bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic scattering from cylindrical shells bounded by hemispherical endcaps.
Authors: Décultot Dominique , Léon Fernand , Lecroq Florence , Maze Gérard
Published: October 2005

The acoustic scattering from infinite cylinders or spheres has shown the great influence of surface wave propagation. Two types of surface waves are distinguished: the Rayleigh or Whispering Gallery waves and the Scholte–Stoneley waves. In this study, experimental results obtained on the finite cylindrical shells bounded by two hemispherical endcaps are presented. These objects are made of stainless steel and filled with air. Their radius is 27 mm and their radius ratio b/a is 0.97 (b is the inner radius and a the outer radius). The direction of insonification is parallel to the main object axis. The reduced frequency range k1a of the study varies from 10 to 40. These experimental results are explained by writing the stationary condition on the large circumference of objects, in the meridian plane. This condition depends on the phase velocity in the length of the cylindrical shell and in the spherical shell. These two velocities are computed separately in relation to the frequency and used to apply the stationary condition. The obtained results are in good agreement with the experimental study.
Acoustic scattering from multiple rigid cylinders.
Authors: Sarkissian Angie
Published: October 2005

Results are presented for acoustic scattering from multiple rigid, axisymmetric cylinders where all the cylinders have a common axis of symmetry with an acoustic field incident from an arbitrary direction. The boundary-element method is implemented to compute the scattered field from cylinders with hemispherical endcaps where the azimuthal dependence is separated first to reduce computation time. Scattering computations are made for various two- and three-cylinder configurations where the dependence of the scattered field on the distance between the cylinders is examined as well as scattering from a large cylinder in the presence of a smaller cylinder.
The effect of irregularity on the scattering of acoustic waves from a ribbed plate.
Authors: Photiadis Douglas
Published: October 2005

The scattered field from an irregularly ribbed fluid-loaded plate is ‘‘measured’’ using numerical simulations. The diffuse field scattered by the irregularity exhibits strong coherent features in the far-field scattering pattern associated with phase matching to locally propagating Bloch waves on the structure. These features are also apparent in the scattering from finite periodic arrays, but are strongly enhanced by irregularity. Some examples of the behavior of the system are presented and the scaling of the cross section with the number of scatterers and irregularity is determined.
Acoustical estimation of bubble concentration in seawater.
Authors: Ding Dong
Published: October 2005

The acoustic backscattering characteristics of seawater were studied by the method of local acoustic measurements within a small volume to infer the bubble concentration in seawater. It was found that the scattering intensities were increased with wind speed, especially to the forming of white caps on the sea surface. In some cases the intensities were related to the sea state of earlier days. Under low wind speeds, the peak of the scattering spectra shifted toward high frequencies and its spectra became narrower. In high winds the spectra reversed its tendencies. The spectra in deep water at high winds had a similar shape as in shallower depth at light winds. The measured data can be fitted by the theoretical spectra constructed on the principles of energy superposition under the assumption of Poisson distribution of bubble number in different sizes per unit of volume. The dependence of bubble concentration on depth can be obtained by the fittings. The concentrations exponentially decrease with the depth. The decaying constant is 8 (1/m) and is independent of wind speed. A definition of effective thickness of the bubble layer near the sea surface was given by a critical density of 10−3 (1/cm3), ΔR=1 μm. The inferred thickness is dependent on the wind speed.
Atmospheric sound propagation using a three-dimensional parabolic equation.
Authors: Delrieux Yves
Published: October 2005

A numerical method for solving the three-dimensional parabolic wave equation (3DPE) is presented to investigate long-range sound propagation in the atmosphere near the ground. An implicit finite-difference scheme based on the alternating directions method is formulated. The pressure field is calculated in cylindrical coordinates for all the azimuth ranges from 0° to 360°, so that only a periodicity condition is required. A hard reflecting ground is considered and a homogeneous boundary condition at the top of the mesh is applied. The validity of the 3DPE is shown by comparison with measurements carried out in an anechoic chamber. The diffraction of sound behind a thin barrier of finite length is studied. A good agreement with calculations is obtained for the sound pressure level behind the barrier. In particular, the term involving azimuth derivatives is taken into account in the 3DPE and enables one to properly calculate the diffraction from both side edges of the screen. Moreover, calculations show that the presence of wind may modify the position of interferences created by the screen. [Work supported by Direction des Recherches Etudes et Techniques.]
Survey for computer-based course in acoustic phonetics.
Authors: Pickett J. M. , Berkovitz Robert
Published: October 2005

Instructors of courses in speech communication listed in the 1990 JASA summary of acoustics courses were surveyed to develop information about numbers and types of students, course names, current text use, available computers, and rating-scale opinions on the potential value of computer-based courses in acoustic phonetics. Responses were overwhelmingly positive. Surprisingly large numbers of courses and students were reported. Equipment was indicated as available for computer-based instruction. Detailed results will be presented on the distribution of courses over academic disciplines and levels of texts in use, to characterize the needs for course development. [Work supported by NIDOCD.]
Teaching acoustics to phoneticians.
Authors: Ladefoged Peter
Published: October 2005

