bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaural Time Delay and Apparent Direction of Clicks
Authors: Mickunas Juozas
Published: November 2005

The relationship between interaural time delay and the apparent direction of the image of a click was investigated at 30 and 60 dB SL (sensation level). A variation of the method of constant stimuli was used to collect the data. The constant stimulus, a steady stream of air, was in the tactile modality; the variable stimulus, a train of dichotic clicks, was in the auditory modality. The stream of air was set 15°, 60°, and 75° from the median plane in the right or left frontal quadrants. The train of dichotic clicks, each 0.2 msec in duration, and the stream of air were presented simultaneously for 3 sec. The subject had to decide whether the sound image was to the right or to the left of the stream of air. Psychometric functions were fitted to the data of three inexperienced subjects. The data show that, up to ±0.5 msec, the same interaural delay produces the same angular displacement at 60 as at 30 dB SL. The relationship between the interaural time delay and the angular displacement of the sound image is linear up to ±0.5 msec. Time delays longer than ±0.5 msec produce different displacements at different intensities; longer time delays are needed to shift the sound image to the same angular displacement at 60 than at 30 dB SL. The relationship between the interaural time delay and the angular displacement of the sound image also departs from the linearity that is found for time delays up to ±0.5 msec. A model based upon a coincidence detector is proposed to explain these results in a manner consistent with the results of experiments on interaural time-intensity trading.
Recent Advances in Speech-Compression Techniques
Authors: Aitken A. R. , Brueck R. L. , Ziemer D. R.
Published: November 2005

This paper discusses recent work in statistical prediction and encoding to permit efficient utilization of speech-communication channels. Fidelity, continuous source information rates, and transmission-channel requirements are described in terms of optimum system trade-offs. A theoretical analysis and statistical evaluation of simulation models is presented. The widely studied techniques of speech compression through selective, but irreversible, removal of signal structure are briefly presented. A mathematical analysis of applicable reversible transformations is given, showing the advantages of removing statistically predictable signal structure. The details of implementing the predictive-encoding (source coding) and subsequent signal-recreation (receiver decoding) operations are presented in functional block-diagram form. In speech-compression systems where existing fidelity requirements have become critical through application of irreversible processing techniques, it is shown that further signal compression may be accomplished without additional loss of fidelity. Alternately, with fixed channel capacity, predictive coding may be utilized to provide increased intelligibility and naturalness of the transmitted-speech source. The predictive encoding may be made adaptible to speaker classification. [This study was supported by AFCRL (OAR) under contract AF19(628)-345.]
Speech-Formant Measurement with a Continuously Tuned Automatic Tracking Filter
Authors: Hellwarth George A.
Published: November 2005

As a solution to the problem of voice-pitch and formant-frequency measurement in real time, a continuously tuned, automatic tracking filter is described. The identification of spectral maxima of speech signals is achieved through the application of automatic frequency-control techniques. The tracking-filter system operates first by translating the speech in frequency by an amount determined by a voltage-tuned oscillator, next by passing the resulting single-sideband signal through a fixed narrow-band filter, detection of the instantaneous frequency of this narrow-band wave, then amplification and low-pass filtering of the frequency function for use as a feedback signal to tune the oscillator. A laboratory circuit of a single tracking filter was used to determine experimentally the response and stability of the nonlinear feedback system to a variety of input test signals. A very promising ability to track voicing harmonics next to the actual formant resonances, of speech is demonstrated. The problem of using three or more filters for formant vocoder transmission is discussed. [This doctoral thesis was supported by a U. S. Air Force contract with the Communication Sciences Laboratory, The University of Michigan.]
Cheap Talk from a Computer
Authors: Slawson A. Wayne , Valentine James W. , Kish Augustine
Published: November 2005

Recently, digital computers have become important as tools for research in speech and psychoacoustics. In particular, it has become possible to synthesize any waveform by approximating the desired waveform with a step function. Almost any reasonable frequency ranges and accuracy of amplitude coding can be approached, depending on available funds. In some cases, university laboratories for instance, the funds for building equipment are often quite limited while those for computer time are, paradoxically enough, considerably less so. An inexpensive device has been designed that will convert digitally-coded information written on an ordinary IBM magnetic tape into a voltage waveform. The tape must be written by an IBM-7090 or comparable computer and an IBM-729IV tape-transport unit must be used in the conversion process. The limitations of the method are discussed and sample output is demonstrated.
Rocket-Sled Environmental-Noise Investigation
Authors: Kamo Roy , Peter Abe
Published: November 2005

