bluuebunny/crossref_metadata_2025 huggingface dataset:
The Discontinuous Growth and Decay of Sound in a One-Dimensional Room
Authors: Miller Harry B.
Published: September 2005

The growth and decay of sound in a one-dimensional room was investigated by using a very special room, namely, a helical spring. Compressional waves in the audiofrequency range were sent down the spring by an electromechanical driver and received at the far end by an electromechanical pickup. Reflection occurred at each terminal, allowing standing waves to be built up. The length of the spring was 30 in. and the transit time was 53.6 milliseconds, giving a propagation velocity of about 4612 ft/sec. The 30-in. spring is thus equivalent to a room about 58 ft long.

Oscillograms were obtained for frequencies below 100 cps, showing the discontinuous nature of the reverberation produced in the one-dimensional room.

During the analysis of the oscillograms, Eyring's mechanism of image sources was found to fail to explain some of the oscillograms. A new mechanism was therefore created, called the Two-Pipe Mechanism, which seems to explain all the oscillograms.

The Two-Pipe Mechanism clarifies: (1) the behavior of a normal mode when decay is started before steady state has been reached; (2) the growth and decay of standing waves on a violin string, by demonstrating the quantized envelope-levels which control this growth and decay; (3) the growth and decay of non-normal modes, by showing how decay can consist of the steady-state frequency alone, even though this is a “not-allowed” frequency.
The Absorption Coefficients of Fir Plywood Panels
Authors: Kenworthy R. W. , Burnam T. D.
Published: September 2005

The absorption coefficients of flat, splayed, and cylindrical panel assemblies made from one-quarter-inch three-ply fir plywood have been measured by the reverberation chamber method under three different conditions. All panels have greater absorption at the lower frequencies (128 and 256) than at higher frequencies. The effective absorption of each type can be increased by using a half-inch kapok felt in combination with it, either mounted on the wall behind the panel or spot-cemented to the plywood. Each type of panel has desirable characteristics under certain conditions. The absorption of all types indicates that such panels are important acoustical materials in the lower frequency range.
Resonant Vibrations in a Water-Filled Piping System
Authors: Callaway D. B. , Tyzzer F. G. , Hardy H. C.
Published: September 2005

The mechanism by which noise is transmitted in liquid-filled piping systems was studied by tests on a straight free-free 2-inch pipe 53 feet long. The vibrations of the system below 1000 cps were characterized by high Q resonant modes consisting of longitudinal vibrations in the water, and both longitudinal and flexural vibrations in the pipe wall. Attenuation for all types of vibrations was very low, ranging from 0.001 to 0.09 db/ft. Large coupling between water vibrations and flexural pipe-wall vibrations was found to exist, so that longitudinal excitation of the water column resulted in flexural pipe-wall vibrations of large amplitude. Because of the large number of high Q modes in a practical piping system, it appears that the modes are the means of transmission of noise. The flexural modes are more numerous than other modes at low frequencies and are also important because of their coupling to radiating surfaces.
Ultrasonic Studies of Weimarn Gels
Authors: Srivastaya Arvind Mohan
Published: September 2005

This paper reports measurements of the elasticities of various Weimarn gels by the use of an ultrasonic pulse reflection method. Considerations of porosity and composite density of the gel lead, theoretically, to an expression for the bulk modulus which agrees remarkably well with the experimental values. Furthermore, the aging of the gel samples gives ground to conclude that the formation of a gel resembles the separation of a solid phase from a supersaturated solution. The variation of the elastic moduli with temperature has been explained by the postulated structure of these gelatinous substances.
Ultra Speed Recording for Acoustical Measurement
Authors: LeBel C. J. , Dunbar James Y.
Published: September 2005

The technique and tests herein described were devised to study possible improvement in rating the acoustical excellence of rooms, by using higher pen speeds than had hitherto been available. Recordings of reverberation decay characteristics, made with the new ultra speed technique, are compared with results from older methods of recording reverberation; and it is found that the new method provides a much more adequate diagnosis of recognized acoustical faults.

The new technique makes possible ink recording of acoustical levels on a db basis at pen speeds of 5000 to 10,000 db per second, or ten to twenty times that afforded by the high speed level recorder. It uses a new stabilized logarithmic Varistor system for instantaneous conversion to a db basis, followed by a direct writing oscillograph. Hitherto unrecognized requirements for the electronic system are indicated as necessary if adequate stability, linearity, and scale range are to be achieved.
On the Generalization of the Concept of Impedance in Acoustics
Authors: Mawardi Osman K.
Published: September 2005

The conventional definitions of acoustical impedances so useful in the investigations of the properties of idealized systems with lumped parameters fail when applied indiscriminately to systems with distributed constants. In general, the present definitions are valid only when the specific impedance is constant on a wave front. By extending the notion of vector fields to specific impedances the previous restriction is removed and the scope of application is considerably increased. A definition for the acoustic impedance, based on energy concepts is also proposed.
DC Potentials and Energy Balance of the Cochlear Partition
Authors: v. Békésy Georg
Published: September 2005

