bluuebunny/crossref_metadata_2025 huggingface dataset:
Bottom loss measurements and analysis in the eastern Mediterranean sea
Authors: Chizhik Dmitry
Published: October 2005

Wideband bottom loss measurements were conducted at two sites in the eastern Mediterranean. The data were processed incoherently to determine bottom loss in one octave bands at center frequencies ranging from 200 to 4000 Hz and spanning grazing angle range of 10°–90°. Geological literature indicated that the bottom at Herodotus abyssal plain location was a ‘‘fast’’ turbidite bottom, while the Nile cone site was characterized by a ‘‘slow’’ silty-clay bottom. The bottom loss model was formulated for each site and was found to be in good agreement with the data. A geometric ray model is often used for bottom loss prediction which includes the refracted (diving) wave arrival at the proper grazing angle. This approach works well at high frequencies and high grazing angles, but gives erroneously low bottom loss values at low frequencies and low grazing angles. A hybrid ray/plane wave model was developed to account for the additional loss due to penetration of the wave into the sediment in excess of that predicted by the geometric ray theory. This correction is most important for ‘‘slow’’ bottoms at low grazing angles and low frequencies, as demonstrated by comparison to data.
Effects of azimuthal coupling on bistatic reverberation
Authors: Smith Kevin B. , Hodgkiss William S. , Tappert Frederick D.
Published: October 2005

The University of Miami PE (UMPE) model [K. B. Smith and F. D. Tappert, MPL Tech. Memo. 432 (1993)] has been upgraded to include azimuthal coupling, making it a fully three-dimensional forward propagation model. By incorporating Tappert’s PE reverberation (PEREV) model [F. D. Tappert, J. Acoust. Soc. Am. Suppl. 1 88, S84 (1990)], the effects of azimuthal coupling on bottom reverberation can be examined. During the July 1993 ONR-ARSRP main acoustics cruise, extensive bistatic data were recorded. using bathymetric data from the ARSRP Natural Laboratory, predictions of bistatic reverberation are made with and without azimuthal coupling. Differences between these two calculations provide quantitative evidence of azimuthal coupling effects. Comparisons with measured data will also be presented. [Work supported by ONR, Code 321OA.]
The influence of sediment scattering and variability on acoustic intensity including data comparisons
Authors: Howell Keith J. , Jacobson Melvin J. , Siegmann William L. , Carey William M.
Published: October 2005

Previous work [Howell etal., 2928 (1994)] has shown that statistics of multimodal intensity could be matched using a three-layer isospeed model that included effects of scattering. To more accurately estimate scattering effects on intensity over a broad frequency range, additional bottom information must be included. In this paper, an analytic treatment of a shallow channel consisting of n isospeed layers is developed for a wide-angle PE propagation model. A scattering layer is introduced at a horizontal water-bottom interface to model effects of attenuation due to interface and sediment scattering. The local mean of intensity is determined and its sensitivity to parameters such as the number of layers, frequency, scattering layer thickness, and correlation length of inhomogeneities is investigated. The standard deviation of intensity is also examined. Comparisons are made between intensity statistics for the multilayer models and depth-dependent profile models consistent with data from a New Jersey Shelf experiment. Additional emphasis is directed toward the number of isospeed layers needed to match experimental intensity over a range of frequencies. [Work supported by ONR.]
New multiple scatter model of the ocean sediment
Authors: Yelton Dennis J. , Chotiros Nicholas P.
Published: October 2005

Reflection, transmission, and scattering properties of an inhomogeneous Biot medium were studied via numerical simulation. The inhomogeneous medium was bounded by a semi-infinite water medium on the source side, and a semi-infinite Biot medium of equivalent average properties on the other side. The inhomogeneous medium was simulated as a randomly layered Biot material. Each layer represented a granular material of particular grain size. By setting the thickness of each layer equal to a random grain size, a randomly stratified granular medium was simulated. Lateral variations in grain size were simulated by performing a coherent ensemble average of results from several realizations of the randomly stratified medium. The free parameters were the grain size mean and standard deviation. Other parameters were chosen to represent water-saturated sand. Reflected and transmitted signals were computed for a 1-MHz normally incident plane wave. Coherent and random components of the reflected signal were calculated. The random component was related to the scattering strength of the medium. It was found to increase with both the mean and the standard deviation of the grain-size distribution. The results are consistent with previous experimental results [Nolle, 1394–1408 (1963)]. [Work supported by ONR code 1125OA.]
Acoustic scattering by marine sediments with irregularities of different types
Authors: Ivakin Anatoliy N.
Published: October 2005

