bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a thermoacoustic transducer for generation of underwater sound
Authors: Gabrielson Thomas B.
Published: October 2005

The standing-wave thermoacoustic driver is force limited rather than displacement limited and, as such, is capable of generating large displacements in the working fluid. An underwater transducer has been constructed that exploits this property to produce large volume velocity from a small radiating area. In this prototype, a thermoacoustic driver excites a gas-filled resonator coupled to the water. While the particle displacement in the water is much smaller than the peak displacement in the gas, this driver still produces a larger water displacement than would be obtained with a water-filled resonator coupled to the water. Test results of this transducer confirm the theoretical radiation efficiency [T. B. Gabrielson, J. Acoust. Soc. Am. Suppl. 1 85, S48 (1989)]. Because the thermoacoustic driver is force limited, the maximum acoustic pressure at the radiating surface is roughly one-tenth of the local cavitation threshold. Since the acoustic energy is produced by direct conversion from thermal energy, the potential exists for high overall energy density compared to battery-operated electroacoustic transducers. [Work supported by Office of Naval Technology.]
General formulation of thermoacoustics for stacks having arbitrarily shaped pore cross sections
Authors: Arnott W. Pat , Bass Henry E. , Raspet Richard
Published: October 2005

Previous theoretical results in thermoacoustics have been developed for stacks with circular pore [Rott, Adv. Appl. Mech. 20, 135–175 (1980)] or parallel slit [G. W. Swift, J. Acoust. Soc. Am. 84, 1145–1180 (1988)] geometries. A general linear formulation has been developed for gas-filled stacks having pores of arbitrary cross-sectional geometry. For compactness in the following, denote by F the functional form of the transverse variation of the longitudinal particle velocity. Generally, Fis a function of the transverse coordinates, frequency, pore geometry, the response functions and transport coefficients of the gas used, and the ambient value of the gas density. It is shown how one may obtain expressions for the acoustic temperature, density, particle velocity, pressure, energy flux, and work flux from knowledge of F. Results are displayed for the special case of stacks having rectangular pore geometries. This analysis will be used as an aid in the design of a thermoacoustic engine with a stack having square pore geometries. Comparison is made to capillary-pore-based porous media theories. [Work supported by ONR.]
Detection of interaural differences of level in multitone complexes
Authors: Dye R. H. , Stellmack M. A.
Published: October 2005

This study examined the effects of diotic components on the ability to detect interaural differences of level (IDL) at the center frequency (753 Hz) of a multitone complex. Threshold interaural differences of level (ΔIDL) were measured as a function of the number of components in the complex (3 and 7) and the frequency spacing (Δf) between components (10, 25, 50, 100, and 200 Hz). A 2IFC procedure was used, with the first interval always presenting a diotic complex and the second presenting either a diotic complex or one containing an IDL at 753 Hz. The left channel was incremented and the right decremented so that intracranial images were lateralized to the left. The starting phases of components were randomized between intervals. IDLs were expressed as the level difference at the target frequency. When compared to ΔIDLs obtained for 753 Hz in isolation, the effect of adding diotic components was to increase thresholds. Oddly, ΔIDLs were smallest at Δf = 10 Hz and increased to 7–9 dB at wider Δf's for both three- and seven-component signals. The data at wider Δf's are consistent with binaural interference effects that have been reported for detection of interaural delays. One explanation for the good performance at small Δf's is detection based on the decorrelation of the waveforms at the two ears that resulted when IDLs were presented. [Work supported by NIDCD and AFOSR.]
Lateralization of bands of noise: Effects of bandwidth and interaural differences of intensity, time, and/or phase
Authors: Buell Thomas N. , Trahiotis Constantine
Published: October 2005

Listeners indicated the intracranial position of narrow-band noises that varied in terms of interaural differences of intensity (IDI), time (IDT), and/or phase (IDP). Extents of laterality produced by IDIs depended greatly on particular combinations of bandwidth and the two other interaural cues. This dependence is inconsistent with the notions that IDIs serve as “weights” (scalars) or act via a (peripheral) time/intensity trade. For example, with narrow-band stimuli, changing IDI by only 3 dB could result in very large changes of laterality (including cases where the image moved from near one ear to near the other). The results will be discussed in terms of current, cross-correlation-based, models of binaural hearing that incorporate “pattern analysis” schemes. [Research supported by NIH and AFOSR.]
Principal components analysis of head-related transfer functions
Authors: Kistler Doris , Wightman Frederic
Published: October 2005

