bluuebunny/crossref_metadata_2025 huggingface dataset:
Early Theories of Hearing
Authors: Rosenblith Walter A. , Békésy Georg V.
Published: September 2005

The intellectual heritage of Greek natural philosophy includes a number of speculations and hypotheses dealing with the perception of sound. Through the middle ages all theories of hearing were characterized by the central role of the “aer internus.” As anatomical data became available concerning the structures in the middle and inner ear, and as the physics of sound became better understood, the need for theories in reasonable agreement with experimental facts arose. In 1683, the collaboration of the anatomist Duverney and the physicist Mariotte yielded the first “resonance theory” of hearing. Duverney identified the bony fibers of the cochlear partition as the tuned elements. This localized the high frequencies at the apex and the low frequencies near the stapes. But Duverney and his contemporaries continued to cling to the belief that air was present inside the cochlea. It was not until 1760 that Cotugno established definitely the presence of fluid throughout the labyrinthine cavity. During the 18th century there was much verbal disagreement among the various physiologists concerning the “resonators” in the ear and concerning the localization of high and low frequencies. In 1822, Magendie dismissed the whole resonance hypothesis with a single sentence since, as he said, “no one believes it at the present day.” When Helmholtz developed his theory in the second half of the 19th century the situation had changed: he had new building stones at his disposal, among which microanatomical data collected by Corti and Hensen, Fourier's theorem and Ohm's acoustic law were the most important.
The Spiral of the Human Cochlea
Authors: French Norman R.
Published: September 2005

Although the human cochlea has long been known to have the form of a spiral, no reference to the particular type of this spiral has been noted in the literature. Using published data, the present study derives the equation of the spiral and uses it to calculate the length of the basilar membrane. The equation has interesting implications. As an example, it implies that the paths followed by the separate nerve fibers, proceeding from the base of the cochlea to their terminations on the individual hair cells arranged along the length of the basilar membrane, are approximately of equal length. The study also uses a limited amount of transit-time data to calculate the velocity along the cochlear duct of an impulse applied to the stapes. The calculated velocities diminish rapidly as the impulse advances toward the helicotrema. The calculations suggest that the absolute values of the velocities, and the manner of their variation with distance, may be related significantly to the positions of maximum response along the basilar membrane to tones of different frequency. The results suggest the need for (1) additional physical measurements of velocities of propagation in the cochlea, and (2) further studies of the cochlear spiral from the standpoint of its possible operational significance.
A Progressive-Wave Method for Transducer Theory
Authors: Cady Walter G.
Published: September 2005

The present treatment has to do with an array of piezoelectric crystals sending acoustic energy in the form of plane waves through a diaphragm into an infinite medium. The problem of this composite vibratory system, undergoing forced simple-harmonic vibrations at any frequency, is solved in terms of waves progressing in the positive and negative directions. Although the basic method is not new, it has apparently not been applied hitherto in the present form for predetermining the performance of transducers. From consideration of boundary conditions a set of simultaneous equations is derived. Their solution yields curves showing the radiated wave amplitude and acoustic power for any frequency and for any ratio of diaphragm thickness to crystal dimensions. Internal losses in crystals and diaphragm can be included if desired. The method is being extended to cover the case in which the crystals have a solid backing-plate on one side as well as a diaphragm on the other.
Design and Construction of a 100-kc Magnetostrictive Transducer
Authors: Camp Leon , Vincent Richard , duBreuil Felix
Published: September 2005

The principles involved in the design of a directional array are presented, and the construction described. The necessary data to illustrate its operating characteristics are given.
Design of Laminated Magnetostrictive Longitudinal Oscillators
Authors: Bundy F. P.
Published: September 2005

In designing the oscillating elements of practical transducers it is convenient to be able to calculate the dimensions of the proper structure to give the desired frequency, sharpness of resonance, and efficiency. In laminated magnetostrictive oscillators these factors are influenced by the ratio of the areas of the radiating face and the magnetostrictive columns, the lamination thickness, the coil position, the magnetic polarization, the relation between the magnetic flux paths and the nodes of the vibrational motion, etc. The following general cases will be treated: (a) simple bars of uniform cross section; (b) simple bars with pistons or diaphragms; (c) multiple bars with symmetrical closed ends; (d) multiple bars with symmetrical closed ends and attached diaphragms; (e) multiple bars with unsymmetrical closed of nearly closed ends; (f) multiple bars with unsymmetrical closed ends and diaphragms; (g) miscellaneous forms.
Transmission of Sound Through Homogeneous Walls
Authors: London Albert
Published: September 2005

