bluuebunny/crossref_metadata_2025 huggingface dataset:
Rigorous spectral theory for azimuthally dependent source-excited fields in a fluid in the presence of a thin elastic spherical shell: Ray parametrization of high-frequency results
Authors: Ho J. M. , Felsen L. B.
Published: October 2005

The asymptotic results deduced from the rigorous formal theory [L. B. Felsen and J. M. Ho, preceding abstract] are examined here within the framework of ray acoustics. It is shown how the saddle points in the two-dimensional complex spectral domain systematically furnish the azimuthal and meridional invariants that appear less directly in previously constructed ray acoustic forms, and how this parametrization also applies to shell-guided nonresonant and resonant interactions. These ray interpretations take place most generally in the nonperiodic infinite azimuthal and meridional domains so as to describe traveling waves that can subsequently synthesize effects due to truncations or other perturbations on the shell. The relation between ray fields in the infinite nonphysical and the physical domains is explored, especially for ray congruences that synthesize resonances on the shell by self-consistent closure. By its very nature, the presentation here emphasizes the intimate connection between ray fields and spectra (wavenumbers), and thereby may furnish some guidelines for spectral processing techniques. [Work supported by ONR and DTRC.]
Chaotic wave propagation
Authors: Pidwerbetsky A.
Published: October 2005

Over the past several years, the development of the science of chaos has led to new insights and understanding of nonlinear dynamics. Wave propagation can also become chaotic in both deterministic and stochastic (random media) environments. This problem has been treated by both ray and wave theory as well as through numerical simulations. In a ray description, chaotic propagation is characterized by exponential divergence of nearby rays with propagation distance (quantified by Lyapunov exponents). In a wave description, propagation is characterized by exponential divergence of narrow wave beams with range. In both cases, this divergence results in the tangling of the wave fields in phase space. In wave propagation through random media. the spreading due to chaotic wave propagation competes with spreading due to diffraction and scattering by small-scale irregularities, leading to different parameter regimes where these different spreading mechanisms dominate. Environments that produce strong multiple scattering by irregularities with a large length scale are most likely to cause chaotic wave propagation. Finally, implications and applications of chaotic wave theory along with remaining questions and issues will be discussed.
When bubbles go bad…. Chaotic shape oscillations of air bubbles in water
Authors: Holt G. , Holzfuss J. , Judt A. , Phillip A.
Published: October 2005

Using optical scattering techniques, the nonlinear oscillations of single gas bubbles are observed. A single bubble is acoustically levitated and driven by a standing-wave pressure field at kilohertz frequencies. The scattered light intensity from a single plane wave (TEM00) is observed as a function of time for both radial and nonradial oscillations. The resulting time series are analyzed using some techniques from dynamical systems theory. These measurements are accompanied by high-speed photographs in an attempt to determine the presence and character of shape oscillation modes. [Work supported by ONR, NCPA, and DFG.]
On modeling high-frequency acoustic scatter from a basic Arctic under-ice experiment: The benchmark ice-block problem
Authors: Chin-Bing Stanley A. , Murphy Joseph E. , Keiffer Richard S.
Published: October 2005

High-frequency underwater acoustic propagation and scattering in the presence of the underside of the Arctic ice canopy have been extensively studied in the last decade. A few promising computer simulation models and some good experimental data have resulted from these studies. As the decade of the nineties begins, it is worthwhile to reflect back on the modeling achievements made in high-frequency Arctic acoustic modeling and to speculate on what is yet needed. While presenting a brief overview of the Arctic modeling achievements, this talk will concentrate primarily on the need for more benchmark modeling-experimental efforts. The ice-block reverberation experimental data taken by Francois and Garrison will be used as an illustration. Under-ice acoustic scattering models based on various approaches (Kirchhoff, edge diffraction, and finite element) will be used to analyze the ice-block data and comparisons of accuracy versus computation effort will be presented. The presentation will conclude with the suggestion that a need exists for more Arctic under-ice acoustic benchmark cases (analogous to the ASA benchmark wedge problem [L. B. Felsen, J. Acoust. Soc. Am. Suppl. 1 81, S39 (1987)]). [Work supported by ONR/NOARL.]
Acoustical mapping of biomass in frontal oceanic systems
Authors: Mathisen Ole A.
Published: October 2005

Primary and secondary production in the oceans and hence abundance of macrofauna is limited by light or more often by nutrients. Any oceanic system that injects new or regenerated nutrients into a body of water creates a center of high biological productivity. While classical oceanographers have identified such production areas and depth zones by measurements of physical parameters and net sampling, the fishermen have done it empirically with sonar and other acoustic devices available to them after the end of World War II. The fisheries biologists started extensively to employ acoustical techniques in their abundance estimations, first with analog and later with numerous digital integrators and echo counters using dual or split beam transducers. This development is illustrated with examples from the Peruvian and Northwest Africa upwelling systems, krill abundance at the ice edge, and mapping of superswarms in Antarctica, and salmon and herring populations in Alaska. A next generation of acoustical systems will be used to map the patchiness of herbivores and carnivores foraging on primary and secondary producers. Once patches have been identified, it is possible to measure the physical characteristics of the water masses with patches and hence study the microstructure of front and boundary layers.
Space-time oceanographic fluctuations:Bandwidth requirements
Authors: Ewart Terry E.
Published: October 2005