Free-field to eardrum transfer functions (HRTFs) measured on human subjects are rich in detail and almost certainly include spectral features (peaks and notches) that are unimportant for sound localization. In an effort to simplify the HRTFs and to model how the spectral features change with changes in source location, a principal components analysis (PCA) of the magnitude components of the HRTFs was conducted. PCA reparametrizes a set of interrelated measurements by reducing the redundancy in the original data while retaining as much as possible of the variation present in the data. HRTFs measured from both ears of each of four subjects at 266 source locations were analyzed. Each of the 532 HRTFs was represented by 150 spectral points (150–15 000 Hz). The results suggest that the original 150 spectral measures can be reduced to 5 measures, or components, that account for approximately 95% of the variance in the 532 HRTFs. The principal component weights were used to reconstruct the magnitude components of the HRTFs for each subject, ear, and source location. These magnitude components were combined with an estimate of the interaural delay at each source position to produce complex HRTFs. The perceptual adequacy of these PCA-derived HRTFs was verified by a sound localization experiment in which stimuli were synthesized by filtering noise bursts with the complex HRTFs. The resultant stimuli were presented to the original four subjects over equalized headphones. The results using PCA-derived HRTFs were indistinguishable from those obtained using stimuli synthesized from the actual HRTF measurements. [Work supported by NIH and NASA.]
Vibration control of distributed parameter systems using spatially distributed transducers
Authors: Hubbard James E.
Published: October 2005

A structured method is presented for the analysis and synthesis of active vibration control systems that may be applied to linear self-adjoint distributed parameter plants as represented by structural beam and plate components. The particular class of transducers applied for observation and control consist of distributed parameter sensors and actuators that may be represented as separable in space and time, i.e., degenerate distributed transducers. The method employs an energy based Lyapunov type of analysis and design technique that exploits plant symmetries and boundary integral representations to simultaneously control multiple plant modes, as well as target selected modes of vibration for plants incorporating nearly arbitrary boundary conditions. It is shown that the general Lyapunov formulation may be specialized to incorporate eigenfunction expansions that permit the interpretation of the Lyapunov controller in terms of the completeness with respect to sensor and actuator distributions. Implications of the latter formulation for the dynamic shape control of structures are highlighted.
Sound propagation in a shallow fresh-water aquaculture pond
Authors: Zagar Joe R. , Gilbert Kenneth E.
Published: October 2005

Measurements made as early as 1943 have shown that gassy freshwater sediments can be excellent reflectors of sound and behave acoustically as pressure-release surfaces. A simple propagation model is presented, based on bottom-reflection coefficients, that indicates one should expect strict mode propagation and sharp cutoffs in a horizontally stratified environment having gassy sediments. Continuous-wave measurements taken in a commercial aquaculture pond are presented and compared to the propagation model. The data show that, between 600 Hz and 3.0 kHz, a gassy sediment layer does behave as a nearly pressure-release surface. A simple mode-inversion technique is used to determine bottom-reflection coefficients for the sediments in the pond. Typical values for the bottom-reflection coefficient are found to be in the range of −0.85 to −0.95. These values, as well as the estimates of the sediment sound speed, are in excellent agreement with those found by others. Additional measurements taken in depths as shallow as 7 cm are presented. These additional data suggest that the acoustic properties of the aquaculture pond that was studied are typical of all shallow water ponds possessing gassy sediments. [Work supported by ONR and USDA.]
Seismic reflection velocity study of a gas-hydrate zone on the continental slope offshore South Carolina
Authors: Shipley Thomas H. , Wood Warren , Stoffa Paul L.
Published: October 2005

The acoustical and physical significance of bottom-simulating seismic reflections (BSR's) remains an observational challenge to geophysical methods. A common depth point (CDP) seismic reflection profile using a 240-channel, 6000-m array with a 177-liter (5- to 60-Hz) source was collected along the continental rise off the eastern U.S. where a BSR reflection is observed along a small portion of the line at about 3200-m depth. These data provide some velocity estimates in the vicinity of the BSR. The CDP data were transformed to the domain of vertical delay time and horizontal ray parameter for velocity analysis purposes. Even so, the resulting velocity profiles have limited vertical resolution (about 200 m) due to the distribution of interpreted sedimentary reflections used in the vertical delay time velocity analysis. Even with this admittedly low vertical resolution, the velocity above the BSR is at least 2000 m/s in an approximately 200-m zone, while the predicted velocity based on the extrapolation of regional gradients indicates that normal sediments should have a velocity of about 1850 m/s. A velocity of 2000 m/s suggests on average about a 50% substitution of hydrate in the pore spaces but the actual vertical concentration gradient is not constrained. This velocity anomaly also extends into other areas just above the theoretical phase boundary position, but where there is no detectable BSR. Beneath the BSR, even with the relatively low vertical resolution, a velocity decrease to about 1700 m/s is detected. This low velocity is observed only in zones with a detectable BSR. It is not observed beneath the theoretical phase boundary position elsewhere. This suggests that the origin of the BSR is not a simple boundary between hydrated and nonhydrated, normal sediments below. Initial investigations of amplitudes indicate significant increase in amplitude with offset. Full waveform, offset modeling of the data is underway.
Estimation of amounts of gas hydrate in marine sediments using amplitude reduction of seismic reflections
Authors: Dillon William P. , Lee Myung W. , Fehlhaber Kristen , Hutchinson Deborah R.
Published: October 2005

