bluuebunny/crossref_metadata_2025 huggingface dataset:
The Several Short Term Effects Following “Mild” Acoustic Stimulation
Authors: Harris J. Donald
Published: September 2005

When a tone terminates, a number of events occur. Oscillation of the moving structures declines to zero, the perception decays along another time scale, there is a return of the state of adaptation to a previous level, reversible fatigue will in time decline to zero, and there may be a residuum of permanent damage. While most of these events are very difficult to quantify as distinct entities, especial confusion has arisen in distinguishing among the states of adaptation, reversible fatigue, and permanent damage. This laboratory has had opportunity to investigate just those stimulus conditions covering the borderlands between adaptation and fatigue, and between fatigue and damage. A tentative conclusion is that adaptation represents a dynamic equilibrium of the ear, capable upon stimulation of changing within 20 milliseconds or less to a new state, much as the eye adapts in response to illumination increase; this process requires longer to reach equilibrium upon cessation of stimulation, occupying an appreciable fraction of a second (just as in the eye, dark-adaptation is much slower than light-adaptation). From the presence of recruitment, it may be inferred that adaptation is a peripheral organ mechanism. Recovery from auditory fatigue takes a different temporal course, being very sharply negatively accelerated; it may be distinguished from adaptation by this means. Recovery curves and equi-noxious exposures will be presented from stimulations of sound pressure levels up to 110 db for 10 minutes. The distinction between reversible fatigue and permanent damage becomes less and less apparent. Extreme reversible fatigue (up to several days) seems to have all the clinical characteristics of permanent damage except permanence; a tentative conclusion is that no sharp division can be made.
Hearing Losses of Aircraft Repair Shop Personnel
Authors: Webster J. C. , Pernell C.
Published: September 2005

The NEL recorded warble-tone test was given to 1133 overhaul and repair personnel at North Island. Using an 18-earphone monaural network, each ear was tested on the frequencies 500, 1000, 2000, 4000, and 7000 cps. The population, primarily male, was considered in ten-year age groupings, and the distribution of hearing losses within these groups will be shown. Correlations between the hearing losses in the left and right ears and between the better and worse ear will be shown, as well as correlations among the hearing losses at the various frequencies.
On the Forces Due to Acoustic Radiation Pressure and to the Hydrodynamic Flow
Authors: Borgnis F. E.
Published: September 2005

Acoustic radiation in a viscous medium is inseparably linked with a steady mass-flow, usually called the hydrodynamic flow. In order to measure radiation pressure alone (as necessary, for example, in connection with measurements on absorption), some sort Of screening is commonly used which stops the mass-flow but allows the radiation to pass. The force due to radiation pressure decreases with the distance from the source at the same rate as the energy density. In measuring absolute acoustic intensities by means of radiation pressure alone, this dependence on distance has to be taken into account by extrapolation to the source. Relative measurements can be made by comparing intensities at a fixed distance. It will be shown, however, by a simple application of the momentum theorem, that the sum of the forces upon an absorber in the path of an acoustic beam of plane waves, due to both radiation pressure and hydrodynamic flow, is (within reasonable limits) independent of the distance from the source and proportional to the acoustic intensity at the source. Devices based on this fact make screening unnecessary in the measurement of acoustic intensity at the source.
Use of Conformal Mapping for the Analysis of Wave Propagation in Inhomogeneous Media
Authors: Heller G. S.
Published: September 2005

Solutions to the two-dimensional wave equation for a variable velocity medium may be found by a coordinate transformation which renders the transformed medium homogeneous. Any conformal transformation w = w(z) from the complex w to the complex z plane will furnish such solutions with |dw/dz| = n, where n is the (variable) index of refraction of the medium. An exponential velocity variation and a medium in which the velocity is a function of two variables will be treated by this method. The transformation has an interesting physical significance in connection with Fermat's principle.
The Absorption of Sound in Mixtures of Gases which Exhibit a Vibrational Relaxation Time
Authors: Angona Frank A.
Published: September 2005

The absorption of sound has been measured in CO2 and CS2 and also in mixtures of these gases. The apparatus consists of a glass tube approximately 0.84 cm in radius and 60 cm long, a movable ribbon speaker, and a fixed condenser microphone. The resulting sound pressure-distance curves were recorded and yield the sound absorption coefficient. The coefficient was then corrected for the tube effect and multiplied by the sound wavelength, giving the absorption coefficient per wavelength (μ). The range of frequencies and pressures used were 2 to 9 kc and 3 to 250 mm of Hg, respectively. Curves of μ vs ratio of frequency over pressure yield μmax = 0.260, frequency of maximum absorption (νmax) = 32 kc for CO2, and μmax = 0.389, νmax = 408 kc for CS2. As pure CO2 was diluted with CS2 the resulting curves gradually increased in height and infrequency of maximum absorption approaching the μmax and νmax of pure CS2. This project was supported by the ONR.
The Generation of Steady Rotational Flow by a Simple Harmonic Velocity Field
Authors: Westervelt Peter J.
Published: September 2005

