bluuebunny/crossref_metadata_2025 huggingface dataset:
Speech Analysis and Synthesis by Linear Prediction of the Speech Wave
Authors: Atal B. S. , Hanauer Suzanne L.
Published: October 2005

We describe a procedure for efficient encoding of the speech wave by representing it in terms of time-varying parameters related to the transfer function of the vocal tract and the characteristics of the excitation. The speech wave, sampled at 10 kHz, is analyzed by predicting the present speech sample as a linear combination of the 12 previous samples. The 12 predictor coefficients are determined by minimizing the mean-squared error between the actual and the predicted values of the speech samples. Fifteen parameters—namely, the 12 predictor coefficients, the pitch period, a binary parameter indicating whether the speech is voiced or unvoiced, and the rms value of the speech samples—are derived by analysis of the speech wave, encoded and transmitted to the synthesizer. The speech wave is synthesized as the output of a linear recursive filter excited by either a sequence of quasiperiodic pulses or a white-noise source. Application of this method for efficient transmission and storage of speech signals as well as procedures for determining other speech characteristics, such as formant frequencies and bandwidths, the spectral envelope, and the autocorrelation function, are discussed.
Investigation of the Timing of Velar Movements during Speech
Authors: Moll Kenneth L. , Daniloff Raymond G.
Published: October 2005

High-speed cinefluorographic films were taken of four normal subjects speaking English sentences containing various combinations of nasal consonants (N), consonants (C), and vowels (V) at normal speaking levels and rates of production. Word and syllable boundaries were designed to fall across the sequences in various ways. From frame-by-frame tracings, measures of velar movement and velopharyngeal opening were made. Results indicate extensive anticipatory coarticulation of velar movement toward velopharyngeal opening in CVN and CVVN sequences such that velar movement toward opening began during the approach to the initial vowel in all cases and some velopharyngeal opening was observed on all vowels. For NC and NCN sequences, velar movement toward closure for the consonant usually began during the preceding nasal such that some velar closure was observed during all plosive and fricative consonants used. These results directly contradict the hypothesis that a CV-type syllable is the minimal unit of coarticulation and production. The data are consistent with the predictions of a model which assumes phone-sized input unit and which incorporates a “look ahead” mechanism whereby an articulatory feature can be systematically anticipated prior to the occurrence of the phone with which that feature is associated.
Mechanism of Absorption of Ultrasound in Liver Tissue
Authors: Pauly H. , Schwan H. P.
Published: October 2005

The dominant part of the acoustic absorption of liver tissue and its components results from macromolecular relaxation processes. The absorption has been investigated over the frequency range 1–10 MHz and the following results have been obtained: (1) About two-thirds of the total absorption arises at the macromolecular level, with the remainder caused by macroscopic structure. (2) The specific absorption of tissue macromolecules, as expressed in absorption per weight percent, varies considerably from one biopolymer to another. (3) The absorption is related to the structure of the biological macromolecule or its hydration and changes with heat denaturation and pH. (4) A similar frequency dependence results for all materials investigated. This dependence is to be expected if one assumes that the molecular processes of absorption are characterized by a broad spectrum of relaxational time constants and activation energies extending over a range of at least 1:7.
Broad-Band Transducers: Radiation Field and Selected Applications
Authors: Papadakis E. P. , Fowler K. A.
Published: October 2005

In many applications, broad-band ultrasonic transducers capable of producing short video pulses are required. Previously, plane-wave analysis with equivalent circuits has proven successful in predicting pulse shape in the time and frequency domains. The present approach is to recognize that piston sources radiate nonplanar waves, and that the frequency spectrum of a broad-band piston source can be measured experimentally. With the spectrum as a weighing function for the field profiles of a monofrequency piston source, a superposition is performed to find the pressure and phase profiles in the radiation field of a broad-band transducer. Experimental measurements are presented that take advantage of the broad-band pulse technique combined with spectrum analysis. These include thickness gauging of thin materials and interface layers, and relative viscosity measurements.
Absorption Coefficients of Surfaces Calculated from Decaying Sound Fields
Authors: Embleton T. F. W.
Published: October 2005

A modified form of the Eyring equation is derived which explicitly takes account of the anisotropy of a sound field due to the deviation of the energy reflection (absorption) coefficient of individual surfaces from the mean value for all surfaces. When all surfaces have the same energy absorption coefficient, the equation simplifies to that of Eyring; when in addition these absorption coefficients are small, the usual simplification to the Sabine equation is valid. Using a simplified version of this modified Eyring equation, one can show that the effective absorption coefficient of a single absorptive surface in a hypothetical reverberation room is a complicated function of the location and total area of randomly oriented scattering panels. Apart from any correction for diffraction, the effective absorption coefficient is also a function of the area of the absorptive surface. In typical situations, this theory predicts that the effective coefficient will be greater (0 to 40%) than the energy absorption coefficient. In general terms, this agrees with measured values. In extreme situations not usually found in reverberation rooms, effective absorption coefficients are predicted to vary more widely and to be either greater or less than the energy absorption coefficient.
Enhancement of Heat Pulses in Crystals due to Elastic Anisotropy
Authors: Maris Humphrey J.
Published: October 2005

