bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of the 2f1−f2 difference tone in human subjects and in a hardware cochlear nonlinear preprocessing model with active feedback
Authors: Harris Frances P. , Zwicker Eberhard
Published: October 2005

Level and phase of the 2f1−f2 combination tone were measured in five human subjects using two methods: Psychoacoustic cancellation and direct cancellation of the distortion-product emission (DPE) measured in the ear canal. A probe assembly, composed of two earphones and a microphone, was placed in the subject's ear canal for the delivery of stimulus tones, f1 and f2, and the 2f1−2f2 cancellation tone and for measurement of DPEs. Frequency of f1 was 1620 Hz with f2 either 1800, 1851, 1944, or 2052 Hz. Level of f1 or f2 was varied in 5-dB steps from 70–30 dB SPL for each frequency pair. Data from these subjects were compared with similar data measured using the hardware model. DPE cancellation levels were 40–50 dB below comparable psychoacoustical cancellation levels for both data sets, however absolute differences varied by frequency separation and level of the primaries and by method. Dependencies of the level and phase of 2f1−f2 on the frequency separation and level of the primaries were similar for all three methods.
A modified ko-independent parabolic equation incorporating range refraction
Authors: Schurman I. W. , Siegmann W. L. , Jacobson M. J.
Published: October 2005

Parabolic equations currently in use to predict acoustic intensity require a judicious choice of the reference wavenumber ko. A new parabolic equation (PE) is presented here which is independent of ko and capable of handling large variations in the index of refraction. This equation is similar to, and ostensibly simpler than, an earlier range refraction PE (RAR-EPE) reported recently by Tappert and Lee. The modified refraction parabolic equation (MOREPE) is obtained by a transformation approach, and operator and multiscale formalisms are also described to validate the equation. Principal properties of MOREPE are discussed. An exact solution with only range variation in sound speed is presented to illustrate differences between standard PE and MOREPE. Propagation examples in range-independent environments demonstrate close agreement between MOREPE and standard PE, while examples with strong range dependence exhibit significant differences between the two equations in their predictions of acoustic intensity. [Work supported by ONR.]
Finite amplitude acoustic propagation in a periodic structure
Authors: Bradley Charles E.
Published: October 2005

Linear wave propagation in periodically inhomogeneous media is characterized by the division of the frequency spectrum into regions known as passbands and stop bands, the waves (called Bloch waves) associated with which are propagated and attenuated, respectively. A dispersion relation is derived for zeroth-order propagation in a rectangular waveguide, which is periodically loaded with rigidly terminated side branches. This dispersion relation exhibits both the characteristic band structure and, in the low-frequency limit, Korteveg-DeVries dispersion. For the case of finite amplitude pure tone excitation, a quasilinear analysis shows that parametric upconversion is effectively blocked regardless of whether the second harmonic frequency resides in a passband or a stop band, though the blocking mechanisms are fundamentally different. A 25.4-mm×38.1-mm×6-m waveguide was built with 38.1-mm-deep side-branches at 0.1 m intervals. Early measurements show dispersion, band structure, and second harmonic behavior qualitatively similar to analytic and numerical results. Possible applications in the study of traveling wave amplification and cnoidal wave/soliton propagation are investigated. [Work supported by Office of Naval Research.]
Effects of random-bottom topography on the parabolic-approximation determination of acoustic intensity
Authors: Mohrmann K. B. , Jacobson M. J. , Siegmann W. L.
Published: October 2005

A model is presented for stochastic variations about a horizontal mean water-bottom interface below a shallow ocean channel. A pressure release surface and a rigid bottom are taken as boundary conditions for solutions of a parabolic approximation to the wave equation, when sound speed is depth dependent. A perturbation approach is used to generate a sequence of differential problems, the perturbation parameter being a measure of the deviation in depth of the random bottom from its mean. Green's functions are used to represent the solution to the first two differential problems. The mean and variance of received intensity are then obtained in terms of statistics of the random bottom. In an example, an isospeed channel is treated, and the ratio of the mean and standard deviation of intensity is expressed in terms of the autocorrelation lengths and variances of the random processes representing bottom height and slope variations. The behavior of this ratio is described as range and bottom statistics are varied. Further, the effect on intensity of bottom depth deviations and slope variations are compared. [Work supported by ONR.]
Exponential growth of multipaths under chaotic conditions in a simple deterministic range-dependent waveguide
Authors: Tappert F. D. , Brown M. G. , Goni G.
Published: October 2005

Propagation is considered in a simple range-dependent waveguide consisting of a constant sound-speed gradient, g, overlying a reflecting sinusoidal bottom. Let a and R denote the amplitude and wavelength of the bottom sinusoid. Previously it has been shown [F. D. Tappert and M. G. Brown, J. Acoust. Soc. Am. 83, 537 (1988)] that when γ = 4π2ac0/Rg exceeds 0.97 ray trajectories exhit global chaos. Under such conditions, ray trajectories have an extreme sensitivity to initial conditions and environmental parameters; they are free to wander without bound in angle-depth space. Under such conditions it is shown that the number of eigenrays connecting a source and receiver on the bottom grows exponentially as the separation between them increases. Meanwhile, the average intensity of the eigenrays decays exponentially. The exponential growth and decay rates are compared to the average Lyapunov exponent for the ray trajectories. These results vividly demonstrate that under chaotic conditions predictability using ray theory is unattainable.
Effect of subbottom roughness on VLF acoustic propagation from a seamount
Authors: Chin-Bing Stanley A. , Murphy Joseph E.
Published: October 2005

