bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical Investigation of the Absorption of Sound by Vibrating Materials
Authors: Rogers Robert
Published: September 2005

The present investigation deals with the absorption of sound energy by materials which owe their absorbing power to the dissipation of energy in internal friction during their vibration. A relation is obtained which enables one to calculate the absorbing power of a plate which may be considered to vibrate as a whole. This condition is fulfilled only at low frequencies but this is the region in which the absorbing power of the material is of interest. From this study one is led to the conclusion that the maximum absorption of the plate occurs at the resonant frequency of the system which is made up of the plate backed by an air tight space. In addition the width of the frequency region in which the plate has appreciable absorption is determined. This region may be narrow but the study indicates how such a material may be modified to give appreciable absorption over a considerable range of frequencies. By changing certain constants of the system the maximum absorption point may be varied at will. Although the above results are obtained only for the absorption at normal incidence, they may be extended to all angles of incidence.
Standard Requirements for Audiometers
Authors: Snyder Wilbert F.
Published: September 2005

There is an increasing interest among various groups today in more exact methods of determination of hearing loss. The instrument known as the audiometer has been found to be the most satisfactory for such measurements. But, as is so frequently the case in the development of instruments in a new field, there is not sufficient uniformity in audiometers of different manufacturers to permit interchange of test data. Two years ago a subcommittee of the ASA Sectional Committee on Acoustical Measurements and Terminology was formed to prepare specifications for audiometers. The specifications in their present form will be reviewed. Attention will be given to several sections of the specifications wherein there has been considerable variance in audiometers of different manufacturers.
A Moving Coil Pistonphone for Measurement of Sound Field Pressures
Authors: Glover Ralph P. , Baumzweiger Benjamin
Published: September 2005

A standard of low frequency sound-pressure was developed following the general theory of previous investigators. The dynamic pistonphone consists of a chamber about 50 cc in volume and a piston 0.3 cm in diameter driven by a moving coil mechanism, capable of executing strokes of approximately 1.0 cm at frequencies between 20 and 100 c.p.s. The stroke is measured by means of a telescope and scale, and the pressure developed is computed assuming isentropic law. A small crystal microphone is used as a pressure indicator within the pistonphone chamber, and becomes a calibrated microphone for the measurement of sound field pressures. The device appears to be more simple and easier to use than pistonphones previously described in the literature.
Absolute Sound Measurements in Liquids
Authors: Klein Elias
Published: September 2005

The fundamental problem of absolute sound measurements in liquids is discussed. Regarding acoustic determinations, reference is made to certain inherent differences between air and water. An outline is presented of three methods now available. A modified radiation pressure apparatus is described which permits a dual check of the basic measurements involved, and at the same time makes possible microphone calibration for secondary standards.
A Calibrator for Sound Level Meters
Authors: Barstow J. M.
Published: September 2005

Experience has shown that a secondary acoustic standard suitable for calibrating sound level meters would be desirable and a certain amount of experimental work has been done toward the development of such a device. A model which generates a sound having a level of 84 db (40 db loudness weighting) and a frequency composition closely simulating that of a general type of room noise has been produced. The apparatus is to be demonstrated and it is suggested that its output be measured with the various sound level meters present as a means of checking the reference points employed.
An Adjustable Tuning Fork
Authors: Schuck O. Hugo
Published: September 2005

A portable tertiary frequency standard, adjustable over a small range, is described. The frequency determining element is a valve-maintained tuning fork, adjustment of whose frequency over a relatively small range is accomplished by changing the position of movable weights on the prongs. Calculations are simplified by the design of the fork, which permits the assumption of lumped constants. The weights may be moved while the fork is running without interfering with its operation. Indication of their position is by means of a pointer reading on a scale graduated directly in frequency units. A precise method of calibration is given. Mechanical arrangements are described for obtaining a uniformly spaced scale, and the possibility of using such a scale in correcting for the temperature coefficient of the fork material is discussed. The relative accuracy of such a fork is greater, the smaller the range of frequency adjustment. In the present development, adjustment may be made over a range of plus and minus three percent of the mean frequency, that is, a musical interval of one semi-tone or 100 cents total change. Incorporation of this fork in the chromatic stroboscope has resulted in considerable simplification as well as an increase in the reliability of the instrument.
The Departure of the Overtones of a Vibrating String from a True Harmonic Series
Authors: Shankland Robert S.
Published: September 2005