The generation of thermal acoustic waves by a heated metallic film on the surface of a dielectric crystal at low temperatures is discussed. It is shown that even if the waves produced correspond to a uniform distribution of directions of wave vector, there may be a large enhancement of energy flow in some crystallographic directions compared to the average. This effect arises because of elastic anisotropy. Explicit expressions are given for the enhancement expected in the principal directions of cubic crystals.
Effects of Unilateral Ménières Disease on Masking-Level Differences
Authors: Schoeny Zahrl G. , Carhart Raymond
Published: October 2005

The release from masking experienced by 12 persons with unilateral Ménière's disease was compared to that of 12 normals. A noise band, 400 Hz wide centered at 500 Hz, was presented at a spectrum level of 54-dB sound-pressure level. The masked monaural threshold for a 500-Hz tone was measured in each ear under the following conditions: SmNm, SmNu, SmN0, and SmNπ. The masked binaural threshold was likewise determined during S0N0, SπNπ, S0Nu, SπNu, SπN0, and S0Nπ conditions. Alternate binaural loudness balancing and simultaneous binaural median plane localization were also explored with the 500-Hz stimulus. The persons with Ménière's disease experienced greater absolute masking and less release from masking than did the normal hearers. They also showed a tendency for the reduction in masking-level difference (MLD) to be related to degree of loss in the affected ear. A limited interdependence between reduced MLDs and either interaural threshold disparity or interaural loudness difference emerged, but these effects are attributed to the influence which degree of loss in the poor ear has on interaural imbalances in threshold and loudness. No systematic relation was observed between size of MLD and performance on the localization task. Finally, the nature of a subject's diplacusis seemed to have a bearing on MLD size.
Acoustical Consequences of Lip, Tongue, Jaw, and Larynx Movement
Authors: Lindblom Björn E. F. , Sundberg Johan E. F.
Published: October 2005

An articulatory model is presented. It defines a procedure for deriving a set of formant frequencies from information on the state of the lip muscles, the position of the jaw, the shape and position of the tongue body, and larynx height. The acoustic and auditory consequences of varying these parameters individually are reported. The introduction of the jaw as a separate parameter—a feature not used in previous articulatory models—makes it possible to explain why “openness” occurs as a universal phonetic feature of vowel production. According to the explanation proposed, the degree of opening of a vowel corresponds to a position of the jaw that is optimized in the sense that it cooperates with the tongue in producing the desired area function. Such cooperation prevents excessive tongue shape deformation. Our results suggest that, in order to reflect this principle of articulatory synergism, “tongue height,” although primary with respect to its acoustic consequences, should be represented as a derived feature characteristic of the final vocal-tract configuration.
Preliminary Observations on the Effects of Exposure to Noise for Seven Days on the Hearing and Inner Ear of the Chinchilla
Authors: Miller James D. , Rothenberg Stephan J. , Eldredge Donald H.
Published: October 2005

Growth and decay of temporary threshold shifts (TTS), small permanent threshold shifts (PTS), and cochlear injury are described for two chincillas exposed to an octave band of thermal noise (0.3–0.6 kHz) at a sound-pressure level (SPL re 0.0002 μbar) of 100 dB for seven days. TTS grew with the duration of the exposure for 24–48 h and remained constant thereafter. After termination of the exposure, TTS decayed slowly and reached near-zero values in about five days. Three months after exposure there were small PTSs (less than 10 dB) for some test tones, reduced cochlear potentials, and clear losses of external hair cells in the second and third turns of the cochlea. Observations of TTS for identical exposures limited to a duration of 193 min are also described.
An Extension of Flanagan's Model of Vocal-Cord Oscillations
Authors: Mermelstein Paul
Published: October 2005

An extension of Flanagan's model for vocal-cord oscillations has been used to excite a transmission-line analog of the vocal tract and thereby synthesize voiced and unvoiced stops. Postulation of a two-spring vibrating system allows the lateral compression of the vibrating vocal-cord mass to be a nonlinear function of the force exerted by the air on the cords. When the supraglottal pressure is low, e.g., for an unconstricted vocal tract, the vibrating system is essentially linear and reduces to that proposed by Flanagan. When the tract is constricted, e.g., for voiced stops, the nonlinearities introduced serve to limit expansion of the glottal area in spite of the higher air pressure on the vocal cords. Unvoiced stops are modeled by an active separation of the vocal cords which switches the oscillator from an oscillatory stationary mode. Examples of simulations of intervocalic voiced and unvoiced stops are given.
A Passive Analyzer for Ultrasonic Shear Waves
Authors: Proctor Thomas M.
Published: October 2005

