bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrasonically Induced Cavitation in Water
Authors: Willard G. W.
Published: September 2005

Using a 2.5-megacycle spherical focusing radiator, cavitation is produced in water at a location remote from any liquid-solid interface. The cavitating region is localized in the high intensity core of the focal region, about one millimeter diameter by 10 millimeters long. A feather-like cavitation burst is sporadically produced within the focal region. High speed camera studies show that the total duration of the burst is less than 3 milliseconds, and that the cavitation at any one point of the burst is completed in a matter of microseconds. The cavitating region propagates along the feather shaped burst from the quill end (nearest the radiator) to the tip end, at a velocity of 5 to 10 meters per second. It is believed that this velocity corresponds to that of the radiation pressure induced streaming velocity of the liquid along the axis, of the focal spot, and that a discrete, traveling, oscillating cavity initiates the surrounding cavitation. These sporadically produced cavitation bursts appear without other effects in degassed water. On the other hand, in aerated water identical appearing bursts produce noncollapsing air bubbles which blow off down stream (because of liquid streaming) providing there is no standing wave pattern present. In the presence of standing waves many of the bubbles are trapped in the standing wave pattern until they grow too large (by accumulation of other bubbles) when they again blow down stream. Slides showing the nature of these phenomena will be exhibited.
Sound Scattering by Fluid Cylinders
Authors: Dyer Ira
Published: September 2005

The scattering of plane waves of sound from an infinitely long circular cylinder has been investigated both theoretically and experimentally. Wave motion in the cylinder cannot be neglected because the properties of the fluid in the cylinder are comparable to the properties of the external fluid. A rigorous series solution for the scattered radiation has been obtained, taking into account the possibility of compressibility, density, and attenuation differences between the two fluids. At high frequencies the series solution is difficult to apply because of the many terms that must be included. Consequently, approximate closed-form solutions have been developed which are useful for high frequencies and which agree essentially with the rigorous series solution in the limit of low frequencies. The approximate solutions follow from an integral equation formulation which has application in other coordinate systems and which is similar to the results of some recent work of Montroll and Hart. Measurements have been performed on cylinders containing mixtures of tertiary butyl alcohol and water immersed in water for wavelengths approximately 18 the diameter. The approximate theory predicts the angular positions of the minima of the scattered radiation within experimental error and the magnitude of the maxima of the scattered radiation within a few decibels.
An Experimental Study of Sound Reflection from a River Bottom
Authors: Urick R. J.
Published: September 2005

Using short pulses of sound in the frequency range 7.5 to 75 kilocycles, the reflection coefficient of a natural bottom has been determined over a wide range of angle of incidence. The structure of the bottom was such that the results are interpretable in terms of the absorption coefficient of a thin overlying layer of mud. These values are believed to represent among the first information extant on the absorption of sound in this frequency range in an undisturbed sediment in situ. The reflection and absorption characteristics are compared with existing applicable theory.
Inharmonicity of Plain Wire Piano Strings
Authors: Young Robert W.
Published: September 2005

The inharmonicity of plain wire strings in situ has been measured in six pianos of various styles and makes. By inharmonicity is meant the departure in frequency from the harmonic modes of vibration expected of an ideal flexible string. It is shown from the theory of stiff strings that the basic inharmonicity in cents (hundredths of a semitone) is given by 3.4 × 1013n2d2/ν02l4, where n is the mode number, d is the diameter of the wire in cm, l is the vibrating length in cm, and ν0 is the fundamental frequency. A value of Q/ρ = 25.5 × 10 10 (cm/sec)2 was assumed for the steel wire, where Q is Young's modulus and ρ is the density. The observations are entirely compatible with the relationship given. In general terms, the inharmonicity of the plain steel strings is roughly the same in all the pianos tested, being about 1.2 cents for the second mode of vibration of the middle C string. Above this point, every eight semitones it is doubled. Below middle C the inharmonicity is consistently less in large pianos than in small ones.
Precise Measurement of the Velocity of Sound
Authors: Smith P. W.
Published: September 2005

Precise measurements of the velocity of sound in a gas at low frequencies have been made by a method of detecting the variations in the driving-point impedance caused by changes in the distance from the transducer diaphragm to a reflecting piston. The electrical terminals of the transducer are connected into the feedback circuit of a bridge-stabilized oscillator so that the frequency of oscillation is determined by the position of the piston. Measurements of the position of the piston are made at points for which the frequency is identical. When careful consideration has been given to all the possible sources of error and proper corrections have been applied, the accuracy of the results is comparable with that of the best measurements made by other means. Measurements made in air at 1000 cps yield a velocity, corrected to standard conditions, of 331.464±0.05 m/sec. The analysis of one source of error has been generalized to apply to other systems whose operation depends upon the reaction of the acoustical field upon the transducer. It is shown that recurrent extrema measured in the electrical circuit which result from changes in the position of the reflecting piston will not in general have a period precisely equal to the half-wavelength of sound.
Construction of Apparatus for Measuring the Velocity of Sound in Gas Mixtures
Authors: Woodburn James
Published: September 2005

