bluuebunny/crossref_metadata_2025 huggingface dataset:
Uniphase Unidirectional Microphones
Authors: Bauer Benjamin B.
Published: September 2005

The unidirectional microphone is treated as a generalized transducer and network which are subjected to sound waves at two points in space. Network relationships are derived to produce unidirectional operation. These relationships are fulfilled in the “uniphase” structure which has a single transducer and a phase-shifting network instead of the two transducers normally used in unidirectional microphones. Acoustical phase-shifting networks applied to a diaphragm-type piezoelectric microphone and to a moving coil dynamic microphone producing a cardioid-type polar pattern are described.
Mechanical and Optical Equipment for the Stereophonic Sound Film System
Authors: Wente E. C. , Biddulph R. , Elmer L. A. , Anderson A. B.
Published: September 2005

The same mechanism employed for propelling the film in both recording and reproducing. To permit recording of the longer orchestral selections without interruption, the machines are designed to handle film in 2000-foot lengths. Special features of the film-propulsion system for obtaining great uniformity of speed at the translation points are described. The three signal- and one control-channel currents are recorded by means of light valves of identical construction. All four tracks are exposed while the film is passing over a free-running supporting roller, mounted on the same shaft with a new type of internally damped roller. In reproduction, each track is exposed, through an objective of high aperture, to light from an incandescent source. After passing through the film, the light from each track is carried by a glass rod to a photoelectric cell.
Vibration of the Walls of a Cornet
Authors: Knauss H. P. , Yeager W. J.
Published: September 2005

Vibrations of the metal walls of a cornet were studied with a crystal pick-up and a cathode-ray oscillograph. For each tone of the scale, the walls were set into vibration at the frequency of the tone played. This vibration was duplicated by electromagnetic driving, and the sound produced by the walls alone was compared with the tone of the cornet as played, by means of a sound level meter. The intensity difference shows that the contribution of the walls is masked completely by that of the vibrating air column. This was checked by loading the walls of a bugle with putty; its tone quality could hardly be distinguished from that of an untreated bugle.
Industrial Noises and Industrial Deafness
Authors: Rosenblith Walter A.
Published: September 2005

Measurements on the intensity and the frequency distribution of industrial noises and the hearing losses of industrial workers show: (a) some degree of correlation between the average noise level and the temporary and permanent hearing losses; (b) an almost complete localization of the permanent hearing loss in the region above 1500 cycles (with a maximum at 6000 cycles), while the most important components of industrial noises are practically always below this frequency-limit; (c) some correlation between the amount of temporary and permanent hearing losses for high frequencies; (d) a very small permanent hearing loss for low frequencies with a very rapid recuperation from temporary loss in this region.
Acoustic Impedance of Porous Materials
Authors: Beranek Leo L.
Published: September 2005

A thorough understanding of the acoustical properties of porous materials is becoming increasingly important because of the wide variety of unusual and important applications in which they are finding use. A simple and useful theory is presented for predicting the normal acoustic impedance of isotropic porous materials in terms of three previously described simple constants, namely, flow resistance, porosity, and effective dynamic mass of the enclosed gas. The variation of normal impedance with angle of incidence for spaced-out or rigidly backed samples is treated. A striking possibility is discussed, namely, that gaseous expansions are isothermal over most of the audiofrequency range in materials made of finely divided particles. Many isotropic acoustical materials appear to fall in this class. This means that an air cavity becomes less stiff to dynamic compression when a very porous finely divided material is added to the cavity than when the material is not present. The results are checked against experimental data. A simple method is described for measuring the porosity P of a material, namely, the ratio of the volume of the air spaces in a material to the total volume of the material.
Methods for Measuring the Performance of Hearing Aids
Authors: Romanow Frank F.
Published: September 2005

A hearing aid can be considered as a sound transmission system which is interposed in the path between the source of sound and the listener's ear. As such its performance can be judged by comparing the sound that reaches the ear first through the air path and then through the hearing aid. The experimental procedure to carry out this concept is, however, time consuming. To obtain a simple laboratory technique for comparative purposes, it is proposed, therefore, that the amplification of a hearing aid be measured by placing its microphone in a known sound field and observing the output of the receiver when terminated in an appropriate impedance. For an air conduction receiver this impedance takes the form of a closed cavity. For a bone conduction receiver the termination is an artificial mastoid. Since in a portable hearing aid compactness is desired, the undistorted pressure that can be developed by the set is limited in magnitude. Also the amplification is a function of the variation of the power supply voltages. Hence it is necessary that these characteristics be measured. As an illustration of the different factors involved characteristic curves for a recently developed vacuum tube aid are shown.
The Translational Dispersion of Sound in Gases
Authors: Primakoff H.
Published: September 2005

