bluuebunny/crossref_metadata_2025 huggingface dataset:
Spherical Waves Coupled to a One-Dimensional Wave Guide
Authors: White J. E.
Published: September 2005

An approximate expression is derived for the disturbance in a one-dimensional wave guide resulting from an expanding spherical wave which is loosely coupled to the wave guide at all points along its length. For the case of a slender rod immersed in a fluid, curves are presented showing axial strain for three ratios of rod velocity to fluid velocity.
Revised Grain-Scattering Formulas and Tables
Authors: Papadakis Emmanuel P.
Published: September 2005

The current theory of Rayleigh and stochastic scattering in polycrystalline materials is reviewed and compared with (1) former theory and (2) experiment. Rayleigh scattering giving ultrasonic attenuation equal to STf4 (S is the Rayleigh scattering factor, T the average scattering volume, f the frequency) occurs when λ > 2πD̄ (λ is the wavelength, D̄ the average grain diameter); stochastic scattering yielding ultrasonic attenuation equal to ΣD̄f2 (Σ is the stochastic scattering factor) occurs when λ < 2πD̄. The average scattering volume and average grain diameter must be evaluated by taking their averages over the grain-size distribution in the metal. When this is done, the current theory accounts rather well for the scattering component of the ultrasonic attenuation in polycrystalline metals. Former theory underestimated the scattering. A tabulation is made of the scattering factors S and Σ in various materials. The computed scattering factors show that polycrystalline samples of the following materials should have low attenuation: aluminum, chromite, chromium, magnesium, magnetite, silicon strontium nitrate, tungsten, vanadium, and YIG.
Vibrational Relaxation Times of Oxygen in the Temperature Range 100°–200°C
Authors: Parker J. G. , Swope R. H.
Published: September 2005

Vibrational relaxation times in pure oxygen have been measured over the temperature range 100°–200°C. An anomalously rapid decrease in the relaxation time is observed for temperatures above 150°C, confirming earlier conclusions based on a comparison of theory and experiment [J. G. Parker, J. Chem. Phys. 41, 1600–1609 (1964)]. This decrease in the vibrational relaxation time may be interpreted as a transition in oxygen from a low-temperature state to a high-temperature state, although the exact nature of the physical mechanism underlying this transition remains obscure.
Thermal Stress-Wave Propagation in Hollow Elastic Spheres
Authors: Tsui T. , Kraus H.
Published: September 2005

In conventional dynamic-thermoelastic problems, the heating rates are sufficiently slow so that the inertia terms in the equations of equilibrium are negligible and time enters as a parameter from the transient temperature in the body. In modern technology, however, one has encountered extremely high heating rates and it is necessary to reexamine the role of inertia. To this end, studies of extremely massive bodies and extremely slender bodies under rapid heating conditions have been made by others. In the former, thermal stress-wave propagation without reflection was examined; in the latter, thermally induced vibrations were considered. It is now of interest to examine the effect of inertia in a rapidly heated body whose dimensions lie between these extremes. As an example, we consider a hollow sphere of arbitrary thickness subjected to a step change of temperature on its inner surface. In the solution, the propagation and reflection of thermal stress waves in the sphere are observed. For comparison, the results of the conventional analysis are obtained as a special case. After passing to appropriate limits, the results are compared to the results of the previous analyses of slender and massive spherical regions.
Sound Propagation in Urban Areas
Authors: Wiener Francis M. , Malme Charles I. , Gogos Creighton M.
Published: September 2005

Outdoor sound communication systems for urban areas have been traditionally designed using relatively few sources of sound, located high above the buildings. Results have generally not been satisfactory because of sound attenuation in the atmosphere and diffraction by buildings. As an alternative, a block by-block coverage system using many sound sources placed in the streets has been investigated. Extensive acoustical and meteorological field tests carried out in city streets showed that sound-propagation conditions are generally favorable there. Typically, the mean wind and temperature gradients are small; consequently, no appreciable sound refraction effects were observed over distances of a city block or two when sound was propagated from a source 10–20 ft above the pavement. Reverberation from the building walls was not detrimental to speech intelligibility when a directive sound source was used with its axis oriented along the street. However, the intelligibility of speech received in a side street some distance away from the intersection was poor owing to excessive sound attenuation and reverberation.
Prediction of Speech Intelligibility at High Noise Levels
Authors: Pickett J. M. , Pollack Irwin
Published: September 2005

Speech intelligibility in noise was measured at noise levels ranging up to 130 db using various speech-to-noise (S/N) ratios. The noise and speech signals were mixed electrically and presented to the listeners over earphones. Five combinations of the following speech and noise spectra were used: speech frequency-emphasis of 0 db and +6 db per octave; random noise spectra with slopes of 0, +6, and −12 db per octave. With S/N ratio held constant, large decrements in intelligibility were observed for all spectra as the noise level was increased within the range studied. Methods of predicting speech intelligibility in noise are evaluated in terms of the results. Three indexes for prediction of speech intelligibility are considered: (1) the over-all S/N ratio, (2) articulation index (AI) computed by the method of French and Steinberg, and (3) AI computed by Beranek's method. The most accurate index of prediction at high noise levels was found to be that of French and Steinberg, when suitably modified according to the present results. The simplest index, the over-all S/N ratio, was found to be reasonably accurate when corrected for high noise levels by a function derived from the test results.
Reflections from Gradual Transition Sound Absorbers
Authors: Miller Norman B.
Published: September 2005

