bluuebunny/crossref_metadata_2025 huggingface dataset:
Boundary-layer transition problems for forced and for thermally driven gas oscillations
Authors: Rott N.
Published: October 2005

The transition of the acoustic (Stokes) boundary layer from laminar to turbulent flow has been observed and also to some extent theoretically explained for forced oscillations of a gas column in a tube. The pertinent critical Reynolds number is the ratio of the particle displacement amplitude to the Stokes boundary layer thickness. For thermally driven acoustic oscillations, there seems to be no experimental evidence for the occurrence of turbulence, in “ordinary” gases that have a Prandtl number of the order 1. For gases with high thermal conductivity (i.e., with near-zero Prandtl number), theory predicts extremely high amplitudes of the second-order velocity (associated with acoustic streaming) in the thermal boundary layer. Even for very weak acoustic oscillations, this means a “shortcut to turbulence.” If the tube or channel width is reduced to the order of the thermal boundary layer thickness, then acoustic streaming effects are drastically reduced and laminar flow is to be expected.
First measurements with a thermoacoustic driver for an orifice-pulse-tube refrigerator
Authors: Swift G. W. , Martin R. A. , Radebaugh Ray , McDermott K. M.
Published: October 2005

The orifice pulse tube is a variant of Stirling-cycle refrigerator in which the cold, work-absorbing piston and crankshaft are replaced by a simple dissipative structure. To date, the oscillatory pressure needed to drive pulse tubes has been provided by complex, unreliable room-temperature pistons and crankshafts. A thermoacoustic engine has recently been built to drive an orifice pulse tube refrigerator. In this composite device, heat flowing from a high-temperature source to a room-temperature sink generates high-amplitude acoustic oscillations in high-pressure helium gas; these oscillations power the orifice pulse tube, thereby pumping heat from a low-temperature source to a room-temperature sink. Thus the device is a heat-driven cryocooler with no moving parts. The first unit reached a no-load low temperature of 89 K and produced 5 W of cooling power at 120 K. It is powered by 3 kW of heat input at 900 K. Experimental data, comparison to theory, and future plans will be presented.
Psychophysical and room acoustical aspects of interaural correlation differences
Authors: Bilsen F. A. , Raatgever J. , Potter J. , van Els A.
Published: October 2005

Many perceptual aspects of room acoustics are largely, and some even uniquely, determined by the properties of human binaural hearing. For the understanding of the differences between monaural and binaural hearing for the different subjective room acoustical aspects involved, and for the development of proper binaural room acoustical criteria, it is necessary to do comparison measurements based on the “binaural impulse response” and to apply or to develop binaural models to interpret these measurements. In the present paper, the subjective attribute of spaciousness will be focused upon. An approach was chosen in which both artificial and realistic signals are used. Thus the discriminability of various dichotic signals with varying interaural correlation functions was measured using a “yes-no” procedure. Also, preliminary measurements in a realistic situation, i.e., in the main auditorium of the University with the Delft Acoustic Research System providing variable acoustics, were performed. The results will be interpreted using existing binaural models like the central spectrum model [J. Raatgever and F. A. Bilsen, J. Acoust. Soc. Am. 80, 429–441 (1986)]. Thus the intention was to find more refined quantities, or at least to provide a psychophysical basis to existing room acoustical quantities.
Free-field masking-level differences
Authors: Saberi Kourosh , Dustal Lynda , Sadralodabai Toktam , Bull Vicki , Perrott David R.
Published: October 2005

Free-field release from masking was studied in a two-alternative, forced-choice adaptive paradigm. Both absolute and masked thresholds were obtained in these experiments. The signal was a train (250 ms) of broadband clicks generated by filtering 50-μs pulses with TDH-49 speakers and adjusting the output with a harmonic equalizer to produce equal dBA/oct over the range 0.9–9.0 kHz. The speaker was placed 1.0 m from the subject. The masker was continuous broadband (0.7 to 11 kHz) white noise presented 1.6 m from the subject. Its level was 44 dBA. Study I tested 36 signal source locations at 10° increments along the horizontal plane as a function of seven masker locations at 30° increments. Study II used seven signal locations along three vertical planes located at azimuthal rotations of 0° (median plane), 45°, and 90°. Study III tested monaural conditions by occlusion of one ear. MLDs were computed after using the absolute thresholds to account for differences in the signal's SPL due to direction. In all three studies, substantial release from masking was observed as the signal and masker were spatially separated: a maximum of 15 dB along the horizontal plane, 8 dB along the vertical, and 8 dB under monaural conditions.
Anomalous acoustic behavior exhibited by gas-rich sediments of the subaqueous Mississippi Delta
Authors: Tinkle Anthony R. , May Jeffrey A. , Meeder Charles A. , Wener Kenneth R.
Published: October 2005

