bluuebunny/crossref_metadata_2025 huggingface dataset:
A Method of Measuring the Velocity and Absorption of Sound in Liquids
Authors: Galt J. K. , Pellam J. R.
Published: September 2005

Measurements of the velocity and absorption of sound at 10 to 30 mc in liquids have been made using some of the pulsing equipment developed by Radiation Laboratory for radar purposes. Accuracies of 5 to 10 parts in 10,000 are quite practical to obtain, and absorptions have been measured to within 1 to 5 percent. A tank has been designed which includes the liquid, a movable crystal projector, and a steel reflector. A one microsecond sound pulse travels in the liquid from projector to reflector and back. The returned signal is fed to a radar presentation unit and appears there at a time determined by the time required for the pulse to travel the path in the liquid. Velocity is determined by measuring the change which occurs in the time at which the signal appears when the liquid path length is changed by a measured amount. Time changes are measured from the intervals between markers put out by a crystal controlled marker circuit. Path length changes are read from a micrometer screw on which the crystal mount moves. Absorption is determined from the electrical attenuation required to maintain the signal amplitude constant as the path length is changed.
Transient Analysis of Linear Systems, Using Underwater Explosion Waves
Authors: Osborne M. F. M. , Carter J. L.
Published: September 2005

The indicial admittance, or response to the unit function, of a simple mechanical system, a tourmaline crystal hydrophone, has been determined from its response to a small underwater explosion wave. The indicial admittance is simply related to the observed response to the explosion wave—the observed response is just the indicial admittance “wrapped around” an exponential, e−t/τ. The relative frequency calibration of two hydrophones obtained by Fourier analysis of their responses to the explosion wave is in good agreement with the direct continuous wave comparison. The peak pressure of the explosion wave is also determined from this Fourier analysis. It is suggested that the explosion wave can be used as a tool in acoustical “circuit analysis” in much the same way that a square wave generator is used in electrical circuit analysis.
Theory of the Transmission of Reverberant Sound through Double Partitions
Authors: London Albert
Published: September 2005

An expression for the sound transmission loss of an obliquely incident plane wave striking a double partition consisting of two identical septa separated by an air space has been derived. It is assumed in the theory that each septum is infinite in extent and behaves like a rigid mass. Previous investigators have shown that in the case of a normally incident wave, there exists a characteristic frequency fc for the air-mass sandwich for which there is total transmission of sound, given by fc = 12π(2ρc2md) 12, where ρ is the density of air, c the velocity of sound in air, m the mass per unit area of the septum, and d the air space thickness. In the present investigation it is shown that Eq. (1) is a special case of a more general expression which holds for any angle of incidence θ, i.e., fθ = 12π cos θ(2ρc2md)12 (2) or, a wave incident at angle θ will be totally transmitted at frequency fθ, given by (2). Since in a reverberant sound field energy strikes the partition at random angles of incidence, it follows that total transmission will not be observed at any frequency. While there may be a particular component of the sound field which has zero transmission loss, there will always exist other waves which do suffer a loss. The expression for the transmission loss corresponding to a wave at angle θ may be integrated over all angles of incidence in accordance with the usual reverberant sound field statistics. The resulting average transmission loss expression may be written as a function of two non-dimensional parameters: (1) the mass ratio, μ = ρd/m, (3) i.e., the ratio of mass per unit area of air in the air space to the mass per unit area of the septum and (2) the frequency ratio parameter, r = f2/fc2. (4) A family of transmission-loss versus frequency-ratio curves with μ as a parameter, having general applicability to any double partition, is plotted. Comparison of the results of this theory with actual double walls used in building construction shows that in some cases the latter are poorer than the theoretical predictions, possibly due to: (1) solid sound conducting paths existing between septa due to studs, and the like, (2) the existence of transverse standing waves in the air space, (3) the occurrence of bending waves in the septa, (4) and the appearance of resonance frequencies of the septa. The results of measurements on some experimental panels designed to estimate the extent to which these worsening influences are operative will be discussed.
Propagation of Sound over Absorbent Surfaces
Authors: Cook Richard K.
Published: September 2005

A mathematical study is made of the propagation over an infinite plane absorbent surface, due to a point source of sound located in the surface. It is assumed that the state of the sound field at the surface is determined by the normal impedance of the material. The results can be applied to determine deviations from the inverse square law when sound is propagated over long distances. Comparisons between the computed effects and published measurements of the transmission of sound over long distances are made.
Absorption of Sound by Absorbent Spheres
Authors: Cook Richard K. , Chrzanowski Peter
Published: September 2005