A hypercard stack has been written that provides an interactive approach to the basic concepts of acoustics. It is assumed that the students will know little or no mathematics. Graphical displays are provided of wave motion and the superimposition of waves. Students can both see and hear the effect of adding waves of their choice. Concepts such as the Nyquist frequency, vibration of air in a tube and in the vocal tract, and the parameters required for synthesizing speech are demonstrated. A section of the stack is concerned with the properties of damped exponential waves. The notions of the addition of sine and cosine waves and the correlation between two waves are demonstrated, as a basis for understanding Fourier analysis. The stack is copyrighted, but is available for nonprofit use at a nominal charge from the author.
Lateral variability of geoacoustic properties of the seafloor.
Authors: Lindwall Dennis , Gettrust Joseph
Published: October 2005

Using deep towed, multichannel seismic reflection data, the spectral response of the seafloor sediment as a function of offset or grazing angle along several kilometers of old Atlantic seafloor near the Blake outer ridge has been measured and variations of as much as 15 to 20 dB in bottom loss over distances of less than 50 m have been found. A video will be shown of this spectrum versus offset (SVO) data that explicitly shows the lateral variations as the DTAGS instrument is towed along just above the seafloor. A few regions of anomalously high shear wave velocities also will be pointed out. These data demonstrate that a seemingly smooth seafloor can be a rough, frequency-dependent scattering surface. [This work is supported by the Office of Naval Technology.]
Comparative evaluation of two structures for mitigation of small arms noise.
Authors: Pater Larry , Sandeen Eric R. , Swenson George , Eldred Kenneth M.
Published: October 2005

An evaluation was made of the noise reduction achieved by two types of noise shielding structures for small arms ranges. One of these was an open front shed with the firing line located within the shed, i.e., a partial enclosure of the firing line. The second structure was a wall barrier located behind the firing line. Theoretical insertion loss was calculated by means of two analytical techniques, one based on the FHWA highway barrier design algorithm and the other a classical diffraction analysis in a spherical coordinate system. Experiments were performed using a shed 7 m high by 6 m deep by 20 m long with a 5.56-mm rifles as noise sources. For guns, which exhibit strong free-field directivity, the experimental results show and the analytical results likewise indicate that directly to the rear the firing shed does not significantly outperform a simple wall.
Penalties for small arms noise assessment.
Authors: Schomer Paul
Published: October 2005

Proper assessment of the noise created by Army testing and training remains a question that is not fully answered. The most difficult noises to assess are the impulsive noises generated by large weapons, small arms, and helicopters. Currently, general community noise is assessed using the A-frequency weighting and some form of ‘‘energy equivalent’’ level. In the United States, the day–night average sound level is used. For clearly impulsive sound, adjustments or ‘‘penalties’’ are sometimes added to the formulation to account for the increase in annoyance generated by the impulsive character of the sound. One purpose of the present test was to further define and develop adjustments or ‘‘penalties’’ that can be used to assess military noise vis-á-vis normal, urban noises. The study was designed as a paired comparison test where the subjects were presented pairs of sounds and asked, for each pair, which was more annoying, the first or the second sound. The test sounds came from one of three categories of military sources that were: (1) tracked vehicles, (2) small arms fire, or (3) large blasts. The other sound in a pair was one of two control sounds that were: (1) the sound of a wheeled vehicle passing by, or (2) a computer-generated noise. This paper concentrates on small arms noise. The results are for measurements made outdoors−even when the subjects are situated indoors. This is considered to be the proper location since common noise such as traffic is normally assessed on the basis of outdoor levels. The small-arms penalty averages about 8–10 dB across conditions of windows closed or open or subjects outdoors.
Predictions and observations of seafloor noise generated by sea surface orbital motion.
Authors: Lindstrom Timothy E. , Frisk George V.
Published: October 2005

A model is developed for the prediction of the seismo-acoustic noise spectrum in the microseism peak region (0.1 to 0.7 Hz). The model uses a theory developed by Cato [J. Acoust. Soc. Am. 89, 1096–1112 (1991)] for an infinite depth ocean in which the surface orbital motion caused by gravity waves may produce acoustic waves at twice the gravity wave frequency. Using directional wave spectra as inputs, acoustic source levels are computed and incorporated into a more realistic environment consisting of a horizontally stratified ocean with an elastic bottom. Noise predictions are made using directional wave spectra obtained from the SWADE surface buoys moored off the coast of Virginia and the SAFARI sound propagation code, with a bottom model derived using wave speeds measured in the EDGE deep seismic reflection survey. The predictions are analyzed for noise level variations with frequency, wave height, wind direction, and receiver depth. These predictions are compared to noise measurements made in ECONOMEX using near-bottom receivers located close to the surface buoys. Good agreement is found between the predictions and observations under a variety of environmental conditions. [Work supported by ONR.]
Stochastic matched-field processing.
Authors: Baggeroer Arthur B. , Kuperman William A.
Published: October 2005