Reflections from gradual transition linings for anechoic tanks are treated theoretically by considering the propagation of compressional waves in stratified media. The reflections are the combined effect of back-scattering in the transition region and round trip transmission through the lining resulting from imperfect absorption of sound by the lining. Sound propagation in the inhomogeneous transition region is fairly complex; the incident energy is absorbed and scattered back and forth, and phase interference occurs in a complicated fashion. If the lining is viewed as a succession of arbitrarily thin panels, however, then the pressure is readily separated into progressive waves, and it is shown that each increment of distance “back-scatters” a fraction of the total incident wave that is proportional to the logarithmic derivative of the characteristic impedance. Certain typical types of linings are considered in detail to determine theoretically the proportions of transition width to total lining width producing minimum reflections. The theoretical results are compared with experimental data for a cone type underwater lining, showing that the one-dimensional theory gives useful results for cone and wedge linings.
Nomograms for Computing Real, Imaginary, and Absolute Values of Vector Ratios
Authors: Bowman Howard S.
Published: September 2005

Two monograms were designed and constructed to compute real, imaginary, and absolute values of two-dimensional vector ratios.
Comparison of Vector and Autocorrelation Pitch Detectors
Authors: Bluestein Leo I. , Rader Charles M.
Published: September 2005

In this Letter, the distance function of vector pitch detection is compared with an approximation derived by Sondhi. Using a geometric interpretation, differences between the two that may effect their pitch-detection capabilities are made evident.
Propagation in an Infinite Elastic Plate
Authors: Sherwood J. W. C.
Published: September 2005

At any single frequency an arbitrary force distribution in an infinite elastic plate must be expressible as a superposition of the plate's eigenvibrations. Since the force distribution may be varied in an infinite number of ways it follows that the plate must possess an infinity of eigenvibrations. Previous work has shown the existence of only a finite number, each being defined by a real propagation constant (unattenuated vibration: finite phase velocity) or an imaginary propagation constant (exponentially attenuated vibration: infinite phase velocity). This investigation yields the complementary infinity of eigenvibrations possessing complex propagation constants (exponentially attenuated vibrations: finite phase velocities). The probable structure of the complete eigenmode system in the low-frequency range has been hypothesized for a plate material with a Poisson's ratio of 0.31. The qualitative variation of this structure with changes in Poisson's ratio may be readily conjectured.

The utility of the complex eigenvibrations is enhanced by transforming them into an equivalent set, each member of which is constant in phase throughout the plate. These reformulated eigenvibrations are unique in that they possess an exponential amplitude variation along the plate together with a superimposed sinusoidal variation.
Particle Suspension Technique for Measuring Scattered Sound Energy
Authors: Buchman A. S.
Published: September 2005

Description is given of a technique of supporting small particles in sonic free field by means of suspension in a gel.
Sound Absorption in Hydrogen
Authors: Parbrook H. D. , Tempest W.
Published: September 2005

Improved absorption results in hydrogen in the range 1 to 37 Mc/sec atmos are reported and their theoretical implications briefly reviewed.
Apparatus for Simultaneous Low-Temperature Shear-Deformation and Ultrasonic-Attenuation Measurements in Superconductors
Authors: Olsen Tore , Claiborne Lewis T. , Einspruch Norman G.
Published: September 2005

This Letter describes the design and construction of an experimental apparatus that will deform in pure shear at liquid-helium temperatures single crystals of metals and that provides for ultrasonic measurements while the load is being applied.
Selective Attenuation of Sound over Seating and over Grassland
Authors: Scholes W. E.
Published: September 2005

Some recent measurements of the attenuation of the direct sound in concert halls have produced results that are qualitatively very similar to results obtained from measurements of the horizontal propagation of sound over open grassland. In particular, both sets of results show large attenuations in the mid- to low frequency region, and the actual frequency of maximum attenuation depends in both cases on the heights of the source and the receiver above the floor or ground. This Letter draws attention to the similarities between the results of the two experiments and concludes that similar processes are involved.
Masking with Two Tones
Authors: Green David M.
Published: September 2005

The masking produced by two, equal-intensity sinusoids on a signal, a third sinusoid located midway in frequency between the two maskers, is measured as a function of the frequency separation between the two maskers. Three signal frequencies are used 250, 1000, and 4000 cps. At small frequency separations, the detectability of the signal is independent of center frequency and simply dependent on the frequency separation of the two maskers. As larger frequency separations are approached, the masking suddenly diminishes and this larger critical frequency separation, which is frequency-dependent, is approximately the width of the envelope of excitation on the basilar membrane when excited by a sinusoid. The interpretation of these results in terms of a simple energy detector followed by a simple integrator is discussed.
Binaural Interaction in the Accessory Superior-Olivary Nucleus of the Cat
Authors: Hall J. L.
Published: September 2005