Sediments of the subaqueous Mississippi River Delta contain high concentrations of free gas, as manifested by anomalous physical and acoustic behavior. Much of the near-delta offshore area is a seismic “no-data zone,” impenetrable to conventional profiling techniques. Specialized techniques developed for direct measurement of sediment acoustic properties reveal that velocities of less than 1000 ft/s (300 m/s) routinely occur in these muds, and acoustic energy at frequencies greater than 100 Hz is almost completely absorbed by only a few tens of feet of very gassy sediment. Severity of the acoustic anomalies typically decreases with depth beneath the seafloor, with the most severe anomalies generally occurring within the first 200 ft subbottom. Trapping of acoustic energy within these near-bottom, gas-charged layers is also observed. The nature and severity of the acoustic anomalies correlate well with both sediment physical properties, and the unstable system of collapse and mudflow features that typify the seafloor morphology of the deltaic no-data zone.
Near-surface gas hydrates in deep-sea sediments
Authors: Flood Roger D. , Manley Patricia L. , Scranton Mary I.
Published: October 2005

Recent studies of depositional processes in deep-sea continental margin and abyssal settings show that early diagenesis of organic-rich sediments can significantly alter physical properties in the upper 5–50 + m of the sediment column. Apparently, in situ methane production leads to sediment methane levels that may be high enough to allow hydrates to form while high CO2 levels may cause localized carbonate precipitation. These diagenetic processes can give rise to a series of near-surface reflecting horizons (and associated physical properties) that are not related to primary depositional processes. Where best studied (in the Argentine Basin at 5000- to 5500-m water depth [P. L. Manley and R. D. Flood, Deep-Sea Res. 36, 611–623 (1989)]), sediment velocities as low as 1.35–1.42 km/s overlie velocities as high as 1.8–3.0 km/s within 30 m of the sediment surface. While the high velocities appear to be related to near-surface hydrate formation, the origin of the low velocities is less well understood. Similar reflecting sequences have been observed in other areas, particularly in the North Atlantic.
Subjective and objective assessment of some reverberation enhancement systems
Authors: Kleiner Mendel , Svensson Peter
Published: October 2005

How much of a difference does active or passive variation of a room's acoustical conditions make? Electronic architecture and reverberation enhancement have become common in the pursuit of better acoustics in multipurpose auditoria by active means. New systems show promising results. The properties of several different installations both in the U.S. and Europe have been investigated. This has been done both objectively by measurement of omnidirectional and binaural impulse responses and subjectively by the use of binaural recording. The binaural recordings used anechoic music replayed in stereo on stage. These recordings were used in pair comparison tests to investigate the dimensions of audible difference between the halls, with and without active or passive treatment of the room response. The pair comparison tests were evaluated using multidimensional scaling. The results show that some systems are able to modify the acoustical conditions to a very large extent. Differences between various system settings may be as large as between halls. Most of the subjectively perceived differences may be explained by changes in reverberation time and lateral energy factor. [Work supported by the Swedish National Council of Building Research.]
Optimally formulated high efficient planar projector arrays
Authors: Joseph P. M. , Pillai P. R. Saseendran
Published: October 2005

Closely packed multi-element transducer arrays are extensively used in underwater applications for achieving better directionality and longer transmission range. With the current tendency of extending their operation toward lower frequency and particularly near resonance, the acoustic interaction among the elements grows stronger and in turn will degrade the predicted transmitting characteristics. This troublesome effect is much alleviated in uniform planar arrays by restructuring it with the optimal interelement spacing at which the interaction force is minimum [P.M. Joseph and P. R. Saseendran Pillai, Acoust. Lett. 12 (11), 190—193 (1989)]. It has been seen from the results of computation that a further reduction in interaction can be achieved by incorporating the nonuniform array concept. A simple method for predicting the optimum configuration of element locations that reduce the interaction to a lower level, without altering the aperture dimension, is proposed in this paper. Here, the element locations are dispersed in accordance with Gaussian distributed random numbers by keeping the optimum spacing as the mean. Even though a large standard deviation value will greatly reduce interaction, a reasonable value is chosen, as large deviations produce deteriorated beams. This optimally formulated array does not exhibit any grating lobes nor does its radiation pattern differ much from the conventional λ/2 spaced and restructured arrays.
The status of federal aviation noise regulations
Authors: Wesler John. E.
Published: October 2005

During its final hours, the 101st Congress enacted the Airport Noise and Capacity Act of 1990, mandating new controls on aircraft noise and airport access restrictions. The Act imposes new requirements for airport use restrictions that are imposed for noise control purposes, and establishes a schedule for the phase out of older, noisier, Stage 2 airplanes in the U.S. These legislative directives are now being translated into specific regulatory language by the Federal Aviation Administration. In summary, the actions continue the overall federal policies for aviation noise control that began in 1968. These policies are reviewed briefly, and the current status of the new regulations and restrictions is described.
Collapse of a long cylindrical bubble
Authors: de Cardenas Jorge E. Lopez , Finch Robert D.
Published: October 2005