Most living tissues are in a state of continuous decomposition and simultaneous regeneration. These processes are usually accompanied by the production of dc potential differences between the various parts of the tissue. Such dc potentials were measured at different points in the cochlea of a lightly anesthetized guinea pig. The existence of these potentials makes it probable that continuous chemical processes are going on in the inner ear. This raises the question whether the electrical energy of the microphonics is obtained from the mechanical energy of the stimulus or from the chemical-energy pool. For a certain static displacement of the cochlear partition it is shown that, during a certain time interval, the amount of electrical energy consumed in the vestibular channel is greater than the amount of mechanical work done in accomplishing the displacement.
Electrical Responses to Acoustic Clicks: Influence of Electrode Location in Cats
Authors: Rosenblith Walter A. , Rosenzweig Mark R.
Published: September 2005

When wire electrodes are placed at certain locations outside the cat's bulla, the electrical responses to intense acoustic clicks differ radically from the standard round window response. The microphonic components of the response are now greatly attenuated, and it is even possible to find a neutral area in which no microphonics are detectable; the neural components are less attenuated and can now be studied without microphonic interference. Making use of the demonstrated electrical spread of neural potentials, it is possible to find electrode locations—all outside the animal's bony wall—that will accentuate various potentials originating in the brainstem and in subcortical centers. By means of differential recording, a particular neural component can be emphasized and selected for study. At the cat's auditory cortex one can observe small potentials attributable to subcortical structures. These potentials are, in latency and behavior, identical with “neurals” that are observed at more peripheral locations. Cortical potentials, similar to those recorded from the surface of the brain (dura mater), can also be picked up by electrodes situated on the animal's intact skull. The use of the technique of recording from intact animals should facilitate the study of many problems of auditory physiology.
On the Dynamics of the Cochlea
Authors: Fletcher Harvey
Published: September 2005

This paper is concerned with the dynamical behavior of the cochlea. It is assumed that a length of the basilar membrane which is equal to its width at each position vibrates as a unit, and that the forces exerted upon it by adjacent units are negligible compared to that exerted by the difference in pressure in the scala vestibuli and scala tympani. The boundary conditions at the stapes end is simply that the pressure difference in the two canals is equal to P0 any desired pressure difference. However, at the helicotrema the pressure difference must be equal to that between the two ends of the capillary opening at the helicotrema.

Then from the fundamental hydrodynamical equations and the experimental constants obtained by Békésy it is shown that the speed of sound through the liquid of the inner ear may be considered infinite compared to the speed of the wave along the basilar membrane. In other words, the liquid may be considered incompressible so that the rate of liquid displacement at the oval window is equal to that at the round window, and is also equal to that produced by flexure of the basilar for frequencies above 200 cps. Below this frequency some of the liquid goes back and forth through the helicotrema.

With these assumptions, the following quantities were calculated from the fundamental dynamical equations and found to be in good agreement with the experimental results of Békésy; (a) displacement amplitudes and phases of the basilar membrane at different distances from the stapes and for different frequencies, (b) time for wave to travel from stapes to various distances from stapes, and (c) volume displacement, at various frequencies, per dyne difference of pressure at oval window and that at round window.
On the Measurement of the Loudness of White Noise
Authors: Pollack Irwin
Published: September 2005

Scales of loudness for complex sounds have usually been obtained by determining the equal-loudness relation between the complex sound under investigation and a sound for which a scale of loudness is already available, e.g., a pure tone of 1000 cps. It is possible, however, to determine scales of loudness for complex sounds without appeal to pure tones or without extrapolation from pure-tone data. This was done in the present experiment. Loudness measurements were carried out by several independent procedures for a 1000- cycle tone and for white noise. The agreement among the different procedures indicates satisfactory internal consistency among the several methods of determining loudness scales. A suggested scale of loudness for white noise, based upon all available data, is presented.
Pitch and Intensity
Authors: Morgan C. T. , Garner W. R. , Galambos Robert
Published: September 2005

This paper presents data for changes of pitch with intensity for 18 ears, for frequencies from 125 cps to 8000 cps, and for intensities up to a loudness level of approximately 100 db. There are wide individual differences, but most observers show very small changes (less than 2 percent) of pitch with intensity. In general, as intensity is increased, pitch falls at low frequencies and rises at high frequencies. Two different methods of measuring pitch-intensity changes showed no significant difference.
Frequency Detection and Speech Formants
Authors: Peterson E.
Published: September 2005

This study is aimed primarily at evaluating the utility of axis-crossing detectors in tracking speech formants. Detectors of the usual type are found subject to an error, fundamental in nature. To remove this source of error speech is modulated up in frequency as a single sideband before limiting and detecting processes are applied. Experimental results with this carrier type of detector on a small number of speech samples are presented, and compared with spectrograms.

