bluuebunny/crossref_metadata_2025 huggingface dataset:
The accuracy of perturbation theory for acoustic penetration of sediment due to interface roughness.
Authors: Thorsos Eric I.
Published: October 2005

Lowest-order perturbation theory (PT) is usually considered valid for modeling scattering from rough surfaces with a small roughness. In particular, for PT to be accurate near the specular direction, it is required that kh≪1, where k is the acoustic wave number and h is the rms surface height. In the case of an acoustic wave incident on the seafloor, a rough interface will scatter sound back into the water and also into the sediment; such scattering into the sediment will occur even when the incident grazing angle is below the critical angle. Here, the accuracy of PT for acoustic penetration through a rough water/sediment interface with a power-law roughness spectrum is examined using exact integral equation results for the 2D problem. It is found that PT remains accurate for kh up to and well beyond unity, when the incident grazing angle is either above or below the critical angle. The reason for this surprising result will be discussed. [Work supported by ONR.]
Near-field scattering through and from a 2-D fluid-fluid rough interface.
Authors: Moe John E. , Jackson Darrell R.
Published: October 2005

A general analytical expression for the time-dependent field intensity scattered from or through (penetrating) a 2-D fluid-fluid rough surface due to a narrow-band incident plane wave and a narrow-band point source are derived and expressed in terms of the bistatic scattering cross section per unit area of the rough surface. Even though the scattering cross section is defined as a far-field quantity, this near-field result is general and exact for the special case of a continuous wave source and incident plane wave. Dispersion of a pulse is a function of medium parameters, the incident and scattered directions, as well the bandwidth and center frequency of the source signal. First-order perturbation calculations for the case of a Gaussian pulse illustrate intensity pulse dispersion effects due to forward scattering into a lossy sediment. [Work supported by ONR.]
Peculiarities of low grazing angle acoustic penetration of the layered absorbing bottom.
Authors: Fokina Margarita S.
Published: October 2005

Acoustic reflection from the bottom and sound propagation are closely connected. In this paper reflection coefficient behavior at high frequencies (above 1 kHz) for the layered absorbing bottom was investigated. Influence of the layered bottom parameters on acoustic propagation was considered. It was shown that for the same set of bottom parameters the sound reflection coefficient at low grazing angles decreases when the grazing angle decreases. Behavior of frequency and angle resonances of the reflection coefficients was analyzed. Two types of bottom connections between sets of bottom parameters and sound losses in a wide frequency band were ascertained.
Overview of SAW materials.
Authors: Ballato Arthur
Published: October 2005

There is now a rich variety of piezoelectric materials available for surface acoustic wave applications. These include crystals in symmetry classes mm2, 32, 3m, 4mm, 6mm, and 4ā3m. Classes 6mm and 4ā3m include most of the binary semiconductors, such as gallium arsenide and related alloys, making integrated acoustic/electronic devices possible. Depending upon use, the SAW substrate material may be chosen to have certain combinations: piezocoupling, temperature coefficient of frequency or delay, small coupling to bulk modes, low sensitivity to acceleration or thermal transients, high acoustic Q, small power flow angle, etc. In this paper, these and other criteria are discussed broadly, with illustrations of pertinent materials and orientations. Also given are recommendations of substances for which the material constants are well enough known to be practical, as well as indications for necessary future work in growth and characterization. A broadband equivalent electrical network for SAW propagation is presented, by means of which the appropriate material parameters may be extracted from network analyzer measurements. The circuit can also serve to represent the salient features of devices in their working environments.
Surface acoustic wave microsensors.
Authors: Vetelino John F.
Published: October 2005

Surface acoustic waves (SAWs) excited on the surface of piezoelectric crystals form the basis of a family of microsensors that is sensitive, portable, cheap, and small. These microsensors can be used in a wide variety of applications to sense low levels of gases, physical quantities such as mass, temperature, pressure, flow and humidity, biological processes, corrosion, ions and particulate matter, and a variety of mechanical and electrical quantities. In contrast to other microsensor technologies, SAW microsensors can sensitively detect both electrical and mechanical phenomena. This is due to the fact that the SAW has both mechanical and electrical fields. In those applications requiring sensitivity, such as gas sensing and biosensing, the selectivity is provided by a receptor film applied to the piezoelectric substrate. In this paper different types of SAWs are described and prototype sensing geometries are presented. Particular attention is devoted to one of the most common SAW microsensor applications, namely, gas sensing. Finally, results obtained using SAW microsensors in a variety of applications are presented and discussed.
Integrality of first inversion C-major chord components.
Authors: Acker Barbara E. , Pastore Richard E.
Published: October 2005