Recently, two range-dependent ocean acoustic propagation and scattering models based on the finite-element (FE) method have been developed: the Finite-element Full-wave Range-dependent Acoustic Marching Element (FFRAME) mode and the hybrid finite element/parabolic equation PE-FFRAME model [J. E. Murphy and S. A. Chin-Bing, J. Acoust. Soc. Am. Suppl. 1 84, S89–S90 (1988)]. These models have been applied to simulate the effects of subbottom roughness on the very-low-frequency (VLF) propagated acoustic field at both near- and long-range distances from a “seamount.” The “seamount” is simulated as an axisymmetric feature with gradual varying slope. Examples are presented that show the value of using these full-wave models (FFRAME and PEFRAME) over the usual one-way parabolic equation model when examining such underwater features. [Work supported by ONR and NORDA.]
A new split-step algorithm for solving acoustic propagation problems
Authors: Berman David H. , Wright Evan B. , Baer Ralph N.
Published: October 2005

A new equation is proposed to mimic the one-way aspects of the Helmholtz equation. This new equation allows a split-step solution like the conventional parabolic equation (PE) does, and thus it can be solved equally fast. Moreover, unlike the PE, the rays associated with high-frequency solutions of this equation are exactly the rays of the Helmholtz equation (even at high angles) for weakly range-dependent environments. For low-angle propagation, the equation reduces the conventional PE, and hence phases in this regime are given correctly. For what are now standard test cases, without severe bottom interaction, this new split-step algorithm performs as well or better than more complicated, and hence slower, one-way wave equation algorithms. [Work supported by ONR.]
Propagation modeling in a three-dimensional wedge using ray theory
Authors: Westwood Evan K.
Published: October 2005

A useful model for shallow-water, sand-bottom coastal regions is the three-dimensional (3-D) wedge. Unlike the 2-D wedge, source and receiver may lie across the slope from each other, rather than directly upslope or downslope. Acoustic propagation in the 3-D wedge is modeled using an extension of the complex ray method developed for the flat waveguide and the 2-D wedge [E. K. Westwood, J. Acoust. Soc. Am. Suppl. 1 83, S79 (1988) and 84, S90 (1988)]. However, due to the phenomenon of horizontal refraction (the bending of multiply reflected rays when viewed from above), each ray field in the 3-D wedge must be expressed as a plane wave integral over two angular variables, rather than just one. Evaluation of the integrals involves finding complex saddle points, each of which consists of a pair of angles giving the eigenray direction. For rays that are reflected near the critical angle, numerical integration along the path of steepest descent must be performed; otherwise, a first-order saddle point approximation may be used. The nature of the field in the 3-D wedge will be discussed, and possible benchmark problems will be suggested. [Work supported by ONR contract N00014-87-K-0346.]
A method for controlling radiation from composite plates using embedded active fibers
Authors: Naghshineh Koorosh , Koopmann Gary H.
Published: October 2005

A novel method of active control is proposed that focuses on controlling the acoustic radiation of a composite plate by directly altering its material properties. By integrating active elements within the plate, its material properties can be made to be time dependent and thus, given a fluctuating load, the material properties can be actively adjusted to produce a minimum radiation condition. The control method in this application can be best described as being quasiactive. In this study, a finite element model of a composite plate made of shape memory alloy fibers and epoxy is used in conjunction with an acoustic radiation model to predict the effectiveness of using shape memory alloy fibers as a means of active noise control. Initial results demonstrate that the radiation characteristics of a simply supported plate comprising one side of an otherwise rigid rectangular box can be altered drastically by using the shape memory alloy fibers.
Further research on active control of flexural power flow in elastic thin beams
Authors: Gonidou Luc O. , Fuller Chris R.
Published: October 2005

In a previous paper, preliminary results on active control of flexural power flow in elastic thin beams were presented [C. R. Fuller and L. O. Gonidou, J. Acoust. Soc. Am. Suppl. 1 84, S47 (1988)]. The work described here will be concerned with further experimental and analytical work on the same subject. In particular, the control of flexural power flow from finite beams with various terminating impedances and different length beams is both analytically and experimentally studied and direct comparisons are now made. Parameters such as discontinuity impedance, bending nearfield generation, and number and location of control actuators and sensors are studied in light of the new test configurations. Mechanisms of control are discussed. The use of a flexural power-based cost function is again demonstrated to be important in designing an efficient control strategy. [Work supported by NASA Langley Research Center.]
Infrasonic emissions from atmospheric microbursts: Theory versus experiment
Authors: Zuckerwar Allan J. , Holmes Harlan K. , Hardin Jay C. , Pope D. Stuart
Published: October 2005