Current methods of measuring the transmission of sound through structures include the random incidence or reverberant sound field method, and the normal incidence or tube method. The latter method has the serious defect that only normally incident sound waves are used to drive the specimen, whereas, in actual use it is probable that waves having oblique angles of incidence will be experienced. Furthermore, considerable deviation from the mass law, in the direction of increasing transmission, occurs as a result of flexural waves induced in the specimen by non-normally incident waves. Random incidence sound-transmission measurements made on homogeneous walls of aluminum, plywood, and plaster-board, are in satisfactory agreement with a theoretical treatment, which postulates that the wall impedance has a resistive component in addition to its mass reactance, and a stiffness reactance resulting from the occurrence of flexural waves.
Measurement of Acoustic Impedance
Authors: El-Mawardi O. K.
Published: September 2005

The acoustic impedance of a sample of material forming one boundary of a shallow cylindrical cavity can be determined by measuring the sound pressure produced when a known volume current is injected into the cavity from a high impedance source. The volume current is effectively determined by observing the pressure when the cavity is terminated rigidly. An impedance determination is thus reduced to measurement of the complex ratio of two observed voltages. By designing a ring source to suppress the first radial mode of the cavity, the upper frequency limit set by uniformity of pressure distribution is extended by at least an octave. By avoiding leaks, measurements can also be extended to very low frequencies. Secondary effects due to finite source impedance, viscosity, and heat losses at the walls have been evaluated. The method appears to be simple, rapid, and precise.
The Acoustic Feed-back Method of Measuring Acoustic Impedance
Authors: London A. , Krishnamurthy C. R.
Published: September 2005

A method of measuring acoustic impedances, either point or transfer impedance, is described. In this procedure the acoustic impedance is utilized as a positive feed-back network in an electrical circuit. The acoustic impedance is connected to the electrical network by means of two transducers, one of which serves as a microphone or pick-up, the other as a loudspeaker or driver. By using a continuously variable filter as the electrical network, the frequency variation of the acoustic impedance may be determined. The system may be used in investigating the normal mode of rooms, walls, cavities, etc. Some experimental results will be given.
Measurements for Aiding in the Evaluation of the Quality of Loudspeakers
Authors: Hall H. H. , Hardy H. C.
Published: September 2005

Only a few of the physical properties which are characteristic of loudspeakers have been studied exhaustively. It is the purpose of this paper to point out some other measurements which are not commonly used but which have been found to have great promise in studying loudspeakers. One of these, the transient response, has been described in the previous paper. Another is the number and magnitude of subharmonics which are produced by the loudspeaker. A good correlation has been found between the number of subharmonics produced by the speaker and the quality rating of the speaker determined by listening tests. A third test is to determine the maximum sound level which is reached before a certain amount of harmonic distortion is produced. This measurement can be conveniently made on the axis of a speaker at a standard distance, and can be presented in the form of a curve of the maximum undistorted sound pressure as a function of frequency. Such a curve differs markedly from the response curves, having dips sometimes 30 db below the rated output level of the speaker. It is important, of course, to measure these data in the enclosures for which the speaker is designed. Curves will be presented showing the subharmonics and maximum undistorted level of several typical loudspeakers. An important advantage of both of these types of measurements is that they can be made with equipment available to most loudspeaker manufacturers.
Electro-Acoustic Phase Shift in Loudspeakers
Authors: Ewaskio C. A.
Published: September 2005

Direct measurements of envelope delay (dβ/dω) have been obtained for a series of commercial and experimental loudspeakers. The modulation phase shift method of Nyquist and Brand has been adapted for direct indication of envelope delay by utilizing a direct-reading electronic phase meter. By suitable choice of modulating frequency, the phase shift of the modulation envelope (between electrical input and sound pressure on the loudspeaker axis) in degrees gives the envelope delay directly in milliseconds. Pressure-amplitude curves measured under the same conditions provide data for a preliminary attempt to interpret the correlation between delay response and pressure response.
Acoustic Absorption in Sand and Soil
Authors: Nyborg W. L. , Rudnick I.
Published: September 2005

The acoustic absorption properties of sand and soil with varying amounts of water, ranging from dry to saturated, have been investigated. In most of the work the frequency range was 10–30 kc, although data were obtained at as high as 150 kc. Two methods were used. In one, the source and a number of equally spaced probe microphones were imbedded in the medium. In the other method the source and receiver were in air and the transmission loss was determined for samples of varying thickness. The unsaturated media were found to have attenuation coefficients ranging from 2 db per cm for nodulous, loose soils to greater than 25 db per cm for finely divided soils and sand, the value for any particular sample depending in an important way on its flow resistance. In water-saturated media the attentuation was found to depend markedly on the amount of gas present in the mixture. Air-free mixtures prepared in an evacuated chamber had attenuation coefficients which were too small to be measurable—probably less than 2 db per cm. On the other hand, for mixtures prepared in the presence of air the attenuation coefficients immediately after mixing were extremely large. For one sample it ranged from 26 db per cm at 10 kc to 64 db per cm at 30 kc. When such a mixture is then left undisturbed the intensity level increases strikingly—as much as 50 db at 30 kc over a period of 100 hours.
Large Amplitude Motions of a String
Authors: Harrison H.
Published: September 2005