The marriage between the disciplines of oceanography and ocean acoustics has always been a little rocky. Oceanographers often glibly say that the oceanography must be known before acoustics can be predicted without discussing “how well known.” Acousticians often ignore our growing knowledge of ocean processes. The relation between our understanding of statistical oceanographic processes and ocean acoustic fluctuations will be discussed. These relevant topics will be presented. The first will be a discussion of the internal wave and fine structure processes required to predict theoretically the scintillation indices, including the spectral decomposition, obtained from MATE. In this case, it is shown that the understanding of the ocean is the limiting factor. The second, based on recent work by Uscinski and Ewart, will address the question “what is the vertical wavenumber bandwidth of the index of refraction required to predict the scintillation index in ocean acoustic fluctuations as a function of range and frequency?” It can be said that the very smallest scales are, in general, not important. The third topic, based on recent work by Ewart and Kaczkowski, will address the question “what is the effect of a strong Markov or correlated medium representation on predictions of the two-point phase moment of a propagating acoustic field?” Here, the details of the ocean model are important.
Covariance analysis of bioacoustic volume reverberation
Authors: Clay C. S.
Published: October 2005

Covariance analysis of the echoes or volume reverberation from macro zooplankton and small nekton is practical with the use of digitally recorded sonar data. Numerical simulations of echoes from an ensemble of randomly located identical scatterers have the same covariance function as an individual. Fourier transformations of the covariances give the (power) spectrum of the scattering function that is within the envelope of the (power) spectrum of the incident ping. Part of the motivation for this research came from new signal-processing capabilities of multichannel digital sonar, and part of the motivation for considering time-domain echo processing came from papers that displayed the time-domain signals scattered by simple objects and revisions to Acoustical Oceanography. [This research was supported in part by NSF (OCE-8817171) and ONR (N00014-89-J-1514).]
Optimum active noise control at the source—A boundary element technique
Authors: Cunefare Kenneth A. , Koopmann Gary
Published: October 2005

The authors have developed a numerical technique to determine the optimum magnitude and phase at which to drive active noise control sources to achieve the best possible reduction in the total radiated power from a noise source/control source combination. Both the noise source and the control source(s) have finite areas, and are assumed to be in an infinite, unbounded domain. Use of the boundary element method leads to a quadratic expression for the total radiated power formulated in terms of the surface velocity distribution on the noise source and on the control source(s). This quadratic power expression, formulated at the surface, represents the basis for the technique. Treating the velocities on the control sources as unknowns leads to a system of algebraic equations, the solution of which yields the global minimum for the radiated power, the best possible reduction. Applications of the technique to numerical models of a sphere and of a rectangular box demonstrate the mechanics of active noise control on extended, three-dimensional radiators.
Experiments on optimization of active noise control on a three-dimensional extended radiator
Authors: Giordano Jeffery A. , Cunefare Kenneth A. , Koopmann Gary
Published: October 2005

In this experiment, a dramatic reduction in the total radiated power of an extended radiator is achieved via active control through optimization of the secondary source strengths. A box-shaped, acoustic radiator has a single panel that is driven in a structural mode. The four corners of the panel are cut out and contain loudspeakers that are used as the secondary sources. An acoustic boundary element program is used as the basis for determining the active source strengths that minimize the total radiated power. The program, which allows the active sources to be modeled at any position on the acoustic radiator, provides the magnitude and phase at which to drive the active sources for a prescribed frequency and normal velocity distribution on the radiator. A computer, which generates and monitors the driving signals to the panel shaker and loudspeakers, provides precise control of the active sources during power measurements. The numerically predicted reduction in radiated power compared favorably to measurements that were performed in a hemi-anechoic chamber.
Detection of silent temporal gaps in sinusoids
Authors: Formby C. , Forrest T. G.
Published: October 2005

Gap detection thresholds were measured by forced-choice procedure for conditions where the duration of a silent gap was varied adaptively between pairs of sinusoids of the same or different frequency. Frequencies of the first sinusoid in a pair were F1 = 500, 1000, 2000, and 4000 Hz. Second-sinusoid frequencies, F2, included F1 = F2, and frequencies 2%, 5%, 24%, and 50% higher than F1. To minimize the influence of extraneous cues, the onset phase of the second sinusoid in each pair of tones and overall duration of each sinusoid in a pair of tones were randomized. Sinusoids were presented in continuous broadband noise (N0 = 30 dB/Hz) at an average E/N0 = 40 dB. Gap detection thresholds increased from 5 to 90 ms as the frequency separation between F1 and F2 was increased. The gap detection thresholds were treated as filter attenuation values by normalizing and converting the data into decibels, and then fitting the roex filter model. On average, the listeners' performances were modeled well by a constant-percentage (7%) bandwidth filter centered on F1. [Research supported by NIH.]
Summation bandwidths measured with two types of stimuli
Authors: Turner Christopher W. , Higgins Maureen B.
Published: October 2005

