bluuebunny/crossref_metadata_2025 huggingface dataset:
Review of Recent Mathematical Theories of Cochlear Dynamics
Authors: Zwislocki Jozef
Published: September 2005

An analysis of several theories of cochlear mechanics has been attempted on the basis of general hydrodynamic theory. The theories are divided into two classes according to the mathematical treatment. The first class assumes that transverse waves propagated along the cochlea are long in comparison to the cross-sectional dimension of the canal: all theories of this class can be deduced from one differential equation when the emphasis put on different factors. The second class assumes that the waves are relatively not long, and the mathematical treatment becomes a boundary problem to which no exact solution has yet been found. The analysis of the individual theories indicates a certain convergence of opinions, and it is clear that definite progress has been achieved toward an understanding of the dynamic behavior of the cochlea. In spite of this trend, however, no one of the theories seems entirely satisfactory.
Acoustic Attenuation between the Ears
Authors: Zwislocki Jozef
Published: September 2005

In an investigation of the acoustical insulation between the ears, various earphones and obturating devices were used. Bone conduction was shown to be chiefly responsible for the acoustical leakage between the ears. Conditions were determined under which interaural insulation could be increased considerably. Most of the measurements were performed with a compensation method which appears to give more precise results than methods previously used, and which permits phase measurements.
Patterns of Cochlear Adaptation at Three Frequency Regions
Authors: Harris J. Donald , Rawnsley Anita I.
Published: September 2005

Auditory adaptation was determined four observers to 100-, 1000-, and 4000-cps tones at 30-, 50-, 70-, and 90-db loudness level. The spread of effect to closely adjacent frequencies was particularly examined. The method of adaptation was used to avoid the intrusion of beats in the simultaneous masking experiment.

Loudness patterns were drawn according to the method of Munson and Gardner, confirming and extending the earlier study. Within the region represented by the differential threshold, no especial peaking of the loudness pattern was found. For example, at 1000 cps, there was broad peak of ±10 cps.

From earlier experiments, adaptation is thought to be confined to the peripheral sense organ. According to this view, the present data would represent a stage in the process of handling frequency information, intermediate between the much broader amplitude patterns and the more precise operations the command of the nervous system.
Description of Some Mechanical Properties of the Organ of Corti
Authors: v. Békésy G.
Published: September 2005

A short historical introduction is followed by a description of the technique for observing the organ of Corti in a lightly anesthetized guinea pig with the help of a slit lamp. The magnification was around 200 times, and stroboscopic illumination was used with a 1-kilowatt high pressure mercury-arc lamp. The relative stiffness of the Reissner's membrane, the tectorial membrane, the reticular membrane, and the Hensen cells were investigated with test needles. It was possible to demonstrate the earlier anatomical concepts of the stiffness of the reticular membrane and the pillars of Corti.

In order to obtain the high sensitivity of the ear, the stiff tissues of the organ of Corti must be mechanically matched (impedance matched) to vibrating energy. of the perilymph. It was found that the organ of Corti is very well suited to work as a transformer for shearing forces.

The difference between the vibration pattern of a series of resonators in the sense described by Helmholtz and the pattern of traveling waves is described. The actual observation of the membranes in the organ of Corti showed only traveling waves during stimulation with a pure tone.

For every given frequency there was one point along the basilar membrane where a transition in the vibration pattern occurred, and the more radial vibrations of the organ of Corti near the stapes went over into longitudinal vibrations on the wave front facing the helicotrema. The place of transition moves with the frequency of the stimulus. Finally, the different traveling waves which may run along an elastic pad like the organ of Corti are described, and their possible roles in the cochlea are discussed. This leads to some possible explanations of why the cochlea is coiled.
Dispersion of Ultrasonic Velocity in Sodium Acetate Solutions
Authors: Chhapgar A. F.
Published: September 2005

Absorption measurements on sodium acetate solutions have shown the existence of a relaxation phenomenon at a frequency less than 7 Mc. An attempt is made in the present paper to determine the existence of velocity dispersion near this frequency. No dispersion is detected.
The Rectifying Property of Polarized Barium Titanate
Authors: Waidelich Donald L.
Published: September 2005

When a high alternating voltage was applied across a wafer of polarized barium-titanate ceramic, a small direct voltage was observed across the ceramic. No such behavior was noted in wafers initially unpolarized. It is believed that the effect is caused by an asymmetrical charging action.
Intensities Produced by Jet-Type Ultrasonic Vibrators
Authors: Monson H. O. , Binder R. C.
Published: September 2005

Intensity and frequency measurements were made with different jet-type generators. High values of intensity were reached at certain nozzle inlet pressures, certain cup positions, and with certain proportions of the generator.
Propagation of Radiation in an Inhomogeneous Medium near an Irregular Surface
Authors: Meecham William C.
Published: September 2005

The intensity of a sound wave propagated in a surface channel is derived using the concepts of ray acoustics and taking into account the roughness of the surface. The attenuation due to rough surface scattering is found, and calculations are made for several types of surface-reflections.
On the Attenuation of a Repeated Sawtooth Shock Wave
Authors: Rudnick Isadore
Published: September 2005