Conclusions are that the average axis-crossing rates cannot be trusted in general to follow specific formants, whether the speech is normal or differentiated. But when the formants are sufficiently localized by frequency selectivity, prospects of tracking the lower formants look promising.
Transformer Analogs of Diaphragms
Authors: Bauer B. B.
Published: September 2005

The use of the conventional analog for diaphragms in equivalent circuits often causes serious difficulties. The action of a diaphragm is shown to be analogous to that of a system of ideal transformers, each corresponding to an area of the diaphragm. The ancillary concept of “acoustical ground” analogy is introduced to facilitate synthesis of equivalent electrical circuits. The analysis includes equivalent circuit representations of a piston diaphragm, multiple diaphragms, diaphragms with subdivided sides, and articulated diaphragms, etc., together with examples. Simultaneous use of the transformer analogy of diaphragms and the transformer analogy of transducer couplings is treated in the Appendix.
Pulse Technique for the Reciprocity Calibration of Microphones
Authors: Terry R. L. , Watson R. B.
Published: September 2005

This paper describes a pulse technique which makes possible a free-field reciprocity calibration of a microphone indoors, without recourse to an anechoic chamber. The method is limited to frequencies above the middle audio range by consideration of the room size and pulse spectrum. An experimental calibration of a microphone is included, and waveforms are presented which demonstrate the validity of the method.
A Piezoelectric Method for Determining Young's Modulus and Its Temperature Dependence
Authors: Stauss H. E. , Martin F. E. , Billington D. S.
Published: September 2005

A resonance method for determining Young's modulus in metals, based on support of the specimen at its central node for longitudinal vibrations, with the supporting rod articulating at its lower end with a piezoelectric crystal, has been developed. Utility of the method was extended by adapting it to measurement of changes in Young's modulus with temperature.
Field and Impedance of an Oscillating Sphere in a Viscoelastic Medium with an Application to Biophysics
Authors: Oestreicher Hans L.
Published: September 2005

With an application to human tissue in view, a theoretical analysis of the behavior of mechanical vibrations in a medium with elastic, viscous, and relaxational properties is made. For this purpose, the equations of wave motion in a viscoelastic medium are discussed in general and solved for two problems, which are significant for the propagation and the transfer of vibrational energy: (1) energy propagation and absorption in plane waves, (2) field and impedance of an oscillating sphere.

The results show that the energy is propagated in two kinds of waves, the relative intensities of which change strongly with frequency: transverse waves, owing to the shear elasticity and viscosity, and compression (acoustical) waves, owing to the volume compressibility of the medium. A more detailed treatment is then accomplished for human muscle tissue by inserting the approximate values of its elastic constants into the general formulas, thus explaining the behavior in a frequency range from 0 up to several hundred kc.
A Theory of the Action of the Cochlear Resonators
Authors: Guelke R.
Published: September 2005

The hypothesis is put forward that the mechanism of hearing may involve a building up of vibrations, and the damping of these vibrations when they reach a definite amplitude. This is able to explain the conversion of sound intensity reaching the ear into impulse frequency as measured on the nerve fibers. The hypothesis also reconciles the speed of response of the ear with the high pitch sensitivity and consequent sharpness of resonance of the aural resonators. A model is described which converts amplitudes into pulse frequencies by using a damping mechanism when a definite amplitude is reached.
The Absorption and Dispersion of Sound in Oxygen as a Function of the Frequency-Pressure Ratio
Authors: Thaler William John
Published: September 2005

The velocity and absorption of ultrasonic waves in oxygen were measured by means of an improved ultrasonic interferometer in the range from one to one hundred Mc per atmosphere. Dispersion of the velocity ranged from 333.14 m/sec, to 357.22 m/sec at 30°C. The ratio (αexper/αclass) dropped from 3.68 to 2.05, and the corresponding value of Cv/R dropped from 2.50 to 1.61. The increase in velocity and the decrease in (αexper/αclass) is interpreted as caused by the slow exchange of energy between the translational and rotational degrees of freedom. The relaxation time for the rotation was 5.24×10−9 second.
The Theory of Sound Absorptive Materials
Authors: Harris Cyril M. , Molloy Charles T.
Published: September 2005

This paper presents a review of the status of the theory of sound absorbing materials. The basic concept of absorption coefficient, as well as the relation between absorption coefficient and acoustical impedance are discussed. Other topics considered are, sound propagation in homogeneous isotropic media, perforated panels, suspended absorbers, and resonant absorbers.
A Mechanical Shock Tester for Instruments and Electronic Apparatus
Authors: Morrow Charles T.
Published: September 2005

A mechanical shock tester of the free-fall type has been designed to produce high accelerations in the form of a square wave. The apparatus is described, and the logical considerations which were used as design parameters are explained. Particular attention is paid to the relation between the shocks an equipment is likely to receive in practice and the optimum type of test apparatus.
Attenuation of Sound in Water Containing Air Bubbles
Authors: Laird Donald T. , Kendig Paul M.
Published: September 2005