Previous work [Acker and Pastore, Percept. Psychophys. (in press)] using a discrimination version of the Garner paradigm found the E and G frequencies of a root position C-major chord to be integral, with both frequencies exhibiting significant redundancy gains in the correlated condition, but with the E exhibiting less interference in the orthogonal condition than the G. This finding raised the question of whether attention was better allocated to the E frequency specifically, or if it was a function of the middle spectral location. The current work addresses this question by evaluating discrimination of chord components in a first inversion chord, where the E is the lowest frequency component instead of the middle component. Subjects completed fixed, correlated, and orthogonal discrimination tasks for each frequency. Replicating the earlier results, both frequencies experienced significant redundancy gains in the correlated condition, and the E frequency again exhibited less interference in the orthogonal condition. These results will be discussed in terms of attention being more easily allocated to the E frequency specifically, regardless of spectral location. [Work supported by AFSOR.]
Nonlinear dynamics of rhythm perception in performed music.
Authors: Large Edward W. , Palmer Caroline
Published: October 2005

Listeners are readily able to identify and track nearly periodic components in complex auditory rhythms such as music, despite the large temporal modulations that commonly exist in music performance. The modulations that performers introduce, however, often communicate musical information such as melody, phrase structure, and meter. A dynamical system model of beat tracking in music performance is first described, in which a performed (external) rhythm serves as driver, and an internal ‘‘attentional rhythm’’ is modeled as a nonlinearly driven oscillator. Next, a coupled two-oscillator network, designed to simulate the perception of multiple beat periods (meter), is introduced. The one- and two-oscillator models’ ability to track beats and recover meter is tested in piano performances of Bach’s Two-Part Inventions. The coupled oscillator network not only extends the model to the perception of meter, but also influences the ability of each component oscillator to track a component periodicity in the external rhythm. The ability of the network to recover other types of musical information, such as phrase structure, from performance timing is discussed. [Work supported by NSF SBR-8920230 and NIMH R29-MH45764.]
Musical stability and melodic implication.
Authors: Thompson William Forde , Stainton Murray
Published: October 2005

Five perceptual principles of melodic implication, derived from Narmour’s (1990, 1992) ‘‘implication-realization’’ theory of melody, were evaluated in an analysis of European folk songs. The principles apply only to unstable or unclosed melodic conditions, and define how such conditions initiate processes of pattern recognition which then generate expectations about the properties of subsequent notes. For instance, the principle of proximity states that unstable events generate an expectation that the next note will be proximal in pitch. Musically stable and unstable events were identified in over 700 melodies, using criteria based on metric stress, tonality, and duration. For each event, the next note (the continuation note) was recorded. Multinomial loglinear analysis assessed whether the five principles, separately or in combination, could predict the frequency with which different continuation notes followed different conditions of stability. For continuation notes following unstable events, statistical support was found for all principles. The link between musical stability, melodic expectation, and composition is discussed.
Mothers and their children hear a musical illusion in strikingly similar ways.
Authors: Deutsch Diana
Published: October 2005

A two-tone pattern, known as the tritone paradox, has certain curious properties. It is heard as ascending when played in one key, yet as descending when played in a different way. Further, when the pattern is played in any one key it is heard as ascending by some listeners but as descending by others. Perception of this pattern has been found to vary in correlation with the geographical region in which the listener grew up, and also with the pitch range of the listener’s speaking voice [D. Deutsch, Philos. Trans. R. Soc. London Ser. B 336, 391–397 (1992)]. A striking correlation is here reported between how a listener hears this pattern and how his or her mother hears it. Fifteen subjects (ten children and five adults) were studied. The subjects were all Californians; however their mothers had grown up in diverse geographical regions, including England, the European continent, and various parts of the United States. The perceptions of all the subjects corresponded more closely to those of their respective mothers than to the average of all the mothers; this effect was highly significant statistically. Implications of these findings are discussed.
Directed attention and perception of frequency changes.
Authors: Acker Barbara E. , Pastore Richard E.
Published: October 2005

What role does attention play in the perception of components within a melody? A paradigm used by Palmer and Holleran [Percept. Psychophys. 56(3), 301–312] provides a basis for addressing this question. Their study investigated different influences on the perception of pitch alterations in three-voiced musical passages, where subjects first learned a four-measure standard, then completed a same/different task. ‘‘Different’’ passages were constructed by altering the original standard, with a harmonically related (HR) or unrelated (HU) frequency change made in the lowest, middle, or upper voices of the musical passage. Results indicated that HR changes were less detectable than HU changes and were the least detectable in the middle voice. The current study uses the same procedures and musical materials as the Palmer and Holleran work, but provides the subjects with cues indicating which frequency region might contain the alteration (low, medium, or high). Results will be discussed in terms of the role directed attention plays as a function of harmonic relationship and frequency region.
A consultant for acoustical product breakthroughs—A tribute.
Authors: Kopec John W.
Published: October 2005