To demonstrate the existence of infrasonic emissions from atmospheric microbursts, and to investigate their properties in the frequency band 2–20 Hz, a computational aeroacoustics technique has been applied to the simulated flow field of such an event. The theoretical development reveals that the emitted infrasonic pressure is proportional to the second time derivative of the vorticity within the flow. Thus peak pressure levels occur during the rapid deceleration and radial outflow developing as a microburst touches down upon the ground surface. The frequency spectrum falls at a rate of approximately 6dB per decade. The computational results are compared to experimental records of naturally occurring infrasound taken throughout the year 1984, and support the point of view that in a certain class of these records the infrasound originated from atmospheric microbursts.
Acoustic waves over a transpiring surface
Authors: Ma Yiping , Van Moorhem W. K. , Shorthill R. W.
Published: October 2005

An investigation of the effect on the acoustic waves due to wall mass injection in a piston-driven closed-end test chamber has been conducted. Dry ice is used as a source of mass injection. Acoustic pressure is measured with a pressure transducer mounted at the closed end. A comparison with the results with no side wall mass addition shows a significant increase in the acoustic pressure amplitude due to the interaction of the acoustic wave and side wall mass injection near resonance. A shift in the lowest resonant frequency between the two cases has also been detected. High-speed flow visualization and hot wire anemometry measurements all suggest that turbulence may occur in the acoustic boundary layer above the transpiring surface. This, in turn, feeds more energy into the acoustic wave. This increase in amplitude has never been reported before to the authors' best knowledge. [Work supported by U.S. Air Force Astronautics Laboratory and Morton Thiokol, Inc.]
At-sea measurements of underwater cavity resonance using a towed catamaran platform
Authors: Elder S. A. , Baker L. G. , Yoshikawa S.
Published: October 2005

Earlier investigations in the USNA high-speed tow tank, using a 4.5-ft towed model, had shown that large amplitude resonant oscillations can be produced by flow over a wall cavity immersed in water. For this case, it was found that critical speed is predictable from a Strouhal number formula derived for resonant cavity oscillations in air. Currently, an attempt to measure radiation from an underwater resonating cavity is being made, using the same towed model. Since “waveguide” cutoff of the tow tank is above oscillation frequency, it has been necessary to perform the measurements in deeper water. For this purpose a 17-ft catamaran has been adapted for use as a towing platform to make it possible to take measurements in Chesapeake Bay. A YP class vessel, equipped for oceanographic research, is used for towing and for recording data. For speeds up to 10 kn, f11 and f12 modes have been detected at the expected speeds. Current results for amplitude and radiation will be described.
Characterization and development of transducer elastomers
Authors: Ting Robert Y.
Published: October 2005

The failure of underwater transducers is often related to problems with the materials used, such as elastomers, ceramics, adhesives, coatings, and fill fluids. The general practice has been to select proprietary materials from different commercial sources, and use them as they are available for the fabrication of a transducer. Such practices allow the designer very little control of the quality of the materials. The result is the production of devices that are doomed to fail because they are nonreproducible, or contain materials incompatible to each other. In recent years, improper choices of elastomer have been typical in causing large numbers of failure in sonar transducers. Research efforts at NRL-USRD have therefore been focused on the development of composition—property relationships for elastomers by using well-characterized samples. Instrumentational techniques were developed for the analysis of chemical and acoustical properties. These techniques were subsequently used for materials evaluation and quality control. Based on these research results, specialty elastomers were also successfully developed for specific transducer applications. [Work supported by ONT and NAYSEA.]
Characterization and analysis of viscoelastic materials over wide frequency and temperature intervals
Authors: Madigosky W. M.
Published: October 2005

Typically, the dynamic behavior of materials is a strong function of both temperature and frequency. An accurate knowledge of the dynamic properties over a wide interval of temperature and frequency is, therefore, essential to the efficient design and engineering use of the viscoelastic phenomenon. Recently, both laboratory and commercial apparatus for making measurements over the required large frequency and temperature ranges have become available. This paper reviews the current status of the measurement techniques, the use of the WLF time temperature shift equation, and presents data on a number of pure materials and polymer blends that illustrate the capabilities currently available. Finally, the data may be analyzed in terms of the fractional operator model that describes both the storage and loss moduli with a single complex equation. The adequacy of the model to fit the data will be discussed.
Propagation and reverberant phase in acoustical spaces
Authors: Liu Lan , Lyon Richard H.
Published: October 2005

Systems with low modal overlap cannot support a “direct field” and have also been shown to have a phase trend and corresponding group delay that is far in excess of the expected propagation delay. The phase trend that is associated with this behavior has been termed “reverberant phase.” The reverberant phase also shows up in systems with high modal overlap, but in such systems, the phase of the direct (or propagation) field is expected to also be present. If the effects of reverberation could somehow be subtracted from the data, one would expect to see the propagation phase. In this paper, a procedure for the decomposition of propagation and reverberant phase components from a received signal is presented, using properties of the complex cepstrum. These ideas are tested experimentally using data from transfer functions for small acoustical chambers. Directions for future work on this topic will also be discussed. [Work supported by NTT Research and Development Center.]
Measuring and using the impulse response of a room
Authors: Palmer E. Paul , Berry David A.
Published: October 2005