Matched-field processing (MFP) exploits the acoustic field to estimate either a source position or environmental parameters. Many have noted that the performance of MFP degrades rapidly with uncertainty about the field especially if adaptive methods are used to suppress sidelobes. It is clear that robust MFP methods are needed for working with experimental data. There are three categories of uncertainty that have been examined: (i) observational (array geometries and sensor responses are imprecisely known), (ii) statistical (ambient field covariances have errors), and (iii) environmental (the propagation is uncertain because of oceanographic characterization). The third category is examined in this presentation. The fundamental issue for robust MFP is to match the stochastic propagation with array processing that responds to an ensemble of replicas not just one from a deterministic model. At high SNRs one can search the ensemble for the appropriate sample vector using efficient searching algorithms such as simulated annealing. At modest SNRs the processing must incorporate errors from the noise. The approaches to MFP with environmental uncertainty are reviewed and some of the relevant signal processing literature for the ‘‘detection of random signals in noise’’ are noted. [Work supported by Mathematical Sciences, ONR.]
Acoustic analysis of glottal gap measurement.
Authors: Yu Jong-Daw , Mori Kazunori , Blaugrund Stanley M.
Published: October 2005

A simple, efficient, noninvasive method for defining the size of the glottic gap in patients with dysphonia would be highly desirable. Current methods for defining the degree of insufficiency involve aerodynamic and videostroboscopic analysis. PARCOR analysis of the glottal area was calculated utilizing DAT recorded data obtained at a 44.1-kHz sampling rate from 15 patients with dysphonia, 14 of which presented unilateral recurrent laryngeal nerve paralysis. Ten thousand data points were calculated for each voiced sample. PARCOR coefficients were obtained and used as a basis for determining the cross-section area of vocal tract, i.e., the glottal area ratio (GAR). GAR, which is a noninvasive technique, was utilized successfully in the verification of the reduction in glottal gap of 15 patients who underwent medialization thyroplasty for glottis insufficiency. Results demonstrate that GAR utilizing PARCOR analysis corresponds favorably with findings obtained using well-attested methods of aerodynamic and videolaryngoscopic analysis.
On the existence of speaker-specific maximum flow declination rate (MFDR)–sound pressure level (SPL) profiles.
Authors: Sulter Arend M. , Schutte Harm K.
Published: October 2005

Oral flow was registered with a Rothenberg mask in two male subjects during the utterance of an /æ/ vowel embedded in a word at three intensity levels (soft, normal, and loud voice), and during the production of crescendos and decrescendos on the same vowel at three fundamental frequencies. Registered signals were digitized and processed with specific hard- and software [J. S. Perkell, J. Acoust. Soc. Am. 89, 1777–1781 (1991)] to give the MFDR. This is a measure for the decrease of airflow through the glottis, during the closing phase of the glottal cycle. MFDR values showed a speaker-specific relationship with SPL. To explore this specificity, MFDR values were measured in 70 subjects during phonation of the vowel /æ/ with soft, normal, and loud voice. The relation between MFDR and SPL can be described with MFDR=a+bSPL. The dependency of the parameters a and b on gender, voice training, and vocal pathology will be discussed. [Support was given by the Foundation for Linguistic Research, NWO.]
Reflection of bulk waves at a piezoelectric crystal–viscous conductive liquid interface
Authors: Shana Zack A. , Josse Fabien
Published: October 2005

The reflection of obliquely incident shear horizontal (SH) bulk acoustic waves at the interface between a piezoelectric crystal and a viscous conductive liquid is theoretically investigated. In addition to viscous entrainment and mass loading effects, it is shown that the presence of a reflection-generated external electric field offers the possibility of acoustoelectric interaction with charged particles and dipoles in the solution. These interaction mechanisms could be exploited for liquid chemical analysis and biosensor applications. Expressions are obtained for the reflection coefficients (amplitude and energy) and phase shift upon reflection in terms of the angle of incidence, wave frequency, crystal parameters, and liquid properties (density, viscosity, dielectric constant, and conductivity) by using the normal wave impedance and the input impedance of the interface. It is shown that the sensitivity of such acoustic wave detectors could be tailored by properly choosing the interdigital transducer (IDT) periodicity, separation, crystal thickness, and the number of bounces.
A robust transfer matrix formulation for the ultrasonic response of multilayered absorbing media
Authors: Lévesque Daniel , Piché Luc
Published: October 2005

An improved version of the transfer matrix approach is presented for ultrasonic wave interaction in multilayered media. Generalized expressions are obtained for reflection and transmission coefficients in either fluid or solid half-space and problems associated with numerical stability are solved efficiently. The formulation is applicable to longitudinal and shear input waves alike, at arbitrary incidence angles and for any sequence of solid or fluid layers. Also, allowance is made for viscoelastic behavior by means of relaxation functions in the Laplace transform domain. Finally, the response to arbitrary incident pulse shapes and beam profiles is described through application of two-dimensional numerical Laplace inversion.
Comparison of three transient solutions for the axial pressure in a focused sound beam
Authors: Hamilton Mark F.
Published: October 2005