The absorption of a plane wave of sound by a spherical absorber is calculated. The calculations are based on the assumption that the state of the sound field at the surface is determined by the normal impedance, which is measured experimentally. By means of previously developed statistics, the absorption coefficients for the spheres in a random sound field are computed from the plane wave absorption coefficients. Absorption measurements made on spheres placed in a reverberation room are compared with the computed values. There is no uncertainty for spheres about the absorption at oblique incidence, as there is for cylinders and flat patches of absorbent material.
An Integrating Audiospectrometer
Authors: Rudmose H. W. , Clark K. C. , Carlson F. D. , Eisenstein J. C. , Walker R. A.
Published: September 2005

Equipment is described which measures the distribution of average power in a complex electrical signal as a function of frequency. The wave form to be studied is separated into 14 frequency bands extending from 20 to 9000 c.p.s. The mean square of the amplitude in each band is integrated and recorded on mechanical counters during a test period of approximately 30 seconds. If a calibrated microphone with a suitable response is used, these analyses will give spectral distributions of average acoustic power. Some examples are shown of measurements of the spectra of speech sounds.
Development of Midget Earphones for Military Use
Authors: Pearson H. A. , Mundel A. B. , Carlisle R. W. , Knauert Wm. , Zaret M.
Published: September 2005

In order to meet the military requirements for a headset that could be worn under the MK-1 helmet, midget hearing aid receivers were redesigned for this application. Data is presented showing characteristics of the original design adopted and of subsequent improvements resulting in improved performance. Some of the methods for securing adequate performance in quantity production and methods for 100 percent inspection of frequency characteristics are described.
Motional Impedance Analysis Applied to a Dynamic Microphone
Authors: White J. E.
Published: September 2005

The receiver analysis developed by R. D. Fay gives a method for calculating the complete performance of an electromagnetic speaker from a plot of electrical impedance measured when the speaker is loaded by a closed tube of variable length. This of course includes the performance of the speaker as a microphone, although the statement is not explicitly made. The present article applies the above analysis to a dynamic microphone and compares the sensitivity thus obtained with an independent calibration at lower audiofrequencies. This method yields a primary calibration, in that neither calibrated source nor comparison microphone is required. The high mechanical resistance of a dynamic microphone and its low coupling constant, as compared with an electromagnetic speaker, result in a much smaller variation in electrical impedance, with changing air load. The variation is of the order of 5 percent of the minimum impedance, as compared with perhaps 80 percent change in speaker impedance. The cross-sectional area of the terminating tube is found to be of considerable importance. The effect of this choice of tube area on over-all accuracy is discussed.
Noise and Vibration Reduction in Felt Mountings
Authors: Hardy H. C. , Tyzzer F. G.
Published: September 2005

Resonant curves of loaded felt pads in compressional vibration give values for the damping and dynamic stiffness which show that felt in vibration is quite different from an equivalent perfect spring with viscous damping. The un-symmetrical resonance curves and the fact that, within experimental error, the stiffness is inversely proportional to the square root of the thickness indicate a decrease in stiffness with increasing amplitude. The increase in stiffness with pressure is so large that the ratio of dynamic elastic modulus to pressure (stiffness over mass) does not vary greatly between pressures of three to one hundred pounds per square inch. In this range the natural frequency of a mass on a felt pad is determined by the thickness of the pad rather than by its area and static load. An analysis of the performance of felt in reducing vibration transmission shows that its effectiveness is limited in most cases to frequencies above forty cycles per second. Practical installations have been studied and tables drawn up to give the acoustical engineer “handbook” information for the solution of problems in vibration reduction.
Embossed Recording
Authors: Morse Milton
Published: September 2005

This paper discusses the ideal requirements for high fidelity sound embossing. It discusses the effect of stylus tip radius with relation to wave form distortion in the embossed groove. It also discusses the maximum amplitude of the embossed groove with relation to frequency. A conclusion is reached that the maximum ratio is one to ten. A nomograph is developed which shows the relationship between the following six quantities: stylus tip radius, amplitude, frequency, linear velocity, wave slope, and attenuation. This nomograph facilitates the design of a recording system where the limits on the above quantities are required.
Stratification of Sound Scatterers in the Ocean
Authors: Duvall G. E. , Christensen R. J.
Published: September 2005

A study of the diurnal migration and geographic extent of the deep layers of sound scatterers found in the ocean has been made with fathograms and oscillographic records of reverberation received with vertically directed projectors. The deep scattering layer was observed consistently throughout the area investigated. The principal features of the diurnal observations are the movement of the deep scattering layer toward the surface in the evening and away from the surface in the morning. Observations of the diurnal migration of plankton made during the acoustic observations indicates that the cause of the sound scattering is associated with organisms. Some observations indicate that the scatterers near the surface are found in “swarms” rather than in well-defined strata. With conditions of strong downward refraction, the layer acts somewhat like a false bottom, giving rise to a pronounced increase of horizontal reverberation strength which is not observed in the absence of strong downward refraction. Forward scattering from the deep layer is observed in transmission measurements as a ragged “pip” following the signal.
The Discrimination of Transducers against Reverberation
Authors: Schafer T. H.
Published: September 2005