The staff at the Riverbank Acoustical Laboratories (RALTM) in Geneva, IL is often asked to recommend an acoustical consultant for a myriad of acoustical related projects. In order to avoid any unfavorable backlash situations, the staff has to be as certain as possible that they recommend a consultant who will successfully fulfill the request at hand. To assist in the selection process a three-level-type list of tasks, including the names of various acoustical consultants that might fulfill these tasks, was compiled. Level three included the names of acoustical consultants that possibly could fulfill, perhaps, one of the more demanding kinds of requests, which was the need for an acoustical consultant that could provide the design of an acoustical breakthrough product. Curt Holmer fulfilled that request three times, and because of that he had earned a well-deserved place on the list of outstanding acoustical consulting accomplishments that at the time of their occurrence provided an acoustical breakthrough.
Evaluation of a technique to identify models of modes in nonlinear structures.
Authors: McCabe S. A. , Davies P.
Published: October 2005

Interactions between modes in nonlinear structures can lead to situations where, for the same excitation, different responses may be observed. The observed response will be a function of the system, of the excitation, of initial conditions, and of the effects of small perturbations to the system. Some responses may be observed more often than others. When the more rarely observed responses are perceived as problem situations, it is often frustrating to demonstrate that the problem exists, because it is difficult to control the test sufficiently to repeatedly observe the behavior. Analysis of system models can be used to identify under what conditions these responses may occur, and indicate how the region where such responses are possible may be approached. In real systems, the model structure for the system has to be identified, which may be an affirmation of a theoretical model structure, and the parameters of these models estimated. Described in the presentation are the results of using a system identification technique to construct models relating the excitation to the response of two interacting modes in a thin plate under tension.
High frequency modeling of vehicle noise performance of aluminum body structure.
Authors: Lee James J. , Holmer Curt , Moeller Mark J.
Published: October 2005

This presentation is dedicated to Curt Holmer’s contribution to acoustics at Ford Motor Co. The presentation material is based on the work he was involved with during the last part of his life. The results of the 1992 Taurus SEA model are used to assess the effect of an aluminum body structure. The noise performance comparison includes airborne and structure-borne paths. The effect of structural damping is also simulated.
A mixed displacement-pressure formulation for Biot’s poroelastic equations.
Authors: Atalla Noureddine , Panneton Raymond , Debergue Patricia , Allard J.-F.
Published: October 2005

Recently, a displacement (u,U) finite element model for the three-dimensional poroelasticity problem has been developed by Panneton and Atalla [J. Acoust. Soc. Am. 98, 2976(A) (1995)]. This model, while accurate, has the disadvantage of requiring cumbersome calculations for large finite element models and spectral analyses. To overcome this difficulty, this paper presents a mixed displacement-pressure (u,P) finite element model. First, the classical Biot–Allard equations are rewritten in terms of the solid phase macroscopic displacement vector and the fluid phase macroscopic pressure. The new coupled equations have the advantage of writing the poroelasticity equations in the form of the coupling between an equivalent elastodynamic equation for the solid phase and an equivalent Helmholtz equation for the fluid phase. In particular, the equivalent fluid model is transparent in the developed equations. Next, the associated variational formulation is presented together with its numerical implementation. Also the acoustic–poroelastic, elastic–poroelastic, and poroelastic–poroelastic coupling conditions are derived. Several examples are presented to show the accuracy and effectiveness of the proposed model and its coupling with elastic and acoustic media. In particular a systematic comparison is made with the (u,U) finite element formulation. [Work supported by Canadair, CRSNG, and FCAR.]
Application of Biot’s poroelasticity theory for nonlinear acoustics.
Authors: Donskoy Dimitri M. , Khashanah Khaldoun , McKee Thomas G.
Published: October 2005

The nonlinear dynamic equations introduced by Biot to model poroelastic media have not been implemented to describe nonlinear acoustic waves in such media. The equations of the semilinear Biot model are revised and a mathematical model depicting the physical nonlinearity is established. A perturbation technique is then applied to find solutions to the nonlinear Biot equations. The computational results are carried out in details for a one-dimensional model in which the contributions of the fast and slow compressional waves into second harmonic wave are analyzed. The correlation between second and third-order Biot coefficients and measurable nonlinear parameters is also presented along with a parameter analysis.
Dispersion relation influence on rise times of sonic boom propagation through turbulence.
Authors: Pierce Allan D.
Published: October 2005

Recent work suggests the ‘‘average’’ turbulence contribution to rise times is accounted for by an extra term in the propagation equation, evolving from an extra term in the dispersion relation k=(ω/c)+F(ω), where c is spatially averaged, and, for mechanical turbulence, F(ω) depends on turbulent energy dissipation rate ε per unit fluid mass. Previous analysis suggests that F(ω) is −7.48 CKeiπ/3ε2/3c−7/3ω1/3. The extra term’s influence is explored with a pulse beginning with a stepfunction in pressure which enters a turbulent atmosphere. After propagation through a distance x, the rise time becomes of order of ε2c−7x3. This cubic growth is eventually curbed by the nonlinear steepening effect; the above prediction is an upper limit to the turbulence contribution. The discrepancy with the 1971 prediction that the rise time scales as ε4/7c−19/7x11/7 is discussed, such being consistent with an ω7/11 term in the dispersion relation. [Work supported by NASA–LRC.]
Acoustic scattering from vegetation.
Authors: Sprague Mark W. , Sabatier James M.
Published: October 2005

