bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Ear Protective Devices on the Intelligibility of Speech in Noise
Authors: Kryter K. D.
Published: September 2005

Articulation tests were conducted to determine the intelligibility of speech in the presence of noise when listeners did not wear earplugs and when listeners wore earplugs (NDRC Ear Wardens). It was found that with a reverberating signal from a public-address system and in the presence of noise that raises the open-ear speech threshold by 60 db or more, the wearing of Ear Wardens increases the intelligibility of speech. But, with direct person-to-person speech, the ambient noise must be of sufficient intensity to raise the speech threshold by 80 db or more before Ear Wardens may be used without interfering with the reception of speech. Since in some military and industrial situations noise is generated that raises the threshold for hearing speech by more than 80 db, the use of suitable earplugs, under those conditions will: (a) maximize the reception of speech and (b) afford protection against the deafening, fatigue, and annoyance effects commonly attributed to sustained intense noise.
Ultrasonic Absorption in Copper Acetate and Ethyl Acetate
Authors: Beyer Robert T. , Smith Myron C.
Published: September 2005

A study is made of ultrasonic acoustic absorption in ethyl acetate and in various concentrations of an aqueous solution of copper acetate. The balance method has been used, in which the radiation pressure on a detector suspended in the sound field is measured by a sensitive balance. In neither case is the theoretical variation of the absorption coefficient with the square of the frequency observed. The relation is more nearly linear over the frequency range 5–20 megacycles. In the case of copper acetate, the absorption increases rapidly with the concentration for very dilute solutions. No transition is observed from an abnormal absorption coefficient at low frequencies to the theoretical value at higher frequencies.
Training for Voice Communication
Authors: Black John W. , Mason Harry M.
Published: September 2005

A training program was devised for improving the intelligibility of Army Air Force personnel in talking over the interphone and radio. The contents of the course, amount of training required, and the training requirements were determined experimentally. This paper summarizes the results of the over-all program and compares them with the improvements that accompanied “partial” training, particularly in voice loudness and precision of articulation.
Noise Levels Due to an Airplane Passing Overhead
Authors: Wiener Francis M. , Marquis R. J.
Published: September 2005

The noise spectra and levels due to an airplane flying overhead in level flight have been measured near the ground. The results of such measurements for an airplane closely corresponding to the Douglas DC-3 transport plane are discussed for altitudes between 100 and 500 feet and maximum engine power.
An Ultrasonic Condenser Microphone
Authors: Bonn Theodore H.
Published: September 2005

A small condenser microphone, for measurement of ultrasonic sound waves in air was designed and constructed. Its free field calibration is essentially constant at a level of 51 db below 1 volt per dyne per sq. cm up to 32 kc. At that frequency, the response of the microphone to plane waves incident at an angle of 45° to the microphone is 10 db below its response to plane waves incident perpendicular to its face. The output of the microphone is fed directly into a cathode-follower power amplifier and thence through a coaxial cable to measuring equipment. The characteristics of the microphone are obtained by: (a) Small size −0.875″ over-all diameter, active diameter of diaphragm 0.385″. (b) Diaphragm 0.001″ thick duralumin stretched almost to its elastic limit. (c) Novel design of the electrode with circular grooves cut in the electrode face, and a cavity behind it.
The Acoustical Concomitants of Cavitation and Boiling, Produced by a Hot Wire. I
Authors: Osborne M. F. M. , Holland F. H.
Published: September 2005

This paper presents data on the properties of a very simple, low power underwater noise generator—a wire heated by a heavy electric current. The dependence of the sound generated upon frequency, input power, wire size, material, and wire history has been determined. The sound has a very broad frequency distribution. For small wires a large part of the sound is supersonic. About one part in a million of the input electrical energy appears as sound. With increasing electric power the sound power passes through a broad maximum. This paper can also be considered as a study of cavitation noise, the cavities being produced by heat rather than by reduced pressure. Thus a new approach to the problem of cavitation noise is provided. As a study in heat flow, this report provides quantitative data on the acoustical concomitants of boiling.
Magnetic Throat Microphones of High Sensitivity
Authors: Martin Daniel W.
Published: September 2005

An analysis is made of the problem of intelligence pick-up from anatomical vibration. Methods for measuring the actual and effective response-frequency characteristics of the throat are described. Measurements on the variation of effective response among different subjects are discussed in connection with the concept of “oral efficiency.” Design and performance data are given for several magnetic throat microphones of relatively high sensitivity.
A General Theory of Passive Linear Electroacoustic Transducers and the Electroacoustic Reciprocity Theorem. II
Authors: Primakoff Henry , Foldy Leslie L.
Published: September 2005

