bluuebunny/crossref_metadata_2025 huggingface dataset:
New Techniques in the Analysis of Motor and Machine Noise
Authors: Fehr R. O. , Henry G. E.
Published: September 2005

Motors and machines are acoustically complex; varied techniques are required for an analysis complete enough to be of practical use. The dynamic sound spectrograph designed by the Bell Laboratories for speech studies, can, with some modification, be used to good effect in determining the precise nature of the transient sounds which up to now have been difficult or impossible to resolve simultaneously in both frequency and time dimensions. Thus, an easy method becomes available for separating electrical from mechanical noise in motors and motor-to-load assembled units, without introducing an external drive. Cavity and case resonances are located by observing which frequencies recur, independently of rotor speed. A second step consists in noting the decay pattern following shock excitation of the suspected member. In most machines, frequencies forced by shaft rotation predominate over formant frequencies. Shaft rotation produces, in addition to its fundamental, an elaborate array of harmonics. Comparison of spectrograms and instantaneous pressure traces (oscillograms) is especially valuable in understanding the complete acoustic system. The limitations of the spectrograph in treatment of sounds below 1000 c.p.s. are caused by the linear frequency scale associated with the present system of heterodyne analysis. This can be overcome by the use of an external rejection filter analyzer with output fed to the marking amplifier.
The Quieting of Transit-Type Diesel-Powered Coaches
Authors: Apps David C.
Published: September 2005

The problem of reduction of curb or pullaway noise of motor coaches used for city operation is attacked by the use of a magnetic wire recorder. The recordings, which will be demonstrated, are used in jury tests and for corroborative information by playback through band-pass filters. The noise sources are attacked and reduced in their order of importance and in a form suitable for production and practical operation.
Spectra and Loudness of Modern Automobile Horns
Authors: Callaway D. B.
Published: September 2005

Measurements were made of the sounds of three types of commonly used automobile horns. Over-all sound levels on the axis at three feet ranged from 108 to 125 db. Loudnesses ranged from 125 to 140 phons. One type of horn gave sound levels of 88 db at 50 feet and 74 db at 300 feet, with corresponding loudness levels of 104 and 81 phons. Fundamental frequencies of all horns ranged between 160 and 380 c.p.s. Two types had harmonic overtones, with large amplitudes below about 2000 c.p.s. and smoothly decreasing amplitudes at higher frequencies. The third type, with the most unpleasant sound, had inharmonic overtones, some of which were greater in amplitude than the fundamental. Sound from a pair of horns at various distances was measured inside a closed automobile The over-all level was 60 db (loudness, 72 phons) at 50 feet and 50 db (loudness, 53 phons) at 300 feet. Filtering out overtones above 1200 c.p.s. reduced the annoying character of horn sounds markedly and reduced the loudness by four phons at 50 feet and only one phon at 300 feet. Since the typical horn is louder than necessary at close range, use of a low pass acoustic filter on automobile horns appears desirable.
A Second-Order Gradient Noise-Canceling Microphone Using a Single Diaphragm
Authors: Wiggins A. M. , Beaverson Wayne A.
Published: September 2005

A close-talking, noise-canceling microphone has been developed which responds to the second order of the pressure gradient and which has only one diaphragm. Since there are four sound pressures involved in a second-order gradient microphone, it has been deemed necessary in the past to have four surfaces for the four pressures to act upon. This microphone has sound entrances to the two surfaces of a single diaphragm spaced and oriented in such a manner as to produce the second-order effect, thereby increasing the signal-to-noise ratio over that obtained in a first-order gradient microphone. Mathematical analyses are made of the microphone first as a purely theoretical microphone with infinitesimal spacing of the sound entrances, then as a microphone with dimensions between sound entrances which are practical for use in a microphone of this type.
Transient Testing of Loudspeakers
Authors: Mawardi Osman K.
Published: September 2005

Recent interest in the use of transient techniques to test loudspeakers springs from the inadequacy of the steady-state pressure response to specify completely the behavior of a loudspeaker. Tone bursts have shown some promise as a useful type of electrical signal to excite loudspeakers for transient testing. It appears, however, that Heavyside's step function or Carson's unit impulse function (the delta-function) may reveal more directly the significant characteristics of a loudspeaker. The response of loudspeakers to each of these latter functions has been examined and typical radiation spectra have been determined experimentally. The results of these analyses seem to yield a substantial amount of useful information about the performance of loudspeakers.
High Efficiency Loudspeakers for Personal Radio Receivers
Authors: Olson H. F. , Bleazey J. C. , Preston J. , Hackley R. A.
Published: September 2005