Acoustic scattering from vegetation is a complicated problem that depends on a number of plant characteristics including biomass distribution, plant spacing, plant height, leaf size and shape, and the acoustic impedance of the plant material. A theory for acoustic scattering from vegetation could be the basis for a noninvasive acoustic measurement of some of these characteristics, particularly biomass distribution. Two possible techniques to characterize scattering from vegetation are the multiple scattering approach and the porous medium approach. In the multiple scattering approach, the vegetation is treated as a slab of scatterers with a random distribution. In the porous medium approach, the vegetation is treated as a porous material with a very high porosity. In this talk, both approaches are examined, and their predictions are compared for forms of vegetation such as wheat, corn, cotton, and soybeans.
Laser thermo-optical source of sound at a fractal surface in a liquid.
Authors: Lyamshev Leonid M. , Lyamshev M. L.
Published: October 2005

Surfaces of real bodies are rough, uneven, or porous as a rule and are characterized by fractal properties. Surfaces may be fractal up to the molecular-level scale. Rough oceanic surface is also fractal. Laser photo- acoustic diagnostics of various media have been developing in recent years. It is based on laser excitation of sound (ultrasound or hypersound). Special features of laser sound excitation in a liquid half-space with the rough statistical fractal surface are investigated. It is assumed that an harmonically modulated laser beam is incident on the liquid surface. The height (amplitude) of surface waves is greater than the sound wavelength and the absorption length of light in the liquid. Fractal properties of the surface are characterized by the Weierstrass function and connected with it by a structural function. The Kirchhoff approximation is used to solve the boundary problem. The influence of fractal properties of the surface and parameters of laser radiation and liquid on the amplitude and spatial characteristics of intensity of the acoustic field excited in a liquid by laser radiation is analyzed.
On the relations among temporal integration for loudness, loudness discrimination, and the form of the loudness function.
Authors: Buus So/ren , Florentine Mary , Poulsen Torben
Published: October 2005

Temporal integration for loudness was measured as a function of level from 2 to 60 dB SL using 2-, 10-, 50-, and 250-ms tones at 5 kHz. The adaptive 2I,2AFC procedure converged at the level required to make the variable stimulus just louder than the fixed stimulus. Thus the data yield estimates of the levels required to make tones of different durations equally loud and of the just noticeable differences for loudness level. Results for four listeners with normal hearing show that the amount of temporal integration, defined as the level difference between equally loud short and long tones, varies markedly with level and is largest at moderate levels. The effect of level increases as the duration of the short stimulus decreases and is largest for comparisons between the 2- and 250-ms tones. The loudness-level jnds are also largest at moderate levels and, contrary to traditional jnds for the level of two equal-duration tones, they do not appear to depend on duration. The level dependence of temporal integration and the loudness jnds are consistent with a loudness function [log(loudness) versus SPL] that is flatter at moderate levels than at low and high levels. [Work supported by NIH-NIDCD R01DC02241 and the Technical University of Denmark.]
Deriving the Weber fraction from loudness functions.
Authors: Hellman William S. , Hellman Rhona P.
Published: October 2005

In a previous paper [W. S. Hellman and R. P. Hellman, J. Acoust. Soc. Am. 91, 2380(A) (1992)], Weber fractions for intensity discrimination were derived from their concomitant pure tone loudness functions in normal hearing. The calculational procedure employed a generalized McGill–Goldberg model. This work extends these findings to more frequencies, to broadband noise, to tones masked by high-pass noise, and to forward masking. Weber functions generated by the model are compared to empirical data for the various experimental conditions and stimuli. In all cases, the calculated Weber functions capture the overall shape of the measured intensity-jnd data over a wide stimulus range. Not only does the model produce the near-miss relation for pure tones in quiet, it also predicts Weber’s law for broadband noise, a rising characteristic in the Weber function above 60 dB SPL for a tone in high-pass noise, and the midlevel hump observed in forward masking. These results show that there is sufficient information in the loudness function to recover the associated intensity-jnd function. This implies that loudness is the primary decision variable for intensity discrimination.
Overview: Modeling ipsilateral loudness adaptation as an indicator of peripheral function.
Authors: Weiler Ernest M. , Temple Jon , Sandman David E. , Huber Teri , Korman Maureen
Published: October 2005