In Part I of this paper, it was shown that the reciprocity theorem for passive linear electroacoustic transducers could be established on the basis of a pair of general linear relations connecting the voltage and current at the electrical terminals of the transducer with the pressure and velocity distribution over the transducer surface provided certain “reciprocity relations” existed among the parameters entering these equations. In Part II it is now shown that on considering a transducer to be comprised of media characterized in the usual manner by appropriate linear constitutive relations between stress, strain, electric and magnetic polarization, charge and current density, and electric and magnetic field intensity, one can establish the validity of the linear relations and the “reciprocity relations” assumed in Part I, provided that certain sufficient conditions are met. These conditions are: (l) That the coefficients in the constitutive relations satisfy certain “symmetry conditions.” (2) That no magnetostrictive media and no static magnetic field are present in the transducer (that is, that the coupling is purely electrostatic or piezoelectric or both), or that no piezoelectric media and no static charge density are present in the transducer (that is, that the coupling is purely electromagnetic or magnetostrictive or both). (3) That the transducer does not radiate electromagnetic waves from its surface.

The validity of the “symmetry conditions” on the coefficients of the constitutive relations is established for frequencies sufficiently low that the harmonic changes in the variables can be regarded as adiabatic in the thermodynamic sense and under certain circumstances at higher frequencies by means of a general argument based on a principle of microscopic reversibility. One may, however, anticipate the possible breakdown of these conditions when appreciable losses due to “relaxation” phenomena in the transducer media are present. The conditions for the validity of the reciprocity theorem derived in this paper are only sufficient, but they may be considerably extended in their generality to include the presence of other phenomena (such as electrostrictive effects) by the application of the same general methods.
Headphone Measurements and Their Interpretation
Authors: Martin Daniel W. , Anderson Leslie J.
Published: September 2005

Methods of acoustical measurement and of data presentation are reviewed, with emphasis on relating headphone data to the requirements of the communications and monitoring fields of application. Data are shown to demonstrate the importance of statistical analyses of the performance of headphones on different wearers. Some effects of presenting too “artificial” an acoustical load to the receiver during measurement are illustrated. An experiment in artificial ear development is described. The requirements for an improved artificial ear are outlined, based in part upon the experimental work.
Factors Governing the Intelligibility of Speech Sounds
Authors: French N. R. , Steinberg J. C.
Published: September 2005

The characteristics of speech, hearing, and noise are discussed in relation to the recognition of speech sounds by the ear. It is shown that the intelligibility of these sounds is related to a quantity called articulation index which can be computed from the intensities of speech and unwanted sounds received by the ear, both as a function of frequency. Relationships developed for this purpose are presented. Results calculated from these relations are compared with the results of tests of the subjective effects on intelligibility of varying the intensity of the received speech, altering its normal intensity-frequency relations and adding noise.
Premodulation Clipping in AM Voice Communication
Authors: Kryter K. D. , Licklider J. C. R. , Stevens S. S.
Published: September 2005

Articulation tests were conducted to assess the advantages of premodulating clipping in A M voice transmitters. The results show that a saving of as much as 14 decibels in carrier power can be achieved, without loss in intelligibility, if the speech wave is first subjected to 24 decibels of peak clipping and then reamplified by 24 decibels in order to obtain 100-percent peak modulation. Three obvious advantages result from this procedure: (1) the effective range of a given transmitter is increased, (2) overmodulation is permanently prevented, and (3) interference to communications on adjacent frequency channels is eliminated. Realization of this third advantage requires the introduction of a low-pass filter between the clipper and the point of modulation. Excessive amounts of premodulation clipping should be avoided whenever speech quality is an important consideration and whenever the microphone picks up large amounts of ambient noise. On the other hand, when communication is impaired by ambient noise and atmospheric static at the receiver location, large amounts of premodulation clipping serve to maximize intelligibility.
Diffraction of Sound around a Circular Disk
Authors: Primakoff Henry , Klein Martin J. , Keller Joseph B. , Carstensen E. L.
Published: September 2005

The sound field behind a circular disk in the presence of a point source of sound on its axis, is computed approximately. The calculation is based on the reduction of the Kirchhoff surface integral to a line integral by the Maggi Transformation. The predictions of the Kirchhoff theory are compared with a more accurate calculation which makes use of the Green's function. The theory is compared with accurate measurements of the sound field, and satisfactory qualitative and quantitative agreement is found.
Acoustic Wave Fronts from a “Piston” Source
Authors: Williams A. O.
Published: September 2005