The point-to-point impulse response of a room is a record of the impulsive sound from a single source to a single microphone. Different systems and signal-processing methods may be used in this measurement depending on the accuracy required. If only the time history of major echoes is desired in order to trace (and correct) reflecting surfaces, the energy-time curve of a time-delay spectrometer system is excellent. An m-sequence signal, with its speed of processing, is versatile for a homebuilt PC-based system and comes closer to a true impulse response. For an impulse response adequate for convolution with a signal, in order to accurately simulate a room, more care is required. The poor frequency response and directionality of the loudspeaker must be nullified to reduce it to a “perfect” point source. A computer-based system to approach this ideal will be described. Further, a real source might be an orchestra rather than a point, and the usual receiver has two ears. Research to graphically display a binaurally recorded impulse response and to deconvolve earphone characteristics (as was done with the loudspeaker) will be reported.
The role of the microphone in parametrizing the acoustics of three rectangular concert spaces
Authors: Mastracco J. M.
Published: October 2005

The scientific method is a principle that states that no theory or model of nature is tenable, unless the results it predicts are in accord with experiment. The concert hall, as a physical system, has long been misunderstood in terms of the effects it has on acoustics. This paper discusses the application of the scientific method to the measurement of acoustical parameters in three renowned spaces: Boston Symphony Hall, the Troy Music Hall, and the Union College Memorial Chapel. The results of the experiments strongly suggest that no characterization of a hall's acoustics is possible without the specification of the microphone used in the measurement. Microphones ranging from a 1/2-in. omnidirectional transducer to an acoustic manikin employing a 1/2-in. omnidirectional transducer produce clearly identifiable differences in reverberation times and other widely used parameters that are calculated from the transient response of the space. These results suggest, contrary to the belief of many, that acoustical science applied to concert halls is not an exact science, but pathological in character. It is concluded that acoustical comparisons between different spaces are not possible unless the type of microphone, as well as its placement and orientation in the space, are specified. [Work supported in part by the Audio Engineering Society Education Foundation.]
Statistical energy analysis modeling and testing of an acoustic guitar
Authors: Hosek Daniel J. , Johnson Glen E.
Published: October 2005

Principals of statistical energy analysis (SEA) were applied to develop a mathematical expression for the time-averaged, space-averaged energy of vibration in specified frequency bands for the top plate of an acoustic guitar. The model predicted energy in terms of string parameters, guitar parameters, and plucking data. Primary assumptions were that the damping of the strings was negligible, that energy flowed from the strings to the resonance box, and that energy was dissipated in the resonance box. Power supplied to the strings was estimated from a classical model of the vibrating string. An experimental plucking apparatus was designed and instrumented with Bruel & Kjaer vibration analysis equipment. The results of the SEA-based computer program were compared to actual experimental data for a Yamaha FG335 acoustic guitar. The SEA model tended to overpredict the energy in the top plate in most frequency bands. Possible causes for the differences were identified and discussed.
Model-based trumpet tone synthesis
Authors: Dietz Paul H.
Published: October 2005

In an effort to produce realistic trumpet tones, a detailed model of the dynamics of the instrument and the player was created. The trumpet was modeled as a collection of linear circuit elements to account for the effects of the mouthpiece, tubing, bell, and radiation impedance. Testing was performed using both impulse response and equivalent length measurements, verifying the accuracy of the model. The model of the player extends from the lungs through the lips and contains both linear and nonlinear elements. The two nonlinearities are due to the inelastic collision of the lips, and the impedance of the lip opening. These models were computer simulated varying three control parameters: the spring constant of the upper lip, the force keeping the lips closed (which can also be thought of as an offset in the spring's zero position), and the pressure in the lung. Listeners report that the resulting simulated tones are quire realistic. These tones demonstrate many of the attributes of real trumpet tones, including the tendency to lock onto the same notes in the harmonic series.
Effects of preceding scale on melodic pitch interval judgment
Authors: Tsuzaki Minoru
Published: October 2005

To investigate interactive aspects of musical scale systems and pitch intervals in human musical cognition, the melodic pitch interval was judged in three preceding scale contexts: (a) diatonic, (b) chromatic, and (c) no scale. Subjects compared standard and comparison pitch intervals using three response categories: “small,” “equal,” and “large.” Standard intervals began with note B, or note C, and ascended by 100, 150, or 200 cents. A “start note effect” is the most prominent for the 200-cent standard in the diatonic context. When it began with note B, i.e., a leading tone in a diatonic context, a peak in the “equal” response histogram disappeared, and the boundary between “small” and “large” response moved far away from its musically equal point. For the 100-cent standard, judgments were rather more precise in the C start condition than in the B start condition, irrespectively of the scale context. For the 150-cent standard, a “start note effect” was not observed clearly in any scale context. Detailed discussion is provided on the role of the diatonic scale system as a referential frame in view of two aspects of pitch interval judgement, that is, size and equality relationship.
Adults' perception of Western and Javanese musical scales
Authors: Lynch Michael P. , Eilers Rebecca E. , Oller D. Kimbrough
Published: October 2005

