bluuebunny/crossref_metadata_2025 huggingface dataset:
An Automatic Sound-Field Mapper
Authors: Baruch Jordan J.
Published: September 2005

The field mapper consists of a mechanism for moving a microphone over a plane in the sound field and suitable equipment for automatically plotting its output. The path of the microphone consists of a number of horizontal lines forming a raster whose spacing may be adjusted from 4 in. to 12 in. The position of the microphone is converted into two electrical signals which control the position of a recording pen by means of a two-dimensional servomechanism. The electrical signal from the microphone is recorded as a contour map of the sound field in the plane, the contours being isobaric lines (lines of constant sound-pressure level) or isotemporal lines (lines of constant phase). The system will plot 5 contours simultaneously, covering a 7-ft. by 7-ft. plane in 11 minutes. The level represented by any contour is arbitrarily set at any integral decibel value in a 30 db range. Thus 5 contours spaced as closely as 1 db may be plotted at once. The resulting map is read directly in db re: 1 dyne/cm2. As many contours as desired may be plotted by rescanning the plane.
On the Detection of Brain Tumors by Ultrasonics
Authors: Hueter T. F. , Bolt R. H. , Ballantine H. T.
Published: September 2005

The investigation reported here verifies Dussik's finding that an ultrasonic transmission method can yield ventriculograms without air injection. The outline of the liquid filled ventricle within the brain is usually deformed in the presence of a tumor. The ventricular geometry is depicted by graphical (automatic scanning) representation of intensity transmitted through the head. Experimental evidence indicates a safe working margin below pain and damage thresholds. The method utilizes the large available range of differential attenuation (order of .01 db/cm in the liquid and 1 to 3 db/cm in brain tissue, at frequencies of 1 to 3 megacycles). Results of basic studies on attenuation, scattering and resolution capabilities are reported.
Devices for Eliminating WOW in the Reproduction of Commercial Disk Records
Authors: Jones R. Clark
Published: September 2005

With modern record reproducing systems, a degree of fidelity of reproduction is attainable in which the wow inherent in commercial records is the limiting factor in the enjoyment of the reproduced music. In the manufacturing steps which lead to the stamper, the mechanical center of the record is lost, and is later re-introduced. In the re-centering, errors of 0.005 to 0.01 inch are typical, and occasional records have centering errors as large as 0.02 inch. At the inner grooves, a centering error of 0.01 inch produces a peak-to-peak frequency modulation of one percent, whereas 0.3 percent is detectable in a free field, and 0.03 percent is detectable in a room. Three different devices have been constructed whose purpose is to reduce the effect of the centering errors on the reproduction. All three employ the amplitude of the lateral oscillation of the reproducing stylus as the measure of the error to be corrected Two of them introduce a motion of the stylus along the groove which is equal in amplitude to, and in phase quadrature with, the lateral oscillation. The third device involves two servo mechanisms which center the record on the turn-table during the first few seconds of reproduction. The advantages and limitations of the three devices will be described.
Measurements of Ultrasonic Absorption in Various Mixtures of Nitrobenzene
Authors: Sette D.
Published: September 2005

The relaxation phenomena which, as now seems fairly well established, cause the difference between classical and experimental values of ultrasonic absorption coefficients in liquids, can be of various nature in the different liquids. It seems worthwhile to consider the case of binary systems in which it might be expected that relaxation phenomena of different nature could be present, depending on the characteristics of the components. We have studied seven binary mixtures having as one component nitrobenzene, whose molecules have a large dipole moment. The experimental results are here reported, measurements having been performed by an optical method. In the systems formed by an unassociated liquid having a large absorption coefficient (benzene, chloroform) and nitrobenzene, the curves of the absorption coefficient versus mol. fraction are like those obtained in the mixtures of an unassociated liquid with large absorption coefficient and an unassociated or associated liquid with a much smaller absorption coefficient. In this case the variation of the coefficient with concentration is caused, essentially, by the decrease of energy losses in the molecules of the first component, as a consequence of the higher efficiency of collisions between molecules on approaching the equilibrium distribution of energy among the internal degrees of freedom. In the systems of nitrobenzene and an alcohol (methyl, ethyl), on the other hand, it is to be expected that the relaxation phenomena are of structural nature. In this case the absorption coefficient, as a function of the mol. fraction, has a minimum at an intermediate concentration, just as it happens in some mixtures of water and alcohols.
Attenuation of Sound in Water Containing Air Bubbles
Authors: Laird Donald T. , Kendig Paul M.
Published: September 2005