The changes in frequency caused by variations in tension due to the amplitude of vibration of a wire are treated by the method of perturbations. The constraints introduced by the bridges at the end nodes as studied by Raman, and on the bending moments due to the stiffness of the wire are included in the treatment. The overtones do not, in general, form a true harmonic series. In general, the combined influence of stiffness and amplitude sharpens the overtones with respect to the fundamental. A new type of monochord has been designed with which a cathode ray oscillograph is used to determine the effect of amplitude on frequency of strings of various lengths, diameters and materials. The absolute frequency is determined with a thyratron scale-of-sixteen circuit in connection with a Riesler standard clock. The electrically maintained vibrations are essentially free vibrations corresponding to the vibrations of piano wires. The degree of departure to be expected from an exact harmonic series for these instruments is shown to be in agreement with the studies by Miller for piano wires.
An Optical Harmonic Analyzer
Authors: Montgomery H. C.
Published: September 2005

An instrument has recently been completed which makes a Fourier analysis of a function by optical means. It is especially adapted to the analysis of speech and music, since it operates directly from a conventional type of sound track on film. The first 30 harmonics can be measured, the time required being a little over one minute. A similar analysis by methods previously available would require several hours. The instrument will handle fundamental frequencies from 65 to 310 cycles, and the amplitude range is about 35 db. A description of the construction and operation of the instrument will be given, together with a discussion of its capabilities and examples of its work.
The Absorption of Vibrating Plates
Authors: Leedy H. A.
Published: September 2005

The problem of obtaining materials having higher absorptivities at the low frequencies has lead to a theoretical and experimental investigation of the absorptivities of vibrating plates. The absorptivities of such materials are theoretically determined by what may be called a pure “impedance method.” This theory shows that maximum absorption occurs at the natural frequencies of the system composed of the vibrating plate and air space. The absorptivities, as determined by the reverberation room method, of 18 in. Celotex board backed by 3 in. and 6 in. air spaces are found to be in satisfactory agreement with the theory. The addition of a layer of 14 in. of cotton on the Celotex board is found to increase materially the width of the frequency range in which the material has relatively large absorption, thus indicating the addition of a considerable amount of damping resistance.
The Relation of Pitch to the Duration of a Tone
Authors: Stevens S. S. , Ekdahl A. G.
Published: September 2005

The traditional problem as to the number of complete cycles required for a short tone to give rise to the perception of a definite pitch can not be answered by a single figure. As the duration of a tone is shortened, several changes occur: the apparent pitch of the tone becomes lower, the uncertainty of the pitch becomes gradually greater, and the sensation comes more and more to resemble a “toneless” click. It can be demonstrated, however, that even when, to casual observation, nothing remains but a click the click is not entirely “pitchless.” Tones lose their pitch gradually, not abruptly, as their duration is shortened, and it appears that as long as any sound remains we can, within certain limits, assign a pitch to it.
Multiple Coil, Multiple Cone Loudspeaker
Authors: Olson Harry F.
Published: September 2005

A consideration of the direct radiator loudspeaker shows that to obtain uniform response, relatively high efficiency and adequate power handling capacity over a wide range requires a large diameter, rugged diaphragm and heavy coil at the lower frequencies and a relatively light weight vibrating system at the higher frequencies. This paper describes a number of direct radiator loudspeaker systems which satisfy these requirements: the double coil, single cone loudspeaker; the single coil, multiple cone loudspeaker; the double coil, double cone loudspeaker; the multiple coil, multiple cone loudspeaker.
Comparison of Sound Absorption Coefficients Obtained Experimentally by Different Methods
Authors: Willig F. J.
Published: September 2005

Coefficients of absorption were obtained out of doors by comparing the sound reflected from a sample with that reflected from a perfect reflector, using a miniature pressure-gradient condenser microphone for the measurements. The microphone, whose directional qualities are very sharp, was placed so it was insensitive to the incident sound. Coefficients were obtained at several frequencies and for angles of incidence varying from 15° to 75°. These values fit the theoretical curve: α = 1 − (Z0 cos θ − ρ0cZ0 cos θ + ρ0c)2 very closely. Normal incidence coefficients obtained by extrapolation of these values agree very well with coefficients obtained from standing wave measurements in a tube. Values of α averaged over all angles of incidence are compared with coefficients obtained in a reverberation room using a high speed level recorder.
The Multitone
Authors: Barrow W. L.
Published: September 2005

A sound source which has been termed a “multitone” for space-acoustic measurements is described that provides a plurality of equi-amplitude tones spaced equally in frequency over a given frequency band. Disk recordings are employed to secure a series of multitones of different mean frequencies but of constant ratio of band width to mean frequency.
Spatial Resonance and Standing Wave Patterns in Small Models of Various Shapes
Authors: Bolt R. H.
Published: September 2005