Results of a theoretical and an experimental research investigation of the various noise sources encountered by a high-speed rocket sled are presented. The objective was to isolate and determine quantitatively the contribution of each noise source to the over-all noise level inside the rocket sled. The noise sources investigated were those due to turbulent boundary layer, base pressure fluctuation, wake noise, and the propulsive jet motors. A wedge-shaped Mach 3.0 rocket sled was heavily instrumented to obtain the interior and pseudoboundary noise levels. At higher Mach numbers, the turbulent boundary-layer noise represents the greatest single noise source with a broad frequency spectrum. Noise due to base-pressure fluctuations was also high, but was confined to a narrower frequency band that can be related to a modified Strouhal relationship. The contribution from the wake noise and the rocket-jet noise diminished with increasing vehicle speed and became insignificant beyond Mach 1.0. Although the instrument compartment was constructed of aluminum honeycomb material and fiberglass lining with a total density of 1.7 lb/sq ft, its acoustic qualities were insufficient to prevent damaging noise levels to electronic and test components within the sled at Mach number approaching 1.0.
Farfield Acoustic Effects of the Launch of the Saturn Space-Flight Vehicle
Authors: Tedrick Richard N.
Published: November 2005

The launch of large space-flight vehicles has resulted in the production of very high levels of acoustic noise. The largest of these to reach flight status, the SATURN C-1 vehicle, generates an estimated 40 MW. Sound-pressure-level measurements were recorded along three widely separated azimuths from the launch pad. Data are presented showing the variation of the sound-energy distribution as a function of both time and range. Spectral information is presented, along with the measured attenuation coefficients. The measured launch data are compared to similar data taken during static test.
Noise Radiation in and near a Jet Flow
Authors: Eldred Kenneth M. , Mann Myron
Published: November 2005

This paper discusses the noise radiation from a hot sonic jet flow with relation to the flow gradients and presents a simplified model of the resulting nearfield. The reexamination of previously published data in terms of the simplified model lends considerable insight into the basic mechanisms controlling radiation of sound from and through the jet flow. [This work was supported by the Flight Dynamics Laboratory, USAF, under Contract AF33(616)-7772.]
Improved Wave-Equation System for Finite-Amplitude Sound in Viscous, Thermally Conducting Fluids
Authors: Blackstock David T.
Published: November 2005

In finite-amplitude acoustics, one of the primary difficulties is how to handle problems in which dissipation as well as nonlinearity is important. Basically, one should like to solve the full equations of hydrodynamics, but because these are exceedingly complicated, one usually resorts to approximation methods. One such method is to derive from the hydrodynamics equations a “next-best approximation” to replace the traditional wave equation c02∇2φ − φtt = 0. Following the pioneering work of Burgers, Cole, and Hopf, Lighthill [in Surveys in Mechanics, edited by G. K. Batchelor and R. M. Davies (1956), pp. 250–351] found an improved yet tractable wave equation for the special case of plane progressive waves in an unbounded, viscous, thermally conducting perfect gas. In the present work, an extension of Lighthill's approximation procedure is used so as to obtain a more versatile “improved wave equation,” actually, a pair of equations. Besides encompassing the case treated by Lighthill, this pair is valid for nonplanar waves, for interacting (e.g., standing) waves, and for waves subject to boundary-layer effects. Moreover, the fluid need not be a perfect gas. An example involving plane waves is given. [This work was supported in part by the U. S. Air Force Office of Scientific Research under Contract AF 49 (638)-1118.]
Output Time Function of a Weighted, Tapped Delay Line used as an FM Signal Detector
Authors: Rowlands Richards O.
Published: November 2005

The use of a tapped delay line with variable spacing for the detection of a Doppler invariant FM signal has previously been described. It is shown here that, if the duration of the signal is greater than that of the delay line, the output time function for the period when the whole of the delay line is occupied by the signal can be expressed by an equation similar to that used for the radiation pattern of a uniformly spaced array. A weighting function derived from a Chebishev polynomial may, therefore, be applied to the taps to optimize the output-signal-peak to minor-lobe ratio. The theory breaks down for the end periods when the signal does not fully occupy the delay line. Graphs for a number of specific weighting functions have been drawn to obtain an indication of the magnitude of the error due to this end effect.
Receiving Response of an Arc Segment of a Cylindrical Hydrophone in a Plane-Wave Sound Field
Authors: Ambrose Edmund G. , Ehrlich Stanley L. , Tudino Janet S.
Published: November 2005

The open-circuit voltage response of an electroded arc segment of a thin-walled complete cylinder varies with electrode dimensions, location relative to the direction of the incident plane wave, and frequency. Since many modes of vibration are excited, the electrical output is the sum of the individual modal components. With symmetrical electrode configurations and/or electrical shading, the relative strength of desired modal outputs can be increased and simpler beam-pattern responses produced. A mathematical expression for arc-segment response was desired to allow further study of beam formation with both symmetrical and asymmetrical electrode configurations. Analysis proved to be extremely difficult, and a measurement program was undertaken. Amplitude and phase measurements are presented for a 15° arc segment of a cylindrical hydrophone. In addition, VILP measurements verifying the symmetry conditions required to accentuate specific modes are presented.
Acoustic Scattering from a Layer of Siphonophores
Authors: Batzler W. E. , Barham E. G.
Published: November 2005