These measurements were undertaken at the Black Moshannon Calibration Station of the Ordnance Research Laboratory in order to attempt to confirm some aspects of a theory due to L. L. Foldy. Bubbles were produced by forcing compressed air through the cloth covering of several trays lying on the bottom of the lake. The distribution in size of the bubbles and the number of bubbles per unit volume were determined by photographing the bubbles and by collecting the volume of air which rose over a given area in a given time, the terminal velocity of rise being a known function of bubble diameter. The attenuation of sound was found to be very large at frequencies for which resonant bubbles were present, and much smaller at the higher frequencies, indicating that resonance absorption was the principal phenomenon observed. However, if a plot of the acoustic attenuation is compared with a plot of the bubble volume distribution function versus the resonant frequencies of the bubbles, the first plot is found to peak at a somewhat higher frequency. This effect can be explained, at least qualitatively, on the basis of Foldy's theory.
The Piston Source at High Frequencies
Authors: Williams A. O.
Published: September 2005

For a circular plane piston of radius a, producing an ultrasonic beam of propagation constant k (or 2π/λ), theoretical expressions are derived for special values of the velocity potential at high frequencies. These apply for ka ⩾ 100 at distances z from the source governed by (z/a)3 ⩾ ka. The velocity potential averaged over a measurement circle equal to the piston is found, and also the potential at the rim of such a circle. The first quantity agrees well with results computed otherwise by Huntington, Emslie, and Hughes. Some remarks on wave front shapes are added. One conclusion is that the assumption of a collimated plane-wave beam near such a source is not universally very good, although it has some approximate relevance.
Amplitude and Phase Measurements on Loudspeaker Cones
Authors: Corrington Murlan S. , Kidd Marshall C.
Published: September 2005

Measurements have been made with a capacitor probe and an electronic phasemeter to determine the vibration patterns during cone “breakup” at various critical frequencies. An attempt is made to correlate these measurements with the sound-pressure curves and the transient responses. The results can be used to improve the design of loudspeaker cones.
The Non-Linear Interaction of a Plane Progressive Wave with a Small Sphere
Authors: Westervelt Peter
Published: September 2005

Under certain circumstances an acoustic wave exerts an average force (on particles) several orders of magnitude greater than the force arising from radiation pressure. Preliminary measurements of the force generated in a wave containing second harmonic distortion were reported previously. The force was 11 orders of magnitude greater than that caused by radiation pressure. The dependence of this force has been evaluated from Oseen's relation for the drag on a sphere. If the sound particle velocity is u = u0[sinωt + f sin(2ωt + φ)], the average force is FAv = − 3r2ρ0u02f sin φ to within 10 percent provided f < 0.4; but FAv = − 2.05r2ρ0u02 sin φ if f = 1; and FAv→ − 2.25r2ρ0u02 sin φ as f→ ∞. Here r is the radius of the sphere, small compared with wavelength; ρ0 is the density of the medium; and f is the fraction of second harmonic. The sphere is supposed not to follow the first order motion of the medium. The previously reported experiment, for which f = 1 and φ = ±π/2 is found to agree well with the theory. Another interesting case arises when a d.c. velocity is superposed on a sinusoidal wave. If u = u0[1 + f sinωt], then FAv = (7.07 + 3.52f2)r2ρ0u02 provided f < 1: If u = u0[sinωt + f], then FAv = 2.25[(1 + 2f2) sin−1f + 3f(1 − f2)12]r2ρ0u02 provided f < 1. In addition to the usual viscous and thermal boundary losses, other losses at the sphere will occur either at large acoustic amplitudes (non-linear absorption) or at small amplitudes provided the sphere drifts through the medium (differential absorption). The non-linear cross section based on the Oseen force, σNL = 9r2u0/c, is directly proportional to the ratio of the sound particle velocity to the velocity of sound c. The differential cross section, σD = 14.1r2udcc−1 | cos(k, udc) |, is proportional to the ratio of drift velocity udc to sonic velocity and to the magnitude of the cosine of the angle between the drift velocity and the propagation vector k. Rough computations indicate that the absorption cross section in the direction of fall of a 1-mm radius rain drop will be two orders of magnitude greater than the viscous cross section of the drop.
The Record-Rerecord Test for Rooms
Authors: Rudmose Wayne
Published: September 2005