Gas hydrates (solid, crystalline water-gas mixtures) exist in sediments just below the seafloor. In seismic profiles, hydrate cementation creates zones of increased velocity and reduced amplitudes of stratal reflections (blanking). By using sediment velocities (estimated by an inversion method), known sediment porosity, and pure hydrate velocity, the amount of hydrate in the highest velocity and most intensively blanked sediments off the southeastern U.S. is calculated; this represents maximum hydrate cementation. To create seismic models of the range of possible blanking effects, ordinary, nonhydrated sediments across a reflecting boundary (caused by a porosity change) are “replaced” with this maximum-hydrate end member in various proportions. Three classes of blanking are defined; class boundaries represent a change in reflection amplitude by a factor of 2, and the classes are relatable to the amounts of hydrate in bulk sediment. In order to estimate the amount of hydrate, these classes are mapped in a grid of reflection profiles processed to preserve relative amplitude, and the first semiquantitative estimate of gas hydrates in deep-sea sediments is produced. [Work supported by DOE.]
Biogenic gas in shallow water sediments as indicated by high-resolution seismic records
Authors: Lambert Douglas N.
Published: October 2005

A 15-kHz narrow-beam (12°) seismic system, designated the Acoustic Seafloor Classification System (ASCS), has been used to identify areas of shallow sea floor gassy sediments. The ASCS was designed to remotely classify seafloor sediments by quantitatively and qualitatively measuring the echo return amplitude and pulse character in ten adjustable time windows that correspond to depth increments in the sediment. In addition, the ASCS produces a very high-resolution analog seismic record of the upper few meters of the seafloor on which the amplitude of the echo return (echo strength) for each of the depth increments is also indicated. This unique combination of data provides an excellent means of identifying sediments containing biogenic gas. Examples of identified gassy sediments shown on ASCS records range from a “speckled” appearance indicating random and isolated small gas concentrations to “white outs” that indicate large gas concentrations that completely attenuate the acoustic signal. Other records show highly reflective sediment layering that is due to a concentration of gas along bedding planes alternating with large pockets of 1ow-reflectivity, degassed sediment that appears to have been “homogenized” by gas movement. These degassed sediment pockets are occasionally accompanied by vertical gas escape conduits seen in the sediment and by the presence of vertical reflectors in the water column indicative of escaping gas bubbles.
Ten years of newer auditorium acoustics measurements
Authors: Bradley J. S. , Halliwell R. E.
Published: October 2005

This paper reviews progress in making newer types of auditorium acoustics measurements over the past 10 years. All of the newer measures require impulse responses to be obtained and the merits and limitations of various measurement approaches will be discussed including the type of source, receiver, and processing that is used. Objective descriptions and the subjective relevance of the various types of newer measures will be reviewed including both monaural and binaural quantities. Four generations of measurement systems will be described including the special problems associated with measuring inter-aural cross correlation coefficients. Finally the questions of accuracy and repeatability will be mentioned along with some discussion of future developments and problems to be solved.
Measurement of impulse response and its applications in room acoustics
Authors: Tachibana H. , Yano H. , Hidaka Y.
Published: October 2005

Impulse response includes almost all physical information of a linear system and it is also very important in room acoustics. Fortunately, owing to the recent development of digital signal processing techniques and instrumentation, it has become possible to make a precise and convenient measurement of impulse responses in rooms. In this paper, the practical techniques for this kind of measurement including scale model studies are introduced. For the measurement in real auditoriums, a sweep pulse is radiated many times from a dodecahedral omnidirectional loudspeaker and the responses are recorded on a DAT through an omnidirectional microphone or a dummy head system. From the recorded responses, impulse responses are obtained by synchronous averaging and deconvolution techniques. In scale model experiments, impulse responses are measured by using a spark discharge source and a scale model dummy head microphone. From the impulse responses measured in such ways, not only various room acoustic quantities are derived but also the sounds including the room response can be synthesized by making convolutions between the impulse responses and arbitrary dry source signals. This technique is effectively used for subjective evaluation of room acoustics. Some examples of the experimental results for real and scale model auditoriums will be demonstrated.
Prediction of room acoustical parameters
Authors: Gade A. C.
Published: October 2005

During a 6-yr period, detailed room acoustical measurements have been carried out in 35 halls in Denmark and in other European countries. By subjecting these data to statistical analyses, it has been possible to confirm old and establish new relationships between design variables and the position-averaged acoustical data. The results are presented in the form of linear, multiple regression formulas that may be used to predict the values of the newer measures of level, clarity, spaciousness, and musicians' conditions on the orchestra platform in halls with given RT and geometry.
Applications of very high-energy density electrostrictive ceramics for underwater projectors
Authors: Ritter A. P. , Pilgrim S. M. , Kuhn P. , Winzer S. R. , Sewell J.
Published: October 2005

