bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibration of the Head in a Sound Field and Its Role in Hearing by Bone Conduction
Authors: v. Békésy Georg
Published: September 2005

In a sound field the head is set into forced vibrations, and the vibrations are sometimes heard by bone conduction. For clinical purposes it is important to know the magnitude of these vibrations of the head so that, in cases of partial deafness, the roles of air conduction and bone conduction can be understood.

The pattern of the head vibrations and the velocity of the deformation waves traveling along the bony wall of the skull were measured. For the velocity we found c = 570 m/sec. In the course of the experiments, a new method of calibrating a vibration pick-up with a sound level meter was developed.

It was found possible to construct an earphone that reduces the amount of “cross-hearing” to a very low value. With this earphone, hearing thresholds can be measured in many cases without using noise to mask the ear with the better hearing, even though the difference between the sensitivities of the two ears is greater than 40 db.

It is shown that the maximal sound insulation that can be obtained with an ear plug is determined by the elastic forces acting between the skin of the ear canal and the bony wall of the ear canal.
The Effect of High Altitude on the Threshold of Hearing
Authors: Rudmose H. W. , Clark K. C. , Carlson F. D. , Eisenstein J. C. , Walker R. A.
Published: September 2005

The threshold of hearing has been measured in a decompression chamber at ambient pressUres corresponding to altitudes of 35,000 feet and sea level. After the data have been corrected for the change of cushion seal and the change in response of the earphone unit with change in pressure, the results show that the shift in the average threshold of hearing for fifteen ears is within ±2.5 db of sound pressure level when the density of the air in the outer and middle ear is decreased to about one-fourth that at sea level.
The Effects of High Altitude on Speech
Authors: Clark K. C. , Rudmose H. W. , Eisenstein J. C. , Carlson F. D. , Walker R. A.
Published: September 2005

The effects of altitude on the human voice have been determined by measuring speech spectra as a function of altitude. The apparatus simultaneously recorded the square of the sound pressure in twelve contiguous bands extending from 60 to 9000 c.p.s. Eleven talkers were used, and data were obtained in a decompression chamber at constant temperature for altitudes up to 40,000 feet. Special attention was given to the method of monitoring and phonation. Vowels, sibilants, words, and connected speech were used as test material. The results indicate that vowels and semi-vowels exhibit a loss in mean square pressure with altitude roughly proportional to the logarithm of the density ratio, while some consonants are little affected by altitude. Measurements indicate that the number of words spoken on one breath of air is proportional to air density if constant sound pressure output is required. Normally, at 35,000 feet, it is necessary to pause for breath about two to three times as frequently as at sea level.
Quantitative Amplitude Representation in Sound Spectrograms
Authors: Koenig W. , Ruppel A. E.
Published: September 2005

The sound spectrograph shows variations in signal intensity by varying shades of gray to black which, because of the nature of the recording medium, are not susceptible to quantitative interpretation. Several methods are described in this paper for recording amplitude variations in measurable steps. These methods include contours, dot spacing, distinctive shadings, and variable area patterns.
Reciprocity Free Field Calibration of Microphones to 100 Kc in Air
Authors: Rudnick I. , Stein M. N.
Published: September 2005

A procedure for obtaining a free field reciprocity calibration of a W. E. 640AA transducer in the frequency range 1–100 kc is described. The basis for the calibration is investigated in some detail, particularly with regard to (a) the validity of electroacoustic reciprocity relations applying to the transducer and (b) the nature of the acoustic calibrating field. The transducers were found to be reciprocal. Factors affecting the acoustic field are the degree of approximation of the source to a point transducer, the effect of walls of the anechoic room, and the attenuation in the air. It is shown that when the separation of the transducers used in these measurements is 30 cm, the transducers are essentially points, the room produces very little effect, but the attenuation in the air can produce a significant error at high frequencies unless correction is made for it. The results of the calibration of two W. E. 640AA transducers are presented, giving their responses as speakers and microphones, the latter with and without a protective grid.
Dispersion of Compressional Waves in Isotropic Rods of Rectangular Cross Section
Authors: Morse R. W.
Published: September 2005