The directivity index characterizes the directional properties of an electro-acoustic transducer with respect to its ability to radiate sound power or discriminate against noise originating in the surrounding medium. Of greater interest in echo ranging is the transducer's ability to discriminate between the echo from the target at which it is pointed and the reverberation returned from all directions. This discrimination may be measured by quantities called reverberation indices, one of which concerns volume reverberation and the other surface and bottom reverberation. In this paper, the directivity and reverberation indices are defined and their inter-relations are studied, and approximate formulas are obtained that enable them to be calculated without performing tedious integrations.
Attenuation of Underwater Sound
Authors: Everest F. A. , O'Neil H. T.
Published: September 2005

The results of sound attenuation measurements made in San Diego Harbor are presented. The source was supported from a dock and the microphone from a small boat, at fixed depths, and the distance between was varied by moving the boat. Sound pressure measurements were made over a 1-km course for frequencies from 128 c.p.s. to 200 kc. Refraction effects were negligible. The effects of reflections at the upper and lower surfaces were removed from the measurements by comparing envelopes of the observed interference pattern with theoretical envelopes computed by a method of images for various assumed values of the amplitude reflection r for the bottom. The phase angle of this coefficient is immaterial. Assuming the magnitude of the coefficient to be |r| = 0.5, the upper limit of the attenuation coefficient a was found to increase from about 2 db/km at 20 kc to about 32 db/km at 100 kc. The uncertainty in |r| is not very serious since the 100-kc upper limit of a is only increased to about 34.5 db/km if |r| is assumed to be 0.7 and is only reduced to 25 db/km if r is assumed to be zero. Below 20 kc the values of a are too small to be measurable by this procedure. For 200 kc a tentative estimate of 60 db/km was obtained from a single run out to only 150 meters from the source. These results suggest that a varies approximately as the square of the frequency to about 60 or 80 kc and that the rate of increase with frequency then begins to decrease.
Echo Formation on Simple Surfaces
Authors: Mongan C. E.
Published: September 2005

When a group of supersonic waves which are being propagated in a fluid strike a surface having a different acoustical impedance from the fluid, an echo is formed. The explicit analytical statement of the echo in terms of the original wave and the geometry of the surface is difficult, more particularly if transients are to be considered. An experimental approach appeared more promising. A laboratory technique was devised which permits the observation of the echo formation. Using this method the forms of echoes from planes, cylinders, and spheres have been observed. The echoes from a plane are similar to the original waves. The echoes from spheres and cylinders show a deviation from the form of the incoming wave group, which deviation isz characteristic of the curvature of the reflecting interface.
A Curvature Meter for Use in Disk Recording
Authors: Sepmeyer L. W.
Published: September 2005

A limiting factor in the reproduction of disk recordings with a modern reproducer is the tracing distortion arising from the finite size of the reproducing stylus. The sharpest groove modulation which can be reproduced is that whose smallest radius of curvature is slightly larger than the tip radius of the reproducing stylus. It is, therefore, desirable to monitor the cutting of disk records with a meter whose indication is based upon this curvature limitation, rather than with a conventional volume indicator. When using a volume indicator alone, overmodulation by as much as 20 db is possible. The theory and construction of such a curvature meter are discussed in this paper.
Transmission of High Frequency Sound Well Beneath the Ocean Surface
Authors: Sheehy M. J.
Published: September 2005

A few experiments have been performed in which thirty-millisecond pulses of sound of 24,000 cycles per second frequency were emitted every second at depths of 150, 300, 500, and 1000 ft. by a relatively non-directional projector, and were received by similar units at the same depths after having travelled 100 to 4000 yards. A recording technique was used which made it possible to resolve the direct and surface-reflected components. Transmission conditions near the surface were poor during the experiments, and the transmission was found to improve as the projector and receiver depths increased. However, there was no significant improvement for depths greater than 300 feet. The attenuation was about 5 db/1000 yd. in addition to the loss caused by the assumed inverse-square divergence of the sound energy. The emitted pulses were square-topped and all of the same amplitude, but the amplitudes of the received pulses fluctuated. The fluctuation of the directly transmitted pulses showed a general tendency to increase with range in proportion to the one-half power of the range. The magnitude of the fluctuation changed from about 5 to 10 percent of the average amplitude at short range to 40 to 50 percent at long range. The fluctuation of the surface-reflected component was greater than that of the direct component and did not depend on range.
Types of Underwater Sound Transmission
Authors: Young Robert W.
Published: September 2005