Performance of Navy sonar transducers is limited by the inherent energy density of the driver material—especially for those size-constrained applications that require very high source levels and/or very low frequencies. Ultimately, the maximum sound-pressure level will be limited by the amount of power that can be generated from the ceramic driver at its maximum engineering limit of 10–15 V/mil (∼0.5 MV/m). Incremental improvements in transducer performance may be possible through design refinements, however, revolutionary large-scale improvements require new approaches to overcome the basic PZT material limitations. Electrostrictive ceramic materials, such as the PMN-based compositions being developed at Martin Marietta Laboratories, have energy density values an order of magnitude higher than Navy PZT's and therefore could significantly improve transducer performance (i.e., maximum attainable source level) if substituted for PZT in conventional transducer designs. Transducer model calculations for comparable PZT- and PMN-driven transducers show ∼ 10-dB gain in the transmitting voltage response for the PMN transducer. These model predictions have been verified by experimental data obtained under a joint Martin Marietta/Navy materials development program.
A unified reciprocity method for two basic types of vibration calibrators
Authors: Ge Li-Feng
Published: October 2005

Two basic types of vibration calibrators, i.e., electrodynamic-type and piezoelectric-type standard vibration generators, can be described by a uniform dynamic model and equivalent circuit [L.-F. Ge, J. Acoust. Soc. Am. 86, 210–214 (1989)]. The calibration factor of both types, which is defined as a ratio of the mechanical output (velocity or acceleration) to the electrical input (current or voltage), viz., the transmitting current or voltage response, is given and formularized by a uniform equation: Ti = (CZ + D)−1(m s−1/A) or Te = (AZ + B)−1(m s−1/V), where Z is the mechanical lead impedance and A, B, C, and D are the reciprocity network parameters of the calibrator. The former is suitable for an electrodynamic-type calibrator, because the thrust of the shaker depends on input current on the basis of the Faraday's law; the latter is suitable for a piezoelectric-type calibrator, since the voltage change leads to motion of the table according to the piezoelectric effect. Measurements performed on piezoelectric calibrators have obtained accurate calibration results at high-frequency range; experiments on a commercial electrodynamic shaker at 1 kHz have also shown that the method is attractive.
Community aircraft noise assessment to determine structural noise attenuation
Authors: Draper David , Young Henry
Published: October 2005

A community aircraft noise assessment was conducted for the City of New York for a major waterfront residential development (7000–8000 units) proximate to Kennedy International Airport in Queens. The development site lay beneath one flight path and immediately to the west of a second. Characterization of the site for aircraft noise by monitoring alone was difficult since the overflying runway was typically used during inclement weather during which monitoring conditions were at their worst. Thus, a combination of monitoring and modeling was conducted to determine the noise exposure of proposed structures and open space. Aircraft noise was monitored at three locations on the site. Modeling of a worst case scenario was performed using the aircraft noise database from the integrated noise model (INM). The model was “calibrated” by simulating specific aircraft flights, predicting to monitored locations and comparing the predicted and monitored noise levels. These predicted levels were used to determine the degree of structural noise attenuation required to meet New York City's interior residential noise requirements of 45 dBA.
Nonlinear pulsations of cavitation vapor bubbles near resonance
Authors: Nicholas R. Edward , Finch Robert D.
Published: October 2005

Studies of the nonlinear pulsations (and sometimes collapse) of cavitation bubbles near resonant size in an ultrasonic field were performed through a numerical solution of nonlinear equations describing the motion of a spherical vapor bubble. A number of plots are presented showing bubble pulsations. These plots show pulsations at the driving frequency with rich harmonic content but also show nonchaotic pulsations at frequencies below the driving frequency as the bubble grows through resonant size. The frequencies observed below the driving frequency seem unrelated to the driving frequency and instead vary with the amplitude of the ultrasonic field.
Signal processing to extract transient microcavitation signals from noise
Authors: Xu Qihong , Holland Christy K. , Apfel Robert E.
Published: October 2005

The time history of the scattered signal from transient microcavitation is different from the signal scattered by other targets, which constitutes most of the noise. The backscattered signals from transient microcavitation (bubbles of micron scale that last on the order of microseconds) are both frequency modulated and amplitude modulated; therefore, a Doppler technique can be one alternative to the detection of transient cavitation, which takes advantage of the fact that the signal is frequency modulated. Numerical simulations of these processing techniques will be presented. [Work supported by NIH Grant 5RO1CA39374.]
Experimental studies of the enhanced effective nonlinearity parameter B/A of a bubbly medium
Authors: Wu Junru , Zhu Zhernin
Published: October 2005

It has been known for some years that the presence of bubbles may enhance the nonlinearity parameter B/A of a medium. Two distinct physical mechanisms are believed to be involved. The first one is due to bubble nonlinear oscillations; bubbles are driven by an acoustic wave near resonance frequency. The second one is due to static properties of a bubbly medium. The effective nonlinearity parameter B/A of water containing a three-dimensional ensemble of randomly distributed uniformly-sized trapped cylindrical bubbles was measured. The measured effective B/A for the system is of the magnitude of 104 to 105. The experimental results also suggest that the dramatic enhancement of the effective nonlinear parameter B/A is mainly due to the nonlinear resonance oscillation of the trapped bubbles. [Work supported by the NIH via Grant No. CA42947 and by the NSF and Vermont Epscor.]
Catalase and cysteamine inhibit indirect sonochemical effects of capitation on cellular DNA
Authors: Miller D. L. , Thomas R. M. , Frazier M. E.
Published: October 2005