An experimental method has been developed for exploring the distribution of sound in reflective enclosures of various shapes, with dimensions of the order of 8″ to 16″. These models are assembled from standardized, plastic units. Sound is introduced through a small opening in one wall. The sound may be detected, by means of a tuned exploring tube and microphone, at any point in the model. A pointer indicates the pick-up position on a full scale plan of the model. Three general steps are followed in the investigation of each model. The intensity response is plotted as a function of frequency, up through the first hundred eigentones, the frequency of the first few eigentones being measured to about 0.1 percent. The standing wave pattern is plotted for several modes of vibration, at enough sections to establish the three-dimensional pattern. Finally the intensity distribution is explored by using a high frequency warble tone which excites a number of eigentones. Theoretical considerations are applied where possible. For the rectangular and cylindrical models, simple solutions of the wave equation are obtainable. In these two cases the observed eigenfrequencies and wave patterns agree with theoretical predictions to within the experimental accuracy of the method. Approximate methods of solution are suggested for some other shapes, and preliminary confirmation is indicated.
Frequency Distribution of Eigentones in a Three-Dimensional Continuum
Authors: Bolt R. H.
Published: September 2005

Rayleigh derived an asymptotic formula for the number of characteristic frequencies or eigentones, N, up to a given frequency, ν, and the derivative form which gives the number of eigentones in the range ν to ν+dν. This dN form was applied successfully to quantum radiation laws. In acoustic terminology the equations are: N = (4πV/3c3)ν3 and: dN = (4πV/c3)ν2 dν where V is the volume of the room and c is the velocity of sound. It is shown that these simple formulae do not apply accurately to sound waves, especially in small rooms and at low frequencies. The discrepancy is attributable to the comparatively small number of eigentones involved, compared to the number of characteristic frequencies usually concerned in the case of electromagnetic radiation. More accurate expressions have been derived, for a rectangular room, from a consideration of the density of characteristic points in frequency space. The new formulae are: N = 4πV3c3 ν3|2Vν+cR122Vν+(c/2)R12|3 and, after expansion and simplification: dN = 4πVc3|ν2+cR122Vν|dν, where R = (LxLy)2+(LyLz)2+(LzLx)2; Lx, Ly, Lz are the dimensions of the rectangular room. These new formulae fit the “exact,” stepped curves very nicely, even for the first few eigentones. These new forms have certain practical applications to experimental acoustics. The lower frequency-limit of uniform resonance response of a room is obtained more accurately than by previous theory. A new formula is given for the average energy, in a room, as a function of frequency. Finally it is suggested that the new equations may be of some value in the theoretical treatment of reverberation as made up of free damped vibrations of a three-dimensional continuum.
The Distribution of Eigentones in a Rectangular Chamber at Lower Frequency Ranges
Authors: Maa D. Y.
Published: September 2005

According to previous calculations the number of eigentones in a rectangular chamber of volume V with frequencies less than ν is given by N = (4π/3)(Vν3/c3) where c is the velocity of waves. This relation only holds [or very large numbers of eigentones, i.e., when ν is very high. For lower frequency ranges the corrected value of N has been found to be N = 4π3 Vν3c3 + π4 Sν2c2 + 12 Lνc, where S is the total surface area and L the sum of three dimensions of the chamber. This formula is suggested to be used in acoustic problems with V taken as the volume, S the total surface area and L the sum of half the perimeter and the height of the chamber.
The Diffraction of Sound by Ribbons and by Slits
Authors: Morse Philip M. , Rubenstein Pearl J.
Published: September 2005

The exact solution of the diffraction problem in elliptic cylinder coordinates is computed by the use of newly compiled tables of Mathieu functions. Curves are given for the distribution-in-angle and total intensity scattered, for the diffraction by a slit or the scattering by a thin ribbon, of waves whose length is the same order of magnitude as the slit or ribbon width. The curves are for different angles of incidence, and for different wave-lengths. Calculations can also be made of the effective area of strips of absorbing material placed on a reflecting wall.
Attenuation of Sound in Tubes
Authors: Fay R. D.
Published: September 2005

Apparatus has been developed for determining the attenuation constant of sound waves in tubes. In the frequency range from 600 c.p.s. to 5000 c.p.s. measurements are consistent to 1 percent for like conditions. By subtracting the effects due to the tube walls, the attenuation of plane waves in free air may be found.
Reversed Speech
Authors: Kellogg E. W.
Published: September 2005

Recording sound and then reproducing it with the rotation of the record reversed is not only a means of amusement, but serves to throw some light on our habits of speech, particularly if one tries reversing the order of the original pronunciation, so that the reproduced sound may be actual words. Some of the writer's observations are given
Research on the Absorption Coefficient Problem
Authors: Hunt F. V.
Published: September 2005

The aim and scope of the absorption coefficient symposium is to clarify, rather than to confuse, the issues involved in determining absorption coefficients for acoustical materials and in applying these materials in the field to secure specified reverberation characteristics. After placing the problem briefly in historical perspective, a critical summary will be given of the physical assumptions underlying the derivation of all of the common reverberation formulas. As an example of current research upon the absorption coefficient problem, alternative and more plausible assumptions will be offered which lead to a new method of analyzing the decay of sound in a room. Although limited in its field applications, this analysis appears to offer an immediate and basic solution of the problem of obtaining consistent absorption data in different laboratories.
Possible Variation of Sound Absorption Coefficients with Intensity
Authors: Willig F. J.
Published: September 2005