Simple theories which assist in understanding certain aspects of underwater sound transmission lead to types of transmission which may be described as: image interference, refraction shadow, simple bottom reflection, and attenuation with divergence. When the experimental data are available on a standardized plot, transparent overlays can be used conveniently to identify some of these types and to evaluate graphically the associated parameters (such as an attenuation coefficient in db per unit distance). Oceanographic conditions are described which may give rise to these types of transmission.
The Propagation of Underwater Sound at Low Frequencies as a Function of the Acoustic Properties of the Bottom
Authors: Ide John M. , Post Richard F. , Fry William J.
Published: September 2005

The correlation and theoretical analysis of a large number of transmission measurements made in the Potomac River and Chesapeake Bay areas warrants the conclusions which follow. Given a source of audiofrequency sound in water, the sound pressure level which may be measured at appreciable distances will be influenced in a complicated way by the boundaries, especially by the bottom. The sea bottom may be classified by its behavior for sound as “soft,” “hard,” or intermediate in character. Specifically, the velocity of sound and the density of the bottom may be estimated from acoustic measurements (hydrophone soundings and range runs), by sampling, and from hydrographic data. The effect of the boundaries on sound propagation from a ship-mounted source may be determined from an analysis of the normal modes of vibration of the acoustic system of the sea between surface and bottom. The analysis is particularly effective for frequencies at which the wave-lengths are comparable to the physical dimensions of the system. For low frequencies and given bottom conditions, the most important factor governing the propagation is the ratio of the depth of the water to the free wave-length of the sound. A detailed interpretation of the observed transmission phenomena may be given in terms of the initial stimulation, the relative attenuation, and the phase velocities of the modes. Damping and phase constants may be determined for each mode by means of special charts which give the propagation and distribution constants in terms of the acoustic properties of the system. The over-all transmission is given as the sum of the effects produced by the individual modes. “Damped” transmission, which occurs over “soft” bottom, is always accompanied by considerable attenuation, the amount ranging in practice from about 12 db/1000 ft. as a lower limit to about 40 db/1000 ft. under conditions of strong bottom absorption. “Soft” bottoms are frequently encountered in land-locked basins such as fiords, estuaries, and river channels. “Guided” transmission which occurs over “hard” bottom at all frequencies higher than a minimum critical frequency, is characterized by negligible damping due to bottom absorption and by an attenuation with distance caused primarily by cylindrical spreading from the source. The latter amounts to 3 db per distance double. “Hybrid” transmission, which occurs over hard bottom at frequencies below the lowest critical frequency, is associated with large and erratic damping from bottom absorption. The critical frequency depends upon the hardness of the bottom, and is slightly higher than the frequency for which the water depth is equal to a quarter wave-length. The acoustic system of the sea between the surface and a hard bottom thus acts as if it were a high pass filter, analogous to an electromagnetic “wave guide.” This type of sound transmission is very commonly encountered, since hard bottom predominates along the sea coasts of all the continents.
Some Acoustic Properties of Marine Fouling
Authors: Fitzgerald J. W. , Davis M. S. , Hurdle B. G.
Published: September 2005

The fouling of transducers by marine organisms imposes a handicap on the use of underwater sound equipment, especially in low latitudes. Sensitivity and sound emitting power are reduced. In order properly to plan counter-measures, quantitative data on the effect that fouling organisms have on the reflection and absorption of sound have been accumulated by measuring a series of test panels which were exposed to fouling in Florida waters. The test panels were measured periodically, using a frequency of 24 kc. The extent of absorption due to fouling can reach a magnitude of 3 db per inch of thickness. Distortion of transducer patterns is another effect of the fouling. Anti-fouling methods are described. The acoustic attenuation of certain anti-fouling paints is found to be negligible.
Surface Reflection of Short Ultrasonic Pulses in the Ocean
Authors: Urick R. J. , Saxton H. L.
Published: September 2005

In the reception of a continuous ultrasonic signal from a submerged source by a transducer near the surface of the ocean, an observed time variation of intensity may be attributed to interference between energy received by the direct path and that reflected from the surface. The transmission of short ultrasonic pulses from the submerged source enables the separation in time of the direct and surface-reflected waves at the receiver, permitting a comparison of amplitudes. An experimental setup for these measurements included a trainable, directional source mounted on a submarine. The ultrasonic pulses emitted were adjustable in length and repetition rate. A trainable and tiltable receiving transducer was mounted beneath a surface vessel in which an amplifier and an oscilloscopic presentation were provided. Observations were made at various ranges with the source on different bearings, with the submarine at various depths, and with different sea conditions. Representative photographs of the c-r tube presentation are shown and discussed.
Reflection of Sound from Rough Surfaces
Authors: Bergmann Peter G.
Published: September 2005