There are two different types of irregularities giving the main contributions to bottom scattering: volume inhomogeneities of the sediment and roughness of its surface and interfaces. The problem of distinguishing and/or separating these contributions is considered using differences in frequency-angular dependencies of the scattering coefficient and analysis of the spatial autocorrelation function of the scattered field. The volume inhomogeneities of the sediment in turn can be considered as one of two types: spatial fluctuations of density and fluctuations of sound velocity. For water-saturated sediments (without gas), density fluctuations are usually stronger and their contribution to the total volume scattering is much more than that due to sound velocity fluctuations. But even low concentrations of gas bubbles can alter acoustic properties of sediments considerably, reducing the effective (average) sound velocity and enhancing fluctuations of sound velocity, with virtually no effect on the density. As a result, some specific features appear in sound scattering, and these can be used for remote acoustic characterization of sediments and determination of the type of bottom irregularities. [Work partially supported by ONR.]
Interaction of lips and mouthpiece in a brass instrument
Authors: Weinreich Gabriel , Chen Fang-Chu
Published: October 2005

The difference between the frequency of a played note on a brass instrument and the frequency of the resonator (defined as the location of the maximum of its input impedance at the mouthpiece) has been experimentally investigated. To avoid the complexity of the lips interacting simultaneously with many modes, a Helmholtz resonator with an attached ‘‘mouthpiece’’ whose diameter is that of a trumpet was used. By having a loudspeaker as one of the walls of the resonator, and driving it with a signal derived from an attached microphone, it was possible to adjust both the resonant frequency and the Q. The input impedance is measured (without the player’s lips leaving the mouthpiece) by comparing the passive response of the resonator with and without a known increase in volume. In the considerable majority of cases, the playing frequency is higher than the resonator frequency, indicating that the lips ‘‘beat outwards.’’ Possible error sources will be discussed. [Work supported by NSF.]
Musical pitchness evaluation through pitch extraction
Authors: Galembo Alexandre
Published: October 2005

Timbre and pitch are different properties of sound according to the ASA definition, but they are closely connected in the sounds from musical instruments. An interesting property is the ‘‘pitchness’’ (or ‘‘pitch strength’’) which refers to the distinctiveness of pitch in the sound. This property was investigated for piano notes, in particular in the bass and treble. In these ranges, the degree of pitchness is an important factor in determining instrument quality. Pitch extraction methods were used to calculate a noise factor in the treble, and an inharmonicity factor in the bass. New methods for judging the sound quality in the treble, and for measuring and evaluating inharmonicity of bass strings are proposed. [Work supported by ‘‘Red October’’ piano factory, St. Petersburg, Russia, and Swedish Institute, Stockholm, Sweden.]
An efficient time-domain model for the piano using commuted elements
Authors: Smith Julius O. , Van Duyne Scott A.
Published: October 2005

A new time-domain model for the piano is proposed which is extremely efficient for synthesizing piano sounds in hardware or software. The model includes multiple coupled strings, a nonlinear damped-spring hammer model, and a linear soundboard and enclosure component which can have arbitrarily large order at very low cost. Simplifications based on the commutativity of linear, time-invariant systems greatly reduce computational complexity [Comput. Music J. 74–91 (Winter 1992); Proc. International Computer Music Conference, Tokyo, pp. 56–71]. The hammer–string interaction is highly nonlinear and therefore does not commute with other components, in principle. However, by introducing a very mild approximation having little or no impact on the sound, commutativity can be achieved, leading to the enormous computational savings. This presentation will review the derivation of the piano synthesis model with special emphasis on the nonlinear hammer component. In its present form, a complete, two-key piano can be synthesized in real time on a single Motorola DSP56001 signal processing chip with 8K words of static RAM and a clock rate of 25 MHz.
A passive nonlinear digital filter design which facilitates physics-based sound synthesis of highly nonlinear musical instruments
Authors: Van Duyne Scott A. , Pierce John R.
Published: October 2005

Nonlinearities, small or large, favorably affect the sounds of many musical instruments. In gongs and cymbals, nonlinearities cause the passive transfer of energy from lower frequency modes to higher frequency modes after the instrument has been struck. While many spectral modifications can be achieved by the inclusion of memoryless nonlinearities (such as square-law or table look-up) within the resonant loops of physics-based digital sound synthesis algorithms, energy conservation cannot be achieved without compensating amplitude scaling. In fact, the greater the nonlinear effect desired, the more difficult it is to maintain passivity. Yet, for gongs and cymbals, a very large nonlinear effect is required. A computationally efficient nonlinear digital filter has been designed based on a physical system constructed from passive lossless elements only. This filter may be incorporated into any physical modeling algorithm (such as Karplus–Strong, digital waveguide, or 2D digital waveguide mesh) where traveling waves are being computed. System loss is decoupled from the nonlinear effect, and may be designed independently. Further, system energy spreads locally in the spectrum, as is found in real musical instruments; the rate and spectral region of energy spreading is controllable. Promising gong sounds have been produced.
Horn reflectance update
Authors: Berners David , Smith Julius O.
Published: October 2005