The compressional wave velocity in rectangular brass rods is measured a function of frequency by means of standing wave patterns made visible by the use of lycopodium powder. An x-cut quartz crystal is used as a driver between frequencies of 200 and 650 kilocycles per second. Results are obtained on rods of different width-to-thickness ratios, the thickness being the same in each case. The dispersion curves are made up of two branches with a discontinuity occurring one of them when the half-wave-length is close to the larger dimension. Each of these branches is shown to be determined by one of the lateral dimensions and a qualitative interpretation is offered in terms of a lateral resonant effect. In the case of a square rod the two branches coincide, and the dispersion is the same as that encountered in a circular rod of the same cross-sectional area. Theoretical calculations are made for the case in which the width is much larger than the thickness. Numerical solutions are found for the dispersion curves of the first symmetrical mode for different values of Poisson's ratio. Calculated values are in good agreement with measured values when the cross-sectional dimensions are in the ratio of 8:1 and the wave-length is smaller than the larger dimension.
Sound Absorption and Transmission Measurements
Authors: Gigli Antonio
Published: September 2005

Report is given of the research performed in the last ten years in the field of architectural acoustics, with special reference to measurements of sound absorption coefficients of materials and sound transmission losses of partitions. The absorption of sound by systems of resonators is particularly handled.
On the Propagation of Sound over Snow
Authors: Watson Robert B.
Published: September 2005

Many qualitative observations have been made on the quieting effect of newly fallen snow. This natural phenomenon must depend on the acoustical properties of such a layer of snow. The physical constants for snow vary over a considerable range, and data for calculating the acoustic constants of snow are meager. The calculated absorption coefficient ranges uniformly front 0.25 at 100 c.p.s. to 0.75 at 2000 c.p.s. Calculations are made of the sound level at an observer's position due to sound transmitted over a layer of snow. Because of the appreciable absorption, the sound level is found to be considerably reduced at distances as small as five hundred feet from the source.
The Attenuation of Audible Sound in Fog and Smoke
Authors: Knudsen Vern O. , Wilson John V. , Anderson Neal S.
Published: September 2005

Measurements of the rate of decay of sound in a reverberation room, first with no fog or smoke in the room and then with fog or smoke of known concentration and particle size added to the room, show that the attenuation of sound in a number of aerosols is in approximate agreement with values predicted by the theories of Sewell, Epstein, and Oswatitsch. In a water fog having a concentration of 2.0×10−6 grams/cm3 and average droplet radius of 6.25×10−4 cm, the attenuation owing to the fog increased from about 5 db/sec. at 500 c.p.s. to 13 db/sec. at 8000 c.p.s. In a quite similar fog of mineral oil, the corresponding attenuation increased from 1.6 db/sec. at 500 c.p.s. to 21 db/sec. at 8000 c.p.s. At very low frequencies, a fog of water is much more absorptive than is a fog of oil; the difference is ascribed to a “relaxation” effect of evaporation from and recondensation the droplets, which is much greater for water than for oil. The attenuation of sound in smoke may become rather high, amounting to 58 db/sec. at a frequency of 6000 c.p.s. for a moderately dense smoke of NH4Cl (180 g in a volume of 6080 cu. ft.).
The Origin of Sound Absorption in Water and in Sea Water
Authors: Liebermann L. N.
Published: September 2005

The absorption of sound in water and in sea water has been measured in the frequency range 120 kc to 1000 kc. The fresh water values were obtained in a lake; the sea water values in the ocean. The fresh water absorption values when extrapolated as the square of the frequency are in agreement with previous values measured in the laboratory at considerably higher frequencies. It is shown that the observed absorption of water has its origin in viscous dissipation; the calculated values for the absorption agree with the observed if recently measured values for the dilatational viscosity as well as the shear viscosity are included in the calculation. The absorption processes in sea water are different. At frequencies below 100 kc the absorption is about 100 times greater than in pure water. Above 1 megacycle the absorptions are similar. It is shown that this behavior can be accounted for by introducing a relaxation mechanism with a relaxation time of 10−6 second. The nature of the relaxation mechanism is not known for certain. The proposal is made that it involves the ionic dissociation of sodium chloride in solution. Calculations are made to show that this process is a possibility.
The Double Crystal Acoustic Interferometer
Authors: Fry William J.
Published: September 2005

A one-dimensional theory of operation of the double crystal acoustic interferometer is presented. The theory is sufficiently general to include both resonance and off resonance operation and any amount of acoustic loading of the crystals. The effects of holder losses and electrical loading of the receiver crystal are also included. A relation is developed which can be used to obtain values of the acoustic velocity and absorption coefficient of the coupling medium from the experimental measurements.
Low Loss Crystal Systems
Authors: Fry William J.
Published: September 2005

Some aspects of the theory of low loss crystal systems are presented. The effect of small losses on the resonant frequency, the difference between the resonant and antiresonance frequencies, and the electrical impedances at resonance and at antiresonance, is calculated. A quality factor is defined and related to the mechanical loads on the crystal.
Air Shock Wave Velocities over Water
Authors: Klein Elias
Published: September 2005