The present paper deals with the construction of apparatus for measuring the velocity of sound in gas mixtures at maximum pressures of 400 psi and 750°F. Experimental results have been obtained on mixtures of CO2 and N2 at a constant mixture pressure and from a temperature range from room temperature to 525°F. The frequency of all measurements has been at 575 kc. A general description of the present apparatus will be presented and also some high pressure gas ultrasonic apparatus in which work is being done at the present on the above gas mixtures. The high pressure apparatus will withstand a maximum pressure of 7000 psi and a maximum temperature of 1000°F.
Solutions of the Generalized Eikonal Equation for Moving Fluids
Authors: Kornhauser E. T.
Published: September 2005

Heller has pointed out that weak acoustic shocks in moving fluids are propagated according to a generalized eikonal equation, |∇φ|2 = μ2[1 − (V⋅∇φ/c0)]2, where c0 is the reference sound velocity, V the vector velocity of the moving fluid, and μ the refractive index. Such an expression has also been used by Milne to obtain approximate solutions for wave propagation in the atmosphere subject to the effect of wind. This equation may be obtained as a very simple extension of the ordinary eikonal equation. Solutions are exhibited for some simple cases involving point sources or plane waves. Solutions obtained by Milne on the basis of a generalized Snells' law are shown to be incorrect except in the case of a plane wave incident from a homgeneous half-space.
On the Propagation of Acoustic Discontinuities in a Moving Inhomogeneous Fluid
Authors: Heller G. S.
Published: September 2005

Consider a moving surface, on which the time derivatives of velocity and pressure are discontinuous but on which the velocity and pressure themselves are continuous. Such discontinuities may correspond to dissipated shock waves or “weak shocks.” Then under the assumption that each moving fluid element undergoes adiabatic changes, it can be shown that the surface is given by the solution of a generalized eikonal equation, which in the case of a fluid at rest becomes the ordinary eikonal equation of ray acoustics. This treatment does not require the usual assumption of infinitesimal amplitudes ordinarily used in acoustics. Conservation laws corresponding to those in ray theory are also derived under the above assumptions.
Intensity Fluctuations of Radiation Propagated in a Randomly-Inhomogeneous Medium
Authors: Mintzer David
Published: September 2005

By considering an approximate solution to the equations of ray propagation, P. G. Bergmann has derived an expression for the fluctuation of the intensity of radiation from a non-directional source, propagated through a medium in which the index of refraction varies randomly with position, subject to the condition that the variations are small compared with unity. It is found that his theoretical results do not give the correct range dependence for the intensity fluctuations. In an effort to remove this discrepancy, the equations have been extended to include the directionality of the source and absorption in the medium. Comparison will be made with experimental results.
Electromechanical Response and Dielectric Loss of Prepolarized Barium Titanate Ceramics under Maintained Electric Bias
Authors: Baerwald Hans G. , Berlincourt Don A.
Published: September 2005

The effect of a maintained aiding direct current bias field on the performance of prepolarized barium titanate ceramics has been investigated with respect to both loss factor and electromechanical response over the temperature range from 25° to 120°C as a function of bias field strength. In addition the effect on the temperature variation of the reversible dielectric constant was studied. The dielectric losses under high ac fields are considerably reduced by the application of bias, and the magnitude of this effect shows a pronounced temperature dependence. Aiding bias also proves beneficial by substantially increasing the electromechanical coupling, and it raises the Curie point by up to about 4°C. Dielectric loss factors were determined semiquantitatively by bridge measurements at moderate ac fields and by means of hysteresis loop areas at higher fields. Both the electrostrictive coefficient u31 relating transversal strain to the square of the total charge density and the linear piezoelectric coefficient g31 relating the increment of strain to the increment of charge density in prepolarized ceramics have been measured directly. From these results, approximate values of retained polarization referring to various physical conditions have been determined; they range to about 11 microcoulombs per square centimeter.
Ultrasonic Propagation in Dry CO2-Free Air
Authors: Ener C. , Hubbard J. C.
Published: September 2005

The ultrasonic properties of dry, CO2-free air have been measured at 32°C and f/p values ranging from 2 to 125 Mc/atmos. Dispersion of the velocity has been found beginning at 30 Mc/atmos, accompanied by a large increase in absorption such that measurements could not be made above 130 Mc/atmos with the equipment used. Changes in velocity, absorption, and specific heat are interpreted as owing to the slowing of energy exchange between translational and rotational states. The relaxation time derived from the dispersion measurements has been found to be 2.29 × 10−9 sec, corresponding to a midpoint of the dispersion curve at 116 Mc/atmos.
Seismic Model Study
Authors: Howes E. T. , Tejada-Flores L. H. , Randolph L.
Published: September 2005