The flared horn is modeled according to Webster’s equation. A change of variables transforms the equation into the form of the one-dimensional Schrödinger wave equation. The Schrödinger form facilitates specification of arbitrary axisymmetric wavefronts for the acoustic disturbance within the horn. To provide a physically motivated choice of wavefront shape, Poisson’s equation is solved inside the horn subject to the boundary condition that the normal component of the potential gradient is zero at the boundary of the horn. Since the disturbance within the horn must satisfy the wave equation, the velocity potential satisfies Poisson’s equation when viscous effects and losses are ignored. Physical data from brass instrument bells are used to model musical horns using the Poisson solution, and results are compared to those obtained by traditional models which assume spherical wavefronts. Results are also compared to acoustic measurements.
A perturbation solution for forced response of systems displaying eigenvalue veering and mode localization
Authors: Pham Hoang , Ginsberg Jerry H.
Published: October 2005

Various aspects associated with eigenvalue veering, such as extreme parameter sensitivity and localization of response, are of paramount importance for predicting the dynamic response of lightly coupled systems having nearly periodic components. This paper presents a perturbation solution that simplifies analysis of forced response of continuous systems whose free vibration eigensolutions display eigenvalue veering and mode localization. In this investigation, the classic two-span beam with a strong torsional restraint at the intermediate pin support provides a prototype for developing the perturbation solution. Offset of the pin from the center position destroys periodicity of the two-span system, whereas the strength of the torsional spring relates the extent of interspan decoupling. A study by Chen and Ginsberg [J. Vib. Acoust. 114, 141 (1992)] established a relationship between the eigenfunctions and the eigenvalues for different values of the pin offset. The previous findings are merged with a Ritz expansion to formulate the forced response. The adequacy of the solution is determined by comparisons to results of baseline ‘‘Sturm–Liouville-type’’ analyses. Flexibility of the perturbation solution is assessed in various case studies of lightly coupled two-span systems.
Sensitivity analysis of structural eigenfrequency to plate design parameters by using neural network
Authors: Yu Z. Q. , Yam L. H. , Leung T. P.
Published: October 2005

The dynamic characteristics of plate structure can be improved by arranging the natural frequencies of the system in specified ranges. The sensitivities of structural dynamic response to design parameters can provide the essential gradient information for deriving efficient optimization procedures. They are used to form an approximate problem for solving the original structural optimization problem, while the sensitivity of geometric parameters to frequency can provide the essential gradient information for deriving efficient design procedures. In this paper, first the training set of neural network is generated by the finite-element method; second, the original design of a cantilever rectangular plate with multifrequency constraints is obtained by using the neural network; third, the sensitivities of the plate eigenvalue to design parameters (i.e., ∂ f/∂Ri) around the point of original geometric design are obtained by using the trained neural network. Finally, the sensitivities of design parameters to eigenvalue (i.e., ∂R/∂fi) are also obtained by using the trained neural network. The influence of frequency on geometric parameters, as well as the influence of geometric parameters on frequency, is also discussed.
Experiments on turbulent boundary layer/flexible structure/sound interactions in accelerated motion
Authors: Maestrello L.
Published: October 2005

Measurements are made of the response and acoustic radiation of a panel structure mounted in a wind tunnel and forced by a subsonic turbulent boundary layer and pure-tone sound. Measurements are made at accelerated speed because the resultant response exhibits a variety of behaviors different from data at constant speed. The structure exhibits broadband response with superimposed pure tone and its harmonics over the band, a nonlinear, nonstationary, and non-Gaussian process. The mechanism by which harmonics are generated becomes clear as the amplitudes of the fundamental and low-frequency band reduce with increasing level of the harmonics—a manifestation of energy transfer. Active control of the panel response using a time-invariant system recovers losses in relative stability as it regains partial reduction of the harmonics.
Observations of vibration-induced fatigue in steel using modal analysis
Authors: Arzoumanian Sevag H. , Koehn Douglas P. , Swanson David C.
Published: October 2005

The acceleration to force transfer functions across a shaker-excited thin band under tension with a deep notch cut through its center is examined up to the point of fatigue-induced failure. An analytical model is developed to track the changes in modal properties evident in the experimental results as a function of band parameters. The progression of the structure toward failure is documented by plots of rotational stiffness and crack length as a function of fatigue time.
Vibration analysis of triangular plates using the ray-tracing technique
Authors: Gunda R. , Vijayakar S. M. , Singh R.
Published: October 2005

A new ray-tracing technique is proposed for the dynamic analysis of thin plates in flexure. This approach is based on the fundamental solution to the plate biharmonic equation and suitably placed image sources which simulate waves reflected from the plate edges. In this paper, this method is applied specifically to a class of triangular plates with certain aspect ratios. Since exact eigensolutions for some plates with simply supported boundary conditions are known, these cases are analyzed first. The method of images is also being extended or arbitrary polygonal plates where all the image sources may not be seen by all points inside the plate unlike the previous cases. Consequently, the image sources have to be selectively chosen depending on the excitation and observation points. Preliminary results, when compared with exact solutions and finite-element calculations, indicate that this method is capable of accurately predicting harmonic response. Another advantage of this technique is that the solution can be obtained within a spectral bandwidth. Convergence studies show that the error norms rapidly decrease with an increase in frequency and damping. Hence, this method is computationally efficient in the high-frequency regime. [Work supported by the Army Research Office.]
Some phrase-level influences on the glottal waveform
Authors: Stevens Kenneth N.
Published: October 2005