A procedure was devised for determining the air blast pressures of the A-bomb at Bikini. In such a disturbance the air particles move with large and finite amplitudes; hence, the propagated waves do not obey the ordinary laws of acoustics. By measuring the ratio of the air shock wave velocity to normal acoustic velocity, an indication may be obtained as to the peak pressure of the explosion. Blast waves in water, on the other hand, follow substantially the familiar acoustic laws and are propagated at a well-known velocity. Measurements were made of transit times at identical positions for the air and the water blast waves. These yielded immediately the desired air blast velocity in terms of the known velocity of sound in water. This procedure eliminated the need for simultaneous measurement of the continually shifting distances between buoys which carried observational equipments. However, careful positioning of the buoys was necessary in order to avoid their destruction and yet record the maximum possible air blast. These positions were calculated on the basis of an equivalent explosion from 20,000 tons of TNT. Since the measurements had to be made automatically and without human observers, special timing and recording systems were provided. All requirements for gathering the data were successfully met in the assembly of apparatus described herein.
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 zero 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 bromo-form-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 concentration of about 25 percent by volume.
Propagation of Sound Waves along Liquid Cylinders
Authors: Jacobi William J.
Published: September 2005

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 liquid walls; (5) 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 (5) above. It is shown that the measured values of phase velocity are in agreement with those predicted by the theory.
Noise in Magnetic Recording Systems as Influenced by the Characteristics of Bias and Erase Signals
Authors: Gratian J. W.
Published: September 2005

In this paper the causes of noise generated by the conventional supersonic biasing and erasing fields used in magnetic recording systems are discussed. The data to be presented emphasize the manner in which this noise varies with the wave form and frequency of an applied supersonic field. The importance of these two factors is shown to be a function of the characteristics of the erase and recording heads and of the inherent frequency response and modulation noise characteristics of the medium. By proper control of the wave form and frequency of the supersonic signal, noise may be reduced to such an extent that the effective noise level of a given recording medium with bias and erase signals applied will be equal to or less than the noise level of a virgin sample of the medium. Under these conditions, values of saturated signal to noise exceeding 80 db may be obtained.
Subjective Testing of Sound Reproducing Equipment
Authors: Goodfriend Lewis S.
Published: September 2005

In listener tests of sound reproducing equipment there are many variable factors that contribute to the validity of the result. Among these factors are the program material, associated acoustical and electronic equipment, the size and nature of the audience, the method used in reporting audience response, and the statistical analysis of the audience response. This paper discusses these variables and proposes a definitive method for recording and presenting the data in a simple and thorough manner.
A New High Speed Level Recorder
Authors: Bruel P. V. , Ingård Uno
Published: September 2005

A high speed level recorder of the “potentiometer type” which is useful both for laboratory and field measurements is described. The recording system consists of a moving coil with translational motion, the speed of which can be varied with a maximum value of about 1000 db/sec. Recording is made by a steel stylus on waxed paper of the same kind as that in the usual Neumann recorder.
The Acoustic Reactance of Small Circular Orifices
Authors: Bolt R. H. , Labate S. , Ingård U.
Published: September 2005

A precise experimental study of the reactive component of the complex impedance of small circular orifices has been made for a number of orifices varying in diameter from 2 cm down to 0.357 cm, with diameter/thickness ratios from 4 to 40, over the frequency range from 200 to 1000 c.p.s. The measurement of the impedance is performed with a precision impedance tube.

A theoretical correction for the influence of the tube walls is applied by considering the orifice to act as a plane piston and taking into account the influence of all possible higher order modes of the tube in the neighborhood of the orifice. Comparison between calculated and measured values of reactance shows that, as far as this quantity is concerned, the assumption that the orifice acts like a plane piston appears valid for radii equal to or greater than 1 cm for “thin” orifices within the range of variables specified above. For orifices of radii less than 1 cm, however, a modification of the radius is necessary to make the classical theoretical equation for orifice reactance fit the measured data. The observations and analyses reported here are restricted to wave-lengths much greater than the hole diameter and to the low velocity region where reactance is independent of particle velocity.
Wave Propagation in Piezoelectric Crystals
Authors: Kyame Joseph John
Published: September 2005

The propagation of plane waves in a piezoelectric medium has been studied. A simultaneous solution of Maxwell's field equations and Newton's law of force gives the necessary conditions for wave propagation in the infinite medium. By piezoelectric coupling, every electromagnetic wave has associated with it an elastic wave. Nonpiezoelectric crystals are, at best, birefringent electromagnetically and trirefringent acoustically. In piezoelectric media, the electromagnetic and elastic modes are coupled, thus giving five phase velocities for both the electromagnetic and acoustic waves. These media are therefore electromagnetically and acoustically pentrefringent. The slower electromagnetic waves are the field variations accompanying the elastic waves, while the fast elastic waves are the mechanical deformations accompanying the electromagnetic wave.