The collapse of a cylindrical bubble was modeled using an approach similar to Rayleigh'solution for a spherical bubble. Rayleigh assumes an incompressible fluid, which, in the cylindrical case, leads to the problem of the fluid having infinite kinetic energy. To overcome the difficulty a “semi-compressible” assumption is used, in which only the fluid contained in the acoustic envelope defined by r = ct is considered in the solution; the fluid outside this envelope being neglected. The results obtained with this approach were compared with solutions computed from a model using a finite element method. As in Rayleigh's solution for the spherical bubble, the calculations of the collapse time for the cylindrical bubble showed very good agreement with the numerical solutions. The results obtained for the pressure generated by the collapse of the cavity provide a qualitative description of cavitation effects produced by jets from shaped changes.
A comparison between “real” and “ideal” gas in theoretical cavitation dynamics
Authors: Church Charles C.
Published: October 2005

Most theoretical formulations for the response of small gas bubbles to acoustic pressure fields assume that the ideal gas equation of state is appropriate for calculating the internal pressure of the bubble. While this assumption is adequate at low amplitudes, at higher pressure amplitudes, and thus larger bubble responses, it leads to predictions of internal gas densities that are on the order of, or greater than, those of metals. A more realistic assumption is a van der Waals equation of state for a “real” gas. In the present work a general expression for the pressure inside a bubble containing real gas is provided, as well as expressions resulting from some common simplifying assumptions. In addition, comparisons between calculated bubble responses using either an ideal gas or van der Waals equation are presented. For these computations one of two models for bubble dynamics will be employed: the Gilmore-Akulichev formulation with temperature estimated polytropically or Flynn's equations in which temperature is calculated exactly. [Work supported by NIH and ONR.]
An experimental test of a theory of nonlinear bubble dynamics
Authors: Hitt Darren L. , Prosperetti Andrea , Roy Ronald A.
Published: October 2005

Nonlinear bubble oscillations in a levitation cell are studied. The experimental levitation number. Le = ρg/|∇p|, can be compared to its corresponding theoretical value to provide a sensitive evaluation of the bubble dynamics theory [Prosperetti et al., J. Acoust. Soc. Am. 83, 502–514 (1988)]. A pulse-echo technique is developed that permits extremely accurate measurements of the bubble location in the pressure field. This technique can then be used to obtain accurate measurements of the levitation number under a variety of experimental conditions. [Work supported by NSF.]
Sound intensity and reflection coefficient measurements in the ear canal
Authors: Rabbitt R. D. , Dragicevic J.
Published: October 2005

The sound power per unit cross-sectional area (specific power) is measured in the ear canal using a three-probe-microphone system. Pressure measurements recorded from locations within the core region of the ear canal are utilized to determine the instantaneous intensity of sound waves traveling in the lengthwise direction. A direct time-domain method provides the specific power contained in waves traveling through the region of the canal containing the microphones. The time average of the instantaneous intensity defines the specific power absorbed by the ear. Furthermore, the time average of the positive part of the intensity determines the incident specific power, or input to the ear, and the time average of the negative part of the intensity determines the reflected, or emitted, specific power. Signal averaged data are collected for pure-tone sweeps from 4 to 15 kHz. [Work supported, in part, by the Whitaker Foundation and the National Science Foundation.]
A physical model for the middle ear cavity (MEC)
Authors: Puria Sunil
Published: October 2005

The input impedance of the cat MEC is modeled by approximating the bulls and tympanic cavities as a cascade of two cylindrical tubes. The small hole in the bony septum, known as the foramen, is approximated as a short cylindrical tube. Nonplanar wave propagation, due to the foramen, and visćo-thermal losses at the cavity walls are included in the model. The model was verified by making impedance measurements on cylindrical cavities for frequencies up to 12 kHz. The intact case, as well as the open bulls case and plugged foramen case, is simulated and shown to be in good agreement with animal measurements [T. J. Lynch, III, Ph.D. thesis, MIT (1981)]. in addition to the bulls resonance near 4.5 kHz, the model predicts that there is a second bulls resonance near 26 kHz. Without the bony septum, the resonances are shown to be near 10 and 20 kHz. It is hypothesized that the role of the foramen is to shift the resonant frequencies.
Soize's theory of structural fuzzy: An examination of fundamental assumptions
Authors: Sparrow Victor W.
Published: October 2005

In 1986, C. Soize introduced a theory of scattering from structures that are known in gross aspects, but whose details are either unknown or only imprecisely known. Soize called his method a theory of structural fuzzy [Resh. Aérosp. 1986-5, 23 and Resh. Aérosp. 1986-5, 49 (1986)], which he applied to scattering in the midfrequency range. In the theory, Soize described complex mechanical subsystems by fuzzy finite elements, elements where the mass, rate of dissipation, and modal density are formulated using uniform probability density distributions. In this presentation, Soize's methods are outlined and the fundamental assumptions that underlay the theory are considered. Specifically, the implications of the uniform probability distributions and other assumptions on the fuzzy finite elements will be reported. Other probabilistic descriptions for these constituent elements may be more realistic. Theoretical limitations will also be summarized for the frequency ranges over which the fuzzy structure theory is predicted to be valid.
Optical measurements of shear waves on a point-driven cylindrical shell excited radially
Authors: Lee Dowon , Kil Hyun-Gwon , Glandier Christian , Jarzynski Jacek , Berthelot Yves
Published: October 2005