Acoustic clicks were presented through earphones to the two ears of anesthetized cats, and the electrical response activity of single nerve cells in the accessory nucleus of the superior olive was studied. Stimulus parameters investigated included interaural time difference, interaural intensity difference, and average intensity. Attention was concentrated on cells that were excited by stimulation of the contralateral ear and inhibited by stimulation of the ipsilateral ear. The experimental results are incorporated into van Bergeijk's model for binaural interaction, for which it is postulated that localization judgments are obtained on the basis of a comparison of the amounts of response activity in the two accessory nuclei. The model yields predictions that are in agreement with results from human psychophysics. The model predicts that the virtual image should be lateralized toward the side receiving prior or more intense stimulation. A time-intensity trading relationship that is in agreement with results from “centering” experiments is derived. The model predicts minimum detectable changes in interaural time difference of 5–10 μsec and minimum detectable changes in interaural intensity difference of 0.1–0.5 dB.
Pure-Tone Acuity and the Intelligibility of Everyday Speech
Authors: Harris J. D.
Published: September 2005

Certain laboratory studies show that it is necessary only to hear up to 1500, or perhaps 2000, cps for normal word-list reception. However, many patients with normal hearing up to 2000 cps but deficiencies at higher frequencies have noticeable difficulty with everyday speech. The discrepancy may arise since ordinary speech is often distorted and/or masked, conditions not usually included in speech-reception studies. Discrimination scores (DS) for sentence material were collected on 52 sensorineural hypoacusics, the speech being distorted by having talkers wear nose clamps, by speed, interruptions, and reverberations. When the mean DS from these four distortions was averaged with the DS for undistorted speech, to create “50% distorted speech,” a condition assumed to represent everyday listening, the important acuities were at 1000, 2000, and 3000 cps. The formula for predicting everyday speech should then utilize the simple average hearing loss at these three frequencies. The Pearson r between this predictor and the DS for 50% distorted speech was 0.74. Multiple-correlation frequency-weighting techniques are inferior to simple averaging across audiometric frequencies for theoretical reasons and because of the almost insurmountable problem of collecting a truly representative sample of hearing-loss patterns. These results confirm those of Kryter, Williams, and Green, who found the region 2000–4000 cps to be the important predictor for reception of loud speech heavily masked by noise.
Threshold of Hearing of a Ring-Billed Gull
Authors: Thiessen G. J.
Published: September 2005

The threshold of hearing of a ring-billed gull was measured by the method of conditioned response. It varies with frequency in a manner quite similar to that of other birds. The minimum threshold occurs at about 2 kc and is about 28 db re 0.0002 microbar. The shape of the curve differs sufficiently from that of the irritation threshold so that the latter is probably not an equal loudness contour.
Temporal Summation in Vibrotactile Sensitivity
Authors: Verrillo R. T.
Published: September 2005

The Zwislocki theory of temporal summation was tested for vibrotactile sensitivity. Vibrotactile thresholds were determined as a function of pulse repetition rate and pulse number for short pulses. Thresholds for various burst durations of sinusoidal signals were also determined. The results indicate that the theory is sufficient to predict vibrotactile thresholds for the temporal patterns used. An earlier finding, which suggested that glabrous skin contains at least two populations of mechanoreceptors, was confirmed by using contactors of varying size.
Signal Detection as a Function of Frequency Ensemble. II
Authors: Veniar Florence A.
Published: September 2005

This paper presents the results of a second experimental investigation of the detection of a signal in noise as a function of signal ensemble size and ensemble frequency range. Data are presented for the three observers who took part in the experiment. The results obtained are compared with (1) predictions based upon three mathematical models, (2) performance expected of a mathematically optimum detector, and (3) results obtained in the first of these investigations.
Quality of Violin, Viola, 'Cello, and Bass-Viol Tones. I
Authors: Fletcher Harvey , Blackham E. Donnell , Geertsen O. Norman
Published: September 2005

The elements that are important in the identification of the violin, viola, 'cello, and bass-viol tones were analyzed. These elements were found to be the harmonic structure of the middle portion of the tone; the harmonic structure of the ending portion of the tone (certain partials decayed rapidly leaving an afterring); the attack and decay of the tones; the vibrato (when present) of the tones; and the noises inherent in the mechanics of producing the tones. With the exception of vibrato, the important elements were determined and successful synthesis was accomplished. By the use of a jury of observers, identification tests were made. A successful description was arrived at when and only when synthetic tones could not be identified from real tones. It was found that there is a vibrato both in frequency and relative intensity.
Stability Criteria for Longitudinal Pressure Oscillations in a Rocket Motor
Authors: Murthy S. N. B. , Osborn J. R.
Published: September 2005