The displacement in the elastic wave will differ in phase by ninety degrees from the electromagnetic wave, its amplitude being proportional to the electric field strength and inversely proportional to the frequency of vibration. The flux of energy will, in general, be in directions different from that of phase propagation. The generalized Poynting vector will be the sum of two vectors representing separately the flux of electromagnetic energy and the flux of elastic energy.

Analysis was made of propagation in a particular direction in sphalerite. The orientation of the vectors involved has been calculated for the fast and slow modes of vibration.

A study of specific boundary value problems gives interesting results. The piezoelectric effect gives a contribution to the reflection of electromagnetic waves at an interface. This results in a small correction to be applied to the familiar expressions for the reflection coefficients. This correction might be used to determine piezoelectric constants, providing it is possible to measure accurately the reflection coefficients and other constants involved.

Slabs of piezoelectric media may be set into vibration by an incident electromagnetic wave. At particular frequencies the crystal may be set into resonance. At resonance for the elastic wave there is almost perfect reflection of the incident electromagnetic wave. It should be possible to detect these resonances by absorption measurements.

The piezoelectric slab, if set into resonance by an acoustic wave, emits a weak electromagnetic signal.
The Substitution Method of Measuring the Open Circuit Voltage Generated by a Microphone
Authors: Hawley M. S.
Published: September 2005

An analysis of the substitution method of measuring the open circuit voltage generated by a microphone is given which shows that the “normal” substitution voltage equals the open circuit voltage for all types of acoustic measurements and for any value of electric impedance loading the microphone. It is shown that the method recently proposed by some authors of removing the acoustic load from the microphone when applying the substitution voltage results in a substitution voltage which does not equal the open circuit voltage. It is also shown that a formula for the response of a transducer derived for a system in which the microphones are open-circuited may be used when the microphones are terminated by finite electrical impedances, by replacing the generated open circuit voltages in the formula by the corresponding “normal” substitution voltages.

Consideration is given to the restriction in the definition of the pressure response of a transducer made necessary by the fact that the pressure on a microphone diaphragm is a function of the electrical impedance terminating the microphone.

An experiment is described which involves a microphone coupled to a chamber, the acoustical impedance of which is high relative to that of the microphone. The results of this experiment agree with the conclusions of the analysis.
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.
Non-Linear Distortion in Dynamic Loudspeakers due to Magnetic Effects
Authors: Cunningham W. J.
Published: September 2005

Two sources of non-linear distortion in a dynamic loudspeaker are considered in this discussion; both are related to the magnetic characteristics of the driving mechanism The first type of distortion arises because of a force of attraction between the voice coil, carrying a current, and the iron of the field structure. This force varies as the square of the current and produces second harmonic distortion. The force may be related to the space rate of change of self-inductance of the voice coil as it moves in the air gap. The magnitude of the distortion produced in this way may be several tenths of one percent, and is greater for low frequencies and large currents. This distortion may be reduced by proper proportioning of the voice coil and field structure and by using a short-circuited winding on the field structure.

The second type of distortion arises due to non-uniformity of the magnetic field in which the voice coil moves. This effect is well known qualitatively, but equations are given here for its quantitative evaluation. These equations indicate that the distortion characteristically is less than one percent, and is greater for large amplitudes of motion. If the voice coil is centered in a symmetrical field, only odd-order distortion is produced. If the field is not symmetrical about the voice coil, even-order distortion is also present. This distortion may be reduced by proportioning the voice coil and field structure so that the mean field in which the coil moves remains as constant as possible.
The Structure of the Middle Ear and the Hearing of One's Own Voice by Bone Conduction
Authors: v. Békésy Georg
Published: September 2005

