bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation of F contours for English sentences from partially specified fundamental frequency templates
Authors: Gramlich Carolyn , Sanders William
Published: October 2005

English sentences are assigned to a small number of intonational classes. Each class has an associated fundamental frequency template, which characterizes the F0 contour by specifying up to two frequency points per word—typically a peak frequency and a final frequency. The F0 contour for a particular sentence is elaborated by cubic polynomial interpolation of the template's frequency points, fixed in time by the actual durations of the words of the sentence. Similar sentences with different numbers of words can be assigned to the same intonational class if short phrases are described by a single pair of frequency points, which are then algorithmically elaborated. In a practical application the name of a template is stored with the text of a sentence, and the spoken sentence is synthesized by applying the template to the sequence of LPC-encoded words in real time. A demonstration tape will be played.
A variable frame rate LPC vocoder using normalized ladder-forms
Authors: Wang J. S. , Lee D. T. L. , Morf M.
Published: October 2005

We present a variable frame rate LPC (Linear Predictive Coding) vocoder based on a normalized exact-least squares ladder-form analysis algorithm by Lee and Morf. This algorithm works on a sample by sample basis, hence no a priori frame rate has to be preselected. As a byproduct of this algorithm a log-likelihood variable is computed that can be used to detect discontinuities in the speech signal such as plosive sounds, pitch pulses, glottal stops and other underlying transitions. Based on this algorithm a complete design of a vocoder is presented, that allows variable frame rates, pitch synchronous speech analysis/synthesis. Such vocoders are of interest in digital communication systems, especially packet oriented systems, or digitally stored speech based systems. Computer simulations of this vocoder using a digitized speech data base are presented, and several alternative implementations are discussed.
Physical modeling of a computer installation
Authors: Wise Russell E.
Published: October 2005

Some results of a two-phase study of the physical modeling of a portion of a large data processing installation are presented. A physical model, as opposed to graphical or computational techniques, was used because of the complex diffraction and reflection effects among the small machines and surfaces that form a computer installation. During the first phase of the study, an installation was selected and a model was constructed and assessed for its adequacy. It was concluded at the end of the first phase that the model simulated the installation to within about 2 dB. This was considered adequate in evaluating changes that could affect installation noise levels. During the second phase of the study, the modeling technique was used to determine the cumulative noise levels of the data processing equipment. Emission data acquired on individual machines in a controlled acoustical environment was used to “calibrate” the model. Immission data for the multiple machine installation could then be determined at any selected position in the installation. The results obtained for several machine configurations are presented. Additional results relative to barrier effects and the prediction of individual machine noise levels will also be shown.
Valve noise prediction and acoustic scale modeling
Authors: Reethof G.
Published: October 2005

The noise from industrial piping systems containing control valves and regulators with compressible fluids is the result of four processes each of which are rather complicated. First, noise generation at the valve orificial element. Second, development of the acoustic field in the downstream pipe. Third, the interaction of the modes of the acoustic field with the like pipe vibratory modes; and fourth, the radiation from vibrating pipe wall surface into the surroundings. Recent research has shown that noise generation formulation based on the free, choked jet, shock-turbulence interaction gives results in good agreement with test. Also, most of the radiated energy is emitted at the coincidence frequencies of the downstream piping. The paper discusses the scaling implications of these relationships with regard to valve size, valve pressure drop, and fluids. Some of the difficulties of applying scaling laws in view of lack of geometric similarities in valve families prevelant in past work is considered.
A comparison of architectural acoustic scale models to their prototype room
Authors: Siebein Gary W.
Published: October 2005

Architectural acoustic models were built at 1:10 and 1:24 scale of the Band Rehearsal (prototype) Room in the Music Building at the University of Florida, Gainesville, Florida. The models were constructed using chipboard and plywood for sound reflecting surfaces, polystyrene foam for sound absorbent surfaces and wood fiber egg cartons for the audience seating. A series of tests were performed using an impulse sound source in the prototype room to measure objective design criteria proposed by numerous model researchers. Similar sets of measurements were made in both the 1:10 and 1:24 scale models. The model measurements were compared to the prototype room measurements by a statistical analysis computer program to determine how much valid acoustical information one could extract from the successively smaller scale models. Both models showed a very close correlation with the prototype room in the reverberating measurements, sound build up measurements, and the sound reflection patterns at individual points in the room. The temporal energy ratio in the smaller scale model showed a greater margin of error from the prototype room than the other criteria.
Acoustoelastic measurement of stress field variations
Authors: Kino G. S.
Published: October 2005

New techniques for measuring the stress field variations near a crack or a weld will be described. The basic method makes use of the perturbation in acoustic velocity of a longitudinal wave in the presence of stress by using a small scanned transducer in a computer-controlled system. It is possible to determine stress field variations over the cross section. Furthermore, if a focused transducer is employed, it is possible to design a phase contrast system which can measure stress field variations in all three directions. A detailed acoustoelastic perturbation theory, based on the change in energy associated with the third-order elastic effects, has been derived and used to predict our experimental results. A brief description of the theoretical techniques employed will be given.
Wave propagation for metalography and materials characterization
Authors: Papadakis Emmanuel P.
Published: October 2005