The problem called “high-frequency combustion instability in rocket motors” has been considered to be one in which the acoustics of the combustion chamber, nozzle, and flame front are significant for determining whether or not a motor will experience pressure oscillations of an acoustic type. To date, no theory has been developed for demonstrating the effects of the location and width of the flame front in the combustion chamber upon the occurrence of pressure oscillations of the longitudinal mode. In this paper, the rocket motor is treated as a constant-diameter duct with a finite width of combustion zone located between two uniform regions. It also is considered to have finite wave-transmission coefficients at the nozzle and the injector ends. For these conditions, stability criteria are established for the longitudinal mode of pressure oscillations. It is shown that, while the energy release rate per unit width of the combustion zone is significant in determining whether the motor will be stable, the location of the combustion zone in the motor, the over-all length of the motor, and the total amount of energy released also influence the stability of the motor in the longitudinal mode.
Wave Solution for Air-to-Water Sound Transmission
Authors: Weinstein Marvin S. , Henney Alan G.
Published: September 2005

The wave solution for sound transmission through an air-water interface is given. Numerical computations are presented for a point directly below the source and compared with the ray-theory solution. The general wave solution for shallow water, treating the bottom as a semiinfinite fluid layer, is also presented.
On the Fatigue Failure of Structures due to Vibrations Excited by Random Pressure Fields
Authors: Powell Alan
Published: September 2005

On the assumption that the forced modes of vibration of a structure, subjected to pressure fluctuations random in time and space, can be approximated by the composition of the motions of the uncoupled natural modes, a general analysis is made using the ideas of vibration theory and spectrum analysis. The power spectrum, and hence the rms value, of any quantity depending linearly upon structural distortions is derived and it involves a quantity (called the “joint acceptance”) concerning the spacewise structure of the pressure field and of the geometry of the modes of vibration. It is shown how this result may be used (on assuming “normal” randomness) to estimate the fatigue life on the hypothesis of cumulative damage.
On the Approximation to the “Infinite” Solution by the Method of Normal Modes for Random Vibrations
Authors: Powell Alan
Published: September 2005

If a plane sheet (membrane of plate), which is excited by homogeneous random pressures, is assumed to be infinite in extent then a very direct method of analysis is possible. However, several important applications concern structures which are far from infinite in extent (e.g., the excitation of panels by boundary layer pressure fluctuations, and the problem of structural vibrations due to jet noise). This restriction may be overcome by using the method of normal modes, which is more cumbersome by its very nature. It turns out that if it is the power spectrum of displacement which is required, then the “infinite” approach can be used only when the sheet is large enough for there to be only negligible reflections from its edges. However, if one is concerned only with the average mean square value of displacement (or related quantities), and if the detailed shape of the spectrum is of no consequence, then the infinite solution may be used, regardless of the magnitude of the damping, provided that the gravest modes are not excited.
Sound Radiation of a System with a Finite or an Infinite Number of Resonances
Authors: Skudrzyk Eugen
Published: September 2005

The sound field generated by a composite vibrator consists of a wattless near field that decreases very rapidly with distance and an energy-carrying radiation field. For radiators more than half a wavelength apart, the sound fields are spatially incoherent. The radiation field of a complex sound generator can therefore be computed by adding up the energy contributions of its various radiating elements. The radiating elements can be grouped as vibrators that are small in comparison to the wavelength, vibrators without nodal lines that are large in comparison to the wavelength, and vibrators with a nodal line pattern.

The radiation resistance of vibrators without nodal lines can, for most practical purposes, be stated with sufficient accuracy in terms of that of the equivalent sphere. The sound radiation of vibrators with nodal lines can be attributed to two causes. For the low-order modes of vibration, the contributions of the zone of positive and negative amplitude do not compensate one another entirely, and the radiation resistance, though small, is different from zero. Such modes may therefore be expected to contribute to the sound pressure if they are excited in their resonance range. For the high-order modes compensation is complete, but a point force or a force distribution along a line or over a finite area also excites to forced vibrations many low-order modes with very few nodal lines. Since the distance between the nodal lines is greater than the acoustic wavelength in the surrounding medium, the radiation impedance for these modes is very nearly equal to ρc. Since these modes are forced to vibrate at frequencies above their resonant frequency, the resistive component of their impedance being negligible in comparison to the reactive component, this sound pressure is independent of the damping of the system. The radiation impedance is computed for the cases mentioned.
Optical-Contact Bonding
Authors: Smith H. I.
Published: September 2005

An optical-contact bond between X-cut quartz rods reflects about 1% of the incident power for ultrasonic waves of 3 and 9 Gc/sec. The physical origin of the optical-contact adhesion forces is discussed, along with bond-thickness estimates. Techniques for making such bonds are described.
Notes on a Technique for the Determination of High-Frequency Hearing Thresholds
Authors: Page Howard J. , Rutschmann J.
Published: September 2005

In an attempt to develop a method for measuring auditory acuity for high-frequency tones, the authors discuss pilot experiments in progress using an electromagnetic method for setting the eardrum into vibration (alternating magnetic fields acting on a permanent magnet fixed to the eardrum).
Radiation-Pressure Forces in Terms of Impedance, Admittance, and Scattering Matrices
Authors: Smith W. E.
Published: September 2005