Ultrasonic cavitation can indirectly cause cellular bioeffects due to the production of toxic sonochemicals. Phosphate buffered saline (PBS) was exposed to 1.61-MHz ultrasonic cavitation at 20°C in a rotating-tube exposure system to build up sonochemical products. Single strand DNA breaks (SSBs) were then induced by treating Chinese hamster ovary (CHO) cells with the cavitated PBS for 30 min on ice. This indirect effect could be explained by the action of cavitation-generated hydrogen peroxide (e.g., up to 16/μm after 30-min exposure) in the PBS. Adding catalase to the cavitated PBS before cell treatment eliminated the effect. Tests with hydrogen peroxide showed that 16 μm H2O2 treatment for 30 min on ice was as effective as 1 Gy of gamma rays in producing SSBs. The SSB effect of H2O2 was reduced by addition of the radical scavenger cysteamine to the cells before treatment. These results indicate that DNA effects from ultrasonic cavitation can occur indirectly without the highly destructive direct interaction of cells and cavities. [Supported by PHS Grant CA42947 awarded by the National Institutes of Health.]
Middle ear muscle effects during gunfire noise exposures
Authors: Price G. Richard
Published: October 2005

A previous study using evoked response audiometry in anesthetized cats [Price and Wansack, J. Acoust. Soc. Am. 86, 2185 (1989)] showed that an impulse with its peak energy in the 4.0-kHz region was surprisingly hazardous. The surprisingly great effect could have been due to the anesthesia itself or the anesthesia could have prevented middle ear muscle contractions (normally not thought to affect the ear's response to gunfire). In order to help discriminate, three groups of ten cats were exposed to 50 midrange impulses at 145 dB peak, fired 3–5 s apart. Group I was anesthetized at the time of the exposure, and groups II and III were not; however, group II was anesthetized for threshold testing immediately after exposure (measured by evoked response audiometry at 2.0, 4.0, 8.0, and 16.0 kHz). Mean threshold shifts at 4.0 kHz 20–30 min post-exposure were 72 dB for group I and 19 dB for group II. Permanent threshold shifts were 44 dB for group I and 5.9 and 5.3 dB for groups II and III, respectively. These data suggest that the anesthetic itself probably does not potentiate the exposure and that the middle ear muscles should be suspected as being protective in any waking cat.
The effect of salicylate on cochlear outer-hair cell usmoregulation
Authors: Chertoff Mark E. , Brownell William E.
Published: October 2005

In vitro experiments have demonstrated that cochlear outer-hair cells (OHCs) can detect an increase in the extracellular osmotic pressure and, in response, regulate their internal pressure. Salicylate exposure reduces the turgor in electrically stimulated OHCs suggesting an interference with turgor regulation. Cytoplasmic pressure was determined by placing OHCs in a phosphate-buffered saline (PBS) solution and increasing the osmotic pressure by dripping a hyperosmotic solution (PBS plus 130 mM raffinose; Osmol = 410–440 mmol/kg) into the chamber. The raffinose perfusion was stopped when cell volume decreased and the osmolarity of the chamber was measured with a vapor pressure osmometer. The cytoplasmic pressure of OHCs in the PBS was 16.1 mmol/kg (±5.7) greater than the PBS. When OHCs were exposed to a PBS solution containing an extra 10 mM NaCl or either 5 or 10 mM Na-salicylate, the pressure difference between the cytoplasm and the bathing medium was decreased to between −4 to 6 mmol/kg. After 10 min, the pressure difference increased to 11.3 mmol/kg (±5.2) for the NaCl solution and 10.3 mmol/kg (±4.16) for the salicylate solution. [Supported by ONR and NIDCD.]
A biophysical model of auditory-nerve responses to acoustic transients
Authors: Mountain David C. , Hubbard Allyn E. , Zagaeski Mark
Published: October 2005

Acoustic transients are an important part of the natural acoustic environment as well as in acoustic communication signals such as human speech. The response to acoustic transients from a biophysically based simulation of the auditory periphery that includes models of cochlear mechanics, inner hair cell (IHC) receptor potentials, and neurotransmitter release at the auditory nerve (AN) afferent synapse were studied. The mechanical model is a 300-section, one-dimensional model of the basilar membrane (BM). Each section of the mechanical model drives an inner hair cell that includes a three-state transduction channel model and a two-state voltage-dependent channel model. The afferent synapse models include an inactivating three-state calcium channel and a single compartment vesicle release model. The ensemble activity as a function of time for each level of the model (BM, IHC, AN) was visualized through the use of a color-raster display by representing the output amplitude of a given level with color. Transient stimuli were synthesized by adding together various simple signals: clicks, short-duration tone pips, exponentially damped sinusoids, and continuous noise. The transients produced distinctive spatial-temporal response patterns even in conditions of poor signal-to-noise ratios. This robustness of the spatial-temporal patterns appears to be due to a combination of the spectral representation created in the cochlear mechanics and the adaptation present in the auditory-nerve synapse. [Work supported by NIH.]
Comparison of continuous and discontinuous models of heterogeneity in the propagation of transient planar stress waves
Authors: Ginsberg Jerry H. , Xiao Xiang
Published: October 2005