A method of studying seismic reflections in reduced scale has been developed which simulates geophysical seismic exploration methods. Use is made of a tank of water for transmission of the acoustic wave from a source to a faulted limestone stratum and return to the receiver. Details of equipment used and slides diagramming the various details along with oscillogram slides of acoustic reflection waves are included.
An Investigation of the Air Chamber of Horn Type Loudspeakers
Authors: Smith Bob H.
Published: September 2005

The classical horn loudspeaker theory is reviewed briefly, and the inadequacy of the classical air chamber analysis for “tweeters” is indicated. The air chamber is treated as a boundary value problem which results in the solution of the wave equation for the general case in which the horn throat enters the air chamber in any circumferentially symetrical manner. The following specific cases are analyzed: (1) when the horn throat enters the air chamber by means of a single orifice, (2) when the horn throat enters the air chamber by means of a single annulus of radius r and width w, and (3) when the horn throat enters the air chamber in “n” annuluses of radii r1⋯rn, and widths w1⋯wn. The theory is verified experimentally.
Barium Titanate Admittance-Temperature Characteristics
Authors: Lane A. L.
Published: September 2005

There is a large amount of data in the literature describing the temperature effects on the dielectric and piezoelectric constants of barium titanate. This paper, however, describes the temperature effects on the admittance of barium titanate transducers operating near resonance. Both pure and leaded ceramic mixtures are compared over the 0°–20°C temperature range. Despite extreme fluctuations of the dielectric and piezoelectric constants over this temperature range, it is possible at a certain frequency near resonance for both the transducer conductance and susceptance to vary very little with temperature. Air and water admittance circle diagrams, sensitivity-frequency, and efficiency curves—all plotted against temperature—are presented and analyzed from an equivalent circuit point of view. One of the significant conclusions derived from this experiment is that the radiated power of a transmitting transducer, properly matched to its source at this optimum frequency, will remain maximized regardless of the temperature variation. While the barium titanate temperature effects were studied for given underwater transducers, the information outlined is of value to anyone encountering temperature variations in a resonant barium titanate ceramic.
Large Amplitude Vibrations of Rods and Tubes at Audiofrequencies
Authors: Brennan J. N.
Published: September 2005

A new apparatus for investigation of sound propagation constants for large amplitude audiofrequency vibrations in metals is described. One novel feature of the apparatus is the use of tuned resonant supports that are tilted with respect to the specimen. The tilting minimizes the tendency to chatter due to the Poisson effect. Because the supports are driven at their resonant frequency, large amplitudes may be achieved without the occurrence of an energy loss due to slipping at the contact surfaces between supports and test specimen. Auxillary equipment permits determination of the resonant frequency of the specimen to better than 1/1000. The error in the determination of the logarithmic decrement varies between 2 percent and 5 percent. The error caused by energy dissipation due to the internal friction of the support is, in most cases, negligible. In those cases where it is not negligible, it can be closely estimated and corrected for. Preliminary results for 61S-T6 aluminum alloy show the decrement to vary as the 14 power of the stress amplitude.
Use of Temperature to Describe Random Noise Fields
Authors: Jones R. Clark
Published: September 2005

It is well known that thermal agitation of the air molecules in an otherwise quiet room produces a precisely calculable spectrum of acoustical noise. The noise level at room temperature is low, so low that it is slightly below the threshold of persons with normal hearing (Sivian, de Vries). In at least one field of science (radio astronomy), temperature is regularly used as the parameter to describe the level of noise. This procedure may also be used in acoustics. One can describe the level of any random sound field in a narrow band of frequencies by specifying its effective temperature. Illustrative values of the temperature will be given for typical sound fields in air and in the ocean.
Velocity of Sound in Liquids—a Simple Laboratory Measurement
Authors: Veneklasen P. S. , Liebermann D.
Published: September 2005

The need for a small scale method for measuring acoustic velocity in certain rocket propellants resulted in a simple method within the scope of ordinary audio-acoustic instrumentation. The method is based upon the excitation and detection of low order radial modes of a liquid enclosed in a spherical glass container. The system is excited by a group of ordinary headphones. The particular modes are selectively detected by means of a probe tube sampling pressure at the center of the sphere. Essential precautions are stressed. Calculation of the effect of the glass envelope is presented. Results for a few common liquids are evaluated.
Acoustic Design of a Contemporary Auditorium for The University of Houston
Authors: Boner C. P. , Lane R. N.
Published: September 2005

The acoustic design for a 1700-seat all-purpose auditorium built for The University of Houston is discussed. This auditorium is almost unique in that the architect followed the advice of the acoustical consultant in every detail. Very large convex plywood cylinders provide the necessary acoustic control at low frequencies. These diffusive elements, along with hardplaster convex ceiling contours, provide diffusion throughout the auditorium as evidenced by the uniform sound level measured on the main floor, balcony, and under the balcony. Data on the reverberation time as a function of location in the auditorium are presented along with data on syllable articulation tests at these same locations. Audience reaction to this auditorium is described.
A Study of the Building Blocks in Speech
Authors: Harris Cyril M.
Published: September 2005