A differential laser Doppler velocimeter (LDV) [Lee et al., Proceedings of the 3rd International Congress on Intensity Techniques, Senlis, France, pp. 181–188 (1990)] has been used to measure in-plane motion associated with waves propagating on a thin cylindrical shell excited radially at a single frequency by a shaker. The endcaps of the shell approximate the case of a simply supported shell with axial constraints at both ends. The fiber optic technology used in the LDV system allows the optical probe head, located at a distance of about 30 cm from the shell, to be scanned over the entire surface of the shell. Data were recorded along an array of 32 points circumferentially and 16 points axially, enough to sample spatially both extensional (fast waves, low wave numbers) and flexural (slow waves, high wave numbers) waves. The data were analyzed with both a two-dimensional spatial FFT algorithm and a Prony algorithm. The analysis clearly reveals both type of waves separately. Theoretical predictions are obtained from the analysis of a point-driven infinite shell and from Forsberg's original paper [AIAA J. 2 (12), 2150 (1964)]. Both theoretical and experimental results clearly show the presence of shear waves propagating on the structure. [Work supported by ONR.]
Behavior of multiple degree of freedom systems having neighboring eigenvalues: Veering of the eigenvalue loci and high mode sensitivity
Authors: Chen Pei-Tai , Ginsberg Jerry H.
Published: October 2005

Interesting phenomena occur when linear systems contain natural frequencies that become close as a system parameter is altered. The behavior of eigenfunctions and eigenvalues is studied by applying a perturbation analysis to a self-adjoint system. Veering of the eigenvalue loci versus the small perturbation parameter is observed and the criterion for the occurrence of veering is identified. It is proven that in the veering region, the eigenfunctions are highly sensitive to the value of the system parameter. A corollary is that in a system, whose individual subcomponents are highly coupled and nearly identical, eigenvalue veering and high mode sensitivity are associated with mode localization, in which some of the system modes are strongly enhanced in a small portion of the domain. An example of a previously studied two-span beam with irregular spacing of the supports displays the correlation and mode localization, the high mode sensitivity, and veering of the eigenvalue loci. Results of the perturbation analysis are shown to be virtually identical to those of the exact solution of the equations of motion. [Work supported by the Office of Naval Research, Code 1132-SM.]
Input mobilities and power flows for edge excited, semi-infinite plates
Authors: Kauffmann Christiaan
Published: October 2005

This paper relies highly on a paper by E. Eichler [J. Acoust. Soc. Am. 36, 344 (1964)], which contains an analysis of the response of a semi-infinite, thin plate excited by a time-harmonic load applied at a stud of width 2a attached to the edge, the remainder being free. Eichler used spatial Fourier transforms in the edge direction to obtain closed form integral expressions for the plate response. The present paper provides full details on the analysis (some of them not yet published) and presents new expressions for the input power fed into the plate. Numerical results covering a wide range of ka are presented, allowing for a simple physical interpretation in three cases: (a) ka ≪ 1: point excitation, (b) ka → ∞: line (or beam mode) excitation, and (c) ka = O(1): interference effects at intermediate frequencies, which are also present in the simple acoustical analogy of a baffled piston. [Work supported by the TNO Institute of Applied Physics, Delft, The Netherlands.]
Comparative investigations of speech and other motor behaviors
Authors: Smith Anne
Published: October 2005

This presentation focuses on the question of how articulator movements are controlled by the nervous system and on the question of whether neural control of speech movements is “special,” that is distinctive from the neural control processes underlying the production of other motor behaviors. To address these questions, muscle activity and movements have been recorded while subjects engaged in a variety of tasks, including speaking, finger tapping, mastication, and voluntarily controlled respiration. The results of these experiments suggest that there are common characteristics in the neural mechanisms underlying the control of speech and other motor behaviors. In addition, however, the experimental evidence suggests that sources of neural drive that appear to generate input to muscles for relatively automatic motor behaviors, such as mastication and respiration, are not equally dominant in controlling muscle activity for speech. Implications of these data for the concept of a “rhythm generator” for speech will be discussed. [This work has been supported by Grant DC00559 from NIH's NIDCD.]
Experimental levels in the analysis of articulatory movements: Implications for speech motor control
Authors: Gracco Vincent L. , Saltzman Elliot L.
Published: October 2005

Kinematic analysis of speech movements can provide important insights into the organization of underlying central processes. As such, much theoretical significance has been attached to movement variations hypothesized to reflect corresponding contrasts in motoric or linguistic goals. Too often, however, important properties of the physical plant and representation of the underlying control signals are ignored when interpreting such variation. Interpretation of movement without regard to the structure and biophysical properties of the controlled system and associated bioelectric events may result in overspecified models of speech production. Further, organizational principles or neural control strategies for speech generated from kinematic observation without concomitant electromyographic observation may result in unrealistic theoretical abstractions. The utility of including, in a general sense, biomechanical and electromyographic levels of analysis in the development of detailed theories and models of speech production will be presented. Tentative speculations on characteristics of the speech motor control process will be discussed. [Work supported by NIH.]
An x-ray microbeam study of Hindi vowel articulations
Authors: Dixit R. Prakash , Daniloff Raymond G.
Published: October 2005