The translational dispersion of sound in gases is discussed from the standpoint of kinetic theory. An explicit relation is derived for the variation of sound velocity with frequency in monatomic gases; this relation is: V = V0(1 – 5.4l2/λ2), where l is the mean free path, and λ the wave-length. The possibility of experimental observation of translational dispersion is briefly discussed.
An Absolute Pressure Generator and Its Application to the Free-Field Calibration of a Microphone
Authors: Kennedy W. Jay , Boner C. P.
Published: September 2005

A device for producing a known pressure at designated points in a progressive plane sound wave is described. The method of using this “absolute pressure generator” to effect the free-field calibration of a velocity microphone over a limited frequency range is outlined, and the results compared with a Rayleigh-disk calibration. Suggestions are given for extending the range over which the generator can be used as a microphone calibrating agency.
Perturbation of Sound Waves in Irregular Rooms
Authors: Bolt R. H. , Feshbach H. , Clogston A. M.
Published: September 2005

A recently developed boundary perturbation theory is applied to the solution of certain problems in room acoustics. Wave patterns and normal frequencies can be calculated for rooms having walls which are distorted by shape irregularities, by non-uniformities of boundary absorption, or by a combination of these. The method is quite general; it is applicable to any form of irregularity if the amount of distortion is “small,” provided solutions for the basic form are obtainable. Specific formulas are derived for trapezoidal shapes and calculations agree closely with experimental patterns and frequencies reported previously. An experiment has been devised to test the range of validity of the perturbation formulas for one case. A small test chamber was built with walls which could be shifted continuously in plan to give trapezoids of constant area, having any desired degree of deformity. A number of normal frequencies were traced through the whole range of shapes. For wall angle shifts up to about 15° the perturbation calculations hold well. The perturbation theory yields certain general conclusions regarding the problem of sound diffusion in irregular rooms. These appear to be of particular interest in the light of recent experience in applied acoustic design.
Comparison Between a Haskell Organ Pipe and a Simple Open Pipe
Authors: Binder R. C. , Hall A. S.
Published: September 2005

An analysis with friction shows that the mobility for a Haskell organ pipe is not exactly equal to that for a simple open pipe. The inclusion of friction probably explains the observation that a Haskell pipe and a simple open pipe blown in exactly the same way show substantial differences in harmonic structure.
An Experimental Study of Subjective Tones Produced Within the Human Ear
Authors: Moe Chesney R.
Published: September 2005

Quantitative measurements are reported on the intensities of subjective tones produced within the human ear under single and dual tone excitation. The measurements are made by the exploring tone method. The even and odd subjective harmonics show some differences, indicating that the organ, or set of organs, producing non-linearity is not the same as the source of asymmetry. The intensities at which these two distorting effects first appear are not the same. The subjective summation tones are, in general, weaker than the corresponding difference tones of the same order. These differences are to be expected if auditory masking is a process occurring within the hearing mechanism.
Supersonic Measurements in CO2 at 0° to 100°C
Authors: Pielemeier W. H.
Published: September 2005

Previous measurements are reviewed and curves are drawn for the velocity of low frequency and of high frequency sound waves in dry CO2 as functions of the temperature from 0 to 100°C. Another set of curves shows how the frequency producing maximum absorption per wave-length depends on the water vapor concentration in the CO2 at approximately one atmosphere pressure. Evidence is presented for two distinct relaxation times for each given concentration. Acetaldehyde is cited as a gas in which three relaxation times have definitely been found. Our recent measurements of the velocity at 98°C check well with the curve but the evidence for two distinct relaxation times was not more definite than at 28°C.
Conditions for Wide Angle Radiation from Conical Sound Radiators
Authors: Carlisle Richard W.
Published: September 2005

The theoretical conditions by which substantially hemispherical radiation can be attained from the concave side of a loudspeaker cone are discussed and experimental data presented.
Use of the Pierce Interferometer for Measuring the Absorption of Sound in Gases
Authors: Hardy Howard C.
Published: September 2005

The empirical Pielemeier equation used for measuring the absorption of sound in gases is derived from theoretical consideration of the principles of the Pierce interferometer and the quartz oscillator. A more complete explanation of the effect of sound resonance on the oscillator is given. The criteria for accurate measurement of the absorption coefficients in gases are set up and verified by experiment.
Acoustic Laboratory in the New RCA Laboratories
Authors: Olson Harry F.
Published: September 2005