A method is outlined for expressing an average generalized force produced by radiation pressures in a lossfree system in terms of the dependence of impedance, admittance, or scattering matrices on the corresponding generalized coordinate. The results provide a theoretical basis for absolute calibration procedures of intensity-measuring instruments utilizing radiation pressures.
General Spreading-Loss Expression
Authors: Eby Edward S. , Einstein Lloyd T.
Published: September 2005

An expression for spreading loss independent of the characteristics and boundaries of a medium is derived and applied to the usual case of interest, that of a cylindrically symmetric medium.
Effect of Pressure on Ultrasonic Relaxation in Liquids. II
Authors: Litovitz T. A. , Carnevale E. H.
Published: September 2005

Ultrasonic absorption and velocity in acetic acid and triethylamine were measured up to pressures of 3280 kg/cm2. The results show that the relaxation frequency in each liquid is independent of pressure to within experimental accuracy (±5%). The pressure data confirm the assumption of Heasall and Lamb that the loss in triethylamine is a rotational isomeric effect. The results in acetic acid are in agreement with the predictions of the monomer-dimer theory.

Comparison with previous results in carbon disulfide and glycerol shows that, depending upon the mechanism, increasing the pressure can cause the relaxation frequency in a liquid either to increase, decrease or remain constant. It appears that the pressure dependence of the relaxation frequency can be useful in distinguishing the type of relaxation present.
Wave Propagation in Transversely Isotropic Circular Cylinders Part I: Theory
Authors: Mirsky I.
Published: September 2005

A two-part study concerning the wave propagation of free harmonic waves in hollow and solid circular cylinders of transversely isotropic material is discussed on the basis of the linear theory of elasticity. The three-dimensional equations of elastodynamics are solved in terms of three displacement potentials, and the resulting frequency equation is discussed for several special cases.
Wave Propagation in Transversely Isotropic Circular Cylinders Part II: Numerical Results
Authors: Mirsky I.
Published: September 2005

Numerical results to the exact frequency equations obtained in Part I [J. Acoust. Soc. Am. 37, 1016–1021 (1965)] are presented here for hollow circular cylinders, and comparisons are made with an approximate shell theory developed previously.
Acoustic Characteristics of a Lake Bottom
Authors: Jones J. L. , Leslie C. B. , Barton L. E.
Published: September 2005

Standing-wave measurements are discussed which show that the bottom of a fresh-water lake near Washington, D. C. behaves acoustically as a pressure-release surface between 50 and 500 cps. A correlation technique is presented which makes it possible to distinguish between the part of an acoustic signal which arrives by a direct path and the part which experiences a bottom reflection. Results of a study of the acoustic behavior of the lake bottom by this method confirm the conclusions reached from the standing-wave measurements for frequencies up to 1600 cps. Correlation and transient measurements of the acoustic velocity in the bottom sediment are presented which indicate that the pressure-release characteristics result from an acoustic velocity in the bottom of less than one-tenth that of water. This low velocity is attributed to the presence of gas resulting from decaying organic matter in the bottom. The gas greatly increases the bulk compressibility of the bottom sediment and hence lowers the sound velocity.
Interference Pattern Observed in Reflections from the Ocean Bottom
Authors: Brown M. Vertner , Ricard James H.
Published: September 2005

A strong interference pattern has been observed in the reflection of monochromatic, acoustic pings from the ocean bottom. In our experiment, performed in the Gulf of Mexico at 24°16′N, 85°15′W, the pings had a frequency of 120.5 cps, a length of 0.12 sec, and were repeated every 5 sec. The transmitter was at a depth of 75 ft and the receiver at 3000 ft. The energy in successive bottom reflections varied by as much as 6 to 1, with a mean fluctuation of 30%. This rapid change in level was largely owing to the fact that the source was shallow and the air-water interface was rough. Averaging the bottom reflections in groups of ten produces a moderately smooth relation between signal level and range. This relation exhibits a pronounced interference structure. The pattern observed can be interpreted in terms of a 130-ft bottom layer having a velocity of 6650 ft/sec.
New Technique for Measuring Transducer Blocked Impedance
Authors: Sabin Gerald A.
Published: September 2005

A pulsing technique for measuring the blocked impedance of an electroacoustic underwater sound transducer is described. The method permits measuring the blocked impedance under free-field acoustic loading conditions without resorting to clamping the transducer or to the usual interpolation method. Both theory and measurements are discussed. A means of readily identifying the natural resonance frequency from either an impedance or an admittance plot is also presented.
Scattering Theory, with Applications to One-Dimensional Problems
Authors: Plutchok Robert , Harrison Mark
Published: September 2005