Using the x-ray microbeam system of the University of Wisconin at Madison, articulatory movement data were recorded from pellets attached to the tongue, upper and lower lips, lower jaw, and velum while a native speaker of Hindi produced ten oral vowels contained in non-sense words of the form bVb. The data do not support the traditional descriptions of Hindi vowels given in terms of either tongue height or vocal tract openness. For example, overall position of the tongue dorsum was higher for /e/ than /ɪ/, and similar for /ᴜ/ and /o/, and also for /ʌ/ and /ɑ/. Position of the jaw was lower for /ɔ/ than for /ɑ/. The lips were more open for /o/, /ᴜ/, and /u/ than for /ɔ/, and more open for /i/ than /ɪ/, /e/, and /ɛ/. Position of the lips for /e/ and /ɛ/ was identical. The velum showed somewhat greater elevation for /e/ than /ɪ/, and identical elevation for /ᴜ/ and /o/. The remaining relations among various structures involved in vowel production were as expected. However, overall relationships among these structures were quite complex.
An x-ray microbeam study of the effect of lexical stress on the articulation of intervocalic velar stops
Authors: Turk Alice
Published: October 2005

Previous research on two speakers showed that the closing and opening gestures of the upper lip during the production of intervocalic labial stops behave differently, depending on the stress of the following vowel [A. Turk. J. Acoust. Soc. Am. Suppl. 1 88, S56 (1990)]. When the consonant precedes a stressed vowel, its closing gesture (characterized by the measurement peak_velocity/vertical_displacement) is slower than its opening gesture. When the consonant precedes an unstressed vowel, its closing gesture is faster than its opening gesture. An analysis of velar stops will show whether the pattern observed for labials can be generalized to another place of articulation. Results to be presented are of tongue movement during closing and opening gestures of the velar, stops in the following words: /k/: locále fóllicle; /g/: cigár vígor vínegar. [Work supported by Sigma Xi.]
Linguo-mandibular coordination in consonant production
Authors: Faber Alice , Farnetani Edda
Published: October 2005

The coordination between the jaw and tongue in regulating tongue position for consonant articulation was explored by simultaneous use of electropalatography and an alternating magnetic field device (Movetrack: Branderud, 1985). Linguo-palatal constriction was monitored via palatography, and tongue body and jaw height and frontness were monitored by small receiver coils adhering to the articulators. Speech materials were real and nonsense words of the form (C)V1CV2, where C ranged over {t d ∫ z I} and V1 and V2 over {a i}. The “real” words were produced in isolation and in sentences. Each token was repeated three times by one female native speaker of Italian. Regression analysis was used both to distinguish between rotational and translational movement of the jaw and to separate between the tongue's independent movement and positional effects caused by jaw movement. Examination of the inherent differences among consonants in tongue position reveals both synergistic and antagonistic patterns of linguo-mandibular coordination. The tongue body is lower for /z/ than for the other consonants, and fronted for (in order) /z ∫/>/t/>/d l/. Comparison with the jaw positions and with the residuals from the regression analyses reveals that the tongue height differences result from a combination of jaw height differences (/z ∫/>/t d/>/l/) and active lowering of the tongue body (relative to the jaw) for /z ∫/. Similarly, the tongue frontness differences result from a combination of (translational) jaw fronting for /z ∫/ and relative retraction of the tongue body for /l/. [Supported by ESPRIT ACCOR II BRA action 3279 and NICDC Grant No. DC-00016.]
Mechanisms for tongue-tip trills
Authors: McGowan Richard S.
Published: October 2005

Possible mechanisms for the production of tongue-tip trills are discussed. It is necessary that energy be transferred from the airstream to the tongue tip to enable it to vibrate. A two-mass model, similar to that of the vocal folds, is one possible model for tongue trills, but there are others that allow the tongue one-degree-of-freedom motion. It is possible that the boundary-layer separation point is affected by the acceleration of air, which is not accounted for in the quasistatic approximation. An argument will be given that the acceleration term produces a favorable energy transfer during trills. Also, the capacitive loading of the vocal tract behind the tongue constriction can provide necessary phase shifts between constriction volume velocity and intraoral pressure for favorable energy transfer. A numerical simulation of the latter model is presented with parameters derived from measurements of oral-nasal volume velocity and intraoral pressure during sustained trills. Some of the features of the trills are reproduced with this simulation.
High-resolution matched-field inversion of ocean sediment parameters with simulated annealing
Authors: Collins Michael D. , Kuperman W. A. , Schmidt H.
Published: October 2005