The bandwidths for summation at threshold were measured using two different types of stimuli to address a reported discrepancy between the experiments of Gässler [Acustica 4, 401–414 (1954)] and Spiegel [J. Acoust. Soc. Am. 66, 1356–1363 (1979)]. Thresholds were measured for complex stimuli consisting of 1–40 pure-tone components spaced 20 Hz apart in a background masking noise. In one experiment, based upon the signals of Gässler, in which the single-component signal was a pure tone at 1100 Hz, and the signal was expanded downward in frequency (for example 1100, 1080, 1060 Hz). The second experiment was similar to Spiegel's, in which the single-component signal was 1100 Hz, and the signal was expanded in both directions surrounding the 1100-Hz tone (for example 1080, 1100, and 1120 Hz). Thresholds for both types of stimuli remained constant as the signal was expanded to approximately one critical band. As the signals were expanded beyond this point, the two data sets differed. The thresholds for the Gässler-type signals increased at a rate of approximately 3 dB per doubling of bandwidth, while the thresholds for Spiegel-type signals increased at approximately 1.5 dB per doubling of bandwidth. In summary, both the results of Gässler and Spiegel have been replicated, and the fact that the slope depends upon the direction of signal expansion has been shown. These results are thought to reflect the change in size of critical bandwidths as a function of frequency.
Speech rate and vowel duration in American English
Authors: Caisse Michelle
Published: October 2005

In an experiment designed to elucidate the manner in which vowel duration in American English is altered by speaking rate and how rate interacts with other duration-affecting factors, vowel durations were measured in nonsense words spoken in frame sentences. The following inherent and contextual factors were manipulated: vowel height and tenseness (/ɪ, I, e, r/); post-vocalic consonant voicing; vowel position in utterance (words were monosyllabic or disyllabic with the target vowel in the initial syllable); and speaking rate. Preliminary results confirm earlier findings that vowel height has an additive effect on vowel duration and consonant voicing interacts with vowel class (tense versus lax) and position. The results further show that rate exhibits similar behavior to voicing. It interacts with vowel class and voicing, and with position in voiced consonants.
Effects of depth on divers' speech
Authors: Grenié Michel
Published: October 2005

The aim of this study was to analyze some of the major acoustic-phonetic changes that occur in French when speech is produced by divers in an air atmosphere at several depths of submersion ranging from sea level to − 50 m (0, − 5, − 10, − 20, − 30, − 40, − 50m). A significant increase in fundamental frequency was found as depth increased. Submersion level seems to have no effect on duration and amplitude. Some significant differences were found in formant amplitude and frequencies. Shifts in the relative energy of formants 2, 3, and 4 were observed on vowels at the deepest conditions. The quantification of the difference in dB between the intensity of the fundamental and the intensity of the largest harmonic in the first formant suggests that phonation varies as a function of depth. At great depths, an increase in vowel effort contributes to speech distortion. These results are mainly discussed in terms of speech production strategies in deep atmosphere.
Magnetic resonance imaging (MRI) film of articulatory movements
Authors: Foldvik Arne Kjell , Husby Olaf , Kværness Jørn
Published: October 2005

A short MRI film will be shown of the pronunciation of a compound Norwegian word, [ˈçimutantnˌ] , giving a sagittal view of the movements of the lips and tongue, as well as the soft palate during the articulation. The word has been chosen in order to show the tongue movements to and from a front-close, a back-close, and a back-open vowel and also nasal plosion. MRI still pictures, based on sustained articulation of particular sounds, will also be shown and discussed. The MRI technique for filming and taking stills of articulation will be explained, previous MRI work on articulation assessed, and further improvements of the technique and its applications discussed.
Characterization of Albunex®
Authors: Levene Harold B. , Moision Robert , Villapando Elaine , Torgerson Jay , Maniquis Jack , Kleinhenz Reinette , Keen Randy , Barnhart James L.
Published: October 2005

Albunex® is an ultrasound contrast agent prepared by sonicating 5% human serum albumin to produce stable, air-filled, albumin microspheres. It is an effective ultrasound contrast agent for use with echocardiography and other ultrasound radiology procedures. The characteristics of Albunex that are responsible for the clinically observed high echogenicity of Albunex are discussed. Albunex is composed of a high concentration of noncoalescing microspheres (400–500 μ/nℓ) with a mean diameter of ≈4 μm and a shell thickness of 30–50 nm, as determined by particle analysis, light microscopy, and electron microscopy. Attenuation and backscatter measurements as a function of ultrasonic frequency and amplitude are reported for varying concentration and size distributions of Albunex.
Talker normalization and speaker recognition by humans: One mechanism or two?
Authors: Logan Robert J. , Pastore Richard E.
Published: October 2005