A cognitive/perceptual model of the processing of musical intervals was investigated by assessing the role of experience with Western music in perception of mistunings in both Western and non-Western scales. Musically inexperienced subjects, persons with limited background in music, and professional musicians heard seven-note major, minor, and Javanese pelog melodies. Each of the melodies contained successively the first, second, third, fourth, fifth, third, and first pitches of each scale, with the first and last pitches always D4 (293.66 Hz). The frequency relationships of the pelog scale were maintained within this framework. Each melody was altered in two ways. First, the top pitch (A4, 440 Hz in major and minor; 461.3 Hz in pelog) was raised along a continuum in ten 0.4% steps. Second, any pitch but the first was randomly selected for sharpening at each of ten 0.5 % steps. PEST was used to estimate the smallest degree of pitch raising on these continua that subjects could reliably perceive for each scale type. As predicted by the model, results indicate a strong relationship between musical training and perception of tuning alterations in the Javanese scale. Musically sophisticated subjects had equal perceptual thresholds across the three scale types. Musically naive subjects had a perceptual advantage for Western scales. Patterns of subject responding differed slightly when pitches were randomly selected for sharpening as opposed to when only the top pitch was raised. [Work supported by Am. Psychol. Assoc.]
One-way propagation models for linearly elastic solids
Authors: McCoy John J.
Published: October 2005

One-way propagation models for acoustic environments have proven to be efficient and robust as bases for general purpose computer programs. The availability of a distortional mode of propagation for a linearly elastic solid environment and the coupling of this mode with the dilatational mode, in the presence of heterogeneity or of lateral surfaces of medium discontinuity, introduce additional complexity that is not yet completely understood. In this talk, an alternative derivation of one-way propagation models to that of giving algorithmic prescription to a square root of a sum of a multiplicative and a differential operator is presented. Also discussed are the difficulties encountered for linearly elastic solids. A number of numerical examples are provided.
Duct attenuation with bulk reacting lining
Authors: Bies David A. , Hansen Colin H.
Published: October 2005

Attenuation of lowest-order modes in lined straight ducts of both rectangular and circular cross section is analytically and experimentally investigated. The lining is assumed to be anisotropic, bulk reacting, and covered by a thin impervious membrane. The effect of flow for low Mach numbers is also taken into account. Frequency averaging within octave bands is used to produce useful design curves. Limited comparison between prediction and measurement will be reviewed and is encouraging.
Propagation of sound in vibrationally excited N2/CO and CO/H2 mixtures
Authors: Ruppel Timothy H. , Shields F. Douglas
Published: October 2005

Measurements of the resonant reverberation of sound in a tube containing N2/H2, N2/He, N2/CH4, and N2/H2O mixtures have shown an amplification of the sound following a rapid excitation of the gas by an electric discharge [F. D. Shields and L. D. Lafleur, J. Acoust. Soc. Am. 83, 2186 (1988)]. This effect has been named SACER (sound amplification from controlled excitation reactions). This paper reports similar measurements in N2/CO mixtures, and also reports preliminary results from measurements in CO/H2 mixtures. It has been possible in the past to determine vibrational relaxation times and relaxation times for the conduction of translational and vibrational energy to the tube wall from the changes in the translational temperature in the gas following the electric discharge. In the work reported here, these rates have been confirmed by direct measurement of the decay times of the CO infrared emission. [Work supported by ONR.]
Propagation of nonlinear transients, such as sonic booms, through an absorbing and relaxing atmosphere
Authors: Kang Jongmin , Pierce Allan D.
Published: October 2005

Recent resurgence of interest in sonic boom propagation through the atmosphere necessitates detailed understanding of how absorption, relaxation, ray focusing and defocusing, and nonlinear steepening interact. Previously used techniques, such as by Bass et al. (1983) for simultaneously treating molecular relaxation and nonlinear propagation, although yielding important insights, have required extensive computation time and have been limited to simple source models. The present paper gives the extension of Burger's equation, with relaxation included, to propagation through inhomogeneous atmospheres using the wedding of nonlinear propagation and ray acoustics suggested by Hayes. It is argued that, in the absence of shock formation, and for lower amplitude waveforms, relatively large step sizes may be used with nonlinear steepening, dispersion, and absorption treated as additive effects, the former being easily handled using the implicit exact solution of the inviscid Burger's equation that incorporates the concept of an age variable. After something that resembles a shock appears, nonlinear effects, relaxation, and absorption must all be simultaneously considered in the computation of waveform details over the narrow risetime of the shock, but a perturbation technique based on the method of multiple scales shows promise of cutting down the computation time. [Work supported by NASA-LRC and by the William E. Leonhard endowment to Pennsylvania State University.]
The relfection of acoustic pulses from arrays of tubes
Authors: Roh Heui-Seol , Sabatier James M. , Raspet Richard
Published: October 2005