High-resolution inversion of ocean sediment parameters is possible with matched-field processing. If the ocean bottom is complicated, matched-field inversion requires an efficient nonlinear optimization method such as simulated annealing [Kuperman et al., J. Acoust. Soc. Am. 88, 1802 (1990)] to search the high-dimensional parameter landscape, which can have many local minima. An efficient propagation model is also essential because the wave equation must be solved many times. Single-frequency matched-field inversion simulations have been performed using various types of source and receiver arrays, including an array of sources beamed toward the ocean bottom, for problems involving fluid sediments, elastic sediments, and range dependence. The acoustic and elastic parabolic wave equations are used to construct replica fields for range-dependent inversion problems. For problems that can be regarded as range independent between the sources and receivers, large gains in efficiency can be achieved by working in wave number space using the synthetic aperture approach [G. V. Frisk and J. F. Lynch, J. Acoust. Soc. Am. 76, 205 (1984)] because the number of wave number samples required for inversion is much smaller than the number of wave number samples required to construct replica fields.
Room acoustics measurements using MLSSA
Authors: Rife Douglas D.
Published: October 2005

The time-bandwidth product of a linear system is defined as the product of its bandwidth and its impulse-response duration. Due to its reverberation, the time-bandwidth product of a typical room is much larger than that of other common linear systems (e.g., acoustic transducers or electronic filters), thus posing special problems to the measurement system. It is shown that maximum length sequence (MLS) based measurements are inherently well suited to large time-bandwidth product systems, including auditoria. The MLSSA measurement system represents the first commercial implementation of MLS measurement methods and provides a variety of post-measurement processing functions for room acoustics applications.
Vibrational modes of piano soundboards
Authors: Brelay Hérve , Rossing Thomas D.
Published: October 2005

The vibrational modes of the soundboards have been compared in two small upright pianos: one of solid spruce and one of three layers (two thin layers of spruce with a core of poplar). The model frequencies are quite similar, although the mode shapes are somewhat different. In the spruce soundboard, the bending wave velocities for the low-frequency modes appear to increase with the square root of frequency, which suggests that the stiffness of the soundboard plus the ribs is approximately the same along and across the grain (i.e., the soundboard is fully compensated). In the layered soundboard, on the other hand, the nodal lines tend to follow the ribs, indicating that the soundboard is overcompensated. Mode damping does not appear to be substantially different in the two soundboards.
Audiometric variability
Authors: Marshall Lynne
Published: October 2005

The size of detectable hearing shifts for individuals in hearing conservation programs is limited by audiometric variability. This talk describes how different audiometric test methods affect threshold. both in terms of accuracy (i.e., the absolute value of the threshold) and precision (i.e., the variability of the threshold). Factors to be discussed include the general test procedure, the number of responses required to estimate threshold in clinical test procedures, the step size used to adjust levels for threshold measurement, and earphone replacement. Data from computer simulations, laboratory tests, and industrial hearing conservation programs will be discussed. [Work supported by VA-DOD.]
Upper crustal properties determined from wide aperture towed array data
Authors: Diebold John
Published: October 2005

Marine seismic reflection/refraction data with unusually large apertures can be collected using two or more suitably equipped ships. Although multiship experiments have classically been designed to delineate deep structure and seismic velocity, the data are, under certain conditions of geometry and sediment/crustal character, useful for the investigation of shallow properties. Three examples broadly define the range of application. Large aperture (0–10 km) CDP measurements in the shallow waters over the thickly sedimented continental margin of the northeast U.S. included first arrivals corresponding to diving rays refracting in the sedimentary column. Straightforward traveltime analysis of these arrivals yields detailed 2-D P-wave velocities from the seafloor down to 3 km, except where velocity reversals are encountered. Data from a similar experiment over the East Pacific Rise, with 0- to 6-km offsets, can be analyzed for crustal velocities as shallow as 100 m below the thinly sedimented seafloor. In the Hudson River, sediments are sufficiently thin and the water shallow enough that upper crustal refractions are seen as first arrivals in single-ship CDP data. In this case, however, sedimentary properties can only be estimated by indirect methods. In each of these three data sets, some combination of velocity structure and experimental geometry allows velocity determination for upper sediments and crust.
Gas temperatures in bubble oscillations
Authors: Prosperetti A. , Kamath V.
Published: October 2005

Sonolumineseenec effects are critically dependent on the temperature field of the gas contained in oscillating bubbles. Polytropic models of the gas pressure-volume relationship are totally inadequate for an accurate determination of the temperature. A better model based on the conservation equations of continuum mechanics is described and its predictions illustrated with a number of examples. The influence of the computed temperature field on a model dissociation reaction is illustrated. [Work supported by NSF.]
Shape oscillations of bubbles driven by modulated ultrasonic radiation pressure: Experiments
Authors: Marston Philip L. , Asaki Thomas J. , Trinh Eugene H.
Published: October 2005

The shape of a bubble in water should change in response to the radiation pressure of an ultrasonic wave. Furthermore, modulation of the radiation pressure at the resonance frequencies for shape oscillations should facilitate the stable excitation of such modes [P. L. Marston, J. Acoust. Soc. Am. 67, 15–26 (1980)]. Recently this method of driving oscillations has been demonstrated by employing a novel ultrasonic levitator developed at Jet Propulsion Laboratory which traps bubbles in the size range of 1- to 5-mm diameter. The quadrupole mode was observed with resonance frequencies in the range from 400 to 40 Hz. Oscillations were detected with the unaided eye and with television and laser light scattering methods. These experiments suggest methods for investigating the nonlinear dynamics of bubbles, effects of surfactants, and the dynamics of bubbles in low gravity. Some comparisons with the dynamics of drops will be noted. [Research supported by ONR and NASA.]
Sonochemistry of volatile and nonvolatile solutes in aqueous solutions: A spin trapping study
Authors: Riesz Peter
Published: October 2005