In the characteristic differential equations governing propagation of linear one-dimensional waves through heterogeneous media, the only properties of significance are the sound speed c and the acoustic impedance ρc. The former occurs in the differential equations governing the (curved) characteristics, while the latter appears in the differential equations governing the evolution of particle velocity and strain along the characteristics. One might attempt to approximate the spatial variation of these material properties in a periodic array of homogeneous layers by smooth interpolating functions. An implicitly stable finite difference representation of the characteristic equations is used in the present work to consider propagation of a transient wave through a bi-material sequence of layers of thickness L. Waveforms are compared to those obtained from a model in which the layer properties are taken to vary sinusoidally, such that ρ = ρ0[1 + ε sin(πx/L)] and c = c0[1 + δ sin(πx/L)]. Of particular interest is the case where the wavelength is L, which, according to Floquet theory, represents a condition of uncertain stability for steady-state waves, but which leads to maximum interference for a harmonic transient wave in the sinusoidally varying medium.
Alumer: A “rigid,” acoustically transparent, composite material
Authors: Dubbelday Pieter S. , Eaggleston Forrest M.
Published: October 2005

The elastic properties of foamed aluminum have been reported in an earlier presentation [J. Acoust. Soc. Am. Suppl. 1 88, S22 (1990)]. When the open-cell structure of this material is impregnated with a light elastomer, a composite material results that has a density and dilatational wave speed close to that of water. The Young's modulus and bulk modulus of this “Alumer” material have been measured, as a function of frequency, for various combinations of foamed aluminum, characterized by relative density and pore size, and polyurethane. The aluminum matrix imparts stiffness to the material, for use as an acoustically transparent backing plate or other structure. The elastomer may be chosen to give more or less absorptive properties to the material. [Work supported by the Office of Naval Research.]
Modeling of impact response in moving chains
Authors: Hayek Sabih I. , Liu Shyi-Ping , Wang K. W. , Chen Francis H. K.
Published: October 2005

A significant contributor to noise from chain drives can be traced to the impact of a roller chain on a sprocket. A model is developed to estimate the impact impulsive load generated by an axially moving roller chain on a sprocket during the meshing process. Due to the dependence of the impulsive impact force on the velocity of the chain before impact, the impulsive load at each impact varies from impact to impact. The meshing process then produces nonperiodic and nonuniform impulsive impact forces. The model is used to analyze the response of the roller chain after each impact. The chain response model is being developed to increase the understanding of the noise generated from engine drive chains. [Work supported by General Motors Corporation.]
Matched asymptotic expansions solution for low-frequency sound radiation from fluid-loaded, baffled plates
Authors: Kauffmann Christiaan
Published: October 2005

The method of matched asymptotic expansions is used to investigate sound radiation from fluid-loaded, baffled, thin elastic plates of dimensions small compared to the acoustic wavelength, i.e., for k0a ≪ 1, where k0 is the acoustic wave number and a is a typical size of the plate. In this low-frequency region both near-field quantities (plate response and surface pressures) as well as far-field radiation properties are obtained. At low frequencies, the plate radiates sound like a monopole, the strength of it being proportional to the net volume velocity of the plate. The consistency of the method is tested by power balance considerations that are shown to be valid up to leading order. [Work supported by the TNO Institute of Applied Physics, Delft, The Netherlands.]
The control and kinematics of human jaw movement
Authors: Ostry David J. , Flanagan J. Randall , Feldman Anatol G.
Published: October 2005

The kinematics of two-dimensional human jaw motion are presented based on x-ray microbeam recordings. The relationship between jaw translation and rotation is described and experimental records are compared with simulations based on the equilibrium point hypothesis (λ model). In general, jaw rotation and translation were found to start and end simultaneously and straight line paths were observed when rotation was plotted against translation. Several manipulations suggest that jaw rotation and translation are separately controlled. For example, when jaw movements in speech were examined, the slope of the relationship between rotation and translation varied with the consonant but did not depend on the vowel or speech rate. The kinematic patterns of jaw motion are well accounted for by the λ model. The model demonstrates that separate central commands can be defined associated with jaw translation, jaw rotation, and coactivation of muscles without motion. Central commands may be superimposed to produce combinations of rotation, translation, and coactivation. Empirical patterns can be captured by the model under the assumption of simple constant velocity shifts in equilibrium governed by central commands.
Translating pellet positions into constriction features
Authors: Ahalt Stanley , Krishnamurthy Ashok , Jung Tzyy-Ping , Beckman Mary E. , De Jong Kenneth , Lee Sook-hyang
Published: October 2005