This research assessed the nature of acoustic information used in talker normalization and speaker recognition, evaluated three models of talker normalization, and investigated the relationship between the mechanism(s) used by talker normalization and speaker recognition. Two experiments were conducted. Experiment 1 was an AX (same/different) verification task designed to assess the ability of listeners to discriminate eight talkers in three stimulus conditions. The results suggested that listeners are consistent in their confusions across stimulus conditions and can use relatively steady-state acoustic information to discriminate the talkers. The confusion matrices from experiment 1 were used to create three talker normalization conditions in experiment 2: single talker, confusable talkers, and discriminable talkers. Listeners in experiment 2 were tested in an AX (same/different) phoneme discrimination task. The results suggest that relatively dynamic information is important for talker normalization and that the contextual tuning model is the most appropriate conceptualization of the talker normalization process. The results are discussed with respect to the relationship between talker normalization and speaker verification.
Further investigations of phonological factors in phonetic perception
Authors: Wannemacher Carol A. , Sawusch James R.
Published: October 2005

Recent investigation has demonstrated an influence of phonological permissibility on the identification of ambiguous phonemes (Wannemacher and Sawusch, 1989). Depending on the speed of response, early phonologically biasing information shifted classification of an ambiguous target. The fast responses showed the greatest influence of permissibility, while at longer latencies this biasing effect decreased. Possible explanations for this pattern of results include tacit use of rule-governed phonological knowledge and the operation of feedback from an interactive system involving lexical access. The present experiment attempts to distinguish these two proposals by examining the time course of permissibility effects. The same basic paradigm as used in the previous experiment was employed here, but with the phonologically biasing information occurring after an amibiguous target phoneme. The results of the late and early biasing conditions will be compared in order to determine the nature of the influence of phonological permissibility on phonetic coding. [Work supported by NIDCD Grant DC00219 to SUNY at Buffalo.]
Perceptual learning of /r/ and /l/ by Japanese speakers of English: Effects of phonetic environment
Authors: Lively Scott , Logan John
Published: October 2005

Six adult Japanese speakers of English were trained for 15 days in a 2 AFC identification paradigm. Training stimuli were minimal pairs contrasting /r/ and /l/ in initial position, initial cluster, and intervocalic positions. The training stimuli were produced by five talkers. Subjects participated in a pretest, a post test, and two tests of generalization. Subjects improved their identification performance from week to week and were differentially sensitive to the voices of the training talkers and to the phonetic environment in which the /r/-/l/ contrasts occurred. These results replicated the earlier findings of Logan, Lively, and Pisoni (1989). The results are discussed in terms of a stretching and shrinking of the nonnative speaker's perceptual space for the /r/-/l/ contrast. [Work supported by NIDCD.]
Children's discrimination of phonologically similar items
Authors: Murphy W. D. , Gerken L. A. , Cooper R. P. , Aslin R. N.
Published: October 2005

Discrimination of a heard target word from phonologically similar and dissimilar items was investigated in seventeen 3.5- to 4.5-year olds and nine adults using a two-choice reaction time (RT) procedure. The target word (“little”) differed from the similar items (e.g., “lettle”) on a single acoustic-phonetic segment and from the dissimilar items (e.g., “cookie”) on all four acoustic-phonetic segments. Predictions based on the similarity neighborhood model (Luce, 1986) and the cohort model (Marslen-Wilson and Tyler, 1980) were (1) since word neighborhoods are less dense in children than in adults, children should show a smaller difference between their RTs to similar and dissimilar items than adults; (1) RTs for correct responses should be faster for dissimilar than for similar items; (3) children should false alarm more to similar than to dissimilar items; and (4) for the similar items, the later in the sequence of acoustic-phonetic segments the change occurs, the more easily confused the item should be with the target, generating higher false alarm rates. Results supported all predictions except the last, suggesting the cohort model may not provide an adequate description of young children's on line processing.
Sound transmission through a double-walled cylindrical shell with radial elastic links
Authors: Cacciolati C.
Published: October 2005

A theoretical model is established to study the direct transmission of sound through a finite cylindrical double shell. Shells comply with Donnells' equations and the theory includes constantly spaced stiffeners in axial and circumferential directions. However, this is limited in the case of a large number of stiffeners. The acoustical excitation is a plane wave located in an infinite medium outside the shell. The two internal media are homogeneous. Absorption is taken into consideration by a complex wavenumber. The direct transmission calculation includes the fluid structure coupling with light fluid assumption and mechanical links between shells. There is a distributed stiffness of constant value per unit length in the radial direction and along circumferential lines. The solution of the equations is obtained by a modal method. The acoustical pressure in each medium and the vibratory behavior of shells is given. An application to aircraft design is presented. Numerical results show the comparison between structural linkage and air gap effects on the transmission of sound inside the inner cavity. [Work supported by Aerospatiale Soc., Toulouse, France.]
Development of a multidiffraction device for improving the noise barrier performance
Authors: Hee Joon Eun , Oh Sung Jun
Published: October 2005