The prosody of an utterance is often described in terms of the locations of attributes such as pitch accents, boundary tones, and vowel reduction. These prosodic descriptions are usually represented in the sound by changes in fundamental frequency, duration, and other temporal and spectral attributes of the segments. This paper presents data showing that the amplitude and spectrum of the glottal pulses, as well as their frequency, undergo modification depending on locations of pitch accents and boundary tones and depending on vowel reduction. The following results were obtained: (1) Reduced vowels tend to have significantly lower amplitude (7 to 13 dB) than nonreduced vowels, together with an increased first-formant bandwidth and an increased tilt in the source spectrum; (2) a nonreduced vowel has a somewhat reduced amplitude (by about 6 dB) when it follows a nuclear pitch accent; and (3) a nonreduced vowel in utterance-final position in a declarative sentence shows a decreased amplitude of the first-formant peak, an increased open quotient, and an increased spectrum tilt. Production mechanisms that could account for these changes include modifications in subglottal pressure, adjustments of the glottal configuration, and influences of constrictions in the supraglottal airway. [Work supported in part by a grant from NIDCD.]
An acoustic device for Prandtl number measurements in gases
Authors: Gillis Keith A. , Moldover Michael R. , Mehl James B.
Published: October 2005

An acoustic method is being developed for measurements of both the thermal and viscous diffusivities of gases using different sets of resonances of a single cavity. The ratio of the diffusivities, i.e., the Prandtl number, is a key parameter in determining the heat transfer from a solid to a moving fluid. Honeycomb inserts placed near the center (z=L/2) of a cylindrical cavity (length L) provide a large surface area with minimal blockage of longitudinal acoustic flow. Odd-order longitudinal modes, which have a velocity antinode at z=L/2, have a strong viscous interaction with the insert. For even-order modes, which have temperature antinodes at z=L/2, the thermal interaction dominates. Measurements of the resonance parameters of both types of modes are analyzed using a model which enables the viscous diffusivity to be determined from the odd modes and the thermal diffusivity from the even modes. Because the same insert is used for both the even and the odd modes, the ratio of the diffusivities is not sensitive to details of the geometry of the insert; thus, the Prandtl number can be determined more accurately than either diffusivity. [Work supported by ONR.]
Capillary bridge modes driven with modulated acoustic radiation pressure
Authors: Morse Scot F. , Thiessen David B. , Marston Philip L.
Published: October 2005

A liquid bridge between two solid surfaces is known as a capillary bridge. In the experiments to be described, the bridge liquid is a mixture of PDMS with a dense organic liquid. The bridge has the same density as the surrounding water bath such that its equilibrium shape between circular posts is a circular cylinder of length L and radius R. Low-frequency modes of such a bridge are known to exist where surface tension provides the restoring force. Even neglecting viscosity, the modal characteristic equation is complicated by the boundary conditions. It is demonstrated that low-frequency modulation of an ultrasonic standing wave in the surrounding bath can be used to excite specific axisymmetric or nonaxisymmetric capillary modes. Coupling to each mode depends on the location of the bridge in the standing wave. The coupling is a consequence of the space-time modulation of the radiation pressure as discussed previously for drops and bubbles [P. L. Martson, 15–26 (1980)]. The predicted decrease of mode frequency with increasing slenderness S=L/2R is confirmed as is the vanishing of the frequency of the most unstable mode as S approaches π. [Work supported by NASA.]
An electromagnetic liquid shock wave generator for the production of a pulsed water jet
Authors: Mortimer Bruce J. P. , Skews Beric W.
Published: October 2005

Water jets can be either continuous or pulsed. Pulsed or discrete water jets have many advantages over continuous jets in certain applications. The production of discrete jets has mostly been due to a momentum transfer from a mass impacting a compression chamber. In this study the feasibility of using a novel adaptation of an electromagnetic source (EMAS) for the production of a pulsed water jet is investigated. This device consists of a high-voltage 4-8 F, 20-kV capacitor which is discharged through a flat pancake coil. An insulated metal disk is in close proximity with the coil. Lorentz forces due to the eddy currents induced in the disk accelerate the disk away from the coil. The disk acceleration produces a shock wave in a liquid-filled cavity. A convergent reflector focuses the wave onto a nozzle. The reflection of the shock wave from the water–air interface produces a discrete water jet. A theoretical analysis of the electrical characteristics of the transducer is presented. A finite-element package was used to optimize the convergent reflector. Experimental results from a prototype generator are given including pressure measurements from a needle hydrophone and schlieren photographs of the water jet. [Work supported by FRD.]
Coherent enhancement of reflected signals in a parametric echo-sounder
Authors: Donskoy Dimitri M. , Sutin Alexander M. , Potapov Andrew I.
Published: October 2005