Some properties of wave fronts or constant-phase surfaces in the acoustic field of a piston-like source are deduced from an approximate expression for the velocity potential. The calculations are limited to certain ranges of frequencies, piston sizes, and distances from the source, of chief interest in supersonics. The results comprise for plane pistons (a) a determination of the place where the wave fronts reverse their curvature from converging to diverging shape; (b) a calculation of the radius of curvature of the fronts at moderately large distances from the source; (c) an approximate theoretical equation for the shape of the wave fronts, which permits plotting the paraxial portion of these surfaces at medium and large distances. For a concave piston, calculations similar to those of (a) are made. A few comparisons with experimental results are given under (a), (b), and (c). Agreement is qualitative to semi-quantitative.
A Curvature Meter for Use in Disk Recording
Authors: Sepmeyer Ludwig 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 having a radius of curvature 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.
Investigations on Acoustic Resonators
Authors: Samulon H.
Published: September 2005

The following paper contains investigations into the resonance sharpness of acoustic resonators. Experimental and theoretical results are compared and found in good accordance.
Acoustic Determination of the Physical Constants of Rubber-Like Materials
Authors: Nolle A. W.
Published: September 2005

Acoustic techniques are well suited to determining the effective dynamic values of elastic and viscous coefficients for rubber-like materials. The values of these coefficients vary with frequency, and the effective dynamic modulus is, in general, larger than the modulus determined from stress-strain curves. Because acoustic attenuation for waves involving shear is large in rubber-like materials, the elastic and viscous coefficients must be computed from rigorous relations involving both sound phase velocity and attenuation rather than from the approximate relations which are often used. The necessary relations for computing Young's modulus and the associated viscosity coefficient from acoustic data are presented. An experimental method is described which has been used to measure the sound phase velocity and attenuation of longitudinal waves in thin narrow samples in the frequency range from one to 26 kilocycles. A vibration generator excites one end of a sample held under small tension, while a receiving element moves along the strip. Records of sound intensity and of phase as a function of distance are plotted automatically, and acoustic attenuation and phase velocity are determined from the records. The r.m.s. error in attenuation measurements ranges from 6 to 12 percent over the frequency range. The r.m.s. error in velocity measurements ranges from 2 to 9 percent. Sample acoustic data and the resulting elastic and viscous coefficients are given for a carbon-black buna-N cement.
Ultrasonic Propagation in Open Air
Authors: Schilling H. K. , Givens M. P. , Nyborg W. L. , Pielemeier W. A. , Thorpe H. A.
Published: September 2005

This paper presents results of studies in atmospheric ultrasonics in unforested areas in the tropics and in the temperate zone. Data of practical interest in regard to the possibilities of ultrasonic signaling were obtained. Fundamental ultrasonic phenomena of propagation were investigated and their causes isolated through correlations with simultaneously observed micrometeorological phenomena. It was found that at times the open air is a scattering, as well as absorbing, medium. Values of absorption coefficients are presented for frequencies up to 30 kc.
High Intensity Ultrasonics: The Power Output of a Piezoelectric Quartz Crystal
Authors: Epstein Leo F. , Andersen Walther M. A. , Harden Lewis R.
Published: September 2005

The maximum ultrasonic power density Υmax which has been experimentally attained with a piezoelectric quartz crystal up to the present time is considerably less than the value computed from the electrical and mechanical characteristics of quartz. Failure of such systems is attributed to dielectric breakdown in the surrounding insulating fluid, and a simple theory is developed in which the maximum power density is predicted from the value of the dielectric strength. If the breakdown voltage gradient for the medium (V/d)max is independent of thickness, the maximum power density does not change with frequency; but if (V/d)max decreases with thickness as is experimentally observed with many substances, Υmax increases with frequency approaching saturation value as ν approaches infinity. Experimentally, an output of 43 watts/cm2 has been achieved at a frequency of 1000 kc. The determination of the power output by a calorimetric substitution method is described.
Reaction of Small Enclosures on the Human Voice. Part I: Specifications Required for Satisfactory Intelligibility
Authors: Morrow Charles T.
Published: September 2005