The term personal radio receiver is used to designate a complete radio receiver with self-contained power supply, and of such physical dimensions that it can be easily carried by hand or in the pocket. The performance and compactness of personal radio receivers are limited by the efficiency with which electrical power is converted into sound power by the loudspeaker. Since the electrical power output is limited in the personal receiver, the efficiency of the loudspeaker is an important factor. A number of loudspeaker systems have been investigated, both theoretically and experimentally, as follows: direct radiator, combination direct radiator and phase inverter, horn, and combination horn and phase inverter. An efficiency of 25 percent has been obtained with the combination horn and phase inverter. This loudspeaker system has been incorporated in a complete four-tube radio receiver, having a content of 25 cubic inches.
Observations on the Effect of High Intensity Sounds in the Ear
Authors: Kobrak H. G.
Published: September 2005

The middle ear of rabbits was photographed during exposure to high intensity sounds. Extreme amplitudes of the eardrum were observed and measured. Rupture of the eardrum occurred when the signal was increased further (motion picture film). The protective devices of the ear against intense signals are discussed. The reflex of the middle ear muscles is demonstrated. Tetanic contractions of both muscles dampen the movements of the ossicles. Another mechanism which most likely acts as protection for the vulnerable inner ear is the change of axis of the stapes at high intensity signals. The stapes movements were studied in fresh temporal bones. A small mirror was attached to the vestibular side of the footplate. Acoustic stimulation was carried out through the outer ear canal. The responses are asymmetrical. The negative amplitude is greater than the positive or sometimes negative only. Signals increasing in intensity produce a gradual change of the axis of vibrations. It was also observed that the stapes may suddenly change the axis of vibration as described previously by v. Békésy. The change of axis is interpreted as a protective device. Other features of the ear which act as protection against overstimulation are discussed.
Standardizing Auditory Tests
Authors: Munson W. A. , Gardner Mark B.
Published: September 2005

An understanding of the over-all process of hearing depends upon proper interpretation of the results of many individual experiments. In the field of subjective experimentation the problem has been complicated by the wide variety of test procedures that characterize available data. If a common technique could be applied to the many different types of auditory tests, such as thresholds of acuity, masking tests, difference limens, etc., the organization of these data would be facilitated. The purpose of the present paper is to describe a test procedure which has shown promise in this direction and to give descriptions of equipment which have been found helpful in minimizing the variability of the test results. The procedure, which we have called the “ABX” test, is a modification of the method of paired comparisons. An observer is presented with a time sequence of three signals for each judgment he is asked to make. During the first time interval he hears signal A, during the second, signal B, and finally signal X. His task is to indicate whether the sound heard during the X interval was more like that during the A interval or more like that during the B interval. For a threshold test, the A interval is quiet, the B interval is signal, and the X interval is either quiet or signal. For a masking test, A is the masking signal, B is the masking signal plus the signal being masked, and X is either A or B repeated. The apparatus for the ABX test is mechanized so all details of the method can be duplicated for each observer, and the variability of manual operation eliminated. The entire test is coded on teletype tape to reduce the time and effort of collecting large quantities of data.
Some Limitations on Formulas for Calculating Speech Hearing Loss from an Audiogram
Authors: Meyerson Lee
Published: September 2005

Recent research has confirmed the clinical observation that there is a relationship between loss of hearing for pure tones and loss of hearing for speech, and several formulas have been proposed for calculating speech hearing loss from an audiogram. These formulas must be used cautiously, however, since they do not make allowance for individual differences in ability to interpret speech stimuli or for individual differences in ability to learn to interpret partially perceived speech patterns. None of the formulas can correctly predict from the audiograms the hearing for speech of subjects who sustained severe losses of hearing before they achieved a firm command of speech and language. For hard of hearing subjects who have had intensive auricular training or who possess unusually good synthesizing ability, formula results are often misleading. Experimental evidence is presented showing a wide range of variation of the threshold for speech hearing in normally hearing subjects whose threshold audiograms did not vary significantly from the normal zero reference level. The implications of this finding are discussed.
A Progress Report of an Acoustic Training Experiment for Profoundly Deaf Children
Authors: Hudgins Clarence V.
Published: September 2005

The paper reports on an experimental program in acoustic training in which profoundly deaf children, ages 9 to 14, participate. An experimental group was provided with specially designed group hearing aid equipment installed in an acoustically treated classroom. The experimental class received all of their daily instruction from the teaching staff in this specially equipped classroom. A control group, using the standard hearing aid equipment of the school and taught by the same teachers, received the same routine training as the experimental group with the exception that they did not use the special hearing aid. The purpose of the experiment is to determine: (a) whether deaf children receive greater benefits from high fidelity, specially designed hearing aids as compared to the run-of-the-mill equipment now available in modern schools for the deaf; and (b) to what degree profoundly deaf children, hitherto considered beyond the reach of acoustic stimuli for all practical purposes, may benefit by acoustic training when provided with equipment capable of presenting undistorted speech signals at sufficiently high levels and at the same time protecting the ears against damage by a form of amplitude limiting. Both groups of pupils were tested periodically with achievement tests to determine their relative improvement in (1) speech perception, (2) speech intelligibility, and (3) general educational achievement. Results show significant differences in favor of the experimental group, especially in the category of speech perception where hearing is employed.
Variable Resonant Frequency Crystal Systems
Authors: Fry W. J. , Fry R. B. , Hall W.
Published: September 2005