Identification of the information bearing elements of speech is important in applying recent thinking on information theory to speech communication. One way to study this problem is to select groups of building blocks and use them to form “standardized” speech which then may be evaluated; a method having the advantage of simplicity is described. Individual recordings of the building blocks were made on magnetic tape, and then various pieces of tape were joined together to form words. Experiments indicated that speech based upon one building block for each vowel and consonant not only sounds unnatural but is mostly unintelligible, because the influences on vowel and consonants are missing which ordinarily occur between adjacent speech sounds. To synthesize speech with reasonable naturalness, the influence factor should be included. Here these influences can be approximated by employing more than one building block to represent each linguistic element and by selecting these blocks properly, taking into account the spectral characteristics of adjacent sounds so as to approximate the time pattern of the formant structure occurring in ordinary speech. There is no a priori method of determining how many building blocks are required to produce intelligible standardized speech. This can only be determined from experiments involving listening tests. Such tests are described.
Representation of Speech Signals in Terms of Articulatory Positions
Authors: Stevens K. N.
Published: September 2005

An electrical analog of the vocal tract has been used to determine empirically some quantitative relationships between the acoustic characteristics of the speech signal and the vocal tract positions during the production of the speech. Relationships between the spectrum of the acoustic signal and the positions of lips, teeth, and tongue are presented in graphical form. It is shown that relatively few variables are required to describe the quasi-periodic variations of the articulatory dimensions from syllable to syllable as continuous speech is produced. The experimental results support the suggestion that it is possible to construct a narrow-band speech transmission system in which voltages proportional to vocal tract dimensions are used as the transmission signals. The channel capacity required for the transmission of these signals would approach the lower limit predicted by information theory.
A Speech Synthesizer
Authors: Harris Cyril M.
Published: September 2005

“Standardized speech” constructed from building blocks called speech modules has been described; it was synthesized by piecing together bits of magnetic tape containing recorded speech sounds. (See paper C7.) An electromagnetic device, a “speech module synthesizer,” is described here which performs the synthesis automatically. When buttons on a keyboard are pressed, a sequence of corresponding speech modules are automatically recorded on tape exactly in tandem. The modules are selected from a group “stored” on a rotating magnetic drum. The pressing of a button causes an electrical signal corresponding to a module to be reproduced—the electrical switching so arranged that only one complete module is reproduced for a single button-pressing. This electrical signal is amplified, biased, and then fed into a constantly rotating recording head which makes contact with stationary magnetic tape and records the signal on it. A 10-kc signal superposed on each stored speech module controls an electromagnetic clutch, which (a) measures the length of the recording accurately, and (b) advances the tape at the completion of the recording by the correct amount so that the next recording forms a connected sequence with it. The same module way be used any number of times and in combination with different stored modules, thereby introducing wider experimental control in standardized speech studies. The principle of this type of device could be applied to other classes of problems involving communication of information, as the conversion into speech of typing or of electronically read printed matter.
Materials and Structures Problems in Noise Control
Authors: Lemmerman Richard D.
Published: September 2005

The materials and structures problems associated with the construction of aircraft noise silencing systems often make classical solutions to the acoustic problems extremely difficult. The associated problems of fluid mechanics and physical construction must be carefully considered along with acoustical requirements at the time of initial design. A review of some of these problems specifically associated with various types of aircraft engines will be discussed. Similarly, the various types of acoustical material suitable for broad-band attenuation will be considered from their structural standpoint.
Noise Characteristics of Pulse-Jet Engines
Authors: Veneklasen P. S.
Published: September 2005

This noise survey was undertaken for the American Helicopter Company, as part of a noise control program. Data presented include the magnitude, spectral characteristics, directional properties, and variation with operating conditions of the noise produced by two sizes of pulse-jet engines.
On Residential Noise: Plumbing and Aircraft
Authors: Watson Robert B.
Published: September 2005

Some experimental data are presented on internal residential noise with especial emphasis on noise arising from the bathroom, in comparison with noises in residences arising from passing aircraft. A brief discussion of suitable structures for combating these noise problems is included, in contrast to conventional practice.
Calculated Pressure Response of Condenser Microphones from Measured Electrical Impedance Data
Authors: Simmons Bernard D. , Biagi Fernando
Published: September 2005

If the condenser microphone is assumed to be represented by a simple four-terminal electromechanical network, the pressure response ρ is given by the expression ρ = 1φ g + jω(C − Co)g + jωC Y = g + jωC is the electrical admittance with a zero mechanical load. Co is the electrical capacitance with the diaphragm blocked, determined from a high frequency measurement of capacitance. φ is determined from a measured value of response at low frequencies, i.e., φ = 1ρ(C − CoC). Calculated values of response are compared with values obtained by the reciprocity technique.
A Pulse Tube for the Measurement of Acoustic Impedance
Authors: Cramer William S.
Published: September 2005