A device has been developed which allows the determination of the direction of shear particle motion generated by a single transducer. The normal ways of determining shear motion are to use another crystal of known polarization or to know the crystallographic geometry. This device analyzes the shear motion by use of reflection modes in a multiwaveguide assembly. The shear motion can be related to the geometry of this waveguide assembly.
Biodynamic Models and Their Applications
Authors: von Gierke Henning E.
Published: October 2005

Progress in modeling the mechanical response of man exposed to various environmental forces is discussed. Starting with a mathematical description of the mechanical and physical characteristics of the integument, soft and hard tissue, the numerous approaches taken and the results obtained from modeling various integrated elements such as the human vertebral column under vibration and impact loads, the chest and respiratory system under vibratory and blast loads and of the whole body system for selected force input conditions and locations are reviewed. Generalized (five-degree and more) freedom models are best suited to understand the correlation between the models derived to understand anatomical and physiological mechanical events and models used to explain the various injury mechanisms under environmental biodynamic loads (impact, blast, vibration, and noise). To derive a capability of modeling specific injury modes or experimentally observed probabilities of injury curves for various parenchymatous and hollow organs as a function of the force input variables, more detailed and specialized models are being used such as, for example, the lumped parameter, discrete parameter, and continuum model of the spine or models considering nonlinear tissue behavior. The status and value of these models for studying the body's physical and physiological response, for understanding and predicting injury mechanisms and probability of injury, for scaling the results of animal experiments, and for applying the models in protection engineering, such as escape and restraint systems design are demonstrated. There is need for further experimental as well as theoretical work in support of these practical biomedical as well as hardware requirements.
Relation between the Normalized Impact Sound Level and Sound Transmission Loss
Authors: Vér István L.
Published: October 2005

An expression relating the normalized impact sound level (Ln) and the sound transmission loss (TL) of a floor is derived. It takes into account both the resonant and the forced response of the floor, thus extending the utility of the formulas derived previously by Heckl and Rathe into the frequency range below the critical frequency. This relation between normalized impact sound level and sound transmission loss permits an experimental evaluation of the potential TL of a floor partition in the presence of certain types of flanking.
Sound Attenuation in Lined Rectangular Ducts with Flow and Its Application to the Reduction of Aircraft Engine Noise
Authors: Ko Sung-Hwan
Published: October 2005

An investigation is made of the sound attenuation in a rectangular duct with two sides lined and with a uniform steady flow. It is found in the study of modal attenuation that the fundamental mode is not necessarily the least attenuated in lined ducts. It is shown that sound attenuation is influenced by the fluid flow; tuning frequency shifts to higher frequency with decreasing peak attenuation for downstream propagation and to lower frequency with increasing peak attenuation for upstream propagation. The effect of acoustic impedance on sound attenuation for a given duct geometry is presented as well as the effect of duct geometry on sound attenuation for a given acoustic impedance. Theoretically predicted attenuation spectra are compared with experimental results (test data for both rectangular flow duct and Boeing 747/JT9D engine). The predicted attenuation spectra are in very good agreement with the experimental results for downstream propagation. However, the present theory overpredicts the sound attenuation for upstream propagation.
ELECTRODE INSERTION TECHNIQUES FOR LARYNGEAL ELECTROMYOGRAPHY
Authors: Hirose Hajime , Gay Thomas , Strome Marshall
Published: October 2005

This paper describes a simplified hooked-wire electrode insertion procedure for laryngeal electromyography. Percutaneous and peroral implantation techniques are combined with an effective anesthesia routine to provide a technically straightforward and medically safe means for obtaining electromyographic data from the five intrinsic laryngeal muscles, simultaneously.
The Vibratory Pattern of the Round Window in Cats
Authors: Khanna Shyam M. , Tonndorf Juergen
Published: October 2005

Round-window displacements were recorded by means of time-averaged holography in live cats and in fresh animal cadaver specimens. Considerable technical difficulties had to be overcome first, before such recordings became feasible. In the majority of cases, the displacement pattern was complex, even at low frequencies, with the maximum displacement occurring in the anterio-superior region. Between-animal variations were relatively large. From the reconstructions, volume displacements and eventually volume velocities were calculated for given frequencies. Since the sound pressures had been directly applied to the stapes footplate, the volume velocities for given sound-pressure levels (SPLs) could be converted into inner-ear impedance values, the assumption being that, for a given situation, volume displacements of the round window should equal those of the oval window. Inner-ear impedances were in the low megohm range; in this respect the results confirm those of an earlier study from this laboratory. However, while in cadaver specimens the results were reasonably uniform, in live animals impedance appeared to increase with exposure to high SPLs. This increase in impedance appears to exert a protective function for the inner ear. Experiments to explore this latter function in more detail are being planned.
Acoustic Wave Propagation in TeO2 Single Crystal
Authors: Ohmachi Yoshiro , Uchida Naoya , Niizeki Nobukazu
Published: October 2005