Ultrasonic wave propagation can be used to substitute for metallography or augment it in certain cases to characterize metals. The two parameters used are attenuation and velocity. Attenuation is related to grain size, grain size distribution, phase transformations, and separate phases within polycrystalline metals through grain scattering, while velocity is related to phase transformations and the continuity of the racial in the presence of other phases of various morphologies through the elastic moduli. Grain scattering will be explained in terms of both diffusion-controlled and diffusionless transformations. Graphite morphology in cast iron will be used to illustrate the industrial use of velocity measurements. Certain situations will be mentioned in which ultrasonic measurements are superior to metallography in practice. The subject matter will be a review of published material.
Acousto-optic method to locate surface inhomogeneities on solids
Authors: Mayer Walter G. , Ngoc Tran D. K.
Published: October 2005

Changes in the profile of a reflected ultrasonic beam incident at the Rayleigh angle are observed and are used to locate small inhomogeneities in the surface of a solid. These beam profile changes are caused by minute changes in the Rayleigh wave velocity. Whether the inhomogeneity is related to variation in the longitudinal wave velocity is determined by observation of longitudinal critical angle reflectivity. [Supported by the Office of Naval Research, U.S. Navy and in part through an award (WGM) by the Alexander von Humboldt Foundation, Bonn.]
Optical detection of acoustic waves for the characterization of materials with unpolished surfaces
Authors: Cielo P.
Published: October 2005

An interferometric ultrasound sensor was developed for use in ultrasonic characterization of materials with unpolished surfaces. A systematic investigation was made of the variation of the sensor's performance with the roughness of the surface to be inspected. Results show that even very rough surfaces can be inspected by this method with little decrease in the modulation index, provided that adequate optical components are used. An analysis of the dependence of the modulation index on the optical parameters is presented. Different applications of this sensor to ultrasonic characterization of materials are presented, and calibration problems encountered with samples of varying angular reflectivity are discussed. The variations in angular reflectivity are caused mainly by microstructure-produced speckle noise and defocussing. A self-calibrating system is presented, making use of a feedback loop incorporated in the electronic stabilisation system, which continuously compensates for the variations in angular reflectivity.
Acoustic surface wave studies of interfacial adhesives
Authors: Knollman G. C. , Hartog J. J.
Published: October 2005

Ultrasonic surface waves have been utilized to study shear modulus gradients near adhesive-adhered interfaces. For a given adhesive, Rayleigh waves are propagated over surfaces of the material which are sequentially exposed from bulk down toward an interfacial bondline. Measured Rayleigh-wave velocity over each exposed adhesive surface is used to determine the corresponding shear modulus at that stratum relative to the interface. The experimental acoustic surface-wave apparatus and its evaluation are described. Also, procedures for adhesive sample preparation and measurement are discussed. Data are presented which display significant gradients in shear modulus through the interfacial region for two different types of adhesive material. [Work supported by the Lockheed Independent Research Program.]
Marine seismic energy sources: Acoustic performance comparison
Authors: Johnston Roy C.
Published: October 2005

A survey of marine seismic energy sources was presented at the 1977 annual meeting of the Society of Exploration Geophysicists. Acoustic performance of 17 sources was given; ten of the sources were air gun arrays. Several of the arrays and other sources are no longer in use. Higher-pressure [13.8 MPa (2000 psi)] air guns, more-efficient air and water guns, and other sources have been developed to replace the discontinued sources. These recent developments are described and their acoustic performance are compared with other sources currently used in production surveys. Two criteria are used for the comparison: (1) farfield acoustic pressure of the initial pulse referenced to one meter and in the 0–128 Hz recording passband and the initial-to-bubble pulse ratio in the same passband, and (2) energy flux spectral density of the farfield signature referenced to one meter from the source.
Geometric aspects of towed air-gun arrays
Authors: Teer T. L. , Curtis T. , Brandsaeter H. , Suter P.
Published: October 2005

Air-gun array technology has developed in the 1970's along the general line of producing tuned arrays with source strengths in excess of 100 bar-meters (peak-to-peak) in the seismic bandwidth and with wavelets of front-to-back ratios in excess of 10:1. Most such arrays are towed in a so-called “point source configuration,” for which a significant amount of energy is beamed in undesireable directions such as forward of the vessel and to each side of the vessel. This paper examines several available air gun array geometries (the SLAG array, in which the air gun source is extended along the axis of a survey line, the SWAG array, in which the air gun source array is extended along an axis perpendicular to the survey line, and the point source array), and shows how noise problem characteristic of certain offshore areas may be reduced by beaming the array in preferred directions. It is shown that this beaming may improve the achievable signal-to-noise ratio—both by increasing power input to the water in desireable directions, and by reducing noise arriving from unwanted directions.
A standard quantitative calibration procedure for marine seismic sources
Authors: Fricke J. R. , Davis J. M. , Reed D. H.
Published: October 2005