The very high temperatures and pressures induced by acoustic cavitation in collapsing gas bubbles in aqueous solutions exposed to ultrasound lead to the thermal dissociation of water vapor into H atoms and OH radicals. Their formation has been confirmed by spin trapping for continuous wave and pulsed ultrasound. Sonochemical reactions occur in the gas-phase (pyrolysis reactions), in the gas-liquid interface, and in the bulk of the solution (radiation-chemistry reactions). The high-temperature gradients in the interfacial regions lead to pyrolysis products from nonvolatile solutes present at sufficiently high concentrations. The sonochemically generated radicals from carboxylic acids, amino acids, dipeptides, sugars, pyrimidine bases, nucleosides, and nucleotides were identified by spin trapping with a nonvolatile nitroso spin trap. At low concentrations of nonvolatile solutes, the spin trapped radicals produced by sonolysis are due to H atom and OH radical reactions. At higher concentrations of these nonvolatile solutes, sonolysis leads to the formation of additional reactions due to pyrolysis processes (typically methyl radicals). A preferred localization of nonvolatile surfactants at the gas-liquid interface was demonstrated. The volatile solutes methanol, ethanol, acetone, and acetonitrile were studied over the complete range of solvent composition. By the use of rare gases with different thermal conductivities, the contributions of individual reaction steps with widely different energies of activation can be evaluated.
Isolation and characterization nf microevents in speech
Authors: Berry David A. , Strong William J.
Published: October 2005

An event-synchronous technique has been designed in an attempt to optimize time and frequency resolution in speech analysis. The technique isolates “microevents” in the speech waveform and then analyzes them, thus differing from commonly used asynchronous methods that employ a fixed frame length stepped forward in constant time increments. A microevent (ME) is associated with a “packet of energy” in the waveform and is initiated by some underlying input or fluctuation of energy. There are four basic types of MEs: (1) a voiced ME is initiated by a pitch pulse; (2) a plosive ME is initiated by a plosive burst; (3) a noise ME is initiated by a positive fluctuation in energy; and (4) a mixture ME. An ME is terminated at the initiation of the next ME or when the energy of the speech signal falls below the background level. ME durations are constrained to lie within a range of 2–20 ms. The current algorithm, developed and tested with portions of the 1988 DARPA TIMIT acoustic-phonetic continuous speech database, isolates over 95% of the MEs correctly. Once isolated, MEs are characterized by their one-third octave spectra. Results will be illustrated with various examples.
A complex ray method using asymptotic expansions applied to the penetrable wedge
Authors: Deane Grant B.
Published: October 2005

The acoustic field in a sloping, isovelocity waveguide (the penetrable wedge) is found by extension and application of a complex ray model. The pressure is computed as a sum of ray fields, each of which is expressed as an asymptotic expansion of a plane wave integral evaluated using the method of steepest descent. A geometrical interpretation of the method is given which should be possible to extend to three-dimensional environments.
RAMSoft II: A computer-based room acoustics measurement system
Authors: Halliwell R. E. , Bradley J. S.
Published: October 2005

A computer-based measurement system has been developed to determine a number of the newer measures used in the acoustical evaluation of rooms. Although the output is similar to the earlier RAMSoft system from which it has evolved, this system is based on a quite different measurement concept. This is a two-microphone system using an MLS sequence as the excitation signal. Fast Hadarnard transforms on the two signals provide both omnidirectional and figure of eight impulse for each measurement position. From these impulse responses 14 acoustical measures, including lateral fractions, are calculated. The reasons for the departure from RAMSoft will be discussed and measurements made with both this system and with the RAMSoft measurement system will be compared.
Experimental evaluation of the backscattered polar response of sound absorbing, reflecting, and diffusing materials
Authors: D'Antonio Peter
Published: October 2005

The sound that we hear in a room is a combination of the direct sound and indirect reflected sounds from room boundaries. Because the amplitude, directionality, and temporal distribution of the indirect reflections affect how one perceives the actual sound source, control of room reflections using absorption, reflection, and diffusion is a central consideration in acoustical design. Effective application of these ingredients is based on an understanding of the backscattered directional response for a given angle of incidence, angle of observation and frequency, i.e., the backscattered polar response. To evaluate the experimental polar response a testing technique using time delay spectrometry was developed [P. D'Antonio and J. Konnert, AES Preprint 2295, 79th AES, New York (October 1985)]. The method allows the evaluation of the backscattered frequency response of a sound modifying material mounted on the boundary surface at any scattering angle, for a given angle of incidence. For sound absorbing materials, for example, these “directional” scattering coefficients augment the traditional random-incidence ASTM reverberation chamber data. The technique will be described and polar response data for sound absorbing, reflecting, and QRD® diffusing panels will be presented. An alternative method using sound intensity will also be discussed and preliminary data presented.
Acoustical design of the National Center for the Performing Arts of Peru
Authors: Jimenez-Dianderas Carlos R. , Panduro-Manrique Manuel
Published: October 2005