Tongue constriction features can be estimated from sagittal x-ray pictures of the tongue surface and vocal tract wall. However, such records cannot be obtained in quantity, making them unsuitable for testing models such as Stevens's quantal theory. The x-ray microbeam allows larger data sets, but records flesh points rather than surfaces. This paper presents an algorithm for relating the two representations. The vocal tract wall is estimated from whole-head scans and a palate trace. Pellet positions are then “warped” into a Cartesian space where location along the tract and distance from it are the x and y values. The algorithm has been applied in a replication of Perkell and Nelson's test of quantal theory using principal component analysis. Quantal theory predicts that the pellet closest to the constriction site will show least variability, and that the most precision will be in the dimension perpendicular to the vocal tract wall for “quantal” vowels such as /i/. In the warped space, then, the principal component of variation for the relevant pellet for these vowels should be parallel to the x axis. This prediction is borne out. [Work supported by the NSF.]
Objective evaluation of vowel pronunciation
Authors: Bakkum Mark J. , Plomp Reinier , Pols Louis C. W.
Published: October 2005

Usually pronunciation is evaluated subjectively by listening. The aim of this research project is to obtain an objective measure of the quality of pronunciation. All 15 Dutch monophthongs and diphthongs spoken by 24 males (deaf, foreign, and native Dutch norm speakers) were spectrally analyzed. The digital, real-time analysis system consisted of 16 bandfilters according to the critical-band model. Besides level and speaker normalization, time averaging was also applied so that all vowels were determined by a single point in a 16-dimensional spectral space. By principal components analysis, the number of dimensions was reduced, thus making a plain visualization possible. The feasibility of the objective evaluation has been investigated by considering to what extent the spectral information, as expressed in various distance measures, does give an adequate description of subjective judgments of the vowels, as obtained by experienced listeners. The overall scores (averaged over 15 vowels, after PCA) show a correlation coefficient of 0.97. Correlations per vowel are lower, but significant in nearly all cases. [Work supported by Netherlands Organization of Scientific Research (NWO) and Institute for the Deaf, Sint-Michielsgestel.]
Effects of emphatic stress and speaking mode on articulatory organization
Authors: Bunnell H. Timothy , Polikoff James
Published: October 2005

An adult male talker recorded multiple repetitions of short nonsense sentences. Each sentence was of the form “A huCl ate a C2uffle,” where C1 and C2 were from the set {/b/,/d/,/g/}. Sentences containing all nine combinations of C1-C2 pairings were recorded in several speaking modes: CLEAR, CONVERSATIONAL, STRESS1, and STRESS2. The latter two conditions entailed production of the sentences in conversational mode, but with emphatic stress on the syllable containing either the first (STRESS1) or the second (STRESS2) variable consonant. These materials were recorded at the University of Wisconsin Microbeam facility and include both acoustic data and tracings of the trajectories of flesh points on the tongue, lips, and jaw. Analyses of the acoustic and articulatory data suggest that local effects of stress on consonant articulation are similar to those of clear speech. The largest acoustic and articulatory differences were observed for consonants in syllable final position. The various significant articulatory effects of stress and speaking mode will be compared to perceptual measures of consonant intelligibility.
Formant trajectories in the speech of normally articulating and misarticulating children
Authors: Forrest Karen , Tsao Ying-Chiao , Weismer Gary , Elbert Mary , Dinnsen Daniel A.
Published: October 2005

In previous papers, it has been shown that analysis of obstruent spectra can be a powerful way to quantify and classify patterns of misarticulation in children. The focus on obstruent spectra fits in with the established idea that a problem with obstruent production is the primary reason why a child may be classified as having an articulation problem, but the lesson from adult articulatory disorders [such as apraxia of speech: see R. Kent and J. C. Rosenbek, J. Speech Hear. Res. 26, 231 (1983)] is that the prominence of obstruent articulatory problems should not obscure the fact that much of the nature of the articulatory deficit can be revealed by examination of vocalic formant trajectories. A formant trajectory analysis of five normal and five misarticulating children will be reported, and the way in which the analysis may bear on the characterization of childhood articulatory/phonological disorders will be described. [Work supported by NIH.]
Timing and displacement in the articulation of prominence
Authors: de Jong Kenneth
Published: October 2005

Macchi (1985) found that linguistic stress expands the degree of jaw opening in vowels and closing in obstruants. Edwards et al. (1991) report that greater accentual prominence is achieved by initiating closing movements later relative to opening movements, thus allowing the jaw to reach a lower position. This paper relates the measures of prominence used in the two studies in a corpus of x-ray microbeam data. Syllables with labial and alveolar consonants and high and mid vowels varied in stress from full but unaccented to stressed (prenuclear accented) to most stressed (nuclear accented). Completed analyses of jaw movement show differences among all three stress levels in the amount of jaw lowering and raising. One subject, in addition, expands the duration of the more prominent items by changing the relative timing of opening and closing jaw gestures, suggesting that multiple strategies are used to increase prominence. The paper will also report on presently incomplete analyses of tongue-movement trajectories.
Inverse methods and detection and estimation theory
Authors: Baggeroer Arthur B.
Published: October 2005