A comparison is made of three simple transient solutions for the axial pressure in a focused sound beam. Each solution is derived on the basis of different approximations. The acoustic source is assumed to be an axisymmetric spherical cap, the vibration of which generates a uniform normal velocity component on its surface. In case 1, the Rayleigh integral (which is strictly valid only for planar sources) is applied to the velocity condition on the curved surface. In case 2, the velocity condition on the curved surface is replaced by a pressure distribution in a plane, and the Rayleigh integral is applied to the approximate planar source condition. In case 3, the parabolic approximation is applied to both the Rayleigh integral and the source condition. The solutions for cases 1 and 3 were derived previously by others, whereas the transient solution for case 2 is a new result that generalizes an existing solution for monofrequency sources. For small aperture angles, the three approximations yield similar results in the focal region and beyond, with significant differences arising only near the source. Calculations are performed for tone bursts and N waves.
Analysis of natural frequencies and modal loss factors of simply supported beams with adhesively bonded double-strap joints
Authors: Rao Mohan D. , He Shulin
Published: October 2005

This paper presents a dynamic model for the transverse vibration analysis of an adhesively bonded composite double-strap joint. The differential equations of motion of the joint system are derived using the energy method and Hamilton’s principle. It is assumed that the energy dissipated by the joint system is contributed by both the shear and longitudinal deformation of the adhesive layers. The combination of natural boundary conditions, forced boundary conditions, and continuity conditions yields the frequency equations to predict the system resonance frequencies and modal loss factors. The effects of structural parameters and material properties of the adhesive layer on the system modal loss factors and resonance frequencies are also studied.
Equation of motion of microparticles in suspension in an insonified medium
Authors: Vignola Joseph F. , Berthelot Yves H. , Jones Steve , Jarzynski Jacek
Published: October 2005

The differential equation that governs the motion of microparticles in suspension in an insonified fluid is derived. Two forces are included in the model: the viscous drag force on the microparticle and the force imparted by the acoustic pressure gradient around the microparticle. This model is useful within the context of the laser detection of sound [see J. Acoust. Soc. Am. 90, 1275–1286 (1991)]. Standard models of particle motion in fluid mechanics with laser Doppler velocimetry usually do not consider the force imparted by the pressure gradient around the microparticle. It is shown that, at low frequencies, the viscous drag force dominates; but at high frequencies, the presure gradient term dominates. The transition frequency is given by 3aη/m, where a is the particle radius, η is the kinematic viscosity of the fluid, and m is the mass of the particle.
Qualitative acoustic analysis in the study of motor speech disorders
Authors: Liss Julie M. , Weismer Gary
Published: October 2005

Traditional measurements performed on the acoustic signals of normal speech are frequently used to quantify the acoustic characteristics of disordered speech as well. This letter demonstrates how important aspects of speech production deficits in motor speech disorders may be overlooked if stringent quantification procedures are employed, especially in the stage of exploratory data analysis. It is suggested that qualitative procedures, wherein phenomena are inferred from visual examination of certain acoustic displays, are useful to supplement traditional measurements, and moreover, that they be used to point to the types of measurements that should be made in the finer-grained stages of quantitative analysis.
An efficient algorithm for the calculation of a constant Q transform
Authors: Brown Judith C. , Puckette Miller S.
Published: October 2005

An efficient method of transforming a discrete Fourier transform (DFT) into a constant Q transform, where Q is the ratio of center frequency to bandwidth, has been devised. This method involves the calculation of kernels that are then applied to each subsequent DFT. Only a few multiples are involved in the calculation of each component of the constant Q transform, so this transformation adds a small amount to the computation. In effect, this method makes it possible to take full advantage of the computational efficiency of the fast Fourier transform (FFT). Graphical examples of the application of this calculation to musical signals are given for sounds produced by a clarinet and a violin.
On numerical prediction of the acoustic source characteristics of an engine exhaust system
Authors: Gupta V. H. , Munjal M. L.
Published: October 2005

The contemporary methods for source characterization rely mainly on experiments. These methods produce inaccurate results in the low-frequency band, where the characteristics are all the more important. Moreover, the experimental methods cannot be used at the design stage. Hence, a numerical technique to obtain the source characteristics is desirable. In this paper, the pressure-time history and the mass-flux-time history obtained by means of the time-domain analysis have been used, along with the two-load method to compute the source characteristics. Two new computational methods for obtaining the source characteristics have been described. These are much simpler, and computationally more economical than the complete time-domain simulation, which makes use of the method of characteristics.
B-scan finite-elements analysis of acoustical image formation model for three-dimensional surfaces
Authors: Bednarczyk Adam , Peikari Behrouz
Published: October 2005

