sensitivities to the initial conditions under several boundary conditions such as a stadium and an ellipse are investigated. It is shown that the reflection points at the boundary are sensitive to small changes in initial conditions, illustrating that changes in the reflection positions have a chaotic property in a 2-D field with mixed-shaped boundaries of curves and lines. In wave theory, the eigenvalues and eigenmodes are analyzed using the finite-element method (FEM), and the wave theoretic characteristics leftover in the ray-chaotic irregular systems by using Δ-statistics and dimensional analysis of the higher modes are shown.
An algorithm for generating reverberation as an application of the chaos technique—Return map derived from initial responses
Authors: Takamiya Tsugumasa , Kishinaga Shinji , Kawakami Fukushi
Published: October 2005

To synthesize the acoustics of a large enclosure with the aid of a computer, an algorithm for adding reverberation to the initial response is proposed. When the initial response is known, the arrival time and the intensity for each subsequent reflective sound are calculated one after another. After calculating the time intervals between each succeeding initial reflective sound and processing them to form a suitable random-number generator, each future arrival time is then successively determined. From this generator, a return map, often used in the chaos technique, is adopted. As for the intensity, with the input value of reverberation time (RT60) the decay rate is determined; from this, the decay rate and the cumulative intensity of the initial reflective-sound decay curve as a standard are estimated. Then each future intensity is determined by comparing the cumulative values to the standard. No awkwardness was heard from the burst tone convoluted with such a calculated response. Dimensional analysis about the time intervals in the long-time response calculated by the same algorithm as that used for initial response did not show that they were from random processes.
Calculation of impulse responses of rooms by using the finite-difference method
Authors: Sakamoto Shin’ichi , Tokita Yasuhiro , Tachibana Hideki
Published: October 2005

As a method of calculating impulse responses in a room, the application of the finite-difference method (FDM) has been investigated. In this paper, the principle of the numerical calculation is introduced first, and its applications for obtaining impulse responses in several two-dimensional spaces with typical shapes are presented. In order to see the validity of the calculation by FDM, the calculated results are compared to the results obtained in scale model experiments. Next, to apply the FDM calculation method to rooms with absorbing boundaries, two physical models based on the mechanical substitution model and the Rayleigh model are proposed. In order to examine these models, the results obtained by numerical calculation and by experiment are compared.
A novel numerical method for analyzing 1.5- and 2-dimensional ultrasound arrays
Authors: Morrow Richard E. , Bedrosian Gary
Published: October 2005

A novel numerical technology based on finite-element methods has been developed for analyzing interaction problems in 1.5- and 2-D ultrasound arrays. A standard finite-element array model consists of structural elements encased in fluid. For accurate solutions, a portion of the fluid must be meshed and truncated with a radiation boundary condition which approximates an infinite domain. The essence of this new technology, termed overlapping grid, is that only the structural elements will actually be meshed. The surrounding air or water is automatically created as a uniform cubic mesh which is invisible to the user and properly connected to the structural mesh. In addition to obvious advantages for mesh creation, larger numerical models can be solved. For a hypothetical 3-D acoustic model where ten are structural and the rest fluid, the total storage required using the overlapping grid technology is one third of that required using the current finite-element storage techniques. The overlapping grid technology also results in a significant speedup in the most time-consuming part of an iterative solver algorithm, which is multiplication of a vector by the stiffness matrix.
Finite-element analysis of planar sonar arrays by a coupled finite-element/modal-expansion method
Authors: D’Angelo John , Morrow Richard E.
Published: October 2005

This paper presents the analysis of infinitely periodic planar sonar arrays by a coupled finite-element/modal-expansion method. Finite elements are used to model the region containing the sonar transducer. Here, the finite-element method solves the scalar Helmholtz equation for the acoustic potential. The finite-element method is well suited to solving the field behavior in the complex shape and heterogeneous material region of the sonar transducer. Coupled to the finite-element region is the semi-infinite region where the acoustic field behavior is periodic. In this region, the field behavior is defined by an infinite series Floquet modal expansion. The number of modes used in the Floquet expansion depends on the geometry and scan angle of the array. Typically, the number of modes is comprised of all the propagating modes plus 10 to 20 evanescent modes. This technique allows for the solution of array field behavior for any arbitrary scan angle. Being an infinite periodic analysis, however, limits the accuracy of the solution to the sonar elements in the middle of the array. This paper describes the use of this technique in two- and three-dimensional analysis and shows results in two dimensions.
Computation of sound fields in a realistic atmosphere
Authors: Stinson Michael R.
Published: October 2005