This paper concerns itself with the acoustical specifications necessary for intelligible speech transmission through radiating enclosures, such as gas masks, placed on the front of the head. The results apply to enclosures whose internal dimensions are small by comparison with the wave-lengths significant for speech. Transmission through larger enclosures is in general poor. A speech transmitting device for a gas mask will ordinarily consist of a diaphragm, a perforated protective cover, and an exhaust valve. The acoustical system, however, must include the cavity between the mask and the face. The enclosures considered here radiate through a circular constriction, a set of perforations, or a diaphragm; specifications for the more complicated case of a diaphragm and cover have not been obtained, but may be inferred from the data presented here. The enclosures all behave as Helmholtz resonators when tested on an artificial voice. They may be specified acoustically by the resonant frequency, and a quantity related to the inertance of the acoustical system. It has been found convenient to express this property of a set of perforations or of a diaphragm in terms of an effective diameter: the diameter of the circular constriction that results in the same resonant frequency. The intelligibility obtainable through an enclosure increases when either the resonant frequency or the effective diameter is increased. In general, the intelligibility will be satisfactory if the resonant frequency is at least as high as 1500 cycles per second, provided that the effective diameter is at least 1.25 inches.
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 and 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.
Some Acoustic Properties of Marine Fouling
Authors: Fitzgerald James W. , Davis Mary E. , Hurdle Burton 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 countermeasures, 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 had been exposed to fouling in Florida waters. The test panels were measured periodically, at a frequency of 24 kc. The extent of absorption caused by fouling can reach a magnitude of 3 decibels per inch of thickness. Distortion of transducer patterns is another effect of the fouling. Antifouling methods are described. The acoustic attenuation of certain antifouling paints are found to be negligible.
The Propagation of an Acoustic Wave along a Boundary
Authors: Rudnick Isadore
Published: September 2005

The sound field of a point source near the boundary of two media cannot be obtained by an acoustic-ray approach. In fact, such an approach which utilizes the reflection coefficient for plane waves leads to completely contradictory results at grazing incidence. A more rigorous solution is obtained, the procedure followed being exactly similar to that initiated by Sommerfeld to derive the electromagnetic field of a vertical dipole situated near a conducting plane. The results of such an analysis as applied to an acoustic point source are presented. As pointed out by Van Der Pol, the resultant solution may be regarded as that due to the point source and a diffuse image. The discussion of the solution is restricted to cases in which the sound source is at the boundary although it is given for all source heights. The solution shows that when the boundary medium has a high real specific acoustic impedance, non-zero fields are obtained at all points along the boundary. For bounding media adequately described by simple porosity theory, the acoustic pressure at the boundary is inversely proportional to the square of the distance and the square of the frequency, at reasonably large distances and low frequencies. Also there appears to be decreased phase velocities along the boundary. Some calculations of the sound pressure as a function of height above Quietone show, among other things, the presence of a minimum occurring some distance above the boundary. At large distances from the source there are very large decreases in amplitude as the receiver height is increased in the region above this minimum.
Some Factors Influencing the Choice of a Medium for Magnetic Recording
Authors: Holmes Lynn C.
Published: September 2005

A definition of signal-to-noise ratio for magnetic recording systems is offered for the purpose of stimulating discussion. Factors involved in the choice of a medium for magnetic recording are then presented and discussed. Considerable attention is focused on modulation noise, a low value of which is necessary for high fidelity recording work. Background noise, crosstalk, and uniformity are the other factors which are presented as being significant in the choice of a magnetic recording medium. The ratio of coercivity to retentivity is suggested as a figure of merit for evaluating the high frequency response of a recording medium.
Attenuation and Scattering of High Frequency Sound Waves in Metals and Glasses
Authors: Mason W. P. , McSkimin H. J.
Published: September 2005

By using a pulse method, attenuation and velocity measurements have been made for aluminum and glass rods in the frequency range from 2 to 15 megacycles. The sound pulses are generated by crystals waxed to the surface of the rod. This wax joint limits the band width of the transmitted pulse and measurements are made using long pulses which approach steady state conditions. The reflected pulses show evidence of several normal modes which can be minimized by using specially shaped electrodes. Longitudinal waves show delayed pulses of smaller magnitude that are caused by the longitudinal wave breaking up into reflected longitudinal and shear waves at the boundary. This effect is small if the diameter of the rod is 20 wave-lengths or more.

The measured losses for aluminum rods show a component proportional to the frequency and another component proportional to the fourth power of the frequency. The first component is the hysteresis loss found for most solid materials. The component proportional to the fourth power of the frequency is caused by Rayleigh scattering losses which are the result of differences in the elastic constants between adjacent grains caused by changes in orientation. Calculated scattering losses agree quite well with the measured values. The fourth-power scattering law holds quite well until the grain size is equal to one-third of a wave-length. For higher frequencies the scattering loss increases more nearly with the square of the frequency. Glasses and fused quartz have a loss directly proportional to the frequency, showing that any irregularities must be of very small size.
Measurement and Specification of Ultrasonic Lenses
Authors: Ernst Paul J.
Published: September 2005

Methods approved in optics are applied to the measurement and specification of ultrasonic lenses.
The Ordnance Research Laboratory Underwater Sound Calibration Station
Authors: Ebaugh Paul
Published: September 2005