The theory and design of low loss variable resonant frequency crystal systems will be discussed. Comparison of experimental results with the theory will be given for a unit operating over the frequency range 40 to 80 kc. The characteristics of such a unit utilized as an ultrasonic generator for fluid media will be compared with the characteristics of fixed resonant frequency units used as ultrasonic generators.
Surface Vibration Patterns of Piezoelectric Radiators
Authors: Nixon J. D. , Williams A. O.
Published: September 2005

An experimental study of the surface vibration patterns of piezoelectric ultrasonic radiators, radiating into liquids, is being made. A quartz X-cut crystal having one surface polished to optical quality is used as one mirror of a Michelson interferometer, with the unpolished surface radiating into a liquid of acoustic impedance ρ1c1, different from that of the quartz, ρc. Examination of the fringes allows the entire surface of the quartz to be inspected directly. Other experimenters have used somewhat similar methods in air. A sonic standing wave system can be used to enhance the result. When the reflection coefficient between quartz and fluid approaches unity (radiation into air) only some five percent of the surface vibrates with appreciable amplitude; this area increases when the reflection coefficient is 0.9 (methyl alcohol). There is a corresponding decrease in amplitude of vibration, as predicted by theory. These measurements are at sonic frequencies of 0.5 and 1.0 mc. A stroboscope of variable phase is contemplated; this might allow direct measurement of the amplitudes of vibration over the whole surface of the crystal at all stages of the vibration.
A New Expansion for the Velocity Potential of a Piston Source
Authors: Carter A. H. , Williams A. O.
Published: September 2005

The Rayleigh formula giving the velocity potential for a piston source surrounded by an infinite rigid flange is a surface integral which reduces to a line integral when the coordinates are suitably chosen, as shown by Schoch and Stenzel. For points within the geometrical cylinder whose base is formed by the piston surface, the line integral was expressed by them as a plane wave term plus a “perturbation” integral. For external points a different integral resulted. In the present work these two complementary expressions are evaluated as series of half-order Bessel functions in kz and polynomials in r/a; k is the propagation constant, a the piston radius, z and r the cylindrical coordinates of a field point. The resulting rigorous equation (valid for all points not on the piston surface) appears to converge for any value of ka and distance z from the source. The theoretical sound field on the surface of the cylinder and on the piston surface has also been investigated. Approximate expansions which under some circumstances are more useful than the rigorous result have been derived for paraxial regions, both from the perturbation integral and from an integral solution of the wave equation given by Bateman.
Measurement, Portrayal, and Interpretation of Some Statistical Properties of Speech Sounds
Authors: Chang Sze-Hou , Pihl George E. , Essigmann Martin W.
Published: September 2005

This paper describes methods for determining some statistical properties of speech sounds with the purpose of providing simple visible representations. Three such parameters are the density of zero crossings (ρ0), the density of points of zero slope (ρm), and the power ((f(t)2)Av)—all averaged over a short time interval. It can be shown that, subject to certain assumptions, these three quantities are related in rather simple ways to the moments of first few orders of the spectrogram, and the initial values of the derivatives of the autocorrelation graph. Experimental techniques involved in the determination, portrayal, and interpretation of the parameters ρ0, ρm, and (f(t)2)Av are described.
The Use of the Pattern Playback in Studies of Vowel Color by Synthesis
Authors: Delattre Pierre
Published: September 2005

The spectrographic analyses of speech leaves many questions unsolved. In fact, an important function of a sound-spectrogram seems to be to raise questions—mostly questions that concern the effects of omission, addition, or modification of the separate components of speech. Such questions call for the synthetic production of speech and can be answered by a speech-synthesizer such as the pattern playback, developed at the Haskins Laboratories. This playback permits one to synthesize speech by transforming hand-drawn spectrograms into sound. It has been used in this way to study the effects upon vowel color: (a) of the presence or absence of each formant; (b) of the frequency modification of each formant, separately, or of all formants simultaneously (high-low); (c) of the width of each formant, separately, or of all formants simultaneously (wide-narrow); (d) of the intensity of each formant, separately, or of all formants simultaneously (strong-weak); (e) of the type of each formant (close, spread, split); (f) of low energy frequencies, apart from the main formants. The practical application of these techniques to the study of nasality in French nasal vowels is discussed.
A Tentative Criterion for the Short Term Transient Response of Auditoriums
Authors: Bolt R. H. , Doak P. E.
Published: September 2005