The computation of sound fields in realistic atmospheres is demonstrated using a Green’s-function parabolic equation approach [X. Di and K. E. Gilbert, in Proceedings ofthe Sixth International Symposium on Long Range Sound Propagation, Ottawa, Canada, 1994] to handle the effects of ground impedance, refractive sound-speed profiles, and atmospheric turbulence. The calculated sound fields are presented as color-coded screen displays and show various effects, including upward or downward refraction, the ‘‘sky wave,’’ scattering into an acoustic shadow, and the effects of turbulence drift. Another program is used during the acquisition of meteorological data to monitor incoming data, to display the vertical sound-speed profiles obtained using similarity theory, and to display in real time the predictions obtained from a ray tracing algorithm.
Binaural sound reproduction in a stereo dipole system
Authors: Tokuno Hironori , Hamada Hareo , Kirkeby Ole , Nelson Philip A.
Published: October 2005

A new transaural system referred to as a ‘‘stereo dipole’’ reproduction system using a closely spaced pair of loudspeakers in front of a listener has been introduced recently. Computer simulations using theoretical models, in which the listener’s head is assumed to be a perfectly rigid sphere, revealed that sound field equalization by the SD system including inverse filtering and also for the virtual source reproduction can be achieved in a wide range of area relative to the standard loudspeaker arrangements. This paper will deal with a further investigation of the SD system in terms of the controlled acoustic field around the head. The theoretical model used in the computer simulation is extended so that one can calculate an impulse response at any point while considering the influence of a rigid sphere. This model is used to compare the sound field around the spherical obstacle due to the SD system with one by the ordinary transaural system.
Computer animation of sound
Authors: DeMetz Brian A. , DeMetz Fred C.
Published: October 2005

The use of computer animation in the study and understanding of sound propagation is demonstrated. Several brief audio/video demonstrations are given to illustrate the spatial-temporal features of sound propagation in complicated environments. Each demonstration is preceded by a summary of the theoretical aspects of the particular propagation problem, followed by the audio/video illustration of the situation. It is shown that sound animation can be a powerful training tool in understanding sound propagation, and for optimizing performance of underwater and seismic sound systems.
Application of a time domain approach to adaptive separation/synthesis of automobile cabin noise
Authors: Hsueh Keng D. , Hollingsworth Larry D. , Lee Garland , Chen Yong , Murawski Keith , Haffey Mike P.
Published: October 2005

Automobile cabin noise is generally categorized by the major contributing sources: powertrain, road, and wind. These three noise components have traditionally been evaluated at their dominant operating conditions, e.g., wide-open throttle for powertrain, which may not represent realistic customer driving conditions and can result in unnecessary vehicle cost/weight. A portable PC-based system using multichannel least-mean-square (LMS) adaptive filtering was developed and validated to provide the capability of separating powertrain, road, and wind noise components (time-domain) under realistic customer driving conditions. By judiciously selecting the locations of reference sensors on the engine and suspension with optimized filter length, the powertrain/road noise components can be successfully separated. Separated noise components from various vehicles can subsequently be used to synthesize total cabin noise for subjective sound quality evaluation. Results of vehicle noise separation/synthesis from various vehicles will be presented and accompanied by an audio demonstration. This newly developed adaptive noise separation/synthesis system using multichannel time-domain adaptive filtering was proven to be a useful tool for automobile noise separation/synthesis and could be extended to potential applications such as wind tunnel fan noise minimization, noise/vibration source/path identification, and benchmarking of vehicle system transfer functions under realistic driving conditions.
High-frequency acoustic wave propagation modeling in shallow water
Authors: Chotiros Nicholas P. , Stern Morris
Published: October 2005

High-frequency sound propagation in a shallow water environment is modeled using a recent version of OASES [H. Schmidt and F. B. Jensen, J. Acoust. Soc. Am. 77, 813–825 (1985)] that has been modified to include poroelastic layers. In shallow water, sound propagation may be strongly influenced by the properties of the bottom. The conditions under which bottom properties become important are identified. Through selected examples, the effects of sediment properties on propagation loss are examined, particularly the differences between elastic and poroelastic approximations of the sediment. Examples of forward reflected and bottom penetrating acoustic pulses are examined. [Work supported by ONR, Code 321 OA.]
Acoustic and temperature fluctuations in very shallow water
Authors: Meredith Roger W. , Mire Christine T. , Stanic J. Stephen
Published: October 2005