By expressing the differential equations for large amplitude motions of an ideal string in vector form, we have derived several results which seem to have been hitherto unreported. These equations become linear not only when the tension is constant or when the transverse wave is absent, but also when the initial tension equals the string's elastic modulus. Even when the tension and the transverse wave have arbitrary values, we can discuss the solution physically without resort to series expansions. By projecting the differential equations onto the string we can show that the tension waves are unaffected by transverse waves. Transverse waves of large amplitude, not necessarily limited to a plane, can propagate in opposite directions through each other without interaction. However, changes in tension not only change the speed of propagation of transverse waves but also, by the impulse-momentum theorem, generate new waves which propagate in opposite directions along the string. These new waves are similar to the initial transverse waves and proportional to the relative change in tension. Actual strings have bending stiffness which causes dispersion without introducing non-linearity. One can calculate this dispersion from a well-known equation. A few flash pictures of an actual string, which illustrate and verify our analysis, will be presented. Professor Harold Edgerton of M.I.T. suggested this problem and provided facilities for making the experimental pictures.
The Absorption of Sound in Air at Reduced Pressures
Authors: Delsasso L. P. , Leonard R. W. , Halley Robert
Published: September 2005

The decay of sound energy in spherical shells has been used to measure the absorption coefficient of air as a function of pressure and humidity. Radial modes are stimulated by introducing the sound through small tubes which terminate at the centers of the spheres. The decay of the sound intensity for these modes depends both on the loss at the boundary and on the absorption in the medium. By determining the reverberation times in pairs of similar spheres of different radii, correction is made for the boundary effect. The measured values of the absorption coefficients for frequencies in the audio range are compared with those calculated for classical and molecular absorption.
Loudness of Speaking: The Effect of Heard Stimuli on Spoken Responses
Authors: Black John W.
Published: September 2005

Twenty-five subjects heard recorded words at five levels of loudness. The subjects heard the recorded stimuli over headsets and were asked to repeat the words in a normal manner. The loudnesses with which the repetitions were made were noted from a Sound Level Meter, the microphone for which was eight inches in front of the speaker's lips. The same procedure was followed, using as stimulus materials sentence questions that required obvious one-word responses. In both instances, the subjects spoke with a loudness proportional to the intensity of the signal. In a follow-up experiment, subjects were instructed that normal behavior was to increase vocal loudness in keeping with signal strength and asked to maintain a constant level of loudness irrespective of the intensity of the signal. The subjects were unable to follow these instructions.
Sound Absorption at the Surface of the Body of Man and Animals
Authors: von Gierke H. E.
Published: September 2005

The results of measurements of sound absorption by the body surface of man and fur-bearing animals are reported for the frequency range 100 to 12,000 c.p.s. The acoustical impedances and the absorption coefficients of the surfaces were determined from the resonance characteristics of an air-filled tube. The end of the tube was closed first by a rigid wall and then by the unknown surface. From the change in the resonance characteristic induced by the unknown surface the desired quantities were calculated. In order to speed up the measurements, which is important with living test material, a second method was used. In this method the air column was excited by sound pulses, and the decay time of the sound pressure was measured from the photographs of the cathode-ray trace. At the higher frequencies an aluminum rod, pressed against the body surface, replaced the air column. The desired quantities were calculated from the change in longitudinal resonance characteristics in a manner similar to that employed for the air column. The absorption coefficient of the human body surface varies frown 10 percent to 0.1 percent and decreases at higher frequency. The resistances per cm2 varies between 103 and 105 ohms and are dependent upon the area of application and the pressure upon the skin and muscles. The measurements on rats show that up to 1000 c.p.s. the absorption coefficient decreases and then increases up to 6000 c.p.s. The behavior below 1000 c.p.s. is determined largely by the tissues beneath the skin while the increased absorption above 1000 c.p.s. is the result of the presence of the fur. This is demonstrated by measurements on shaved animals where the absorption decreases steadily as the frequency increases, whereas in the case of furred skin supported on a rigid wall the absorption increases as the frequency increases. These absorption coefficients permit the estimation of the sound energy absorbed by a whole animal. The sound intensity required to cause heat death can then be calculated approximately.
Levels and Spectra of Transportation Vehicle Noise
Authors: Bonvallet G. L.
Published: September 2005