Modern facilities for development and research in all branches of acoustics are provided in the new RCA Laboratories. The new Acoustic Laboratories include the following: a free-field sound room, a large sound stage, a standard living room, a soundproof room for life tests, dust-free rooms, magnetic laboratory, a live room, a field laboratory and towers, and conventional communication type laboratories. The free-field sound room is designed to provide acoustical conditions as obtained in free space outdoors under ideal and normal test conditions. The large sound stage is designed for tests of sound pick-up in standard conventional settings. By a change in “acoustics” the sound stage may be converted into a small theater for sound reproduction tests. The living room laboratory is designed to be the acoustical equal of the ideal living room in which sound reproducing instruments such as radios and phonographs may be developed and tested for normal home use. The soundproof room is provided with special walls and doors for testing loudspeakers at high levels without annoyance to adjoining rooms. The magnetic laboratory is equipped with apparatus for making magnetic measurements and several types of magnetizers for magnetizing permanent magnets. The dust-free rooms are used for assembling structures. The live room is designed for testing of sound-absorbing materials. The conventional laboratory bays include all types of measuring equipment: oscillators, amplifiers, recorders, bridges, etc. Multiple audiofrequency lines are provided so that laboratories may be interconnected. The remotely located field laboratory is used for conducting free-field response, power, and life tests.
The Action of a Direct Radiator Loudspeaker with a Non-Linear Cone Suspension System
Authors: Olson Harry F.
Published: September 2005

During the past few years a number of mathematical investigators have directed their efforts toward the solution of differential equations with variable coefficients. These analyses are useful in explaining some of the phenomena which occur in electroacoustic vibrating systems with non-linear elements. In particular, this mathematics may be used to explain the various phenomena exhibited by a direct radiator loudspeaker with a non-linear cone suspension system. One of the effects is a jump phenomenon in the response frequency characteristic. Another effect is the production of harmonics and subharmonics.
The Effect of Radiation on the Vibrations of a Circular Diaphragm
Authors: Lax Melvin
Published: September 2005

Circular plate with a fluid on one side: The free and forced vibration problems of a clamped plate in an infinite baffle are solved exactly in terms of a set of self- and mutual radiation impedances Zmn(ω), associated with the normal modes of a plate vibrating in a vacuum. Computations of these impedances have been made for the lowest four modes over a sufficient range in frequency to solve the forced vibration problems that occur in practice as well as the free vibration problem of these modes. The magnitude of the influence of the fluid on the plate is shown to depend only on the frequency of vibration and the non-dimensional parameter β = ρ0R/2ρh, where R is the radius of the plate, 2h the thickness, and ρ0/ρ the relative density of fluid to plate. The shift in resonant frequency, and the change in shape of the lowest four modes due to the reaction of the fluid on the plate are computed as a function of β. These changes are found to be important in the range 1 < β < 8. They are negligible for β < 1, the case of radiation into air.
The Velocity of Sound in Vapors
Authors: Matta K. , Mokhtar M.
Published: September 2005

The study of sound propagation in gases has revealed useful data concerning molecular behavior. Vapors, with little known about their absorption and dispersion to sound at audible frequencies, provide a natural field for extending such studies. In the present investigation, a form of Kundt's tube is employed in which a hot wire records the amplitude in the stationary wave system. It is calibrated by the use of dry air and of oxygen. The results obtained for the velocity of sound are in good agreement with those determined by other methods.
On the Theory of the Directional Patterns of Continuous Source Distributions on a Plane Surface
Authors: Jones R. Clark
Published: September 2005

This paper contains a study of the directional patterns which may be obtained by driving a plane surface with specified normal velocities. Part I is devoted to the general theory of such distributions. The directional pattern at any distance from an arbitrary continuous distribution of sources is first obtained. The approximate relation which holds at large distances is then derived, and the simpler formulae which hold when the surface distribution has several different kinds of symmetry are developed. In particular, the case is studied in which the sources are distributed along a line. An interesting relation between linear distributions and those with circular symmetry is pointed out. Part II contains the derivations of a number of directional patterns corresponding to specific source distributions. It is pointed out that although it is easy to specify a source distribution which will yield any directional pattern satisfying certain methematical conditions of convergence, such distributions are usually of infinite extent, and therefore do not correspond to distributions which are of practical interest. A method of attack is suggested for the problem of determining the distribution of specified extent which yields the directional pattern of optimum characteristics for any particular application. Part III contains 22 tables, 21 of which are tables of the directional patterns of the source distributions considered in Part II. In addition to the column giving the argument, each of the 21 tables contains three columns, the first giving the relative sound pressure, the second the square of the relative sound pressure, and the third, ten times the common logarithm of the inverse square of the relative sound pressure. Table II, which is more detailed than the others insofar as the interval is smaller, is a table of the directional pattern of a circular piston.
Singing Flames
Authors: Jones Arthur Taber
Published: September 2005