There has been some evidence indicating correlation between the subjective acoustical quality of an auditorium and the amplitude and time delay of reflections occurring in the first several hundred milliseconds after a short pulsed carrier is emitted from a source in the auditorium. Recently Haas has reported some studies on the influence of a single echo on the subjective “hearing quality” of speech. By combining some of Haas results with other data on room quality one can formulate a tentative criterion for this short term (0–400 m sec.) transient response. This tentative criterion agrees well with “quality” judgments reported by Mason and Moir, and with some theater measurements carried out at this laboratory. The criterion indicates that reflections of greater amplitude than the direct sound may be desirable if they arrive within 35 m sec. of the direct sound. From 40 to 200 m sec. the echoes should lie below a line having approximately a slope corresponding to 0.5 sec. reverberation time. From 200–400 m sec. the sound decay rate depends on the volume of the room, the slope corresponding to the usual optimum reverberation time for the particular room.
Techniques for Determining Acoustics of Amphitheaters by Scale Model Studies with High Frequency Sounds
Authors: Hardy H. C. , Tyzzer F. G.
Published: September 2005

Techniques are described for high frequency tests used in small scale models of architectural structures. The two models tested simulated large outdoor amphitheaters with open-sided roof structures. One project, sponsored by the Chicago Park District, was an amphitheater seating 25,000 with roofed area seating approximately 4000. The other was a covered amphitheater for 3000 listeners now under construction at Ravinia Park near Chicago. The scales for the models were 16 to 1 and 20 to 1, respectively. Wave-length similitude was maintained by using proportionally higher frequencies. Steady-state measurements at frequencies between 2 and 30 kc were made to determine sound levels in the stage area and distribution of sound in the audience area. The effect of an audience was simulated by use of acoustical absorbents. Studies of oscillograph patterns for sound pulses gave information on reverberation times and smoothness of decay curves for various microphone positions. Changes in stage design were needed for both amphitheaters to reduce variations in sound level in the seating area. Observed decay slopes corresponded to reverberation times between 1.4 and 2 sec. in the roofed areas of the prototypes. For the larger amphitheater, the output requirements for the sound amplifying system were determined. The cost of such model studies is found to be under two percent of the construction cost. The results enable the designer to eliminate many costly mistakes.
On the Measurement of Impedance and Absorption Coefficients of Acoustical Materials for Sound of Oblique Incidence
Authors: Ingård Uno , Bolt R. H.
Published: September 2005

A method is reported for the measurement of complex impedance of a material in free field with plane waves incident at oblique angles. The pressure and phase of the sound in steady state are measured at a point in the absorptive surface and compared with pressure and phase measured at the same point in space at the surface of a perfectly reflecting material, or at the same point in space without any surfaces in the vicinity. From these data are determined the phase and magnitude of both the incident and the reflected waves, and this information in turn yields both the complex impedance and the free wave absorption coefficient for the particular angle of incidence involved. Tests have been made with an 8 ft. sq. sample of material mounted in an anechoic chamber and rotated about a vertical axis in the presence of a fixed horizontal beam of approximately plane waves. The pressure magnitude and phase were recorded graphically, continuously as a function of angle as the sample was rotated. The necessary transformations of data have been reduced to chart form. An independent check on the validity of the method is obtained by using an idealized acoustical material specially developed for this purpose. Perforated panels are mounted with air space backing and with the holes covered by resistance screens selected to give ρc matching at resonance. With the backing space divided into small cells, the acoustic impedance is independent of angle of incidence. Without such subdivision the absorption depends strongly upon angle of incidence. In both configurations the acoustic performance of the material can be accurately calculated from theory. Measured and calculated values agree within a few per cent for angles from normal to 75°. A discussion is given of the problems involved in integrating this free wave absorption coefficient over angle to yield the statistical coefficient assumed in simple reverberation theory.
A Null-Balance Apparatus for Measuring Acoustic Impedance
Authors: Cox J. R. , Ihde W. M. , Peterson A. P. G.
Published: September 2005

A direct-reading electroacoustic apparatus has been developed for the measurement of acoustic impedance. It is a null-balance, bridge-like device composed of two adjustable electrical networks and two acoustical networks. The acoustical networks are short cavities, each with a sound source at one end. One cavity is terminated at the end opposite the source by the unknown acoustic impedance. The other cavity is terminated by hard plug. The electrical portion of the apparatus is arranged so that the input currents to the electrical networks are proportional to the pressures in the cavities. The unknown acoustic impedance may be read directly from the value of the impedance of one of the adjustable networks, provided the electrical networks have been properly selected, and provided a null-balance has been obtained across the two electrical networks. The sources and magnitude of the error are considered in some detail. In particular, it is shown that temperature variations cause negligible error because of the balanced arrangement of the acoustical networks. The manner in which the complex value of the unknown impedance affects the error is also shown. Some measured results are presented.
The Steady Force Exerted on a Small Sphere in a Plane Progressive Wave Containing a Second Harmonic Component
Authors: Westervelt Peter , Sieck Peter
Published: September 2005