A recently developed analytical method employing an integral-equation technique is used to compute the reflection coefficient, as a function of frequency, of an acoustic wave encountering a one-dimensional scattering layer. The reflection coefficients are calculated for inhomogeneous layers in which the propagation function varies in a complicated manner and also for homogeneous layers in which the propagation function remains constant. The validity of the integral-equation technique is demonstrated, and it is shown that due to rapid convergence only a few iterations are needed to calculate the reflection coefficients with reasonable accuracy.
Experiments on the Influence of Flow on Sound Attenuation in Absorbing Ducts
Authors: Meyer Erwin , Mechel Fridolin , Kurtze Günther
Published: September 2005

The influence of a turbulent air stream on the sound attenuation in ducts, lined with sound absorbing materials or structures of different kinds, has been experimentally investigated. For linings consisting either of porous materials or sufficiently damped Helmholtz resonators, decrease of absorption with increasing flow velocity has been observed, together with an increase of the frequency of maximum absorption in the case of the resonators. Somewhat surprising results have been obtained for undamped or weakly damped Helmholtz resonators, where an attenuation minimum is observed above the resonant frequency, the frequency of which increases linearly with increasing flow velocity, and which—for undamped resonators—even reaches negative attenuation values. Aside from the negative attenuation, a self-excitation of the duct is observed under certain conditions, the frequency of which is not identical with the attenuation minimum.
Linear Modeling of Long Underwater Acoustic Paths
Authors: Walker W. F.
Published: September 2005

The effective treatment of signal-transmission problems requires an analytical representation or “model” of the signal path. Long underwater acoustic-signal paths fall in the class of randomly time-varying dispersive channels, which show approximate linearity and short-term statistical stationarity. A mathematical model for such paths is proposed that is based on the statistical behavior of the time-varying impulse response h (η,τ). This model has sufficient generality to account for the fluctuating dispersive characteristics of underwater paths and their property of increasing attenuation with frequency. Certain constraints may be included, however, so as to provide the model with a high level of mathematical manageability. The effects, of the channel model on the transmission of white noise, stationary random signals, and CW signals are treated. In addition, the use of the complete model in the optimization of a simple binary communication system is illustrated. The detailed treatment is confined to the point-to-point transmission situation although some discussion presented on the more complicated problem of multiple-input/multiple-output channels, including interior reflective and refractive bodies.
Noise Shield for Microphones Used in Noisy Locations
Authors: Hawley Mones E.
Published: September 2005

A rubber noise shield was developed which significantly improves the speech-to-noise ratio at a military microphone. The construction and evaluation techniques are described, and the advantage of introducing acoustic damping material is shown.
Demonstration of Masking-Level Differences by Binaural Beats
Authors: Egan James P.
Published: September 2005

Binaural beats that result from low-frequency sinusoids, one to each ear, are not nearly as prominent as monaural beats. However, when in-phase noise N0 is added to the sinusoids, the stimulus changes back and forth between N0-S0 and N0-Sπ, and the binaural beats are quite noticeable.
Two-Crystal Interferometric Method for Measuring Ultrasonic Absorption Coefficients in Liquids
Authors: Musa R. S.
Published: September 2005

Methods for measuring α, the sound amplitude absorption coefficient in liquids, using two matched quartz crystals are outlined. A standard signal generator drives one of the crystals continuously. The amplitude of the resulting pressure waves is measured at the other crystal by means of a communications receiver and a voltmeter. Partial wave analysis allows the voltage observed at the second crystal to be expressed in terms of the absorption coefficient. Three cases are identified: low, high, and intermediate absorptions, and the above expression is simplified for each of these cases. Data, obtained by these methods, are presented. The internal consistency encountered suggests an accuracy of ±3%.
Characteristic Impedances for Flexure Waves in Thin Plates
Authors: Thomas Dan A.
Published: September 2005

Boundary conditions are applied to the general solution of the thin-plate wave equation to obtain the solution for outgoing flexure waves in an infinite plate. This solution is used to obtain expressions for a bending moment characteristic impedance and a shear force characteristic impedance. Graphs of these impedances are presented.
Method for Training a Speaker to Phonate at a Given Fundamental Frequency
Authors: Schwartz Martin F.
Published: September 2005

A subject can be trained aurally to phonate at a given fundamental frequency by having him zero-beat his fundamental frequency against a reference tone. If the reference tone is presented through a loudspeaker, a sound-level meter can be adjusted to respond to the beats and thereby provide the speaker with a visual indication of his performance. The addition of visual information appears to facilitate the training procedure.
Temporal Coherence of Surface-Scattered Signals
Authors: Hartley R. R.
Published: September 2005

Data are presented on the coherency of surface scattered signals from explosive sources. Coherency figures are high and well-grouped but the effects of surface grazing angle and frequency bands are inconclusive.
Noise-Generation Mechanisms
Authors: Ribner H. S.
Published: September 2005