The flames considered are those which maintain vibration of the air in a surrounding “air tube.” Earlier theories are reviewed. Rayleigh's theory involves standing waves in the gas supply tube and leads to certain lengths of gas tube for which singing does not occur. It is now found that maintenance of vibration in the air tube may be excellent when the gas tube is so long that no appreciable standing waves are formed in it, and that under suitable conditions there are no lengths of gas tube for which a flame will not sing. Rayleigh's theory is modified by taking into account (1) the increase in viscosity which the flame brings about in the orifice from which it burns and (2) the progressive waves that run downward through the gas tube. These waves involve a maximum rate of efflux of gas near the phase of least pressure in the air tube, whereas Rayleigh's theory involves a maximum rate of efflux a quarter of a period earlier or later, depending on the length of the gas tube. If the most rapid efflux is near the phase of least pressure, and if the flame gases rise from the orifice to the top of the flame in approximately half a period, maintenance is possible. In thirteen cases where the flame sang, values obtained for the time of rise run from 0.6T to 0.9T; and in sixteen cases where the flame was silent, they run from 1.2T to 3.3T. In view of approximations made in reaching these results they are regarded as satisfactory. When the gas tube is of only moderate length, standing waves in it may be superposed on the running waves. This superposition leads to the possibility of lengths of gas tube for which the flame will not sing. Regions of silence are more likely to occur when the flame is small. The size of the flame is also a factor in determining the distance to which it must be inserted in the air tube before maintenance is possible. The distance is a minimum for flames of moderate size. The amended theory gives explanations of these facts and of several others. The initiation of the vibration is attributed to the slight disturbances that are always present in the atmosphere.
Observed Classical Sound Absorption in Air
Authors: Pielemeier W. H.
Published: September 2005

A brief treatment of the theory and methods of measuring absorption of sound in gases precedes the data which are presented in the form of curves. The measurements were made with a Pierce acoustic interferometer at a frequency of 1927 kc/sec. in air. This frequency is high enough to satisfy Hardy's and Krasnooshkin's required conditions to obtain reliable results by this method. The experimental result agrees with Krasnooshkin's value of α0λ02 = (225 ± 5)(10)−6 cm.
A Frequency Standard for Use at High and Low Frequencies
Authors: McLoughlin Rogelio P.
Published: September 2005

A secondary frequency standard is described for use at high and low frequencies, consisting of a tuning-fork oscillator which controls an Abraham and Block multivibrator. An amplifier of adequate selectivity allows the selection of any harmonic of the fundamental voltage. This is accomplished by the use of a multivibrator and a regenerative amplifier of high selectivity which allows selection of any harmonic of the fundamental frequency in the band 1 kc to 2 mc. The tuning-fork oscillator presents the following advantages: 1. Possibility of adjusting the frequency by varying the amplitude of oscillation of the tuning fork. 2. Automatic adjustment of the amplitude to the desired value. 3. Automatic adjustment of the phase difference between the amplitude and the applied force. 4. Visual indication of amplitude. 5. Visual indication of the phase difference. 6. Possibility of manual adjustment of the phase difference. These properties permit indirect measurement of the frequency at any moment making it possible to change tubes without making necessary new calibration by comparison with a primary frequency standard.
Group Audiometry
Authors: Harris J. Donald
Published: September 2005

The use of commonly available apparatus is described for a group test of auditory acuity as a function of frequency. Reliability is only slightly less than that of a careful individual examination. The techniques which produce highest reliability are described. Validity is satisfactory in terms of deviation from results of an individual test. The test is simple to take. Several checks on malingering are provided which make group audiometry practicable with populations not highly selected for age or intelligence.
The Theory of the Herschel-Quincke Tube
Authors: Stewart G. W.
Published: September 2005

A former discussion of the theory of the Herschel-Quincke tube is continued and supplemented by the investigation by Professor H. S. Uhler of a more general case. With the areas of the bifurcated conduits different, it is found that the number of frequencies giving zero transmission is again more numerous than determined by the condition of a difference of phase corresponding to that of one-half wave-length in the two branches. In the more general case the former fixed relations between these phase differences no longer holds. They are now connected by the equality S2 sin α3 = −S3 sin α2, where S2 and S3 are the areas and α2 and α3 the phase differences in the corresponding branches.
A General Theory of Passive Linear Electroacoustic Transducers and the Electroacoustic Reciprocity Theorem. I
Authors: Foldy Leslie L. , Primakoff Henry
Published: September 2005

A theory of the operation of passive linear electroacoustic transducers is developed on the basis of the most general linear equations (in this case, integral equations) relating the pressure and normal velocity at each point on the transducer surface and the voltage and current at the transducer's electrical terminals. These, together with the appropriate solutions of the wave equation expressed through the use of Green's functions for the medium in which the transducer is immersed and the equations defining the electrical termination of the transducer, completely characterize the behavior of the transducer and allow explicit calculation of such quantities as impedances, responses, etc., in terms of four parameters entering the fundamental equations.