Acoustic phase velocity surfaces and ray directions in paratellurite, TeO2, have been calculated. Characteristic features of the wave propagation in this highly anisotropic medium have been optically confirmed using the shadow method and Schaefer-Bergmann diffraction technique. A small misalignment of the wave normal direction has been found to degrade seriously the performance characteristics of acoustic or acousto-optical devices composed of a highly anisotropic medium such as TeO2. The existence of the transverse mode with a zero temperature coefficient of velocity has been also confirmed by the present calculation and experiment.
Sound Dissipation by a Small Cylindrical Obstacle
Authors: Attenborough K. , Walker L. A.
Published: October 2005

Scattering of a plane wave, obliquely incident on an infinite-elastic conducting solid cylinder, which is freely suspended in a viscous conducting fluid, is considered. The wave motion in both fluid and solid is analyzed into viscous (shear), thermal, and dilatational components. Thus the dissipation, associated with the generation of highly damped viscous and thermal fluid waves at the boundary of the cylinder, is calculated. For a given frequency, this is shown to be a function of the cylindrical harmonic amplitudes of the scattered dilatational wave and of the angle of incidence. Results are presented for the simplified situation of normal incidence and small cylinder radius.
Vibration and Stability of a Uniformly Curved Tube Conveying Fluid
Authors: Chen Shoei-sheng
Published: October 2005

This paper presents a theoretical study of the vibration and stability of a uniformly curved tube containing flowing fluid. The assumption of the inextensibility of the tube is applied to derive the equation of motion. A solution for the natural frequency is obtained and numerical results are presented. The effects of flow velocity, fluid pressure, and the Coriolis force on the natural frequency are discussed. It is shown that when the flow velocity and fluid pressure exceed a certain value, the tube becomes subject to buckling-type instability. Critical loads in terms of the flow velocity and fluid pressure are presented for fixed-fixed, hinged-hinged, and fixed-hinged end conditions.
An Experimental and Theoretical Investigation of Elastic Wave Propagation in a Cylinder
Authors: Zemanek Joseph
Published: October 2005

A high-speed computer was used to investigate the problem of wave propagation in an isotropic elastic cylinder. Dispersion curves corresponding to real, imaginary, and complex propagation constants for the symmetric and the first four antisymmetric modes of propagation are given. The radial distributions of axial and radial displacements and of shear and normal stresses are given for the symmetric mode. By using a finite number of modes of propagation, an approximate solution is found for the problem of the L(0,1) mode impinging on a traction-free interface. The reflection coefficient is determined in this way and the accompanying generation of higher order modes at the interface is shown to cause a high-amplitude end resonance. Experimental results obtained by using the resonance method in conjunction with a long rod are presented to substantiate the calculated reflection coefficient and the frequency of end resonance. Phase velocities, based on measurements of the wavelength of standing waves and resonance frequencies, were obtained for the symmetric and first two antisymmetric modes. These measurements extend into the frequency range of more than one propagating mode. The rms deviation between theoretical and experimental results is in general less than 0.2% with the exception of the dispersion curve for the L(0,2) mode which deviates by 0.7%.
Vibrational Relaxation in Moist Nitrogen
Authors: Evans L. B.
Published: October 2005

The vibrational relaxation time of a nitrogen-water-vapor mixture has been determined at room temperature. The relaxation time for one molecule of nitrogen in pure water vapor, τAB, was found to be 8.85 μsec.
Comment on Insulkrete and Aluminum
Authors: Benedetti V. P.
Published: October 2005

The generation of gas bubbles on aluminum in an alkaline water solution is easily prevented by applying a clear acrylic spray to the aluminum.
Numerical Study of Sound Refraction by a Jet Flow. II. Wave Acoustics
Authors: Schubert L. K.
Published: October 2005

The equations appropriate to the propagation of sound in a realistic jet flow have been solved by finite-difference methods for the case of a sinusoidal point source on the axis of a subsonic jet. Each numerical solution provides detailed phase and amplitude information throughout the sound field. At the high-frequency limit the finite-difference results agree with ray-tracing results. Also, the computed farfield directivity patterns generally agree with available experimental data and lend further support to the view that the downstream “valley” in jet noise is due to refraction rather than to the inherent directivity of the sound generated within the region of turbulence. Unexpected findings are that the flow beyond 100 nozzle diameters continues to deepen the refraction valley significantly, and that the sound-pressure level reduction at a fixed point on the axis at first increases as the source is moved downstream from the nozzle. For the application of the refraction results to the computation of jet noise directivity, is found that the distortion of the constant phase surfaces can be neglected except at high frequencies.
Auditory Thresholds of a Killer Whale Orcinus orca Linnaeus
Authors: Hall John D. , Johnson C. Scott
Published: October 2005