Starting from the Navier-Stokes equations for a viscous fluid, a general equation governing the generation of vorticity Ris obtained, ∇2R=μ0−1∇×∇⋅〈ρ0uu〉, wherein R is the time independent vorticity in the Eulerian frame and ρ0uu is the first-order Reynolds stress dyadic and the angular brackets indicate time average, while ρ0 and μ0 are the ambient density and viscosity, respectively, of the medium. The solution to the vorticity equation properly transformed to the particle coordinates is shown to be without divergence. A specialization of the vorticity equation to the case of solenoidal first-order motion is shown to lead to the generating term employed by Rayleigh and by Schlichting; a specialization to the case of irrotational first-order motion is shown to lead to the generating term employed by Eckart. The sum of the two specialized driving terms does not equal the general term, indicating that the contributions to vorticity from rotational and compressible effects are not independent of one another. The theory outlined is applied to a problem first investigated by Eckart—namely, the streaming generated by a well-defined beam of sound. Results similar to those recently obtained by Eckart and Markham are verified. When applied to a two-dimensional standing wave problem, first treated by Rayleigh, the configuration and magnitude of the streaming velocity are found to differ from the results obtained by Rayleigh. Finally, the effect on streaming of a time-dependent viscosity is examined.
A System for the Rapid Evaluation of the Polar Characteristics of Microphones
Authors: Carrell R. M.
Published: September 2005

The system displays the polar characteristic of a microphone upon an ordinary oscilloscope. The microphone rotor is coupled to a control unit outside the anechoic chamber by a pair of selsyns. Provision is made for manual positioning of the microphone from outside the chamber. The system has been used with low level, low impedance gradient microphones.
The use of the Reverberation Chamber for Random Field Measurements
Authors: Hardy Howard C.
Published: September 2005

The reverberation room such as used for measurement of acoustic materials makes a very convenient laboratory for acoustic calibration of sound sources and microphones under random field conditions. The randomness of the sound field is maintained by having a large volume and by using rotating vanes, diffusing cylinders, and signals from a broad-band noise or warble-tone source. The total absorption of the sound in the room can be quickly measured for acoustic power determinations. Generally, only one reference microphone is needed, since the space variation of the sound field averaged with time does not exceed ±2 db above 100 cps and over most of the frequency region is less than ±0.5 db. Data will be presented on (1) the power and efficiency spectra of loud-speakers, which check the free-field integration within the error of free-field measurements, (2) the random field calibration of microphones and sound level meters, (3) the measurement of the acoustic power spectra of noise sources such as fans, appliances, and automobile horns.
Wave Motion in Circular Jets
Authors: Wegel R. L.
Published: September 2005

A fluid jet in a nonviscous incompressible medium is capable of sustaining a number of vibrational modes in analogy with electromagnetic waves in a wave guide. This paper enumerates and classifies modes that would be excited by small disturbances at the orifice of a circular jet. By means of perturbation theory these modes are shown to be of the form Φ = [AIn(kr) + BKn(kr)] exp[−inθ−ikz+iωt], where In and Kn are modified Bessel functions and Φ is the velocity potential. Physically these represent waves propagating down the jet which increase in amplitude from the source of the disturbance until jet rupture occurs and turbulence results.
The Propagation of Radiation in an Inhomogeneous Medium near an Irregular Surface
Authors: Meecham William C.
Published: September 2005

In the treatment of the propagation of radiation in an inhomogeneous medium bounded by a rough surface, it is frequently necessary to consider both reflection and refraction effects. A method of treating such problems was presented at the meeting of the Acoustical Society at San Diego last fall. By using a Laplace transform technique it has been possible to obtain information on a wide variety of problems of experimental interest. One of the outstanding characteristics of the solution is that in many cases the attenuation of the field is but weakly (logarithmically) dependent on the surface parameters. This may explain why it has been so difficult to demonstrate the dependence of attenuation in acoustic experiments upon the state of the sea surface. The predicted attenuations at large ranges for various sea surface models will be presented. In general, they show that the attenuation is reduced for surfaces which scatter more energy into rays making larger angles with the surface (but which still remain trapped within the surface layer).
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 a valuable type of transducer for phonograph pick-ups. Originally designed for 78-rpm records, two groove sizes now indicate the use of dual styli. A pick-up structure is described in which dual styli are used back-to-back on one lever. A mechanism is provided on the bottom of the pick-up 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 pick-up, as the additional mass required for the second stylus tip 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 with a frequency range to over 8000 cps with a tracking force of 6 grams for microgroove and 9 grams for old standard-groove records.
Electro-Optic Sound-on-Film Modulator
Authors: Carpenter Robert O'B.
Published: September 2005