Traditionally marine source evaluation has been a subjective and qualitative study. This is particularly true in the case of source spectral characteristics. As a result, source evaluation, development, and array design based on seismic energy over a specified frequency band has been impossible. Further, the transient nature of source wavelets lend themselves to energy analysis rather than the more traditional relative power analysis. This paper details the methodology required to achieve a calibrated quantitative estimate of marine seismic source energy. Basically the procedure involves two steps. First a calibrated high fidelity measurement of the source signature is required. Second, the signatures must be analyzed by a suite of computer algorithms designed to extract quantified measures of amplitude and energy. Results of the analysis include a time domain signature calibrated in ANSI units of pressure and a frequency domain spectrum calibrated in ANSI units of energy flux. These results provide figures of merit for evaluation of individual source characteristics (i.e., energy flux over seismic bandwidth, and total source energy). Additionally, the results provide data for a quantitative comparison of any two or more sources. Illustrative examples of source studies are included.
Spectral analysis of coal-mine roof vibrations
Authors: Palmer E. Paul , Czirr J. Bart
Published: October 2005

A study was made of the possibility of assessing coal-mine roof integrity by using audio-frequency-range spectral analysis of the vibrations produced by tapping the roof. Laboratory tests of rock slabs and field tests of mine-roof slabs showed that characteristic bending, torsional, and extensional vibration modes are excited and easily measured. Modes characteristic of a wave bouncing between the face and back of a slab spread and dissipate too rapidly to allow spectral analysis; thus, slab thickness is not measurable by this technique. Solid roofs give broadband, noise-like spectra with little low-frequency energy. “Drummy” roofs give line spectra characteristic of slab vibration modes and usually have considerable energy in the 0–400 Hz range. Spectral analysis can indicate “drummy” versus “nondrummy” but can reveal little about thickness or mounting of a roof slab and can contribute little to practical mine safety. Recommendations are made for better use of normal hearing in mine-roof testing, better protection for those doing the testing, safer mining methods, and for studies of microseismic emissions coming immediately after coal cutting.
Beamlike dynamic vibration absorbers
Authors: Nobile Matthew A.
Published: October 2005

Although the concept of the dynamic absorber and its potential for vibration reduction were first discussed in the early part of this century, John Snowdon's comprehensive work in this area was certainly a pioneering effort. By rephrasing the standard equations in terms of complex dynamic moduli, it became possible to treat viscoelastic (rubberlike) absorber damping, as well as the conventional viscous damping. For either type, Dr. Snowdon provided expressions and curves for the socalled optimum tuning and damping conditions, thus placing the solutions to many practical vibration problems within reach. In this paper, the performance of several beamlike dynamic vibration absorbers is analyzed and, in selected cases, confirmed by experiment. The absorbers are employed to suppress the transmissibility at resonance across a simple mass-spring vibrator, a stanchion, and a simply supported rectangular panel. The absorbers comprise either single or double cantilever beams that are mass loaded at their free ends, or clamped-clamped beams that are centrally mass loaded. Analyses are based throughout on the Bernoulli-Euler beam and thin-plate theories without simplification.
Transmissibility across simply supported and clamped plates with various leading conditions; theoretical and experimental work of J. C. Snowdon from 1972–1976
Authors: Ochs J. B.
Published: October 2005

Based upon his earlier work with dynamic absorbers and based upon his analysis and reciprocal experimental studies of beams, John Snowdon's research expanded to include analytical studies of the transmissibility across simply supported and clamped homogeneous thin plates with external damping, point mass loads and other loading geometries. Experimental studies of these plates verified his theoretical development and verified his novel use of a complex Young's modulus (internal damping) to model externally applied damping material. Precise experimental data were collected for a series of loading configurations that were of great interest but which had theoretically intractable geometries. From 1972 to 1976 John Snowdon with whom I had the honor of studying, produced four publications based upon this work. This tutorial will review his work on plates as represented by those four JASA articles. [J. C. Snowdon, J. Acoust. Soc. Am. 56, 1177–1184 (1974); J. B. Ochs and J. C. Snowdon, J. Acoust. Soc. Am. 58, 832–840 (1975); J. B. Ochs and J. C. Snowdon, J. Acoust. Soc. Am. 59, 350–360 (1976); J. B. Ochs, J. C. Snowdon, and R. L. Kerlin, J. Acoust. Soc. Am. 59, 1347–1360 (1976)].
Lumped element vibrators
Authors: Skudrzyk Eugen J.
Published: October 2005