Acoustic phase and amplitude fluctuations are compared to vertical and horizontal temperature fluctuations in very shallow water. Two examples are presented, one during a weaker internal wave event and one during a stronger internal wave event. The data were collected in 12 m of water depth off the beach of Panama City, FL, during April 1995. Each example is 5 min of acoustic data at 110 kHz, for a single source/receiver distance of 87 m and a repetition rate of 1 ping per second. Two 6-channel thermistor arrays, with a 1.2-m aperture, recorded temperature changes in the vertical and horizontal to within ±0.01°C. The thermistor array is used to compute temperature spatial correlation lengths and times as well as for statistical comparison with acoustic phase and amplitude. Statistical differences in the acoustic phase and amplitude characteristics are presented as well as horizontal and vertical temperature distributions. Both phase and amplitude distributions are more similar to temperature distributions for the stronger internal wave event. Acoustic phase distribution most closely matches vertical temperature distributions.
Frequency dependence of broadband acoustic propagation in coastal regions
Authors: Badiey M. , Simmen J. , Forsythe S.
Published: October 2005

Coherence of broadband acoustic signals in very shallow-water regions is examined. To measure the frequency-dependent spatial and temporal variability of sound propagation in coastal regions, experiments were conducted using sound impulses in the form of m sequences centered from 0.6 to 22 kHz. In these experiments the water depth was approximately 15 m. The receiver hydrophones, with spacing less than a few meters, were located in a range of 200–800 m from the source. High-resolution oceanographic data taken simultaneously with the acoustic data were used to analyze the broadband propagation. It is shown that the temporal coherence changes significantly as a function of frequency and that the nature of this variation depends on location and time, since the ocean environment (e.g., the sound-speed variability, current, and the surface/bottom boundary conditions) is location and time dependent. However, for hydrophone spacings of a few meters, no significant spatial decorrelation of the signal has been observed.
A preliminary numerical study of the nonlocal small slope approximation
Authors: Broschat Shira L. , Thorsos Eric I.
Published: October 2005

Modeling the effect of a rough air–sea interface on an acoustic signal is of considerable practical importance; for example, it is relevant in the detection of underwater mines, torpedoes, and submarines. Several promising theories have been developed for rough surface scattering. Among the most successful is the small slope approximation (SSA) [A. G. Voronovich, Sov. Phys. JETP 62, 65–70 (1985)]. Recent numerical studies [see S. L. Broschat and E. I. Thorsos, submitted to J. Acoust. Soc. Am. (1996), and references therein] have shown that the higher-order SSA gives excellent results over a broad range of scattering angles for rms surface slopes up to 1. However, at the lowest forward grazing angles the results become somewhat high. At these angles multiple interactions with the surface at distant points have an appreciable effect on scattering levels. Voronovich recently modified the SSA to extend the nonlocal scattering effects [A. G. Voronovich, Waves in Random Media 6, 151 (1996)]. In this paper, a preliminary numerical study of the nonlocal small slope approximation (NLSSA) is presented. The equations for the lowest-order bistatic scattering strength are derived, limiting cases are considered, and numerical results for a Gaussian spectrum are presented and compared with both original SSA and integral equation results. [Work supported by ONR.]
On the relative importance of refractive index fluctuations and sea surface roughness to amplitude variability in a multipath environment
Authors: Lyons Anthony P. , Di Iorio Daniela , Akal Tuncay
Published: October 2005

Pulses of 29, 50, 82, 120, 192, and 326 kHz were transmitted at a shallow-water site uniformly 12 m in depth. From this data set amplitude fluctuation as a function of source–receiver separation distance was obtained. The seafloor at the study site consisted of soft muds so that the direct path and a surface bounce path were the primary components of the received signal. In order to estimate turbulence parameters, direct path arrivals were analyzed at ranges where they were separated in time from the surface bounce arrivals (for separation distances less than 130 m.) Analysis of the log-amplitude variance of direct arrivals shows agreement with weak scattering theory using a Kolmogorov turbulence model and yields an average structure constant C2n≊8×10−9. The estimated values for the structure constant were used to predict the contribution of the refractive index fluctuations to total amplitude variability for the entire range of source–receiver separation distance. It was found that for this environment amplitude variability is dominated by sea-surface roughness for source–receiver separation distances out to ∼200–250 m and by refractive index fluctuations for greater separation distances.
High-frequency sound diffraction by an underwater ridge with a soft boundary
Authors: Zhou Ji-Xun , Chase Yun S. , Zhang Xue-Zhen
Published: October 2005