Using standard operant conditioning techniques, a killer whale, Orcinus orca Linnaeus, was trained to respond to pure-tone auditory signals by pushing a response manipulandum. An audiogram was obtained for frequencies between 500 Hz and 31 kHz. Greatest sensitivity to the signal was observed at 15 kHz at a level of −70±5 dB re 1 dyn/cm2. The observed upper limit of hearing was 32 kHz. At no time during training or testing did the animal respond to an undistorted signal above 32 kHz. Frequencies below 500 Hz were not tested, owing to high ambient tank noise levels.
The Central Origin of the Pitch of Complex Tones: Evidence from Musical Interval Recognition
Authors: Houtsma A. J. M. , Goldstein J. L.
Published: October 2005

The human auditory system's ability to recognize simple melodies that correspond to fundamental periods in sequences of periodic sounds devoid of fundamental energy was studied through musical interval identification experiments. Stimuli comprising two randomly chosen successive upper harmonics were presented both monotically (two harmonics to one ear) and dichotically (one harmonic to each ear). Subjects could recognize melodies equally well with both modes of stimulus presentation. The results imply that the pitch of these complex tones is mediated by a central processor operating on neural signals derived from those effective stimulus harmonics that are tonotopically resolved.
Simultaneous Two-Channel Signal Detection. I. Simple Binaural Stimuli
Authors: Pastore Richard E. , Sorkin Robert D.
Published: October 2005

Human observers performed two simultaneous increment detection tasks, one in each ear. This task, together with monaural and binaural control conditions, was used to investigate interaural time sharing, sensory inter-actions, internal noise, and binaural decision spaces. When the signals were binaurally in phase, there was no evidence of cross-channel facilitation or inhibition, and the observers were able to perform the task without performance decrements relative to single-channel control conditions. For one observer, the derived estimate of the between-channel correlation in the absence of an external masking noise was +0.40 and was consistent across different experimental conditions. Differences in the results for 180° phase-shifted signals indicated probable changes in the nature of the processing mechanisms involved in the detection of the different types of signals. The paradigm and related analyses should be of value in the study of other kinds of perceptual phenomena.
Intensity Perception. III. Resolution in Small-Range Identification
Authors: Pynn C. T. , Braida L. D. , Durlach N. I.
Published: October 2005

In most previous experiments on the ability to identify sound intensity, the stimulus set has been chosen such that the range of intensities is many times larger than the value of the “just-noticeable difference” in intensity that has been derived from the results of intensity discrimination experiments. In such cases, the resolution obtained in the identification experiment is much worse than would be expected merely on the basis of the pairwise discriminability of the stimuli. In this paper, we report the results of a study designed to explore the prediction [Durlach and Braida, J. Acoust. Soc. Amer. 46, 372–382 (1969)] that this discrepancy between identification and discrimination does not occur if the range of intensities employed in the identification experiment is sufficiently small. Generally speaking, the results of this study support the prediction.
Duration as a Cue in the Recognition of Synthetic Vowels
Authors: Ainsworth W. A.
Published: October 2005

Sets of synthetic vowel sounds which differed in first-formant frequency, second-formant frequency, and duration were presented to a group of listeners for identification. It was found that listeners' judgments depended on all of these factors. Duration was a relatively more important cue for vowels located in the center of the F1-F2 space where a vowel might more readily be confused with one of its neighbors. The perceived duration of a vowel was found to be biased by the rhythm of the sounds that preceded it. In the case of sounds lying near perceptual boundaries, this was sometimes sufficient to change the identity of the vowel.
Influence of Utterance Length upon Bilabial Closure Duration for /p/
Authors: Schwartz Martin F.
Published: October 2005

An inverse relationship exists between the duration of the bilabial closure for /p/ in the first word of an utterance and the total number of words in the utterance.
An Alternative MD-SCAL Analysis of the Graham and House Data
Authors: Singh Sadanand , Woods David R. , Tishman Abraham
Published: October 2005

Graham and House (1971) used a non-Euclidean metric (r = 1.5) to scale children's perceptual errors of 16 consonants in a four-dimensional configuration. They found that neither the Chomsky-Halle linguistic features nor traditional phonetic features were good interpretants of their dimensions. Using a Euclidean metric (r = 2.0), we found a two-dimensional configuration, whose dimensions could be interpreted without misclassification (1) stop versus continuant and (2) sonorant versus obstruent. The obstruents were further distinguished as (3) sibilant/nonsibilant along the second dimension.
Review of Underwater Acoustics Research: Noise
Authors: Wenz Gordon M.
Published: October 2005

The purposes, problems, and progress of radiated noise, self-noise, and ambient noise research are reviewed. Purposes are related primarily to national defense, but applications to fishery and to the utilization of other natural resources are also noted. Basic problems, most of which were recognized 20 years or more ago, involve ascertainment of properties of the noise, identification of noise sources and mechanisms of noise generation, and the discovery and definition of noise dependencies on environmental factors. Many radiated and self-noise sources and mechanisms have been identified. Major problems are those of noise measurement, noise reduction, and prevention. In the field of ambient noise, most measurements have been of sound-pressure level. Some of the noise sources and environmental factors have been identified, and a capability for qualitative and gross prediction has been achieved. Recommended are further investigations of the variation of ambient noise with receiver depth, directionality of the noise field, statistics of both noise level and instantaneous noise values, additional work at frequencies below 10 Hz, and additional geographic coverage, making full use of current knowledge to fashion models for experimental guidance. Challenging problems exist in procedures and instrumentation for noise studies.
Twenty Years in Underwater Acoustics: Generation and Reception
Authors: Hueter T. F.
Published: October 2005