On the basis of this theory, a proof of the reciprocity theorem for electroacoustic transducers relating their speaker and microphone responses is presented embodying the conditions necessary for its validity. These conditions are essentially the existence of certain symmetry relationships among the transducer parameters. When these symmetry relationships may be expected to hold is to be discussed in Part II of this paper to appear later. Some applications of the theory are presented and others are outlined.
The Conical Sound Source
Authors: Bordoni Piero Giorgio
Published: September 2005

An asymptotic expansion has been derived from a formula given by W. N. Brown, which allows the plotting of directional and response curves for a vibrating cone in an infinite baffle. The results are compared with those pertaining to a flat disk of same radius.
Tentative Code for Measurement of Performance of Hearing Aids
Authors: Kranz Fred W.
Published: September 2005

These specifications for methods of measurement of hearing aids were drawn up by a technical committee organized by the American Hearing Aid Association, including engineering representatives from most of the larger manufacturers of hearing aids as well as technical representatives from non-commercial groups who have been working in this field. It is believed that these specifications represent the best of present practice, although additions may be made later to cover further material such as methods of applying correction factors for the baffle effect of the body of the wearer, for the difference between the pressure and the free field characteristics of the ear, and for possible leakage of sound between the ear and the ear insert, as well as standardized methods of measurement of instruments with bone conduction receivers and of carbon type hearing aids. Since sufficient information is not yet available to reach definite conclusions on these points, the code is offered in its present form for consideration by those interested in this subject.
Dependence of Tuning of Wind Instruments on Temperature
Authors: Young Robert W.
Published: September 2005

Observations by Pottle on the change of tuning of musical wind instruments with ambient temperature are here summarized by a single coefficient representing each instrument tested. The largest effect was observed on the BB♭ sousaphone where the increase with ambient temperature occurred at the rate of 2.6 cents/°C. This is equivalent to a fractional frequency coefficient of 1.6 × 10−3/°C. The cent is a logarithmic unit of frequency ratio such that 1200 cents equals one octave. A theory is developed by which the average temperature (and thus the velocity of sound) of the air within a wind instrument may be inferred from the empirically determined dependence of equilibrium tuning on ambient temperature. The theory also provides a qualitative estimate of the change in tuning which occurs while the instrument is first being warmed by the player's breath.
Generalized Plane Wave Horn Theory
Authors: Salmon Vincent
Published: September 2005

By the use of dimensionless variables and simplifying transformations Webster's plane wave horn equation is recast into a form permitting separation of the effects of horn contour and frequency. A generalized expression for the admittance also displays this separation. Further interrelations among the variables are developed which permit the formal synthesis of a horn from a given conductance or susceptance function. The conditions for realizability of the horn thus synthesized are discussed. Several applications of the results are presented, including a comparison with Freehafer's exact theory for the hyperbolic horn.
A New Family of Horns
Authors: Salmon Vincent
Published: September 2005

A new family of horns is synthesized in which the exponential forms a central member. This permits the effect of perturbations from the exponential contour to be estimated. From other members of the family unique impedance characteristics are obtained, and are discussed with possible applications in mind.
Acoustic Transmission through a Fluid Lamina
Authors: Rudnick I.
Published: September 2005

The acoustic wave equation is derived for a moving fluid medium in which all changes follow an adiabatic law, and it is shown that it may be written in a form which is very similar to the usual wave equation. Following this, the transmission and reflection coefficients for a fluid lamina in uniform motion are derived, and it is shown that it is only the component of motion in the direction of incidence which affects these coefficients. Finally, measurements are reported on the transmission coefficients of a non-turbulent thermal lamina whose motion has no component in the plane of incidence. The acoustic frequencies range from 2 kc to 14 kc and the angle of incidence from 0° to 89°. These measurements are compared with those calculated for a theoretically approximated lamina. The results are in reasonable agreement. It is shown that there is considerable transmission for angles greater than the critical angles and that for very thin lamina the transmission coefficient is a uniformly decreasing function of frequency.
The Analysis of Plane Discontinuities in Cylindrical Tubes. Part II
Authors: Miles John W.
Published: September 2005

The theory of plane discontinuities developed in Part I is applied to a “window” and change of cross section in tubes of both circular and rectangular cross section. In the case of the rectangular tube conformal mapping is introduced as an alternative approach to the problem. Reflection and transmission coefficients are determined from the equivalent circuit of Part I, and the theory is also applied to the analysis of certain types of cavity resonators. Finally, the experimental determination of equivalent circuit impedances is discussed.
A New Aspect of Ultrasonics
Authors: Sahay B. K.
Published: September 2005

With the present generators, it has been possible for the ultrasonics to reach up to the wave-length of visible light but there is a wide divergence between the order of their frequencies. The improvement of ultrasonic wave generators is suggested to reach still higher frequencies which might exhibit some of the dormant properties of the ultrasonics. The investigation of interaction of such high energy ultrasonics with matter is interesting, and it may decide whether the sound wave has also got a dual aspect.
Absorption and Scattering by Sound Absorbent Cylinders
Authors: Cook Richard K. , Chrzanowski Peter
Published: September 2005