A theoretical investigation has been carried out of the scattered sound when a plane sound wave is incident on a surface which differs from an infinitely extended plane surface by small random irregularities. While the methods applied are in the nature of an approximation method, it is believed that they lead to valid results in many practical cases. By means of a generalized Fourier transformation treatment, it is found that the directivity pattern of the scattered wave intensity depends algebraically on the so-called power spectrum of the surface irregularities. The power spectrum is here defined as the Fourier transform of the two dimensional autocorrelation coefficient of the deviations of the scattering surface from the perfect plane.
Supersonic Radar Trainers
Authors: Teeter Charles E.
Published: September 2005

The idea of using the propagation of supersonic waves in liquids to simulate the propagation of microwaves in air was first thought of by the British. It was adapted during the war to a series of trainers for various types of radar equipment. The developments at the M. I. T. Radiation Laboratory were primarily for airborne radars intended for navigation and bombing, although a Loran trainer was also constructed. The essential problem in a supersonic trainer divides itself into two parts—the propagation of a supersonic beam as nearly as possible identical in pattern with the microwave pattern sent out by the radar, and the reflection of that beam by a supersonic map which will give a return as nearly as possible like the radar return from the actual terrain. Study of these problems leads to many interesting facts concerned with supersonic propagation in liquids. It is hoped that peace time research will have an opportunity to explore much more fully the theory of sound propagation and reflection as exemplified in the supersonic radar trainer, as well as perfecting this device and making it more nearly universal in its application to all types of radar sets.
High Frequency Whistles
Authors: Nyborg W. L. , Schilling H. K. , Thorpe H. A.
Published: September 2005

Two types of whistles will be described which have been useful as high power sources for work in atmospheric ultrasonics. The first has an annular windway, an annular lip and cavity; weighs 2.5 oz.; is capable of delivering 0.1 watt at mouth blowing pressure and 10 watts when the pressure drop across the whistle is 8 lb./sq. in., and the air flow is 10 cu.ft./min. The second weighs 0.5 oz.; puts out 0.005 watt when mouth blown, and 0.5 watt when the airflow is 0.5 cu.ft./min., for a gauge pressure of 20 lb./sq. in. An experimental study of ultrasonic whistles has been carried out to discover how the intensity and frequency of their output depends upon their dimensions and upon the airflow. The relationships noted can be explained qualitatively by assuming that the whistle is a system of two oscillators, the first being the air in the cavity, and the second the “jet and edge,” which functions as driver and produces edge tones having properties similar to those observed by Brown in his studies of edge tones of lower frequencies and at lower air velocities.
Temperature Coefficient of Ultrasonic Velocity in Solutions
Authors: Willard G. W.
Published: September 2005

Utilizing ultrasonic light-diffraction methods, extensive measurements have been made at ten megacycles of the temperature dependence of ultrasonic velocity in liquids and liquid mixtures. All single liquids tested, except water, were found to have large negative temperature-coefficients in the temperature range of zero to 80°C. Water has a large positive coefficient at room temperature, decreasing to zero at 74°C, and then becoming negative (with a peak velocity of 1557 meters/sec.). Solutions in water of various other liquids (and of some solids) give parabolic velocity vs. temperature curves like that for water but with the peak-velocity and peak temperature values shifting with the concentration of the solution. In general increasing the concentration raises the peak velocity slightly and lowers the peak temperature markedly from the values for water alone.
The Velocity of Sound in Superheated Steam
Authors: Woodburn James
Published: September 2005

Experimental apparatus has been designed and constructed for determining the velocity of sound in superheated steam for various pressures and temperatures. The temperature range was 300° to 800°F, the pressure range was 25 to 100 lb./sq. in. abs., and the frequency used was 575 kc. The interferometer is of the movable piston type and is constructed entirely of stainless steel in order to withstand higher steam pressures and temperatures for future work. The velocity measurements are good to ±0.11 percent, and the measurements of the state of the steam are good to ±0.4 percent. The existing values of the ratio of specific heats of superheated steam agree with the acoustic determinations within the experimental errors of the apparatus.
The Use of Irregular Boundaries in Studio Design
Authors: Morrical K. C.
Published: September 2005

Early experiences with the use of irregular surfaces for studios are described. Reasons for employing such surfaces are given together with some results.
Convex Wood Splays for Broadcast and Motion Picture Studios
Authors: Rettinger Michael
Published: September 2005

The purpose of this paper is to present both theoretical and experimental findings in the use of convex wood splays for broadcast and motion picture studios. After a discussion of the term “diffusion,” there follow some calculations intended to circumscribe the term mathematically. An experiment is described using pillars for added diffusion in a sound recording studio, and some criteria are enumerated for the use of such splays in studios.
A Method of Reducing Amplitude Distortion in Engraving Lateral Electrical Transcriptions
Authors: Harrison C. E.
Published: September 2005