The drag force acting on a small sphere moving relative to a viscous medium can be written to include a term depending on the square of the velocity u: Force = 6πrμ0u(1 + k|u|), where k is a constant to be determined experimentally, r is the radius of the sphere and μ0 the viscosity coefficient. A second harmonic term in u can be shown to result in an average value for this force; the direction of the force depends on the relative phase of the fundamental and second harmonic components. This force has been measured by suspending a wax sphere of 137-micron diameter from a 10-micron Nylon fiber 3.5 cm long in a horizontal tube three inches in diameter. A loudspeaker is fixed at one end of the tube 3 meters from the sphere; the opposite end is connected to a 1-meter long ρc termination 1 meter from the sphere. Sound pressure measurements are obtained from a crystal microphone placed near the ρc termination. The pendulum deflection of the sphere, observed through a glass window in the tube, is taken to be a measure of the force acting. Measurements were made with a fundamental sound pressure level of 132 decibels at a frequency of 400 c.p.s. Injecting a second harmonic component of equal amplitude caused the sphere to deflect 0.15 cm toward or away from the source, depending on the relative phase of the two frequency components. The magnitude of the deflection was found to be directly proportional to the relative sound pressure of the second harmonic, for a constant amplitude of the fundamental.
Sonic Wind and Static Pressure in Intense Sound Fields
Authors: Walker J. P. , Allen C. H.
Published: September 2005

In the free field above a piston source 12 cm in diameter vibrating sinusoidally at 14.6 kc there exists a sonic wind, similar to quartz wind in water, directed away from the source along its axis. Its speed is found to be proportional to the square of the source amplitude. The theory of Carl Eckart has been applied to the experimental conditions with some simplifying assumptions and a qualitative agreement obtained both as regards magnitude and distribution of velocities. In this same field positive static excess pressures exist on the axis which are directly proportional to the sound intensity at the point of measurement. At an acoustic level of 156 db this pressure was 10 dynes/cm2. A plane wave field was simulated by mounting a tube (34 in. inside diameter) directly above the source, airtight except for the open, far end of the tube. An excess static pressure was found in the tube, which again is proportional to the acoustic intensity, but is negative and approximately eight times the magnitude of that in the free field. Comparison with the theory of Jenkins Thuras and O'Neil shows agreement in sign and in variation with acoustic intensity but the experimental values are 3 db too low.
The Measurement of the Acoustic Properties of Sound Absorbent Panels at High Hydrostatic Pressures
Authors: Trott W. J. , Darner C. L.
Published: September 2005

Measurements of underwater sound reflection and transmission properties of several sound-absorbent materials in the frequency range from 10 to 150 kilocycles per second at hydrostatic pressures up to 350 pounds per square inch are presented, and the method of measurement is described.
Matrices of Piezoelectric, Elastic, and Dielectric Constants
Authors: Van Dyke Karl S.
Published: September 2005

Great convenience results from the systematic arrangement of the complex array of piezoelectric and associated data, particularly when the intended use involves more than first-order numerical solutions. Reference is made to a collection of such constants arranged in matrix form which includes complete data for twelve different piezoelectric crystals of present day interest and in addition the computed matrices for several of these crystals referred to other axes which have been rotated away from the crystallographic axes. Special value in piezoelectric computation follows from a choice of the powers of 10 in terms of which to list the several constants which differs for some constants from the conventional usage. Reciprocal relations between the four common piezo-elasto-dielectric matrices by pairs are obtained by writing two of the eight basic thermodynamic-type equations as solved for the negative of the variable. Facility in checking matrix computations has been found to be enhanced by adopting matrices which are reciprocals of each other where possible. The matrix arrangement which has been adopted, when used in combination with the recent Piezoelectric I.R.E. Standard, greatly simplifies the teaching and learning of this field.
Wave Equation Studies of Stamni (Sonic True Airspeed and Mach Number Indicator)
Authors: Corey Victor B.
Published: September 2005

The acoustical method designated Stamni, which may be used for the measurement of Mach number, true airspeed and true air temperature, has been under development by the author and his coworkers since 1946. Under a null balance condition the Mach number is measured in direct proportion to a length. The ratio of this length to a measured acoustic transit time represents true airspeed, while the transit time itself determines true air temperature. For some time Stamni operating principles have been based entirely upon ray acoustics, and have received experimental confirmation only over part of the subsonic velocity range. Recently, however, Stamni operation has been studied intensively in terms of acoustic field theory, starting with the work of Miles. Conclusions based upon ray acoustics are found, in general, to be well substantiated. Complete solutions for the supersonic velocity range contain contributions from advanced as well as retarded velocity potentials. In agreement with the analysis of ray acoustics, Stamni measurements in this range appear to be possible only if the terms associated with advanced velocity potentials are attenuated by emitter directivity. Comparative viewpoints of ray acoustics and field theory are presented.
Behavior Patterns of the Laboratory Mouse under Auditory Stress
Authors: Frings Mable , Frings Hubert
Published: September 2005