In the search for schemes to quantize the acoustical performance of rooms the method of record and rerecord has been explored. A loudspeaker, microphone, two magnetic recorders, and associated amplifiers have been equalized to give a system response with essentially uniform characteristics over a wide frequency range. Recorded word lists have been used as follows to obtain articulation functions for rooms. With a given microphone and loudspeaker location the word list from the master recording is played and the acoustical pick-up at the microphone is recorded. This is called, for convenience, the first recording. This first recording now becomes the source for the second recording or rerecording. This process of rerecording is continued until the multiplied deficiencies in the acoustic characteristics of the room reduce the intelligibility to a low value. Data taken in the anechoic chamber indicate intelligibility is still acceptable at the tenth recording. Thus for any room an articulation function of percent articulation vs. the number of recording is secured. Such functions have been obtained in studios and rooms representing a wide variety of acoustical treatment. In certain rooms articulation functions have been obtained for several microphone-loudspeaker locations. A number of master lists are used and scrambling of the recordings as played back to the articulation crew reduces word learning. The advantages and limitations of the record-rerecord test will be discussed and articulation functions will be compared with reverberation, transmission, and spatial characteristics as well as with jury judgments.
On the Design of Sound Absorbing Ducts
Authors: Ingård U. , Baruch J. J. , Beranek L. L. , Labate S.
Published: September 2005

General design charts for square and circular sound absorbing ducts have been developed by an application of Morse's theory for the transmission of sound inside pipes. These charts have been developed specifically for ducts with all four walls lined with an absorbing material with or without an air space behind it. Interesting results of this study are that attenuations of 15 to 20 db per wavelength can be obtained over a frequency range of about one-half octave and that by scaling the size of the duct and the impedance of the acoustical material on the side walls this peak in attenuation may be placed at any desired frequency. Measurements on ducts ranging in size from 8×8 in. to 4×4 ft. show that the measured attenuation curves result in somewhat higher values of attenuation above and below the peak value and a slightly lower value at the peak than are calculated from the charts. For those ducts in which an air space is used behind the absorbing inner wall, the partitioning of the air space plays an important part. In order to realize the calculated values of attenuation, the partitions should be spaced at intervals of about one-quarter wavelength.
A Comparison of Sound Pressures Developed in Earphone Couplers and in the Ear
Authors: Corliss Edith L. R. , Brown R. F. , Lemmon K. T.
Published: September 2005

As part of the study being made in the Sound Laboratory of methods for standardizing hearing diagnostic equipment, measurements have been made comparing the sound pressures developed by earphones in several couplers, used at various laboratories in the calibration of earphones, with the sound pressures developed at the entrance to the ear canal when the earphones are placed over the ear itself. The couplers used in the comparison are the NBS Coupler No. 9A, the “Type I” coupler of the American Standards Association Standard for Coupler Calibration of Earphones, and a British coupler developed at the National Physical Laboratory. Necessarily, only a small number of human subjects could be employed. However, these data are being used primarily for orientation with respect to the design of a new coupler which will present to the earphone a better replica of the acoustical load afforded by the ear.
Frequency Vibrato as a Factor in the Loudness and Quality of Musical Tones
Authors: Oncley Paul B.
Published: September 2005

The importance of the vibrato in musical tones has been emphasized in many studies by Seashore and others. This paper demonstrates theoretically the intricate overtone structure produced by the frequency modulation of a complex wave, and endeavors to explain the subjectively observed dependence of loudness and quality on such modulation. Some conjectural points are raised regarding certain musical devices such as “tone clusters,” “chorus effect,” etc.
A Search for Non-Auditory Factors Correlated with Masked Auditory Thresholds
Authors: Pepinsky A. , Gales R. S.
Published: September 2005