The mechanical elements of lumped element vibrators are all independent of one another and their theory is more involved than that of vibrators with continuously distributed parameters. One very informative parameter is the locus of the admittance in the complex plane. Unless the vibrator is heavily damped, the driving point admittance is a spiral whose turns are transcribed in a clockwise sense as the frequency is increased. In contrast, some of the turns of the transfer admittance may be transcribed in an anticlockwise sense. Lumped element vibrators may also have “active modes,” although the whole vibrator is passive. This means that exciting the vibrator in a certain frequency range reduces its input resistance. An example of a vibrator with an active mode is a magnetic transducer. Circuit theory makes it possible to deal efficiently with lumped element vibrators. A few very simple rules help to greatly simplify the computations and to predict the dynamical behavior of such vibrators. The most important of these rules will be derived and the theory will be illustrated with the detailed analysis of two coupled dumbbell vibrators, which represent the simplest possible mechanical bandpass filter. Such a filter has a considerably more complex behavior than an electrical bandpass. Unless the receiver is located at the proper point, the coupled dumbbell vibrators may act like an all pass, or exhibit no or very deformed pass ranges. [This work was sponsored by the Office of Naval Research, Code 474.].
Noise control at the Tanglewood Music Shed
Authors: Menge Christopher W.
Published: October 2005

The introduction of popular music concerts to the Tanglewood Music Shed, Lenox, MA, brought noise complaints and legal action against the Boston Symphony Orchestra (BSO); several noise control approaches were investigated, with mixed results. Property-line noise measurements indicated that some popular music concerts produced significantly higher A-weighted sound levels than BSO or Boston Pops Orchestra concerts. Closing the side of the shed in the direction of the complainant's property provided significant noise reduction but was unacceptable for practical reasons. A temporary property-line barrier was constructed and tested for noise reduction effectiveness. Flanking by trees in the high-frequency region and loss of existing ground-effect attenuation in the 500-Hz region prevented the 15-ft barrier from providing more than a few decibels of overall noise reduction. The complainant issued criteria for acceptable sound levels, which provided guidelines for a sound level control program instituted for the popular music concerts. Sound levels were controlled at the sound control board, requiring cooperation from the performing group. Success was dependent on the degree of cooperation received and the nature of the performing group.
Physical and political problems of outdoor amphitheater site selection
Authors: Jaffe Christopher
Published: October 2005

Technology, economics, and social attitudes have spawned a phenomenon known as “the rock concert.” Audiences of three thousand to three-hundred thousand attend these events daily in theaters, coliseums, amphitheaters, pavilions, stadiums, race tracks, and parks throughout the United States. The stage stacks used to amplify these events produce sound pressure levels of over 115 dB 4 ft from the loudspeaker assemblies. In enclosed buildings, these levels, though potentially dangerous to those exposed, rarely produce problems related to violations of community noise standards. However, performances in amphitheaters, music pavilions, and park settings are another matter and complaints are mounting regarding the noise pollution created by these concerts. This paper discusses the physical and political problems related to finding sites for new facilities in urban and suburban locations. Experiences in Concord, California and Dallas, Texas are described with examples of solutions developed to meet local ordinances and reduce annoyance factors.
Frequency analysis in the peripheral auditory system of anurans
Authors: Lewis Edwin R. , Capranica Robert R.
Published: October 2005

The two auditory organs—amphibian and basilar papillae—in an anuran's inner ear are anatomically distinct and both lack basilar membranes. Of fundamental interest is whether these organs nevertheless are capable of a systematic frequency analysis (i.e., tonotopic organization) and how the response properties of their auditory nerve fibers compare with those of other vertebrates. Anatomical and electrophysiological studies in our laboratories during the past several years have focused on these issues. Each auditory fiber in the anuran's eighth nerve is characterized by a “V”-shaped tuning curve which is fairly selective about its own best excitatory frequency (BEF). In primitive frogs, the fibers fall into two disjoint populations based on their BEF's (low-frequency sensitive and high-frequency sensitive) and susceptibility to two-tone suppression, with each population derived from a separate papillae. In more advanced species a third population arises, associated with the amphibian papilla and sensitive to the mid-frequency range. Electrophysiological studies with paired clicks and pure tones predicted that a place mechanism is operative in the amphibian papilla but not in the basilar papilla. The implication of a place principle in the amphibian papilla was further reinforced by the presence of an extension of this organ's sensor macula in advanced species. Recent Lucifer yellow dye injections in single auditory fibers confirm the tonotopy in the amphibian papilla which is not present in the basilar papilla. These combined anatomical and electrophysiological studies are currently aimed at elucidating further correlations between hair cell locus, morphology, and auditory nerve fiber response properties.
The effects of electrode position and stimulus period on the hearing sensations in a multiple-channel cochlear implant patient
Authors: Tong Y. C. , Blamey P. J. , Dowell R. C. , Clark G. M.
Published: October 2005