Normal incidence coefficients were measured by means of standing waves in a heavy brass tube 1012 inches in diameter and 7 feet 4 inches long. Both ends of the tube were carefully sealed to prevent leakage, and the sample was not removed during the course of a set of measurements on a given material. A selective amplifier of the degenerative feed-back type was used to eliminate any possible effect due to variation of harmonic content with intensity. Measurements were taken on a wide selection of materials over a range of 30 to 40 decibels. Any variation in the value of the absorption coefficient due to change in the intensity of sound was not more than 1.5 percent.
The Journal of the Acoustical Society
Authors: Watson F. R.
Published: September 2005

The Acoustical Journal is the official publication of the Acoustical Society. It includes scientific papers describing important developments in acoustics, also various miscellaneous items of interest. It reaches a wide circle of readers at home and abroad, thus satisfying the demand for authoritative information about acoustics.

The Journal is managed by an Editorial Board that determines the policy of the magazine, reviews all the material intended for publication and has general charge of the Journal activities. The final editing of papers is delegated to the capable supervision of the Editorial office of the American Institute of Physics, which also makes arrangements for the printing.

The papers published cover a wide variety of subjects—the fundamental characteristics of sound, the phenomena of hearing, supersonics, the control of sound in buildings, the characteristics of musical sounds with reference to speech, music and musical instruments, etc.—all of which indicate the active interests in acoustics in the United States.

The Journal is an integral unit in the Acoustical Society, setting forth in a permanent record the progress and accomplishments of this young and vigorous organization.
A Demonstration of Combination Tones
Authors: Bragg Sir William
Published: September 2005

The history of the subject of combination tones is reviewed and the conditions for their objective existence is demonstrated by means of a pair of current bearing coils placed on a common center and at right angles to each other. One is free to vibrate about an axis in a way such that the amplitude of vibration depends at every instant on the amplitudes of the currents carried by each coil.
An Ear to the Future
Authors: Knudsen V. O.
Published: September 2005

A report is made of recent and prospective progress on the amelioration of impaired hearing, on the conquest of noise, and on the application of modern acoustics to music. Hearing aids which utilize binaural hearing with high quality, selective amplification are considered, and the results of experiments are presented which indicate the advantages of such aids. The ill effects of noise on humans are reviewed, and the benefits which may be derived from the use of properly designed ear defenders are discussed. The golden age of music may come as a result of modern developments in acoustics. What may we anticipate? What should we do?
The Development of Modern Microphones
Authors: Coile R. C.
Published: September 2005

The development of radio broadcasting about 1920 greatly stimulated electroacoustics. The carbon telephone transmitter was redesigned to use a stretched diaphragm and two buttons. E. C. Wente's condenser transmitter was applied to broadcasting. General Electric engineers developed a photoelectric microphone, called the Pallo-photophone. Westinghouse engineers developed a cold-cathode microphone using a direct-current glow discharge in air about 1923. In Europe the Marconi-Sykes magneto-phone—a moving coil microphone—was used in England, and the Reisz carbon microphone in Germany and France. The ribbon microphone was proposed by Gerlach and Schottky in 1924. H. F. Olson was the first to realize the advantages of the directional response of the velocity ribbon microphone and developed a practical microphone about 1931. C. A. Hartman brought out a pressure-actuated ribbon microphone in Germany in 1931. The directional pattern of the ribbon microphone has found wide application in motion picture recording and broadcasting especially since 1933 when J. Weinberger, H. F. Olson, and F. Massa designed a unidirectional ribbon microphone. The moving-coil microphone was invented and patented by Siemens in 1877. The British Broadcasting Corporation in 1923 began using the Marconi-Sykes magnetophone. In 1931 Bell Telephone Laboratories engineers announced a new type of high quality moving-coil microphone which was improved in 1935 to have a nondirectional response. In 1919 Western Electric engineers under A. M. Nicolson made an extensive study of piezoelectric crystals. Some crystal microphones and phonograph pickups were used in English broadcasting in 1922 but the commercial application of piezoelectricity to acoustic devices was not made until 1930. By then, the Brush Development Laboratories had developed a cheap method of growing large crystals and cutting procedures as simple as wood-working shop methods enabling them to make microphones, phonograph pickups, recording cutting heads, and loudspeakers.
The Attenuation of Sound in Ducts
Authors: Rogers Robert
Published: September 2005