Weiler and Hood [Audiology 16, 499–506 (1977)] and others found that a highly accurate model could be constructed to account for adaptation found by the classic method of simultaneous dichotic loudness balances. However, when the ipsilateral comparison paradigm (ICP) was devised to avoid complications of binaural/interaural effects, the SDLB model did not seem to fit [Weiler et al., J. Gen. Psychol. 114, 411–421 (1987); errata, 1988] and others. Recently, studies by R. Tannen and K. Jones [unpublished MA theses in progress, University of Cincinnati (1996)] seem to have provided the basis for a conversion from the SDLB model to ICP results. A critical assumption is that binaural loudness effects are double that of ipsilateral adaptation. Work by the authors and others will be reviewed with discussion of the strengths and weaknesses of the model for ipsilateral adaptation.
Timing of fundamental frequency control in word accent of the common Japanese.
Authors: Fujisaki Hiroya , Ohno Sumio , Ueno Tohru
Published: October 2005

The accentual patterns in Japanese can be consistently described in terms of rapid rises and falls in pitch, and their timing can be quantitatively specified by the onset and offset of the underlying accent command applied to a model for F0 contour generation [H. Fujisaki and K. Hirose, J. Acoust. Soc. Jpn. (E) 5, 233–242 (1984)]. The present paper describes a quantitative study on the timing of accent commands relative to the acoustic-phonetic characteristics of the morae and phones in utterances of the common Japanese. The speech material consists of words of varying length, phonetic constituents, and accent types, embedded in a carrier sentence. The timing of the accent command was estimated from the F0 contour by analysis-by-synthesis, while the timing of phones and morae was detected by referring to the frequency-time-intensity patterns. It was found that the relative timing of the accent command can be consistently described in reference to the onset of vowel rather than the onset of a mora when the latter starts with a consonant. Systematic variations in the timing due to phonetic constituency and accent type are formulated as rules for speech synthesis.
An acoustic evaluation of variation in the overlap of consonant and vowel gestures induced by speaking rate change.
Authors: Tjaden Kris , Weismer Gary
Published: October 2005

There is a growing body of empirical data supporting a gestural-based view of speech production in which adjacent speech gestures temporally and spatially overlap one another. Recent work suggests that certain acoustic measures are sensitive to changes in the overlap of adjacent consonant and vowel gestures [G. Weismer et al., J. Phon. 23, 111–126 (1995); E. Zsiga, J. Phon. 22, 121–140 (1994)]. Utilizing a graded speaking rate task, eight speakers produced 160 repetitions of ten target words embedded in a carrier phrase. F2 onset frequency, measured at the consonant–vowel boundary of test syllables, was used to index the degree of spectral-temporal overlap of adjacent consonant and vowel gestures. Regression analyses were used to evaluate the extent to which F2 onset predicted temporal variability in F2 formant trajectories due to speaking rate change. Results suggest that consonant and vowel gestures do not simply temporally slide away from each other with slowed speaking rate. Rather, modifications in the form and magnitude of vowel gestures are required to account for the present acoustic data. An empirically based acoustic model of variation in gesture overlap induced by speaking rate change is offered. Individual speaker differences also are discussed.
Competing hypotheses concerning the articulation of stress in English.
Authors: Harrington Jonathan , Palethorpe Sallyanne , Fletcher Janet , Beckman Mary E.
Published: October 2005

Previous studies have suggested two different hypotheses concerning the articulation of stress contrasts in English. Examination of low vowels surrounded by labial consonants generally shows lower jaw in accented as opposed to unaccented syllables, a result originally interpreted as a lower and hence louder vowel [Edwards et al., J. Acoust. Soc. Am. 89, 369–382 (1991)]. On the other hand, a study of nonlow back vowels in alveolar contexts showed higher and backer tongue body in accented syllables, suggesting a more peripheral vowel [de Jong, J. Acoust. Soc. Am. 97, 491–504 (1995)]. This paper reexamines the two hypotheses by looking at both jaw and tongue for both phonemically low and high vowels. Five speakers of Australian English read 20 tokens of two short discourses which placed the name ‘‘Babber’’ or ‘‘Beaber’’ twice each in accented and deaccented positions. Jaw and tongue positions were recorded simultaneously using a magnetometer. On average, the jaw was lower in all accented syllables, although the difference was smaller for the high vowel. At the same time, the tongue body reached significantly higher positions in accented high vowels, and somewhat lower positions in accented low vowels. Thus the two hypotheses can be reconciled by their application to the two different articulators. or
Acoustic signal analysis using Gabor-type windows.
Authors: Gertner Izidor C. , Lucci Stephan , Antrobus John
Published: October 2005