The individual differences in noise-masked thresholds reported by Webster, Lichtenstein and Gales indicated the presence of certain non-auditory factors. A further search for such factors was undertaken. This was made a part of a pilot study, designed to provide information concerning tests promising usefulness in predicting the efficiency of candidates selected for training as operators of electronic detection equipment. A heterogeneous group of 56 college students were given a large battery of intelligence, vocational interest, and personality tests which have to date provided 127 different scores for each of the subjects. Pure-tone audiograms and masked thresholds were also obtained. Each subject then stood a 3-hr. listening watch, divided into four parts by 10-min. rest periods, reporting on hearing 800 cycle tone signals of 1-sec. duration introduced at various intensities, both above and below threshold into a background of white noise. The subject was harnessed and connected by electrodes to provide ten synchronized channels of bio-potential information, including EEG, PGR, superorbital muscle spikes, sphygmomanometer, cardio- and pneumograph during the entire listening watch. An analysis of variance of the scores obtained on efficiency of detection as well as selected concomitant data indicated that the originally obtained masked threshold values accounted for only five percent of the total variation between individuals whereas a number of the personality factors did quite as well or better. The factor of social extro-introversion was especially significant in that it explained more than 10 percent of the total variation. However, only 25 percent of the total variation is as yet explained. Simple correlation technique promises that much of it will be recovered from the information given by the biopotential data and the projective tests of personality given in the battery of tests. Interesting effects of learning and fatigue were observed as well as indications of subliminal response.
A Duplex Theory of Pitch Perception
Authors: Licklider J. C. R.
Published: September 2005

In the theories of pitch perception now widely supported, pitch is regarded as a unitary attribute of auditory experience. There is good evidence, however, that there are actually two pitch-like attributes, and it is reasonable to suppose that the duplexity of pitch is a reflection of duplexity in the auditory process. The first step in the process is analysis in frequency, performed by the cochlea, which distributes stimulus components of various frequencies to spatially separated channels. The second step, according to the scheme postulated here, is autocorrelational analysis, performed by the neural part of the auditory system, of the signal in each frequency channel. The basic operations of autocorrelational analysis are delay, multiplication, and integration. The nervous system is nicely set up to perform these operations. A chain of neurons makes an excellent delay line. The spatial aspect of synaptic summation provides something very close to multiplication. And the temporal aspect of synaptic summation is essentially running integration. The duplex theory suggests, therefore, that neural circuits following the autocorrelation model supplement the cochlear frequency analysis. The postulated neural autocorrelator of course does not compute autocorrelation functions of the acoustic stimulus: it operates upon afferent neural signals. Because the markedly non-linear process of neural excitation intervenes between the stimulus and the autocorrelation, the latter gives rise in certain instances to pitches that are not readily explained if the relatively linear cochlear analysis is considered to be the only one. “The case of the missing fundamental” and Schouten's residue effect, for example, are readily accounted for by the duplex theory. In addition, the theory provides a rational basis for the octave relation and for the consonance of other simple harmonic relations.
The Neural Components of the Round Window Response to Pure Tones
Authors: Rosenblith Walter A. , Rosenzweig Mark R.
Published: September 2005

Recent work on the electric potentials recorded from the cochlea in response to click stimuli has emphasized the importance of the so-called neural components (action potentials) of this response. During recent years Galambos and Davis, Wever, and Davis and his collaborators a have been concerned with the relation between microphonic and neural potentials for pure tones. This relation. is of obvious interest to a physiologically founded theory of hearing. In the electric response to pure-tone stimuli the aural microphonic usually predominates over the neural components. Hence there is a lack of quantitative information in the literature concerning the behavior of these neural potentials in response to pure tones. In this preliminary study we have sought the answers to three questions: (1) Where in the cycle of microphonic potential do the neural potentials occur when the frequency is varied over a range of several hundred cycles? (2) How does a change in the intensity of the stimulus affect the magnitude and the position in the cycle of the neurals? (3) What is the effect of exposure to loud sounds upon these neural potentials?
A Study of Some Aspects of the Intensity-Pitch Relationship
Authors: Nickerson James F. , Tebow Kenneth B.
Published: September 2005