This paper deals with the propagation of sound in ducts with particular reference to the coefficient of attenuation. A theory is developed which may be shown to be in substantial agreement to a first-order approximation with that given by Sivian. Cases which have not previously been considered are here investigated, namely that case in which only one or two sides are lined with a material, and the case for high frequencies. It is shown experimentally that the dependence of the attenuation coefficient on the ratio of the perimeter to the area follows the theoretical prediction. Further, the impedance of the material, which must be used in calculating the attenuation coefficient, is shown to agree with impedances measured by the standing wave method. At low frequencies the attenuation coefficient is found to decrease with the frequency to such an extent that the reduction of the sound level in a tube sixteen feet in length is of the order of about ten decibels. In order to find a material which attenuates the sound more highly at low frequencies, experiments are being carried out on samples which have a complex impedance, i.e., on vibrating materials.
Noise and Vibration Isolation
Authors: Leedy H. A.
Published: September 2005

The characteristics, stiffness factor and damping factor of resilient supports which will effectively reduce the transmission of vibrations and noise from vibrating machines are usually determined from the “transmissibility” curves which give the ratio of force amplitude transmitted to the base through the resilient support to the amplitude of the driving force as a function of the driving force frequency. Since such curves are calculated on the assumption that the base on which the machine is mounted is immovable, in which case the vibration transmission must be zero, it is desirable to know what happens in the case where the base on which the machine is mounted is free to vibrate. By considering the forced vibrations of coupled linear oscillators, the ratio of the vibration amplitude of the base when the vibrating machine is mounted on a resilient support, to the vibration amplitude of the base when the machine is mounted directly on the base, has been determined. In particular limiting cases, this ratio is equal to the transmissibility. However, in general, this is not the case and curves showing how the above amplitude ratio varies with frequency and type of resilient support are given.
Filtration of Oblique Elastic Waves in Stratified Fluid-Solid Media
Authors: Lindsay R. B.
Published: September 2005

Previous work has been done on the problem of the transmission of compressional elastic waves normally and obliquely through a stratified medium consisting of alternate plane parallel layers of two different fluid substances. Such a structure acts as a low pass elastic wave filter, and in the case of oblique transmission the bands depend characteristically on the angle of obliquity of the wave front. The present work extends the problem to the case in which one of the substances is solid. Account must here be taken of the fact that compressional waves in the fluid layers give rise to both dilatational and shear waves in the solid layers. The result is somewhat more complicated than in the previous case but the structure still turns out to be a low pass elastic wave filter for angles of obliquity less than the critical angle. As before the transmission and reflection bands are a function of the angle. In the special case in which the thickness of the solid layers is small compared with that of the fluid layers one obtains the elastic wave analogue of the Bragg reflection law for x-rays, that is, one gets reflection approximately for the wave-lengths λn = 2l/n⋅sin θ, where l is the distance between successive solid layers and n is integral.
Interaction Impedance of a System of Circular Pistons
Authors: Klapman S. J.
Published: September 2005

When two pistons, vibrating in the same infinite plane, are radiating into a semi-infinite medium, there is an interaction between them. There has been reported a method for obtaining an approximation to the real part of the interaction when the two pistons are vibrating in phase. In the present paper the resistance term or “aid” is obtained exactly in contrast to the use of numerical integration in the approximation method mentioned. Also, basing an approximation method on a numerical integration of a generalized elliptic integral, numerical forms are obtained for both the real and imaginary parts. Because both the resistance and reactance have been obtained for the case of two circular pistons vibrating in phase, the results may be easily extended to the case of an arbitrary number of pistons, in the same plane, with arbitrary phases.
Remaking Speech
Authors: Dudley Homer
Published: September 2005

Speech has been remade from a buzzer-like tone and a hiss-like noise with automatic control of the pitch and timbre by the talker's speech that is being remade. The newly created speech may be altered from the original in a variety of ways since the fundamental variables of speech are under experimental control between the steps of speech analyzing and synthesizing that together remake the speech. The demonstrations will show in detail the steps in remaking speech as well as the effects of changing various elements. Included among these demonstrations will be the automatic raising and lowering of pitch, changing the octave range of pitch, reversing the inflection, removing the melody from song, transforming voiced speech to a whisper, the relative contributions of the buzz and hiss to the remade speech, etc. The demonstrations will show some striking characteristics of speech such as its recreation under the control of currents too low in frequency to be audible and the use of timbre for intelligibility and of inflection for emotional content. The synthesizing process here used provided the basis for the synthesis of speech by the manipulation of keys as accomplished in the Voder, one of the Bell System's exhibits at this year's World's Fair.
The Influence of the Soundboard on Piano Tone Quality
Authors: Bilhuber Paul H. , Johnson C. A.
Published: September 2005