A multidiffraction device has been studied, both theoretically and experimentally, based on an expanded concept of the double barrier principle. The device, which has four diffraction leaves, is intended to be used on top of an existing noise barrier to improve the barrier efficiency. The multiple diffractions provided by the four diffraction leaves was found to be the major contributor to the improved performance of the barrier. However, the interference of the primary rays with the reflected ones from the bottom surfaces between the diffraction leaves was also found to play a role, indicating the possibility of designing an optimum device for a given situation. The performance tests, carried out both in an anechoic chamber using a scale model and in the field using an actual device, indicate about 5-dB improvement in noise reduction on the average. [Work supported by Hyosung Al. Co.]
Biological oceanography of the Gulf Stream front: Inference from acoustic remote sensing
Authors: Nero Redwood W. , Clay Clarence S. , Magnuson John J.
Published: October 2005

Acoustics is used to determine the relationship between current flow, temperature structure, and biological processes at fronts. In 1985 surveys were made of acoustic volume reverberation at the boundary of the slope water and the Gulf Stream, 120 km northeast of Cape Hatteras, using towed 70-kHz sonars. Scattering theory and net samples suggest the scatterers were macrozooplankton of about 2-cm length. Two-dimensional images of 200-m depth by several kilometers distance give views of internal biological patches across the front. From them the spatial arrangement and behavior of animals have been observed and animal type inferred. For large-scale surveys covering several hundred kilometers and days, obtained during April 1989 (BioSYNOP program), a synoptic view, from which the influence of large meanders of the Gulf Stream on the macrozooplankton can be observed, was obtained. Finally, better resolution of animal type, function, and size is possible with multifrequency sonar. Multicolor imaging of 38-, 70-, and 200-kHz sonar profiles suggest a difference in the animal size composition between the Gulf Stream and adjacent waters. [Work supported by ONR and NSERC of Canada.]
Emergency siren system performance
Authors: Margulies T. S. , Long S. L.
Published: October 2005

Current emergency response plans and preparedness at commercial nuclear power plants include means for notifying the public surrounding the facility in a situation involving real or potential radiological hazards. An alerting system may employ various means, including, for example, fixed sirens or mobile siren vehicles. In this paper emergency planning concepts and guidance are reviewed and an assessment of a set of recently collected data at operating plants is provided. Data were gathered from event notification reports on both inadvertent soundings and failures of sirens over about a 3-yr period. Siren system vulnerabilities are discussed; in addition, some insights are provided on rates of occurrence of both false alarms and failures, and likely causes of these events.
Dissipative and nondissipative fluid wave propagation in pipes
Authors: Mfonfu G. B. S. , Grader A. S.
Published: October 2005

This presentation focuses on the pressure response at various locations along a finite fluid-filled pipe to changes in the conditions at one end of the pipe. Initiated changes in the conditions represent valve operations that may be sudden valve closure or opening, or a gradual valve operation. The properties of the fluid are calculated via an equation of state, and the model presented is capable of simulating nondissipative and dissipative fluid dynamics. In addition, varying pipe diameters are considered along with pipe elasticity. For the nondissipative (no friction losses in the pipe) configuration, the numerical model is compared with a newly derived analytical solution, which describes the water hammer phenomena along the pipeline in response to a sudden valve closure. The pressure response propagates at the speed of sound through the fluid and oscillates in a combination of step changes. For the dissipative (with friction losses along the pipe) configuration, the kinetic energy is transformed into elastic energy of fluid and pipe by the valve operation. Also, the pressure response declines due to the friction energy losses. This model may apply to any pipeline setting such as transportation pipelines, oil, gas and water wells, water distribution systems, and plant circulating systems.
The noise generated by turbulent boundary layer flow over an axisymmetric body with a flat nose
Authors: Zhe Shang
Published: October 2005

The noise generated by hydrodynamic flow over an axisymmetric body with a flat nose is described quantitatively. Flush-mounted hydrophones were used to measure that part of the turbulent boundary-layer pressure fluctuations that propagates as true sound. Power spectra of sound pressure were measured in a 200-Hz to 150-kHz frequency range over a wide range of Reynolds numbers (Ux D/ν = 2.52 × 10, where D is the diameter of the body) for the model operating in the China Ship Scientific Research Center 038 water tunnel. The power spectra of the noise measured in the laminar flow regions correspond little to those measured in the transition and fully developed turbulent regions of the flow. Free-stream turbulence intensity and transition regions of the model were measured by using a laser doppler velocimeter. The transition regions have been compared with the computation results and it was found that they agreed rather well with the experiment. In addition to the experiment, 12 axisymmetric bodies were calculated and compared with the experiment. Results indicate that when the prismatic coefficient and DF/D is fixed, the model has fairly good flow properties. When DF/D is fixed and the prismatic coefficient is decreased, or the prismatic coefficient is fixed and the DF/D is decreased, separation point or transition point is delayed.
The development of the filtered-U algorithm for active noise control
Authors: Eriksson L. J.
Published: October 2005