A formula which describes the space rate of change of amplitude of a repeated finite amplitude sawtooth wave is derived by application of the Rankine-Hugoniot shock relations. Experimental evidence is in agreement as to the form of the amplitude change but gives lower rates of change than indicated by the formula.
The Particle Size Distribution in Fog Produced by Ultrasonic Radiation
Authors: McCubbin T. King
Published: September 2005

The author describes fog produced by 2.4-mc sound generated in water and focused on the upper surface. With soap in the water no fog appears. Fog particle diameters, determined by microscope, are grouped around 4 to 5 microns.
Discussion of the Paper by C. Eckart on Sea Surface Scattering
Authors: Mintzer David
Published: September 2005

In evaluating Helmholtz's theorem for the sound scattered from a rough surface, Eckart assumes the same boundary conditions on the pressure as in the plane surface case. In this note a correction term is found for the boundary condition on the normal derivative of the pressure in order to obtain the conditions under which Eckart's approximation is valid. It is found that Eckart's long-wave results are valid only for sound wavelengths small compared with water wavelengths, or for grazing incidence and non-grazing observation.
The Impedance of a Resistance Loaded Helmholtz Resonator
Authors: Ingard Uno , Lyon Richard H.
Published: September 2005

The impedance of a Helmholtz resonator damped by a thin porous layer in the form of a screen or cloth is calculated as a function of the distance between the aperture and the screen. It is shown that the input resistance of the resonator decreases very fast as the distance between the screen and aperture increases, whereas the aperture mass reactance passes through a maximum. The importance of these results with regard to design of resonators and perforated facings is discussed.
A Miniature Piezoelectric Microphone
Authors: Medill John
Published: September 2005

A new rochelle salt microphone has been developed for use as a secondary standard in production testing, sound level measurements, high quality transmission of sound, and similar applications. The diameter of the new microphone (1 18 inch) is half the diameter of similar units in current use. Frequency response, directional characteristics, and moisture protection have been improved without a significant loss in sensitivity.
A Miniature Microphone for Transistorized Amplifiers
Authors: Bauer B. B.
Published: September 2005

A new magnetic microphone has been developed for use in hearing aids and communication and similar equipment which requires a small, light, medium-impedance microphone. The new microphone has a diameter of 1 inch and a thickness of 38 inch, and it weighs 10 grams. The sensitivity is high enough to override the relatively high noise level of transistors in the frequency range most useful for voice transmission.
The Theoretical Sensitivity of Three Types of Rectangular Bimorph Transducers
Authors: Thurston Edward G.
Published: September 2005

The theoretical sensitivity for operation below resonance of three types of rectangular, bimorph transducer elements is derived using the results of elasticity theory. The cases treated are first, the widely used corner-loaded square bimorph; second, the rectangular bimorph simply supported along two sides and uniformly, transversely loaded; and third, the latter loaded only over a strip in its center.
On the Measurement of Power Radiated from an Acoustic Source
Authors: Cady Walter G. , Gittings Curtis E.
Published: September 2005

This paper describes an experimental test of the theory that the total force on an absorber receiving a beam of plane waves is a measure of the acoustic power generated at the source, provided that certain conditions are satisfied. The exponential decay in acoustic intensity is accompanied by a corresponding exponential increase in the force due to the hydrodynamic flow, as has been verified experimentally. The sum of these two forces, plus a possible further force that may exist at the emitting surface due to local hydrodynamic conditions or to a “pumping effect,” should be independent of the distance from the source to the absorber. The verification of this prediction is the chief result of the investigation. From the results it can also be inferred that the “pumping effect,” if it exists at all, is probably very small in liquids.

As absorbers, slab of ρc rubber, a 90° wedge, and a cavity radiometer were used.

The reacting force on the transducer was also measured, and found, within the limits of measurement, to be equal to that on the absorber. This result indicates that acoustic power can be measured by observing this reacting force without the need of an absorbing system.
Signals in a Borehole Due to Plane Waves in the Solid
Authors: White J. E.
Published: September 2005

This paper presents a theory describing the acoustic waves set up in a fluid-filled borehole by the passage of plane elastic waves in the surrounding solid. It consists of a mathematical development of the following process. A stress in the solid around the borehole will in general cause the hole to contract or expand. A contraction compresses the fluid and causes pulses to radiate in both directions as tube waves. At some observation point, one of these pulses is observed after a delay due to the propagation as a tube wave. A complex wave in the solid is expressed as a combination of stresses distributed along elementary lengths of the borehole, and the total acoustic wave received at a point is expressed as the summation of elementary pulses arriving after suitable delays. The expressions derived give pressure or fluid particle velocity in terms of motion or stresses in the solid for plane compressional waves and plane shear waves arriving at any angle. The method can be extended to the case of a spherical wave cutting the borehole.
Seismic Model Study
Authors: Howes E. T. , Tejada-Flores L. H. , Randolph Lee
Published: September 2005

A method has been developed for studying seismic sound pulses in reduced scale models which simulate geophysical seismic exploration methods. Use is made of a tank of water for transmission of the acoustic wave from a source to a faulted limestone stratum and return to a pressure sensitive receiver.