High-frequency sound diffraction over an undulating sea bottom, including underwater ridges and hills, has become of increasing interest to the ocean acoustic community. In many cases, the top layers of the seabed are relatively soft. Thus, sound diffraction by an underwater ridge with a very soft boundary (closed-cell foam material) is investigated in a laboratory tank. The diffracted acoustic pressure is measured in the penumbra, along the ridge and along vertical axes behind the ridge. Experimental data are compared with Fock and Pierce’s theory, which originally described the diffraction field of an electromagnetic wave propagating over a curved conducting surface. Experimental data and numerical results are in good agreement. The insertion loss caused by the underwater soft ridge is much higher than that caused by a rigid ridge. [Work supported by ONR.]
Overcoming energy spreading loss (ESL) for characterization of broadband frequency dispersion
Authors: Fabre J. Paquin , Wilson James H. , McDermid Jack G.
Published: October 2005

A shallow water, high-frequency active acoustic data set is being examined for the existence of a broadband frequency dispersion phenomena (BDP). Two scenarios, an up-slope source-to-receiver propagation path and a shallow-to-shallow path are studied in detail using a time domain finite element parabolic equation model and measured environmental parameters. It was expected that the analysis of the shot data from the AEAS exercise off the Pacific West Coast would result in confirmation that echoes or reflection events from bottom reflectors would be distinguishable from echoes of water column reflectors. This expected result could be detected only for the up-slope propagation path where energy spreading loss (ESL) was relatively low. The shallow-to-shallow propagation paths were dominated by ESL and it was determined that the ESL must be modeled accurately before the BDP can be analyzed and utilized for very shallow water propagation paths. ESL is modeled for the two propagation scenarios and the impact of ESL on active high-frequency operations in very shallow water is discussed. Signal processing solutions to ESL degradation are also presented. [This work was funded by the Office of Naval Research.]
Reflection coefficients for scattering from a pressure-release, sinusoidal surface
Authors: Purcell Anthony
Published: October 2005

This paper deals with the scattering of an incident plane wave from a pressure-release, sinusoidal rough surface. As was shown by Uretsky [Ann. Phys. 33, 400–427 (1965)] this problem is equivalent to solving an infinite set of linear equations (involving the matrix V0m,n) for the quantities ψm, the Fourier components (apart from a phase factor) of the normal derivative of the pressure on the surface. Holford showed that the ψm satisfied an infinite set of linear equations of the ‘‘second kind’’ (involving the matrix V1m,n) and deduced the existence and uniqueness of solutions. This paper shows that the matrix elements V0m,n and V1m,n can be expressed as a single sum over products of integer index Bessel functions, subject only to the slope restriction Kd<0.6627. These series representations of the matrices V0m,n and V1m,n are used to prove the result that Rayleigh’s equations are exact up to the slope limit Kd<0.6627. It is also shown that the reflection coefficients Rn satisfy an infinite set of linear equations of the second kind, valid provided the maximum slope Kd<0.6627. The matrix elements involved in the equations for the reflection coefficients Rn are proportional to a single integer Bessel function. Consequently, these equations may be easily solved by the method of reduction.
Scattering of a horizontally polarized oblique wave by a pair of surface-breaking cracks
Authors: Ciarletta Michele , Passarella Francesca , Sumbatyan Mezhlum A.
Published: October 2005

Antiplane scattering is studied in the context of an oblique incident plane wave in the presence of two (parallel) vertical cracks. In particular, the influence of these cracks on the oscillation of a free surface for various values of physical and geometrical parameters is investigated. The developed model is solved numerically for a wide range of the frequency parameter. The amplitude of the surface oscillations can be reduced by choosing appropriate values of the geometrical parameters, leading to possible solutions of problems of importance in seismology.
Acoustic wave propagation through porous media revisited
Authors: Geerits Tim W.
Published: October 2005

In this article a new macroscopic theory for acoustic wave propagation through fluid-saturated porous media will be derived in which losses of the interface type are incorporated. It is argued that in order to explain the occurrence of a slow compressional wave (which is typical for fluid-saturated porous media), a discontinuity in the tangential components of traction and particle velocity at the microscopic fluid/solid interface is essential. The method of spatial volume-averaging will be applied in order to translate the microscopic field equations pertaining to the constituents of the porous medium to the macroscopic level (i.e., several times the wavelength). This method clearly demonstrates the interaction between the fluid and the solid phase at the microscopic fluid/solid interface by means of surface integrals which arise as a consequence of the averaging procedure. These surface integrals are assumed to be linearly related to the volume-averaged state quantities of the phases involved. In this way the interface-type losses are also incorporated. These losses are assumed to be of the inertial type and are triggered by the possible strong fluctuations in the spatial gradients of the microscopic fluid/solid interface (tortuosity). The resulting macroscopic theory, which is assumed to be valid at relatively high frequencies (the frequency range where we observe a slow P wave), mathematically has the same appearance as the most general Biot theory but with a different physical interpretation.
Green’s function for anisotropic half-space solids in frequency space and calculation of mechanical admittance
Authors: Tewary V. K. , Mahapatra M. , Fortunko C. M.
Published: October 2005