If we assume that in the evolution of the mammalian ear nature has made the best possible use of physical and acoustic principles, we are led further to assume (1) that the middle ear provides maximal sensitivity combined with optimal quality and (2) that the middle ear is so adjusted as to minimize noise pick-up from the speaker's body during talking. In terms consistent with these assumptions, it is possible to explain: why mammals have two vocal cords; why a bony rod lies on the eardrum; why the point of rotation of this bony rod is at the edge of the eardrum; why the mass of the ossicles appears so exaggerated; why the eardrum is conical in shape; why the membrane of the footplate of the stapes is so small; why the footplate of the stapes has an elliptical form; why a joint is necessary between the stapes and the incus; and why an animal with thin head bones has a bulla.
Beats and Nodal Meridians of a Loaded Bell
Authors: Jones Arthur Taber
Published: September 2005

A small load on a bell usually changes the rapidity of beats and shifts the positions of nodal meridians. A study of the first three partials of one bell leads to the following conclusions. If the antinodal meridian nearest the position at which the load is to be applied is associated with the lower [higher] pitched of two beating components, the addition of the load increases [decreases] the rapidity of the beats, and also shifts the nearest antinodal meridian of the lower component toward the position of the load. Small increases in the load increase these effects.
Diffraction of Sound by a Circular Disk
Authors: Leitner Alfred
Published: September 2005

The near and distant diffraction fields of a circular disk of zero thickness are plotted according to an exact theory. The results are compared with the Kirchhoff approximation and recent experimental data.
The Loudness and Loudness Matching of Short Tones
Authors: Garner W. R.
Published: September 2005

A monaural loudness matching technique was used to study differential sensitivity to intensity as a function of tonal duration. The probable error (p.e.) of the loudness matches was used as the measure of differential sensitivity. With one technique, a standard tone of 500 milliseconds duration was followed by a tone of variable duration (10–500 milliseconds) after a silent interval of 50, 100, or 500 milliseconds. In another technique, both standard and comparison tones were of the same duration (10–500 milliseconds) with the same silent intervals between tones as before. (1) When the standard tone was always 500 milliseconds, the p.e. of the loudness matches increased with a decrease in the duration of the comparison tone from approximately 0.60 to 2.30 db, and the length of the silent interval had no effect on the function. (2) When both the standard and comparison tones had the same duration, the p.e. again increased with a decrease in duration; in this case, however, a silent interval of 500 milliseconds caused an increase from approximately 0.60 to 2.50 db while a silent interval of 50 milliseconds caused an increase to only 1.00 db. These differences are explained in terms of two different processes: a dissimilarity effect, and an interference effect. (3) When a standard tone of constant duration is used to obtain loudness matches, the mean of the matches becomes a measure of the loudness of tones as a function of duration. These measures showed a clear distinction between the six observers used. For three observers, the change in duration caused practically no change in loudness. For the other three, changes in loudness as great as 8.5 db were recorded. This order of loudness change agrees with that reported by Békésy, but is considerably less than that reported by Munson. Possible explanations for the differences are mentioned.
The Audibility of Thunder
Authors: Fleagle Robert G.
Published: September 2005

The relatively short range of audibility of thunder is explained by use of the observed vertical distributions of temperature and wind velocity in the neighborhood of thunderstorms.
Sound Transmission through Multiple Structures Containing Flexible Blankets
Authors: Beranek Leo L. , Work George A.
Published: September 2005

A general theory of sound transmission for normal wave incidence is developed for a structure containing two impervious layers, an air space, and two acoustical blankets. Equations for more simple structures are derived from the general case by setting some of the parameters equal to zero. A number of design charts are presented giving attenuation in decibels vs. frequency for different structures with specific acoustic resistivity of the blanket material as a parameter. Experimental results are found to be in good agreement with the theoretical predictions. It is found that panels deviate from mass law behavior as their thickness is increased. Mass law behavior is obtained for panels of any thickness when a laminated construction is used to damp out flexural waves.
Building to the Acoustical Optimum New Mutual-Don Lee Broadcasting Studios
Authors: Carruthers Walter W. , Love Donald P.
Published: September 2005

The acoustical design and construction of the new Mutual-Don Lee Broadcasting Studios in Hollywood were done under novel and very favorable arrangements. First, a careful check was made of the optimum acoustical characteristics to which it was decided to design the studios. Some of the best auditoriums for broadcasting were measured, and from these data as well as comments regarding the excellence and shortcomings of these auditoriums, the optimum characteristics for the new studios were determined.

During the course of construction, acoustical measurements were made several times for the purpose of “tailor-making” the acoustical characteristics of the studios. On the basis of the measurements, it was found that only a few minor modifications in acoustic treatment were necessary, such as changing the mountings of the Acousti-Celotex materials in order to change the low frequency absorption characteristics as desired, and the areas used of these materials.