Results obtained demonstrating the geometric aspects of the propagation, reflection, refraction, and diffraction of sound pulses are described and illustrated on accompanying plates.
Acoustic Streaming at Low Reynolds Numbers
Authors: Andres J. Milton , Ingard Uno
Published: September 2005

This paper is a continuation of an analysis of acoustic streaming begun in a previous paper where streaming at high Reynolds numbers (order of several hundred) was treated. The corresponding problem for low Reynolds numbers (order of ten) is now considered, and it is shown that the flow pattern obtained around a cylinder in a sound field is opposite to the one corresponding to high Reynolds numbers. The Reynolds number is defined as R = U0a/v, where U0 is the particle velocity in the incident sound wave, a is the radius of the cylinder, and v is the kinematic viscosity. The two types of flow associated with different values of Reynolds numbers seem to correspond to the two types of circulations that have been experimentally observed and reported in the literature.
Ray Theory for Moving Fluids
Authors: Kornhauser E. T.
Published: September 2005

The generalized eikonal equation for moving fluids is obtained from a very simple physical argument. Elementary solutions for uniformly moving media are discussed. A generalized form of Snell's law is derived, and it is specialized in three separate ways to yield formulas useful for solution of problems in stratified media. Examples of its application are given in each case.
Hydrodynamic Flow and Oseen's Approximation
Authors: Westervelt Peter J.
Published: September 2005

It is proved that a linearization of the hydrodynamic equations in the manner of Oseen does not lead to a description of the steady flow phenomena which occur in connection with oscillatory flow past solid obstacles.
A Speech Synthesizer
Authors: Harris Cyril M.
Published: September 2005

“Standardized speech” constructed from building blocks called speech modules has been described; it was synthesized by piecing together bits of magnetic tape containing recorded speech sounds. An electromagnetic device, a “speech module synthesizer,” is described here which performs the synthesis automatically. When buttons on a keyboard are pressed, a sequence of corresponding speech modules are automatically recorded on tape exactly in tandem. The modules are selected from a group “stored” on a rotating magnetic drum. The pressing of a button causes an electrical signal corresponding to a module to be reproduced—the electrical switching is so arranged that only one complete module is reproduced for a single button-pressing. This electrical signal is amplified, biased, and then fed into a constantly rotating head which makes contact with stationary magnetic tape and records the signal on it. A 10-kc signal superposed on each stored speech module controls an electromagnetic clutch which (a) measures the length of the recording accurately, and (b) advances the tape at the completion of the recording by the correct amount so that the next recording forms a connected sequence with it. The same module may be used any number of times and in combination with different stored modules, thereby introducing wider experimental control in standardized speech studies. The principle of this type of device could be applied to other classes of problems involving communication of information, as the conversion into speech of typing or of electronically-read printed matter.
Some Experiments on the Recognition of Speech, with One and with Two Ears
Authors: Cherry E. Colin
Published: September 2005

This paper describes a number of objective experiments on recognition, concerning particularly the relation between the messages received by the two ears. Rather than use steady tones or clicks (frequency or time-point signals) continuous speech is used, and the results interpreted in the main statistically.

Two types of test are reported: (a) the behavior of a listener when presented with two speech signals simultaneously (statistical filtering problem) and (b) behavior when different speech signals are presented to his two ears.
On the DL for Frequency
Authors: Rosenblith Walter A. , Stevens Kenneth N.
Published: September 2005

Difference limens for three frequencies (250, 1000, and 4000 cps) were determined for two trained observers by two psychophysical methods: the ABX procedure and the method of constant stimulus differences or AX procedure. Though the two observers differ considerably insensitivity, their DL's for the AX procedure are less than one-half of their DL's for the ABX procedure. Comparison of these data with data in the literature on DL's for frequency indicates a wide range of values for different psychophysical procedures and for different subjects. Some observations are reported that illustrate the effect of such factors as practice and ensemble of stimulus conditions upon the size of the DL. The influence of the stimulus ensemble upon judgement time is discussed briefly. In view of all the experimental data, it would be rather imprudent to postulate a “true” DL, or to infer the behavior of the peripheral organ from the size of a DL measured under a given set of conditions. While there is undoubtedly some relation between the size of the DL and the so-called channel capacity, there is little reason to assume that the relation is a particularly simple one, given the different operations by means of which these two quantities are determined.
Wave Motion in the Cochlea Caused by Bone Conduction
Authors: Zwislocki J.
Published: September 2005

Psychophysical and physiological experiments have shown that a tone transmitted to the cochlea by bone conduction can be compensated by an airborne sound. From these experiments it has been deduced that the vibration pattern of the cochlear partition does not depend upon the path by which sound is transmitted to the cochlea. This hypothesis has been confirmed by direct observation of the vibration pattern in cochlea models and by measurements of cochlear microphonics. From both kinds of experiments attempts have been made to draw conclusions concerning the theory of cochlear dynamics.