The speculations concerning the intensity-pitch relationship or illusion as well as divergent findings stimulated a variation of the usual experimental approach to the intensity-pitch phenomenon. Two subjects were presented with test tones either gradually increased from zero intensity to comparison level or increased to maximum intensity and then decreased to comparison level. Immediately upon presentation of the test tone the subject was presented with a comparison tone and asked to vary its frequency to match the final pitch of the test tone. Three or more attempts were made and a median value accepted. Thus, half the test tones were increased in intensity to the comparison level and half were carried on to maximum intensity and then decreased to the comparison level. Five frequency levels were employed, 100, 300, 1200, 2800, and 4000 c/sec. Comparison levels for test tones varied by 5-db steps from just above threshold to the threshold of feeling. The results of this pilot study partially confirm earlier studies; variations up to 150 cents (112 semitones) particularly on the lower tones, lower tones depressed and higher tones raised in pitch with an increase in intensity (some exceptions in the lower tones), marked individual differences and rather poor consistency in pitch judgments. Pitch judgments were almost impossible at maximum intensity levels and judgments made on tones with intensity decreasing from maximum to comparison level are in contrast to those made on the same intensity level when intensity was increased from zero. These findings indicate the pattern of pitch response is markedly irregular, The dissimilarity of the pitch curve of ascending and descending intensities might indicate some physical compensation and attenuation of the ear mechanism itself or perhaps a non-linear spread of stimulation in the cochlea together with some form of “after-image” or slow recovery, or perhaps some similar phenomenon at the cortical level.
A Feedback-Controlled Calibrator for Phonograph Pick-Ups
Authors: Woodward J. G.
Published: September 2005

The methods and devices currently employed in the measurement of the response-frequency characteristics of phonograph pick-ups are reviewed. A new type of electro-mechanical device suitable for calibrating phonograph pick-ups between 20 and 20,000 c/sec. is described and results obtained with a typical pick-up are shown. The calibrator uses electromechanical feedback to secure an essentially uniform response throughout the range of frequencies in which pick-up testing is carried out. Some of the principles and problems of a general nature encountered in the design of an electromechanical feedback system are discussed, and are illustrated by the operational characteristics of the calibrator.
Determination of Electromechanical Parameters of Condenser Microphones
Authors: Simmons B. D. , Biagi F. , Cook R. K.
Published: September 2005

Values of electromechanical parameters for a condenser microphone may be determined from measurements of pressure response and output impedance. Electromechanical equations for a condenser microphone, in the linear approximation, may be written as e=Z11i+Z12u,p=Z21i+Z22u; (1) e is the voltage at the electrical terminals, i the current, p and u are the pressure and volume velocity at the diaphragm. These variables are assumed to be sinusoidal. Z11 = 1/jωC0, where C0 = C0′+C0″ is the blocked diaphragm electrical capacitance, C0″ is a passive shunt capacitance, and C0′ the blocked value of the variable capacitance. Z12 = Z21 = − E0C0′/jωV0C0, where E0 is the polarizing voltage, V0 is an equivalent volume given by the product of effective plate separation and area. Z22 = ZM − (E0/V0)2C0′C0″/jωC0, where ZM is the impedance of the diaphragm structure, Z22 = ZM with E0 = 0. The pressure response of the microphone is ρ = (e/p)i=0 = −E0C0′/jωV0Z22. The electrical admittance, with a negligible acoustic load is i/e = Y = g+jωC=jωC0+φ2/(ZM−φE0/jωV0), (3) where ω = E0C0′/V0, C0 is the measured value of capacitance at resonance, or at high frequencies (100 kc). The resonant frequency is determined by the frequency of maximum g, or very closely the 90° phase point of the response; φ is determined from C − C0 = φ2CM and ρ = φCM/C0 at the low frequencies, where CM is an effective compliance. The remaining parameters Z22 and V0 may be determined from the admittance and response values. Data will be presented for several condenser microphones.
Direct Radiator Loudspeaker Enclosures
Authors: Olson Harry F.
Published: September 2005

Direct radiator loudspeaker mechanisms are usually mounted in cabinets. Most of the considerations concerning the design of cabinets for direct radiator loudspeaker mechanisms have involved the volume or over-all dimensions of the cabinet which, together with the loudspeaker mechanism determines the performance of the combination of the loudspeaker mechanism and cabinet in the low frequency range. There is another important factor in the design of direct radiator loudspeaker cabinets, namely, the exterior configuration of the cabinet. The configuration of the outside of the cabinet markedly influences the response in the mid and high frequency ranges due to diffraction effects. These effects are usually overlooked, and the anomalies in response are unjustly attributed to the loudspeaker mechanism. Therefore, in order to determine the effects of diffraction, it appeared desirable to obtain the performance of a direct radiator loudspeaker mechanism in such fundamental shapes as the sphere, hemisphere, cylinder, cube, rectangular parallelopiped, cone, double cone, pyramid and double pyramid, and variations and combinations of these fundamental shapes. The result of these tests indicates that the outside configuration of the housing introduces variations in the response frequency characteristic of as much as 12 db.
Absolute Measurement of Small Vibration Amplitudes
Authors: Koidan Walter , London Albert
Published: September 2005