The project is based on the design of a cultural complex for the National Center for the Performing Arts which includes a 1200-seat opera house, a 750-seat concert hall, a small auditorium for master classes, and an amphitheatre for 1500. The interest in this project came from the lack of cultural facilities in Peru. Furthermore, it is an established methodological alternative to the architectural acoustic design; so the Center is the result of the integrity of a two-design process combined into one architectural and acoustical design. The site for the project was determined from the evaluation of several possibilities through analysis of successive approximations. The analysis includes the urban acoustical study of the metropolitan area of Lima. The final decision about the site was done through acoustical measurements of urban noise. The acoustical design of the auditoria includes ray-diagram analysis, reverberation time, early decay time calculation, and final sound level in some positions.
Some experimental studies in elastic wave propagation
Authors: Kolsky H.
Published: October 2005

A number of experimental studies of elastic wave propagation in solids, with which the author has been associated, are reviewed. These concern the propagation and reflection of mechanical pulses in elastic solids. In most of these studies, unexpected mechanical response has been observed. The problems discussed include that of a glass beam subjected to flexural loading [H. Kolsky, Dynamic Crack Propagation, edited by G. C. Shih (Noordhoff, Groningen, 1973), pp. 399–414; V. Kinra and H. Kolsky, Eng. Fracture Mech. 9, 423–432 (1977); H. J. Schindler and H. Kolsky, J. Mech. Phys. Sol. 31, 427–437 (1983)] and it has been shown that the time for the fracture to be completed is equal to the time it takes the extensional compressive wave generated by the growing crack to travel to the free ends of the beam and be reflected back as a tensile pulse. Another problem discussed is that of the elastic impact of a sphere on a plate. When the plate is sufficiently thick, i.e., its thickness is such that the sphere separates from the plate before reflected waves reach the region of contact. The problem, which was first treated by Hertz, has more recently been treated by S.C. Hunter [J. Mech. Phys. Solids 5, 162 (1957)], who showed that about 1% of the energy is converted into elastic vibrations of the block. C. Zener [Phys. Rev. 59, 669 (1941)] has shown that the low coefficients of restitution observed for thin plates can be explained in terms of flexural plate waves. More recently, M. G. Koller and H. Kolsky [Int. J. Solids Structures 23, 1387–1400 (1987)] have studied the problem in detail in terms of the propagation and reflection of the waves generated by the impact and shown two unexpected phenomena, namely the propagation of a longitudinal disturbance at the S-wave velocity, and an enhancement of amplitude on reflection of an outgoing P wave. Other studies which will be discussed are the change in pulse shape which occurs when a unidirectional pulse is reflected at the boundary between two noncollinear rods [J. P. Lee and H. Kolsky, J. Appl. Mech. 39, 809–813 (1972)], and between a rod and a half-space [S. Boucher and H. Kolsky, J. Acoust. Soc. Am. 52, 884–898 (1972)].
Elastic waves in rods and optical fibers
Authors: Thurston R. N.
Published: October 2005

This talk reviews elastic waves in rods, with mention of their possible importance in optical fibers. The formal solution of the boundary value problem of the three-dimensional theory of elasticity for waves in rods was given over a century ago by Pochhammer and Chree. It was only about 50 years ago that important computations were done that enabled calculated results to be compared with experimental data for longitudinal waves [D. Bancroft, Phys. Rev. 59, 588–593 (1941)] and flexural waves [G. E. Hudson, Phys. Rev. 63, 46–51 (1943)]. The modulation or scattering of light by acoustic waves in optical fibers can be either harmful as in catastrophic stimulated backward Brillouin scattering [E. P. Ippen and R. H. Stolen, Appl. Phys. Lett. 21, 539–541 (1972)] or it can be put to practical use as has been attempted in devices such as acoustically mode-locked fiber lasers [Phillips et al., Opt. Lett. 14, 680–682 (1989)].
Hearing loss compensation from the worker viewpoint—Technical aspects
Authors: Bruce Robert D.
Published: October 2005

Workers view hearing loss and compensation for hearing loss from a very personal perspective. Although agencies administering compensation programs may have made significant efforts to take into consideration the total impact of hearing loss on an individual when standards were set for compensation, it is clear that there is a discrepancy between the amount allowed under existing compensation systems and the value that an individual places on his/her hearing. In an effort to understand the worker viewpoint, this paper will compare the loss of hearing (and its acoustic and nonacoustic impacts) with other accidental injuries in industry, review some of the existing compensation systems (state, federal, and private) for hearing loss and for other injuries, review the impairment concept as it relates to hearing loss, summarize the adjustments in compensation that have occurred during the past 20 years, and present a forecast for the future.