In an effort to explain the fact that the vibration pattern of the cochlear partition is independent of the path by which the sound is transmitted to the cochlea, a mathematical analysis has been performed. First, by means of the hydrodynamic principle of continuity, it has been demonstrated that the vibration of the cochlear partition caused by a tone introduced into the cochlea either through the bony wall or through an artificial window can be canceled by a tone transmitted through the oval window, irrespective of the dynamic properties of the partition. Second, a general differential equation of hydrodynamic surface waves has been established, which shows that transverse waves are propagated along the cochlear partition every time there is a difference in pressure between the two sides. According to this equation, the wavelength is independent of the place at which the sound is introduced into the cochlea. Third, it has been deduced from Hamilton's principle of stationary energy that transverse waves in the cochlea must travel from the base towards the apex, irrespective of the location of the sound source. Hence, in agreement with the experiments, the mathematical analysis shows that the vibration pattern of the cochlear partition does not depend upon the way in which sound is transmitted to the inner ear. Furthermore, it shows that the introduction of sound through the bones or through an artificial window does not provide any new clues for the explanation of this pattern.
Second Viscosity Coefficient of Liquids
Authors: Karim S. M.
Published: September 2005

It is known that the experimental value of the absorption of ultrasonic waves in most liquids is in excess of the theoretically calculated one. While attempts have been made to explain the discrepancy in different ways, a phenomenological approach is through the second viscosity coefficient.

Recently Eckart has discussed the streaming set up in a liquid when a beam of ultrasonic waves passes through it, and has shown that it is dependent on both the bulk and shear viscosities.

The conclusions arrived at from an experimental investigation carried out on the basis of Eckart's theory are:

1. The value of the ratio of second viscosity to shear viscosity is positive in conformity with the theory.

2. The agreement between experimental and theoretical values is closer in the case of pure liquids than in the case of solutions. For pure liquids the value of μ′, the second viscosity, appears generally to be greater than the value of μ, the shear viscosity, at ordinary pressures and temperatures.

3. The values of μ′ as obtained by experiment and as calculated from the excess sound absorption data are in fair agreement in the case of the liquids used.

4. In some solutions the two coefficients are either equal or the shear viscosity is the greater.

5. The values of μ′/μ obtained by independent workers with different methods are in fair agreement.

Although the anomalous absorption of sound may be accounted for by the second viscosity coefficient, more data are necessary before a final conclusion can be drawn as regards the precise mechanism of the sound absorption.
A Study of the Factors Influencing the Damping of an Acoustical Cavity Resonator
Authors: Lambert Robert F.
Published: September 2005

This paper presents a systematic study of experimentally significant losses contributing to the damping of an acoustical cavity resonator. Absorption measurements in air on the 0, 1 wave of a round cavity were made by a resonance response method employing a transverse particle velocity pickup device. This study reveals that mechanical losses due to the vibrations of the walls are experimentally significant. Empirical relaxation time formulas are established for air at 24 and 27°C. The thermal and viscous boundary-layer loss formula is fitted to these data by choosing the thermodynamic ratio νρ0/μ equal to 1.31.
The Attenuation of Sound in Small Tubes
Authors: Kemp G. T. , Nolle A. W.
Published: September 2005

An experimental investigation of the attenuation of sound in two air-filled tubes of 0.238 and 0.0292 cm inside radius in the frequency range from 3.8 to 20 kc was conducted, and the results were compared with values of attenuation calculated from the Kirchhoff theory for rigid walled tubes. Agreement of experimental with theoretical values was found within the accuracy of the experiment, provided that the comparison made only with the portion of attenuation proportional to square root of frequency, as suggested by Fay. The attenuation was determined by a method which was different, in some respects, from those previously employed. The variable length, closed tube was driven with a high-impedance source, and the input pressure was sampled with a high-impedance microphone probe. The input pressure was recorded as a function of closed tube length. Since the input pressure can be assumed to be proportional to input impedance for these conditions, the attenuation can readily be determined from the ratio of the pressure maxima or minima.
On Radiation and Scattering from Small Cylinders
Authors: Miles John W.
Published: September 2005

The original work of Rayleigh on scattering and radiation of harmonic disturbances by small cylinders is extended to transient disturbances. The analysis is closely related to Ward's treatment of the aerodynamics of slender bodies in supersonic flow.
The Scattering of Sound in a Turbulent Medium
Authors: Kraichnan Robert H.
Published: September 2005

The scattering of a sound wave in a medium undergoing shear flow confined to a finite region is investigated under the assumption that the total velocity field is everywhere small compared to the velocity of sound. Formulas are obtained for the angular distribution and frequency distribution of the scattered wave in terms of the four-dimensional Fourier transform of the shear velocity field.