In situ visual and photographic observations of organisms made during a dive of the bathyscaph Trieste in waters off San Diego, California, have been compared with acoustic volume-scattering measurements made simultaneously from a nearby surface ship. The dominant organisms observed in zones of peak reverberation were the physonectid siphonophores, Nanomia bijuga. These colonial coelenterates consist of a number of different individuals, one of which is modified into a gas-filled flotation sac. Acoustic-scattering coefficients, which were measured at 12 kc/sec during the course of the dive, vary from −48 to −58 dB over the most densely populated portion of the layer and show a variation with depth similar to that indicated by visual estimates of population density. Although the filamentous structure of a colony and its waterlike consistency reduce the effective scattering cross section, the gas floats borne by the siphonophores are near resonant size for this frequency and depth and they alone can account for the observed scattering levels. Because of the high scattering coefficients obtained and because these organisms have a wide geographic distribution, we believe that siphonophores should be considered seriously as perhaps the major cause of the deep scattering layer throughout the oceans of the world.
Nature of Primary Auditory Neurons in the Monkey
Authors: Katsuki Yasuji
Published: November 2005

Electrophysiological as well as histological studies at our laboratory indicate that the cochlear nerve of monkey, unlike those of cat and guinea pig, is composed almost exclusively of axons of primary auditory neurons. The thresholds of neurons that have characteristic frequencies below about 6 kc/sec fall into two statistically different groups. It is proposed that the groups of neurons with lower and higher thresholds originate at the outer and inner hair cells, respectively. If impulse frequency is plotted as a function of sound intensity, the group of neurons with lower thresholds can be further subdivided on the basis of the slopes of these curves. It is further suggested that the units characterized by smaller slopes correspond to the external spiral fibers, while those with steeper slopes correspond to the external radial fibers. The impulses of the primary neurons elicited by a continuous background tone could be temporarily suppressed by a second tone burst, if the frequencies and intensities of the two sounds are appropriately chosen. Though the nature of this phenomenon is not clear, inhibition by efferent fibers can be excluded because of the very short latency of the onset of the suppression phenomenon.
Dynamic Hardness of Plastics
Authors: Walkling Robert A.
Published: November 2005

The dynamic hardness is defined as the ratio of the normal driving force to the normal displacement of a rigid spherical indenter. An instrument to measure this quantity has been developed in which the displacement is sensed by a seismic-displacement pickup and the driving force is produced by the inertial reaction at the midpoint of a free-free bimetallic bar driven magnetostrictively. The indenter is maintained in sliding contact with the plane surface of the material under test by a static bias load. Measurements have been made on a sample of a polyvinyl chloride acetate copolymer sliding at a velocity of 0.8 cm/sec under a 1-mil sapphire indenter vibrating at 500 cps, for bias loads ranging from 0–3 g. Typical results indicate that the dynamic hardness is unexpectedly small for very light loads, that the hardness behaves almost as predicted by the Hertz theory of elastic contact for intermediate loads, and that the hardness remains nearly constant for heavy loads. [This work was supported in part by the U. S. Office of Naval Research.]
Periodic Shock Motions in a Linear Medium
Authors: Hudson George E.
Published: November 2005

Consider a column of fluid having an equilibrium length L, for which the pressure p and density ρ are related by p = k(1 − ρ0/ρ), where k and ρ0 are constants. Let one end of the column be held motionless and let a piston move back and forth at the other end with a period T, so that it has a piecewise uniform velocity. Assume no dissipation. An exact solution of the shock-discontinuity relations, and the differential equations of continuity and motion in the medium can be found satisfying these conditions. It corresponds to a system of (m+1) oscillating shockfronts of uniform strength Δpm = kζm, where ζm = ε(f+m)/f(1 − f), 0⩽f⩽1, m=0, 1, 2, …, and ε is the mean amplitude of the piston motion divided by L. The quality f+m=2L/UT, where U = (k/ρ0)12, is the dimensionless frequency of the motion. The shock motions are piecewise quadratic functions of time, while the particle motions, like that of the piston, are piecewise linear functions of time. [This research was supported by the Acoustics Branch of the U. S. Office of Naval Research.]
Propagation of Acoustic-Gravity Waves from a Small Source in an Isothermal Atmosphere
Authors: Pierce Allan D.
Published: November 2005

A theoretical discussion is presented of the influence of gravity on sound propagation from a point source in an isothermal atmosphere, where ambient pressure and density decrease exponentially with height. A previous theory by Sretenskii [Izv. Akad. Nauk. SSSR Ser. Geofiz. (1954)] is found to be incorrect. Our study shows that, if reflections from the gound are ignored, waves with angular frequencies between (γ − 1)12g/c and (γ/2)g/c and between 0 and (γ − 1)12(g/c) cosθ will not be propagated in a direction making an angle of θ with the vertical axis. When appropriate boundary conditions at the ground are included, the solution appears as a sum of a direct wave, a reflected wave, and a surface wave. Reflection coefficients for the reflected wave are given, and the magnitude of the surface wave as a function of horizontal distance is discussed.
Sound Propagation in Homogeneous Deciduous and Evergreen Woods
Authors: Embleton T. F. W.
Published: November 2005