Basic noise-generation mechanisms are discussed in terms of simple physical models. Examples of these and more-complex mechanisms are illustrated with pressure-time histories, frequency spectra, sound-pressure levels, directionality, etc. The outline reads: (1.) Introduction. (2.) Simple Source (Pulsation)—power emission; gas bubbles in water; other examples; pulsed flow (auto engine, pulse jet); heat release (sparks, combustion); vibration of a general surface; moving source (sonic boom). (3.) Dipole Model—power and directionality; oscillating force (Aeolian tones); steady force on moving member (propeller noise). (4.) Quadrupole Model—power and directionality; oscillating force-pair (stress); jet noise. (5.) Boundary Layer and Duct Flow—flow noise; noise from excitation of wall vibration; grills and horn diffusers as airfoil noise generators.
Thermal Circuit Approach to Vibrations in Coupled Systems and the Noise Reduction of a Rectangular Box
Authors: Eichler Ewald
Published: September 2005

Stationary, wide-band vibrations of complex dynamic systems are treated in terms of energy quantities, neglecting details of structure and excitation. Approximate relations between the average energies in loosely and conservatively coupled systems are obtained in terms of modal densities, internal losses, and coupling losses. It is shown that the products of modal density and coupling-loss factor are equal within each pair of subsystems. The general theory is applied to study the noise reduction of a rectangular box, and experimental results are compared with theoretical predictions with generally good agreement. The transmission behavior of a box at a given frequency is shown to depend on the relation of this frequency to the lowest mechanical- and acoustic-resonance frequencies and the critical frequency of the walls. Theory and experiment show that near the lowest mechanical resonances the pressure in the box may considerably exceed that in the incident sound field.
Isotopic Techniques in the Study of the Sonochemical Formation of Hydrogen Peroxide
Authors: Del Duca Michael , Yeager Ernest , Davies M. O. , Hovorka Frank
Published: September 2005

Isotopic techniques involving oxygen-18 have been used to study the processes involved in the sonochemical formation of hydrogen peroxide during cavitation in oxygen-saturated solutions. Both tracer and equilibration experiments were carried out in an all glass system with converging ultrasonic fields providing maximum intensities of 103 w/cm2 at frequencies of 600 and 800 kc/sec. In oxygen-saturated water, one-third of the hydrogen peroxide oxygen was found to be derived from the oxygen gas while in solutions containing 30% (by volume) methanol, all of the peroxide oxygen was derived from the oxygen gas. In both cases, the oxygen molecule appears to be incorporated as a unit in one peroxide molecule without formal cleavage of the O - O bond.

Conditions associated with ultrasonically produced cavitation appear sufficient to dissociate water into H and OH and to rupture the C - H bond in organic molecules such as methanol but not sufficient to dissociate molecular oxygen. The oxygen molecule is involved in secondary reactions with hydrogen atoms, and hence, contributes to the formation of hydrogen peroxide. The experimental results can be explained most readily in terms of the large temperature rises which are presumed to occur within cavitation during compression but do not exclude electrical phenomena within the cavitation bubbles as a possible mechanism for the dissociation processes.
Judged Noisiness of a Band of Random Noise Containing an Audible Pure Tone
Authors: Kryter K. D. , Pearsons K. S.
Published: September 2005

The experiments reported were designed to obtain further data on the perceived noisiness of complex sounds consisting of a steady-state pure tone imbedded in a background of random noise. From these data, a method for including a “pure-tone correction factor” in the calculation of perceived noisiness in PNdB is derived. The proposed procedure should have practical application for the evaluation of sounds from modern-day jet aircraft or other broad-band sounds that may contain relatively intense, audible pure-tone components. Various problems involved in the measurement and interpretation of band spectra for the location of steady-state pure-tone components in broad-band random noise are discussed.
Elastic Moduli of Single Crystal Germanium as a Function of Hydrostatic Pressure
Authors: McSkimin H. J.
Published: September 2005

The adiabatic elastic moduli of single crystal germanium are reported as a function of hydrostatic pressure to 50 000 psi, and for a temperature range of 0–75°C. The variation with pressure of bulk modulus is found to compare favorably with isothermal values obtained by P. W. Bridgman. The techniques used for measurement are detailed.
Acoustic Streaming near a Boundary
Authors: Nyborg Wesley L.
Published: September 2005

An approximate solution is developed for sonically-induced steady flow near a fluid-solid interface. The result is valid, subject to stated conditions, for the flow near any portion of surface in the vicinity of which the irrotational oscillatory velocity distribution ua is known. The principal condition on the validity is that the acoustic boundary layer parameter (ν/ω)12 (where ω is the angular frequency and ν is the kinematic viscosity coefficient for the fluid) should be small compared to the scale of ua. Applications of the general result are made to special situations, one case of particular interest being that of a small source near a rigid plane. The conclusion is reached that small compressible bodies, and especially resonant gas bubbles, resting on boundaries, are likely sites of pronounced microstreaming a sound field.
On the Attenuation of High Amplitude Waves of Stable Saw-Tooth Form Propagated in Horns
Authors: Rudnick Isadore
Published: September 2005

The attenuation of high amplitude saw-tooth waves of stable form in horns is investigated theoretically. The shock associated with each wave is assumed to be weak. An expression for the power loss for a generalized horn is obtained. Two quantities, the limiting particle velocity amplitude and the limiting power which is transmitted per refit throat area, occur in the solution. For long, gently tapering horns these are the limits to which the particle velocity and power tend as the input to the throat is increased. Uniform bore tubes, and exponential and conical horns, are discussed as particular examples of the general case.
Time-Separation Pitch Associated with Correlated Noise Bursts
Authors: McClellan Max E. , Small Arnold M.
Published: September 2005