Under typical conditions, the cross sections for the scattering of a plane wave of frequency ω by a shear flow of given scale and spatial structure are approximately of the form ω4M2, where M is a characteristic Mach number of the flow. The coupling between the shear and longitudinal velocity fields has a tensor character such the the scattering vanishes at 180 degrees and at 90 degrees. The spectrum of the scattered sound wave is very sharp in the forward direction and becomes broader at larger scattering angles.

Explicit expressions for the cross sections are obtained for the case of scattering from a region of isotropic turbulence. When the frequencies of importance in the turbulence are small compared to the frequency of the incident sound wave, the average differential scattering cross section can be expressed directly in terms of the energy spectrum of the turbulence.
Reflection of Acoustic Waves from an Inhomogeneous Fluid Medium. I
Authors: Heller G. S.
Published: September 2005

The reflection coefficient for plane waves incident obliquely on a medium in which the velocity decreases exponentially is computed approximately using the WKB method and compared with a computation from the rigorous solution. The approximate reflection coefficient 1/[16(ω/g)2 cos6θ+1] where ω is the angular frequency, g is the velocity gradient at the start of the exponential decrease, and θ the angle of incidence is within 0.05 percent of the rigorous value for ω/g ⩾ 5 at normal incidence and within 5 percent of the rigorous value for ω/g ⩾ 20 for angles of incidence up to about 45°.
Apparatus and Procedure for Measuring the Absorption of Sound in Gases by the Tube Method
Authors: Angona F. A.
Published: September 2005

An apparatus for measuring the absorption of sound in gas mixtures has been developed and tested. The apparatus consists of a sound tube, a movable ribbon-type speaker, and a fixed condensor microphone. The absorption is determined by recording the sound pressure as the path length between the speaker and the microphone is increased. The measured attenuation coefficient is corrected for the effect of the tube and also for the attenuation due to the viscosity and heat conduction of the gas. Both frequency and pressure are variable and range from 2 to 10 kc and from 3 to 300 mm of Hg, respectively.
Acoustic Streaming near a Small Obstacle
Authors: Westervelt Peter J.
Published: September 2005

Steady rotational flow is known to occur in the vicinity of a smooth rigid object oscillating to and fro in a viscous incompressible fluid. For a small oscillation amplitude the steady flow is shown theoretically to be invariant to the coordinate transformation which renders the object stationary.
A Simple Calibration Technique for Low-Sensitivity Transducers
Authors: Galloway William J.
Published: September 2005

The cavitation threshold of water supersaturated with air at hydrostatic pressure is utilized as a pressure reference level against which the output of a transducer may be referred. The threshold may be determined within 0.2 decibel in a purely radial standing-wave field. A simple system is described for performing the measurements.
Electronic Sound Absorber
Authors: Olson Harry F. , May Everett G.
Published: September 2005

The electronic sound absorber is so named because it absorbs sound or reduces the sound level by means of an electronic transducing system, as contrasted to conventional sound absorption by direct conversion from acoustical to heat energy. The electronic sound absorber consists of a microphone, amplifier, and loudspeaker connected so that, for an incident sound, wave and sound pressure at the microphone is reduced. Thus it will be seen that the electronic sound absorber is a feedback system which operates to reduce the sound pressure in the vicinity of the microphone. The sound pressure in the neighborhood of the microphone can be reduced 10 to 25 decibels over a frequency range of three octaves in the low-frequency portion of the audio-range. The electronic sound absorber may be used to reduce the noise over a small volume, that is, spot type noise reducer or it may be used with an acoustical resistance to obtain a high order of sound absorption in the low-frequency range.
Measurements on Nonreciprocity in an Electromechanical System
Authors: Black L. J. , Scott H. J.
Published: September 2005

Relations for an electromechanical network that contains both electrostatic and electromagnetic coupling and has the antireciprocal transfer characteristic described by McMillan are developed. The effect of hysteresis and eddy currents is included. An equivalent electrical circuit that makes use of the “ideal gyrator” to give the antireciprocal characteristics presented. Several sets of experimental measurements are described which clearly show the nonreciprocal characteristics of the system.
On the Mechanism of the Photographic Effect of Ultrasonic Waves
Authors: Bennett G. S.
Published: September 2005

Experimental data are submitted indicating the existence of a direct action of ultrasonic waves on a photographic emulsion, contrary to the views of some other workers. All of the evidence obtained here indicates a closer correlation with the softness of the emulsion than with the known behavior of ultrasonically produced luminescence. Information is presented as to temperature dependence of the image, effect of ambient pressure, light shielding, and the behavior of various types of commercial emulsions.
An Acoustic Lens as a Directional Microphone
Authors: Clark Malcolm A.
Published: September 2005

An acoustic lens combined with a conical horn can be used to obtain a highly directional microphone without some of the disadvantages of the parabolic microphone. The directional characteristics can be calculated satisfactorily if one assumes that the horn provides uniform flooding of the lens aperture.
The Measurement of Noise with the Sound Spectrograph
Authors: Peterson Gordon E. , Raisbeck Gordon
Published: September 2005