The electro-optic effect in the crystal ammonium dihydrogen phosphate, NH4H2PO4, provides a high speed light valve with ruggedness, long life, and ease of handling not possessed by the similar Kerr effect in liquids. In this paper the design of a practical sound reproduction head for making variable density 35-mm tracks will be described. Frequency response of the light valve is flat to 40 000 cps, the over-all system being limited to about 10 000 by the slit width film speed effect. Tests of distortion and sound quality in the sound tracks obtained will be described.
The Modern High Fidelity Amplifier
Authors: Pomper V. H.
Published: September 2005

The modern high fidelity amplifier is a complex unit in which amplification is only one of many functions. In addition to amplifying an initial signal more than 100 billion times, the amplifier must compensate for weaknesses in or characteristics of associated equipment, for room acoustics, and for a wide variety of recording curves. Psycho-acoustic compensation is also required to meet the listeners' preferences regarding tonal balance, to provide high level quality at low volume levels, and to reduce extraneous noise, rumble, etc. The characteristics of the latest types of amplifiers and the circuits used will be described. The reasons both physical and psycho-acoustical for certain control characteristics will be analyzed.
Electronic Organ Installation for the 1952 Presidential Nominating Conventions
Authors: Kent Earle L.
Published: September 2005

Some of the problems related to the temporary installation of an electronic organ in the Chicago International Amphitheater are presented. The auditorium has a volume of approximately 3 500 000 cubic feet and the reverberation time is quite long. The instrument was required to supplement or dominate the high “noise” level produced by 12 000 people. The floor space allotted for the organ was 45 square feet. Details of the amplifiers and loudspeakers are given as well as a sample of how the organ sounded by tape recording.
On Rotational Relaxation as a Cause of the Anomalous Ultrasonic Absorption of Ethyl Acetate
Authors: Freedman Eli , Beyer Robert T.
Published: September 2005

The analysis by Kneser of the ultrasonic absorption data for ethyl acetate (H3COC-OCH2CH3) reveals the existence of two relaxational processes, the larger of which has a characteristic frequency of 70 Mc/sec. The hypothesis will be advanced that the mechanism of this process is the relaxation of the hindered rotation (more precisely, libration) of the ethoxyl (−OCH2CH3) group. Applying the usual two-state theory to Kneser's value for the maximum of the excess absorption per wavelength shows that the relaxational heat capacity must be 0.17 cal/mole/C°. The fact that the dipole moment is temperature-independent shows that the barrier which restricts the rotation must be greater than 10 RT. Hence the approximation of a harmonic oscillator may be used to calculate the barrier height that would give rise to this heat capacity. The result is about 15 kcal. To check this a formula of Chandrasekhar was used to compute the barrier height required by a relaxation frequency of 70 Mc/sec. The result here is about 13.5 kcal, in reasonable agreement considering the approximations involved. The results of more refined calculations will be presented, and other possible applications will be considered.
Measurement of Elastic Constants at Low Temperatures by Means of High Frequency Ultrasonic Waves
Authors: McSkimin H. J.
Published: September 2005

Pulse-modulated ultrasonic waves (shear or longitudinal) in the 10–30 Mc range are transmitted down a fused silica rod, through a polystyrene or silicone one-quarter wavelength seal, and into the solid specimen. Phase comparison of waves reflected back and forth within the specimen yields values for velocities of propagation and elastic constants. Advantages of the method are: (1) the specimen need not be large to insure a fair degree of accuracy—a thickness of one-quarter inch is usually sufficient; and (2) the quartz crystal transducer initiating the waves is maintained near room temperature, thus insuring well-defined wave trains. Illustrative data obtained over a temperature range of 78° to 300°K for silicon and germanium single crystals and 1.6° to 300°K for fused silica are given. For the latter, a high loss is noted, with an indicated maximum near 30 degrees Kelvin.
Acoustic Birefringence of Liquid Polystyrene
Authors: Bennett G. S. , Hall D. A.
Published: September 2005

This paper reports preliminary qualitative results of observations of acoustic birefringence in a polymer of α-methyl-styrene (Dow Resin 276-V2) at different frequencies, concentrations, and temperatures.
High Frequency Attenuation in Suspensions
Authors: Stakutis Vincent J. , Beyer Robert T.
Published: September 2005

Ultrasonic attenuation in suspensions of lycopodium spores (diameter = 3 × 10−3 cm) in water has been measured by the pulse method at fifteen megacycles. The attenuation coefficient has been determined as a function of concentration, and also as a function of temperature at two different concentrations. The losses are mainly due to scattering. The results are compared with the theoretical treatment of Epstein. Further work is in progress at other frequencies, and also with particles of smaller diameters. A report will be made on these results.
Interference Patterns at Boundaries in Reverberant Sound Fields
Authors: Waterhouse Richard V.
Published: September 2005