A method was developed to minimize the amplitude distortion that arises from the failure of the curved path of the reproducing head to coincide with the straight radial path of the cutting head. A mathematical analysis of the vectors involved in both recording and reproducing 16″ electrical transcriptions was the first step. An approximate solution to the problem was found in an adjustment of the orientation of the track of the carriage of the recording head to permit the cutting needle to lead behind the conventional radial path for the first half of the recording time and then lag it for the remaining half. The new path of the cutting needle is a straight line at a seven degree angle with the conventional radial path, crossing the latter at the center of the usual recording zone. A secondary axial adjustment of the cutting needle in the recording head is necessary to keep the face of the needle perpendicular to the direction of movement of the disk beneath it. No change is necessary in the standard reproducing apparatus. Harmonic analyses of electrical reproductions of sine waves recorded by this method have shown an over-all reduction of amplitude distortion from 8 percent, to less than 2 percent.
Some Physical Aspects of Magnetic Recording
Authors: Kornei Otto
Published: September 2005

The various factors controlling the performance of a magnetic record, viz., magnetic properties of the recording medium, its physical dimensions and velocity, are discussed and evaluated. Based on these partially experimental, partially theoretical findings, a picture of the mechanism of longitudinal magnetic recording and reproducing is presented and a qualitative analysis of the frequency response curve given. Its shape is found to depend, for a given recording medium, on the effects of demagnetization, limited magnetic penetration, and the finite width of the exploring gap. The features of two improved recording media, namely, the electroplated and the powder coated type are described in the light of the new findings.
Wow Meter
Authors: Hansen W. W.
Published: September 2005

This instrument was designed to make a graphical record of small speed variations in any sound recorder capable of producing a millivolt output at about 1000 c.p.s. It consists of the following sequence of components: amplifier→clipper→bandpass filter→frequency discriminator→demodulator→oscillograph. The clipper eliminates amplitude variations and the filter passes only the fundamental frequency of the clipped wave. The discriminator is a parallel T equivalent of a Wien bridge balanced near the upper cut-off frequency of the filter. The oscillograph is a model BL-201 direct-inking instrument made by the Brush Development Co. Over-all calibration of the wow meter is accomplished by an RC oscillator and calibrating switch which changes the oscillator frequency 1 percent. Preliminary estimates and tests indicate that speed variations of less than 0.1 percent can be measured reliably if these variations occur between 12 and 100 per second.
Master Wire Recorder
Authors: Boyers J. S. , Zenner R. E.
Published: September 2005

In the preparation of commercial recordings, the live performance is usually recorded by the use of equipment of the highest possible quality, so that the duplicates made from the master record may still be of satisfactory quality despite the losses which are inevitable in any duplication process. A wire recorder has been constructed for use as a master recorder. Design of the unit is discussed, including (1) mechanical drive system, (2) electronic circuits, and (3) properties of the recording wire and heads.
Recent Developments in Magnetic Recording for Motion Picture Film
Authors: Camras Marvin
Published: September 2005

Magnetic recording gives an ideal sound system for use in motion picture work. Equipment for making the record is light, simple, and inexpensive. The material can be edited by “cutting,” or by erasing a re-recording. Sound can also be added after the pictures are complete. Conventional projectors are used with the magnetic system. Response comparable to optical recording is obtained with low distortion and noise. Recording heads, circuits, and mechanical drives for use with various systems are described.
Vibrational Modes of a Right Circular Cylinder
Authors: Kendig Paul M.
Published: September 2005

A right circular cylinder was constructed of thin oxide annealed nickel tape. A thin coat of thermosetting cement was applied to the tape after it was annealed. The tape was then wound on a cylindrical mandrel and kept taut with a weight while it was consolidated in an oven, thus producing a rigid thin-walled shell. The cylinder was toroidally wound with copper wire with a direct current used to provide magnetic polarization. The magnetostrictive property of nickel was used to drive the transducer. Two coupled fundamental modes were observed whose frequencies are given by the following relationship: ν = 12πa{[j2 + 1 ± ((j2 − 1)2 + 4j2σ2)121 − σ]nρ}12 where ν = frequency, a = mean radius, n = rigidity modulus of elasticity, σ = Poisson's ratio, ρ = density, j = πa/l, l = length. These two frequencies correspond to a longitudinal mode and a radial mode which are mechanically coupled, the coupling coefficient being simply Poisson's ratio. Experimental results indicated excellent agreement with the theoretical relationship above. The theory indicates that the amplitude of radial vibration varies along the length of the cylinder, with the greatest amplitude in the middle. This should produce a shaded diffraction pattern as the transducer is rotated about an axis perpendicular to the longitudinal axis of the cylinder.
The Diffraction of a Progressive Sound Wave by the Human Head
Authors: Wiener Francis M.
Published: September 2005