The absorption and scattering of a plane wave of sound by an infinitely long circular cylinder, whose axis is perpendicular to the direction of propagation of the wave, are calculated. The surface of the cylinder is assumed to have a known normal acoustic impedance. The calculations take account of diffraction effects. Absorption measurements were made on long cylinders placed in a reverberation room, where the incident wave directions are at all angles to the axes of the cylinders, and were compared with the calculated values. In order to make the comparison, The reverberation room statistics appropriate for cylinders (which are different from the statistics for flat patches of absorbent material) are developed and applied. The theory predicts, and measurements confirm, that absorbent cylinders can have coefficients of absorption greater than unity. Fairly good agreement between the calculated and measured coefficients is found. The reverberation room statistics appropriate for spherical absorbers are also developed, although no measurements were made on spheres.
The Sound Spectrograph
Authors: Koenig W. , Dunn H. K. , Lacy L. Y.
Published: September 2005

The sound spectrograph is a wave analyzer which produces a permanent visual record showing the distribution of energy in both frequency and time. This paper describes the operation of this device, and shows the mechanical arrangements and the electrical circuits in a particular model. Some of the problems encountered in this type of analysis are discussed, particularly those arising from the necessity for handling and portraying a wide range of component levels in a complex wave such as speech. Spectrograms are shown for a wide variety of sounds, including voice sounds, animal and bird sounds, music, frequency modulations, and miscellaneous familiar sounds.
Visible Speech Translators with External Phosphors
Authors: Dudley Homer , Gruenz Otto O.
Published: September 2005

This paper describes some experimental apparatus built to give a passing display of visible speech patterns. These patterns show the analysis of speech on an intensity-frequency-time basis and move past the reader like a printed line. The apparatus has been called a translator as it converts speech intended for aural perception into a form suitable for visual perception. The phosphor employed is not in a cathode-ray tube but in the open on a belt or drum.
A Determination of the Wave Forms and Laws of Propagation and Dissipation of Ballistic Shock Waves
Authors: DuMond Jesse W. M. , Cohen E. Richard , Panofsky W. K. H. , Deeds Edward
Published: September 2005

Experiments to ascertain the wave forms and laws of propagation and dissipation of ballistic shock waves to large distances (80 yards) from the bullet trajectory are described. Calibers 0.30, 0.50, 20 mm, and 40 mm were studied. In every case an N-shaped wave profile was observed consisting of a sudden rise in pressure, the “head discontinuity,” followed by an approximately linear decline to a pressure about equally far below atmospheric and then a second sudden return, the “tail discontinuity,” to atmospheric pressure. The peak amplitudes of this disturbance are found to diminish about as the inverse 34 power of the miss-distance (perpendicular distance from the trajectory) while the period T′ (measured between the discontinuous fronts) increases about as the 14 power of the miss-distance for calibers 0.30, 0.50, and 20 mm. For 40-mm shells the amplitude decays a little faster, about as the inverse 0.9 power of miss-distance over the range studied. A theory taking account of the dissipation of the N-wave energy into heat is developed to explain the observed behavior. A method of measuring absolute N-wave amplitudes by observing the rate of change of period T′ with propagation is described. The theory leads to an absolute relationship at large distances between distance, amplitude, and period in which no arbitrary constants appear.
Motional Impedance Analysis Applied to a Dynamic Microphone
Authors: White J. E.
Published: September 2005

An article by R. D. Fay presents a method for calculating the complete performance at any frequency of an electro-magnetic speaker from a plot of its electrical impedance measured when the speaker is loaded by a closed air column of variable length. The present article applies this method to a dynamic microphone, yielding pressure sensitivity at lower audiofrequencies and providing a means of calculating microphone mechanical impedance and other characteristics. Improvement in accuracy which may be achieved by proper choice of area for closed air column is discussed.
Problems of High Altitude Communication
Authors: Weichbrod J.
Published: September 2005

The use by the Army Air Forces of high altitude for strategic bombing made the long standing and complex problem of voice communications these high altitudes a matter of considerable urgency. The problems of high altitude communication and solutions thereto dealing with the various components in the system, namely, the microphone, interphone amplifier, and headset receivers are discussed in a general way.
Transmission, Reflection, and Guiding of an Exponential Pulse by a Steel Plate in Water. II. Experiment
Authors: Osborne M. F. M. , Hart S. D.
Published: September 2005