Starting with the definition of a diffuse sound field as having equal energy density at all points, the waves converging on any point being random in phase and direction, an analysis is given showing that a reflecting boundary large compared with the wavelength destroys the diffuseness of such a field by setting up an interference pattern. For a perfectly reflecting plane surface, the interference pattern can be expressed analytically as a mean square sound pressure varying as [1 + (sin2kx/2kx)] where x is the distance from the surface and k is the wave number. Similarly, the mean square particle velocity varies as 1 − sin2kx2kx + 1k2x2(sin2kx2kx − cos2kx), and the combination of these two expressions gives a mean energy density variation with distance proportional to 1 + (1/2k2x2)[(sin2kx/2kx) − cos2kx]. Thus the energy level at the surface is about 2.2 db higher than at points further away where the interference pattern is negligible. The effects of such interference patterns on transmission loss and reverberation room measurements are discussed. The patterns are not much affected by the frequency band widths habitually used in room acoustics. Experimental confirmation of the theory is given.
Neighborhood Reaction to Noise: A Survey and Correlation of Case Histories
Authors: Stevens K. N. , Rosenblith W. A. , Bolt R. H.
Published: September 2005

More than fifteen case histories involving the reaction of people in residential areas to intruding noise have been examined and correlated. In each case, statistical data on the physical characteristics of the noise (such as the level, spectrum, and time character) are examined, and the nature of the neighborhood reaction or response is described. The case histories cover a wide range of neighborhood reactions, which are arranged on a rank order scale from negligible complaints to vigorous legal action. On the basis of this experience, a scheme is suggested for predicting the reaction of a community to an intruding noise from a knowledge of pertinent physical characteristics of the noise in question and of noise to which the community has been exposed in the past. The procedure is to combine the physical properties of the stimulus into an empirical formula, from which a so-called composite noise rating is derived. The composite noise rating determines (within a range of statistical variability) the neighborhood response to the stimulus. The scheme breaks down in situations where public reaction is strongly influenced by emergencies or other stresses.
Low Frequency Temperature Coefficient Barium Titanate Ceramics Which Are Stable with Time
Authors: Mason W. P.
Published: September 2005

By incorporating various impurities in a barium titanate ceramic, the Curie temperature is raised and the second transition temperature is lowered. The frequency constant rises to a maximum between these two temperatures. Several compositions have been found which place this maximum at 25°C, and for these compositions the frequency varies only about 0.1 percent over the normal indoor temperature range. These compositions have moderate electromechanical coupling coefficients and mechanical Q's of 1000 to 1200. All barium titanate ceramics have an aging effect that causes the dielectric constant and piezoelectric constant to decrease and the Young's modulus and Q to increase in periods of time of about 6 to 9 months at room temperature. By heating these materials to a higher temperature which is under the Curie temperature, this process is speeded up and a complete aging takes place in a time less than two weeks. It is shown that these aging effects are due to very slow domain wall motions caused by residual stresses stored up when the crystal becomes ferroelectric. The domain wall motion is controlled by an activation energy process having an energy barrier of 19.2 kilocalories per mole which represents the energy barrier which has to be surmounted when unit cells change from one direction to a direction 90° from this. This process indicates that the most likely model for barium titanate is one in which definite bonds are formed by the titanium and oxygen atoms.
A Determination of the Lowest Mode Resonant Frequencies of Water- and Central-Mass Loaded Circular Plates
Authors: Peake W. H. , Thurston E. 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 loaded on one side, simply supported and clamped at the edge. These results are compared with those of Lamb and others. Experimental data are presented for the clamped-edge case. These data are combined with the theoretical results and presented in the form of a series of corrected design curves for such a system when radiating into a finite volume rather than the infinite half-space postulated in the theory.
An Adaptation of The Impedance Tube for Testing Large Samples at High Frequencies
Authors: Northwood T. D. , Pettigrew H. C.
Published: September 2005

Impedance tube methods of testing acoustical materials are restricted to frequencies below the value for which the wavelength is about two-thirds of the diameter of the tube. Above this frequency, extraneous modes of propagation interfere with measurements. The restriction is a serious one for typical acoustical materials which cannot adequately be sampled in less than one square foot. It has been found that the difficulty may be circumvented by using a horn to couple a large sample to a small impedance tube. Comparisons between horn and tube measurements have been made for a range of absorptions.
Higher Formants in the Human Voice
Authors: Oncley Paul
Published: September 2005

Most of the recent research in connection with the voice has stressed the movements of the first and second formants which are of prime importance in vowel recognition. The third and fourth formants, lying generally between 2000 and 4000 cps play an important role in the over-all richness or sonority of the voice and may be largely responsible for the “carrying power” of certain voices. A study of over 300 singers at the Westminster Choir College over a three-year period has shown the development of these high formants in the process of training. The presence of “antiformants” or “antiresonances” causing sharp nulls at certain frequencies is also shown in many cases, and an explanation of their origin is suggested. The study has been supported by the Research Corporation and the Higgins Fund at Columbia University.
Transmission of Sound in Air at Low Pressures
Authors: Goldman R. B. , Bohn J. L. , Nadig F. H.
Published: September 2005