The sound spectrograph principle may be employed in the quantitative measurement of noise. Measurements may be made with the conventional amplitude section circuit in which, in the customary use of the sound spectrograph, each section provides observation during a few milliseconds of the signal time. A long integrating time circuit for the amplitude sectioner has been developed which provides integration over a period of as much as one or two seconds of signal time. The amplitude sectioning circuit of the sound spectrograph may be employed to determine the relationship between the level of a pure tone and the power-per-cycle of noise. Measurements were made for various types of amplitude analysis with the sound spectrograph. A study was made of the degree to which the section displays conform to the computed values of noise level.
Recent Advances in Hearing Aids
Authors: Hector L. Grant , Pearson Harry A. , Dean Neal J. , Carlisle Richard W.
Published: September 2005

The experience gained in fitting a large number of impaired persons with hearing aids is presented, showing illustrative ranges of impairment between 30 and 100 decibels fitted with three progressively-powered hearing aids.

General features of such hearing aids are discussed, showing circuits and arrangements for peak clipping and automatic gain control.

The microphone and air and bone receivers are described, considering features developed for providing optimum reliability in service such as moisture proofing, and design arrangements providing miniaturization concomitant with ruggedness.
Dual-Stylus Ceramic Phonograph Pickup Development
Authors: Koren H. W. , Pearson H. A. , Klingener H. , Sabol R. W.
Published: September 2005

The freedom from humidity and temperature limitations have made ferroelectric ceramics valuable type of transducer for phonograph pickups (originally designed for 78 rpm records). Two groove sizes now indicate the use of dual styli. A pickup structure is described in which dual styli are used hack-to-back on one lever. A mechanism provided on the bottom of the pickup whereby the stylus assembly can be turned over to present the proper stylus to the record. This structure imposes no dynamical limitations on the performance of the pickup, as the additional mass required for the second stylus is only a small percentage of the total mass, and no additional stiffness constraints are imposed on the system.

Reasonably flat characteristics have been obtained. In one commercial model a sensitivity of over one-half volt is achieved on microgroove records, with a frequency range to 10 000 cps with a tracking force of 6 grams for microgroove and 9 grams for standard-groove records.
A Jet-Tone Orifice Number for Orifices of Small Thickness-Diameter Ratio
Authors: Anderson A. B. C.
Published: September 2005

The dependence of a jet-tone orifice number tf/(Δp/ρ)12 on Reynolds number [ρt(Δp/ρ)12]/μ is shown for thin sharp-edged circular orifices whose thickness and diameter both vary from approximately 18 to 38 in, where t is thickness of orifice plate; f, frequency; Δp, pressure difference across orifice; ρ density; and μ, viscosity of gas. Each jet-tone, in general, is composed of harmonics (fundamental and over-tones) as well as subharmonics (tones whose frequencies are less than the fundamental). The subharmonics are relatively unsteady in amplitude compared to the harmonics and may at times have a greater amplitude. The jet-tones at low Reynolds numbers appear relatively free of noise background. In general, as Reynolds number is increased to high values the noise background at first engulfs the subharmonics, then the harmonics. The fundamental is the last to remain, finally disappearing the noise background.
Mean Force on a Sphere in a Spherical Sound Field. I. (Theoretical)
Authors: Embleton T. F. W.
Published: September 2005

The mean force acting on a rigid sphere placed in a progressive spherical sound field has been obtained by integration of the individual contributions from the velocity potential and particle velocity acting on each element of the sphere's surface. Motion of the sphere under the action of the first order pressure variations in the sound field has been taken into account. The radiation force has been expressed as an infinite series of inverse powers of the source distance, each term of which is multiplied by an infinite power series in terms of sphere radius. At very large distances from the source the radiation force obeys an inverse square law of repulsion. As the source of the field is approached, the repulsion decreases to zero and then becomes a force of attraction. The extent of this region of attraction is determined both by the frequency of the sound field and by the size of the detecting sphere; lower frequencies and smaller spheres both extend the region. Even when allowance is made for an inverse square law, the attractions may be many times greater than the repulsions in the same sound field.
Mean Force on a Sphere in a Spherical Sound Field. II. (Experimental)
Authors: Embleton T. F. W.
Published: September 2005

The theory of the previous paper has been verified by a series of quantitative experiments. Several hollow glass spheres (0.228 to 3.029 cm radius) were suspended in turn by a fine glass fiber in the sound field in air; the deflection of each was measured at known frequencies (300 to 7000 cps) and amplitudes (0 to 1400 d/cm2) of the sound field. Care was taken to protect the sphere from any gas streaming to or from the source and to insure that the field was accurately spherical. All measurements were made under such conditions that the sound field was substantially sinusoidal. Good agreement was obtained between theory and experiment within the range of the variables investigated. In the region where radiation forces of attraction existed, this agreement was always within a few percent, even though the magnitude of the forces changed by a factor of 100 or even 1000 to 1 in a single experiment. In the region of repulsion, measurements could not be made with any great accuracy, but even so the agreement here was within the limits of experimental error.
Decay of Spherical Sound Pulses Due to Viscosity and Heat Conduction
Authors: Keller Joseph B.
Published: September 2005