Mice of three strains (Albino, dba, and C-57) were tested for susceptibility to running fits and seizures in the age range 15 to 50 days. The sound stimulus was a 10 kc/sec. note at an average intensity of 99 db. The seizure pattern and pre-seizure behavior of the mice were studied in detail. There are few interstrain or sex differences in behavior or susceptibility to seizure. In general, C-57's seem least susceptible and dba's most susceptible, but great individual variation in susceptibility and pattern was found even within the same litter.
Destruction of the Pinnae of White Mice by High Intensity Air-Borne Sound
Authors: Frings Hubert , Senkovits Irma
Published: September 2005

The pinnae of white mice, when exposed to high intensity airborne sound waves, exhibit an immediate inflammation followed by degeneration. Treated pinnae were compared histologically with normal pinnae, with pinnae treated with high temperatures, and with pinnae of mice which were depilated around the ears and treated with sound so that no heat could be produced by absorption of sound in the fur. The results showed that the major factor in destruction of the pinnae is heating in the fur, but some of the effects produced by sound are probably the results of mechanical agitation or a combination of heating and mechanical agitation.
Resonances of Biological Cells at Sonic Frequencies
Authors: Ackerman Eugene
Published: September 2005

The rate at which Paramecium caudatum is destroyed in a sound field of fixed intensity increases markedly in the neighborhood of 1.2 kc/sec. Similar optimum destructive frequencies have been found for six other species of paramecium and for a blepharisma species. Although the shapes of these animals are too complex to treat on a theoretical basis, reasonable theories can be developed for spheres having radii equal to the average radius of the animal. One theory, based on the existence of a non-rigid membrane with interfacial tension, T, separating two incompressible liquids, gives T = ca. 3 dynes/cm, agreeing in order of magnitude with values found for other cells by very different methods. An alternate theory postulates a rigid envelope surrounding the cell giving coefficients of rigidity about 104 dynes/cm2; this is within the range of values of fibrin gels. Either type of vibration would be excited readily by cavitation. The formulas for these modes and their derivation will be discussed.
The Impedance of an Oscillating Sphere in a Viscous-Elastic Compressible Medium
Authors: Oestreicher Hans L.
Published: September 2005

In order to understand the mechanism of the transfer of vibratory energy to the human body through a wide frequency range, it is useful to study the field and the impedance of an acoustical radiator in a medium with shear-elasticity, viscosity and compressibility. As a radiator, the oscillating sphere in an unlimited medium is chosen because this model shows the essential features of a very general class of radiators. The field of this sphere is computed by means of Lamb's aggregates of spherical harmonics, after having obtained the equations of wave propagation in a viscous elastic medium. From this field the impedance is calculated. The results show that the energy is radiated in the form of shear and compressional waves, having relative intensities, which change strongly with the frequency. For low frequencies, shear waves are predominant, while at higher frequencies acoustical behavior prevails. Only at still higher frequencies, viscosity becomes important again. Finally a more extended discussion, using numerical values, is given by inserting the approximate values of the elastic constants of human tissue into the general formula.
Techniques for Exposing Biological Suspensions to Air-Generated Sound
Authors: Nyborg W. L. , Nertney R. J. , Spencer J. W.
Published: September 2005

Various techniques have been considered for supporting liquid suspensions (e.g., of bacteria) in intense airborne sound fields, as are obtained from a siren, in such a way as to obtain specifiable exposure conditions. A method we have found satisfactory consists basically of putting the suspension in a vertical stainless steel tube, closed at its lower end by a thin diaphragm, and placing this tube in the upward-directed sound field of interest. Acoustical measurements may be made under actual operating conditions; peak sound pressures of 0.1 atmos. and greater are obtainable over the 3–30 kc range. Observed sound pressure distributions are in fair agreement with those calculated on the basis of transmission line theory. A JER-type whistle is a sound generator consisting of a jet-edge (JE) system plus a resonator. Specially constructed whistles of this type make inexpensive and convenient devices for applying pressure amplitudes of 0.1 atmos. or more to small liquid specimens. Much turbulence may be seen in the whistle exposure cell under some circumstances; at times a regular vortex motion may be observed which is associated with a particular arrangement of air cavities or bubbles.
Effects of High Intensity Sound upon Micrococcus pyogenes, var. aureus
Authors: Kinsloe Helen , Choman B. R. , Reid J. J. , Nertney R. J. , Nyborg W. L.
Published: September 2005