A phenomenon which affects the transmission of sound in air at reduced ambient pressures is the dependency of microphone and loudspeaker characteristics on the ambient pressure. The sensitivity of a transducer operated as a microphone usually increases as the pressure is reduced. It follows then, by the reciprocity theorem, that the sound pressure produced at a point in space by a transducer operated as a loudspeaker does not vary directly as the ambient pressure. The frequency response is affected as well. For example, where the mechanical damping of a transducer diaphragm is provided principally by the radiation loading at atmospheric pressure, the sensitivity at the resonant frequency becomes enormous at low pressures. This results in a deterioration of the transient response which is of importance when the transducer is pulsed. Photographs of the response of a high-quality condenser microphone to pulses will be shown at various ambient pressures to illustrate the effect. Some general relations will be derived and correlated with experimental data.
Acoustic Loci and Transitional Cues for Consonants
Authors: Delattre Pierre , Cooper Franklin S. , Liberman Alvin M. , Gerstman Louis
Published: September 2005

Previous research with simplified, synthetic speech has shown that formant transitions, i.e., relatively rapid shifts in frequency, can be cues for the aural identification of various consonant phones and, further, that the same transition will apparently serve for consonants that have the same articulatory place of production. The data of the present series of experiments permit a tentative specification of certain frequency-positions, or “loci,” which appear to be characteristic of consonants according to their place of production, and toward which the transitions of the vowel formants point. Taking account of these loci provides a basis for an economical description of many of the data concerning the role of transitions in consonant identification.
Duration and Intensity as Physical Correlates of Linguistic Stress
Authors: Fry D. B.
Published: September 2005

English contains many pairs of words, e.g., contract, subject, digest, in which a change of meaning (from noun to verb) is accompanied, in the practice of many speakers, by a change of strong stress from the first to the second syllable. Spectrograms of 6 such pairs, uttered by 12 American speakers, were made and the duration and intensity ratios of the sounds in each word were examined. These measurements showed that when the stress was shifted from the first to the second syllable the most marked variations took place in the relative duration and intensity of the “vowel” portions of the speech wave, while other parts of the wave remained remarkably constant in these respects. By means of the pattern playback equipment, test words were synthesized and recorded in which the duration and intensity ratios of the two vowels in each word were made to vary over the critical range. This material was arranged in suitable test form and a group of American listeners was asked to judge, for each test item, whether the noun or the verb form had been uttered. The data obtained show that there is a good correlation between the perception of stress and the vowel duration and vowel intensity ratios. They also show the uncertainty range along these two dimensions for each pair of words and indicate that, in stress perception, duration and intensity changes may compensate for each other.
An Acoustical Study of the Tractrix Horn
Authors: Lambert Robert F.
Published: September 2005

When predicting and comparing the acoustical properties of horns it is customary practice to formulate the propagation as a one-parameter plane wave-front problem. However, when particular attention is paid to the rapid flare near the mouth of a horn structure such as the Tractrix, it also seems plausible to formulate the propagation on the basis of a one-parameter spherical wave-front theory. By visualizing the surfaces of constant phase as spheres of constant radii a and the flow lines as tractrixes having a generating arm of length a, one-parameter equations for acoustical wave propagation and impedance characteristics may be derived. Solutions to these equations have been obtained by wave perturbation methods and by techniques used for handling nonuniform transmission line problems. Experimental axial excess pressure response, off-axis response, polar response, and throat impedance characteristics are presented and discussed for a single-cell Tractrix structure of length 24 inches, mouth diameter 20 inches, and having a lower cut-off frequency of 180 cps. The response measurements are compared with theoretical calculations postulating first a spherical and the a plane piston radiation law. It appears that the most satisfactory explanation lies somewhere in between these two limiting cases.
A New Line of High-Fidelity Loudspeakers
Authors: Olson Harry F. , Preston John
Published: September 2005

Three direct radiator dynamic loudspeaker mechanisms have been developed for high-fidelity sound reproduction. These units are of three sizes, namely, 8-, 12-, and 15-inch mechanisms. The improvements include smoother response frequency characteristics, broader directivity patterns, improved transient response, and lower nonlinear distortion. These characteristics have been obtained by employing the proper configuration for the cone, a special pulp for the material of the cone and a damping ring in the outside suspension of the cone. In the case of the 15-inch duo cone loud-speaker an additional feature, namely, a series of conical domes are cemented to the low-frequency cone. The high-frequency response is improved by these domes because of the smaller solid angle into which the high-frequency cone operates. The directivity pattern is broadened due to the diffraction effects produced by the domes.
An Ultrasonic Machine Tool
Authors: Clark Neil
Published: September 2005