Development in the art of transducer design and array configuration has been spurred on mainly by two motivating forces: (1) Extensive research in underwater propagation has established the advantages of increasingly lower frequencies for long-range detection and localization of targets and noise sources. (2) The advent of new piezoelectric and structural materials and of solid-state electronic devices has led to substantial improvements in transducer performance with regard to sensitivity, power output, and depth of submersion. Theory has kept abreast with these developments, particularly in handling large arrays with their mutual impedance problems, in pointing to digital multibeamforming techniques, and in revealing the significance of waveform design to detection performance. A few new concepts were born and have won acceptance during this period. These include: the generation of sound by hydroacoustic means, the employment of compliant metal tubes for acoustic focusing and reflection, the exploitation of structural flexing modes for sound radiation, and the use of free-flooded cavity structures as deep submergence sources. As we continue to adapt our sources and receivers to the ocean's transfer functions, noise patterns, and targets—false and true—there will be an increasing need for fundamental research into the acoustic properties of materials and for field test of experimental acoustic detection systems.
A Review of Reverberation, Scattering, and Echo Structure
Authors: Horton Claude W.
Published: October 2005

The last 20 years have seen a tremendous amount of work in the area of reverberation and scattering. An effort is made to summarize with graphs and charts the amount and nature of this work. Comparisons are made between the results of measurements at sea, measurements with models, and theoretical calculations. Since theoretical solutions of scattering from randomly rough surfaces involve numerous approximations, these different solutions are classified with the aid of tree diagrams so that one can chart a path through the various approximations. Most of the unclassified work on echo structure has been devoted to intensive analyses for targets of relatively simple geometric shape. For example, the sphere and the cylinder (with and without internal structure) still present interesting problems.
The Logarithmic Dependence of Surface-Generated Ambient-Sea-Noise Spectrum Level on Wind Speed
Authors: Crouch Wayne W. , Burt Peter J.
Published: October 2005

A mathematical description of ambient sea noise is presented that takes into account the two dominant sources—surface agitation and distant shipping. The contribution from surface agitation is shown to be linearly dependent upon the logarithm of wind speed for depths between 400 and 2500 fathoms at several sites near Bermuda. When this is taken into account, the ambient-noise data that include both sources can be analyzed to determine the individual levels of the sources. Also, the standard deviations of the two sources can be determined from the standard deviations of the measured levels.
Backscattering of Underwater Sound in Saanich Inlet, British Columbia, Including Observations of Scattering from a Fish School
Authors: Scrimger J. A. , Turner R. G. , Heyd G. J. H.
Published: October 2005

The frequency dependence of acoustic volume backscattering strength has been measured at depths of 100, 200, 300, and 400 ft in Saanich Inlet, British Columbia, Canada, over a 24-h period. The measurements were made for comparison with open-ocean (Pacific) results, since the biology of the inlet has been extensively studied, and it serves to some extent as a reference water volume. In the course of carrying out the above measurements, the backscattering spectral characteristics and strength of a school of young hake, of apparent mean size of 11 in., was obtained. The time series measurements revealed unchanging scattering characteristics at the 300- and 400-ft depths, with broad peaks near 1.2 and 4.8 kHz superimposed on otherwise flat spectra. Greater variability was observed at the 200-ft depth, while the greatest variability was observed near the surface, i.e., at the 100-ft observation depth. The fish school, which was observed to be closely packed (less than a fish length spacing near the surface) and randomly oriented, was shown to have a flat backscattering spectrum between 1 and 9 kHz and an estimated backscattering strength of −47±3 dB.
Radiation Resistance of a Baffled Beam
Authors: Wallace C. E.
Published: October 2005

The radiation resistance of a beam is theoretically determined from the total acoustic power radiated into the farfield. The beam is supported in an infinite baffle, with both hinged and clamped supports considered. Asymptotic solutions are derived for frequencies well below the critical frequency. Curves, covering the entire frequency range between the low- and high-frequency asymptotic solutions, are obtained through numerical integration for the first ten modes of beams with various width-to-length ratios. For frequencies well below the critical frequency, the ratio of the radiation resistance of a beam clamped at each end to that of a beam hinged at each end is 0.851 for the first mode, 0.711 for the second mode, and asymptotically approaches 2 as the mode number tends to infinity. For both hinged and clamped supports, the radiation resistance of all modes increases with the beam width-to-length ratio.
Flexural Vibrating Free-Edge Plates with Stepped Thicknesses for Generating High Directional Ultrasonic Radiation
Authors: Barone Alfonso , Gallego Juarez Juan A.
Published: October 2005