In this paper are given the results of an experimental study of the interaction of an explosion wave with a water-backed steel plate. Data are given showing the dependence of the transmitted and reflected waves on the angle of incidence, and of the diffracted wave on position behind the plate. These data are illustrative of the use of the explosion wave in acoustical research. The plate acts as a filter, removing the high frequencies from the transmitted wave and the low frequencies from the reflected wave. The reflected wave is approximately constant in shape, or time scale, with varying angle of incidence. Its amplitude has a broad maximum at normal incidence. In addition to the reflected, transmitted, and diffracted waves, waves can travel along the plate, in which case the plate acts as a wave guide. As a consequence of dispersion in the guided waves, a precursor precedes the explosion wave as it travels along the plate. The dependence of the frequency, length, and amplitude of this precursor upon orientation of the plate, position, and time has been determined.
The Absorption of Ultrasonic Waves in Benzene
Authors: Quinn John
Published: September 2005

The coefficient of absorption of ultrasonic waves in benzene was measured as a function of the temperature by means of the sonic interferometer. The frequency-free coefficient varies from 0.66 × 10−14 to 0.85 × 10−14 over the temperature range from 7.2°C to 73.5°C. It appears that the absorption of ultrasonic waves in liquids is effected by two causes, viz., the viscosity effect deduced by Stokes, and a second effect of uncertain origin. In benzene, the second effect pre-dominates overwhelmingly and determines the over-all temperature dependence of the absorption coefficient.
Theory of the Propagation of Sound in Scattering and Absorbing Media
Authors: Givens M. P. , Nyborg W. L. , Schilling H. K.
Published: September 2005

A theory for the transmission of sound waves through a medium which is both scattering and absorbing is presented. The theory predicts that in such a medium curves of physical transmission loss against distance should be convex upward if the sound is detected by means of a directional microphone directed toward the source. The curve should be concave upward if the microphone is directed perpendicular to a line from the source. The theory also predicts the directionality of sound in the medium. The theory is applied to transmission through forests and through open air containing inhomogeneities.
Theory of Propagation of Sound in a Half-Space of Variable Sound Velocity under Conditions of Formation of a Shadow Zone
Authors: Pekeris C. L.
Published: September 2005

This paper treats the propagation of sound from a point source situated at some depth below the surface of a half-space in which the sound velocity decreases with depth. There is then a “limiting ray” which forms the boundary of a “shadow zone” into which no rays penetrate. Our chief interest is in the intensity of the diffracted radiation that penetrates into the shadow zone and its dependence on distance from source and on frequency. In Part I a detailed study is made of propagation of sound in a medium in which sound velocity decreases at a constant rate a with depth. It is found that inside the shadow zone the intensity I of monochromatic sound of frequency f falls off essentially exponentially with distance from the shadow boundary: I(P)=I(B)R0Re−Ar, A=5.93ca1f1, (A) where B denotes the point on the shadow boundary at the depth of the point of observation P, R0, and R the ranges of B and P, r=R−R0, and c the sound velocity. The intensity on the shadow boundary I(B) decreases with decreasing frequency on account of interference between the source and its image. As a result there exists at each point inside the shadow zone a frequency of optimum penetration. The solution inside the shadow zone is given in terms of normal modes. It is shown that in case of explosive sound the travel time for a point in the shadow zone is such as to indicate that part of the trajectory is covered near the surface with the surficial sound velocity. Details are given for computing the pressure-time curve in case of an exponentially decaying pulse at the source. In order to study the effect of a variable sound velocity gradient with depth, an investigation is made in Part II, using asymptotic methods, of propagation of sound in media in which c=c0/(1+αz+βz2)12. It is found that Eq. (A) is still valid for extremely high frequencies, where a now denotes the surficial velocity gradient. For moderate and low frequencies the decrement may be less or greater than that given by Eq. (A), depending on whether the velocity gradient decreases or increases with depth. In general, for high frequencies the decrement is largely determined by the surficial velocity gradient, while for low frequencies it is increasingly dependent on the velocity distribution in the deep layers. The general theory of propagation of sound in media with arbitrary vertical variation of sound velocity is developed from the stand-point of normal modes and asymptotic solutions. It is emphasized that for certain media the normal mode solution needs to be supplemented by branch-line integrals.
Ray Computation for Non-Uniform Fields
Authors: Saby John S. , Nyborg Wesley L.
Published: September 2005

A formula is derived which simplifies the computation and tracing of rays in non-uniform sound fields. In applying it, a field is first assumed to be equivalent to an array of horizontally homogeneous strata each with a uniform gradient of the speed of sound. Then the “range” of the ray through the whole array can be computed by the formula in one step, rather than several, to a degree of approximation considered adequate for many experimental situations. Special problems encountered in applying the formula under certain types of conditions are discussed. The method is particularly useful in the study of the propagation of ultrasonic waves through the atmosphere near the ground, where micrometeorological conditions often produce rather complicated gradient conditions.
Propagation of Plane Sound Waves in Rarefied Gases
Authors: Tsien Hsue-Shen , Schamberg Richard
Published: September 2005