A relatively new machine tool utilizing ultrasonics for the cutting of hard brittle materials such as ceramics and the carbide metals has been developed for commercial use. The equipment uses a magnetostriction transducer capable of high amplitudes with a suspended abrasive to perform intricate operations on the “unmachinable” materials. The transducer is coupled to the load by resonant mechanical transformers in an effort to match more nearly the impedance of cutting load. Power for the transducer is obtained from an electronic control unit. Mounting of the transducer and vibrating members has received special attention since a rigid, controlled positioning mechanism is necessary for use as a machine tool.
An Electronic Flowmeter
Authors: Kalmus Henry P.
Published: September 2005

A new flowmeter is described in which velocity of a fluid is determined by measuring the phase difference between an upstream and downstream ultrasonic wave of, say, 100 000 cycles. The functions of the transmitting and receiving transducers are interchanged at a fast rate, say 100 cycles per second, allowing the use of a synchronous rectifier. In this way, no long-time stability of the phasemeter is required so that very small flow rates can be measured. Velocities as low as 0.1 cm/sec were successfully measured. A special commutator switch with very low transfer capacitance and, as an alternative, an electronic switch are described. The transducers used are barium titanate crystals mounted in a manner so that their contact with the fluid is avoided.
A Mechanism for Obtaining Damping Material with a Uniform, Prescribed Acoustic Impedance
Authors: Black R. D.
Published: September 2005

One of the problems involved in controlling the response of a transducer is that of obtaining damping material with a given acoustic impedance. In the past, the difficulty encountered has not only been that of procuring material with certain desired acoustic properties, but also that of obtaining quantities of material with these properties. A mechanism has been devised which can calender a thermo-plastic material such as Nylon, Orlon, etc., to obtain a wide range of acoustic impedances. This mechanism has three variables: heat, pressure, and speed. These variables are manipulated until the acoustic impedance of the cloth, as measured with a calibrated detector, falls within the calculated limits necessary to obtain the desired response of the transducer. The mechanism combines the processes of calendering and acoustic-impedance measurement and the result is a damping material with a uniform, prescribed acoustic impedance.
Results of an Experiment on Acoustic Streaming in Gases
Authors: Medwin Herman
Published: September 2005

An ultrasonic streaming experiment based on an extension of Eckart's theory has been carried out for three gases. The source was a 3-in. diameter BaTiO3 disk radiating a 185-kc sound beam into a closed 6-in. diameter tube terminated by a glass wool absorber. An A.D.P. probe microphone moved transverse to the beam to record a graph of the actual acoustic field. Tobacco smoke and Lycopodium powder were used as tracing particles. Their motion, when observed through a calibrated telescope, gives the speed of the streams. The variation of streaming with distribution of the radially symmetric acoustic pressure was studied for the region in which streaming is proportional to intensity. Conclusions are: (1) a complete knowledge of the acoustic pressure distribution P(τ) enables one to predict the streaming profile at that same cross section with excellent experimental check; (2) the variation in axial streaming velocity near the source (the “quartz wind”) can be explained by the attenuation and divergence of the sound beam; and (3) for a gas (argon) of known (zero) bulk viscosity, the absolute value of the velocity given by the extended Eckart theory is experimentally verified within 4 percent. The variation of streaming with the constants of the medium was studied for argon, dry nitrogen, and moist air. For a known acoustic field, the axial streaming velocity may be used to evaluate the sum of all attenuative mechanisms. In this sense streaming experiments may be added to the list of various types of attenuation techniques for the determination of the constants of a fluid.
Reflection and Scattering of Ultrasonic Waves from Water-Filled Sand
Authors: Hoyer W. A. , Mifsud J. F. , Nolle A. W. , Runyan W. R. , Ward M. B.
Published: September 2005

An experimental study has been made of the reflection and scattering of ultrasonic waves froin several packed water-filled sands at frequencies of 0.5 inc and 1.0 mc. Graded sands were used ranging in size from 170–200 mesh (average particle diameter of 0.08 ram) to 25–30 mesh (average particle diameter of 0.66 ram). The backward scattering coefficient, general scattering coefficient, and reflection coefficient of the water-filled sands are measured as a function of grazing angle of the incident sound wave on the water and water-filled sand plane interface. The scattering coefficients are approximately constant for grazing angles above the critical angle of the water-filled sand and decrease for angles below the critical angle. For the range of sands and frequencies used in these experiments, the scattering coefficients are proportional to the second to fourth power of particle size and to the third or fourth power of frequency; the reflection coefficient shows no dependence on particle size of the sand or on frequency. The pressure loss at the water and water-filled sand interface is about 11 db at large grazing angles and about 1 db at grazing angles below the critical angle. A pulsed-signal system is used and all the experimental data is taken in a large, glass-walled tank.
Articulation Testing and Standards for Articulation Tests
Authors: Hawley Mones E.
Published: September 2005