In the years immediately preceding the war an informal program of the study of traffic, transportation vehicle, and industrial noise was undertaken in the Chicago area. In the recent past another but much more exhaustive program has been initiated, and further and more detailed work has now been done. One phase of the work has been a study of the noise within the various types of vehicles generally employed in transportation. These include older and newer type trolley cars and trolley buses, elevated lines and subway cars, suburban electric and steam trains, and passenger automobiles. Measurements were made in these vehicles not only of total sound level but of components in octave bands in the audible frequency range. The work has therefore permitted a comparison of the acoustic spectra in these vehicles, and curves to show these characteristic differences will be shown.
Improved Sound Transmission Measuring Technique
Authors: Ramer L. G. , Tyzzer F. G. , Ancell J. E.
Published: September 2005

A study is being made of sound transmission of walls, doors, and panels at the Riverbank Acoustical Laboratories with the purpose of relating the measurements more closely to the properties of the test wall alone, instead of the test wall plus the adjoining rooms. The possibility is being investigated of measuring the effective “impedance” of a wall with random distribution of incident sound. This method is similar to that used at Harvard in tests on small airplane panels for sound at normal incidence. In order to allow for phase differences in the motion of the test wall, measurement of the transmitted sound is to be made at a distance from the wall in a long narrow room with one end covered by absorbing wedges. To evaluate test conditions, the sound fields have been explored on either side of a test wall. Pressure distribution on the source side (reverberation chamber) of the wall is given as a function of frequency and reflector position. This also indicates the state of “randomness” in the reverberation room. Results are also given for preliminary tests on the transmitted sound field.
A Comparison of Artificial Ear Couplers
Authors: Morrical Keron C. , Glaser John L.
Published: September 2005

Comparison is made of the response of a number of earphones measured on several types of earphone couplers. Points of difference are noted and the attempt made to explain them through the use of some specially designed couplers. Certain characteristics were observed which might influence the design and use of couplers for purposes of determining earphone response.
Theory of Passive Linear Electroacoustic Transducers with Fixed Velocity Distributions
Authors: Foldy Leslie L.
Published: September 2005

On the basis of the general theory of passive linear electroacoustic transducers developed by H. Primakoff and the author, a number of interesting theorems may be established for the class of transducers for which the surface velocity distribution has a form independent of the mode of excitation of the transducer It may be proved for such transducers that the maximum power which may be absorbed by the transducer (when the velocity distribution of the transducer is kept fixed but other transducer parameters are varied) is given by λ2I/4πδ where λ is the wave-length, δ is the directivity index relative to the direction from which the wave is incident, and I is the intensity of the plane wave. The absolute efficiency of a transducer is defined to be the ratio of the power transferred by the transducer to the maximum power which can be transferred by the transducer. For a transducer operating as a speaker, the absolute efficiency is equal to the actual efficiency when the transducer is driven from an impedance conjugate to its own impedance. For a transducer satisfying the reciprocity conditions, the absolute efficiency as a speaker and microphone are equal. This is not, in general, true for the ordinary efficiencies. The signal-to-noise ratio of a transducer operating as a microphone may be shown to be proportional to its absolute efficiency as a microphone and inversely proportional to its directivity index. This last result indicates the value of the concept of absolute efficiency as a criterion for good design of a transducer.
Direct Measurements of the Attenuation of Audio Frequency Sound Pulses in the Open
Authors: Delsasso L. P. , Leonard R. W. , Silent H. C.
Published: September 2005

Equipment has been developed for the direct measurement of the attenuation of short pulses of audiofrequency sound in the open. The source consists of a 500-cycle, one-quarter wave pipe which is excited at intervals of about 10 sec. by an explosive mixture of acetylene and oxygen. The damped sound wave thus produced is first received by a near reference microphone and after an interval of time at a second distant microphone. Appropriate calibration and timing circuits are provided to actuate a single sweep oscilloscope as the sound pulse passes each microphone. The signal from the distant station is returned to the near station by f-m. Both signals are recorded automatically by a solenoid operated camera. A second oscilloscope and continuous film camera provides accurate transit time records. By observing the reduction in sound intensity between the two stations and making correction for the divergence of the sound wave, the attenuation is computed. The values thus obtained are compared with those calculated from laboratory measurements under similar temperature and humidity conditions.
Consideration and Acceptance of Hearing Aids
Authors: Carter Howard A.
Published: September 2005

This paper is a short discussion on the consideration and acceptance of hearing aids by the Council on Physical Medicine of the American Medical Association. Some of the problems and the method of considering hearing aids and audiometers will be presented. A list of accepted hearing aids will be available for distribution.
Assessment of Impaired Hearing by Articulation Scores
Authors: Davis Hallowell
Published: September 2005