The results are, close agreement between optimum and finally measured acoustical characteristics, and very satisfactory broadcast programs.
Aural Microphonics in the Cochlea of the Guinea Pig
Authors: Davis H. , Gernandt B. E. , Riesco-MacClure J. S. , Covell W. P.
Published: September 2005

Electro-acoustic equipment and methods for the study of aural microphonics and action potentials of laboratory animals are described. A new feature is the placement of electrodes not only on the round window but also in one or more very small holes drilled into the cochlea of the guinea pig.

Analysis of the aural microphonics so recorded confirm the conclusions of Wever and Lawrence, of Békésy, and others. The microphonics generated at the apex by low tones or near the round window by high tones axe conducted electrically to the other end of the cochlea with an attenuation of at least 10 db. The effects of the local injury caused by the small holes are described, and their relation to anatomical position confirms the earlier data of Stevens, Davis, and Lurie. Detailed comparisons of phase relations, wave form, etc., at different positions did not prove feasible because of electrical leakage of the aural microphonic from one turn to the next through the bony partitions.

At high intensities the microphonic for a tone of 3000 c.p.s. or higher may show a very strong “sub-harmonic” at the apex although the sub-harmonic component is very small at the round window. The threshold for appearance of the sub-harmonic is very sharp.
Ultrasonic Radiation from Curved Quartz Crystals
Authors: Fein Louis
Published: September 2005

From transmitting frequency responses in water, admittance measurements in air and water, and radiation patterns in water, calculations were made of the electro-acoustic efficiencies at 1250 kc of four one-inch square X-cut quartz crystals of practically equal thickness having radii of curvature of ∞, 25, 7, and 4 centimeters, respectively. Efficiency values calculated from acoustic measurements do not check as well with the calculated potential efficiencies as do those calculated from admittance measurements. The latter values indicate that the radiation resistance the same for the four crystals. Focusing measurements show agreement with A. O. Williams' prediction that the point of maximum acoustic intensity in the radiation pattern is not necessarily at the center of curvature of the crystal. Resonance frequencies obtained from admittance measurements in air make plausible the deduction that the effective mass of a crystal decreases with increasing curvature.
On the Reciprocity Free-Field Calibration of Microphones
Authors: Wathen-Dunn Weiant
Published: September 2005

The physical conditions for a valid reciprocity free-field calibration are examined in considerable detail. The expression for the absolute value of the reciprocity parameter J is derived in a general manner. The result shows that J is actually a transfer admittance relating the volume current Q of the linear, reversible transducer to the pressure P this unit causes at a certain point in space. The usefulness of this concept in other than free-field conditions is pointed out. The formula for the sensitivity of the unknown microphone is derived by a method which emphasizes the significance of the physical arrangement, and the limiting conditions are stated. Practical methods for determining the validity of the calibration are suggested.
A Theory of Low Frequency Sound Absorption in Solids with Application to Soda-Silica Glasses
Authors: Korn Granino A.
Published: September 2005

This paper deals with the theory of a class of relaxation mechanisms which may in part account for the absorption of sound in certain solids. The basic postulates of Eyring's theory of absolute reaction rates are applied to the development of general differential equations describing structural-chemical state changes. The macroscopic effects of transitions between the activated and unactivated states of complexes of atoms are discussed, and the results are applied to the problem of sound absorption and mechanical relaxation due to structural-chemical changes in soda-silica glasses. It appears that the transition of alkali ions from holes in the glass lattice into the interstitial space, as in electrolytic conduction, is associated with the acquisition of a certain activation energy, so that the transition probabilities are finite. The process is thus of the nature of a relaxation mechanism which is capable of causing sound absorption. The functional dependence of absorption on frequency predicted by the theory and the predicted functional dependence of the relaxation time on temperature are found to agree with experimental results.
Theory of Speech Masking by Reverberation
Authors: Bolt R. H. , MacDonald A. D.
Published: September 2005

A general statistical theory is developed for the masking effect of reverberation on the intelligibility of words. Speech is considered a series of discrete pulses distributed statistically over a 30-db range in sound pressure level in a given frequency band. The articulation index is calculated as a function of reverberation time, using preliminary values of speech pulse lengths and spacings obtained from Visible Speech spectrograms. The percent articulation for words is then calculated from the articulation index and is compared with Knudsen's experimental values. The theoretical values agree precisely with the measured values at reverberation times less than two seconds and differ by less than 17 percent out to six seconds. The calculations are extended to include a combination of background noise and reverberation.
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 nearly two years 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 40-year old piano rose on the average 5 cents (0.3 percent in frequency) for each increase of 10 percent in weighted relative humidity. A working hypothesis is developed by which to organize the experimental results.
Universal Phonograph Styli
Authors: Reid John D.
Published: September 2005