A descriptive account of the testing facilities of the Black Moshannon Calibration Station of the Ordnance Research Laboratory is presented. Included also is a brief account of the procedures involved in the calibration of underwater sound transducers.
Decay Rates of Piano Tones
Authors: Martin Daniel W.
Published: September 2005

Decay curves were recorded for an upright piano, a baby grand, and an electronic spinet. For some tones the partials were recorded separately. Decay rates for the electronic piano were measured at different levels of piano amplification. Analysis of the data reveals the degree of control exerted by the sounding board upon decay rate, particularly in the initial stage of decay. The significance of this control by the sounding board is discussed, in relation to the problem of electrical amplification of piano tones.
Acoustical Properties of Homogeneous, Isotropic Rigid Tiles and Flexible Blankets
Authors: Beranek Leo L.
Published: September 2005

Studies on rigid acoustical tiles and soft blankets are described in this paper. It is shown that two waves travel through the material—one primarily airborne and the other primarily structure-borne. From a knowledge of the density of the sample, the volume coefficients of elasticity of the air and of the skeleton of the material, the porosity, the air flow resistance, the inter-fiber frictional resistance, and the structure factor, the propagation constants of each of these waves can be calculated. The experimental results indicate that the theory is useful in calculating the performance of the flexible, airplane type of blankets over the entire audible frequency range. For rigid tiles, however, the theory appears to fail at frequencies above 1000 c.p.s. if the flow resistance is high, and it fails at all frequencies for materials with low flow resistance. Experiment shows that the condensations and rarefactions of the gas in blankets take place isothermally at low frequencies and adiabatically at high. The transfer from one state to the other occurs gradually in the 100 to 2000 c.p.s. region. A more complete theory is required to explain the effects of thermodynamic and viscous losses on the propagation constant of rigid materials.
The Equivalent Circuit for a Bifurcated Cylindrical Tube
Authors: Miles John W.
Published: September 2005

Using the impedance concepts developed in earlier papers, the problem of the diffraction of sound, caused by a bifurcation of a cylindrical tube, is solved. The equivalent circuit elements are shown to be related to the analogous changes of cross section. It is shown that the transmitted power is divided between the two tubes resulting from the bifurcation in proportion to their areas and without frequency distortion or reflection, and that the bifurcation may, therefore, be regarded as taking place in a virtual plane parallel to, but somewhat removed frown, the geometrical plane. A formula is given to locate this plane.

The results are applied to a concentric-circular bifurcation and to a rectangular-tube bifurcated parallel to one of its walls. Numerical results are given which may be applied both to the circular change of cross section and to the concentric bifurcation of a circular tube.
Construction and Calibration of an Improved Bone-Conduction Receiver for Audiometry
Authors: Carlisle R. W. , Pearson H. A. , Werner P. R.
Published: September 2005

The construction of an acoustically shielded bone-conduction unit is described. The masses and springs have been proportioned for optimum purity of wave form at low frequency and for extension of the high frequency range to over 12,000 cycles.

The precautions taken in preparing an acoustical loudness-balance calibration are described, and the reproducibility of observations is considered. Methods of specifying the response of productions units are shown.
Broadened Criteria of Hearing Aid Performance
Authors: Mundel August B. , Carlisle Richard W.
Published: September 2005

The requirements of hearing aid users include, besides adequate acoustic response, low reaction to “noise” excitation and other characteristics.

Methods used in reducing unwanted sensitivity are discussed. Other operational features of a hearing aid are considered, and a single chart method of presenting acoustic input-output characteristics, frequency response, and distortion is described.
The German Use of Sonic Listening
Authors: Holt Lee E.
Published: September 2005

The most successful German sonic listening device, the GHG Gruppen Horch Gerät, is described in general terms. Reference is made to the types of ships using the equipment and to the arrangement and placement of the hydrophone arrays. A brief account is given of the steps taken by the Germans to improve the operation of the GHG by streamlining the array and by altering its position on the hull. The simple but efficient electrical training device is explained, and bearing accuracy and range data, as reported by the Germans, are presented. The paper is based on technical reports received from Germany and on subsequent investigations. The most important of the sources consulted is the Navy Technical Mission Report prepared by Mr. Laurence Batchelder.
A Musician Looks at Modern Acoustics
Authors: Hanson Howard
Published: September 2005