A transducer for the generation of high directional ultrasonic radiation in fluids is studied. It consists of a plate of particular shape set in oscillation by an adequate vibrator. Since the directional pattern depends substantially on the phase with which the single elements of the plate vibrate, the radiating surface is shaped into steps covering areas vibrating with the same phase, the height of the steps being equal to a half-wavelength of the radiated sound, in order to obtain a coherent acoustic radiation. To facilitate the design of such plates, an approximate theory of their vibration is shown, and the experimental proofs, whose results confirm the full validity of the adopted method, are described.
Large Deflections of Impacted Helical Springs
Authors: Phillips James W. , Costello George A.
Published: October 2005

A theoretical formulation of the large deflections of helical springs is given, and coupled nonlinear equations of motion for a typical spring element are derived. Linearized forms of these equations are solved numerically and compared with experimentally obtained streak photographs of an impacted spring. The agreement between theory and experiment is good, as long as adjacent coils of the spring do not touch.
Damping Additions for Plates Using Constrained Viscoelastic Layers
Authors: Torvik Peter J. , Strickland Daniel Z.
Published: October 2005

An analysis is given for a damping addition employing several thin viscoelastic sheets and thin metallic layers. The damping layers are alternated with the constraining layers, which are segmented and are not anchored to the base plate. The effectiveness of such additions in increasing the damping of thin simply supported square plates is evaluated and methods for optimizing the design are considered. An experimental investigation of the effectiveness of such damping additions is also reported. Additions weighing a few percent of the weight of the base plate were found to produce substantial increases in the damping of the system. A nonoptimal design was found to produce less, but still substantial, damping.
On the Medium from the Point of View of Underwater Acoustics
Authors: Berman Alan , Guthrie Albert N.
Published: October 2005

This paper gives a brief survey of the state of knowledge in ocean acoustics circa 1948 and reviews the advances made during the past two decades. Twenty years ago the thermostructure of the ocean was known in moderate detail. while the character of the boundaries could be specified less precisely. A principal deficiency was in the ability to handle a mathematical model of the ocean which would give a prediction of the acoustic field in detail. While much remains unknown today, the past 20 years have seen a considerable accumulation of knowledge concerning the geographic and seasonal variations of the medium. Reasonably good specifications of the ocean boundaries are now available. The acoustic absorption coefficient in the ocean is known imperfectly, and the ability to specify the thermo microstructure is poor. Nonetheless, the intensive efforts of many investigators over the last 20 years have yielded a computational capability which now allows a general specification of propagation in relatively great detail.
The Inertance of a Smooth-Edged Orifice
Authors: Holger D. K. , Wilson T. A. , Beavers G. S.
Published: October 2005

Three analytical models for the potential flow through a smooth-edged orifice are discussed and the prediction of the acoustical inertance obtained from these models is compared with experimentally determined values of orifice inertance as a function of the ratio of wall thickness to orifice diameter. It is shown that the simple hyperbolic wall model predicts corrections for wall thickness which are of the wrong order of magnitude for thin-walled orifices and are inaccurate for thick-walled orifices. An improved model, consisting of the super-position of a hyperbolic flow field and a ring vortex, is used to represent an orifice boundary with finite curvature at the throat and finite thickness. By matching either the curvature or the wall thickness of an orifice, upper and lower bounds for the inertance are obtained. By adding another singularity in the potential flow analysis, both the curvature at the throat and the wall thickness of the actual orifice can be matched, and the values predicted by this model are in good agreement with the experimental results.
Degraded Performance of Nonlinear Array Processors in the Presence of Data Modeling Errors
Authors: McDonough R. N.
Published: October 2005

By properly weighting and summing the individual signals received by an array of acoustic sensors, the performance of the array can be improved. In order that the weights can be chosen in a rational manner, some mathematical model must be postulated for the received array data. In this study we examine the effects of a class of data modeling errors on the directivity of linear and nonlinear array processors. We derive a measure of the extent to which the array response may change as a result of Gaussian deviations of the amplitude and phase of the modeled data from those of a nominal model. Among all array processors the simple beamformer is shown to have minimum sensitivity to small model perturbations of this type, and thus to be robust to errors in model selection. For a certain proposed high-resolution estimator, we show that cases exist in which the sensitivity is very large. An array processor having large sensitivity to modeling errors is mathematically analogous to a superdirective electromagnetic array, with the data model perturbations corresponding to perturbations in the exciting currents, or radiator positions, of the latter. Large perturbation sensitivity of an accoustic array processor is analogous to superdirectivity in phased array antenna design.
Duration Discrimination of Noise and Tone Bursts
Authors: Abel Sharon M.
Published: October 2005