The sound attenuation due to trees has been measured (under atmospheric conditions requiring no corrections) at about 20 locations, representing four selected types of woods. 9000 readings of sound-pressure level allow good accuracy in the means and standard deviations of results even when broken down by frequency, species of tree, and distance from the source—instrumental errors are eliminated from the values of excess attenuation by the use of the same instruments and operators at both ends of each propagation path. A constant excess attenuation of 7 dB/100 ft was found at frequencies below 2000 cps, in disagreement with previous workers. With the sound source in the open at the edge of the woods, effects due to change of medium were observed, viz., an increase of sound-pressure level in the woods and a distinctive S-shaped curve of attenuation vs frequency. This is suggestive of resonant absorption, although a theory developed according to such a hypothesis, while having the correct frequency dependence, fails to predict the magnitude of the observed results by a factor of 103. Transverse modes of vibration of the branches were shown to be the oscillators active in the frequency range of interest, 250 cps in the lower branches to about 1100 cps near the top of the tree; indications were that trunk resonances might also be important.
Sound Radiation from Vibrating Surfaces
Authors: Chertock George
Published: November 2005

The radiation field of a vibrating surface can be computed from the Kirchoff-Helmholtz integral if the surface pressure, as well as the velocity distribution, is known at the vibrating surface. We first discuss some cases where it is practical to estimate the surface pressures from the known velocity distribution. Then, we describe an iterative solution to the integral equation for the surface pressures in the case of an arbitrary velocity distribution on a surface of revolution. The iterative solution for the surface pressures and also a subsequent solution for the farfield pressures are both programmed for automatic computation.
Mechanisms and Measurement of Structural Damping
Authors: Kerwin Edward M.
Published: November 2005

The first part of this paper presents a brief review of some common mechanisms of structural damping in beams and plates. The mechanisms reviewed involve dissipation in viscoelastic materials, specifically in the so-called free and constrained viscoelastic layers, and the thickness-resonant viscoelastic layer. In each case, the parameters governing damping effectivness are defined, and the dependence of damping on these parameters is discussed. Radiation damping is also reviewed briefly. In the second part of the paper, some of the problems encountered in determining the damping of complex systems are discussed. Such problems are found where the damping is moderate or high, or where the system is extensive or involves coupled subsystems. Important considerations here are the distribution of vibrating energy throughout the system, the degree of coupling among subsystems, and the type of vibratory excitation. Some damping measurements in complex structures are discussed. Preliminary guides for performing damping measurements in complex systems are given.
Damping and Fatigue Properties of Metal-Plastic Sandwiches
Authors: Kurtze Günther
Published: November 2005

Sandwich structures of suitable design show extremely high loss tangents but have a structural frequency dependence in addition to the frequency response of the plastic core material. The two response curves are shifted in opposite directions when the temperature is changed. For optimum performance, material and geometry, therefore, must be carefully matched to the desired frequency and temperature ranges. Results of frequency-response measurements of loss tangents, extended over the temperature range between −40° and +80°C, are reported for different types of sandwich panels. Setups are described for comparative fatigue tests in which sandwich panels of optimum design showed a fatigue life increased by factors 10 to 100 as compared to homogeneous sheet metal of the same weight. [The work reported in this paper has been sponsored in part by the Aeronautical Systems Division of the U. S. Air Force Systems Command, through the European Office, Aerospace Research.]
Stability and Effectiveness of Active Vibration Dampers
Authors: Lawther James M. , Rockwell Thomas H.
Published: November 2005

Additional progress has been made in the investigation of vibration damping of multiresonant structures by means of feedback. The stability analysis previously developed has been extended, showing that damping effectiveness may be greatly enhanced through the use of properly designed networks in the feedback path. Of at least academic interest is the possibility of utilizing a conditionally stable feedback loop to further increase effectiveness. For the absolutely stable case, in specific application to a uniform beam with off-resonance point mobility in the 10−3-in./sec/lb range, the theoretically predicted damping has been verified experimentally. Using modified commercial components, it has been possible to design for a useful band of better than 10 kc/sec.
Ultrasonic Vibrational Relaxation in Dense Gases
Authors: Madigosky W. M.
Published: November 2005

Ultrasonic-absorption measurements were made in high-density methane over a range of densities from 400–560 amagats at 25°C and from −30° to 30°C at 400 amagats. The absorption may be accounted for by a single vibrational relaxation time including at least the two lowest modes. Application of a modified cell model correctly predicts the density dependence and gives a collision diameter of 3.45 Å. The temperature dependence of the collision efficiency agrees with that found by Eucken and Aybar and is compared with the Schwartz-Slawsky-Herzfeld theory. All results are interpreted as supporting the concept that only binary collisions were responsible for the energy-transfer process.
Attenuation of Guided Sawtooth Waves
Authors: Medwin H.
Published: November 2005