Measurements of the attenuation of sound in water containing air bubbles were undertaken in order to confirm some aspects of a theory due to L. L. Foldy. Bubbles were produced by forcing compressed air through the cloth covering of several trays lying on the bottom of the Black Moshannon Lake. The distribution in size of the bubbles and the number of bubbles per unit volume were determined by photographing the bubbles and by collecting the volume of air which rose over a given area in a given time, the terminal velocity of rise being a known function of bubble diameter. The attenuation of sound was found to be very large at frequencies for which resonant bubbles were present, and much smaller at other frequencies, indicating that resonance absorption was the principal phenomenon observed. For the particular bubble distribution investigated, which contained 0.045 percent air by volume, the attenuation was found to be in satisfactory agreement with the theory and a maximum attenuation of approximately 20 db per inch was measured. Amplitude and phase fluctuations made it impossible to measure the phase velocity, but this quantity was computed from the bubble distribution.
Frequency-Band Multiplication or Division and Time-Expansion or Compression by Means of a String Filter
Authors: Vilbig Friedrich
Published: September 2005

A frequency band multiplication or division has been performed by string filters. An exact relationship between the input and output frequencies has been shown. Two different methods have been used.

The first multiplies frequencies by rectification with the aid of a push-pull electrostatic pick-up. Alternating plus-minus polarizing techniques are employed to suppress the undesirable sum frequencies. The resolution of such a doubling system, which will not pass the sum frequencies, is approximately 1.5 times the band width of the single filters. However, the band width is limited by the transit time of speech.

The second method multiplies and divides by exciting the harmonics or subharmonics of the single strings. This is done by employing light, stiff “fingers” to disturb the free oscillations of the damped strings. The excitation and the resulting frequency band division and multiplication are investigated.

It is shown that in order to get time compression or expansion, it is only necessary to record the multiplied or divided frequency bands and play them back with the corresponding diminished or increased speeds.

The results given have a general application to similar type filters such as reed, crystal or magnetostrictive.
Multiple Scattering of Radiation by an Arbitrary Configuration of Parallel Cylinders
Authors: Twersky Vic
Published: September 2005

A formal solution in terms of cylindrical wave functions is obtained for the scattering of a plane acoustic or electromagnetic wave by an arbitrary configuration of parallel cylinders which takes into account all possible contributions to the excitation of a particular cylinder by the radiation scattered by the remaining cylinders. The solution, satisfying any of the usual prescribed boundary conditions simultaneously at the surface of each cylinder, is expressed as the incident wave plus a sum of various orders of scattering. The first order of scattering (the usual single scattering approximation) results from the excitation of each cylinder by only the plane wave or primary excitation. The second order results from the excitation of each cylinder by the first order of scattering from the remaining cylinders, and so on to an infinite order of scattering. The first order therefore consists of waves scattered by one cylinder; the second order of waves scattered by two cylinders, etc. The scattering coefficients of the m'th order of scattering are expressed recursively in terms of the previous orders, and finally as sums of products of m scattering coefficients of the single cylinder and Hankel and trigonometric functions depending on the geometry of the configuration.
Directionality Patterns for Acoustic Radiation from a Source on a Rigid Cylinder
Authors: Laird Donald T. , Cohen Hirsh
Published: September 2005

The directionality patterns produced by an acoustic source located on a rigid cylinder of infinite length have been investigated for the case in which the source strength may be represented as a separable function of azimuth angle and axial dimension. It is observed that the pattern in a plane orthogonal to the axis of the cylinder is independent of the axial distribution of the source, and is, in fact, identical with the pattern given by Morse for a source of infinite axial extent. For the particular case in which the ratio of circumference to wavelength is 14, patterns in this plane have been computed numerically using an IBM Card-Programmed Calculator. Patterns in a plane containing the axis of the cylinder have also been investigated.
The Design of Optimum Directional Acoustic Arrays
Authors: Davids N. , Thurston E. G. , Mueser R. E.
Published: September 2005

A transducer array has been designed according to underlying theory originally applied to broadside electromagnetic antenna arrays by Dolph. The properties of Tschebyscheff polynomials have been employed to obtain an optimized relationship between minor-lobe level and main beam width.

The shading design of a 130 element circular array is carried out utilizing a distance between stack centers of 5λ/8. Experimental measurements of the resulting transducer give a peak sensitivity of −70 db below 1 volt for a field of 1 dyne per cm2, 11 degrees main beam width at the 3-db down points, and suppression of side lobes to more than 32 db below peak sensitivity.
The Free Vibrations of a Gas Contained within a Spherical Vessel
Authors: Ferris Horace G.
Published: September 2005

Numerical values of the lowest 84 natural frequencies of vibration for the spherical acoustic resonator are calculated and listed in appropriate tables. Consideration is given to the geometrical structure of the nodal surfaces associated with each mode of vibration and to the degeneracy of each natural frequency.
The Modes of Vibration of a Semi-Flexible Rod under Tension
Authors: Kenworthy Ray W. , Jennings Vernon A.
Published: September 2005