A B-scan acoustical image formation model based on finite-element analysis is introduced. The proposed model accurately predicts images of a three-dimensional (3-D) surface reflector under nonideal conditions. It is shown that the reflector may be located outside the uniform pressure zone of the focused transducer and the distance between the transducer and the surface as well as the angle of incidence may vary. In developing the model, essential elements in the B-scan acoustical image formations process are identified. It is shown that the phase, as well as the magnitude of the pressure wave, must be incorporated in the model. Phase interactions result in a strong sensitivity of the magnitude of the acoustical image to the angle of incidence. In the examples presented, it is shown that a 10-deg change in the angle of incidence results in a 50% magnitude attenuation. It is also shown that the temporal characteristics of the transducer can be neglected, and for angles of incidence less than 10 deg, the phase of the reflection coefficient can be ignored.
Broadband measurements of sea surface backscattering strength in the Gulf of Alaska
Authors: Ogden Peter M. , Erskine Fred T.
Published: October 2005

Measurements of low-frequency (70–1000 Hz) sea surface backscattering strength were made in the Gulf of Alaska during February–March 1992 as part of a surface backscatter and air–sea interaction experiment. The measurements described here used explosive charges (SUS MK-59 MOD1a) as sources and a towed horizontal line array of hydrophones as receiver. The experiment objective was to measure surface backscattering strength as a function of frequency, grazing angle, and environmental conditions of the air–sea boundary. Scattering strengths were obtained during 18 tests (each of duration approximately 30 min) conducted from 24 February to 1 March for wind speeds that varied from approximately 4 to 18 m/s. The experiment uses a direct path test geometry for which the measured surface backscatter originated from surface/near-surface regions at ranges of several km or less. Surface grazing angles for these measurements varied from about 5 to 30 deg. Results are compared to earlier surface scatter measurements below 1000 Hz and are interpreted relative to concurrent air–sea boundary environmental measurements.
Oceanic whitecap coverage in the Gulf of Alaska during the February–March 1992 surface scattering and air–sea interaction experiment
Authors: Monahan Edward C. , Wang Qin , Wang Wei , Wilson Martin B.
Published: October 2005

The fraction of the sea surface covered by stage-A whitecaps, i.e., spilling wave crests, was determined for some 300 ten-minute daylight intervals between 19 February and 1 March 1992 from the analysis of video records collected from U. S. and Canadian research vessels in the Gulf of Alaska. These average stage-A whitecap coverage values were related to the relevant 10-m elevation wind speed values using the approach of Monahan and O’Muircheartaigh [Int. J. Remote Sensing 7, 627–642 (1986)], and the resulting functional relationship was compared to similar expressions derived from the analysis of stage-A whitecap records obtained during earlier open ocean experiments. The possible relationships between stage-A whitecap coverage, rate of bubble injection into the oceanic mixed layer, and the production of sound at discrete positions on the sea surface are described. [Work supported by the Office of Naval Research via Grants N00014-92-J-1167 and N00014-90-J-1538.]
New method to characterize the surface-generated bulk acoustic waves in piezoelectric substrates
Authors: Zhang Yuwen , Desbois Jean , Boyer Laurent
Published: October 2005

A new method is proposed to characterize the bulk acoustic waves (BAWs) that can be excited by electrical sources at the surface of a piezoelectric substrate used in electroacoustic devices for signal processing. Using the concepts of harmonic source and of acoustic radiation admittance and impedance, the method allows one to compute, as a function of the acoustic slowness, the absolute magnitude of BAW radiation efficiency. Moreover, a relationship is established, giving the individual contributions to the real part of the surface admittance or impedance due to each BAW mode. Numerical applications of the method are carried out for a number of substrates currently used in surface acoustic wave devices, such as YZ-LiNbO3, 128° YX-LiNbO3, XZ-LiNbO3, and 36° YX-LiTaO3, as well as a 42.5° YX-quartz. It is found that the radiation efficiency of BAWs depends on not only the piezoelectric coupling constant, but also on the mode coupling between them. The analysis of the results obtained may lead to a deeper understanding of the mode-interaction mechanisms of the surface-generated bulk waves.
Elastic scattering at various incidences by a thin cylindrical shell bounded by hemispherical endcaps
Authors: Dubus Bertrand , Lavie Antoine , Décultot Dominique , Maze Gérard
Published: October 2005

The elastic scattering by a thin shell cylinder bounded by hemispherical endcaps is analyzed using a coupled finite element–boundary element method (ATILA and EQI codes). The target is made of steel and filled with air. The ratio of the inner radius b to the outer radius a is 0.97. The ratio of the total length L to a is 4. Axial, normal, and oblique incidences are considered for ka≤10 (k is the acoustic wave number in the fluid). The displacement field of the scatterer, the radiated and scattered pressures in the near field and far field, and the directivity patterns are provided. From these results, the peaks in the backscattered pressure are correlated to resonances of the structure and flexural or extensional waves propagating in the solid. Computed results are compared to experimental data obtained with the same target immersed in water. These results are performed by the quasiharmonic method M.I.I.R. (method of isolation and identification of resonances). This method allows one to obtain backscattered pressure spectra and patterns. [Work supported by D.R.E.T. Paris.]
Word recognition using an auditory model front-end incorporating spectrotemporal masking effect
Authors: Obara Kazuaki , Aikawa Kiyoaki , Kawahara Hideki
Published: October 2005