Transients in speech and other acoustic signals are usually irregular and very difficult to analyze because of their short and nondeterministic duration. Therefore the traditional Fourier analysis technique does not give satisfying results. The classical Gabor technique uses a Gaussian waveform window. However, it is not numerically stable and it has slow convergence. In order to do time-frequency analysis of acoustic signals, a window transform is proposed that is derived from a Gaussian using the Zak transform. The resulting window possesses good locality properties in both the time and frequency domains. The computational procedure, which based on the FFT algorithm, is robust and fast. It will be shown that transform yields accurate estimates of onset and offset times for periodic and aperiodic signals as well as for vowel centers and the ramp frequencies of formant transitions.
Acquisition of FM waveform parameters from vibration of rotational machine elements using FM wavelet template matching.
Authors: Van Dyke Michael B. , Swanson David C. , Reichard Karl M.
Published: October 2005

Vibration signals obtained from rotating machinery exhibit frequency modulated components resulting from torque variations due to wear and irregularities in the elements. The characteristic shape of the FM signal and degree of modulation can be useful metrics for the determination of the nature and extent of element degradation. A nonorthogonal FM wavelet template matching technique is used to quantify these parameters. Results are compared with FM waveforms obtained by signal demodulation, demonstrating fairly good accuracy.
Use of multiresolution analysis to calculate pitch in presence of noise.
Authors: Cerdá Salvador , Romero J.
Published: October 2005

The aim of this work was to determine the effect of noise presence at time to evaluate the pitch, and the study of possible improvements. Several algorithms (Terhardt, Duifhuis, Cepstrum, simple FFT, and visual determination) were studied. These algorithms were applied to different Spanish vowels with a progressively increased noise level; conclusions about the precision of each method are presented. In general, the noise causes a loss of accuracy because time-domain data are blurred and spurious components appear in the spectrum. At this point the multiresolution analysis (MRA) technique becomes a useful tool to eliminate the effect of elevated noise level. MRA was used to smooth the vowels analyzed and then the algorithms under study were applied another time. With this procedure an accuracy improvement in all methods that work in the frequency domain was observed.
Extraction and analysis of individual wavefield components from borehole space-time arrays.
Authors: Ekstrom M. P. , Randall C. J.
Published: October 2005

Spectral analysis approaches have been shown to be useful for the purpose of analyzing dispersion characteristics from borehole acoustical measurements [M. P. Ekstrom and C. J. Randall, J. Acoust. Soc. Am. 98, 2867 (1995)]. In this approach, the receiver wave fields are processed using a hybrid spectral estimator, with the space-time array first being transformed into the space-frequency domain, and a high-resolution estimator based on the matrix pencil used to estimate the wave numbers at each frequency of interest. In the frequency-wave-number domain, the spectral estimates are of sufficient quality to allow the decomposition of the spectral description into its constitutive parts. The frequency-wave-number plane is segmented to capture the loci of poles for an individual mode or headwave, and the spectral components within this segment extracted from the spectral descriptor matrices. This allows an individual mode to be isolated from the multicomponent wave fields, and the subsequent detailed analysis of its slowness and attenuation. Furthermore, the extracted spectral information can be used to reconstruct the space-time description for the individual mode, thereby providing the complete duality of viewing the individual components in both the space-time and frequency-wave-number domains. This procedure will be demonstrated using both model [C. J. Randall, J. Acoust. Soc. Am. 90, 1620–1631 (1991)] and field data sets.
Forward scattering at 400 Hz from rough seas in the presence of a range-independent underwater bubble layer.
Authors: Norton Guy V. , Keiffer Richard S. , Novarini Jorge C.
Published: October 2005

Of fundamental interest to the underwater acoustics community is the role that bubbles may play in connection with scattering from the rough air/sea interface. In this paper a high fidelity waveguide propagation and sea surface scattering model known as FEPE-CM [G. V. Norton et al., J. Acoust. Soc. Am. 97, 2173–2180 (1995)] is applied to the problem of forward scattering from a rough air/sea interface in the presence of a depth- dependent (horizontally statified) bubble layer. The numerical experiments considered were designed to explore the role of upward refraction (due to the presence of the bubbles) on forward scattering from the air/sea interface. Results from these numerical experiments will be presented. Preliminary results show an enhancement to the forward surface scattered field. [Work supported by ONR.]
Scattering from a fluid loaded elastic spherical shell in proximity to a rough interface: Numerical results.
Authors: Smith Judy , Bishop Garner C.
Published: October 2005

A null field T-matrix formalism is developed and used to calculate plane-wave scattering from a fluid loaded elastic spherical shell in proximity to sound hard, sound soft, fluid–fluid, and fluid–elastic interfaces with periodic surface roughness. For each type of interface, the Helmholtz–Kirchhoff integral representation of the various scattered pressure and displacement fields are constructed; the surface fields are required to satisfy the appropriate boundary conditions and the scattered fields are required to satisfy the extended boundary condition. Spherical basis functions are used to construct a free field T-matrix for the elastic shell and rectangular vector basis functions are used to construct a representation of the free field T-matrix for the rough interface. The free field T-matrices are introduced into the Helmholtz–Kirchhoff equations for the scattered fields and the null field equations for the shell-interface system and an ‘‘exact’’ analytical solution is obtained. Numerical results are obtained that demonstrate the effects of boundary type, elastic parameters, roughness geometry, amplitude, and slope on the scattered pressure field and on the ability to ‘‘see’’ the scatter from the elastic shell.
Computing the acoustic field scattered from proud, partially buried, or totally buried cylindrical objects.
Authors: Fawcett John A.
Published: October 2005