The three-dimensional delta-function representation for the elastodynamic Green’s function of anisotropic half-space solids is extended to the frequency space. The Green’s function is used to calculate the frequency dependence of the elastic waveforms due to a harmonic source on the free surface of an anisotropic half-space solid. An expression for the point mechanical admittance of solids is derived. Numerical results are reported for anisotropic half-space solids exhibiting cubic symmetry and an orthotropic carbon fiber composite. The real part of the admittance of a half-space solid is found to be proportional to the square of the frequency.
Multiple multipole expansions for elastic scattering
Authors: Imhof Matthias G.
Published: October 2005

This paper presents a new approach to solve scattering of elastic waves in two dimensions. Traditionally, wave fields are expanded into an orthogonal set of basis functions. Unfortunately, these expansions converge rather slowly for complex geometries. The new approach enhances convergence by summing multiple expansions with different centers of expansions. This allows irregularities of the boundary to be resolved locally from the neighboring center of expansion. Mathematically, the wave fields are expanded into a set of nonorthogonal basis functions. The incident wave field and the fields induced by the scatterers are matched by evaluating the boundary conditions at discrete matching points along the domain boundaries. Due to the nonorthogonal expansions, more matching points are used than actually needed, resulting in an overdetermined system which is solved in the least-squares sense. Since there are free parameters, such as location and number of expansion centers, as well as kind and orders of expansion functions used, numerical experiments are performed to measure the performance of different discretizations. An empirical set of rules governing the choice of these parameters is found from these experiments. The resulting algorithm is a very general tool to solve relatively large and complex two-dimensional scattering problems.
Application of the perfectly matched layer (PML) absorbing boundary condition to elastic wave propagation
Authors: Hastings Frank D. , Schneider John B. , Broschat Shira L.
Published: October 2005

A method is presented for application of the perfectly matched layer (PML) absorbing boundary condition (ABC) to the P-SV velocity–stress finite-difference method. The PML consists of a nonphysical material, containing both passive loss and dependent sources, that provides ‘‘active’’ absorption of fields. It has been used in electromagnetic applications where it has provided excellent results for a wide range of angles and frequencies. In this work, numerical simulations are used to compare the PML and an ‘‘optimal’’ second-order elastic ABC [Peng and Toksöz, J. Acoust. Soc. Am. 95, 733–745 (1994)]. Reflection factors are used to compare angular performance for continuous wave illumination; snapshots of potentials are used to compare performance for broadband illumination. These comparisons clearly demonstrate the superiority of the PML formulation. Within the PML there is a 60% increase in the number of unknowns per grid cell relative to the velocity–stress formulation. However, the high quality of the PML ABC allows the use of a smaller grid, which can result in a lower overall computational cost.
Some results on the scattering of guided elastic SH waves from material and geometric waveguide discontinuities
Authors: Ditri John J.
Published: October 2005

The scattering of guided elastic SH waves from step discontinuities in the material properties and/or geometry of otherwise uniform flat layer waveguides is analytically/numerically analyzed. Analytical results for the case of a step discontinuity in material properties in a layer of uniform thickness are presented for comparison with later numerical results. The case of a sudden change in thickness of the waveguide, possibly in conjunction with a change in material properties, is solved numerically. The solution is based on an expansion of the wave fields on either side of the discontinuity in terms of the normal modes permissible in the analogous infinite layer and subsequent determination of the modal expansion coefficients. A ‘‘non-coupling’’ condition is proposed and proven which explains why particular modes are not generated in the scattering process. A ‘‘perfect-coupling’’ condition is also introduced, and the exact transmission amplitude of any mode satisfying the condition is given explicitly.
Dynamics of an oscillating spherical gas/vapor bubble
Authors: Dassie G. , Reali M.
Published: October 2005