An auditory model front-end that reflects spectrotemporal masking characteristics is proposed. The model gives an excellent performance in the multi-speaker word recognition system using a cochlear filter. Recent auditory perception research shows that the forward masking pattern becomes more wide spread over the frequency axis as the masker-signal interval increases [E. Miyasaka, J. Acoust. Soc. Jpn. 39, 614–623 (1983)]. This spectrotemporal masking characteristics appears to be effective for eliminating the speaker-dependent spectral tilt that reflects individual source variation and for enhancing the spectral dynamics that convey phonological information in speech signals. The spectrotemporal masking characteristics is modeled and applied to a multi-speaker word recognition system. The current masking level is calculated as the weighted sum of the smoothed preceding spectra. The weight values become smaller and the smoothing window size becomes wider on the frequency axis as the masker-signal interval increases. The power spectra are extracted using a 64-channel fixed Q cochlear filter (FQF). The FQF covers the frequency range from 1.5 to 18.5 Bark. The current-masked spectrum is obtained by subtracting the masking levels from the current spectrum. Recognition experiments for phonetically balanced 216 Japanese words uttered by 10 male speakers demonstrate that the introduction of the spectrotemporal masking model improves the recognition performance in the multi-speaker word recognition system.
Neural network approach to assist markings of syllabic nuclei for multi-language database
Authors: Li K.-P.
Published: October 2005

The manual marking of syllabic nuclei is not difficult for a trained person. For a large amount of speech data, it is time consuming, and human error can introduce inconsistencies. The problem becomes worse when the person is not familiar with the language. To provide an automatic procedure for reducing the marking time and eliminate human errors, an adhoc algorithm was developed to find syllabic nuclei using a set of acoustic features. The initial error rate is 15%. The overall time spent marking automatically and correcting errors manually, however, was less than hand-marking by itself. An improved machine learning approach using a backward-error-propagation multi-layered perceptron, with the same acoustic features as inputs, was applied to the training speech. The hand-corrected markings was used as the teacher. Testing on the training data showed only 3%–5% misalignment. The time required to verify markings has further been reduced. When the training extended to a database of 43 different languages, the marking errors dropped to 2%, less than the errors in the initial hand-markings. Finally, when the network is used to mark 7 h of a multi-language database, there is no significant increase in marking errors.
Sound absorption of complex slit panels with partitioned air cavities of different sections
Authors: Furue Yoshihiro
Published: October 2005

Sound absorbing materials, which have high absorption at an arbitrary specified frequency band, are often needed in architectural acoustics. In such cases some resonator-type absorbers such as perforated boards with circular holes or slit panels with air cavities are widely used. To get high absorption at not only specific (resonant) but also other frequencies by such panels some porous material like fiberglass may also be filled in the air cavity. This work shows experimentally that rigid slit panels with partitioned air cavities of a few different shaped sections (which is called as complexslitpanel) have high absorption at a broad (ranged two or three octaves) frequency band without any other absorbing material. According to measurements in the reverberent chamber, complexslitpanels have higher absorption than conventional slit panels consisting of identically partitioned air cavities or slit structures without partitions in the air cavity. The complexslitpanels mentioned above will be made of fiber concrete and so they may be suitable as outdoor absorber because of their ease of maintenance.
Scattering from rough surfaces over a layered media
Authors: Dubberley John
Published: October 2005

It has been observed in both the recent surface acoustic backscatter experiments and the well-cited Chapman–Harris experiments that at certain frequency ranges and sea state conditions backscatter is enhanced over that which would be expected from rough surface scattering alone. One explanation for this anomaly is that a diffuse layer of bubbles may be affecting the low grazing angle backscatter by steepening the incident wave through refraction. A model for testing this theory in one dimension will be presented. The operator expansion surface scattering method will be tied to a simple one-way anisotropic media propagation model to examine the backscatter behavior. This model will be compared to some experimental data as well as to benchmark examples.
Modeling the azimuthal dependence of monostatic backscatter from the sea surface
Authors: Keiffer Richard S. , Dubberley John
Published: October 2005

It has been suggested [Erskine etal., J. Underwater Acoust. 42, 217–280] that the ability at low frequencies (<300 Hz) of first-order perturbation theory to model experimental data implies that scattering at the sea surface is the dominant contributor to backscatter. If one makes reasonable assumptions on the azimuthal dependence of the fully developed sea surface spectra, or if one uses a numerically derived spectra, then a strong azimuthal dependence in the monostatic backscatter is an almost unavoidable aspect of the acoustic modeling. On the other hand (though not directly looking for the azimuthal dependence at these frequencies), the data collected show an apparent lack of azimuthal dependence. In this paper, the second-order symmetric operator expansion method, which has been shown to be accurate for scattering from the sea surface, is applied to numerically derived 2-D sea surface spectra from CST-4. The objective of this investigation is to use the numerically derived 2-D sea surface spectra to obtain an understanding of the azimuthal dependence on the backscatter that is free of specific assumptions concerning the state of development or directionality of the sea surface.
Numerical integral equation solution for scattering from a one-dimensional penetrable fluid interface and a buried rigid cylinder
Authors: Ludwigsen Daniel O. , Tang Dajun
Published: October 2005