An apparatus is described with which the acoustic impedance at an interface can be measured in water for normally incident sound. It consists essentially of a thick-walled steel tube 6 feet long with an internal diameter of 212 inches, which is mounted vertically and filled with water. A crystal transducer, mounted at the bottom of the tube, produces a pulsed acoustic signal which travels up the tube. At the top this signal impinges on the surface under study and is reflected back with characteristic changes in amplitude and phase to the transducer which then acts as a receiver. The amplitude and relative phase of the reflected signal are measured by superposing a continuous oscillation of the same frequency on the received signal and adjusting the relative amplitude and phase so that complete cancellation of the reflected signal occurs. These results are compared with those similarly obtained with a reflector of known properties located at the same point in the tube. The frequency range is 10 kc/sec to 40 kc/sec, and the pulse duration is about 1 millisecond. The top of the tube can be closed and hydrostatic pressure applied to the system.
Measurements of Turbulence Noise Radiated by Small Jets
Authors: Lee R. , Fitzpatrick H. M.
Published: September 2005

The noise fields resulting from turbulence generated by small jets of sizes from 14 to 112  inches in diameter and flow velocities up to sonic velocity have been measured. The measurements were made in a reverberant chamber and also in a free field. Directional surveys of the noise radiated for half-octave frequency bands in the audible range have been made. From these measurements the total acoustic power has been calculated. Results indicate that the total radiated acoustic power P of an air jet of diameter D at a flow velocity U may be expressed simply in the following form: P = KρD2U8c−5, where ρ and c are the ambient air density and acoustic velocity. The acoustic power coefficient K is found to be influenced only slightly by the Reynolds and Mach numbers of the flow and is of the order of 10−4. Experimental results are in agreement with Lighthill's recent theory on turbulence as a source of sound. The spectrum of the noise is also presented. The importance of the reduced frequency parameter fD/c and the directional characteristics of the noise is discussed. It is believed that the results may have application with respect to noise control problems on jet engines in airports and test facilities.
Short Duration Auditory Fatigue after White Noise Stimulation
Authors: Tonndorf Juergen , Brogan F. A.
Published: September 2005

Short duration auditory fatigue was tested after exposure for two seconds to white noise (level variable between 30 and 110 db re 0.0002 dyne/cm2). Following stimulation the change from a predetermined threshold of a probe tone was assayed. The free interval between stimulus and probe was adjustable between 0.025 and 7 seconds (10 steps within the first second, full second steps thereafter). The probe consisted either of a 0.04-second white-noise or pure-tone pip (500 to 8000 cycles in octave steps) or of a click. In addition to the absolute change in threshold at various intervals, the slope of return to the pre-exposure level was assessed; for the sake of simplicity the latter was expressed as the percentage difference in threshold change at two relatively distant points on the time axis. Tests were conducted on trained and untrained subjects with normal hearing for pure tones. Variation in and among subjects was evaluated in order to determine the applicability of the three different forms of probe as a routine test measure.
Limits on Airborne Noise in Naval Shipboard Spaces
Authors: Strasberg M.
Published: September 2005

Criteria are presented to guide the specification writer in setting limits on airborne noise in shipboard spaces of U. S. Navy vessels. Limits are given for three objectionable effects of airborne noise: (1) permanent hearing loss, (2) interference with speech communication, (3) discomfort. The limit for any specific ship space depends on which, if any, of these effects can be tolerated without interfering with the function of the space. Limits for hearing loss and discomfort are expressed in terms of octave-band spectra. The hearing-loss-avoidance limit is that suggested by Hardy. The comfort limit is based on criteria of Lippert and Miller. The limits for interference with speech are expressed in terms of the “speech-interference level,” i.e., the arithmetic average of the levels in the 4 octave bands covering 300 to 4800 cps, following the scheme of Bolt, Beranek, and Newman. Maximum permissible speech-interference levels are tabulated as a function of the distance to the speaker, the voice level, and the acoustic absorption in the space. For typical ship spaces, tentative noise-level limits are suggested, based on present usage of the spaces.
Periodic Fluid Flow Through Circular Orifices
Authors: Thurston George B. , Martin Charles E.
Published: September 2005

The results of an experimental investigation of both the linear and nonlinear analogous acoustic resistance and inductance of circular orifices with water and 10 centistoke Dow Corning Silicone fluid are presented. Experimental determinations of the end corrections for resistance and inductance are in good agreement with the classical end correction as given by Rayleigh for inductance. A series of determinations of the criterion for the onset of nonlinearity in resistance and inductance, together with photographs of the fluid flow patterns developed, are presented. A characteristic of one of the fluid flow patterns is correlated with the onset of nonlinearity.
An Experimental Study of the Hydrodynamic Flow
Authors: Cady W. G.
Published: September 2005