The theory of sound propagation in and the reflection of sound from rigid porous media is well established [K. Attenborough, J. Sound Vib. 99, 521–544 (1985)]. This theory has been applied to regular arrays of straight tube to develop a low-reflectivity surface. Low reflectivities require high porosities in order to minimize the surface admittance. A 15.25-cm-i.d. tube terminated by arrays of rectangular tubes has been constructed to verify the theory in the limit of high porosity. Work is in progress to examine the effect of varying pore radius with depth.
Confirmation and rejection of the “precedence effect”
Authors: Saberi Kourosh , Perrott David R.
Published: October 2005

A series of experiments designed to investigate the “precedence effect” in lateralization space were conducted using a two-alternative, forced-choice paradigm. Stimuli consisted of 40-μs transients separated by inter-click intervals (ICIs) of 0.38f–30 ms. In a two click paradigm (experiment 1) interaural differences of time (IDT) thresholds were determined independently at click positions 1 and 2. Thresholds measured at click 2 ranged from 12 μs at extended (over 5 ms) and short duration (less than 1 ms) ICIs to a peak of 250 μs at ICIs of 1.75–2.35 ms. Thresholds measured at click 1 were uniform across ICIs, constant at approximately 15–25 μs. Experiment 2 consisted of a three click paradigm where the ICI between clicks 2 and 3 was held constant at a value where subjects in experiment 1 had peaked (1.75–2.35 ms), while the ICI between clicks 1 and 2 was varied from 0.38 to 10 ms. IDT thresholds were measured for click 3. Results show a U-shaped function for which thresholds drop below 30 μs for click 3 at ICIs between 2–8 ms, with the effect returning at long and short duration ICIs. Experiment 3 consisted of click trains of n = 2, 3, 4, 5, 6, and 12 where ICI was held constant at subjects' peak value in experiment 1 and IDT thresholds were measured at the last click in the train. Results show a negatively decelerating function as n increases, wtih IDT thresholds falling from 250 down to 20 μs. The most dramatic find in these series of experiments, however, was the surprising yet compelling dissipation of “suppression” in the temporal window of interest (1- to 5-ms ICIs) over multiple runs. Thresholds fell by 5 to 10 folds, matching values reported by Perrott et al. (in press) in the free field. Across variations of stimulus duration, form, intensity, or frequency, highly trained subjects showed no recovery of the precedence effect. [Work supported by NSF and NIH.]
Effects of roving level on binaural performance in normal-hearing and hearing-impaired listeners at 500 and 4000 Hz
Authors: Curliss P. , Koehnke J. , Colburn H. S. , Owen G. A.
Published: October 2005

Measurements of NoSπ thresholds and interaural time and intensity jnd's with and without a 10-dB roving level for both normal-hearing (4000 Hz) and hearing-impaired (500 and 4000 Hz) subjects have been obtained. This extends previous measurements of the effects of roving level on binaural detection and interaural discrimination at 500 Hz for normal-hearing listeners [J. Koehnke and H. S. Colburn, J. Acoust. Soc. Am. Suppl. 1 82, S10g (1987)]. All measurements were made using an adaptive, four-interval, two-alternative, forced-choice procedure and 1/3-oct noise bands. For detection, the target was a tone burst centered in the noise band. Binaural detection and interaural time discrimination show no effect of roving level at 500 Hz. However, interaural intensity jnd's at 500 Hz for the hearing impaired listeners are consistently larger with the roving level. In contrast to the data obtained at 500 Hz, at 4000-Hz performance of all the subjects for interaural intensity discrimination and NoSπ detection is worse with the roving level. For interaural time discrimination, there is no apparent effect of the roving level at 4000 Hz. [Work supported by NIH.]
The establishment of a new phonetic category by German learners of English
Authors: Bohn O.-S. , Flege J. E.
Published: October 2005

This paper reports experiments examining the production of English vowels (/i, ı, ıɛ, æ) and German vowels (/i/ɪ, ɛ, ɛ:,a/) by two groups of native German speakers differing in English-language experience. In experiment 1, German and English monolinguals read lists of English bVt words. Similar recordings were made of German front vowels by the German subjects. On the whole, duration and spectral measurements indicate that the distance between /i/ and /ɪ/ in an F1/F2 space is about the same in German, English, and native Germans' English. The vowels /i/ and /ɪ/ of English and German differed acoustically. Both experienced and inex perienced Germans approximated but did not reach the English monolinguals' values for /i/ and /ı/. Experienced but not inexperienced native Germans differentiated English /æ/ and /ɛ/ acoustically, probably because German lacks an /æ/ category. The acoustic results of experiment 1 were consistent with experiment 2, which examined monolingual English listeners' categorization of the German speakers' English bVt words. The results support Flege's [J. Phonetics 15, 47–65 (1987)] model of L2 learning which predicts that extended foreign language experience will lead to the establishment of phonetic categories for new (e.g., /æ/) sounds in L2. [Work supported by NIH Grant 20963.]
S'pose a vowel is lost
Authors: Fokes Joann , Bond Z. S.
Published: October 2005