This paper describes an acoustic method for the absolute measurement of small vibration amplitudes and which, as a by-product, results in a method of calibrating vibration pick-ups. Vibrations generated by an electrodynamic device are transmitted to a piston arranged to vibrate within a cavity. The diaphragm of a condenser microphone is coupled directly to the cavity, and the pressure change in the cavity resulting from the motion of the piston is detected by the microphone and transformed into an electrical output. One side of a parallel plate condenser is rigidly attached to the piston, forming a direct electrostatic pick-up. Transformation into electrical energy is accomplished in both cases by a low noise-level electronic circuit after Van Zelst, which provides a sensitive coupling device and eliminates the danger of stray fields. The output of the microphone circuit as a function of sound pressure is found independently by a reciprocity calibration, while the amplitude of motion of the piston is computed from the observed sound pressure. With the electrostatic device used as a pick-up, the method can be used to measure the absolute amplitude of vibration of other structures without loading them. Preliminary measurements of the order of magnitude of 10−9-cm displacement have been made. The frequency range of the instrument as presently constructed is 20 to 6000 cycles per second but could be readily extended.
Simplified Measurements of Phase and Frequency Modulation Caused by Flutter in Sound Recording
Authors: Shepard Ward , Levine Irving
Published: September 2005

Laboratories and small manufacfacturers are frequently faced with the problem of accurately measuring the flutter content of sound recording equipment, but are not able to do so because of the cost and/or measuring limits of commercial flutter meters. Although flutter is basically undesirable speed variations of the recording medium due to imperfections of the mechanical drive system, the principal annoyance value that flutter causes is frequency modulation of the intelligence signal. This paper describes flexible and comparatively simple methods of measuring phase and frequency modulation effects caused by flutter and how these measurements can be used to determine quantitative and qualitative values of flutter.
Distortion of Sofar Signals
Authors: Condron T. P.
Published: September 2005

During preliminary Atlantic experiments in underwater sound transmission in the deep sound channel, explosive sounds were received on bottom mounted hydrophones at ranges of over 2000 miles. The characteristics of these signals were in almost perfect agreement with predicted characteristics based on ray theory computations. Later experiments in the Pacific Ocean have shown that the slope of the bottom on which the hydrophones are planted has a pronounced effect on the signal characteristics. Signals which arrive at the Pacific hydrophones from bearings where the slope was greatest were distorted slightly by bottom reflections, while those arriving at the hydrophones from bearings closely paralleling the continental shelf were seriously distorted. When a sea mount which penetrated the sound channel was present between the source and the hydrophones, a shadow was caused for those rays which penetrated to depths below the sea mount summit. This type of distortion is easily recognized and it should therefore be possible to detect and locate unknown sea mounts by SOFAR techniques.
Transmission of Sound through Plates in Water
Authors: Fay R. D. , Fortier O. V.
Published: September 2005

An extensive series of measurements has been made of the transmission of sound through steel plates immersed in water as a function of angle of incidence and the product of frequency and plate thickness. The results indicate certain modifications to be made in the classical criteria for effective transmission through plates of infinite extent. These modifications are formulated.
Ultrasonic Relaxation Phenomena in Oxygen in the Range from One to One Hundred Megacycles per Atmosphere
Authors: Thaler William J.
Published: September 2005

Ultrasonic velocity and absorption in dry, CO2-free, oxygen in the range from one to one hundred megacycles per atmosphere have been measured with the improved ultrasonic interferometer described in the previous abstract. A velocity increase of the order of seven percent has been found in this region with the accompanying anomalous absorption characteristic of relaxation phenomena. These effects are attributed to a rotational relaxation in oxygen.
An 11-Mc/sec Ultrasonic Interferometer for Gases
Authors: Greenspan Martin , Thompson Moody C.
Published: September 2005