The musician of today often finds himself somewhat at the mercy of the sound engineer, the radio control operator, or the designer of electronic musical instruments. He is bewildered by the language of the cycle and decibel and by the complexity of the circuits, controls, and equipment. The engineer on the other hand is frequently unable to appreciate the viewpoint of the artist, whether through lack of training or by virtue of his temperament. The purpose of this paper is to emphasize the community of interest between the two fields, and to indicate the directions which the writer feels acoustic and electro-acoustic research might take in order to contribute most effectively to the aesthetic development of music.
An Institute of Musical Science—A Suggestion
Authors: Fletcher Harvey
Published: September 2005

This paper suggests the establishment of an Institute of Musical Science designed to provide a scientific basis and techniques whereby music may contribute more fully to the esthetic life of a larger number of people. The program of research of the Institute extends from the physics of the production of musical sounds to the psychology of their appreciation by listeners. It would measure and study audience reaction under a wide variety of conditions. It would undertake the experimental development of new musical instruments, and of new electro-acoustical systems for the production or reproduction of esthetic sounds; and it would study the possibilities of synthetic orchestras and new techniques or orchestration. It would experiment in the application of sound effects to dramatic and operatic performances. Techniques would be worked out for the measurement of musical talent, and scientific apparatus developed for the musical education of individuals and the training of choral or instrumental groups. It would apply to the problems of music the techniques and instrumentalities which have been developed in the fields of acoustics, electrical communications, and electronics. Particular attention would be given to music in the home, and to applications to its needs of devices inherent in recent engineering advances.
Reaction of Small Enclosures on the Human Voice, Part II: Analyses of Vowels
Authors: Morrow Charles T.
Published: September 2005

In a previous paper, the specifications necessary for intelligible transmission of speech through enclosures such as gas masks were discussed. In the present paper, harmonic analyses are presented to show the distortion of vowels by enclosures against the mouth in a number of typical cases. A partially successful attempt is made to devise a theory for these distortions on the basis of an equivalent circuit suggested by Crandall for the human voice. Enclosures may be divided into radiating and non-radiating types, according as the major interest is in the sound radiated or the sound pressure developed within the enclosure. In the first category belong gas masks; in the second, noise shields and oxygen masks. Theory predicts that the two formant frequencies characteristic of each vowel will be split into three by a small radiating enclosure, and that the distortion will increase as the aperture and resonant frequency of the enclosure are decreased. The analyses confirm this and indicate that it is largely responsible for the characteristic hollowness of the speech. The distortion is less than theory predicts, however. Theory predicts that the effect of a small non-radiating enclosure will be primarily a rise in the two formant frequencies. According to the analyses, there is such a tendency, but correlation with the theory is poor, and the frequency shifts are often erratic.
Baldwin Electronic Organ
Authors: Jordan J. F.
Published: September 2005

A new electronic organ operating on the formant principle is described. Sawtooth wave forms are generated in a vacuum tube generator and are modified by a variety of filter circuits to provide desired tone colors. Modified square wave forms are also utilized for certain effects. There are twelve tuning adjustments, each controlling one of the frequencies in the top octave. All notes in the lower octaves are obtained by frequency division in the ratio of 2 to 1. A frequency vibrato is used. Keying transients are eliminated by the use of graduated resistance type switches.
Photo-Electronic Synthesis of Musical Tones
Authors: Erlandson P. M. , Watson R. B.
Published: September 2005

The factors involved in the design of a photo-electronic generator of musical tones are described. The generator employs the basic principles of a sound-on-film system, but avoids mechanical motion by the projection of one or more radial-line film patterns onto the mosaic of a television camera tube. The resultant image on the tube is scanned by an electron beam. The patterns are disposed to produce pulse phase modulated voltages at the output of the camera tube. The generator is designed to produce both steady-state and transient tones, with amplitude and phase control of harmonic components. The use of gaseous discharge light sources, excited by radio frequency power, is being considered for the optical system.
An Electrical Method for Measuring the Intonation of Cup Mouthpiece Instruments
Authors: Webster John C.
Published: September 2005

A method has been devised for driving an acoustic transmission line such that the driving point is a pressure anti-node when the distant end of the line is open and the line is in resonance. The method has been verified by an extensive series of measurements on cylindrical tubes. In this work, the velocity of sound transmission was measured both by conventional complete-series resonance, and by odd-series resonance in which the driving point was at the closed end of the tube. The maximum deviation from the average result was substantially below 1.0 percent. By cutting off the mouthpiece of a trumpet at the throat constriction and driving it electrically at that point, the resonant frequencies are found to be those actually played, provided that the actually played frequency is not unduly influenced by the performer's ear, nor by habitual “lip-set.” Extensive experimental work has been done to eliminate the effects of this personal equation in obtaining a comparison between player performance and electrical measurements. This has included the use of non-harmonic intervals between successive test notes, several bell designs involving small differences in performance, and one special design (conical) that cannot possibly be played in tune for more than a few notes.
Plate Vibration of Stringed Instruments at the Wolfnote
Authors: Kessler J. A.
Published: September 2005