The phonetically balanced “PB” lists are an effective tool for measuring the ability of impaired ears to hear correctly words of varying degrees of difficulty. If we know the position of a patient's PB articulation curve on the scales of intensity and of discrimination, we can estimate the percentage of ordinary words that he can hear adequately when speech is (1) faint, (2) average, and (3) loud. The average of these three scores constitutes our Social Adequacy Index for hearing. The location of the foot of a patient's articulation curve on the intensity scale can be most quickly and accurately determined by threshold tests once we know the average articulation score that corresponds to the particular threshold test employed. The equivalent PB articulation scores have been determined experimentally for Test No. 9 (spondee words), Intelligibility of Connected Discourse, Test 4C (2-digit numbers), and Test No. 12 (simple sentences).
A Method for the Measurement of Acoustical Impedance
Authors: Bazeley Arthur J.
Published: September 2005

The concept of acoustical impedance introduced in 1919 by A. G. Webster has made possible direct analogy between electrical and acoustical systems. The most commonly used method for measuring acoustical impedance today is by a study of the standing waves in a long tube, with the unknown at one end, by means of a small microphone or probe tube. The method herein described consists of a source of sound pressure directed into a small chamber, at the other end of which is an unknown impedance, beyond which is another small chamber. The sound pressure is measured in each chamber by means of small microphones in the chamber walls, and the circuit is solved by direct analogy with electrical circuit theory.
Dynamic Force Generators
Authors: Brown A. Dix , Langevin Robert A.
Published: September 2005

Generators providing metered sinusoidal forces are useful tools in electromechanical and electroacoustic research. The design considerations involved in several devices of this type are investigated by the use of equivalent circuit techniques, and several methods of calibrating the force meters are established. Three force generators are described which were designed and built in accordance with these principles. Finally, various applications of these generators to electromechanical and electroacoustic measurement problems are outlined.
Measurement of Mechanical Impedance
Authors: Langevin Robert A.
Published: September 2005

A method is described for measuring the mechanical impedance of electromechanical transducers by independent measurements of blocked force and free velocity. The theory and limitations of the method are analyzed, and it is then applied to measure the mechanical impedance of a “Bimorph” crystal element and a phonograph pick-up over a wide frequency range. The mechanical impedance of the pick-up and sundry other experimental data are used to evaluate all the elements in the equivalent circuit of a phonograph pick-up. From this equivalent circuit, the constant velocity and constant amplitude/constant velocity response curves of the pick-up are calculated and compared with the experimental response obtained from a standard frequency record.
Applications of the Acoustic Sing-Around Circuit
Authors: Hanson R. L.
Published: September 2005

The sing-around circuit has been suggested for air navigation use and has been employed for sound velocity measurements in solids. It consists of a triggered pulse generator which transmits a pulse into the medium and a receiver which picks up the pulse and returns it to the generator as a trigger voltage to set off a new pulse. The frequency of the resulting repetitive signal depends upon the time of travel of the pulse between the two points in the medium. A discussion will be given of the use of the circuit to measure temperature, distance, and air velocity and as a tool for exploring the acoustic properties of auditoriums.
Spectra of Ultrasonic Edge Tones
Authors: Nyborg Wesley L. , Burkhard Mahlon D.
Published: September 2005

Spectra of edge tones in the 10- to 200-kc range have been studied with a recording analyzer, which plots intensity vs. frequency, for jet-edge systems having wind channels 0.006 to 0.020 in. wide, orifice-to-edge distances h of 1 to 20 mm, and utilizing air speeds U extending beyond 130 m/sec. Some spectra consist essentially of harmonically related lines, fundamentals having been noted up to 170 kc—for large U and small h values. Others are inharmonic series with or without continuous “background.” When U and h are both large the spectra are usually very complex and often change rapidly in time.
Improvements in Ultrasound Velocity Measurements by Optical Methods
Authors: Giacomini Amedeo
Published: September 2005

The optical method worked out by E. Hiedemann and his co-workers for measuring ultrasound velocity in liquids has been improved by using progressive ultrasonic waves instead of standing waves. The traveling ultrasonic grating is rendered visible by a new ultrasonic stroboscope which is built up by two ultrasonic sources radiating progressive waves on parallel paths, but in opposite directions. In order to avoid phase changes in the modulated light flux, a liquid having a zero velocity-temperature coefficient may be used for the modulating cell. In a general way the new method has the advantages and not the defects of both the Hiedemann and Lucas and Biquard methods. Details concerning the measuring arrangements and technique are given.
Ultrasonic Lenses of Plastic Materials
Authors: Sette Daniele
Published: September 2005