The attenuation of guided “plane” progressive repeated shockwaves has been measured in circular tubes of radius ranging from 0.96–5.4 cm at several frequencies and intensities for air and other gases. Analysis of the data leads to the conclusions: (a) the wall attenuation of a guided sawtooth wave corresponds to that of a single shock and shows no dependence on frequency; (b) correcting for wall loss by subtracting the experimental wall-attenuation term from the total attenuation does not eliminate the fundamental disagreement between theories for attenuation of infinite sawtooth waves and the experimental attenuation of guided sawtooth waves. Preliminary hot-wire-anemometer probings reveal that during repeated shock propagation the influence of the guide wall extends inward as much as 30 times as far as for an acoustic boundary. It is postulated that the nonacoustic interaction of the shockwaves with the boundary is the source of the continuing discrepancy between theory and experiment. [This work was supported by the U. S. Office of Naval Research.]
Calculation of Ultrasonic Nearfield Pressure Distributions
Authors: Brunschwig Fred S.
Published: November 2005

This paper reports results of insertion of transducer parametric values into yon Helmholtz's integral equation for the prediction of axial-pressure distributions. Subsequent integration by digital computer is presented. In particular, the nearfield of an ultrasonic transducer is discussed in detail. It is shown that the pressure-distribution maxima converge at the transducer to one-half the farfield maxima value. Inclusion of the local velocity component of the field before integration brings about a difference between this prediction and that of previous work on the subject. The difficulty inherent in predicting nearfield-pressure distributions in the laboratory is discussed with reference to nonuniform distributions of velocity over the transducer face. [This work was supported by a grant from the National Science Foundation.]
Experimental Study of Dispersion in Ultrasonic Waveguides
Authors: Lastovka J. B. , Carome E. F.
Published: November 2005

An experimental study has been made of the velocity of ultrasonic pulses in cylindrical, water-filled, metallic waveguides of various inner diameters. A pulse-coincidence method was used for measurements over the frequency range from 1–5 Mc/sec. The diameter of the acoustic sources and receivers was 0.5 in., and measurements were made in guides with diameters of 0.5, 1.0, and 1.25 in., and also under freefield conditions. At 5 Mc/sec, all of the measured velocities are essentially the same. At the lower frequencies, however, the velocities obtained in the smaller-diameter waveguides are substantially below those obtained under freefield conditions. For the 0.5-in. guide, the differences range from approximately 6 m/sec at 1 Mc/sec to 2 m/sec at 3 Mc/sec. Consideration is given to possible sources for these results. [This work was supported by the U. S. Office of Naval Research.]
Resonant Interaction of Two Ultrasonic Waves in Solids
Authors: Rollins Fred R.
Published: November 2005

In a recent theoretical paper, Jones and Kobett [J. Acoust. Soc. Am. 35, 5 (1963)] have shown that two monochromatic elastic waves in a nonlinear solid interact rather strongly if they intersect at a certain angle. When this condition of resonance is satisfied, the theory further predicts that a 3rd wave may be generated at the “point” of intersection. The generated wave will have a frequency (ω1±ω2) and wavevector (k̄1±k̄2), where the subscripts refer to properties of the two primary waves. An experimental study of interaction between pulsed ultrasonic beams has shown that the theoretically predicted 3rd wave can be detected with easily attainable primary wave intensities and frequencies in the 1- to 15-Mc/sec range. Both sum and difference frequencies have been generated in specimens of fused silica, polycrystalline aluminum, and polycrystalline magnesium. Experimental details are given and possible methods of measuring third-order elastic constants are discussed. [Work supported by the Aeronautical Systems Division, Wright-Patterson Air Force Base.]
On the Properties of the Deep-Fired Explosive Phenomenon
Authors: Epstein David
Published: November 2005

Relationship between the shockwave and bubble pulse in the deep-fired long-range explosive phenomenon, observed during a Daystrom electric-field exercise, is discussed in terms of results previously reported. At the ranges and depths considered, the blast-gauge data showed a strong resemblance, both in amplitude and general shape, between the shockwave and the first bubble pulse. Fourier analysis revealed a remarkable coherence between pulses extending throughout the entire frequency spectrum; in fact, the observed regular succession of alternate maxima and minima could be readily synthesized by assuming the explosive waveform to consist of two identical exponentials spaced a bubble-pulse interval apart. The comparison formulas [D. E. Weston, Proc. Phys. Sec. (London) 76 (1960)], based on near-surface studies, are extrapolated to great depth and long range. The observed shockwave to bubble-pulse peak-pressure and time-constant ratios, the rise times, and bubble-pulse interval are compared with the corresponding calculated quantities. Summarizing, although a general agreement between observed and calculated results obtains, nevertheless it appears that a definite depth effect, hitherto unaccounted for quantitatively, exists. It is noted that in the deep-fired long-range problem a point is quickly reached where the bubble pulse exerts a profound influence on the total explosive waveform.
Calibration of Piston Transducers at Marginal Test Distances
Authors: Sabin Gerald A.
Published: November 2005