Various types of reduction can be observed in casual speech, one being vowel loss in unstressed syllables as in “s' pose.” The question, how is the phonetic detail of this specific reduction implemented, is the focus of the study. Three types of test words were selected for investigation, initial /sp/ and /sk/ clusters, two and three syllable words beginning with an unstressed /a/ + V followed by /p/ or /k/ in the stressed syllable, and a word with a cluster created by the loss of the vowel, such as sport, support, and s'port. Male subjects read each test word in context five times. Measurements included (1) duration of the /s/, (2) duration of the stop closure, (3) voice onset times, and (4) total time from the beginning of the /s/ to the onset of the stressed vowel. Results indicated two different speaker patterns but consistency within each subject. Differences between the subjects occurred in the length of the /s/ in all types of test words, voice onset time, and the total time. For one of the speakers, voice onset time was relatively short regardless of the cluster or word types. For another speaker, VOT was short for the /sp/ clusters while values for the /sk/ cluster, for the created clusters, and for the two and three syllable words became increasingly longer. This speaker differentiated between real clusters and created clusters by means of voice timing.
The effects of relative formant intensity on vowel perception revisited
Authors: Tsoi Kam-Cheong
Published: October 2005

The effects of relative formant intensity on the phonetic identity of vowels were investigated in the present study. Ambiguous stimuli which were near the phonetic category boundary of /a/-/ɔ/, /u/-/ᴜ/, and /ɛ-/æ/ series were used to construct experimental stimuli by varying the intensity ratio between F1 and F2. The results showed that the perceived identity of these three sets of stimuli shifted towards /a/, /ᴜ/, and /æ/ when the intensity of F2 was increased, and shifted towards /ɔ/, /u/, and /ɛ/ when the intensity of F2 was decreased. The magnitude of effect was largest in stimuli of the /a/-/ɔ/ series, and smallest in stimuli of the /ɛ/-/æ/ series. The results suggest that (1) the relative intensity of formants does affect the phonetic identity of the stimuli, and (2) the frequency range within which spectral integration between adjacent formants can take place is not limited to 3 Barks, but follows a continuous probability function. [Work supported by NIH.]
Results from two shallow-water experiments utilizing synthetic bandwidth (“stepped FM”) signals to estimate compressional wave speed in the seabottom
Authors: Williams Neil J. , DeFerrari Harry A.
Published: October 2005

Two experiments were performed to investigate the utility of synthetic bandwidth or “stepped FM” signals [H. A. DeFerrari and H. B. Nguyen, J. Acoust. Soc. Am. Suppl. 1 82, S74 (1987)] for acoustic remote sensing of geoacoustic properties of the seabottom. In each experiment, pseudorandom codes with carrier frequencies ranging from 100 to 1600 Hz were transmitted consecutively at a fixed range to a moored vertical array. After every other complete sweep of the entire bandwidth, the range was increased and the transmission was repeated. The experimental sites were 42 nautical miles SE of Corpus Christi, TX and 75 nautical miles E of Lewes, DE. The water depth in each case was about 60 m and the range from source to receiver varied from 300 m to 2 km. The data have been reduced to pulse responses with a resolution of 6 ms. This, combined with the angular resolution of the array, aids in the identification of eigenrays and inversion of the data to yield estimates of compressional wave speed in the seabottom. [Work supported by ONR.]
Target strengths of Antarctic krill
Authors: Foote K. G. , Everson I. , Bone D. G. , Watkins J. L.
Published: October 2005

Encaged aggregations of Euphausia superba have been ensonified at 38 and 120 kHz and the echo energy measured. Derived estimates of target strength are considerably lower than previously measured values.
Study of intensity in the focal lobe for a focused ultrasonic stone removal device
Authors: Singh V. R. , Agarwal Ravinder
Published: October 2005

In modern surgical practice, the operative procedures for stone removal are still finding difficulty in their acceptance by the patients. Thus it gives motivation for finding a new and alternative, noninvasive technique for the removal of kidney stones. Focused ultrasound is used in the disruption of such stones. Intensity pattern prarmeters in the focal lobe are studied for a transducer used for removal of kidney stones.
Temperature measurements and photographic observations of evolving adiabatic shear bands
Authors: Duffy J.
Published: October 2005

Experiments are described in which the local temperature and local strain distribution are measured during the formation of adiabatic shear bands in steels. The specimen employed is a short thin-walled tube loaded dynamically in a torsional Kolsky bar (split-Hopkinson bar). Local temperature is determined by measuring the infrared radiation emanating at 12 neighboring points on the specimen's surface, including the shear band area. Indium-antimode elements are employed for this purpose to give the temperature history during deformation. In addition, high-speed photographs are made of a grid pattern deposited on the specimen's surface, thus providing a measure of the strain distribution at various stages during shear band formation. The results provide a picture of the developing strain localization process, of the temperature history within the forming shear band, and of the consequence loss in the load capacity. It appears that plastic deformation follows a three-stage process that begins with a homogeneous strain state followed by a generally inhomogeneous strain distribution, and finally by a narrowing of the localization into a fine shear band. Experimental results are compared with predictions of various models.
Theory of superpotentials in a graded-index dielectric waveguide
Authors: Kaul Raj K. , Hoffend Thomas R. , McArthur Raymond P. , Burke Kenneth T.
Published: October 2005