The wolfnote observed frequently in cellos near F♯ on the D string (about 190 c.p.s.) is characterized by high emission of sound energy from the instrument with a rapid cyclical variation in intensity. The tone produced by the instrument is hard for the player to control and unpleasant in character. According to Raman, two modes of string vibration exist in this case. Because of rapid dissipation of energy from the string at this frequency, the string alternates between the two modes, with a resultant cyclical variation in the intensity of the sound produced by the instrument. The high energy dissipation from the string at this frequency is associated with particularly strong radiation from the instrument, as shown by a distinct peak in cello response curves. A comparable response peak occurs in the same relative part of the compass of violins and violas. In all three instruments, the wolfnote peak is the first marked peak above the main air body resonance, and lies in the range where the belly of the instrument is the principal radiating element. The work reported here identifies the principal mode of plate vibration at the wolfnote frequency. This same mode was observed on a number of violins, violas, and cellos; it was also observed under a variety of conditions on a flat brass plate shaped like a violin. A number of plate modes are illustrated by means of Chladni sand figures, and the influence of the bass-bar and soundpost on normal plate modes is discussed. Several methods of reducing the strength of the wolfnote are mentioned.
A Hydrophone System for Very Low Frequencies
Authors: Snavely Benjamin L.
Published: September 2005

The Acoustic System Mark 1 was developed by the Naval Ordnance Laboratory for measuring and recording pressure variations in the frequency band between 0 and 200 c.p.s. It has had numerous applications including a seismic investigation of Bikini Atoll as a part of Operation Crossroads. A 1000-c.p.s. carrier is modulated by pressure variations applied to the hydrophone which comprises a variable inductance in one arm of a bridge. The diaphragm is resonant at about 1800 c.p.s. and can be used at depths up to 200 feet without pressure compensation. Although the hydrophone unit contains no amplifiers it may be used at distances exceeding 3 miles from the amplifying and recording system. Amplification of a million between motion of the diaphragm and motion of the recording pen are easily obtained. At a lower amplification the instrument may be used to follow changes in pressure caused by tides. Problems encountered in the development of the system included the mechanical design of an extremely rugged hydrophone and the electrical design of an oscillator of unusual amplitude stability and a circuit permitting easy and rapid balance of the bridge.
A Survey of Magnetostriction Transducer Research at the Harvard Underwater Sound Laboratory 1941–1945
Authors: Hunt F. V.
Published: September 2005

Under the sponsorship of Division 6, NDRC (OSRD Contract OEMsr-287), extensive research and development work by many individuals was devoted to magnetostriction transducers for underwater sounds in the frequency range 0.1–150 kc. This paper, reviewing the work of the HUSL transducer group, will present a survey of the portions of the program which have so far been declassified. The program included studies of (a) the magnetic properties of magnetostrictive materials, (b) theoretical considerations involved in transducer design, (c) shop practices for fabricating magnetostriction transducers, (d) electrical and acoustical techniques for evaluation and calibration. Useful transducer designs will be illustrated by selected examples of tube-and-plate types (moderate efficiency and sharp resonance), radially vibrating tubular types with internal windings (low efficiency and wide-range response), laminated ring-stacks (high efficiency and controllable sharpness of resonance), and longitudinally vibrating laminated stacks (high efficiency and dull resonance).
Attenuation and Scattering of High Frequency Sound Waves in Metals and Glasses
Authors: Mason W. P. , McSkimin H. J.
Published: September 2005

By using a pulse method, attenuation and velocity measurements have been made for aluminum and glass rods in the frequency range from 2 to 15 megacycles. The sound pulses are generated by crystals waxed to the surface of the rod. This wax joint limits the band width of the transmitted pulse and measurements are made using long pulses and approach steady state conditions. The reflected pulses show evidence of several normal modes which can be minimized by using specially shaped electrodes. Longitudinal waves show delayed pulses of smaller magnitude that are caused by the longitudinal wave breaking up into reflected longitudinal and shear waves at the boundary. This effect is small if the diameter of the rod is 20 wave-lengths or more. The measured losses for aluminum rods show a component proportional to the frequency and another component proportional to the fourth power of the frequency. The first component is the hysteresis loss found for most solid materials. The component proportional to the fourth power of the frequency is caused by Rayleigh scattering losses which are due to differences in the elastic constants between adjacent grains due to changes in orientation. Calculated scattering losses agree quite well with the measured values. The fourth-power scattering law holds quite well until the grain size is equal to one-third of a wave-length. For higher frequencies the scattering loss increases more nearly with the square of the frequency. Glasses and fused quartz have a loss directly proportional to the frequency showing that any irregularities must be of very small size.
Broad Frequency Response from Stepped-Frequency Transducers
Authors: Bundy F. P.
Published: September 2005