Propagation velocity and attenuation of elastic waves have been measured in some synthetic materials to determine the most convenient ones for use in ultrasonic lenses. In this respect the most favorable of the different materials tested was polymethylmethacrylate (Plexiglas) which has a velocity of 2100-m sec.−1 for longitudinal waves in rods, and of 2820-m sec.−1 for bulk waves. Its specific acoustic resistance is 3.3×105 g cm−1 sec.−1, and a rather high attenuation has been observed at 8 Mc, which must be considered when designing lenses. From preliminary experiments the most convenient shapes seem to be the plane-cylindrical and plane-spherical ones, the incident waves being parallel to the plane surface. The analytical treatment of such lenses agrees fairly well with their measured behavior. The energy focusing obtained is very important, and the sound power required to get a given energy density in a small region can be reduced ten times with a plane-cylindrical lens, and one hundred times with a plane-spherical one. The common defect of plastic lenses—that is, their solubility in many organic liquids—has been avoided by placing the lens in an envelope which has a mica window for the propagation of waves and is filled with a liquid which does not damage the Plexiglas. The acoustical characteristics of this liquid must be chosen to yield satisfactory energy focusing and good transmission through the double lens structure. Water and carbon disulfide seem to be the most satisfactory for many cases.
Differential Sensitivity of the Ear to Changes of Frequency and Intensity
Authors: Spector A.
Published: September 2005

The published data concerning differential sensitivity of the ear to changes of frequency and intensity have been studied, assuming the applicability of widely held views of the hearing process. The present analysis provides an additional method for correlating the position of maximum stimulation on the basilar membrane with the frequency of a tone which produces that stimulation.
Propagation of Sound Waves in Liquid-Filled Tubes
Authors: Jacobi William J.
Published: September 2005

Sound wave propagation through liquid-filled tubes differs from that through gas-filled tubes because of the yielding of the walls. The most interesting features occur when the wave-length becomes comparable to the cross-sectional dimensions of the tube so that the “transverse” modes are transmitted; for tubes of ordinary size, the frequency range involved for a liquid like water is roughly that from 10 to 100 kc.p.s. In this paper a theoretical and experimental treatment is given of guided sound wave transmission along circular cylinders of ideal liquid with various non-dissipative boundary conditions. The field patterns, phase velocities, and cut-off frequencies are calculated for the natural modes of propagation in the following cases: (1) liquid cylinder with rigid walls; (2) liquid cylinder with pressure-release walls; (3) liquid cylinder embedded in infinite liquid; (4) liquid cylinder with thin solid walls. The problem of determining the field produced by an arbitrary excitation in terms of the natural modes is also discussed. Experimental results are presented for cases (2) and (4) above. It is shown that the measured values of phase velocity are in agreement with those predicted by the theory. Applications of liquid-filled tube transmission are suggested for measuring acoustical parameters of liquids, such as those of interest in underwater sound. For this purpose the pressure-release boundary condition appears particularly suitable, especially at the higher frequencies.
Application of Activated Ceramics to Transducers
Authors: Koren H. W.
Published: September 2005

The conditions under which titanate ceramics may be made to have piezoelectric properties suitable for application to transducers are described. These conditions involve a selection of the titanate material to give a Curie point well above the working temperature, polarization from an external voltage source within certain limits of potential gradient and time duration, and mechanical structure. Most common transducers have a mechanical impedance far below that of a solid block of ceramic. Multilamellar strips have been developed to provide the mechanical impedance required in a phonograph pick-up, microphone, or the like. These consist, in general, of a metal strip with a thin plate of ceramic soldered to one side or with thin plates soldered to both sides. As the multilamellar strip cools below the solidification point of the solder, the ceramic becomes pre-stressed in compression. This strip is then used in flexure in a transducer. It has many unique properties, especially for applications involving extreme conditions of humidity. Applications of this strip for a phonograph pick-up and to a microphone are shown. Precautions involved in controlling production of a pick-up are discussed.
The Propagation of Sound in Composite Media
Authors: Urick R. J. , Ament W. S.
Published: September 2005

A theory is outlined for the propagation constant in media containing numerous small spherical particles. Using expressions derived by Lamb for the zeroth- and first-order scattering coefficients of a particle free to move in a sound field, an expression for the complex propagation constant is derived whose real part yields a velocity which reduces to the homogeneous case for extremely small particles, and whose imaginary part yields an absorption coefficient identical with that derivable from the viscous-drag theory outlined in a previous paper. Using both an interferometer and a pulse-reflection method, measurements of sound velocity and absorption at megacycle frequencies have been made on mercury-in-water and bromoform-in-water emulsions of non-uniform particle size up to a volume concentration of about 50 percent of emulsified liquid. These materials, though showing considerable deviation from a homogeneous behavior, are found to have a velocity and absorption in good agreement with the theory up to a concentration of about 25 percent by volume. Similar measurements on suspensions of quartz sand in water exhibit small deviations of velocity from the theory that may possibly be attributed to the non-spherical shape of the quartz particles.
A Composer's Music Box
Authors: Watson R. B.
Published: September 2005