The distance separating two underwater-sound transducers in a calibration measurement must be selected to satisfy opposing requirements. Large distances are needed to satisfy sufficiently well the plane-wave requirement; short distances are advantageous to reduce the effect of unwanted reflections from the boundaries of the medium. The problem considered is that of sensitivity measurements involving two piston transducers. Guidelines for the selection of adequate test distances are derived and discussed in terms of the transducer dimensions and the wavelength. Applicable correction factors are computed to be used either in a reciprocity or a comparison calibration when short distances are necessary.
Practical Problems of Assessing Damping Treatments
Authors: Mead D. J.
Published: November 2005

This paper discusses firstly the practical situations in which damping treatments can be beneficial in attenuating noise and vibration. Brief consideration is given to systems under periodic excitation, after which randomly excited systems are considered in greater detail. Reference is made to jet-excitation vibrations of airplane structures (to the associated stress levels and transmitted noise) and also to vibrations excited by boundary-layer pressure fluctuations. The manner in which these various response quantities depend on the basic structural parameters (stiffness, damping, and mass) is discussed next with a view to defining the most desirable characteristics of an artificially damped structure. This leads to the development of certain criteria for assessing the effectiveness of damping treatments. The limitations, in this respect, of the simple flexural loss factor become apparent. The problem of selecting the best damping treatment for a given situation is then dealt with. Considered next are the difficulties of estimating the damping and stiffness of a treated reinforced-plate structure. The measurement of the damping of such systems is also discussed, and some recent work is described. Some typical values of the damping required and obtainable for airplane structures are considered. Finally, the needs for further work are outlined.
Corrugated Addition for Increased Damping in Flexure
Authors: Torvik Peter J. , Lazan B. J.
Published: November 2005

Various types of surface additions that incorporate viscoelastic adhesive layers for high damping are reviewed and their limiations discussed. A new type of configuration having the general form of a corrugation is shown to be capable of dissipating large damping energy through cyclic shear in a viscoelastic adhesive layer. Expressions are derived for the energy dissipation in one particular form of this configuration. The optimum geometry, for maximum damping is discussed with respect to several critical parameters. Corrugated configurations were constructed and tested to check the theory. Satisfactory agreement was found between the experimental results and the values predicted by the theory for shear strain in the viscoelastic layer, for the large increase in damping associated with the adhesive shear mechanism, and for the optimum thickness of the viscoelastic adhesive for maximum damping. As an indication of the increase in damping realized through the corrugated-addition approach, the loss coefficient of an aluminum beam at a cyclic stress of 4000 psi was increased from approximately 0.01 to 0.2 by the corrugated addition.
Viscoelastic High-Damping Materials
Authors: Ball George L. , Salyer Ival O.
Published: November 2005

An intensive investigation of polymers, polymer systems, and fillers was conducted that provided a material that effectively damps steel-plating up to 2 in. thick. The damping material exhibited greater than 3% critical damping over two decades of frequency and a 25°C temperature range, at a 13 plate-weight application. At an optimized temperature, the material exhibited greater than 9% critical damping over a decade of frequency. The damping material significantly reduced vibration and noise when applied to light- and moderate-gauge steels. The investigation also revealed three effects of fillers useful in increasing the damping properties of a polymer system.
Experimental Study of Dilatational vs Distortional Straining Action in Material-Damping Production
Authors: Mentel T. J. , Chi S. H.
Published: November 2005

Experimental test setups for measuring material damping in structural metals have invariably been limited to producing states of strain wherein the distortional component is dominant. In the case of flexural vibrations of plates and shells, however, this condition is often reversed, sometimes with the elastic energy associated with dilatational straining action exceeding the corresponding distortional component by an order of magnitude. It has, therefore, been conjectured that effects due to dilatational straining, small enough to be masked by experimental scatter in the aforementioned tests, might become significant under conditions of pronounced dilatational straining, viz., plate vibrations. For this purpose, a test machine was designed to measure material damping in thin-walled, cylindrical specimens subject to combined internal pressure and axial cyclic loading. Tests were carried out on a number of manganese-copper alloy specimens for which prior studies, already published, had established damping properties under uniaxial cyclic stress. The new tests extended the ratio of dilatational to distortional strain energies from a fraction up to a factor of 2, the latter limit being determined by possible onset of stress-history effects, which were avoided. The results display a small but definite influence of dilatational straining action in producing additional material damping to that arising from distortional straining action. As a consequence, a modified formula is suggested for the treatment of material damping in plate vibrations.
Measurement of Average Mechanical-Power Input to a Structure Excited by Frequency Bands of Noise
Authors: Noiseux Denis U. , Dietrich Charles W.
Published: November 2005