This paper deals with the design, construction, and tests of an experimental transducer containing loosely coupled elements of three different frequencies and with radiating faces small in comparison to the wave-length in the acoustic medium (water). The vibrating elements consisted of consolidated stacks of nickel laminations. A single winding linked all six of the elements. The unit was housed in an air-filled box. Acoustic contact with the water was made through a rubber face which formed one side of the box. Electrical impedance as a function of the frequency was determined for the transducer in air and in water. These measurements showed definite motional impedance loops for each of the three frequencies of resonance. The frequency responses and directivity patterns as a transmitter and as a receiver were measured in a free acoustic field. Also the phase relationship between the sound pressure in the water and the electrical signal generated in the windings of the transducer was determined. The results of the measurements all agreed reasonably well with the predictions of theory.
Remarks on Just Intonation and Musical Scales
Authors: Jones R. Clark
Published: September 2005

Any keyboard musical instrument may be tuned so that the intonation is just for any one key. Unfortunately, however, the intonation is no longer just if the instrument is played in any other key. In order to preserve just intonation, it is necessary to add two new notes in each octave for each sharp or flat which is added to the key signature. Thus, in order to be able to play a keyboard instrument so that it is justly tuned in each of the fifteen major keys which are recognized by musicians, it is necessary to provide 7 + 14 × 2, or 35 notes in each octave. It will be shown how it is possible to reduce the number of notes from 35 to 24 per octave if one will permit an error of 0.057 percent (0.98 cent) in some of the intervals. Thus, it is possible to obtain a musical scale with 24 notes to the octave in which any musical interval in any key is in error by not more than 0.98 cent. For the sake of comparison, it may be noted that errors in the major and minor thirds in the equally tempered scale are 13.7 and 15.6 cents, respectively. A tabular method is described which permits the rapid determination of the frequencies of the notes which must be added as sharps and flats are added to the key signature. The tabulation makes evident a striking lack of symmetry of the customary (Ptolemaic) just intonation. It is shown that the asymmetry is due to the fact that Ptolemy's just intonation is only one of two possible intonations which are equally just. The second was discovered by Robert Smith two hundred years ago, and was rediscovered about twenty years ago by the late John Redfield.
A Comparison and Demonstration of Two Systems of Intonation of Keyboard Instruments
Authors: White W. B.
Published: September 2005

The system of tuning keyboard instruments in equal temperament, now universally accepted, had its first practical demonstration at the hands of Sebastian Bach during the first quarter of the 18th century. Some 250 years previously, a system had been worked out which satisfied the requirements of a less developed musical art. This was the so-called mean-tone system, which, at least until the middle of the 18th century, remained the generally accepted system. Its peculiarities entitle it to recognition even today, although it has long since been forgotten by musicians. Music written during the days of its supremacy bears various characteristics that have been completely lost under the regime of equal temperament. The principles on which the mean-tone system was worked out will be demonstrated practically upon a pianoforte, while the accepted system of equal temperament will be shown simultaneously and discussed upon another instrument, standing by the side of the first one. Music will be played on both instruments for the purpose of demonstrating the differences of intonation between the two systems, and of illustrating how music of the 17th and early 18th centuries actually sounded.
A Slide-Rule for the Study of Music and Musical Acoustics
Authors: Waddington L. E.
Published: September 2005

Musical data and acoustics related to music are readily adaptable to slide-rule presentation since they involve relationships which hold good regardless of the key in which they are considered. Musicians are seldom concerned with the mathematical background of their art, but an understanding of the underlying physical principles of music can be very helpful to the student in considerations of problems related to harmony, intonation, and general band instrument design. A slide-rule has been developed to present chord structures, scale building, instrumental transposition, interval relationships, and degrees of scale as adjustable information. This can be related to a base of the piano keyboard with reference to its chromatic notation, a standard subscript notation and semitone count as a frequency level determination. Frequencies are listed for each tone within the range of the piano keyboard. Instrumental scales are, of course, based upon the equally tempered scale using the American standard pitch of A4 = 440 vibrations per second where the reference frequency of C0 = 16.352 cycles per second and where 1/12th of an octave = one semitone = (2)1/12 = 1.059463. Ready reference information includes a range chart for all the string, reed and brass instruments, referred to the subscript system as a staveless notation.