The increase in sound pressure at the eardrum over the free-field pressure in a progressive sound field is caused by a combination effect of diffraction by the head and pinna and resonance in the auditory canal. In an earlier paper the pressure distribution in the auditory canal was determined on a number of subjects in a plane progressive sound field. Expressed in terms of the ratio of the sound pressure at the eardrum to that at the entrance of the ear canal, it was found to be essentially independent of the orientation of the observer with respect to the sound source, as might be expected from theory. This fact makes it possible to separate the two effects and to measure the diffraction by the head by inserting a probe microphone near the entrance of the ear canal and comparing the sound pressure measured there with the free-field pressure. To the obstacle effect of head and pinna, so determined, the pressure increase due to resonance in the auditory canal is to be added. The subjects were placed in front of a loudspeaker in a room free from acoustic wall reflections. The measurements were carried out in an essentially plane progressive wave over the frequency range extending from 200–6000 c.p.s. and covered a range of azimuths of 360 degrees. From these data the average ratio of the sound pressures at the two eardrums for six observers was determined as a function of frequency and azimuth. This quantity, important in the mechanism of binaural localization, was found to be in fair agreement with the values obtained by Sivian and White from threshold measurements.
The Electroacoustic Reciprocity Theorem
Authors: Kennedy R. J.
Published: September 2005

This paper outlines the theory and results of the use of the reciprocity theorem in the case of an acoustic field containing transducers; the free field is treated as a limiting case. The necessary and sufficient conditions on transducers and medium in order that the theory may be applicable are derived.
The Propagation of Sound in Gases at Reduced Pressures
Authors: Delsasso L. P.
Published: September 2005

As a preliminary step in the investigation of the propagation of sound in gases at reduced pressures, apparatus has been constructed which records both the resonant frequency and sharpness of resonance of short cylindrical gas columns. Good agreement is observed in nonreactive gases with the Kirchhoff-Helmholtz expression for velocity in tubes to pressures as low as 1 mm Hg. Reduction in resonant frequency as great as 8 percent are observed.
A Modern Version of the Old Theory of Telephone Quality
Authors: Fletcher Harvey
Published: September 2005

In 1921 a method was formulated for calculating the articulation—the percent of speech sounds interpreted correctly during a telephone conversation—from the physical characteristics of the telephone system and the noise environment of the listener. This paper describes this empirical theory as recently revised to correspond to modern techniques. A quantity A is calculated which is called the articulation index and which is related to the various kinds of measured values of articulation. In particular, if s is the percent of the fundamental sounds correctly perceived by the listener A = −p log (l-s), where p is a factor depending upon the skill of the crew making the articulation tests. For a well-practiced crew the value of p is between 0.5 and 0.6. The value of A is calculated by the equation A = F⋅V⋅E, where F is the maximum value of A, and V a factor which is zero at threshold intensity of the speech received by the listener and grows as the received speech intensity increases reaching unity for intensities between 60 and 70 db above threshold. The factor E is unity below this intensity but decreases from unity to 0.85 as the intensity levels increase to 60 db above these levels. The factor F is calculated by the equation F = ∫0∞D⋅Wdf, where D is a function of the frequency f, and W is a function of the relative response of the system. The functions D and W have been determined directly from articulation data. The factors V(x) and E(x) are determined directly from articulation data. The value of x for systems in a quiet place is equal to a weighted average of the response of the system. When a noise is present which produces a masking M at each frequency at the listener's ear, the same functions are used for determining F and V, but the response R at each frequency is replaced by R − M. However, for this case the x in E(x) is increased by an amount Δ, a quantity calculated directly from the masking M of the noise and the intensity of the received speech.
The Effect of Airplane Noise on Human Efficiency
Authors: Egan J. P. , Stevens S. S. , Waterman T. H. , Miller Joseph , Knapp R. H.
Published: September 2005

Exposure to intense airplane noise (115 db) for periods as long as 7 hours did not affect the performance of 5 subjects on a wide variety of psychological, physiological, and psychomotor tests. The noise was sufficiently intense to cause marked temporary hearing losses and tinnitus. It interfered seriously with communication and was reported as “annoying” by the subjects, but its effects on general efficiency were apparently nil. Following an extensive training period designed to minimize subsequent change in performance due to learning, the subjects were tested throughout 16 seven-hour sessions, half of which were “noisy.” Eighteen different measures were applied to sample such functions as: motor coordination, reaction time, muscular tension, metabolism, breathing, speed of eye movement, speed of accommodation, dark adaptation, coding, reversible perspective, steadiness, etc. For many of the tests the data were so extensive that differences in performance of the order of 1 percent could have been detected with high reliability. Other functions, particularly those of a physiological nature, depended so much on the individual tested that generalizations were impossible. In general, the results of these experiments agree with common sense: although as a subjective experience noise is disagreeable and tiring, most types of mental, motor, and physiological activity are affected very little by noise as such. This research, begun under an OSRD contract, is continuing under contract with the U. S. Navy, Office of Naval Research. A full report of the present study is available from the Publications Board, Dept. of Commerce, Washington, D. C. (PB No. 8334, OSRD No. 274).
Short Duration Auditory Fatigue as a Method of Classifying Hearing Impairment
Authors: Gardner Mark B.
Published: September 2005