An impedance head is used to measure the average power fed into a complex structure excited by frequency bands of random noise. The same technique also yields the average driving-point impedance and the correlation coefficient between the force and the velocity. The technique is described, and measurements are presented for a plate with and without damping. The results are compared with those obtained by direct measurement of acceleration and reverberation time of the plate under the assumption that a reverberant vibration field exists. Satisfactory agreement is obtained. [This work was supported under U. S. Air Force Contract No. AF 33(657)-9118.]
Memory Effect in Sound Localization
Authors: Hanson R. L.
Published: November 2005

If, under free-space conditions, one listens to a real sound source at an azimuth of zero degrees, or to the image resulting from a pair of symmetrically located in-phase sources, he senses an image at or near zero degrees. If the image is shifted to one side for several seconds and then the original condition is restored, he hears an image several degrees away from the original position in a direction away from that of the side image. Various conditions that affect this image shift are discussed.
Comparison of Voicing Periodicities and Formant Frequencies for One Speaker in Air and in a Helium-Oxygen Mixture at Various Pressures
Authors: Wathen-Dunn Weiant , Copel Michel
Published: November 2005

In order to prevent bends, Naval divers who go below 100 ft are supplied with a mixture of approximately 75% helium and 25% oxygen at a pressure equal to that of the surrounding water. As a result, the diver's speech, heard topside over his voice-communication system, is even less intelligible than when his supply consists of air under comparable conditions. This paper reports measurements of the fundamental voicing periodicities and the formant frequencies for the speech of a single male talker in a decompression chamber with pressures equivalent to sea level and to depths of 70 and 200 ft for both air and a 76/24 helium-oxygen mixture.
Evaluation of Various Analysis-Synthesis Speech Systems
Authors: Gunnar C. , Fant M. , Risberg Arne , Stevens K. N.
Published: November 2005

During the Stockholm Speech Communication Seminar, the performance of several vocoders and speech-synthesizer systems was demonstrated on an equal-speech-input basis. More-recent evaluations of a part of this material by means of consonant articulation and subjective quality tests are reviewed.
On the Redundancy of Speech and Articulation and Perception
Authors: Lieberman Philip
Published: November 2005

Highly redundant messages were recorded at normal and fast rates of talking. Certain words were gated out of these messages and listening tests were performed on these words. Nonredundant messages were then recorded using these same words in similar phonetic environments. The same words were again gated out and listening tests were again performed. Quite apart from these listening teats, two operational measures of redundancy were derived. One measure was based on a finite-state model of perception and readers were asked to guess what word n would be after they had read all the words through word n − 1 in a sentence. The second measure was based on the hypothesis that people reserve their final decision on the recognition of each word until they perceive an entire sentence. Readers read an entire sentence in the midst of which a word was represented by a dash. They were then asked to guess what the missing word was. Our index of redundancy was the percent of correct guesses. The results of our listening tests show that the intelligibility of the gated words is inversely proportional to the redundancy index obtained by the second measure of redundancy.
Adjacent Context and the Intelligibility of Words Excised from Fluent Speech
Authors: Pickett J. M. , Pollack Irwin
Published: November 2005

Conditions of fluent utterance may so modify a spoken word that it is not intelligible when taken from context. This experiment explores certain factors in the intelligibility of such excised words. Four talkers recorded short paragraphs of English prose at 3 rates of fluent utterance: normal rate, deliberately slow rate, and deliberately fast rate. Segments containing 1–7 words were then excised from the recordings and presented to 15 listeners for identification. Intelligibility is primarily dependent upon the duration of the sample: intelligibility at a given rate improves with the number of presented words: intelligibility also improves with slower reading rates with a constant number of presented words. Samples from the fast reading rate, however, yielded somewhat lower intelligibility for equal samples in the range 200–800 msec. Relatively small effects were associated with the position of a word within the sample and its grammatical function. Implications for computer recognition of speech are briefly discussed.
Subjective Bases of Sound-Insulation Requirements
Authors: Northwood T. D.
Published: November 2005

Existing sound-insulation requirements are based on the performance of certain traditional constructions that are known to satisfy occupants of multidwelling structures. It is proposed to consider more basically the relations between sound-transmission loss and various subjective criteria of disturbance and annoyance.
Effect of Eardrum Loading on Bone Conduction
Authors: Tonndorf J. , Duvall A. J.
Published: November 2005

As first described by R. Barány (1910) and since confirmed by numerous other investigators, eardrum loading improves BC responses in the low frequencies while diminishing them in the high frequencies. E. Barány (1938) had explained this phenomenon by his concept of ossicular inertia. The effect of the eardrum loading was included in a series of experimental BC studies in cats recently conducted in this laboratory. Amplitude and phase changes of cochlear microphonics were recorded, indicating the altered BC transmission under various load conditions. The results permitted the conclusion that (a) the resonant frequency of the responding inertial system shifts downward with increasing loads (thus confirming Barány's concept) and that (b), at the same time, the damping of the system increases. [This research was supported by a Public Health Service grant.]
Normal Mode Theory as Applied to the Image-Interference Region of an Underwater Acoustic Surface Duct
Authors: Gordon D. F. , Pedersen M. A.
Published: November 2005