This paper deals with the theory of dielectric waveguides in a graded-index media. The theory is first developed in terms of electrical and magnetic potentials and a gauge condition which is a generalization of the Lorentz gauge used in classical electromagnetic theory for the isotropic, homogeneous medium. The existence of these potentials under the generalized Lorentz gauge in the context of a generalized Helmholtz theorem are then proven. Even though this generalized gauge uncouples the governing equations, it does not lead to partial differential equations in the normal form. To alleviate this problem, superpotentials of the Hertzian variety are introduced and it is shown how equations governing the vector superpotential can be reduced to a form which is amenable to standard analysis. Then several uniqueness theorems associated with this superpotential are proven. As an illustration of the use of the superpotential and its relative merits, it is applied to certain waveguide problems in an inhomogeneous medium with variable permittivity.
Prosodic structure in language understanding: Evidence from tone sandhi in Mandarin
Authors: Speer Shari R. , Shi Chi Lin
Published: October 2005

Two experiments show that listeners can use phrase-level prosodic information to disambiguate local lexical ambiguities that occur due to the operation of the tone sandhi rule in Standard Mandarin Chinese. In Chinese, each word is associated with a tone; changes in a word's tone that occur in relation to the tones of words nearby in phrasal context are referred to as “tone sandhi,” e.g., ([L] → [LH]/_[L]). In experiment 1, listeners identified lexical tones for ambiguous, unambiguous, and nonsense words in phrasal contexts where the tone sandhi rule might have applied. Comparable results in the lexical versus nonsense conditions indicate that judgments did not rely simply on lexically stored tonal information, but also made reference to prosodic structure. In experiment 2, subjects chose the correct written English translation for auditory sentences of Mandarin. Global prosodic information was manipulated to create different levels of “prosodic closeness” between two critical items in a tone sandhi environment, but the syntactic relation between these items was held constant. Results show that listeners relied on the prosodic structure of the phrases to determine whether or not the tone sandhi rule had applied, and consequently to identify individual lexical items. The evidence is taken to support the notion that prosodic structure influences auditory language comprehension processes. [Work supported by NICHD.]
Spectral slope as a cue for the perception of breathy and non-breathy stops in Shanghainese
Authors: Ren Nianqi , Mattingly Ignatius G.
Published: October 2005

In Shanghainese, breathy excitation following release distinguishes category 2 (so-called “voiced unaspirated”) stops from category 1 (“voiceless unaspirated”) stops. The most obvious acoustic correlate of bresthiness is relative spectral slope: During the first 50–100 ms after release, H1-H2 is greater for category 2 than for category 1 in both word-initial and word-medial (morpheme-initial) stops (Ren, unpublished). To investigate the perception of breathiness, a series of synthetic disyllables was prepared in which the spectral slope during the 100 ms following the release of the word-medial stop was increased step by step increasing the value of the “open quotient” in the computation of the glottal waveform—a technique previously used for the synthesis of breathy vowels [C. Bickley, Work. Papers MIT Speech Commun. Lab. 1, 71–81 (1982)]. Other potential cues (closure duration, pulsing during closure, tone contour) were neutralized. Ten Shanghainese speakers labeled the stimuli with greater spectral slope as category 2 and those with smaller spectral slope as category 1. [Work supported by NICHD Grant 01994.]
The separation of two voicelike signals
Authors: Vaidya P. G.
Published: October 2005

If two persons are talking or singing at the same time, human beings can selectively listen to only one of them, even if they are producing notes that are in unison. This paper presents an attempt to simulate this task by a computer. An elementary model of the voices of the two speakers has been used. Using this model, two voicelike signals are generated and mixed. The resulting signal is analyzed for the coherence of the trans-phase. Trans-phase is the phase difference between the components at two different frequencies when one of them has been sent through a nonlinear filter. If the trans-phase shows coherence, the signals are said to be transspectrally coherent. A justification for the assumption of such coherence in voicelike signals has been presented. The data for the transspectral coherence have been sent through a processor that yields an estimate of the individual sound separately.
Force anisotropy in resonant acoustic levitators
Authors: Barmatz M. , Aveni G. , Robey Judith L.
Published: October 2005

In general, the forces positioning a sample in an acoustic levitator depend on direction, which is to say they are anisotropic. The anisotropy of the acoustic force for several classes of levitating modes in rectangular and cylindrical resonators has been investigated. The degree of anisotropy depends on the chamber geometry, mode that is excited, and properties of the sample. The force anisotropy has been studied as a function of these variables for single mode levitators. The force field anisotropy is evaluated for small displacements from equilibrium. Also, the anisotropic properties for the maximum positioning forces in the resonator that maintain the sample within the acoustic potential well have been studied. Optimum chamber dimension ratios for maximizing the latter force fields will be presented. Experimental measurements verify the theoretical optimization predictions. Finally, it is shown that there is an unexpected isomorphism between the force fields in rectangular and cylindrical positioning modes.