The first study involved the categorization of sensations produced by decreasing and increasing electrical stimulus period (SP) trajectories as “Questions” or “Statements” (corresponding to rising or falling pitch). Separate studies were conducted with the 300 ms SP trajectories superimposed on: (i) individual electrodes with no variation in electrode position (EP), and (ii) electrode trajectories shifting in succession from one electrode to another in the basal or apical direction. Statistical tests showed that the slopes of the linearized categorization functions were significantly different from zero, and there was no significant difference between the individual electrode and the electrode trajectory results. The second study investigated the perceptual dissimilarities of nine periodic stimuli by the method of triadic comparisons. The 300-ms stimuli were the nine possible combinations of three electrodes, spaced 3-ram apart, at three SP's (4, 8, 12 ms). A two-dimensional solution by nonmetric multi-dimensional scaling showed that the stimulus points were ordered approximately on a rectangular grid with axes corresponding to the two physical dimensions, EP and SP.
Perceptual dissimilarity and discrimination studies using two-electrode stimulation with a multiple-channel cochlear implant patient
Authors: Dowell R. C. , Tong J. C. , Blamey P. J. , Clark G. M.
Published: October 2005

The stimuli used in the two studies were trains of biphasic current pulses delivered to pairs of the ten electrodes implanted in the patient's scala tympani. The first study investigated the perceptual dissimilarities of ten two-electrode stimuli by the method of triadic comparisons. Electrode separations from 1.5–10.5 mm were used. A nonmetric multi-dimensional scaling analysis of the data obtained showed a two-dimensional solution to be appropriate with dimensions corresponding to the position of: (i) the more basal electrode, and (ii) the more apical electrode of the combinations. In the second study, pulse period discrimination was assessed for a set of two-electrode combinations in a same-different task. Electrode separations from 3–9 mm were used. Analysis using nonparametric indices of discriminability and response bias showed that the discrimination improved with increasing electrode separation, and for constant separation discrimination was better for more apical combinations.
Pitch and loudness studies on a multipie-channel cochlear implant patient
Authors: Blamey P. J. , Tong Y. C. , Dowell R. C. , Clark G. M.
Published: October 2005

Electrical stimuli, 300 ms in duration, were delivered to individual electrodes in the following two modes: (i) a single pulse per period (SPP), and (ii) multiple pulses occurring in the first half of each period (MPP), keeping the total charge delivered during the 300 ms constant. In the first study, subjective loudness as a function of current level and stimulus period were measured by magnitude estimation. For SPP, loudness was a power function of current level with exponent greater than 10. MPP was always louder than SPP with a greater difference at lower current levels. The variation of loudness with stimulus period was greater for SPP than MPP. In the second study, stimuli with periods between 1 and 12 ms were used. Ratio estimation with a fixed reference indicated pitch ratios varying over 1.5 to 2.0 decades for both modes. In the third study, a 2I-2AFC paradigm measured stimulus period difference limens in the range 2.0%–3.3% for a 10 ms period and 3.6%–5.8% for 5 ms. MPP limens were 0.5%–1.0% lower than SPP limens.
A comparison of two transforms from speech signals to tactile signals
Authors: Becker Robin D.
Published: October 2005

Various methods of transforming speech signals into tactile signals have been investigated. Comparison of the results, however, is complicated by differences in training methods, training times, feedback, etc. In order to obtain a direct comparison between LPC-derived area function coding and spectral coding, naive subjects were trained successively on both coding schemes, using identical paradigms and speech tokens. The subjects were tested on identification and discrimination of four different b-V sounds presented to the index finger via a 6 × 10 portion of a vibrotactile array (Optacon). The vowels were /i/, /ε/, /ɑ/, and /u/, and three tokens of each b-V were used. The utterances were first processed to yield LPC coefficients, and then coded either in area function form or in spectral form using a technical mel vocoder. A “line” display was employed so that the number of active vibrators was constant for all stimuli. The durations of the stimuli were approximately equal. There were five sessions per week of approximately 35 min each, extending for up to eight weeks. The relative merits of the coding schemes, as well as the testing methods, are considered. [This work supported by NSF.]
Use of multiple training paradigms for the comparison of tactile speech displays
Authors: Fluster Matt
Published: October 2005

Past investigations comparing the relative merits of vibrotactile speech displays may have been unduly biased by the particular training and testing methods used. In order to minimize methodological dependence, two distinct training methods have been employed in a 2 × 2 (display method × training method) design. The two training methods have been specifically designed to model strategies used in teaching and learning language, and are used to train separate groups of subjects. One method is called the “building block” strategy, a step-by-step approach by which a subject first learns to identify small, meaningless tactile patterns and progresses to larger and meaningful structures. The other, the “holistic” strategy, immediately immerses the subject in the final step of the “building block” process. The two displays employed were a vocoder type and a flowed spectrographic type. Building block subjects learn to identify individual tactile phonemes and words before learning phrases. But preliminary results indicate that holistic subjects can learn to identify the phrases without necessarily knowing the constituent tactile words (out of context) or even having an awareness of the phonemic structure of the words. Conclusions are drawn concerning the use of these two different training strategies for the comparison of tactile speech displays. [Work supported by NSF and NIH training grant 5T32GM07057.]
A mean multipath intensity relation for sound propagation through a random ocean front
Authors: Neubert Jerome A.
Published: October 2005