In determining the efficiency of a transducer it is desirable to know whether some of the electrical energy is expended in a pumping action at the transducer surface, as distinguished from the hydrodynamic flow due to absorption of energy in the medium. The force due to the total unidirectional flow from a plane-wave transducer in water, acting upon a thin membrane placed at various distances, can be measured, together with the intensity of radiation passing through the membrane. The transducer is also suspended in the water in such a way that the total force reacting upon it can be observed. From these data and the losses in crystal and mounting, one can calculate how much of the applied energy goes into radiation. Experimental results are discussed.
Acoustic Streaming in a Thin-Walled Cell
Authors: Nyborg Wesley L.
Published: September 2005

Calculations of steady flow, commonly associated with high intensity sound fields, have been made in only a few cases. In this paper a solution is given, valid for any two-dimensional sound field but for only a very special boundary condition. The problem treated is that of the rotary flow induced within a small thin-walled “test cell,” the walls transparent to sound waves, supposed centered at any point P(x, y) in a sound field. The inner streaming speed proves to be proportional to the value at P(x, y) of ∇xF*, where F* is a second-order quantity connected with radiation pressure. In the far field of a directional source the streaming speed depends on the position of the cell relative to the various lobes. For liquids the rotary speed is likely to be very small unless the ratio of absorption constant α to shear viscosity coefficient μ is unusually great, as in a bubbly medium.
Equipment for the Study of Undersea Echoes at Reduced Scale at Frequencies of 200 to 1000 kc
Authors: McRae Daniel B.
Published: September 2005

This paper describes equipment for study of undersea echo formation on a reduced scale. A novel feature is a 2500-gallon tank having 16 glass ports for observation and photography. An echoless support for a variety of buoyant and nonbuoyant targets permits positioning in three dimensions as well as rotation about a vertical axis, which can be adjusted to pass through any desired part of the object. Individual transducers for specific frequency ranges are built on standard circular plates which are quickly interchangeable in a common mount. This is rotatable through a wide range of azimuth and tilt angles. It is moveable across the width of the tank along a graduated scale. A slow motion device operates over any selected 30 cm of this path. Pulses having a duration as short as ten cycles can be produced at the chosen frequency. Repetition rate can be varied from 50 to 300 per second, or single isolated pulses can be produced. Received echoes are presented on a 247A oscilloscope and photographed on single frames of 35-mm film. A special camera arrangement provides positive, automatic identification for each frame. The equipment has proved useful for a variety of acoustical experiments.
Pitch and Intensity: Additional Data
Authors: Nickerson James F.
Published: September 2005

The data included in this report are taken from a study in progress attempting to explore the pitch-intensity function of various types of complex tone. These data cover that portion of the study which presents the changes of pitch with changes in intensity of pure tones for 11 ears. Due to the limiting conditions of the study in progress, the methodology departs somewhat from the conventional procedure, yet the data correspond closely and corroborate the recent data on 18 ears reported by Morgan, Garner, and Galambos. Mean pitch shifts rarely exceed 2 percent (approximately 35 cents) and the interquartile range does not exceed 4 percent (approximately 70 cents). There is evidence of low consistency in test-retest results apparently dependent upon intensity level, the frequency, the individual ear, and the individual subject.
Temporal Fluctuations of the Masked Auditory Threshold
Authors: Licklider J. C. R.
Published: September 2005

An auditory threshold is not a static, unvarying quantity. It fluctuates from moment to moment, hour to hour, day to day. The measurements to be described are part of an effort to quantify these temporal variations. A Gaussian pulse of tone of fixed frequency and intensity is presented every 2 seconds against a background of white noise. The listener reports whether he hears the pulse (1) or not (0). The series of 0's and 1's obtained in this way is then analyzed. Autocorrelation functions of such series indicate that there is no marked periodicity in the temporal variation of the threshold in the range 0.05 to 0.5 cps. Estimation of the conditional probability structure out to fourth order reveals little if any conditionality. The significance of these and other results for the theory of auditory thresholds is discussed.
The Masking of Tones by White Noise as a Function of Interaural Time or Phase Displacements. II. 167 cps
Authors: Jeffress Lloyd A. , Blodgett Hugh C. , Deatherage Bruce H.
Published: September 2005

In recent papers the authors have described the effects upon masking of varying the interaural phase position of a 500-cps tone and of either the phase position of the 500-cps masking component or the interaural time displacement of the whole masking noise. The present paper extends this work to a lower frequency, 167 cps, in order to discover whether there is an optimal interaural time difference for masking level reduction. The results do not encourage such an interpretation but favor, rather, an explanation based on interaural correlation. This work was performed under Bureau of Ships Research and Development Contract NObsr-52267.
Instrumentation for Psychoacoustic Testing
Authors: Dieter C. L. , Bauman R. C.
Published: September 2005