The history of piano development indicates that tone quality has often suffered because the soundboard lacked the optimum response to vibration of the strings. This lack has been particularly noticeable in the high treble notes. Early experimentation in design attempted to correct this difficulty by extreme variations in size and shape of the board and by the use of special resonating chambers. Eventually such radical departures were discarded in favor of the present type of soundboard. This paper describes experimental work that has been conducted in an effort to determine some of the factors of soundboard behavior which influence the tone quality of the piano. Apparatus was constructed for measuring the amplitude of vibration at different points over the surface of the board when the keys were actuated by a mechanical striker. The results show that for a given piano the most acceptable tone quality is obtained when the soundboard vibrates more or less as a diaphragm with the maximum amplitude near the center. Changes in the compression or loading of the board which tend to reduce this diaphragmatic action also produce a less acceptable tone quality. In order to retain desirable tone quality in small pianos, it was necessary to compensate for the limitations of shorter strings and smaller soundboard area by changes in the structural design of the soundboard itself. Comparative measurements made on small pianos with old and new types of soundboards show that in the latter (1) the board vibrates more nearly like a diaphragm, (2) the treble tones have a higher initial intensity and (3) the treble tones decay at a slower rate.
An Audiofrequency Harmonic Generator System
Authors: Frick R. H. , Veneklasen P. S.
Published: September 2005

For proposed research in musical acoustics, a simple compact generator system is needed in which the relative phase and amplitude of each harmonic may be varied independently. In order that the fundamental frequency may be shifted freely, it is necessary to secure sinusoidal wave forms from the individual generators without recourse to electric circuit filtering. The principle of operation is similar to that employed by Firestone and also by Kurtz and Larsen. However, relative amplitude is controlled by mechanically varying the condenser gaps, while the polarizing potential remains constant. Relative phase is controlled by angular displacement of the harmonic stators relative to the fundamental stator. The theory has been developed for the rotor and stator tooth forms which will give a sinusoidal rate of change of capacity between the two elements. The theory indicates that this stator form discourages the production of even ordered harmonics of the rotor tooth form. Results of harmonic analysis of the individual generators show that the production of undesired harmonics is very low. Any remaining harmonic impurity may be eliminated by means of a cancellation principle.
Speech Production as Revealed by Vocal Cord Photography and Sound Wave Analysis
Authors: Steinberg John C.
Published: September 2005

For more than a century, wide differences of opinion have been held as to the function of the vocal cords in speech production. In the present paper, this problem is approached by utilizing high speed motion picture photography to determine the vibrations of the cords during phonation and a method of Fourier analysis to determine the characteristics of the sound waves.

By taking pictures at a rate of 4000 per second and projecting them at the normal viewing rate of 16 per second, the motion is slowed down by a factor of 250 to 1. Thus, if the cords execute 250 vibrations in one second, they appear to make one vibration per second and the details of their movements may be seen. Pictures suitable for monocular viewing, and also stereoscopic pictures showing the movements of the cords in full relief, have been obtained.

For the lower pitches, the cords appear to be completely relaxed, and there appears to be a phase difference between the movements of the lower and upper surfaces. They do not move as units, but more as folds or lips, the motion of the upper surfaces lagging behind that of the underneath surfaces. The tension increases as the pitch is raised, the cords elongate and tend to move more nearly as units with somewhat smaller amplitudes than for low pitches. The movements appear to begin toward the front end of the cords and to extend progressively toward the back, so that the motion has a horizontal as well as vertical phase difference.

The analysis of the vocal cord vibrations indicates a vibration form composed of a fundamental having a frequency equal to the vibration rate of the cords and overtones, which diminish in amplitude with increasing order or number of the overtone. Such vibration forms do not possess the distinguishing characteristics of the different speech sounds. The latter characteristics are produced by the passage of the sound waves through the throat, nose and mouth cavities.

The paper will be illustrated by motion pictures showing the movements of the cords in ultra-slow motion, and by variable area recordings of the sound waves and their corresponding analyses. Stereoscopic motion pictures will be available for limited viewing so that the cord movements may be seen in relief.
A Digest of Modern Voice Research
Authors: Bartholomew Wilmer T.
Published: September 2005

A review of the more significant work in this field, and an attempt to synthesize from the available material a picture of how the vocal apparatus works as a whole.
Statistical Measurements on Conversational Speech
Authors: Dunn H. K. , White S. D.
Published: September 2005

Several types of measurement are reported. R.m.s. pressures in one-eighth-second intervals, from the speech of a single voice, are compared with similar measurements in one-fourth-second intervals. The values obtained in the first case are only slightly more widely distributed than in the second, and the difference is least when attention is confined to high frequencies.

To earlier r.m.s. measurements, on the voices of six men and five women, is applied the relation found more recently between pressure at a point and total voice power. The resulting curves represent average spectra of voice power for the men and women.