By combining the results of Kirchhoff and Knudsen, the effect of viscosity and heat conduction on a spherical sound pulse are found. A rectangular pulse becomes Gaussian, its peak moves with sound speed, its width increases proportionally to √t, and its amplitude decreases proportionally to x−1, where x denotes radial distance from the origin. This behavior is exactly the same as that of a pulse in one dimension, except for an extra factor of 1/x which accounts for the spherical spreading.
Measurement of the Velocity of Sound in the Ocean
Authors: Brown Richard K.
Published: September 2005

An underwater sound velocity meter, which makes continuous recordings of the velocity of sound in the ocean as a function of depth, is described. A phase comparison system of measurement is employed at 500 kilocycles. Several velocity and temperature records are given for comparison.
Perforated Facing and Sound Absorption
Authors: Ingard Uno
Published: September 2005

In the analysis of the absorption characteristics of a porous layer with perforated facing, it is usually assumed that the facing contributes only a mass reactance to the total impedance. In the present paper it is shown that the facing also causes an additional acoustic resistance which is often larger than the acoustic resistance of the porous layer itself. This resistance obtained only when the porous material is in close contact with the facing and becomes practically zero when the air space between facing and material exceeds approximately one perforation diameter. The effect is due to the near field (higher mode) losses in the porous material around the perforations. The resulting effect on the absorption characteristics considerable, as demonstrated in some examples, and may at least partly explain reported disagreement between measurements and previous calculations.
The Lowest Resonant Frequency of a Water-Loaded Circular Plate
Authors: Peake William H. , Thurston Edward G.
Published: September 2005

The resonant frequency for the lowest mode of a circular plate is calculated for the conditions of concentrated mass loading at the center, water loading on one side, simply supported and clamped at the edge. These results are compared with those of Lamb and others.
Sound Field of a Moving Cylinder and a Moving Sphere
Authors: Zatzkis Henry
Published: September 2005

Most investigations of the sound field of a moving source deal only with point sources. We have examined the sound field of finite sources, moving with constant velocity. The simplest possible vibrators have been chosen, viz., a pulsating circular cylinder and a pulsating sphere. The solution is an infinite series in terms of Mathieu functions in the two-dimensional case, and in terms of prolate ellipsoidal functions in the three-dimensional case. Besides the rigorous solutions, asymptotic formulas valid for large distances away from the source are given.
Measurements of Sound Absorption in Aqueous Salt Solutions by a Resonator Method
Authors: Wilson O. B. , Leonard Robert W.
Published: September 2005

This paper presents the results of measurements of the sound absorption in aqueous solutions of several salts. While magnesium sulfate is the salt of primary interest in this case, some results for sea water at different temperatures, solutions of magnesium acetate, zinc sulfate, and beryllium sulfate are given. The frequency range of the measurements is approximately 50 to 500 kc. Although the resonator method used is not very precise, it is the only known laboratory method which is able to give reliable absorption measurements in water and water solutions in this low-frequency range where the sound absorption in these liquids is extremely small.
Sound Velocity in Some Aqueous Solutions as a Function of Concentration and Temperature
Authors: Barthel Romard
Published: September 2005

Precision sound velocity measurements are reported in sucrose solutions in the concentration range up to 3 molal, and in solutions of NaCl and Pb(NO3)2 up to 2 molal. Measurements were made at three temperatures—24.76°C, 40.37°C, and 59.60°C—using 15-Mc sound. For sucrose and NaCl the velocity vs molality relation is linear out to about 1 molal, where a slight decrease in slope sets in. For Pb(NO3)2 the velocity vs molality relation has a negative slope, and a rise from linearity is already evident at 0.5 molal.

A simple theory of the concentration dependence of the sound velocity in solutions is developed and correlated with experimental data.
The Backscattering of Sound from a Harbor Bottom
Authors: Urick R. J.
Published: September 2005

When underwater sound strikes the bottom of the sea in shallow or deep water, a portion of its intensity is scattered back toward the source of sound. A study of the backscattering from the bottom as a function of pulse length, frequency, and tilt-angle at several locations in a harbor along the East Coast, was made by using a tiltable transducer mounted on a barge. The results are expressed in terms of quantity called the “scattering strength” of a unit area of bottom.

The results suggest that the backscattering of sound from a natural bottom is due more to its roughness rather than to the fact that it consists of sedimentary particles. Even at normal incidence the bottom of a sea or bay appears sufficiently rough so that little sound is returned by specular reflection. Some evidence in support of these conclusions is given.
Ultrasound and Medicine. A Survey of Experimental Studies
Authors: Herrick J. F. , Krusen Frank H.
Published: September 2005

Experimental investigations indicate that ultrasound may prove useful for therapy, for diagnosis, and for biologic measurement.

Ultrasound, although it may be dangerous in unskilled hands, is an excellent agent for the structural heating of living tissues. The term “structural heating” is used to denote heating at abrupt interfaces.The living organism presents numerous abrupt interfaces.