The present work describes a physico-mathematical model for the dynamics of a single spherical gas/vapor bubble of uniform instantaneous pressure in an incompressible liquid under the action of an acoustic field. A noteworthy feature of the model is a detailed treatment of vapor/liquid phase change and of gas diffusion across the bubble/liquid interface. These phenomena may significantly affect the dynamics of the bubble/liquid system under some pressure-temperature ambient conditions. The temporal evolution of thermodynamic fields of interest has been computed for an air/water-vapor bubble of initial radius 10−3 cm in water under the action of a monochromatic acoustic field for ambient pressures of 0.1 and 1 bar and for ambient temperatures of 20 and 40 °C. For the numerical solution of the present physico-mathematical model a specific computational code, which utilizes coupled analytico-numerical techniques for ordinary and partial differential equations, has been developed.
Vibrational impact of high-speed trains. I. Effect of track dynamics
Authors: Krylov Victor V.
Published: October 2005

The dramatic increase in speeds of modern passenger trains makes it important to consider the vibrational impact of such trains on the built environment. In the author’s earlier paper in which a quasistatic approach to the calculation of track deflection curves had been used [V. V. Krylov, Appl. Acoust. 44, 149–164 (1995)], it had been shown that a very large increase in generated ground vibration level (about 70 dB, as compared to conventional trains) may occur if train speed exceeds the velocity of Rayleigh surface waves in the ground. Such a situation might arise, for example, with French TGV trains for which speeds over 515 km/h have been achieved. The present paper investigates the effect of track bending waves propagating in the system track/ground on railway-generated ground vibrations. It is shown that for train speeds approaching the minimal phase velocity of bending waves the level of generated ground vibrations is reduced. Theoretical results are illustrated by numerically calculated frequency spectra of ground vibrations generated by single axle loads traveling at different speeds and by TGV or Eurostar high-speed trains.
Identification of the resonances of a cylindrical shell stiffened by an internal lengthwise rib
Authors: Klauson Aleksander , Metsaveer Jaan , Décultot Dominique , Maze Gérard , Ripoche Jean
Published: October 2005

A theoretical and experimental study of the acoustic response of a submerged stiffened cylindrical shell is presented. The internal rib is modeled as a clamped-free plate mounted inside the shell perpendicular to the shell surface. The stiffened shell is excited by a normally incident acoustic pressure wave. Wave propagation around the circumference of the shell and associated sound radiation are discussed. From the directivity of the monostatic scattering, the resonances in the scattered sound pressure field can be separated into three different types. A mechanical admittance is used to help identify the different types of resonances excited in the fluid-loaded stiffened shell. Each type of resonance is shown to be associated with a particular type of interaction between the shell and the rib in terms of the components of the coupling forces: i.e., the normal force, the transverse force, and the coupling moment. For kR ranging from 16 to 35, the normal coupling force is shown to control the symmetric flexural vibration field in the shell, while the coupling moment controls the antisymmetric vibration field. The rib interacts with the membrane vibrations in the shell via the transverse coupling forces.
Effects of modal truncation errors on transmitted dynamic power estimates in discretely joined component assemblies
Authors: Farstad Jerry E. , Singh Rajendra
Published: October 2005

In an earlier paper [J. Acoust. Soc. Am. 97, 2855–2865 (1995)], the authors proposed a new formulation based on modal synthesis methods for computing the mechanical power transmitted among components in vibrating assemblies. The formulation is exact if all component modes are included in the analysis, but errors may be introduced if incomplete sets of component modes are used. The effects of such modal truncation errors are examined in this paper. A new approach for determining truncation errors in assembly modal properties obtained from modal synthesis formulations is developed and applied, which reveals that the authors’ original formulation is susceptible to truncation errors. A modified formulation is developed which retains the advantages of the original, but yields more accurate results over a particular frequency range when small subsets of component modes are used. An example involving the flexural vibration of a beam is examined using both formulations. The example verifies the improved accuracy of the modified formulation, and also illustrates several important issues associated with estimating transmitted dynamic power.
Spectral analysis for ultrasonic nondestructive evaluation applications using autoregressive, Prony, and multiple signal classification methods
Authors: Saniie J. , Jin X. M.
Published: October 2005

In the ultrasonic nondestructive evaluation (NDE) of materials, spectral analysis of backscattered echoes is a useful tool for flaw detection, frequency-shift estimation, and dispersive echo characterization. In order to evaluate the local information, spectral analysis must be applied to short data segments and must offer high-frequency resolution. In this paper three high-resolution model-based spectral estimation techniques, i.e., the autoregressive (AR) method using the Burg algorithm, Prony’s method for exponential signal representation, and the multiple signal classification (MUSIC) method, have been studied for ultrasonic NDE applications. These algorithms have been applied to both simulated data and experimental measurements for frequency estimation and flaw detection. The maximum energy frequency estimates using these methods show significant sensitivity to changes in the frequency of ultrasonic echoes. The AR method shows a more robust performance for frequency estimation than the Prony or MUSIC methods.
Vibro-acoustical modal analysis: Reciprocity, model symmetry, and model validity
Authors: Wyckaert Katrien , Augusztinovicz Fülöp , Sas Paul
Published: October 2005