The filtered-X algorithm discussed by Widrow and Burgess is a modified form of the LMS algorithm for use when there are transfer functions in the auxiliary path following the adaptive filter. To ensure convergence of the algorithm, the input to the error correlators is filtered by a copy of these auxiliary path transfer functions. More recently, Eriksson has presented a new approach to active noise control in the presence of acoustic feedback that uses an infinite impulse response (IIR) filter structure with a modified form of the RLMS algorithm. This algorithm may be described as a filtered-U algorithm since it uses a copy of the auxiliary path transfer functions to filter the generalized input vector to the error correlators of both the direct and recursive elements of the filter to ensure convergence. The relationship of the filtered-U to the filtered-X algorithm and other earlier concepts will be discussed.
Adaptive on-line modeling technique for active noise control systems
Authors: Kuo Sen M. , Tapia Javier
Published: October 2005

Active noise control (ANC) systems are required to model direct and acoustic feedback paths as well as the error path on an on-line basis. In this paper a new adaptive on-line error-path modeling technique is presented. An adaptive IIR filter using SHARF algorithm is used to generate the canceling signal. The error path is modeled by a LMS adaptive filter. This new modeling technique uses the canceling signal to train an adaptive model that is placed in parallel with the error path. This process is performed only when certain conditions are satisfied in order to avoid undesired undulations. The modeling process technique differs from two other methods. Ericksson et al. [ U.S. Patent number 4,677,676, 30 June 1987] used an additional auxiliary low level, uncorrelated noise for training processes. Warnaka et al. [U.S. Patent number 4,473,906, 25 September 1984] used the canceling signal for modeling, but the plant being continuously modeled is not really the error path. Comparative performance and real-time testing results show that this new technique is suitable for active noise control systems.
Active control of harmonic noise in large reverberant spaces
Authors: Mitchell-Dignan M. , Abe G. A. , Clift J.
Published: October 2005

A study was conducted on the control of a distributed harmonic source in a reverberant space of moderate to high modal density. Many large reverberant spaces exhibit high modal density at the operating frequencies of the sources they enclose. Often, the sources in such a space must be treated as distributed sources and cannot be practically controlled by placing secondary sources near their surface. Therefore, the noise must be controlled with secondary sources placed in the reverberant field. Both analytical and experimental models were used to develop a control system for a large reverberant laboratory in which the noise, generated by a distributed source, was controlled using multiple secondary sources. The secondary source locations were optimized based on a modal model of the space. Significant reduction of the total acoustic energy was attained near a peak composed of several resonances. A modest reduction in acoustic energy was seen at a frequency near an antiresonance. Less impressive reductions were observed at frequencies of higher modal densities.
Boundary element simulation of long-range facet reverberation
Authors: Schmidt Henrik , Gerstoft Peter
Published: October 2005

Simulation of seismoacoustic facet reverberation in an ocean waveguide requires solution of the full two-way wave equation. Such simulations have been performed by means of finite difference and finite element methods. However, the computational requirements of these discrete methods have prohibited simulation for ranges larger than a few water depths. Here a hybrid boundary element-wavenumber integration approach is presented to simulate long-range facet reverberation. For a facet inhomogeneity in an otherwise horizontally stratified environment, the total field is expressed in terms of Green's theorem. By choosing a Green's function satisfying the boundary conditions at all horizontal interfaces, only the interface between the irregularity and the layered medium contributes to the surface integral in Green's theorem. Thus, only the boundary of the inhomogeneity needs to be discretized, with a spatial sampling independent of range. Here a modified version of SAFARI [H. Schmidt and F. B. Jensen, J. Acoust. Soc. Am. 77, 813–825 (1985)] is applied to compute all Green's functions involved in the boundary integral, allowing analytical integration of the influence functions over each boundary element. After solving the boundary element equations, the total reverberant field is again computed by means of SAFARI. The approach is both efficient and general, allowing the exterior as well as the interior region to be a stratified elastic medium. Simulations will be presented for reverberation from a salt dome buried in the seabed as well as from Arctic ice facets. [Work supported in part by ONR Arctic Program Office.]
Scattering and reverberation measurements from the CEAREX 89 Arctic experiment
Authors: Hayward Thomas J.
Published: October 2005

Reverberation data collected during the CEAREX 89 experiment in the Greenland Sea are analyzed to describe the spatial variability of surface and bottom reverberation and estimate short-range backscattering strengths. Features of the time-azimuth decay of reverberation are identified by comparison with model propagation calculations, and backscattering strengths are estimated from the data using the measured reverberation and calculated propagation losses. Statistical measures of variability are applied in an attempt to characterize the spatial variability of surface (under-ice) and bottom reverberation. [This work was supported by the Office of Naval Research (ONR) Arctic Sciences Program, Code 1125AR.]
Properties of iceberg underwater echoes
Authors: de Heering Philippe
Published: October 2005