If the density of gas is very small, the conventional Navier-Stokes equations are not accurate enough. The present investigation includes the effect of the so-called third approximation to the solution of Boltzmann-Maxwell equation as obtained by D. Burnett. The results of this more accurate calculation show that, even under extreme conditions, the velocity of propagation deviates from its usual value by only 2 percent.
On the Absolute Pressure Calibration of Condenser Microphones by the Reciprocity Method
Authors: DiMattia A. L. , Wiener F. M.
Published: September 2005

Through cooperation among the Bell Telephone Laboratories, the National Bureau of Standards, and the Electro-Acoustic Laboratory at Harvard University, the technique of obtaining absolute pressure calibrations of condenser microphones by the reciprocity method has been perfected and standardized to a gratifying degree of accuracy. Numerical data are given for a Western Electric Type 640-AA instrument which was calibrated at the three laboratories in succession, showing the accuracy to be expected at the present state of the art.
Violation of the Reciprocity Theorem in Linear Passive Electromechanical Systems
Authors: McMillan Edwin M.
Published: September 2005

A simple energy argument is used to show that the theorem of reciprocity is not necessarily valid for linear passive electromechanical systems. It is found that in the case of crystal or electrostatic transducers the theorem is satisfied, while in the case of magnetic or electrodynamic transducers it is satisfied in magnitude but not in sign. It is further shown that by combining the two types of transducers, systems can be constructed that violate reciprocity in magnitude.
A Fifty Horsepower Siren
Authors: Jones R. Clark
Published: September 2005

This paper contains a description of the theory, construction, and testing of a siren with an acoustic output of fifty horsepower, at an efficiency of seventy percent. The siren is of the traditional type in which the air stream from a compressor passes through an orifice which is opened and closed at an audiofrequency. Part I contains a development of the theory on which the design was based. The theory is developed with the aid of an equivalent circuit diagram (Fig. 1) in which the various acoustic impedances are represented as lumped circuit elements. The theory is for the most part based on the customary linear equations for sound propagation, but the non-linear nature of the impedance of the port is taken into account. Mere inspection of the equivalent circuit diagram is sufficient for the understanding of the considerations which are important for the obtaining of a high efficiency. According to this theory the best efficiency can be realized in a siren when the orifice is provided with a suitable acoustic horn, when the excess pressure of the air supplied by the compressor is small compared with the absolute pressure of the atmosphere, and when the operations of opening and closing the port occupy a small fraction of the period of one cycle. Expressions are obtained for the theoretical efficiencies of several types of sirens, and are found to be near one hundred percent for a good design. Part II contains a description of the siren which was constructed to operate with a compressor that supplied 2500 cubic feet of air per minute at a pressure of five pounds per square inch. The siren contains six ports with a total area of 22 square inches, which are opened and closed by a rotary chopper at a frequency of about 500 cycles per second. Each of the ports is provided with an exponential horn whose cut-off frequency is 125 cycles per second. The theoretical efficiency of this siren is computed to be between 70 and 90 percent. Part III is devoted to a description of the testing of the siren and a discussion of the results obtained. The tests indicated that at full output the siren produces an average level of 138 db at a distance of 100 feet. The measured level at the mouth of the horns is 174 db, and the calculated level in the throat of the horns is 184 db above 10−16 watt per square centimeter. The level in the throat of the horns corresponds to a sound intensity of 260 watts per square centimeter. The most reliable method of determining the efficiency, based on thermodynamic principles, indicates that the efficiency of the utilization of the available energy in the air from the compressor is about 72 percent.
The Masking of Speech by Sine Waves, Square Waves, and Regular and Modulated Pulses
Authors: Stevens S. S. , Miller Joseph , Truscott Ida
Published: September 2005

The ability of three standard wave forms to mask speech, by raising its threshold of perceptibility, was measured as a function of the intensity and frequency of the masking signal. Depending on the other parameters of the interfering signal, optimal masking is produced when the fundamental frequency lies in the range 100 to 500 c.p.s. Intense sine waves mask best when their frequency is about 300 c.p.s., whereas for weaker sine waves the most effective frequency is about 500 c.p.s. Square waves are less critical as to frequency and intensity; fundamental frequencies between about 80 and 400 c.p.s. mask with approximately equal effectiveness. Pulses of 10-microsecond duration are most effective at a prf of about 200 p.p.s. When the time interval between successive pulses is made irregular (random interval-modulation), their ability to mask speech is dramatically increased. The increase in masking is a function of the original prf, the rate of modulation (determined by the spectrum of the modulating voltage), and the range of modulation. By a proper adjustment of the parameters of its random interval-modulation the train of pulses can be made to sound like a band of white noise.