This research investigates the human observer's ability to discriminate difference in duration for noise bursts and gated sinusoids. Two observers compared two durations T and T+ΔT in a two-alternative forced-choice procedure. The value of T ranged from 0.16 to 960 msec. For each T the value of ΔT for 75% discrimination was determined. The results showed that for most of the range investigated ΔT was proportional to T12. Performance was not affected by a change in bandwidth from 3500 to 200 Hz. Values of ΔT for 75% correct did decrease, however, when the observers were given audible spectral cues from very short pulsed sinusoids. The theory best describing the results was the neural counter model proposed by Creelman [J. Acoust. Soc. Amer. 34, 582–593 (1962)].
Frequency Discrimination and the MLD
Authors: Gebhardt Carol J. , Goldstein David P. , Robertson Ronald M.
Published: October 2005

Binaural frequency difference limens in noise were obtained under homophasic and antiphasic conditions. Signal frequencies of 200, 300, 500, 700, and 1000 Hz were investigated at 5- and 10-dB sensation levels while 500 Hz was also explored at 15, 20, and 25 dB. The masker was a bandlimited noise with a spectrum level of 55 dB. Results indicate significant changes in discrimination behavior as a function of phase condition and sensation level. Alternative interpretations of the data are considered.
An Analysis of Lesion Development in the Brain and in Plastics by High-Intensity Focused Ultrasound at Low-Megahertz Frequencies
Authors: Robinson T. C. , Lele P. P.
Published: October 2005

Thermal factors are believed to play a dominant role in the development of the structural and functional effects of irradiation of the nervous system with focused ultrasound at low-megahertz frequencies. Similar mechanisms are postulated to underlie the effects of irradiation in methacrylate, which is frequently used as a test material to evaluate the influence of various factors on the results obtained. This study was undertaken to determine if thermal mechanisms alone can explain the development of trackless focal alterations (lesions) and all of their measurable characteristics in plastic as well as in brain. A purely thermal model is assumed and analytical prediction of lesion development and lesion size and shape for varying values of ultrasonic and thermal constants and controllable variables (frequency, focusing, dosage, target depth, etc.) is attempted. An empirical equation to describe the axial and radial ultrasonic energy distribution at the focus in water is derived. Appropriate heat transfer equations are developed for temperature distributions resulting from ultrasonic irradiation. The computed temperature profiles are plotted against nondimensionalized parameters. Temperatures at the lesion boundary were determined experimentally. Lesion dimensions read off the computed temperature profiles at the measured lesion boundary temperature are compared with experimental data. Agreement of analysis and data shows that, within the range of ultrasonic parameters used in this study, the development of lesions in the brain are explained by thermal mechanisms.
Voices of Men and Machines
Authors: Flanagan J. L.
Published: October 2005

Talking computers are likely to become a fixture in modern society. The range of information services that can be provided by voice from computers depends largely upon how clever computers become at imitating human speech. This, in turn, depends upon the fundamental acoustic and linguistic knowledge that can be imparted to the machine. This article summarizes the principles of human speech generation, traces some historical interests in speaking machines, and indicates present capabilities of talking computers.
Noise Field of a Supersonic Mach 1.5 Cold Model Jet
Authors: Yu James C. , Dosanjh Darshan S.
Published: October 2005

Systematic surveys of both the near and far noise fields were made for a supersonic (nozzle design Mach number 1.5) cold model jet. The operating conditions selected for this investigation were (a) shock-free mode at operating pressure ratio (reservoir pressure/ambient pressure), ξ=3.57 and (b) underexpanded mode at ξ=4.74. The experiments were conducted in an anechoic chamber. The purpose of this investigation was to extend the existing understanding of the noise field of a supersonic shock-free jet at a moderate exit Mach number and the variations in its acoustic behavior when the nozzle was operated at its underexpanded mode, where strong shock waves were present. The main experimental results are presented. It was found that the broad-band pressure spectra of apparent sources in each of the individual characteristic flow regions were grossly similar. The strongest source for the shock-free jet was located in the region between the laminar core tip and the supersonic core tip, whereas for the underexpanded jet the strongest source was found near the middle of the flow region containing repetitive shock waves. It is shown that the significant increase in the noise output at the underexpanded mode of operation was primarily due to high-frequency components.
Theory and Measurement of Modal Spectra in Hard-Walled Cylindrical Ducts
Authors: Bolleter Ulrich , Crocker Malcolm J.
Published: October 2005

The propagation and interaction of acoustic modes in ducts is of importance for the measurement and control of sound generated by ducted fans and compressors. A method is presented by which the modal spectra (pressure and power spectral densities) for the first nine cross modes can be determined from pressure cross-spectrum measurements in the duct. The flow noise, a potential source of errors, is suppressed by placing the two microphones sufficiently far apart in the duct. The modal spectra and some of the modal interaction terms (modal correlations) for a number of fans are presented. The method should have many applications in verifying modal propagation, absorption of linings, and scattering of modes as well as in identifying sound sources.