Eleven free-floating and ice-locked icebergs of estimated masses ranging between 300 and 2 million tons were observed by means of a 36-kHz sonar mounted in the hull of the Canadian icebreaking freighter M.V. ARCTIC for the purpose of characterizing their acoustic target properties. The echo data showed that their average target strength could be modeled, with reasonable accuracy, as that of a smooth ice sphere with no internal reflections, of a mass equal to the iceberg estimated mass. The average echo duration was observed to be related to the radius of the same sphere. The maximum detection ranges in open water, which were generally limited by the downward refracting conditions, were consistent with the berg's estimated draft, whereas ice-locked bergs exhibited detection ranges approximately twice as long. [Work supported by the Canarctic Shipping Company, Ottawa, Canada and Transport Canada.]
Spherical cavity resonators: Effects of imperfect geometry
Authors: Oxborrow Carol Anne , Mehl James B.
Published: October 2005

Spherical acoustic resonators are useful tools for high-accuracy measurements of the speed of sound in gases partly because of the insensitivity of the radial-mode eigenfrequencies to imperfect geometry. The mean frequencies of acoustic and electromagnetic (microwave) multiplets are also insensitive to geometric imperfection. The effects of imperfect geometry have been investigated experimentally by joining two metal hemispheres with variable-thickness cylindrical spacers. The effects of this distortion on the acoustic and electromagnetic eigenvalue spectra have been studied. The results are compared with the theoretical prediction [J. B. Mehl and M. R. Moldover, Phys. Rev. A 34, 3341–3344 (1986)] that the frequencies of the radial acoustic modes and the mean frequencies of acoustic and electromagnetic multiplets depend, in the lowest order of shape-perturbation theory, on the cavity volume. The effects of cavity size thus drop out of suitably chosen ratios of acoustic and electromagnetic eigenfrequencies leading to the possibility of direct determination of the ratio of the speed of sound to the speed of light.
Transition from acoustic oscillation to irregular pressure fluctuation in a thermoacoustic engine
Authors: Gabrielson Thomas B.
Published: October 2005

In the course of experimentation with an air-filled thermoacoustic source radiating into water, a transition has been observed from acoustic oscillation to an irregular, very low-frequency fluctuation. The amplitude spectrum of the fluctuation is roughly 1/f. Before the fluctuations start, a large and rapid internal pressure change occurs immediately after the acoustic oscillation ceases, suggesting an abrupt change in the “static” conditions across the stack. The reverse transition from fluctuation to acoustic oscillation has not been observed; furthermore, the fluctuations can be induced directly without prior acoustic oscillation. A videotape of the transition and the subsequent fluctuations will be shown.
Measurements on a general thermoacoustic heat engine
Authors: Ceperley Peter H.
Published: October 2005

Low-power measurements have been made in a general test setup on a class of thermoacoustic devices operating at moderately low acoustic power levels (approximately 110 dB). The setup includes two loud speakers mounted on either end of a tube filled with a porous solid and air at one atmosphere. A heater and a cooling coil allow a temperature gradient to be established from one end of the tube to the other, while thermocouples and microphones allow the temperature and sound fields to be monitored by a computer (which also controls the speakers). Measured acoustic gains as a function of power level, frequency, and phasing will be reported. [Work supported by ONR.]
Acoustic propagation in electrically conducting media in high magnetic fields
Authors: Horwath T. G.
Published: October 2005

Acoustic waves in electrically conducting media such as metals and sea water experience strong attenuation if simultaneously subjected to strong magnetic fields. The causes for this attenuation are induced eddy currents, which are generated by the volume elements of the media moving in the magnetic field with acoustic velocities. Dissipation of energy takes place as a result, which can be significant at magnetic fields obtainable with superconductors. The fundamental theory of this phenomenon is discussed in one dimension. Generalization to three dimensions is outlined, and possible practical applications to vibration isolation, structural damping, and structural quieting are discussed.
The Im/Re method: A new experimental determination of resonances
Authors: Lenoir O. , Izbicki J. L. , Rembert P. , Pareige P.
Published: October 2005

The determination of resonances of elastic targets immersed in water has been performed by an impulsive method (A method). If one transducer is used alternatively as an emitter and as a receiver (monostatic method), the power spectrum of a part of the backscattered signal (i.e., the first echo have been omitted) by plates, solid cylinders, or pipes by an algorithm of fast Fourier transform (FFT) allow peaks that correspond to the resonances of the target to be isolated. In this paper a new method is proposed using the processing of the whole signal: The calculation of the FFT gives for each frequency a complex number. The ratio between the imaginary part and the real part of the complex number is plotted versus frequency: The Im/Re spectrum is obtained. When a resonance is excited, sharp transitions on the spectrum are observed. The reflected and transmitted signals by plates are studied. The cases of an aluminum plate and a PVC plate are investigated. The results are compared with those obtained by the A method. The sensitivity of the new method is better: For instance, at normal incidence, with the same experimental devices, the excitation of transversal waves in the PVC plate due to the diffraction pattern of the incident beam, is shown on the Im/Re spectrum, while no resonance is obtained with the A method. This method, called the Im/Re method, seems to be very accurate in the detection of resonances of elastic or viscoelastic targets.
Application of the Im/Re method: Detection of the resonances of an aluminum plate coated with an absorbent
Authors: Lenoir O. , Reinbert P. , Pareige P. , Izbicki J. L.
Published: October 2005