For low-frequency applications, a modal approach can be useful to describe vibro-acoustical coupling. Based on combined vibrational/acoustical frequency response function measurements, either with respect to acoustical or structural excitation, modal vibro-acoustical analysis can be carried out. This paper presents a consolidation of the theory behind the vibro-acoustical modal model. The model formulation is shown to be a nonsymmetrical formulation. It is shown that this is not contradictory to the well-known vibro-acoustical reciprocity principle. The implications of the nonsymmetry for the modal model are discussed. It is pointed out which variables must be measured and what kind of scaling must be used in order to end up with a consistent modal formulation. The theory is illustrated and verified by measurements on an experimental vibro-acoustical system, consisting of a rigid cavity with one flexible wall.
The response of transiently excited thick transducers at low frequencies
Authors: Harris Gerald R. , Myers Matthew R. , Gammell Paul M.
Published: October 2005

The generation of acoustic transients via short-pulse excitation of thick piezoelectric disks has proven to be useful in a number of applications, including broadband measurements of attenuation, directivity, and frequency response. However, one aspect of this technique that has received little attention is the lower-frequency limit. In the present study the frequency response was analyzed theoretically using the Mason/Redwood model for a thickness-expansion drive transducer. Two factors were found that limit the useful range of the technique at low frequencies. The first is related to the negative capacitance that appears in the equivalent circuit of a thickness expander. This element can be ignored in some transducer applications, but its presence must be accounted for in the low-frequency case. The second factor is due to the finite measurement time available, which for small transmitter/receiver separation distances is equal to the acoustic transit time through the piezoelectric disk. For an air-backed transducer radiating into water, the two limitations restrict the usable bandwidth to frequencies above approximately (10h2εS/πzTxT)exp(2h2εS/πcTzT ) and cT/xT, respectively, where h is a piezoelectric constant, εS is the clamped dielectric permittivity, and zT, xT, and cT are the transducer characteristic impedance, thickness, and speed of sound. For a 2.5-cm-thick lead zirconate titanate transducer (Navy Type I), the lower limit considering both factors is approximately 200 kHz. This limit is acceptable for determining the frequency response of hydrophones used in diagnostic ultrasound field measurements, but it is insufficient for characterizing hydrophones used to measure extracorporeal shock-wave lithotripsy pressure pulses.
Complex eigensensitivity-based characterization of structures with viscoelastic damping
Authors: Lin R. M. , Lim M. K.
Published: October 2005

Damping plays an important role in structural stability and vibration control and different methods have been developed to design structures with maximum possible damping capacity. The most effective measure to date is perhaps the viscoelastic damping treatment. However, the dynamic properties of viscoelastic materials are generally frequency and temperature dependent. This makes the dynamic characterization of viscoelastically damped structures a tremendously difficult task. Conventional approximate methods, such as the direct frequency response method and the modal strain energy method, become quite inaccurate when the damping of a structure to be analyzed becomes high. An iterative complex eigensolution algorithm, though it is exact, requires a tremendous amount of computational effort since, for each mode, repeated complex eigensolutions are required until converged results are obtained. In the present paper, a new iterative complex eigensensitivity-based characterization method is presented. Based on the real eigensolution performed using finite-element analysis, the proposed method successively updates the complex eigenvalues and eigenvectors until required accuracy is achieved. As compared with conventional methods, the new method improves considerably numerical accuracy while it maintains the computational efficiency required for practical applications. A multilayer sandwich beam structure is used to demonstrate the practicality of the proposed method and the results show that the method is numerically very accurate and computationally very efficient.
Modal radiation from an unbaffled rotating disk
Authors: Beslin Olivier , Nicolas Jean
Published: October 2005