Many composers desire to hear musical passages at the time of composition, and hence play these passages on some instrument. The Composer's Music Box is an electronic device by means of which the composer may produce various tones with a minimum of distraction from writing his musical score. The operation of the device is much like writing on paper with a pencil. A “pencil” is moved about on a piece of “paper,” which may be ruled much like a musical score. The tone is started or stopped as the pencil is placed on or removed from the paper. Change of pitch is produced by motion of the pencil up and down on the paper, while volume is controlled by moving the pencil back and forth across the paper. The electronic circuits are arranged to control the quality, and the attack and decay times, of the tone.
Refracting Sound Waves
Authors: Kock Winston E. , Harvey F. K.
Published: September 2005

Focusing and refraction of airborne sound waves will be demonstrated by the use of lenses and prisms. Separation of different audiofrequencies by dispersive prisms will be discussed. The use of lenses in combination with loudspeakers provides a useful field of application.
Simplified Acoustic Impedance Measurements
Authors: Leonard R. W.
Published: September 2005

This paper describes an impedance measuring assembly consisting of a piston and pressure microphone arranged in such a manner that the ratio of the pressure to the particle velocity may be measured in both magnitude and phase at the surface of the piston. The assembly measures the driving point impedance at the surface of the piston. The sample to be measured is confined in a tube of diameter equal to that of the piston and is placed almost in contact with the vibrating surface of the piston. Thus, the pressure and particle velocity at the surface of the sample are prescribed by the velocity of the piston and the specific acoustic impedance of the sample. Constructional details and performance characteristics of the assembly are given.
Uniform Speech-Peak Clipping in a Uniform Signal-to-Noise Spectrum Ratio
Authors: Martin Daniel W.
Published: September 2005

A graphical function W(r, c) has been determined experimentally, in which W is word articulation, r is the relative level of unclipped speech and the noise, and c is the amount of uniform, symmetrical, speech-peak clipping. Preemphasis of the speech signal gave an approximately uniform speech spectrum prior to clipping. Uniform, random noise was mixed with the clipped speech before post-equalization, making the final noise spectrum similar in shape to the speech spectrum. The real-ear response of the earphones was compensated electrically to yield a uniform orthotelephonic response for the communication system, in the frequency range contributing significantly to articulation index. For constant clipping cn the function W(r, cn) approaches W(r, 0) as a limit for sufficiently large values of r. For c < r + 5, W ≑ W(r, 0). For the case of no clipping W(r) when transformed to W(A), A being articulation index, resembles closely the curve by Pollack.
Analysis and Synthesis of Speech-Like Sounds
Authors: Cooper Franklin S. , Borst John M. , Liberman Alvin M.
Published: September 2005

The study of the perception of speech is aided by instruments capable of representing physical patterns which are complex in frequency, time, and intensity. The sound spectrograph developed by Potter and co-workers provides visual patterns which are highly suggestive for the isolation of the distinctive aspects of auditory patterns. However, comparison and judgment by ear are desirable, and this requires additional instrumentation to play back modified spectrograms, or completely synthetic spectrographic patterns which differ only in the particular characteristic under examination. The spectrograph developed for these studies records on film, portraying a dynamic range of ca. 40 db by a linear density variation of 2.0. The use of a Photoformer to control the recording light permits compensation for non-linearities of other components, or the intentional introduction of high contrast (compression), black-to-white reversal, or intensity-contour characteristics into the spectrograms. The pattern playback uses these spectrograms directly, or after retouching or printing, to control the modulation at syllabic rates of an optical scanning beam which is then converted into sound. Synthetic spectrograms, hand-drawn on a transparent medium, are used in a similar manner. Spectrograph and playback were designed for specific application to speech-like sounds and to studies of the perception of such sounds. Design considerations and performance data are discussed.
The Speaking Machine of Wolfgang von Kempelen
Authors: Tarnóczy T. H.
Published: September 2005

Wolfgang von Kempelen made significant contributions to the investigation of the human mechanism of speech production around 1770-90. During the preceding century there had been considerable speculation on various aspects of speech by linguists, teachers, physiologists and others. Kempelen became interested from the standpoint of the problem of the deaf-and-dumb. About this time also Professor Kratzenstein produced five vowel sounds synthetically with some degree of satisfaction. Kempelen who made a hobby of building intriguing mechanisms proceeded experimentally to set up mechanical equivalents of the parts of the human vocal system on a cut-and-try basis. He used a bellows for the lungs, a slit membrane for the glottis, a box with two variable cavities for the mouth and a set of controls for the various openings—lips, nostrils, and tongue-palate. With some use of one hand for resonance effects he fingered the keys to produce all the consonant and vowel sounds or approximations thereto. The quality was evidentally good enough for visiting observers to recognize a number of words, particularly Italian and French. Kempelen was thus the first to produce a complete synthetic speech mechanism which he described in detail in a book titled Mechanismus der Menschlichen Sprache nebst der Beschreibung seiner sprechenden Maschine published in 1791. For general interest the oral presentation will include other early speech-producing machines.
The Effect of Room Characteristics upon Vocal Intensity and Rate
Authors: Black John W.
Published: September 2005