Saline suspensions of Micrococcus pyogenes, var. aureus, prepared from 24-hour growth on nutrient agar, have been subjected to high intensity sound at frequencies ranging from 5 kc to 24 kc. Exposures were made in a chamber irradiated up to 90 minutes by the upward-directed beam of a siren, as described in the previous paper; free field r.m.s. pressures in the fundamental ranged from about 0.03 to 0.06 atmosphere. Counts of living bacteria were made before and after exposure and following centrifugation of the suspensions the supernatant fluid was examined serologically in an effort to detect fragmentation of the organisms. The data indicate that destruction is critically dependent on physical exposure conditions. At 6.5 kc exposure to a free field r.m.s. pressure of 0.06 atmosphere for 90 minutes caused a high percentage of killing and a copious yield of antigenic material. However, small changes such as decreasing the free field sound pressure by 2 db or decreasing the exposure time from 90 to 60 minutes caused a considerable diminution of these effects. Also there is evidence of a marked frequency dependence but further work will be necessary to isolate the effect of frequency change from that of certain other physical factors which vary simultaneously with the frequency.
Ultrasonic Interferometry for Highly Dissipative Media
Authors: Stewart James L. , Stewart Ellen S.
Published: September 2005

The exact theory of the acoustic interferometer will be discussed following the three stages of its development. First will be discussed the original approximation introduced to simplify the solution in the case of moderately dissipative media. Second will be discussed the more rigorous solution necessary in the case of highly dissipative media, including the approximation for low acoustic impedance to simplify the solution in the case of gases at low pressures. Third will be discussed the exact solution necessary in the case of very highly dissipative media now being approached in H2 and He. This indicates a departure of the maxima and minima of the real part of the acoustic impedance from the simple hyperbolic functions, necessitating corrections to the absorption and reflection calculations. Also at very high dissipation these maxima are no longer a half-wave-length apart, requiring corrections to velocity calculations.
Dispersion in the Ultrasonic Absorption and Reflection Coefficients in Hydrogen and Deuterium
Authors: Stewart Ellen S. , Stewart James L.
Published: September 2005

There have previously been observed in the region of rotational relaxation the dispersion in the velocity of sound due to the change in specific heat and the molecular absorption due to the relaxation. In addition to these there should also be dispersive effects associated with the change in thermal conductivity which will appear as an increase in the classical Kirchhoff absorption and an increase in the Herzfeld reflection coefficient in addition to their classical dependence on frequency. Absorption and reflection coefficients have been measured through the region of rotational dispersion in hydrogen and deuterium. Experimental values of these coefficients will be compared with theoretical values in light of the above discussion.
Propagation of Sound in Rarefied Helium
Authors: Greenspan Martin
Published: September 2005

The velocity and attenuation of sound at 1 Mc/sec. were measured in He at pressures as low as 0.1 mm Hg (sound frequency about twice mean collision rate) using a two-crystal interferometer. The observed dispersions are very large and they, as well as the observed attenuations, agree very well with existing theories except at very low pressures where uncertainties are introduced by lack of gas purity. Universal curves, in terms of non-dimensional parameters, will be shown for the theory of Stokes and Kirchhoff and for that of Wang Chang.
Mechanisms of Sound Absorption in Fluids
Authors: Markham Jordan J.
Published: September 2005

A survey has been made of the various mechanisms that have been suggested for the absorption of sound in fluids. These can be classified into two groups, viz., (1) viscosity absorption and (2) relaxation absorption. In the second group are included the effects of heat radiation, heat conduction, thermal relaxation, structural relaxation, and a more general type of relaxation proposed here. This last mechanism includes both thermal and structural relaxation as special cases. For mechanisms of the second group the expression relating the absorption coefficient and the velocity with the frequency can be derived by starting with the first law of thermodynamics and arriving at an acoustical equation of state. This transformation can be made without any special assumption as to the nature of the substance. The equation of state permits one to make a simple comparison of the various approaches to the problem. A study of the velocity and absorption as a function of frequency shows important differences between the two classifications. Thus the assumptions that the additional absorption in water (beyond the classical viscosity contribution) is due to structural relaxation (Hall) or dilatation viscosity (Eckart and Liebermann) are not precisely equivalent.
Ultrasonic Absorption in Liquids
Authors: Moen C. J.
Published: September 2005

Using a reverberation method the absorption of sound at frequencies down to 140 kc has been measured in a number of liquids of widely different properties. For glycerol the experimental result agrees well with that predicted by classical theory. For benzene and water good agreement is found with the values calculated using the modified theory employing the values of second viscosity determined by Liebermann. The absorption in carbon disulfide agrees well with Ouang's result. For these four liquids the absorption is found to be proportional to the square of the frequency, but results indicate that toluene has a relaxation frequency of the order of 105 sec−1. The reverberation method is especially useful at the lower ultrasonic frequencies where longer wave-lengths and lower absorption render methods used at higher frequencies less reliable or even useless.
New Methods for Measuring Ultrasonic Velocity in Solids
Authors: Willard G. W.
Published: September 2005