Ocean bottom scattering problems involve contributions from both the roughness of the seafloor and inhomogeneities within the sediment or buried objects. Here, a numerical procedure has been developed to find an exact solution for scattering from an infinitely long rigid cylinder buried beneath a one-dimensional rough interface. In this model, the water–sediment interface is a penetrable fluid boundary with the conditions that pressure and vertical particle velocity are continuous. The cylinder surface is rigid, i.e., the vertical particle velocity on the boundary is zero. A boundary integral approach is used: the pressure field and its normal derivative on the rough surface, and the pressure field on the cylinder surface, are determined, then used to find the far-field scattered field. This method was previously used for a pressure-release boundary condition [E. I. Thorsos, J. Acoust. Soc. Am. 83, 78–92 (1988)] and the penetrable boundary [E. I. Thorsos, J. Acoust. Soc. Am. 90, 2232(A) (1991)]. It is now developed for the combination of a penetrable boundary and a rigid cylinder to validate possible approximation methods. As a benefit of this formalism, the shape of the buried object may be readily varied to model elliptical and perhaps other cylinder cross sections.
Measurements of low grazing angle bottom backscatter at frequencies from 220 to 1000 Hz in the central Mediterranean Sea
Authors: Sundvik Michael T. , Reilly Sean M.
Published: October 2005

In June 1991 bottom scattering strength measurements were obtained with directional sources and receivers using short CW pulses at frequencies between 220 and 1000 Hz from three locations in the central Mediterranean. Two sites were at the southern edge of the Messina Cone in the Ionian basin (3400- to 3800-m water depth), and one site in shallow water (500-m water depth) at the eastern edge of the Medina bank. Reverberation data were processed using a sonar equation approach (using a flat bottom approximation) to obtain scattering strengths versus grazing angle. Average scattering strengths in the basin calculated from 1-s CW pulses and equivalent beam geometries vary 6 dB between 225 and 880 Hz, and show little dependence on grazing angle from 8 to 25 deg. Scattering strengths show a dependence on pulse length at all frequencies sampled, which can be interpreted as due to the dominance of sub-bottom effects. Scattering strengths from the shallow site show a similar dependence on pulse length, but a relationship to grazing angle similar to Lambert’s rule. Comparisons of the results to both the empirical Lambert’s rule and a high-frequency acoustic composite roughness and volume scattering model [Jackson etal., J. Acoust. Soc. Am. 79, 1410–1422 (1986)] met with limited success, implying a need for a more complete description of bottom and sub-bottom properties in treatment of bottom scattering at these frequencies. [Work supported by SPAWAR.]
Estimate of sea-bottom scattering in shallow water with a thermocline
Authors: Jin Guoliang , Zhang Renhe
Published: October 2005

Sea-bottom scattering coefficients for extremely low grazing angles have been estimated from sound propagation data in shallow water with a summer thermocline. Explosive charges were detonated under the thermocline and two hydrophones were located, respectively, above and below the thermocline. At moderate and long ranges the signals received by the upper hydrophone are composed of two parts: signals propagating from the source to the receiver and the signals scattered from the sea bottom induced by the sound propagating under the thermocline. The former arrived earlier and was much weaker than the latter. This offers one an opportunity of estimating the characteristics of sea-bottom scattering. The bottom scattering coefficients and their directivities for frequencies 0.8, 1, 2, and 4 kHz are estimated by adjusting the scattering coefficients so as to fit the calculated waveforms of scattered signals to the received ones. The incident field was estimated from the signals received by the lower hydrophone. The effective incident grazing angles are less than 2.5 deg. The bottom reflection losses due to bottom scattering are also estimated.
Classroom acoustics for hearing-impaired children
Authors: Crandell Carl C.
Published: October 2005

The present investigation examined ambient noise levels, reverberation times (RT), and noise/reverberation reduction treatments in 32 classrooms utilized for hearing-impaired pediatric listeners. Unoccupied classroom noise levels were measured with a precision sound-level meter (Bruel & Kjaer model 2209) equipped with a 1-in. condenser microphone. Noise measurements were obtained on A-, C-, and linear-weighting networks. Room reverberation was measured at 500, 1000, and 2000 Hz. Noise/reverberation reduction treatments, such as carpeting, draperies, acoustic tile, and furniture treatments, were documented in each room. Results indicated mean ambient noise levels of 50.2 dBA, 65.9 dBC, and 74.4 dB linear. The mean RT was 0.52 s. None of the classrooms met recommended acoustical criteria for ambient noise levels (30–35 dBA), while only 9 rooms (28%) complied with recommended standards for reverberation (RT=0.4 s). Moreover, few of the classrooms exhibited adequate acoustical treatments. These data will be discussed in view of achieving appropriate classroom acoustics for hearing-impaired children.
Trading relations for puretone analogues of speech
Authors: Auther Linda L. , Ochs Marleen T. , Ohde Ralph N.
Published: October 2005