This paper deals with the acoustic radiation from an unbaffled rotating disk. It is shown that when the disk is rotating, the natural modes are no longer stationary modes but are transformed into rotating waves. Using the concept of rotating waves instead of the retarded time potential method, rotation effects are taken into account in the vibratory part of the problem. Thus no assumption has to be made on the rotation speed and the near pressure field can be evaluated. A new collocation method is proposed to solve the double-layer potential problem which does not require evaluating double-surface integration as when using classical methods. A new analytical formula is established to evaluate the Hadamard finite part of the auto-influent terms. Radiation efficiencies of unbaffled rotating waves are calculated and charts are given which are useful for designing quiet circular disks such as saw blades or rotating wheels. Rotating waves are classified as radiating and nonradiating. The disk is not assumed to be baffled as it is the classical case; therefore, the charts given in this study can be used directly for real cases.
A transform domain optimization to increase the convergence speed of the multichannel filtered-X least-mean-square algorithm
Authors: Bouchard Martin , Paillard Bruno
Published: October 2005

The main drawback of the multichannel filtered-X LMS (FX-LMS) algorithm for the active noise control (ANC) of broadband disturbances is its low convergence speed when the filtered reference signals are strongly correlated, producing a large eigenvalue spread in the global correlation matrix. This correlation can be caused either by autocorrelation of the signals of the reference sensors, or by coupling between the ‘‘error paths’’ which introduces intercorrelation in the filtered reference signals. Multichannel versions of fast convergence monochannel algorithms exist (Newton-LMS, RLS, fast Kalman), but these algorithms either require too many computations for practical implementations, or they require the optimization of the controller to be performed at each sample, which can be a serious constraint. The purpose of this paper is to introduce a multichannel algorithm that has a high convergence speed and a low computational load, close to the FX-LMS. It is called the cosine transform filtered-X LMS (CTFX-LMS) because it uses a discrete cosine transform to eliminate the correlation that slows down the convergence process. The fundamental differences between this algorithm and many previously published frequency domain algorithms will be explained. Results of active noise control experiments in ducts will validate the convergence behavior of the new algorithm.
Spatial information of sound fields for room-acoustics evaluation and diagnosis
Authors: Abdou A. , Guy R. W.
Published: October 2005

Numerous subjective attributes of the listening experience in auditoria, particularly concert halls, can be described by the many available contemporary room-acoustic indicators. Subjective response is also known to be influenced by the spatial distribution of sound energy. The spatial distribution is not only desirable to diagnose acoustical defects, but also to visualize and quantitatively appreciate the extent to which the various interior design features influence acoustic quality. The objective of the present work is to demonstrate the usefulness of spatial acoustic information for quality assessment and defect diagnosis within enclosures. A new measurement method based on transient sound intensity is employed for obtaining the spatial information and examples of applications are presented together with a discussion of the method’s potential.
Some new techniques for panel measurements
Authors: Piquette Jean C.
Published: October 2005

Several methods for improving conventional panel measurement methodology are described. Methods for reducing the low-frequency cutoff of conventional echo-reduction tests, and for simulating impulse-response testing are presented. The new methods are demonstrated to reduce the low-frequency cutoff for conventional echo-reduction tests by an octave (to 5 kHz), and evidence is provided that suggests that lowering by another octave is feasible. The simulated impulse-response testing was achieved by radiating, through the use of exact transient-suppression methods, broadband interrogating waves, centered on 10 kHz, of single-cycle and half-cycle duration. A new, approximate method of staged transient suppression that permits significantly enhanced projector output relative to that achieved with exact transient suppression is described. The staged transient-suppression method is applicable to the improvement of insertion-loss tests. Finally, a new method for correcting edge-diffraction-contaminated insertion-loss measurements of panels fabricated of decoupling materials is presented. The new method was demonstrated in the frequency range of 500–11 000 Hz, and utilizes staged transient suppression in its implementation.
A physical model of sound diffraction and reflections in the human concha
Authors: Lopez-Poveda Enrique A. , Meddis Ray
Published: October 2005

An approximated physical model of the frequency transfer function of the human concha is developed in this paper. This formulation includes diffraction, reflection, and interference phenomena in the concha cavity. The performance of the proposed diffraction/reflection model is compared with that of the single-delay-and-add approximation by checking their predictions against the experimental transfer function of a metal spiral-shaped diffracting/reflecting system. Results show that the diffraction/reflection model performs considerably better at predicting both the absolute center frequency of spectral minima and the relative frequency spacing between them. The diffraction/reflection model is then applied to a realistic concha shape and its predictions are compared with experimental head-related transfer functions for azimuth- and elevation-varying sound sources. In this case, the model predicts the elevation-dependent spectral features related to the transverse dimensions of the concha. Additionally, the diffraction/reflection model predicts that, because of sound diffraction, similar spectral features must be generated in the concha for sources at all azimuths within the frontal part of the ipsilateral hemisphere. Experimental and theoretical evidence supporting this prediction is presented.