A boundary integral equation method which utilizes the Green’s function for a 2-half-space acoustic medium and the Fourier–Bessel representation of the acoustic field within a cylindrical object is presented. This formulation allows for the accurate computation of the acoustic field scattered from a cylindrical object (possibly, with interior layering) which can be above, below, or intersect the waveguide interface. The waveguide Green’s function and its radial derivative are expressed in terms of wave-number integrals. The asymptotic (large wave-number) behavior of these integrals is then evaluated in terms of Hankel functions and asymptotic reflection and transmission coefficients. The numerical treatment of these terms must be considered carefully; in particular, for the case of the partially buried cylinder. Spectral backscattering curves are computed for cylinders with varying degrees of burial. Also, the results of two-dimensional full field computations are shown.
Seafloor acoustic backscattering from different geological provinces in the Atlantic Natural Laboratory.
Authors: Greaves Robert J. , Stephen Ralph A.
Published: October 2005

The characteristics of acoustic signals backscattered from inside-corner oceanic crust and outside-corner crust are investigated using acoustic reverberation data from the 1993 ARSRP Acoustics Cruise. Specifically, the seafloor dip distribution is compared between areas of each crustal type and correlations are sought between true grazing angle and backscattered signal strength. Beamformed and match filtered acoustic data from the monostatic, wideband, LFM experiment at Site A are used to find the scattering strength corresponding to specific areas of the seafloor. Scattering strength determined from intersecting beams of different segments are summed to reduce left–right ambiguity. At the scale of analysis, high scattering strengths are found to correspond to steep flanks of seafloor features and can be used to map their shape and orientation. Some of these features are characteristic of specific crustal regions. Scattering strength is found to increase with increasing effective grazing angle at a rate of about 0.1±0.01 dB/degree. However dip values are so scattered that the seafloor dip, on the scale of a few hundred meters cannot be used to predict backscatter intensity. Some other characteristics of steeply dipping areas, such as subsurface heterogeneities or smaller scale surface features, strongly influence the level of backscattered signals. [Work supported by ONR.]
Vertical spatial and temporal coherence of ocean bottom reverberation.
Authors: Tang Dajun , Frisk George V. , Sellers Cynthia J. , Li Dan
Published: October 2005

An experiment to study acoustic backscattering from deep-ocean sediments was conducted in July 1993 as part of the Acoustic Reverberation Special Research Program (ARSRP). An acoustic source transmitting chirp signals in the frequency range 250–650 Hz and a 24-element vertical receiving array attached to the source were suspended near the seafloor over a sediment pond in the vicinity of the Mid-Atlantic Ridge. In a previous paper [Tang et al., J. Acoust. Soc. Am. 98 508–516 (1995)], a study on bottom scattering due to sediment volume inhomogeneities in this area was presented. Here, the spatial and temporal coherence of the scattered field using the data collected on the vertical array will be examined. The scatterers are modeled as point scatterers. It is shown that when the coherently reflected signals due to sediment layering are removed from the measurements, the results of the point scatter coherence model agree satisfactorily with data. [Work supported by ONR.]
A note on scattering by a stack of rough interfaces.
Authors: Tang Dajun
Published: October 2005

Scattering by a stack of random rough interfaces is studied. Such interfaces are common in both shallow water and deep ocean sediments due to the natural sedimentation processes. When the roughness of each interface is small, first order perturbation theory of Bass and Fuks [Wave Scattering from Statistically Rough Surfaces (Pergamon, New York, 1979)] is employed to formulate the scattered field due to such an interface. If the distances between interfaces are small compared to the acoustic wavelength and the variations of sediment properties are small, it is found that the collective scattered field due to a stack of random interfaces can be related to that due to a weak scattering volume where sound speed and density are randomly varying. Thus low-frequency subbottom scattering due to either weak volume inhomogeneities or a stack of rough interfaces can be formulated in a unified fashion. [Work supported by ONR.]
Angular variation in the simulated reflection and scattering properties of granular poroelastic ocean sediments.
Authors: Yelton Dennis J. , Chotiros Nicholas P.
Published: October 2005