A basically new method of measuring ultrasonic velocity in materials is of especial interest when applied to solids (transparent or opaque), since past methods have not generally combined simplicity and accuracy. The ultrasonic light diffraction equipment, as arranged by the author to make sound beams visible, is immediately adaptable to the new method. In one variation of the method, the original sound beam in the tank liquid is split into two parts, one passing unobstructed through the liquid, the other passing normally into a flat acoustic face of the test specimen. In this case the specimen must be optically transparent and have two parallel optical faces normal to the acoustic surface. The light beam passing successively through the two portions of the sound beam produces on the image screen a light and dark band interference pattern, as though the two sound beams had coexisted. The spacing of the bands d, as measured in the object plane, is related to the sound frequency f, the assumed known velocity of the liquid v1, and the unknown longtudinal velocity of the specimen v2 by 1/f⋅d = 1/v1 − 1/v2. In a second variation the original sound beam is split as before by the specimen, which now is in the form of a prism (may be opaque) with two acoustic faces inclined to each other by a known angle θ. The sound beam passing through the prism, and into the liquid again, is angularly deviated relative to the reference beam in the liquid. From the region beyond the prism an interference pattern is again produced on the screen. The band spacing e is a most accurate measure of the deviation angle φ, sin (φ/2) = v1/2ef, which together with the known values of θ, v1 and f again determines the desired velocity v2. A third variation is especially suited to measuring shear velocity. In all cases only traveling sound beams are used. Good optical effects are obtained with low intensity sound beams. Accuracy of one percent is easily obtained.
Attenuation of (n,o) Transverse Modes in a Rectangular Tube
Authors: Beatty Ralph E.
Published: September 2005

The attenuation of (n,o) transverse modes due to heat conduction and viscosity at the walls of a rectangular tube can be calculated very simply by treating the tube as a duct whose side walls have a different admittance from the top and bottom walls. The (n,o) transverse modes may be represented as a sum of two plane waves at oblique incidence with respect to the side walls and at grazing incidence with respect to the top and bottom walls. Using Cremer's results for the wall admittance as a function of angle of incidence in conjunction with an extension of Morse's formulas for attenuation in rectangular ducts, an expression is found for the attenuation of all (n,o) tranverse modes; the dependence on the type of mode enters only through the cut-off frequency, fc. This theoretical expression for the attenuation will be compared with the experimental results of Hartig and Lambert on (1,0) transverse modes.
Measurement of Bulk Modulus and Associated Loss Factor for Rubber and Plastics
Authors: Sandler Charles S.
Published: September 2005

To measure the bulk modulus of elasticity and associated loss factor of various rubbers and plastics, an apparatus similar to that described by Meyer and Tamm was constructed. For acoustically absorbent materials a complex elastic modulus of the form Ē = E(1 + iη) may be postulated wherein E is the appropriate elastic modulus and η is a measure of the energy dissipated. The apparatus consists of a water-filled steel tube one meter long, with 38-in. wall thickness. Standing waves are set up in the water column by means of a magnetically driven diaphragm mounted at the bottom of the tube. The sample to be measured is inserted at a pressure antinode and, by considering the water column as a resonant transmission line, the bulk modulus and the loss factor are deduced from the change in Q and shift of resonant frequency when the sample is inserted. The operating frequency is 1500 c.p.s. and a beat-frequency technique is used for measuring the small changes in frequency involved. Temperature is closely controlled at 30°C by surrounding the steel tube with a heated water jacket. Results are given for various rubbers and plastics.
The Effect of Ultrasonic Waves on the Hydrogen Electrode
Authors: Yeager Ernest , Bugosh John , Dietrick Harry , Hovorka Frank
Published: September 2005

If a polarized hydrogen or oxygen electrode is irradiated with ultrasonic waves, an alternating component is produced in the electrode potential. This effect is believed to depend primarily on the formation of a gas phase at the surface of the electrode. Indications are that the acoustical sensitivity is a function of the polarizing current and the nature of the electrolytic solution as well as the frequency. Pulse techniques have been used in the investigation of the effect in order to avoid the complications associated with electromagnetic coupling. The response of the polarized hydrogen electrode has been observed to be as large as − 150 db re: one volt per dyne/cm2. Such an effect may find interesting amplications in acoustics, since it can be utilized in the form of virtually a point probe.
A Method for Determining the Propagation Constants of Plastics at Ultrasonic Frequencies
Authors: McSkimin H. J.
Published: September 2005

A pulse technique particularly suited to dissipative materials is described for measuring attenuation and phase-shift constants of plastics, using either transverse or longitudinal waves in the frequency range of 5 to 50 mc/sec. A thin wafer of the material under test is placed between two identical fused silica buffers; and waves generated by quartz crystals at the ends of the assembly are transmitted simultaneously through the specimen in both directions. Comparison of transmitted and reflected components by means of a special balancing circuit provides information from which the dynamic rigidities and viscosities can be calculated. Illustrative data for polyethylene and Nylon are given.