This paper presents some results of a normal mode theory based on the so-called bilinear model of a surface channel. Early work by Furry in electromagnetics and Marsh in acoustics treated the case of a few modes at long range. With the aid of high-speed digital computers, it has now become possible to improve their methods and to extend them to the calculation of propagation losses, including those at short ranges. In this study, as many as 40 modes are considered and the accuracy at very short ranges is limted only by the number of modes. Computed propagation losses in the image interference region are in close agreement with experimental data. Ray-theory results presented for the identical model give nearly identical results in the image-interference region, although the two theories diverge at larger ranges. The two theories produce the interference pattern in markedly different manners.
Reciprocity Calibration within a Rigid-Wall Water-Filled Tube
Authors: Beatty L. G.
Published: November 2005

A reciprocity technique for the absolute calibration of underwater-sound transducers within a rigid-wall water-filled tube at audiofrequencies has been developed. The reciprocity parameter, subject to certain restrictions, can be computed from easily measured system parameters. The paper describes the technique and its related theory, and shows some results of its application.
Sound Reverberation from Smooth Ocean Floors
Authors: Goodman R. R.
Published: November 2005

Recently both Mackenzie [J. Acoust. Soc. Am. 34, 66 (1962)] and Urick [J. Acoust. Soc. Am. 34, 1721 (1962)] have reported experiments measuring reverberation over deep, flat ocean floors. Both give data that may be empirically described by Lambert's law, at least over certain ranges of time. These results seem somewhat surprising since Lambert's law scattering is usually associated with very rough surfaces (compared to wavelength), quite unlike the deep ocean floors. In an effort to find a mechanism for reverberation, calculations have been made for a source located above a plane boundary separating two fluids. No roughness on the boundary was assumed. A reverberation “tail” was found to follow the specularly reflected signal. Computations show, however, that this “tail” is many orders of magnitude too small to account for the results of Mackenzie and Urick. Reasons for this discrepancy are considered. The possible interpretation of reverberation measurements for oceanographic data taking is discussed.
On the Use of Simple Mathematical Models to Predict SOFAR Propagation Effects
Authors: Carter A. H.
Published: November 2005

A major feature of pulsed sound transmission between points on the SOFAR axis is the abruptly terminated crescendo associated with the decreasing time separation of purely refracted arrivals. Of the nonreflected paths, the first to be received corresponds to a comparatively large horizontal angle at the source, whereas the last is the axial or zero-angle arrival. Ray calculations, using simple analytic functions to represent the sound-channel velocity profile, however crudely, have been thought to describe the principal characteristics of SOFAR propagation, at least qualitatively. Thus, for example, the small-angle solution of Goodman and Duykers [J. Acoust. Soc. Am. 34, 960 (1962)] for a locally parabolic profile predicts the existence of equally spaced convergence zones along the axis. It is shown, however, that their approach fails to give even approximately the observed relationship between arrival velocity and ray angle at the source. Examination of other models of the velocity profile tentatively suggests that those which do yield semirealistic travel time results do not exhibit pronounced convergence effects. In addition, smoothing of convergence peaks is to be expected in broadband pulse transmission from the fact that the ranges at which focusing occurs are dependent on frequency, as revealed by normal-mode calculations. [This work was supported by the Bureau of Ships, U. S. Navy.]
Effect of Bending on Vibrations of Spherical Shells
Authors: Kalnins A.
Published: November 2005

This paper is concerned with the vibration analysis of spherical shells closed at one pole and open at the other by means of the linear classical bending theory of shells. Frequency equations are derived in terms of Legendre functions with complex indices, and for axisymmetric vibration the natural frequencies and mode shapes are deduced for opening angles ranging from a shallow to a closed spherical shell. It is found that for all opening angles the frequency spectrum consists of two coupled infinite sets of modes that can be labeled as bending (or flexural) and membrane modes. This distinction is made on the basis of the comparison of the strain energies due to bending and stretching of each mode. It is also found that the membrane modes are practically independent of thickness whereas the bending modes vary with thickness. When the opening angle is large and the shell may be considered shallow, only then are the modes distinguished by predominantly large transverse or longitudinal displacements, which were investigated recently for shallow spherical shells by Kalnins [in Proc. 4th U. S. Congr. Appl. Mech. (1963)]. Previous analyses of axisymmetric vibration of spherical shells by Lamb, Love, and more recently by Baker [_J. Acoust. Soc. Am. 33, 1749 (1961)] with the use of membrane theory have shown that one of the two infinite sets of modes is spaced within a finite interval of the frequency spectrum. It is shown that this set of modes is a degenerate case of bending modes, and, if deduced by means of membrane theory, it is applicable only when the thickness of the shell is zero. When the bending theory is employed, then the frequency interval for this set of modes extends to infinity for every value of thickness that is greater than zero. [This work has been supported by a grant from the National Science Foundation.]