Measurements of the distribution of instantaneous pressures in speech are also given.
Some Practical Aspects of Architectural Acoustics
Authors: Knudsen Vern O.
Published: September 2005

Recent developments in the theory of room acoustics may seem baffling to the architect and engineer, but there inhere in these developments some useful findings which apply directly to the acoustical design of architectural interiors. Such important matters as the best shape of a room and the most advantageous distribution of absorptive materials in a room are certain to be elevated from the realm of empiricism to the more exact realm of scientific planning. The present paper discusses these and related matters; in addition, it outlines typical procedures in acoustical designing which recently have come to the writer's attention, some of which lead to good and others to unsatisfactory results.
Practical Application of Acoustical Correction in University Buildings
Authors: Horner George L.
Published: September 2005

The University of Iowa has for many years recognized the value of sound control and has at different times dealt with all its various divisions. It is not often though that all the various divisions of sound control are embodied in one problem. Such was the problem in designing the University Theater.

The first division was the audition qualities of the auditorium, and after consulting acoustical experts, a design was worked out whereby it was thought all acoustical treatment might be omitted. The design proved successful and no sound absorbing materials were required in the auditorium.

The second division, reducing the noise level, was also considered in connection with rehearsal rooms; however, insufficient funds have prevented the carrying out of this correction 100 percent.

The third division, sound isolation, the most difficult in many ways to correct, was corrected by the use of sound barriers. Most of these barriers are of structural materials, brick and tile. In ventilating ducts, duct lining was used and all air is handled at low velocities to reduce air noises.

The fourth division, the control of noise generated by machinery, was probably our most serious problem. Great care was used in mechanical design and all motors were specified “special quiet”. All machinery was mounted on rubber isolators. Most equipment was designed to meet a 30-decibel reading in the auditorium.

The theater as used by the Dramatics Department requires a very low sound level and through the use of care in design and the corrections as outlined, this result was obtained.

The Music Building, various classrooms, lecture rooms and laboratories have been treated acoustically—the majority for better audition qualities although some, the Music Building, have been treated for sound isolation and reducing the noise level.

It is quite obvious that a University is a fertile field for acoustics, particularly its application, in fact too fertile. Too many classrooms and laboratories need sound control of some kind and insufficient funds usually hamper the completion of projected plans.
Planning Functionally for Good Acoustics
Authors: Maxfield J. P. , Potwin C. C.
Published: September 2005

The science of architectural acoustics has now taken its position as one of the bases of creative design. Planning of the interior shape of the auditorium to fulfill both the acoustic and the functional requirements is but two phases of a single problem.

This paper will present an empirical study of the control of auditorium acoustics by the correlation of the internal geometry with the amount and placement of absorbing materials. A brief discussion will be given of some of the subjective experiences which led to the development of the empirical design technique.
What Acoustical Treatment Will and Will Not Do
Authors: Sabine Hale J.
Published: September 2005

It is sometimes found that acoustical materials, installed for the purpose of correcting auditorium acoustics or quieting noise, produce results which either exceed or fall short of expectations. A number of typical examples are described and explained in terms of the physical and psychological factors involved. Comments are given on the results which can and cannot be expected in various applications.
Correlations Between Air and Bone Conduction Acuity Measurements in Different Types of Deafness
Authors: Reger Scott N.
Published: September 2005

Several audiograms of various types of deafness, indicating both air and bone conduction threshold measurements, will be shown and discussed from the standpoint of the value of the correlations between the air and bone conduction determinations. A method of ascertaining the functional efficiency of the ear drum and ossicles on the basis of bone conduction acuity measurements with the ear canal open and then occluded also will be described. The necessity of masking while making bone conduction measurements will be considered briefly.

Some of the deficiencies of tuning forks and various types of bone conduction receivers or vibrators supplied with audiometers will be discussed and constructive criticism offered from the clinical point of view.
Alteration in the Liquid Structure of Electrolytes as Indicated by Acoustic Waves
Authors: Corey Victor B. , Stewart G. W.
Published: September 2005

The use of supersonic stationary waves for the determination of the velocity of sound in liquids is well known. With water, and frequencies of the order of 106 per second, the acoustic velocity is independent of the viscosity and is the reciprocal of the square root of the product of the density and the compressibility. Stewart has shown that the solution of strong electrolytes in water alters the liquid structure of the solute and has suggested an arbitrary x-ray diffraction method of estimating the magnitude of the change of the structure. Measurements of compressibility have been made with aqueous solutions of NH4C2H3O2, NH4Cl, NaCl, KCl, MgCl2, CoCl2, Co(NO3)2, Co(C2H3O2)2. It has been found that the rate of change of compressibility with mole fraction of the strong electrolyte has a correspondence in relative magnitude with the rate of change. of liquid structure per mole fraction as crudely estimated by x-ray diffraction methods. This adds evidence to the view that the structure of the water is altered by the ions.
Measurement of Impact Sound Transmission Through Floors
Authors: Lindahl Robert , Sabine Hale J.
Published: September 2005

Existing methods of measuring the transmission of impact noise through floors and of stating the results are inadequate in two respects: (1) Published data give the difference in intensity of impact noise measured above and below a given floor construction, but do not permit an accurate comparison of the noise transmitted by different constructions. (2) No attempts have been made to determine the comparative transmission-frequency characteristics of different constructions.