Reflection and scattering properties of an inhomogeneous poroelastic medium were studied via numerical simulation. The inhomogeneous medium was modeled as an ensemble average of randomly layered poroelastic material. Each layer represented a granular material of a particular grainsize. The thickness of each layer was related to the associated grainsize and porosity by a conservation of mass relationship. Lateral variations in grainsize were approximated by performing a coherent ensemble average of results from several realizations of the randomly stratified medium. Poroelastic medium parameters were chosen to represent water-saturated sand. The mean and standard deviation of the grainsize distribution were chosen to match existing experimental data in order to test the model. Specifically, the inhomogeneous medium was modeled as bounded by a homogeneous water half-space on the source side, and a homogeneous poroelastic half-space of equivalent average porosity on the other side. Reflected signals were computed for high-frequency plane waves incident at various grazing angles. Coherent and random components of the reflected signal were calculated. The coherent part was related to the reflection coefficient. The random component was related to the scattering strength of the medium. Results were compared with existing experimental data. [Work supported by ONR.]
Directional radiation by wind instruments.
Authors: Hoekje P. L.
Published: October 2005

As with most musical instruments, the radiation patterns of wind instruments include directional components that can provide the listener with important timbral cues in a room. The most significant radiation comes from vibrations of the internal air column that are transmitted either through the woodwind tone holes or the opening of the brass instrument bell. For each of these, a cutoff frequency can be defined that marks the boundary between low frequencies that are radiated isotropically and the very directional high frequencies. Thus the listener in a room with reflecting surfaces is presented with several ‘‘views’’ of the instrument, and each view has a different spectral distribution. The vibration of the walls of the brass instrument provides another but much smaller directional component. The amplitude of this signal is of the order of 40 dB smaller than the signal radiated directly from the vibrating air column, and so it will usually be masked. However, the longer decay time of this signal increases the chance of its detection. The radiation patterns of this signal are also much different, as well, being quadrupole or higher in order. [Supported by the Iowa Science Foundation.]
Wrapping a violin with planar near-field acoustic holography.
Authors: Wang Lily M. , Burroughs Courtney B.
Published: October 2005

Planar near-field acoustic holography gives one the ability to reconstruct the sound pressure radiated from a source in a three-dimensional field from a single two-dimensional near-field measurement. Traditionally, only one measurement plane has been used which gives the sound radiation in a half-space. In this paper, the near-field acoustic holography is modified to measurements taken on six planes configured as a ‘‘box’’ surrounding the source, thereby giving the sound radiation in all directions. Any source may then be put into this ‘‘box’’; in this case, a violin is used as the source from which sound radiation patterns can be determined. Preliminary simulations using the modified near-field acoustic holography with six planes are presented. Also, methods of violin excitation with a bowing machine and the positioning of the violin within a measurement frame are described. It is expected that many violins may be tested with this setup, therefore providing a tool for assessing the effects of different modifications to violins on sound radiation. [Work supported by NSF and an AT&T GRPW Grant.]
Directivity analysis of piano sounds.
Authors: Nakashima Hidetoshi , Giron Franck , Tohyama Mikio
Published: October 2005

The authors investigate the directivity of sounds radiated by a piano and derive spatial impulse responses for representation of the piano directivity in spatial directions. To obtain the radiation patterns of piano sounds, the radiation field was measured in an anechoic room where a microphone array was placed on a spherical surface with a 2-m radius. The microphones used to measure the radiation field were placed every 10 deg from the top of the piano to 130 deg on the lower side of the piano. The microphones were rounded every 10 deg from 0 deg to 350 deg on the horizontal plane. A reference microphone was placed at the center of the sphere on whose surface the measurement microphone array was placed. The spatial impulse responses were obtained as follows: (1) The power spectra of both the radiated sound in all directions and the reference sound at the reference microphone were calculated; (2) the ratio of the radiated spectrum to the reference spectrum was taken; and (3) minimum phase directivity filters were made using the power spectrum ratios obtained through the above procedures. These directivity impulse responses and filters are useful for binaural room simulations including piano sounds, and for synthesizing piano tones in a computer.
A DSP implementation of source location using microphone arrays.
Authors: Rabinkin Daniel V. , Ranomeron Richard J. , Dahl Art , French Joe , Flanagan James L. , Bianchi Michael H.
Published: October 2005

The design, implementation, and performance of a low-cost, real-time DSP system for source location is discussed. The system consists of an eight-element electret microphone array connected to a Signalogic DSP daughterboard hosted by a PC. The system determines the location of a speaker in the audience in an irregularly shaped auditorium. The auditorium presents a nonideal acoustical environment; some of the walls are acoustically treated but there still exist significant reverberation and a large amount of low-frequency noise from fans in the ceiling. The source location algorithm is implemented in a two-step process: The first step determines time delay of arrival (TDOA) for select microphone pairs. A modified version of the cross-power spectrum phase method [M. Omologo and P. Svaizer, Proceedings of IEEE ICASSP 1994 (IEEE, New York, 1994), pp. II273–II276] is used to compute TDOAs and is implemented on the DSP daughterboard. The second step uses the computed TDOAs in a least-mean-square gradient descent search algorithm implemented on the PC to compute a location estimate. [Work supported by a contract with Bell Communications Research.]