The possible modes of vibration of a rod under conditions which are intermediate between a perfectly flexible string under tension and a stiff bar without tension have been calculated from existing theory. An experimental investigation of the first ten modes gave results in agreement with the theory within approximately 0.5 percent. Deviation from a harmonic series increases with the number of the mode of vibration, but is considerably less than for a stiff bar.
Frequency Discrimination for Damped Waves
Authors: Stevens K. N.
Published: September 2005

Measurements of frequency discrimination for single damped waves are reported for frequencies between 200 and 5000 cps, and for values of the damping σ between 0 and 500 sec−1 (σ is the reciprocal of the time constant of the envelope of the damped wave). There is an increase in the difference limen for frequency as the damping increases, or as the effective duration decreases. The increase in the difference limed is accompanied by a loss in the pitch character of the stimulus, and there is usually a sharp deterioration in discrimination above a certain value of damping, i.e., above a certain band width of the stimulus. The results are related to existing data on the perception of short sinusoidal stimuli.
Total Sound Absorption for Upholstered Theater Chairs with Audience
Authors: Lane R. N. , Botsford James
Published: September 2005

The total absorption for theater chairs with back and seats upholstered in mohair has been measured from 250 to 9000 cps in the Defense Research Laboratory reverberation chamber. Values are given for the chairs with (1) seats up, (2) seats down, and (3) occupied by adults.
An Inexpensive Acoustic Treatment for Gymnasiums, Civic Coliseums, and Similar Structures
Authors: Lane R. N. , Seay Frank , Boner C. P.
Published: September 2005

The acoustic treatment of an excessively reverberant civic coliseum is described. Before treatment the structure, originally an aircraft hangar, had a sharply peaked reverberation time of eight seconds in the region between 600 and 800 cycles per second. Thirty-two thousand square feet of two-inch-thick Fiberglas panels were suspended in horizontal V's six feet below the parabolic metal ceiling. After treatment, the reverberation time is essentially uniform from 100 cps to 800 cps, with an average value of approximately 1.2 seconds. The method of construction and the mounting of the panels is described. Sound absorption coefficients for these panels are given, and a comparison made between the value obtained from the coliseum installation and the value obtained for 72 square feet of identical panel hung in the Defense Research Laboratory polycylindrical reverberation chamber.
The Dynamics of the Middle Ear and Its Relation to the Acuity of Hearing
Authors: Fletcher Harvey
Published: September 2005

The transformer action of the middle ear as measured by Bekésy is shown to be the principal cause for the low acuity of hearing for low frequencies. Because of the very low mechanical impedance across the basilar membrane at low frequencies, large acoustical pressures in front of the ear drum produce appreciable acoustical pressures across the basilar membrane. For example, at 100 cps this pressure is 30 times and at 6000 cps it is 1/10 that created across the basilar membrane.
The Jaw Motions Relative to the Skull and Their Influence on Hearing by Bone Conduction
Authors: Franke Ernst K. , von Gierke Henning E. , Grossman Frederick M. , von Wittern Wolf W.
Published: September 2005

Opening and closing the mouth increases the sound pressure produced by bone conduction in the closed auditory canal by as much as six to ten decibels in the frequency range between 40 cps and 700 cps. This difference is explained by vibrations of the lower jaw relative to the skull. The resonance curve of this motion was measured and used to calculate the influence of the lower jaw motion on the sound level in the closed auditory canal. The results show that the measured frequency response of the difference in sound pressure open mouth vs closed mouth, may be explained entirely by vibrations of the lower jaw.
The Masking and Pitch Shifts of Pure Tones near Abrupt Changes in a Thermal Noise Spectrum
Authors: Webster J. C. , Miller P. H. , Thompson P. O. , Davenport E. W.
Published: September 2005

When a pure tone is mixed with a noise of uniform spectrum, its threshold is raised. At levels above threshold, its loudness and pitch are changed by the presence of the noise. Introducing abrupt changes in the slope of the noise spectrum by filtering out (rejecting) one octave changes these effects in the vicinity of this gap.

The masked threshold for a pure tone varies from the value for unfiltered noise at the edges of the gap to a value approximately 25 db lower at the middle. This indicates that gapped-noise may be used to mask out sounds outside of the gap without unduly raising the threshold of sounds in the gap.

Presence of white noise.generally raises the pitch of a pure tone whose frequency is between 500 and 4000 cps. Presence of noise with the gap does not raise the pitch of a pure tone located in the upper half of the gap. For a tone located in the lower half of the gap, the pitch is raised more than it would be in the presence of unfiltered noise.