By considering the stochastic nature of phase fluctuations in the ocean, the conventional ray theory intensity relation was extended in an earlier paper [J. A. Neubert, J. Acoust. Soc. Am. 51, 310–322 (1972)] to permit consideration of partial coherence in multipath problems. Although this relation worked well in the open ocean [J. A. Neubert, J. Acoust. Soc. Am. 62, 326–334 (1977)], it proves to be incomplete for sound propagation through a random ocean front. By considering also the amplitude fluctuations, a mean multipath intensity relation (as well as its standard deviation σ1) is found that takes into consideration the strong horizontal sound-speed gradients that occur in certain important ocean frontal regions.
Generating random sound speed fields in water using heating or cooling
Authors: Levenson Coleman , Posey Joe W.
Published: October 2005

Both heating and cooling techniques have been developed for generating random sound speed fields along a ten meter acoustic propagation path in a 14 m tank having a 3.7 × 3.7 m cross section. A 1.5-MHz cw signal was propagated along this path for the purpose of studying high-frequency acoustic signal fluctuations in a random medium. Previous investigators of acoustic fluctuations have produced random sound speed distributions by locating heating elements beneath the propagation path. Localized heating of water generates bubbles due to degassification, and it has been suggested that observed fluctuations may be due to resonant scattering by these rising microbubbles [J. A. Neubert and J. L. Lumley, J. Acoust. Soc. Am. 64, 1148–1158 (1978)]. Preliminary qualitative results indicate that statistically similar random sound speed fields generated by heating from below or by cooling from above produce similar acoustic fluctuations.
Simulation of propagation in fluctuating oceans using the radiation transport equation
Authors: Ko D. S. , Tappert F. D.
Published: October 2005

We have developed a radiation transport code, based on the Monte Carlo numerical method, which applies to low-frequency deep ocean propagation with random oceanic fluctuations. Refraction in the sound channel is done by means of a bi-cubic spline interpolation in the angle-depth coordinates. Scattering is accomplished by appropriately sampling several scattering kernels including those given by Wilson and Tappert [J. Acoust. Soc. Am. 66, 256 (1979)]. Numerical experiments show that the mean positions of arrivals are significantly displaced, but that spreading about the mean is suppressed due to the anisotropy of the fluctuations and especially due to the presence of the sound channel itself. [Work supported by ONR.]
Dispersive properties of a fluctuating parabolic waveguide
Authors: Bates Bruce J. , Bates Susan M.
Published: October 2005

The acoustic field of the fluctuating parabolic waveguide was expressed as an eigenmode expansion of the Green function. The field was assumed to be negligibly influenced by the boundary conditions and the source/observer locations were on the waveguide axis. Variations in pressure, arrival time, and angle for each mode, m, and source frequency, ω, were examined for fluctuations in axis velocity, C0, and waveguide curvature parameter, a. The results showed the measurable quantities to be approximately ten orders of magnitude more sensitive to fluctuations in the waveguide curvature parameter than to fluctuations in axis velocity. The arrival time asymptotic behavior was tA/t0 ∼ O(exp(−ωm2/4ω2)) for large source frequencies, ω ≫ ωm = (2m + 1)aC02, and fluctuations in the waveguide curvature parameter resulted in negligible variation in arrival time. For source frequencies near the mode-dependent cutoff frequency, ωm, arrival times showed extreme sensitivity to fluctuations in the waveguide curvature parameter. Mode-dependent arrival angles were least sensitive to fluctuations in the curvature parameter near grazing angles of π/4 radians. Fluctuations in pressure exhibited similar sensitivity to the waveguide parameters and intrinsic high-order moments.
Elastic wave propagation in materials with columnar grain structure
Authors: Fitting Dale , Adler Laszlo , Oliver Ben , Dewey Bruce
Published: October 2005

Several important structural materials (i.e., austentic stainless-steel welds and centrifugally-cast piping) are strongly anisotropic as a result of a columnar grain structure. Progress in modelling ultrasonic wave propagation in such materials is presented. Because elastic wave propagation in polycrystalline metal having a columnar grain structure is so complex, initial studies were directed toward components of these structures. Large single crystals of nickel were grown and the coordinate axes determined by x-ray diffraction. The elastic constants for the crystalline samples were measured using an ultrasonic pulse-transit-time technique. Specimen properties were input to a finite-element model of wave propagation. Results for elastic wave interactions at sample boundaries are given. [This work is supported by Basic Energy Science Program D.O.E.]
Frequency dependence of ultrasonic waves scattered from surface breaking cracks
Authors: Fitting Dale , de Billy Michel , Adler Laszlo
Published: October 2005

An ultrasonic spectroscopy system is used to study frequency dependence of scattered ultrasonic waves from surface breaking cracks in metals. Crack parameters such as depth, length, and surface conditions are correlated to the frequency dependence of the scattered amplitude. Both bulk and surface waves have been used. Experimental results have been compared to existing theories. [This work is supported by ARPA/AFML. Program on QNDE through Ames Laboratory.]
Rayleigh wave spectroscopy for measuring the depth of shallow open fatigue cracks
Authors: Burger C. P. , Testa A. J.
Published: October 2005