This research investigated factors affecting the perceptual trading relation (TR)between first formant onset frequency and silent gap duration in pure-tone analogs of speech. Nonspeech analogs of /se/ and /ste/ were modeled after those used by Best etal. [Percept. Psychophys. 29, 191–211 (1981)]. Subjects’ descriptions of the stimuli and identification and discrimination performance before and after several hours of testing were examined. Based on identification performance and subjective stimulus descriptions, two groups of listeners emerged, similar to groups described by Best etal. Six of nine subjects described the nonspeech analogs as speech, exhibiting categorical perception and evidence of a TR. Three subjects described the stimuli as nonspeech sounds. In these subjects, a TR did not spontaneously develop following several hours of listening to the stimuli. The ‘‘nonspeech’’ listeners had more difficulty discriminating silent gap durations than did the ‘‘speech’’ listeners. It was hypothesized that the complex acoustic characteristics of these stimuli created a difficult perceptual task, interfering with integration of time and frequency cues by the ‘‘nonspeech’’ listeners. [Work supported by NIH DC00464 and BRSG ♯28-36.]
Kinematic synthesis of auditory motion
Authors: Jenison Rick L. , Lutfi Robert A.
Published: October 2005

A technique is presented for headphone simulation of sounds moving in auditory space using the mathematics of kinematics, or mechanics of pure motion. Doppler shifts, as well as changes in interaural time delays and interaural intensity differences can be shown to have transformation invariant dependencies based on kinematics. For example, the Doppler effect represents a pattern of change that is invariant for a particular velocity and distance, and independent of the frequency and amplitude of the sound pressure waveform. In principle, these invariants intrinsic to the sound pressure wave of a moving object are available to the listener. The continuous kinematic approach differs from the more traditional approach of considering static localization cues strung together to reconstruct the dynamic event, and allows programmatic simulation of arbitrary acoustic trajectories through the environment. A series of experiments was designed to assess the sufficiency of synthesized kinematic information for simulating sounds moving in the horizontal plane. Subjects were asked to judge the trajectory and direction of a simulated moving sound under headphones using the combination of a visual display of the path and a pointing device. Results support the sufficiency of kinematic information in judging trajectory and direction. Furthermore, the variability of judgments was comparable to other studies of headphone simulation of static free-field listening. [Work supported by ONR and Wisconsin Alumni Research Foundation.]
Energy exchange between the coupled media of impulsively excited fluid-filled cylinders
Authors: Fuller Chris R. , Brévart Bertrand J.
Published: October 2005

The time domain response of an infinite fluid-filled pipe to an impulsive line force of various azimuthal distribution (circumferential modes 0 and 1) is first derived, based on the Donnell–Mushtari shell equations fully coupled to interior acoustic field and computing a double Fourier integration in the wave number and the frequency domain. The transient radial displacement of the shell is then used to compute the coupled pressure field in the fluid and investigate the instantaneous intensity vectors in the near field closely hugging the wall. These vectors, evaluated at several distances from the input force, give insight into the exchange of energy between the structure and the fluid as the various waves propagate through the system. [Work supported by ONR.]
Spectrum of synchronous picosecond sonoluminescence
Authors: Hiller Robert , Putterman Seth , Barber Bradley P.
Published: October 2005

Measurements of the spectrum of sonoluminescence (SL) indicate that it extends from above 700 nm to below 190 nm. Furthermore the spectral density increases as photon energy increases. Calibration of the spectrum indicates that it accurately matches the tail of a 25 000-K blackbody. At lower ambient temperatures (≤10 °C) the spectral weight shifts even further into the UV so that SL appears to match the spectral tail of a 100 000-K blackbody. In order to gain further insight as to the physical origin of the spectrum, the air bubbles are replaced with argon bubbles and the effects of various solutes are studied. [Work supported by the US DOE Division of Advanced Energy Projects.]
Higher-order Lamb resonances and their critical frequencies
Authors: Werby M. F.
Published: October 2005

All the resonances generated on elastic shells are studied for a ka from 0 to 1000 for steel, aluminum, and WC for a shell thickness of 5% relative to the object radius. This study briefly illustrates the lowest-order symmetric and antisymmetric model or Lamb resonances, newly studied water borne and pseudo-Stoneley resonances, and the higher-order Lamb modes Ai and Si, where i=1,2,3... . This study concentrates on the higher-order Lamb resonances, derives simple expressions that predict their onset (critical frequencies), and illustrates how to classify each of the resonances for specific material. The phase velocities of some of the relevant resonances out to a ka of 1000 are plotted. For example, there are 13 resonances that can be classified for steel with a specific ordering. The ordering scheme is rather different for aluminum and WC. It is shown that the S0 Lamb mode does not asymptote to the plate velocity as predicted in thin shell theory but rather to the Rayleigh phase velocity, the same as the flexural mode. It is demonstrated by use of partial wave analysis that the new expressions that predict the onset (critical frequencies) of the higher-order Lamb modes are reliable. Further, interesting phenomena occur at the inception of some of the resonances and some of those cases are discussed.