The changes in the judged loudness of pure tones partially masked by a gapped-noise reaffirm the importance of the tails of the excitation pattern in their effect on loudness.
Control Methods Used in a Study of the Vowels
Authors: Peterson Gordon E. , Barney Harold L.
Published: September 2005

Relationships between a listener's identification of a spoken vowel and its properties as revealed from acoustic measurement of its sound wave have been a subject of study by many investigators. Both the utterance and the identification of a vowel depend upon the language and dialectal backgrounds and the vocal and auditory characteristics of the individuals concerned. The purpose of this paper is to discuss some of the control methods that have been used in the evaluation of these effects in a vowel study program at Bell Telephone Laboratories. The plan of the study, calibration of recording and measuring equipment, and methods for checking the performance of both speakers and listeners are described. The methods are illustrated from results of tests involving some 76 speakers and 70 listeners.
Transmission of Ultrasonic Waves through a Thin Solid Plate at the Critical Angle for the Dilatational Wave
Authors: Makinson K. Rachel
Published: September 2005

The transmission, through an isotropic solid plate immersed in a liquid, of ultrasonic waves incident at the critical angle for total reflection of the dilatational wave, is examined experimentally and theoretically. It has previously been held that total reflection does not occur at this angle when the thickness of the solid is less than or comparable with the wavelength of the dilatational wave in it. It is now shown that, owing to interference between the dilatational and rotational waves, total reflection does occur at or very near this angle for a considerable range of thickness in this region. It is therefore possible to use the total reflection method for the determination of the dilatational velocity in a solid even when only thin specimens of the solid are available.
New Methods of Ultrasonoscopy and Ultrasonography
Authors: Ernst Paul J. , Hoffman Charles W.
Published: September 2005

Four groups of new methods of indirect ultrasonoscopy and ultrasonography are developed: those using temperature-sensitive chromotropic compounds, those using leucobases of dyes, those using thermo-stimulable phosphors, and those using special temperature-sensitive phosphors. Various techniques are described and some results shown in the illustrations. Finally, a new method of direct ultrasonography is proposed. This method makes use of the possibility to detonate certain labile chemical compounds by ultrasonics.
Transverse Vibrations of Uniform Thin Bars
Authors: Heller Ralph
Published: September 2005

Continuing the theoretical work of Strehlke, Seebeck, and Lord Rayleigh, the transverse vibrations of uniform thin bars subject to the following end conditions are considered: (a) both ends free; (b) both ends fixed; (c) one end free, the other fixed. Accurate values for the position of the nodes, antinodes, and points of inflection and of maximum curvature are calculated for the first few principal modes of vibration, several errors of long standing are rectified, and the amplitudes at the antinodes are computed (Tables I and II). Approximate expressions, valid for the modes of higher order, are given for the node and antinode positions (Tables III and IV) as well as for the amplitudes at the antinodes (Sec. 6).
On the Failure of Plane Wave Theory to Predict the Reflection of a Narrow Ultrasonic Beam
Authors: Weinstein Marvin S.
Published: September 2005

In past studies of the interaction of an ultrasonic beam with a solid plate immersed in water, the general practice has been to assume that a narrow radiation pattern is a sufficiently close approximation to a plane wave to permit the use of plane wave theory to predict the results. Reflection measurements made in water with a three-degree radiation pattern at a frequency of 3.35 megacycles per second, using both air-backed aluminum plates of thicknesses ranging from 0.250 to 0.025 inch and a two-inch aluminum slab to approximate a semi-infinite medium, indicate that under certain conditions this assumption is not valid. Experimentally, the excess pressure of the reflected wave is considerably lower than that predicted by plane wave theory when the angle of incidence is such that the change of phase of the wave upon reflection varies greatly with a small change of the angle of incidence. It is apparent that at these angles of incidence a divergent beam which is several degrees wide cannot be used to approximate a plane wave. The nature of the phenomenon indicates that it should be of equal importance in the study of transmission phenomena.
Measurement of Dynamic Shear Viscosity and Stiffness of Viscous Liquids by Means of Traveling Torsional Waves
Authors: McSkimin H. J.
Published: September 2005

A short periodically repeated train of torsional waves is transmitted along a glass or metal cylindrical rod. After reflection from the free end, these waves are sent back to the quartz crystal which serves as both transmitter and receiver. The phase shift and added attenuation caused by immersing the rod in the test liquid are measured by means of a special balancing arrangement, and yield a calculation of the impedance presented to the rod surface.

From an analysis of wave propagation both in the rod and in the liquid, one can calculate the characteristic shear impedance of the liquid, and the dynamic viscosity and stiffness.

Data for polyisobutylene liquids with static viscosities up to 2000 poises are given for the frequency range 25–150 kc. High frequency data (5–25 mc) for the same liquids obtained by a method previously reported on (see reference 10(b)) are correlated to the present work. Some results for polypropylene, polyisoprene, polybutadiene, and polypropylene sebacate are also given.
The Impedance of the Human Mastoid
Authors: Franke Ernst K.
Published: September 2005

The impedance of the human mastoid was determined by means of a vibrating piston, one end of which was placed in firm contact with the body surface. The impedances of several subjects were measured. The compliance c and the resistance r were calculated from the results; the average values were c = 1.5×10−8 cm/dyne and r = 1.0×104 dyne/cm/sec, for an area of the piston base of 1 cm2 and an application force of 250 g. It is shown how the impedance depends on the area and the application force of the piston. A critical review of the literature on the subject is given.
Waves in Liquid-Filled Cylinders
Authors: Fay R. D.
Published: September 2005