The energy in a Rayleigh surface wave is essentially contained in a surface layer less than two wavelengths deep. A broadband pulse will, therefore, have all its high-frequency components close to the surface with only the low frequencies penetrating to the deeper layers. This property of a Rayleigh wave, whereby the frequency spectrum of a pulse varies with depth below the surface, is used to find the depth of open surface breaking fatigue cracks with depths less than the lowest frequency component of the incident wave. The technique is not affected by the path of the crack, its inclination, branching roughness or the presence of residual stresses. It, therefore, measures accurately that property of surface cracks which arc most significant with respect to fracture, life prediction and safety assurance. The paper describes the technique and shows how automatic on-line pattern recognition procedures can be used to measure the depth to a resolution of 0.2 mm. Examples are given for the profiling of a rough surfaced crack.
Limitations on the use of short-pulse ultrasonic transducers for characterisation of small targets in solids
Authors: Weight J. P. , Brown A. F.
Published: October 2005

A convenient model explains the field pattern of a short-pulse broadband ultrasonic transducer in terms of a plane wave propagating in the geometrical region straight ahead of the face, together with a diffracted edge wave. That these waves actually exist is demonstrated by visualization and field-probing techniques. Interaction of plane and edge waves produces field patterns which, for the special case of continuous waves, lead to the definition of the nearfield and farfield regions. This paper extends the results of Weight and Hayman [J. Acoust. Soc. Am. 63, 396–404 (1978)] to solids. A simple model is proposed to take account of mode conversion of short pulses and hence to explain the added complexities of the echo system which arise from the use of these pulses to improve resolution. The consequences for materials evaluation are discussed.
Some parameters affecting backscattering reflection of ultrasonic waves at the Rayleigh angle for a liquid-solid interface
Authors: de Billy M. , Adler L. , Quentin G.
Published: October 2005

It has been reported before that an ultrasonic beam incident at the Rayleigh angle to a liquid-solid interface will produce a backscattered wave [S. Sasaki, Jap. J. Appl. Phys. 2, 198 (1963); W. G. Neubauer, J. Acoust. Soc. Am. Suppl. 1 68, S63 (1980); M. de Billy, these de doctorat d'etat (1980)]. Experimental results will be presented for various metals and glass. It appears that the backscattering is not due to grain structure or surface roughness alone but it is a finite beam phenomena. Results will be given for the effect of the beamwidth. This backscattering phenomena can be applied to measure the surface wave velocity for anisotropic materials.
PVF2 transducers and imaging arrays
Authors: Fesler K. , Weinstein D. , Zitelli L. T. , Shaw H. J. , Frank C. W.
Published: October 2005

A summary of the known piezoelectric mechanisms of PVF2 is presented. Properties of interest in regard to acoustic devices are explored. Calculations and experiments are used to examine the potential uses of PVF2 in acoustic devices. An integrated, multielement PVF2 imaging array is described. The array was constructed using photolithography, which allowed accurate, simple construction. Bulk wave imaging was performed at 2.25 MHz using this array. The line response and resolution of the array are compared to theory. A similar array was used for focused surface wave line scanning at 5 MHz on a silicon nitride substrate. The line response of the array was measured and compared to theory. Simple flaws were also detected. [Work supported by the Office of Naval Research under Contract N00014-77-C-0582, the Air Force Office of Scientific Research under Grant AFOSR-77-3386 and the Electric Power Institute under Contract RP 609-1.]
Electret transducers for use in optoacoustic spectroscopy
Authors: Farrow L. A. , Richton R. E.
Published: October 2005

The optoacoustic effect is based on the conversion of electromagnetic to sound energy, which is then detected by a microphone whose output is amplified. The resultant signal is predicted theoretically using a classical stretched drum type electret microphone as the transducer in a cylindrical optoacoustic cell filled with gas which absorbs single frequency laser radiation. These calculations simulate the conditions under which a series of experiments on chemical kinetics were performed; the experimental results are shown to be in good agreement with the predictions at gas pressures ≳ 0.5 Torr. Below 0.5 Torr, the microphone equation breaks down because the mean free path of the gas becomes comparable with the microphone electrode separation. This breakdown is observed experimentally at low gas pressure in the cell. Based on these considerations it is possible to use the optoacoustic effect to measure gas phase collisional relaxation rates and rate constants for homogeneous gas phase chemical reactions. Since some of the gases encountered are corrosive, gold is substituted for the usual aluminum evaporated onto the polymer to form the electret microphone diaphragm material.
Electret microphones with backplate electrets
Authors: Zahn Rolf W.
Published: October 2005