A parametric echo-sounder is used for sea sub-bottom profiling and target (cables, mines, etc.) finding. It generates a modulated high-frequency signal (pump signal). Due to the nonlinearity of water, part of the pump energy is converted into a low-frequency wave named the secondary signal. The high-frequency pump signal reflects mostly from a bottom surface and has high signal-to-noise ratio. The low-frequency secondary signal penetrates deeper under the bottom and reflects from sub-bottom layers and buried objects. However, the level of these reflected signals is low, often below noise level. In order to enhance the signal-to-noise ratio for these reflected secondary signals, the coherent average technique can be employed with the use of the reflected pump (high-frequency) pulses as reference signals. The feasibility of this approach is based on the following considerations. (1) The pump and the secondary signals are always correlated. (2) Average from one pulse to another does not depend on deviation in distance between the transducer and the bottom (due to the pitching, drifting, etc.) because the reference signal (reflected from the bottom pump signal) always follows this deviation. (3) The front of the pump signal is much sharper as compared with the front of the secondary signal. Therefore coherent averaging of the secondary signals can be done precisely. (4) For the ‘‘frozen’’ sub-bottom structure time delays between the first reflected signal and the all following reflected signals are fixed; therefore the coherent accumulation will take place for all of these signals. The proposed method was proved during feasibility field test performed at Barents Sea.
Cochlear modeling since Fletcher
Authors: Siebert William M.
Published: October 2005

In 1951, Harvey Fletcher published a comprehensive analysis of the macromechanical dynamic behavior of the cochlear partition in response to sound. Although not the first to derive the now-familiar one-dimensional long-wave differential equation, Fletcher’s discussion is so clear and so careful that it had considerable impact at the time and remains today a model of elegant biophysical thinking. His results, moreover, matched the observations then available (primarily those of von Bekesy). The last 44 years, however, have seen the introduction of a variety of new experimental observations casting serious doubts on whether the cochlea can usefully be considered a linear passive system as Fletcher and his contemporaries assumed. And new analytical tools, notably the wide availability of extensive computational facilities, have substantially altered our idea of what constitutes a workable mathematical model. This paper will review the place of models of the Fletcher type in our current understanding of cochlear behavior.
The auditory filterbank: Fletcher’s functional model of hearing
Authors: Patterson Roy D.
Published: October 2005

Fletcher [Rev. Mod. Phys. 12, 47–65 (1940)] summarized his observations on pitch, loudness, and masking in terms of ‘‘auditory patterns—spiral lines representing the cochlea with shaded regions showing neural responses to sinusoids. The auditory filterbank was a set of overlapping auditory patterns spanning the frequency range of hearing—a concept that has served as a functional model of auditory frequency analysis ever since. It has four main components: the filter shape, its bandwidth, the distribution of filters across frequency, and the detection criterion at the filter output. Fletcher identified these components and focused attention on them with his famous ‘‘band-widening’’ experiment in which a tone is masked by a variable width noise centered on the tone. The current paper reviews four areas of research spawned by the components of Fletcher’s filterbank concept. The research has shown that the band-widening experiment is actually rather insensitive, and subject to a confounding which led to underestimation of filter bandwidth and overestimation of the detection criterion. But the more important assumptions about filter shape and distribution were proven essentially correct. As a result, current, computational, auditory filterbanks are surprisingly similar to Fletcher’s original conception.
The excitation-pattern model according to Fletcher
Authors: Buus So/ren
Published: October 2005

This talk reviews how Fletcher used excitation patterns to understand auditory processing. In the 1930’s, Fletcher suggested that the relation between place of maximal excitation on the basilar membrane could be derived from measurements of critical bandwidths and frequency difference limens. He also showed that loudness and masking were closely related and that loudness for an arbitrary sound could be calculated on the basis of patterns of excitation integrated along the basilar membrane. Likewise, he suggested that discrimination of level differences between sounds could be understood on the basis of their excitation patterns. These concepts remain valid 60 years later.
Fletcher and the power spectrum model of hearing
Authors: Carlyon Robert P.
Published: October 2005

Fletcher’s famous band-widening experiment demonstrated that the masking of a pure tone by a continuous broadband noise was determined only by those components of the noise close to the signal frequency. This formed the basis of the pervasive ‘‘power spectrum’’ model of hearing, according to which the threshold of a signal of a given frequency is determined by the amount of masker energy passing through an auditory filter centered on that frequency. This rigorous prediction has aided the identification of additional forms of auditory processing, which have been revealed by exceptions to the power spectrum model. The interpretation of such findings, which include CMR, profile analysis, informational masking, and the overshoot effect, is greatly facilitated by the existence of a ‘‘default’’ model which accounts for a large amount of other data. In addition to reviewing these developments, new evidence will be presented demonstrating that the shape of a masker’s excitation pattern can also be affected by the shape of its (temporal) envelope.
Evaluating human neural tuning curves from a mechanical model of the cochlea by relating them to psychophysical masking data
Authors: Garbes P. A. , Allen J. B.
Published: October 2005