The classical method of isolation of the resonances of a plane structure, insonified by short pulses at normal incidence, consists in the spectral amplitude analysis of its elastic response. It needs the temporal filtering of the specular echo. In the study of an 8-mm-thick aluminum plate coated with a 1-cm-thick absorbent within the frequency range 200–800 kHz, this method allows no detection of the resonances of the aluminum plate. Absorption is important enough to prevent the detection of the energy freely backscattered by the aluminum plate: The amplitude of the first echo reflected by the bilayered structure is 15 dB less than the amplitude of the first echo reflected by the single aluminum plate. On the other hand, the Im/Re method, which implies the study of the ratio of the imaginary part to the real part of the fast Fourier transform (FFT) of the whole backscattered signal, allows the detection of the aluminum resonances, via sharp transitions. The Im/Re spectrum of the transmitted signal is also investigated. Interpretations are proposed.
Isolation of resonances of cylindrical targets: Comparison between different experimental methods (MIIR, short-pulse MIIR, and Im/Re)
Authors: Rembert Pascal , Lenoir Olivier , Pareige Pascal , Izbicki Jean-Louis , Maze Gérard , Ripoche Jean
Published: October 2005

Two different kinds of experimental methods allow the isolation of resonances of cylindrical elastic targets immersed in water: a quasiharmonic one, the method of isolation and identification of resonances (MIIR) [G. Maze et al., J. Acoust. Soc. Am. 73, 41 (1983)] and an impulsive one, the short-pulse MIIR [P. Pareige et al., Phys. Lett. A 135, 143 (1989)]. In both cases the experimental results only involve the spectral amplitude of the signal, so that the information provided by the phase spectrum is never used. A new method is proposed which uses the evolution with the frequency N of the ratio Im(N)/Re(N) of the complex number provided by the FFT of the whole backscattered temporal signal (for details see O. Lenoir, preceding abstract). The Im/Re spectra are compared to the spectra obtained by the two previous methods. Several elastic and viscoelastic cylinders and tubes are investigated. That the Im/Re spectrum provides as much information as the backscattered and resonance spectra obtained by the two different MIIR can be noticed. The first two methods allow the identification of the mode number of each isolated resonance; in the same way the Im/Re ratio at a given frequency versus the azimuthal angle is studied. The signification of the symmetric shape of the so-obtained angular diagrams is discussed.
Noise levels that are tolerable when listening to speech
Authors: Nabelek Anna K. , Tucker Frances , Letowski Tomasz R.
Published: October 2005

It is known that speech understanding declines with increased background noise. It is unknown, however, what noise levels are tolerated by individuals when they are listening to speech. A story recorded by a female was played through an earphone at a comfortable level. A noise was added and the subject was asked to set the noise level at the highest level that would not exceed tolerable listening conditions. The interferences were (1) a babble of 12 voices, (2) speech spectrum-shaped noise, (3) traffic noise, (4) music in a Muzak style, and (5) noise from a pneumatic drill. The subjects were (1) young adults with normal hearing, (2) elderly (at least 65 yr of age) with essentially normal hearing, (3) elderly who were successful hearing aid users, and (4) elderly who rejected their hearing aids. The following results will be discussed: (1) differences between young and elderly subjects, (2) differences among noises, and (3) differences between successful and unsuccessful hearing aid users. [Research supported by AARP Andrus Foundation.]
Potential benefits of varying the frequency-gain characteristic for speech reception in noise
Authors: Zurek Patrick M. , Rankovic Christine M.
Published: October 2005

Adaptive linear filtering is currently employed in some single-microphone hearing aids in an attempt to improve speech reception in noise. The potential benefit of this strategy depends on the spectral spread of masking and the degree to which the spread can be reduced by changing the frequency-gain characteristic. In this study these effects for subjects with normal hearing under static listening conditions are examined. In the unprocessed condition, subjects were presented with nonsense syllables masked by a 96-dB SPL octave-band noise centered on a low, mid, or high frequency. A frequency-gain characteristic was then imposed with the goal of reducing the overall level in the frequency band containing the octave-band noise. This processing resulted in large increases (about 45 percentage points) in consonant-correct scores compared to the unprocessed condition for the low-frequency octave noise band, and smaller increases for the mid- and high-frequency noise conditions. A similar pattern of improvement in speech reception threshold was observed by van Dijkhuizen et al. [J. Acoust. Soc. Am. Suppl. 1 86, S82 (1989)] under comparable stimulus conditions. Results will be discussed in the context of articulation theory, which can serve as a basis for the design of adaptive filtering algorithms. [Work supported by NIH.]