Articulation tests are frequently used for four purposes: (1) audiometry, (2) evaluation of building acoustics, (3) evaluation of speech communication equipment, and (4) research in speech, hearing, and related topics. Several different kinds of tests are used, but all are relatively difficult to administer and evaluate, require special training or facilities for the experimenter, and are expensive. Frequently, training of the subjects poses a major problem. Quite a few laboratories are using articulation tests, but at present it is difficult to reproduce results among them. A subcommittee of the American Standards Association is endeavoring to write a standard for procedures in these tests which will result at least in the same rank order among a group of systems when each group is tested by several different laboratories. The major concerns of this committee have been test materials, selection and training of subjects, talker and listener levels, system usage, and the reporting of results. Recorded samples of a few tests will be reproduced.
Hearing Losses Among Submariners
Authors: Webster J. C. , Solomon L. N.
Published: September 2005

The NEL warble-tone audiometer test was administered from tape recordings to groups of 18 submariners in the forward torpedo rooms of their respective submarines. The boats were moored in the harbor at the time. A sample of over 1000 men was obtained. Hearing losses of less than 5 db could not be measured at 500 cps because of the ambient noises in the testing areas. At the other test frequencies (1000, 2000, 4000, 7000 cps) any value of hearing loss could be measured. Airborne noise level measurements were made in all compartments of a typical submarine under representative operating conditions. These measurements allowed the determination of the noise environment of each crewman's working and living area. Questionnaires given each crewman gave information on previous noise history, work and living area on the boat, time on boat, age, rate, etc. The hearing losses of enginemen were compared to hearing losses of all other crewmen, as a function of time on boat, for each frequency. Although there were minor reversals, the general trends showed the enginemen to have greater losses at all frequencies. The amount of loss was slightly less than the predicted loss based on the 1954 American Standards Association publication, The Relations of Hearing Loss to Noise Exposure.
Theory of the Sound Radiated into the Liquid by the Gas-to-Liquid Entry of an Object
Authors: Franz G. J.
Published: September 2005

A theoretical treatment of the production of sound by the impact of an object on the surface of a liquid is given in which the instantaneous sound pressure appearing in the liquid is related to the doublet formed by the displacement of liquid by the object entering the surface. The efficiency of conversion of kinetic energy of the entering object into sound energy radiated into the liquid is shown to be proportional to the third power of the ratio of impact velocity to the velocity of sound in the liquid, whereas the durations and frequencies of the instantaneous sound pressure are determined by the ratio of linear size to impact velocity. Accordingly, the sound pressure occurring at some fixed distance from the splash is proportional to the linear size of the entering object and to the third power of the impact velocity. The instantaneous sound pressures to be expected from the entry of spheres, cones, and wedges will be discussed.
The Vibration, Shock, and Noise Environment in Military Aircraft and its Effects on Electronic Components
Authors: Mintz F. , Levine M. B.
Published: September 2005

The widespread use of electronics in military aircraft requires constant evaluation of the design criteria as related to reliability. One of the important environmental factors is mechanical shock, vibration, and noise. This paper examines the existing environments as measured aboard both reciprocating and jet engine aircraft, and draws a comparison with current military specifications governing shock and vibration testing of electronic components. In addition, the results of shock and vibration testing on representative airborne electronic components are presented. Also included are the effects of high-intensity sound on certain components. Some recent work shows that high-intensity acoustic excitation can produce malfunctions of electronic components, although no Government specifications cover acoustic effects. Much of the work discussed was sponsored by Wright Air Development Center.
Underwater Ultrasonic Scattering by a Radial Cylindrical Temperature Gradient
Authors: Grant P. E.
Published: September 2005

The scattering of a one-megacycle underwater ultrasonic beam by a radial cylindrical temperature gradient perpendicular to the beam is studied as a function of position and gradient strength. To achieve temperature gradients large enough to scatter the beam, it is found advantageous to use large currents in a thin copper wire, whose own beam scattering is negligible. Because of the presence of free convection currents it is necessary to make time average studies of both the temperature and scattering distributions. From these studies average (0–1 minute) temperature and scattering distributions are constructed, and it is found that a possible diffraction region exists between temperature gradients of 14.5 and 26.5°C/cm. In addition, there is evidence that a transition from wave to ray acoustics occurs between gradients of 26.5 to 36.5°C/cm.
Mistuning Desirable in Organs, Pianos, Choruses, and Orchestras
Authors: Little Edward M.
Published: September 2005