Human neural threshold tuning curves are estimated by scaling the parameters of Allen’s [J. Acoust. Soc. Am. 68, 1660–1670 (1980)] resonant tectorial membrane model of the cat cochlea. A way to evaluate the derived tuning curves using psychophysical data is developed, based on a psychophysical detection model which relates the physiological tuning curves to psychophysical masking data. A detection criterion, defined by a relationship among the bandwidth of the frequency tuning curves, expressed as an equivalent rectangular bandwidth (ERB), the width of the excitation patterns, expressed as an equivalent rectangular spread (ERS), and the psychophysical critical ratio, is explored and verified using cat data. The detection criterion is then used to test the derived human curves by making predictions of psychophysical masking and comparing the predictions to experimental data. The detection model may also provide a deeper understanding of the frequency resolving properties of the cochlea.
Fletcher and loudness
Authors: Humes Larry E.
Published: October 2005

In this presentation, some of the pioneering work performed by Harvey Fletcher and colleagues on the loudness of simple and complex sounds will be reviewed. The focus will be placed on the model and data presented by Fletcher and Munson [H. Fletcher and W. A. Munson, J. Acoust. Soc. Am. 5, 82–108 (1933)]. In this classic paper, the authors lay a solid foundation for the understanding of loudness which remains remarkably intact today in light of contemporary psychophysical and physiological knowledge. They provide thorough descriptions of several loudness phenomena, including loudness growth, monaural loudness additivity, and binaural loudness summation. Among other things, they demonstrate that loudness for a single tone grows as a function of the cube root of stimulus intensity, that loudness is additive for stimulus components in separate auditory filters or in separate ears, and that loudness of partially masked stimulus components is also additive once adjustments for partial masking have been made. Fletcher and colleagues were also interested in applying their model of loudness to hearing-impaired listeners. Their prior efforts in this area will be updated by the review of contemporary data on loudness growth and summation in the hearing impaired.
The acoustic characterization of a new reverberant water tank
Authors: Weyer Richard , Capone Dean , Szwerc Richard
Published: October 2005

A reverberant water tank has been constructed at the Pennsylvania State University. The background noise, diffusivity of the sound field, and the reverberation time in the tank have been measured as a function of frequency in one-third octave bands, from 80 Hz to 63 kHz. The techniques used to characterize the tank are presented. The characteristics of the tank are compared to other known water tanks. It is demonstrated that the tank is suitable for the experimental determination of the radiation efficiency of a structure by comparing data obtained in this tank with previously presented data for a flat plate. [Work supported by ONR.]
Shape optimization of foam liners in double panel systems
Authors: Kang Y. J. , Bolton J. S.
Published: October 2005

Although elastic porous materials such as foams are widely used for passive control of aircraft and automobile interior noise treatments, numerical models of these materials have only recently became available [Y. J. Kang and J. S. Bolton, J. Acoust. Soc. Am. (1995)]. In the work described here the procedures of optimal design were combined with elastic porous material finite elements to optimize the shape of the foam liners. Specially, the surface contour of the foam lining was adjusted to minimize the sound transmission through a foam-lined double panel structure system in a waveguide. This model is a simple representation of an aircraft fuselage segment. The foam finite element was based on a complete elastic porous material theory that accounts for the three wave types known to be significant in foams. The procedures for coupling the foam finite element with adjacent acoustical and structural elements will also be presented. In the example problems, a plane wave is assumed to impinge on the incident surface of the double panel structure. The shape and material parameters of the foam liners were used as design variables, and the performance measure was the frequency-averaged sound transmission loss in the frequency bands of interest, e.g., the speech interference range.
Tailoring material properties of acoustic blankets for reducing radiated noise
Authors: Burroughs Courtney B.
Published: October 2005

The development and application of a mathematical model that considers the reduction in acoustic radiation produced by varying the material properties of a viscoelastic blanket in the direction parallel to the surface of the blanket are presented. The blanket covers an elastic plate which is driven on the side opposite the blanket by an incident acoustic wave. The model is used to compute the spatial distribution of the pressure on the top surface of the blanket. The total acoustic radiated power, normalized to the magnitude of the pressure incident on the plate, is computed from the surface pressure. Examples of the effectiveness of homogeneous and nonhomogeneous blankets in reducing acoustic radiation are presented. The effects of damping in the blanket are also examined.
The use of structural coatings to attenuate transmitted flexural wave-induced vibration
Authors: Keltie Richard F.
Published: October 2005

This study examined the used of a compliant coating on a plate to attenuate the transmitted structure-borne sound at the interface between the coating and the ambient acoustic medium. In order to gain physical insight into the problem, the layer was modeled as a fluid with dissipation. Although realistic layers are likely to be visco-elastic materials, the fluid layer approach has been used to provide for a tractable and useful analytical model. The performance of the layer model was evaluated by calculating the displacement field at the layer/medium interface in response to structural excitation. The 3-D wave-number-frequency response amplitude spectrum of the dynamic compliance was examined. This provided for the identification of the dominant processes determining the layer response. A simple physical interpretation of these results was shown to involve the dispersive characteristics of plate waves and acoustic waveguides. It was shown that the structural effects of the plate could be eliminated from the analysis, resulting in a model involving only the layer itself. The subsequent performance of the layer as a displacement (or velocity or acceleration) attenuator or amplifier was then examined. [Work supported in part by Naval Undersea Warfare Center, New London, CT.]
A modal/spectral analysis of mass distribution effects in a fluid-loaded plate
Authors: Babish John , Ginsberg Jerry H.
Published: October 2005