The advent of “slow-speed” records with fine grooves has resulted in the introduction of 3-speed phonographs which are unduly complex in operation. A great simplification in their mechanical complexity and in turn in the operating procedure can be obtained if the problem of changing the needle for the various types of records is eliminated. With a universal stylus, the phonograph may be designed with one-tone arm, one cartridge and the only additional operation required of the user is the selection of the correct speed. Several solutions to the problem of a universal stylus will be presented.
Intonation of Solo and Ensemble Performance of the Same Melody
Authors: Nickerson James F.
Published: September 2005

A study was made of solo and ensemble performance of the same musical material as related to systems of intonation postulated by certain acoustical, musical, and psychological theories. In particular, it was desired to check earlier findings that unaccompanied performance and listener preferences approximate Pythagorean intonation and to extend a similar line of investigation to ensemble performance.

Solo and ensemble performances by 24 well-trained string quartet players were recorded from which stratified random samples of tones were obtained for frequency analysis. This analysis was made through the use of 16-mm sound-on-film loops with a chromatic stroboscope (Stroboconn).

The results confirm earlier findings for unaccompanied melodies and indicate that Pythagorean intonation is also most typical of ensemble performance. This tendency appears to dominate any “cultural conditioning” which may exist for equi-tempered intonation.
The Effect of Sound on Laminar Propane-Air Flames
Authors: Loshaek S. , Fein R. S. , Olsen H. L.
Published: September 2005

The application of sound of known intensity and a frequency of 12.7 kc to a laminar propane-air flame is found to produce a shift in the stability limits of the flame. The sound alters the flashback limit so that the flame becomes more stable and the blowoff limit so that the flame becomes less stable. It is shown that the normal burning velocity is not changed with the application of sound and that the flow-velocity profile in the tube is likewise unchanged. From the Lewis and von Elbe theory of flame stabilization it is then concluded that the “penetration distance” must be increased. The “penetration distances” are calculated from the flow-velocity distribution and the normal burning velocity and, near stoichiometric, are found to increase about 20 percent at the maximum sound intensity of 10 milliwatts/cm2. Sound at a frequency of 18.3 kc is found to affect the blow-off limit in a similar manner as the lower frequency but no appreciable effect is noted on the flashback limit.

It is concluded that these results in combination with further experimental studies should yield useful information about the nature of the “penetration distance” and flame holding in general, but that sound at these low frequencies does not offer a useful tool for studying flame propagation. It is recommended that the effects of sound on practical burners be given careful study because the results presented indicate that the maximum quantity of energy that can be released in a given burner volume may be limited by the sound level in the combustion chamber.
Scattering of an Underwater Ultrasonic Beam from Liquid Cylindrical Obstacles
Authors: Tamarkin Paul
Published: September 2005

An ultrasonic beam (frequency, 1.145 mc/sec.; wave-length, 0.13 cm) produced in water by a quartz crystal is scattered by various liquid cylindrical obstacles (diameter, 1.3 cm). These obstacles are composed of methyl and amyl alcohols, ethyl alcohol-H2O solutions, NaCl-H2O solutions, and diethylaniline. They provide a range of values of acoustic impedance, acoustic velocity, and ratio of obstacle diameter to wave-length. Pressure amplitude distributions are measured over various cross sections of the scattered beam for a fixed position of the obstacles relative to the source. The scattered wave fronts are also obtained. These two types of measurements lead to the conclusion that the scattering is diffractive rather than ray acoustical. Other evidence is given which exhibits the presence of a scattered wave.
Pressure Distribution in the Acoustical Field Excited by a Vibrating Plate
Authors: Pachner Jaroslav
Published: September 2005

Pressure distribution in the acoustical field excited by a vibrating circular plate clamped at the edge in an infinite wall is calculated for the points the distance of which from the center of the plate is greater than 10–20 times its radius. For completeness a short survey of the theory of forced vibrations of plates is given in this paper too.
Acoustics of School-Band Rehearsal Rooms
Authors: Patrick Nelson G. , Boner Charles R.
Published: October 2005