Earlier studies have classified deafness cases into two general groups, those having functional disorders of the middle ear and those having impairments resulting from atrophy of the nerve fibers terminating along the basilar membrane (conductive and nerve deafness types, respectively). Such classifications have been made using bone-conduction threshold measurements and unilateral loudness balance results as the basis for differentiation. Bone-conduction results, however, are often subject to considerable error while the unilateral loudness balance technique can only be applied to individuals having one normal and one impaired ear. These limitations introduce a need for a completely independent method of classifying deafness types. This is particularly true for the selection of suitable candidates for operative procedure such as in the creation of the fenestra nov-ovalis. The present paper is concerned with an investigation of short time auditory fatigue as a method of obtaining an impairment analysis. In this study it was found that the fatigue of the conductively deafened observer was similar to the normal observer except the onset of fatigue was shifted by the amount of the threshold loss. For the nerve deafened observer, on the other hand, the onset of fatigue was found to occur at normal intensity levels. The occurrence of excessive fatigue in one of the nerve type impairment cases investigated appears to offer additional information on the nature of the lesion.
Standard Lag Line for Phase Measurement
Authors: Schuck O. Hugo
Published: September 2005

The available methods for electrical phase measurement are reviewed, and the usefulness of one using a standard lag line as a reference is pointed out. Ways of using such a line for various types of measurements are discussed. The construction of two particular lines for measurements in the 10-kc to 80-kc range is described, and a method of calibration is outlined. An investigation of errors indicates that accuracies to within 14° can be attained.
Effects of Differentiation, Integration, and Infinite Peak Clipping upon the Intelligibility of Speech
Authors: Licklider J. C. R. , Pollack Irwin
Published: September 2005

Previous experiments on the effects of distortion in voice communication circuits have shown that intelligibility is impaired surprisingly little by the type of amplitude distortion known as peak clipping. It has been found, in fact, that conversation is possible even over a system that introduces “infinite” peak clipping, i.e., that reduces speech to a succession of rectangular waves in which the discontinuities correspond to the crossings of the time axis in the original speech signal.

The intelligibility of the rectangular speech waves depends critically upon the frequency-response characteristics of the speech transmission circuits used in conjunction with the “infinite clipper.” In the present experiments, resistance-capacitance circuits with sloping frequency-response characteristics (tilting circuits) were introduced into the system at points preceding and/or following the clipping circuit. The interactions of the nonuniform frequency characteristics of the resistance-capacitance circuits with the nonlinear amplitude characteristic of the clipping circuit were studied by means of articulation tests. That there was strong interaction is evidenced by the fact that word articulation scores of 97 and 15 percent were obtained with two systems consisting of the same components in different orders. The components were (1) a tilter with a frequency-response characteristic rising 6 db per octave (a “differentiating” circuit), (2) an infinite peak clipper, and (3) a tilter with a frequency-response characteristic falling 6 db per octave (an “integrating” circuit). When these distorters were cascaded in the sequence 1-2-3 the speech output consisted of triangularly shaped waves which sounded very much like normal speech and which were highly intelligible (97 percent). When the reverse sequence (3-2-1) was used, the speech output consisted of sharp pulses giving rise to extremely poor quality and very low intelligibility (15 percent).

Tests with single distorters and with pairs of distorters indicated that: (1) In the absence of frequency distortion, infinitely clipped speech is of poor quality but moderate intelligibility (50 to 90 percent depending on the listeners skill and familiarity with the test words). (2) A differentiator or an integrator preceding the clipper determines the degree to which intelligibility is impaired by infinite clipping. (3) A differentiator or an integrator following the clipper (or used alone in a linear system) affects the quality but not the intelligibility of the speech transmitted by the system.
The Effect of Noise in One Ear upon the Loudness of Speech in the Other Ear
Authors: Egan James P.
Published: September 2005

Although a sufficiently intense noise in one ear will mask speech heard in the contralateral ear a weaker noise has the opposite effect: it enhances the loudness of speech heard in the other ear. Procedure: one earphone is used to introduce speech at a constant intensity into one ear. Another earphone introduces a white noise into the other ear. The listener first listens to the speech heard monaurally (ear 1) with no noise in the contralateral ear (ear 2). If noise is now introduced into ear 2, the loudness of speech heard in ear 1 increases. Most listeners report a change in the localization of the speech: it is localized nearer to the center of the head when noise is introduced into the opposite ear. This paper concerns these phenomena.