Inverse methods have long been used to determine models for geophysical processes. These methods are closely related to the topics of parameter estimation and system identification in the detection and estimation theory literature, yet results from this area are seldom exploited in inversions. System concepts such as controllability and observability are important in specifying an inverse operator; threshold concepts are needed when parameters are nonlinearly related to observables and/or perturbations are employed; yet they are seldom used. More important, there are many bounds upon the performance of parameter estimators that can be applied to inverse problems in geophysics. This presentation will discuss how methods in system theory and detection and estimation can be applied to geophysical inverse problems. [Work supported by ONR.]
On the use of ocean dynamics to improve acoustic tomography estimates
Authors: Chiu Ching-Sang , Miller James H.
Published: October 2005

The resolution of maps obtained from ocean acoustic tomography is largely determined by the trajectories of the acoustic multipaths connecting sources and receivers. Since the distribution of crossings of the multipaths is nonuniform, tomographic resolution generally varies in space. Thus, depending on the characteristics of the sound channel and the scales of the ocean variability, “pure acoustic maps” can be inaccurate in those locations where spatial resolution is poor. In order to improve the resolution of the maps, it is necessary to add independent information to the inverse problem. In a computer experiment, the improvement in the tomography maps resulting from the incorporation of ocean dynamics is assessed. Here, the integration of dynamical information into tomography is accomplished using a Kalman filter. For the assessment, the maps obtained by assimilating synthetic tomography data into a nonlinear, quasigeostrophic ocean model are compared with the “pure acoustic maps.” Moreover, the sensitivity of the Kalman filter output to the inexact specification of ocean dynamics is examined.
Violin admittance measurements using a one-dimensional mass-louding technique
Authors: Yoder Levon L.
Published: October 2005

The input admittance of a violin can be determined from load/no-load load measurements of the vibration velocity of the bridge [Weinreich and Yoder, J. Acoust. SOC. Am. Suppl. 1 81, S83 (1987)]. In the most successful of these experiments [Boutilion, Weinreich, and Michael, J. Acoust. Soc. Am. Suppl. 1 84, S179 (1988)], the load was a mass attached directly to the bridge. Since the bridge motion is three dimensional, the load impedance is also. The problem involved a 3 × 3 admittance matrix and required nine load/no-load measurements. This was accomplished by using three different acoustic irradiating fields and measuring the vibration velocities in each of the three directions. This paper presents a method of applying a one-dimensional load to the bridge by attaching a cylindrical mass to one end of a long sewing needle and immersing it in an air column to form a surrounding air cushion and to hold it upright. The data acquisition and analysis are reduced to three independent problems requiring only one acoustic field and separate mass loading for each direction. The admittance can be studied as a problem in one, two, or three dimensions. Experimental results in two dimensions will be presented.
Acoustics of a yangqin
Authors: Tsai Jianming , Rossing Thomas D.
Published: October 2005

The yangqin is a Chinese hammered dulcimer with a trapezoidal soundboard. It is played with two bamboo hammers and is used as a solo instrument as well as in Chinese traditional music ensembles. The instrument we studied, approximately 1 m by 0.5 m, has 54 notes coveting a 4-octave range G2 to G6 (98–1568 Hz). It has five bridges and a total of 125 strings with sliders and rollers for fine tuning and for rapid modulation. The soundboard, which is crowned to a height of 4 cm in the center, is supported by seven unequally spaced transverse ribs. The ribs also divide the body into eight air chambers, which are connected by four or five holes (2.8 cm in diameter) through each rib; it is not clear whether these air chambers play an important role in the acoustics of the yangqin, however. Vibrational modes of the soundboard in the frequency range 100–700 Hz have been studied by impact modal analysis as well as by scanning with an accelerometer as the soundboard is driven by a small shaker. Nodal lines tend to follow the stiff transverse ribs. Model shapes indicate that the transverse stiffness is substantially greater than the longitudinal stiffness in the braced soundboard. The impedance at most points on the bass bridges shows a maximum around 100 Hz and then fails off at roughly 6 dB/octave. The impedance on the treble bridges, on the other hand, reaches a broad maximum around 2 kHz and falls off quite slowly with frequency, at least up to 5 kHz.
Numerical modeling of guitar radiation fields using boundary elements
Authors: Brooke Matthew , Richardson Bernard E.
Published: October 2005

Boundary element (BE) methods have been used to supplement an existing numerical model of the classical guitar. This model computes, from fundamental parameters, the transfer between the plucking force at a point on the string and the acoustic pressure at the listening point. Structural mode shapes are determined from finite element (FE) analysis. The computed surface velocities are then used to determine the coupling between the top plate and strings and also the coupling between the top plate and Helmholtz air resonance of the body cavity. The resultant acoustic radiation is calculated using the BE formulation, in which the entire surface of the guitar body is divided into boundary elements with surface velocities being specified over the top plate and zero elsewhere (to simulate “rigid” back and sides). The computed radiation fields will be compared with measurements on real systems. Future work will involve coupling of the FE and BE methods in order to account for fluid loading.