The purpose of this investigation was to study the acoustical characteristics of certain school instrumental practice rooms that have been adjudged as satisfactory by the music teachers who use them. Public-school band and orchestra directors long have realized that special acoustical consideration must be given to the rehearsal space assigned to them for teaching purposes if they are to teach critical listening, intonation, musical balance, tone production, and dynamic control of tonal intensity. It is not likely that these attributes can be taught within the same acoustical conditions as that of the normal classroom or performance situation. This study located six rehearsal rooms that were reported as being satisfactory acoustically for teaching purposes by the music teacher. These rooms were analyzed for their acoustical characteristics. The study revealed that the several common factors existing among the six rooms differ considerably from the present standards of school music-room construction.
Synthesis of Wind-Instrument Tones
Authors: Strong William , Clark Melville
Published: October 2005

Clarinet, oboe, bassoon, tuba, flute, trumpet, trombone, French horn, and English horn tones have been synthesized with partials controlled by one spectral envelope (fixed for each instrument regardless of note frequency) and three temporal envelopes. Musically literate auditors identified natural tones with 85% accuracy and our synthesized tones with 66% accuracy; a number of the confusions were intrafamily. With intrafamily confusions tolerated in the scoring, the auditors identified natural tones with 94% accuracy and our synthetic ones with 77% accuracy.
Phonemic Analysis of Consonants in Helium Speech
Authors: Sergeant Russell L.
Published: October 2005

A phonemic-confusion matrix for speech in a helium atmosphere was constructed for use in predicting intelligibilities of specially constructed vocabularies for such environments. There is a marked similarity between helium speech and speech in air when intelligibility according to linguistic classification is observed. However, unaccountable differences do exist between the two breathing media for ranked intelligibilities of specific consonants.
Use of Thick Transducers to Generate Short-Duration Stress Pulses in Thin Specimens
Authors: Peterson Ronald G. , Rosen Moshe
Published: October 2005

It is shown how the pulse-echo method for determining sound velocities and acoustic attenuation can be applied to thin specimens by generating short stress pulses with thick transducers. The method is described in conjunction with its use in the observation of phase transformations in which both transit-time data and attenuation measurements are used to determine the mechanism and kinetics of the transformation. Results are shown for the β → α a phase transformation in high-purity plutonium.
Nearfield Pressure For an Infinite Phased Array of Circular Pistons
Authors: Mangulis V.
Published: October 2005

The nearfield pressure and the radiation impedance for an infinite phased array of circular pistons (with the same velocity magnitude) in a rigid plane baffle are calculated. A slowly convergent infinite series expression for the pressure, obtained from the appropriate Green's function, is transformed by the use of Poisson's sum formula into a more rapidly convergent infinite series expression. Numerical results are presented. A rough estimate of the location and value of the maximum pressure in the nearfield is obtained under certain restrictions. The radiation impedance of a piston in the infinite array agrees well with the average radiation impedance of a piston in a large finite array.
DIMUS Processing with Seven-Element Active-Sonar Arrays
Authors: Remley Winslow R. , Upton Donald V. E. , Del Giorno Donald L.
Published: October 2005

The aural detectability of a seven element DIMUS array for active sonar has been studied experimentally. The array was simulated with sonar data recorded at sea. It was found that a DIMUS array consisting of as few as seven elements can be effectively used. Doppler detectability is preserved. If the interference consists of reverberation from a pulse having a sinusoidal amplitude distribution, the clipping loss is about 2.5 dB for small signal-to-reverberation levels. This loss is independent of the bandwidth of the transmitted pulse. If the interference is local noise, the clipping loss is less than 1 dB. It was also found that when equal pulse lengths are used, the detectability of slow targets is much greater with broad-band transmission pulses than with conventional Continuous-wave pulses in reverberation-limited conditions. The improvement in detection with the broad-band pulses was preserved with DIMUS.
ABSORPTION OF SOUND IN LIQUIDS BY POROUS METALS
Authors: Fand R. M. , Gogos C. M. , Jackson F. J.
Published: October 2005

Experimental measurements of the acoustic impedance of two porous-metal plates in a liquid (water) have been made using the impedance-tube method. The results, although restricted to a single frequency (5850 Hz), indicate that porous metals are potentially useful materials for absorbing sound in liquids.
Theoretical Studies on the Scattering of Acoustic Waves from a Rough Surface
Authors: Horton C. W. , Muir T. G.
Published: October 2005

The theory for the scattering of acoustic waves from a stochastic surface that was developed by Eckart is applied to surfaces with various statistical properties. Specific formulas for the scattering coefficient, both for the low- and the high-frequency cases, are computed for isotropically rough surfaces whose autocovariance functions are exponential, Gaussian, and sinusoidal. The low-frequency scattering is examined for other autocovariance functions having interesting properties. The relative effect of the size of the insonified region and the area of coherent surface relief is considered in two examples.