A situation is described wherein, contrary to previously findings, a pitch related to delay is perceived when a repetitive train of noise bursts is delayed with respect to an identical train, mixed together, and presented monaurally.
Shallow Water Test of the Theory of Layered Wave Guides
Authors: Tolstoy I.
Published: September 2005

Quantitative agreement between theory and experiment has been secured for the acoustical radiation field of a simple harmonic point source of known power output, at low frequencies in shallow water. The experiment covered the range of frequencies of 88–148 cps in water 22.6 m deep in a location on the Atlantic seaboard. All instruments were calibrated. Absolute sound levels and details of mode interaction agree quite well with those predicted by the guided wave solution for a three layered liquid half space, proper account being taken of locally measured mode attenuation coefficients. These are small and are essentially introduced into the undamped theory in a posteriori, phenomenological fashion. Emphasis is given to the importance of correctly determining the acoustical parameters of the various layers, and it is shown that minor changes in these may produce effects sufficient to destroy agreement between theory and experiment. The use of various criteria, and in particular of dispersion and mode-interaction wavelengths is illustrated in this connection.
Automation of Sound Transfer from a Tape Recorder to the Sonagraph
Authors: Frydman J.
Published: September 2005

By using a step-by-step selector relay, 2 striker pins, a fully automatic cycle is set up for transfering recorded sound from a tape player to the drum of a Sonagraph; calibrating tone is also automatically recorded on the drum. The system described in this Letter offers simplicity of operation and proved to be helpful in use.
Comments on Fitzgerald Resonances
Authors: Hopkins I. L.
Published: September 2005

Resonances in Alnico and steel, similar to those reported by Fitzgerald in other materials and attributed by him to internally generated particle waves, are demonstrated to be normal modes of vibration of the mechanical system used.
Space-Time Correlation in Isotropic Noise Fields
Authors: Usher Theron
Published: September 2005

The crosscorrelation between signals produced by two omnidirectional transducers located in a field of many scattered noise sources is considered. Both spherical, three dimensional distributions and circular, two-dimensional distributions are analyzed. Graphical Interpretations of the general equations used for computing the crosscorrelation are given. Specific results for a Markov-type noise spectrum and a narrow bandpass noise spectrum are included. Upper limits of the crosscorrelation for both spectra are computed. A technique for determining the ridges and valleys of a mad of the crosscorrelation as a function of transducer separation and electrical time delay is also developed for the case of the narrow bandpass noise spectrum.
Wide-Band Modulation of a Laser Beam, Using Bragg-Angle Diffraction by Amplitude-Modulated Ultrasonic Waves
Authors: Hance Harold V. , Parks J. K.
Published: September 2005

Light valves based on the ultrasonic-diffraction effect are capable of producing high-index intensity modulation of a light beam, but they are subject to a fundamental bandwith limitation associated with the finite time of transit of an ultrasonic wave across the light beam. It is shown theoretically that modulation bandwidth can be maximized by converging the incident light beam to a focus to minimize beam diameter and by confining the ultrasonic beam to the vicinity of the focal plane. Under properly chosen conditions, modulation bandwidth can be as large as 1/7.7 times the ultrasonic carrier frequency. An experimental investigation was carried out using water as the ultrasonic medium to verify the theoretical dependence of modulation bandwidth on ultrasonic- and optical-beam parameters and to evaluate constants of the theory. The experiments also showed that the wavefronts near the focus of a convergent light beam are sufficiently plane to produce Bragg-type diffraction when conditions are otherwise favorable. Bragg diffraction was used in the modulation bandwidth measurements. The dependence of diffracted-beam intensity on ultrasonic amplitude was investigated experimentally and, in accordance with theory, it was found that nearly all of the incident (zero-order) light can be transferred to a selected first-order diffracted beam. This fact permits either the zero-order or a first-order beam to be chosen as the useful output of the modulator.
Propagation and Reflection of Viscoelastic Waves
Authors: Cooper Henry F. , Reiss Edward L.
Published: September 2005

A formal method that is essentially an extension to viscoelasticity of the Karal-Keller method for elastodynamics is presented for solving three-dimensional wave-propagation problems for a wide class of homogeneous, isotropic, and linear viscoelastic media. As applied to high-frequency time-harmonic waves, it consists of asymptotically representing the solutions in a series of inverse powers of the frequency. However, the expansion method is not necessarily limited to time-harmonic waves. The approximation given by the first term in the expansion is called the geometrical theory of viscoelasticity. Subsequent terms provide corrections to this theory. The method can be employed to solve problems for media that contain boundaries. Applications are given to the reflection of incident waves from smooth obstacles and “asymptotic” reflection laws are derived. As an example, the first two terms are determined in the expansion of the reflected waves that result from a time-harmonic plane dilatational wave striking a rigid plane.