Feit and Johnson [ 2309(A) (1991)] showed that the signal scattered by a plate is greatly affected by the spatial distribution properties of an attached mass. Ginsberg etal. [ASME Proc., paper 93-WA/NCA-20 (1993)] used the surface variational principle (SVP), which describes the surface pressure and displacement as a set of interacting waves, to examine a fluid-loaded plate with attached point mass in an infinite baffle. In their analysis the mass distribution was represented as a Fourier series in an effort to determine how coarse the model could be, and still accurately represent the direct point mass solution. Their conclusion was that a series length of eight terms is adequate to describe the system behavior in the frequency range kL≤3, but a series of fewer than six terms is substantially inaccurate. The current work uses the in-vacuo modes of the spectrally smoothed mass–plate system as Ritz functions for displacement. The solution in terms of these modes is compared to the results obtained from the Fourier series representation, in order to identify why a critical number of terms is required for the spectral description of mass distribution.
Attenuation of waves in plates and bars using a graded impedance interface
Authors: Vemula Chandrasekar , Norris Andrew N. , Cody George , Storch Gerry V.
Published: October 2005

A new method is proposed for attenuation of reflected energy at the edges of plates and bars, using a graded impedance interface. A standard approach is to embed the plate edges in sand. However, it has been verified that a graded impedance interface at the edges is far more effective in damping the radiating structural energy. It is well known that impedance mismatch causes complete reflection of energy at the free edge of a plate. Hence, it seems reasonable to expect a reduction in reflected energy when impedance is varied gradually. Experimental results for 1-in. plates indicate that at most 30% of the energy is damped for frequencies above 2 kHz when sand is used, whereas as much as 60%–80% of the energy is damped between 2 and 10 kHz using a graded impedance. Experiments on bars also give similar results. A theoretical formulation for a bar with graded impedance interface at the edges is presented, using both the Kirchhoff and Mindlin theories. The Mindlin theory predicts the level of energy damping that is observed in experiments, while the Kirchhoff theory predicts much lesser energy damping. The shear effects are modeled more accurately in the Mindlin theory and they seem to be important in this problem.
Nonlinear combinational sound scattering by discontinuity-like defects in solids and its possible usage for crack diagnostics
Authors: Belyaeva I. Yu. , Zaitsev V. Yu.
Published: October 2005

One of the important problems in structural control of solids is the problem of discontinuity-like defects diagnostics. The main drawback of conventional linear diagnostic methods is the complicated differentiation between a weak ‘‘useful’’ signal originated due to a crack and the waves scattered by other inhomogeneities of the material, which are not interesting from the viewpoint of flaw detection. In view of this problem, new acoustic diagnostic methods based on measuring nonlinear acoustic characteristics have recently begun to attract the attention of researchers. The effect of acoustic waves scattering nonlinearly from a thin discontinuity-like defect in a solid is analyzed. The defect is considered as the interface between two surfaces covered with bulges characterized by different initial deformation. It is shown that the nonlinear scattering into combinational-frequency waves is much more sensitive to the loading of the interface contacts compared with the scattering into the wave of fundamental frequency. The observation of nonlinear scattering by crack-type defects should allow one to distinguish cracks from other scatterers and can be used for creation of new methods of crack detection and positioning.
Theoretical analysis of dynamic characteristics of piezoceramic polymer composites with 2–2 connectivity
Authors: Zhang Q. M. , Geng Xuecang
Published: October 2005

A dynamic model of piezoceramic polymer composites with 2–2 connectivity is presented. It can be used to evaluate the dispersion curves for the thickness resonance and the stop band edge resonance, the effective velocity of the longitudinal wave, as well as the distributions of strain, stress, and the electric field in a composite. Based on these results, the electromechanical coupling factors are determined using two different methods according to the IEEE recommendation. It is shown that the thickness mode coupling factor kt obtained from the difference of the effective longitudinal velocities at the constant electric field and constant electric displacement is in good agreement with the experimental values. It is also shown that, due to the composite structure, the piezoelectric shear coefficient e15 has a strong effect on both the effective velocity of the longitudinal wave vD and kt even at the limit where the composite thickness is much larger than the period. On the other hand, kt calculated from the energy consideration is much higher than the experimental values and cannot account correctly for the effect of e15 on kt. From the model, the evolution of the thickness mode and the stop band edge resonance with the thickness of a composite and the modes coupling between the two can also be elucidated.
The effect of length on the acoustic attenuation performance of concentric expansion chambers
Authors: Selamet A. , Radavich P. M.
Published: October 2005