If a system comprising a water column bounded by a steel cylindrical shell is driven at a fixed frequency, the pressure amplitude has been found to vary along the axis in a complex manner. On the hypothesis that this phenomenon results from the excitation of two or more modes of vibration having different speeds of phase propagation, an investigation has been made of waves in liquid-filled cylindrical shells. It is shown that, in addition to the modes associated with boundaries of high impedance, there is also a possible mode associated with each type of free wave in the shell. The phase velocities of several symmetrical free waves are calculated by an extension of the method employed by Love for solid cylinders. A comparison with measurements appears to confirm the hypothesis.
Axially Symmetric Vibrations of a Finite Isotropic Disk. I
Authors: Aggarwal Ram Ratan
Published: September 2005

Some frequencies for the symmetrical normal nodes of a finite, isotropic disk are calculated by satisfying the boundary conditions exactly at the flat surfaces and approximately at the curved surface. It is found that two sets of frequencies occur for each vibration pattern. One set approaches the odd order thickness compressional frequencies, whereas the other approaches the even order thickness shear frequencies, as the radius of the disk increases indefinitely. As a test of the validity of the approximations, the maximum residual stresses at the curved surface are compared with the compressional component of the stress at the center of the disk.
Acoustic Design of Aircraft Gas Turbine Test Cells
Authors: Fehr R. O. , Wells R. J. , Bray T. L.
Published: September 2005

The high noise level associated with aircraft gas turbine operation creates two noise problems: (1) The reduction of the noise in the neighborhood of the installation to an acceptable level, and (2) the protection of operating personnel from excessive noise. This paper reports work done by the Aircraft Gas Turbine Division of the General Electric Company at their plants in Lockland, Ohio, and in Lynn, Massachusetts. Permissible sound levels were established for surrounding residential areas. The attenuation due to spherical divergence, and also the probable deviation due to varying atmospheric conditions, was determined. Thus, the sound level permissible at the exhaust stacks of the test cells was obtained. Knowing the noise level inside the test cell, the required sound attenuation of the stacks was calculated. Various acoustical treatments were investigated. An acoustical design is proposed which makes use of a combination on various duct treatments, and which meets the established design objectives. The permissible noise level inside the control room is discussed, and the required attenuation through the barrier between test cell and control room is calculated. A design for a control room meeting the established noise-level criterion is proposed.
The Loudness of Bands of Noise
Authors: Pollack Irwin
Published: September 2005

The contribution to the loudness of noise made by various frequency bands was studied over a wide range of noise levels. Paralleling results with pure tones, the contribution of noise of the middle frequency range to loudness is greater than that of low and high frequency noise (for bands 250 to 300 mels in width). In order to produce maximal loudness with a fixed over-all sound level, it was found, in most cases, more economical to spread the noise spectrum over a wide frequency range than to concentrate the noise spectrum in a restricted range of frequencies.
Natural Vibrations of Rectangular Quartz Plates and Determination of the Dispersion of Sound in Ethyl Ether
Authors: Özdoğan Belkis
Published: September 2005

An acoustic interferometer is used to measure the modes of vibration of rectangular quartz plates in air. The same instrument is used to study the dispersion of sound in ethyl ether vapor over a range of frequencies from 163.5 kc to 2482 kc and a range of pressures from 15 mm of mercury to 340 mm of mercury.
A Phase Principle for Complex-Frequency Analysis and Its Implications in Auditory Theory
Authors: Huggins W. H.
Published: September 2005

A filtering scheme that utilizes the phase-frequency characteristic of a filter is shown to have certain advantages for analyzing signals, such as speech, which are produced by shock or noise excitation of a physical system having one or more resonances. The phase principle is shown to be particularly well suited to neural mechanisms of inhibition and facilitation, and evidence is presented that such a principle may be used by the ear to achieve its analysis of the sound that it receives.
Control Tower Language
Authors: Frick F. C. , Sumby W. H.
Published: September 2005

Shannon and others have estimated that written English is about 60 percent redundant. These estimates are arrived at by considering linguistic constraints on our use of speech symbols; they do not consider additional restrictions imposed by the audience and the situation in which the speaker finds himself. In order to estimate the effects of such nonlinguistic constraints, an informational analysis has been made of the “sublanguage” used in the control of aircraft by Air Force control tower operators. When the situational, as well as linguistic, contexts are taken into account, the estimated redundancy is raised to 96 percent.
The Information-Bearing Elements of Speech
Authors: Peterson Gordon E.
Published: September 2005

This study deals with those aspects of speech which are phonetically significant. A technique has been developed with which phonetically equivalent speech samples may be obtained different phonetic contexts and from different speakers. Data on two front vowels by different types of speakers are presented. The technique has also been applied to the evaluation of words containing these two vowels.
Duality in Mechanics
Authors: Le Corbeiller P. , Yeung Ying-Wa
Published: September 2005