Groups of 23 males read 12 test phrases in each of eight rooms. The rooms represented two sizes, shapes, and reverberation times. Microphones led to two meters that registered vocal intensity and, in one instance, duration of the phrases. Each set of measurements was treated by analysis of variance. Both rate and intensity of reading were affected by the size and reverberation time of the room and not by the shape. Rate was significantly slower in the larger and the less reverberant rooms. Apparently vocal intensity was greater in the smaller and less reverberant rooms; and readers consistently increased their intensity as they read the 12 phrases in the less reverberant rooms. Differences in this regard, occasioned by the sound treatment of the rooms, were highly significant.
Musical Scales and Their Classification
Authors: Barbour J. Murray
Published: September 2005

A musical scale is a sequence of musical intervals in a certain range, such as an octave; a mode is a cyclic permutation of a scale; a key is a mode at a certain pitch-level; a raga is a melodic pattern of a key. Most writers, confusing scales and modes, have listed fewer than 13 the possible scales. The older writers, such as Delezenne, Gandillot, Ellis, and Hatherly, were further limited by harmonic considerations. Slonimsky's 1330 scales and melodic patterns (1947) are mostly ragas, in which as with Schillinger (1946), symmetry is paramount; Slonimsky's pentatonic and heptatonic scales are actually modes. The inverse of a scale contains the same intervals in reverse order. The complement of a scale contains all the notes of an octave not in the scale itself. A scale may be measured by the total mean-square deviation of all its intervals, the index for complementary pairs of scales differing by a constant. The notation of a heptatonic scale as a harp scale (with seven different letter names) agrees with the deviation index. However, the function of notes in the scale may often be expressed by fewer than seven letter names or by two names for the same note.
Influence of Humidity on the Tuning of a Piano
Authors: Young Robert W.
Published: September 2005

A six-foot grand piano has been studied for the change of its tuning with relative humidity. During more than a year of observations in the living room in which the piano is located, the relative humidity varied between 20 and 70 percent. The change of tuning lagged the rise and fall of humidity as if the structure were characterized by a “time constant” of the order of 15 days. The relative humidity weighted according to this time constant varied only between 35 and 62 percent. Within the three central octaves, the tuning of this 39-year old piano rose on the average 5 cents (0.3 percent in frequency) for each increase of 10 percent in weighted relative humidity. This rise would result if the sound board would swell enough to lift the bridge at the end of the A4 (440 c.p.s.) string 0.5 mm.
Twenty Years of Research in Phonological Biophysics
Authors: Voelker C. H.
Published: September 2005

This interim report will emphasize the great number of books published which were of prime interest to the research worker in this speciality at the time of the founding of the Acoustical Society of America. It will continue by outlining the development of the broader issues with reference to the glottal source, labial coupling and give particular attention to the recently suggested hypothesis that the glottal-labial tube may be an acoustic filter.
Sound Transmission of Walls With Known Receiving Room Conditions
Authors: Tyzzer F. G. , Ramer L. G. , Ancell J.
Published: September 2005

Previous study of an improved sound transmission measuring technique at the Riverbank Acoustical Laboratories was reported at the November, 1948 meeting. This technique was shown to have promise in measuring properties of test walls instead of properties of the test walls plus the adjoining rooms. Further study has shown that practical measurements can be made which are directly related to the effective “impedance” of a test wall or panel with random sound on the incident side. The random incident sound is provided by the sound field of the reverberation chamber. An exploration has been made of the transmitted sound field in a narrow room with hard walls except for a very absorbent wall opposite the test panel. Results are given which indicate a fairly uniform energy flow from the test panel to the absorbing wall. The effect of high Q cross modes, which do not greatly affect this energy flow, can be minimized by the use of velocity microphones directed toward the test panel. Since the area of the test panel is less than the cross-sectional area of the room at which measurements are made, a correction must be made. This is a function of frequency since considerable beaming is found at the higher frequencies. By the use of pressure microphones to obtain an average sound pressure on the incident side of the test wall and velocity microphones in the transmitted sound field, chart recordings can be made, giving incident pressure and transmitted velocity as a function of frequency. Examples are shown for several test walls, and also curves of effective wall impedance versus frequency. An analysis of the probable error in these measurements is given and compared with some of the errors in the older technique.