Following an earlier analytical and computational work of Sahasrabudhe etal. [Noise Control Eng. J. 38(1), 27–38 (1992)], the present study investigate the effect of the length on the acoustic attenuation performance of concentric expansion chambers. Three approaches are employed here to determine the transmission loss: (1) a two-dimensional, axisymmetric analytical solution; (2) a three-dimensional computational solution based on the boundary element method; and (3) experiments on an extended impedance tube setup with nine expansion chambers fabricated with the fixed inlet and outlet duct, and chamber diameters, and varying chamber length to diameter ratios from l/d=0.2–3.5. The results from all three approaches are shown to agree well. The effect of multidimensional propagation is discussed in comparison with the classical treatment for the breakdown of planar waves. The study also provides a simple relation between the l/d ratio of the expansion chamber and the number of repeating attenuation domes prior to the domination of higher-order modes.
General proof of the nonscattering of sound by sound in the lossless dispersionless case
Authors: Westervelt Peter J.
Published: October 2005

Introducing the variable π=ρsc20+L+ΛV into Eq. (14) of Westervelt [P. J. Westervelt, 200 (1957)], two equivalent dissipationless wave equations are obtained for the scattered variable ρsc20: Eq. (1) is ⧠2[π+2(ψ2),00]=ΓV,00 and Eq. (2) is ⧠2[π−Λ(ψ2),00]=ΓT,00 in which ⧠2ψ2=L and Γ=−(2+Λ). Outside the region of interaction π=ρsc20 so the source for ρsc20 can be either ΓV,00 or ΓT,00 and since, in general, T≠V, ρsc20 must be zero (except for unidirectional waves when T=V in which case the well-known solution is still restricted to the interaction zone). As an example, consider two colliding waves for which the interaction energies satisfy T12=−V12 requiring ρsc20 from Eq. (1) to be the negative of that from Eq. (2) which demands that ρsc20=0. Within the interaction region the solution to either equation is ρsc20=(Λ−2)(φ+φ−,00+φ−φ+00−2φ+,0φ−,0), where ψ=φ++φ− the sum of right and left traveling waves. The scattered pressure ps=ρsc20+ΛV. For scattering to occur outside the interaction region, there must exist losses, as witnessed in the parametric array, or dispersion [see, e.g., P. J. Westervelt,‘‘Scattering of Sound by Sound,’’ in FiniteAmplitudeWaveEffectsinFluids, edited by L. Bjo/rno/, Proc. 1973 Symp. Copenhagen (IPC Science and Technology, London, 1974), or interaction with real sources [P. J. Westervelt, VirtualSourcesinthePresenceofRealSourcesinNonlinearAcoustics, edited by T. G. Muir (Proc. of Univ. of Texas at Austin Conference, Nov. 1969)].
Nonlinear elastic wave propagation along free surfaces of a thick plate
Authors: Hamilton M. F. , Il’inskii Yu. A. , Zabolotskaya E. A.
Published: October 2005

Nonlinear elastic wave propagation along free surfaces of a thick isotropic plate is investigated theoretically. The finite thickness of the plate introduces dispersion. In the linear approximation the solution is a superposition of symmetric and antisymmetric modes, and the wave field undulates along the surfaces of the plate. Nonlinearity is taken into account with the Hamiltonian formalism used to model Rayleigh waves of finite amplitude [Zabolotskaya, 2569–2575 (1992)]. The resulting coupled spectral equations were integrated numerically to investigate harmonic generation and waveform distortion in an initially monochromatic wave generated on one side of the plate. Two different plate thicknesses were considered, 20 and 100 shear wavelengths. For the thicker plate, and with a shock formation distance much smaller than the dispersion length, the solutions resemble those for nonlinear Rayleigh waves in a half-space. For the thinner plate, and with the two length scales of the same order, propagation curves for the second harmonic component exhibit the ‘‘growth-decay cycles’’ that have been measured in experiments and discussed in a previous article [Shull etal., 418–427 (1993)]. [Work supported by NSF, Schlumberger, and the Office of Naval Research.]
Comparison of the whistle structure of six species of dolphin
Authors: Evans William E. , Ding Wang , Würsig Bernd
Published: October 2005

Spectral and statistical analyses were used to compare the whistle structure of six species of dolphin; Stenellalongirostris, Stenellafrontalis, Stenellaattenuata, Lagenorhynchusobscurus, Tursiopstruncatus, and Sotaliafluviatilis. A consistent pattern existed in the various coefficients of variation calculated for the different species. In general, the frequency variables had the lowest coefficients of variation (cv). The values of cv for maximum frequency were usually the lowest. Compared to other species Tursiops had relatively large coefficients of variation of the frequency variables indicating that the frequencies of Tursiops whistles were more diverse. The other five species had similar frequency ranges which had higher upper frequencies than Tursiops. The results of discriminate analysis indicated that here were significant differences between the whistle structures of the different species, and that these differences were related to taxonomic relations, body size, and habitat. The magnitude of the differences in whistle structure correlated with taxonomic relationships of the various species studied. The pelagic species emitted whistles in a relatively higher frequency range and greater frequency modulation than the coastal or riverine species.