Given an electric network Ev which has M meshes and P node-pairs, its electric dual Ei will have P meshes and M node-pairs and its classical mechanical analog Mf will have M+1 nodes, M independent node-pairs, and P independent node cycles. A second mechanical system Mv, the classical analog of Ei, will have M cycles and P node-pairs. If, for example, M = 2, P = 3, the systems Ev and Mv, analogs in the Firestone or “mobility” method, will be governed by two mesh equations, expressing that the algebraic sum of the voltages or velocities around any loop is zero; the systems Ei and Mf, also Firestone analogs, will satisfy two node equations, expressing that the algebraic sum of the currents or forces leaving any node is zero. These four sets of equations are identical, interchanging symbols suitably. The consideration of the four systems, Ev, Ei, Mv, Mf, forming a complete set, shows the advantages of the Firestone over the classical system of analogies and suggests a systematic use of duality in mechanical as well as in electrical systems.
Periodic Fluid Flow Through Circular Tubes
Authors: Thurston George B.
Published: September 2005

Some aspects of the periodic flow of an incompressible fluid through a circular tube of large length to diameter ratio have been studied. Expressions for the analogous acoustic resistance and inductance of the tube are presented. An experimental investigation of the resistance and inductance is described in which the tube dimensions, the viscosity of the fluid, and the frequency of the periodic motion are varied over a wide range. The experimental results are found to be in good agreement with the predictions of the hydro-dynamical theory.
Theoretical Sensitivity of a Transversely Loaded, Circular Bimorph Transducer
Authors: Thurston Edward G.
Published: September 2005

With the advent of barium titanate as a piezoelectric material, the construction of transducers whose active elements can be in a wide variety of shapes became possible. The theoretical sensitivity of an interesting structure consisting of a transversely loaded, centrally supported, circular, barium titanate bimorph is calculated using the results of elasticity theory. Some experimental verification is presented.
Axially Symmetric Vibrations of a Finite Isotropic Disk. II
Authors: Ratan Aggarwal Ram
Published: September 2005

The calculations presented in Part I of this paper have been extended so as to include vibrations, which are antisymmetric with respect to the central plane of the disk. Curves showing the normal components of the displacements at the boundary surfaces are also drawn, to get the vibration patterns according to the theoretical assumptions made.
An Investigation of Sound Vibrations in a Tube Containing a Heat Source
Authors: Neuringer Joseph L. , Hudson George E.
Published: September 2005

The aerothermodynamic process inside a tube in which is placed heat source and through which air is flowing is investigated theoretically. The formulation is based partly on the assumption that the average state of the medium inside may be approximated by a step distribution in the gas variables, simplifying hypothesis suggested by experimental observations by Lehmann (see reference 4). The zeroth-order (mean hydrodynamic flow) and first-order (acoustic) solutions inside the tube are first obtained using a heat transfer law for the heater which depends on some arbitrary function of the local values of the gas variables, velocity-gradient, and source temperature. Upon the basis of a few hypotheses regarding turbulent flow and turbulent heat transfer, the possible existence of heaters whose heat transfer rate depends essentially on the negative of the velocity gradient of the flow through them is demonstrated. The solution is then specialized to those types of heaters, and it is shown that, in agreement with the so-called Rijke effect, growth of the fundamental tone may occur with the heater almost anywhere in the first half of the tube from the blower end to the node, with decay almost everywhere else. The exact positions of the regions of growth and decay of sound inside the tube are then investigated.
Vibrations of Evaporating Liquid Drops
Authors: Holter Norman J. , Glasscock Wilford R.
Published: September 2005

An unusual type of vibration of flattened spheroidal liquid drops, occurring under certain conditions, is described and illustrated. Appropriate liquids placed on a sufficiently hot horizontal surface float on a film of their own vapor, which vapor insulates the drop so that it evaporates quite slowly, this phenomenon being known as the Leidenfrost effect. It is under these conditions that drops have been found capable of sustaining large amplitude regular radial vibrations whose driving force is probably related to the radial flow of vapor below the drops. The vibrating drops are approximately polygons which may have any of 2, 3, 4,…n sides, seen by the eye as drops with 4, 6, 8…(2n+2) regular lobes around the circumference. Methods of exciting and recording the effect are described.
Systematic Errors in Indirect Measurements of the Velocity of Sound
Authors: Smith P. W.
Published: September 2005

An analysis is made of certain methods of measuring the velocity of sound. Specifically, attention is centered on those methods based upon measurements of the electrical driving-point impedance of the transducer and the observation of some phenomenon of that impedance which is recurrent as the position of the reflector in the acoustic chamber is changed. Consideration is given to the influences of small losses in the propagation of sound in the chamber and of the existence of nonplane wave fronts. It is shown that such measurements can be subject to significant systematic errors arising from the method itself. The nature and magnitude of such errors are discussed.