A new method of measurement is described. The impact noise is generated by a mechanical tapper, and the sound transmitted is measured with a sound level meter. By means of band pass filters the sound level in each of six octave-wide frequency bands is determined. The sound transmitted by a bare concrete slab is arbitrarily assigned a level of zero decibels for each frequency band, and the levels measured for other constructions are stated as decibel reductions at each frequency referred to the zero levels for the concrete. The over-all rating for each construction is taken as the average of these decibel reductions for the six frequencies 128 to 4096 cycles. Comparative ratings arrived at in this way agree satisfactorily with subjective estimates of the comparative “noisiness” of the transmitted sound.
Stylus-Groove Relations and their Influence on Phonograph Reproducer Design
Authors: Hunt F. V. , Pierce J. A.
Published: September 2005

As part of a continuing study of high fidelity sound reproduction from phonograph records, we have made a survey of the groove shapes being used in current release records. The results of this survey provide data for considering the stresses set up in the record material for various configurations of the stylus-groove contact. In connection with our previous work on tracing distortion, this analysis establishes certain requirements which must be satisfied in order to secure positive tracking in reproduction from lateral-cut records. The structure of currently available “high fidelity” reproducers will be discussed in the light of these requirements. A preliminary report will also be presented concerning an analysis of “translation losses,” harmonic distortion, and other effects of transient elastic deformations of the groove wall by the reproducer stylus.
Studies of the Vocal Cords in Relation to the Quality of Certain Speech Sounds
Authors: Cowan Milton
Published: September 2005

Recent experimental investigations by W. Trendelenburg, H. Wullstein, W. Hartmann and F. Trendelenburg are reviewed. Three experiments on fresh calf and human larynx preparations and one on human subjects are described.

W. Trendelenburg and Wullstein made simultaneous recordings of glottal lip movement, shadowgraphs of the glottal chink, and oscillograms of air vibration at various points above and below the glottis. The vocal cords constituted the moving plate of a condenser microphone for registration of the lip movements. An optical system sent a beam of light from the trachea through the glottal chink and this photographed shadowgraphs above when the cords were brought into vibration by means of a controlled current of air up through the trachea. A condenser microphone was used to record air vibrations. Plastellin forms approximating the shapes of the supralaryngeal cavities for the vowels “a” and “o” were placed above the larynx. The recordings showed that, with or without the resonators, the lip movements were essentially sinusoidal, that there was no back-coupling between cavities and cords, that the glottis was open for a relatively short portion of the cycle, that the formant frequencies were especially noticeable immediately following the glottal opening and closure and were highly dampened during the closure phase of the glottal cycle.

Hartmann bored through the side of the larynx at the level of the cords and obtained simultaneous shadowgraphs of the lateral and vertical movements of the cords. The maximum glottal opening coincided with the highest point reached in the vertical movement. After closure the downward movement of the cords continued to a minimum at about the middle of the glottal closure phase. Averages: total vertical movement = 1.25 mm; glottal opening = 1.43 mm; ratio = 1:1.15.

Hartmann and Wullstein recorded glottal shadowgraphs and light density variations simultaneously. Maximum density coincided with maximum glottal opening. On the human preparation, light density decreased after the glottal closure, indicating a pressing together of the cords. When the cords were made opaque by staining, light density variations coincided with the area of the aperture.

Following up the observation that formant frequencies were especially prominent immediately following the glottal opening and closure, W. Trendelenburg found subjects who were able to intone vowels so that the first cycle was essentially the same as the succeeding ones in frequency, intensity and overtone structure. The typical energy maximum coinciding with the opening phase of the glottis was again apparent in the first cycle and was named the “initial group.” Further work with F. Trendelenburg utilizing octave filters showed that it is possible to determine the time of glottal closure in any cycle of a vowel. The records from the octave filters will show two vibration groups or vibration maxima which can be related to the opening and closure of the glottis.
Tone Production on the Stringed Instrument
Authors: Small Arnold
Published: September 2005

The bowing factors involved in tone production and the means of their control have been studied and measured. This makes possible a more complete understanding of their control for artistic ends. Left-hand considerations in tone quality have also been analyzed. They likewise offer experimental bases for artistic and pedagogical procedure. The implications of these studies for the string player will be emphasized.