Ultrasound promises to become a reliable diagnostic tool. Either the transmitted or the reflected ultrasonic energy can be used in this application. Tumors, gallstones, kidney stones, stones in the salivary glands, foreign bodies, and abnormal collections of fluid have been located accurately.

Preliminary observations on the use of ultrasound for certain biologic measurements are encouraging. Instrumentation for biologic measurement includes ultrasonic flowmeters, devices for measuring thickness of some tissue structures, and equipment for measuring the viscosity of blood.
The Processing Possibilities of Ultrasonics
Authors: Mattiat Oskar
Published: September 2005

Ultrasonic processing possibilities are limited mainly by the economic factors of high first cost of equipment and high-power cost per unit of processed material. In addition transducers suitable for large volume applications have only recently been developed. Processing possibilities which have led to industrial applications or which seem quite promising are reviewed. Among them are ultrasonic maturing of liquids, extraction, dispersing of dyes and pigments, emulsification, floatation ore dressing, degassing of water, oil and glass, soldering of aluminum, drilling, and cleaning of metal parts.
Uses of Ultrasonics in Degreasing Processes
Authors: Kearney Thomas J.
Published: September 2005

Ultrasonics is one of the newest tools to be applied to metal cleaning. Through the years abrasives, soaps, compounded alkaline materials, and solvents have been used to remove soils from metals. Trichlorethylene Solvent degreasing has had a wide reception in industry since its introduction in 1930. The Detrex Soniclean process combines sound energy and trichlorethylene solvent degreasing for metal cleaning. This is accomplished by immersing especially treated barium titanate transducers in chlorinated solvents producing cleaning results previously unobtainable. Crossrod, conveyorized equipment incorporating constant distillation and filtration of the solvent in the sonics chamber and providing a final vapor rinse and drying is now producing as many as 8000 parts per hour in industrial plants.
The Dispersion of the Velocity of Sound in Water between 500 and 1500 Kilocycles
Authors: McCubbin T. King
Published: September 2005

Dispersion of the velocity of sound was measured by simultaneously transmitting continuous trains of sound waves of the two frequencies through water. One transducer was used to generate the two signals and a second transducer, which could be moved in the direction of the sound beam, received the signals. Dispersion was determined by measuring the change in the relative phase of the two received signals as the length of path between the transducers was varied. These measurements indicated that the velocity of sound at 500 kc was equal to the velocity at 1500 kc to within one part in 290 000.
Note on Longitudinal Vibrational Amplitudes of Solid Conical Horns
Authors: Quint Robert H.
Published: September 2005

An equation is given for the amplitude multiplication factor of a longitudinally vibrating solid resonant cone; showing, that from simple theory, as one of the diameters reduces to zero, the amplitude multiplication factor remains nonzero.
Finite Amplitude Sound Produced by a Piston in a Closed Tube
Authors: Keller Joseph B.
Published: September 2005

The problem stated in the title is solved for a gas with γ = − 1 by the method of a previous paper. First an arbitrary piston motion is considered. Then more detailed results are given for the sinusoidal case.
A Transducer to Reduce Standing Waves
Authors: Darner C. L.
Published: September 2005

An underwater sound transducer having a directivity pattern rotated 10 degrees from the normal to the face of the transducer has been constructed and tested for use in making c-w acoustical measurements in a small tank. Standing waves between the faces of the two instruments involved were thus eliminated or substantially reduced.
Suppression of Flexural Vibrations of Barium Titanate
Authors: Darner C. L.
Published: September 2005

Thickness resonance excitation of barium titanate causes development of an intense shear mode which, because of conservation of angular momentum, produces transverse waves and a directivity pattern with high fixed-angle side lobes. Suppression of the flexural waves is discussed and illustrated.
Sound Absorption by Perforated Porous Tiles. I
Authors: Ingard Uno
Published: September 2005

Several theoretical studies of the acoustic properties of homogeneous isotropic porous material have been presented in the past, and the results have been shown to be in good agreement with experiments. However, no corresponding satisfactory theoretical analysis of the commonly used perforated porous tile seems to have been given. In this paper this problem is treated in some detail, and from the resulting formulas and equivalent circuits the acoustic properties of the tile can be calculated in terms of the geometry and the properties of the porous material. As an example, the acoustic impedance and absorption coefficient have been calculated as a function of perforation depth for a typical tile, and the results are shown to be in good agreement with measurements.
Speed of a Plane Wave in a Gross Mixture
Authors: Chambré P. L.
Published: September 2005

The speed of a plane compression wave in a gross mixture (a suspension or a porous medium) which obeys a simple density mixture law is derived. The results agree with a relation proposed by Wood and others. The derivation of these investigators requires an addition to a density mixture law an assumption concerning the compressibility of the mixture in terms of the constituent compressibilities. It is shown that the latter assumption is a direct consequence of the density mixture law, and is hence not required. It is indicated that the derivation is applicable to waves of arbitrary amplitude.