See paper D1, American Physical Society meeting, June 26, 1951. Tone quality of a chord depends on more than the strength of harmonics. Organ builders have for years included “celeste” stops amongst the softer stops. They consist of two or more ranks of pipes, mistuned about 0.1 semitone (approximate pitch threshold of ear) to produce beats which increase in frequency with pitch; when a chord is played there is a scintillation of tone which is more subtle than the tremulo in which all tones vary in volume synchronously. A pipe organ played at full volume needs no intentional mistuning as there are then many pipes speaking one pitch and it is impossible to have all pipes for a given pitch, tuned perfectly to each other. Electric organ companies have failed to realize the importance of “celeste” or “chorus” stops—two use them but only in a limited way. The same effect is observed if the three strings of a piano note are not too well-tuned. A chorus sounds better than a quartet and a full string orchestra sounds better than a string quartet for the same reason—no two violinists (or singers) can possibly play (or sing) exactly the same pitch.
Information-Analysis and Power-Spectrum Model of Hearing
Authors: Pikler Andrew G.
Published: September 2005

Quantization of the acoustical signal space is based on the sound relaxation hypothesis (phonon-s); quantized are also two auditory message spaces (peripheral and cortical). Passive transfer models (Ohm's acoustical law; transduction) are rejected. The true auditory transfer function is identified as running power-spectrum analysis. The digital power-spectrum model of hearing is used to explain seven types of auditory resolution errors: Pitch- and intensity discrimination errors follow from the density of coding; phase-deafness (monaural) is inherent in spectrum-analysis; octave errors result from octave-periodicity represented in the cortical layout underlying scanning; flicker-fusion starts when repetition rate interferes with cortical scanning; the broad spread in transient spectra is interpreted as a consequence of drifting psychophysical time flow; sound-absorption by enclosed sound fields generates spectrum-broadening and is perceivable in the form of stereophonic sensations; unresolvable dissonances between simultaneous tones represent diffuse; consonances represent distinct spectra. Binaural interactions follow from informational coupling and smoothing of the two monaural time series. Diplacusis results from discrepancies between monaural codes and from interaural time drift. Musical hearing implies autocorrelational evaluation of the running spectrum. Chord qualities are identified as autocorrelational patterns. Diatonic consonances represent the highest autocorrelations as compared with dissonances characterized by lower autocorrelations, and noises with respective autocorrelations decreasing to zero. Successive diatonic intervals are detected by storage of the components and their autocorrelational evaluation. Sound timbres of clangs and, eventually, phonemic and noise-patterns are also auto-correlated. Suggestion is made to explain interaural phase-sensitivity on the basis of time and expansion.
The Localization of the Sound from Two Sources in Phase
Authors: Teas Donald C.
Published: September 2005

Three loudspeakers, equidistant from the subject, one in front and one at 40° to each side, when employed in pairs with the speakers of the pair in phase, provided three phantom sources to be localized. This method of presenting the stimulus brings about a different relationship between the stimulus factors for localization, time and intensity, from what occurs with a single source. The results show that in the low-frequency region from 500 to 1200 cps localization is dependent principally upon interaural time differences. In the range from 1200 to 1750 cps, time- and intensity-differences can combine to produce large bias errors. At frequencies from 2000 to 5000 cps, individual differences in sensitivity and other factors appear to destroy any simple relationship between interaural intensity and localization.
Tone Production in the Organ Flue Pipe
Authors: Mercer Derwent M. A.
Published: September 2005

A number of measurements have been made of middle C open diapason organ pipes during variation of the voicing adjustments. The effect on the spectrum and on the initial transient of alterations in height of mouth, languid setting, and wind pressure are presented. The effect of nicking is shown to be a decrease in the random noise background. Theories of action of the flue pipe are reviewed. Measurements on pipes with bodies removed show that the natural edge-tone frequencies of the flue/upper lip combination coincide with the whistles and other noises given by pipes before they come to full speech, but the edge-tone appears to have no part in the mature speech of the pipe. A mechanism of operation similar to the older “air-reed” theories, which explains the basic phenomena and also many facts empirically known to pipe-voicers, is presented and discussed.
A Miniature Barium Titanate Gauge for Measuring Shock-Wave Pressures
Authors: Siegelman A. , Mintz F.
Published: September 2005

This paper describes the construction, application and operating theory of a small titanate ceramic pressure sensor. The gauge has been used chiefly to measure pressure loading contours on small models placed in shock tubes. However, many other applications are possible in dynamic pressure measurements. The sensing element of the gauge makes use of a cylindrical shell of radially polarized barium titanate. In one form this shell has an outside diameter of 1/8 in., a length of 1/8 in., and a wall thickness of approximately 0.019 in. The end of the cylinder is usually capped to increase axial pressure loading and reduce the effects of radial strains. The small size and fast response time of this gauge result in excellent resolution of pressure-time relationships. Calibration procedures are discussed as well as methods of minimizing the thermal sensitivity. The sensitivity for pressure loading is considered in terms of the primary stress components in the ceramic shell.