An automatic programming and data-tabulating apparatus has been developed for use in studies of the aural recognition of pulsed signals in noise backgrounds. The equipment provides considerable precision and flexibility both in the control of the signals and backgrounds presented to the subject and in the processing and tabulating of the operators' responses. Pulsed signals up to eight seconds in length are available, and filter band widths from one thousand cycles per second down to one-fourth cycle per second are provided for filtering the signal and noise before they are presented to the test subjects. The subjects' booths are located in a sound isolated room to minimize the effect of airplane and building noise on the experiments.
Audibility of Intense Ultrasonic Sound
Authors: Deatherage Bruce H. , Jeffress Lloyd A. , Blodgett Hugh C.
Published: September 2005

When an intense ultrasonic source is brought into contact with any of the head bones, either by pressing the transducer firmly against the head or jaw or by placing the transducer in water in which a portion of the head is immersed, the subject will hear a high pitched tone. Thresholds for the phenomenon are of the order of 1000 dynes per square centimeter. Any frequency from the normal sound frequencies up to higher than 70 kilocycles will elicit the experience. The pitch of the tone heard is not dependent upon the frequency of the sound but apparently is simply the highest tone the subject can hear. A demonstration of the phenomenon will be made. This work was performed under Bureau of Ships Research and Development Contract NObsr-52267.
The Effects of Very Narrow Band Filtering on the Aural Recognition of Pulsed Signals in Noise Backgrounds
Authors: Bauman R. C. , Dieter C. L. , Lieberman G. , Finney W. J.
Published: September 2005

Experiments have been conducted to determine the dependence of aural recognition of pulsed signals on the pulse length, signal-to-noise ratio, and the bandwidth of the filter through which the signal and noise were passed. The pulse lengths used ranged from one-fourth second to four seconds, and the filter bandwidths ranged from one-fourth cycle to one thousand cycles and were centered at eight hundred cycles. Signals randomly spaced in the noise background were presented to eight trained subjects. Least-square estimates of the signal-to-noise ratios required for fifty percent signal recognition were made, and their values were plotted as a function of pulse length and filter band width.
A Field Meter for Sound Velocity Measurements
Authors: McLoughlin Robert C. , Chiles James R.
Published: September 2005

The travel time of sound across a fixed gap between diaphragms of transmitting and receiving transducers is recorded each 1/500 second. From this the interdiaphragm velocity is computed. It is a function of both temperature and wind. Spurious travel time changes introduced by phase shifts in the receiver are minimized by using a 500-cps intelligence signal amplitude modulating a 10-kc carrier. Experimental errors when operating in air with interdiaphragm distances of 3 feet are less than 2 percent in the temperature range from 70° to 200°F, but the application of the instrument is not restricted to this range. A circuit for recording velocity directly on a paper tape is described. Although designed primarily for air, the unit is readily adaptable to other media. It should also be of special interest to the micrometeorologist.
The Return of Sound from the First and Second High Temperature Regions over the Southwestern United States
Authors: Johnson C. T.
Published: September 2005

The abnormal propagation of sound over the California-Arizona desert has been studied over the course of a year. Explosions of 1200 pounds of TNT produced signals which were abnormally propagated to distances of from 100 to 340 km. Returns from the first high temperature region at an altitude of about 30 to 50 km were received to the east in winter and to the west in summer. Sounds which traveled to the high temperature region at 80- to 100-km altitude were received about one-fifth of the time. The signals returned from this second region were received somewhat better to the east in summer and to the west in winter.
Combined Translational and Thermal-Relaxational Dispersion of Sound
Authors: Greenspan Martin
Published: September 2005

The proper interpretation of sound-propagation data relating to thermal relaxation of rotational modes in (say) diatomic gases requires a knowledge of how the effect combines with that of translational relaxation whenever the relevant “frequency/pressure ratios” overlap. In effect, it is necessary to solve the Stokes-Kirchhoff equations for complex values of specific heats and thermal conductivity. An approximation which does not affect the general character of the solution and has only a minor quantitative effect allows the equation to be factorized and a solution to be obtained in simple form. It is shown that the combination of attenuation and velocity changes by simple addition is valid only when they are small. However, for frequencies well above the thermal relaxation frequency the total attenuation may be smaller than that resulting from translational effects alone.
Free-Molecule Propagation of Sound Through Gases
Authors: Cook Richard K. , Greenspan Martin , Thompson Moody C.
Published: September 2005

Measurements have been made of the attenuation and phase shift of sound propagated through gases at very low pressures. The 11 Mc/sec double-crystal interferometer described earlier was used. The range of pressures studied extends from about 1.5 mm Hg to less than 0.1 mm. The amplitude and phase shift of the received sound were measured at distances of less than the mean free path. A simple theory, based on the assumption of no collisions, was developed. This theory shows that the propagation approaches (ix)12 exp[−3(ix/2)23] asymptotically for large x, x = (γ/2)12ωh/c0 (c0 = the ordinary velocity of sound in the gas, γ = ratio of specific heats, ω = 2π times frequency, h = distance from source to receiving crystal). The theory agrees with the main features of the measured propagation. For example, with increasing h, the phase velocity increases roughly like h13 and is independent of pressure.
A Study of Finite Amplitude Distortion of a Sound Wave in Air
Authors: Geertsen O. Norman
Published: September 2005