Present electret transducers utilize either an electret diaphragm or an electret coated back electrode. Transducers based on the latter principle allow the freedom to use a variety of materials as the membrane. For example, proper membranes can be placed under high tension resulting in an increase in resonance frequency. Investigations of the average membrane deflection, and thus the sensitivity, of circular electret microphones show that the radiation impedance damps the resonance peaks and shifts them to lower frequencies. The phase shift between the incident sound wave and the ac output voltage is affected in a similar way. The influence of different surrounding gases on the frequency response can be calculated by changing the gas constants. Several gases, for instance helium, neon, CO2, and ethane, have been investigated. Studies of the vibration sensitivity of electret microphones, which is controlled by the mass of the membrane, the mass loading of the surrounding gas, and the sensitivity to airborne sound, are also presented.
Prediction of perceived phonetic distance from short-term spectra—a first step
Authors: Klatt Dennis H.
Published: October 2005

Some models of speech perception (and many speech recognition devices) posit a process whereby short-term speech spectra are compared with a set of reference templates. These schemes will succeed only to the extent that metrics can be found that are (1) sensitive to phonetically relevant spectral differences such as those caused by formant frequency changes, and (2) relatively insensitive to phonetically irrelevant spectral differences associated with a change in speaker identity or recording conditions. Judgements of phonetic distance between pairs of static synthetic vowels and fricatives have been collected in which the stimulus ensemble included formant frequency changes and a number of acoustic changes that turn out to have little phonetic relevance (e.g., spectral tilt, relative formant amplitudes, high-pass and low-pass filtering). These data can be used to evaluate a spectral distance metric. For example, distance calculations based on the sum-of-squares of differences in critical-band filter bank outputs and those based on the linear-prediction residual correlate poorly with the vowel distance-judgement data. A metric based on spectral slope differences near the peaks in the criticalband spectra to be compared can be made to correlate very well (0.95) with the perceptual data. Sensitivity of the correlation coefficient to several design parameters of this metric (such as number of critical-band filters, filter bandwidths, and aspects of the weighting function) will be discussed. [Work supported in part by an NSF grant.]
Towards comprehensive but effective evaluations of the performances of commercial speech recognizers
Authors: Lea Wayne A.
Published: October 2005

Tests were designed for assessment of the accuracy of isolated word recognition under various controlled conditions. Desiderata guiding the design of the recommended tests included testing of all commercial recognizers by an independent agency, under identical controlled conditions that are representative of (or readily extrapolated to) expected field conditions, with all factors that affect accuracy carefully monitored, several performance measures used, and databases of sufficient size and appropriate design to assure statistical adequacy of results. Specific test conditions have been designed for speaker characteristics, training procedures, vocabularies, database recording procedures, rates of data entry, noise and channel conditions, etc. To simplify the multidimensional experimental design, and reduce the required data collections, a method of regression analysis known as “response surface methodology” has been applied. Testing is also truncated as soon as a device exhibits a substantial number of errors, so less accurate systems need less testing. Emphasis is on difficult recognition tasks that quickly reveal device limitations.
Some basic applications of the mean-value theory
Authors: Skudrzyk Eugen J.
Published: October 2005

The geometric mean between the resonance peaks and the antiresonance minima in the driving point response of a vibrator represents the mean line through the logarithmically recorded response curve. This mean is independent of the damping and is a simple function of the frequency difference, εν between successive mode resonance frequencies and the mode masses, Mν. The height of the peaks above this line and the minima below it are given by a factor β = 2εν/πωB ≈ εν/ωB, where ωB is the bandwidth, as long as the peaks are well separated (β > 4). With decreasing β, peaks and minima decrease drastically and for β ≈ 1 the response curve is smooth without peaks and minima. The driving point admittance usually has a small reactive component (wattless field), but by adjusting ενMν it can be made real and matched to any prescribed resistance. Thus, it is possible to modify the frequency response of a vibrator within reasonable limits. Because the mean line through the response curve is not affected by reflections of the wave fields at the boundaries or by boundary conditions, coupled vibrators and vibrators with inhomogeneities, such as welds, ribs, and mass loads, can be easily investigated by the mean-value theory. Examples will be presented. [This work was sponsored by the Office of Naval Research, Code 474.]
An overview of acoustic-structural interactions: Vibration and acoustic radiation
Authors: Pierucci Mauro
Published: October 2005

The structural vibration and the resulting acoustic radiation is a fully decoupled problem in a gas and a fully coupled problem in a fluid. The fluid-structure interaction problem encompasses a broad spectrum of areas of interest in engineering applications. This ranges from mechanically existed structures (acoustic radiation) to acoustically induced vibrations (elastic scattering) to hydrodynamically applied forces (flow noise). The coupled fluid-structure interaction for each of these problems is essentially the same; the difference lies in the manner utilized in applying the prescribed forcing function to the structure, in satisfying the interface boundary condition, and in analyzing the radiated acoustic field. The common link relating these problems is the fact that the same governing equations for the fluid and the structure are applicable in each of these areas. This commonality between the diverse fluid-structure interactions will be stressed. The different techniques being used to solve the problems for each of the three types of problems will be presented and a brief review of the state of the art will be given.