It has been shown by Thuras, Jenkins, and O'Neil that the theoretical magnitude of the extraneous frequencies, generated in air by very intense sounds, are obtained from an approximate solution of the exact differential equation of wave propagation in air. The solution shows that the pressure of the extraneous harmonic frequencies generated in air increases with (1) the frequency of the fundamental, (2) the magnitude of the fundamental pressure, and (3) the distance from the source. Taking into consideration the loss at the side walls of the tube in which the plane wave is propagated, we may write the ratio of the pressure of the generated second harmonic to that of the fundamental pressure as P2/P1 = KP0XR, where K = (√/4) (γ+1/γP0) (ω/c), P0 is the rms pressure of the fundamental at X = 0, X is the distance from the source, R is the loss factor 1 minus; (α2X/2), α2 is the loss per unit distance in the second harmonic pressure. It was found that the loss along the tube was essentially that at the side walls of the tube. This was expressed by Beranek as α equals; 3.18 × 10−5 (f12/r) nepers/cm, where f is the frequency and r is the radius of the tube. Thuras, Jenkins, and O'Neil found the absolute magnitude of the generated tones in the tube, of all measured values, to be about 3 db lower than the theoretical values. In this restudy of the problem, done under a Naval Research contract at U.C.L.A., it was found that the measured values of the generated second harmonic pressure were in good agreement with the theoretical values.
The Physical Interpretation of the Expression for an Outgoing Wave in Cylindrical Coordinates
Authors: Junger Miguel C.
Published: September 2005

The sound field generated by a vibrating cylinder of infinite length, whose dynamic configuration is periodic in φ and z, is expressed in terms of acoustic impedance ratios. It is noted that symmetrical modes of vibration are suppressed at certain frequencies because the corresponding reactive impedance is infinite, and that all z-dependent modes become nonradiating below certain “cut-off” frequencies, the corresponding impedance being purely reactive. Graphs are presented for the impedance ratios corresponding to certain modes. For modes independent of z, the sound field is in the form of concentric cylindrical waves. For z-dependent modes, as the plane wave wavelength increases from zero to a certain critical “cut-off” value, the sound field successively assumes the form of a set of concentric cylindrical waves and of two sets of conical waves of decreasing vertex angle; at and beyond the “cut-off” point, the conical waves have degenerated into a set of plane standing waves normal to the z axis. Simultaneously the sound field has ceased being periodic in the radial direction, the phase velocity having become infinite. Practical applications of these phenomena are suggested.
A Sequential Statistical Analysis for Word Articulation Tests
Authors: Hawley Mones E. , Wong Walter , Meeker Willard F.
Published: September 2005

The problem of deciding when the intelligibility of one speech communication system is equivalent to the intelligibility of another system has been solved utilizing the techniques of sequential statistical analysis. If the experimenter is willing to tolerate some arbitrary probability (a) that the method will reject the system when it should be accepted and some arbitrary probability (b) that the method will accept the system when it should be rejected, he may make a rapid, running analysis which will indicate whether he should accept the system, reject it, or continue testing. The system should be accepted when σ22  ∑ α=1m x1α − σ12  ∑ α=1m x2α≦σ12σ22 loge[b/(1 − a)] + m(σ22 − σ12) (μ1 − μ2)/2. The system should be rejected when σ22  ∑ α=1m x1α − σ12  ∑ α=1m x2α > σ12σ22 log[(1 − b)/a] + m(σ22  − σ12) (μ1 + μ2)/2. where, in both cases, σ1 = standard deviation of the scores of the first system, σ2 = standard deviation of the scores of the second system, m = number of the tests, x1α = score of the first system on the αth test, x2α = score of the second system on the αth test, μ1 = mean value of the scores of the first system, and μ2 = mean value of the scores of the second system. If neither condition is satisfied, testing should continue. The method checks with the longer analysis of variance which is used at present.
Propagation of Radiation near an Irregular Surface in an Inhomogeneous Medium
Authors: Meecham William C.
Published: September 2005

The exact solution of the problem of propagation of radiation in an inhomogeneous medium with a plane boundary has proved extremely difficult even in the simpler cases. The introduction of an irregular surface as a boundary for this problem places the exact solution beyond present methods. An attempt has been made to solve the problem by introducing two simplifying assumptions. It will be assumed first that the phases of reflected waves contributing to the intensity at a particular point are random, and second that the wavelength of the radiation is sufficiently short to permit ray tracing. On the basis of these two assumptions a transport equation similar to the transport equations of statistical mechanics is set up. Some comments will be made upon the solution of the problem of acoustical propagation in a linear velocity gradient near a rough surface.