An 11-Mc/sec “double-crystal” interferometer for use with gases at low pressures is under construction at the National Bureau of Standards. Previous experience indicates that the principal difficulties associated with such an instrument arise from impurities in the gas (at low pressures), variable electrical cross-talk between the transmitter and the receiver, and acoustical cross-talk through the solid parts of the apparatus. The rather high operating frequency was chosen so that for a given dispersion a higher gas pressure would suffice than at a lower frequency. The sound is introduced into the gas through a long coupling rod so that the distance between transducers changes by only a small fraction during a run. The electrical cross-talk is thus approximately constant and can be neutralized. The receiver crystal is mounted in a labyrinth of several concentric cylinders to provide a long path for leakage of sound between crystals. The output of the receiver is preamplified and converted to an intermediate frequency for further amplification and filtering. The interferometer screw is driven synchronously with two recorders, one of which records the phase of the output relative to that of the input, and the other the amplitude of the output on a logarithmic scale.
The Acoustic Impedance of Human Blood
Authors: Carstensen Edwin L.
Published: September 2005

The use of ultrasonic energy for medical purposes has created a need for information concerning the acoustic properties of the body. Blood, as a relatively homogeneous collection of cells, is chosen for basic study. Measurements are given of the phase velocity and absorption of sound as a function of frequency, volume concentration of erythrocytes, and temperature. The cellular content of the blood is almost entirely responsible for absorption. The predominantly linear dependence of the absorption on frequency over the range from 300 to 2500 kilocycles indicates that the mechanism of the absorption may be ascribed to elastic hysteresis. Only small temperature effects are observed in the range between room and body temperature.
Effects of Ultrasonic Radiation upon the Eye
Authors: Bowyer C. M. , Fox F. E. , Lavine O. , Langenstrass K. , Thaler W.
Published: September 2005

Experiments have been made with ox eyes immersed in water. Ultrasonic radiation from a three megacycle per second source was focused at various points inside the eyes. Permanent localized opacities have been produced in the lens (cataracts) and on the cornea. The manner in which their production depends upon intensity and exposure time indicates that the effect is probably due to heating produced by absorption in the focal region. Temperature measurements made with a small thermocouple inserted in the lens at the sound focal region confirm this hypothesis.
Spatial and Temporal Attenuation and Dispersion of Sound
Authors: Lindsay R. B.
Published: September 2005

If in the expression pe = Aei(ωt−kz) for the excess pressure in a plane progressive harmonic sound wave it is assumed that k is complex and we write k = kr+iki, the solution corresponds to a damped wave with absorption coefficient α = −ki, measuring attenuation of pressure amplitude with distance. This may be called spatial attenuation. If, on the other hand, it is assumed that ω is complex, with ω = ωr+iωi, the solution corresponds to a damped wave with absorption coefficient ωi, measuring attenuation of pressure amplitude with time. This may be called temporal attenuation. It is not commonly emphasized that the associated dispersion is in general quite different in the two cases. Thus, in absorption in a fluid due to heat conduction and viscosity the phase velocity increases with frequency for spatial attenuation but decreases with frequency for temporal attenuation. At low pressures in gases the difference might be detectable. Typical dispersion and absorption curves are presented for the above-mentioned cases as well as for thermal and structural relaxation mechanisms in which the situation is rather different.
A Liquid with Unusually High Sound Velocity
Authors: Weissler A. , Del Grosso V. A.
Published: September 2005

During a study of the effect of molecular structure on sound velocity in liquids, a liquid was found in which the velocity of sound is 3000 meters/second at 20°C, as measured by a 3-Mc ultrasonic interferometer. Previously the highest value known was less than 2000 meters/second, for glycerine. The new liquid is a viscous concentrated aqueous solution of sorbitol, prepared by heat dehydration of the commercial syrup “Arlex.” Sorbitol was selected for study, even though it is a solid, because its chemical structure is that of a double glycerine molecule. Concentrated sorbitol solutions also show a dispersion of sound velocity with frequency in the megacycle range (reminiscent of the behavior of polyisobutylene as described by Mason) and absorption coefficients many times larger than that of glycerine.
Temperature Dependence of the Ultrasonic Absorption in Carbon Disulfide
Authors: Sette Daniele
Published: September 2005

Measurements of ultrasonic absorption coefficient were performed in carbon disulfide in the temperature range between −23°C and the boiling point. point. A pulse method was used at 31 Mc/sec. The temperature dependence of the absorption coefficient is not linear as usually assumed in the literature, and ∂α/α∂t varies gradually from the value 7.3 10−3 deg−1 for −23°C to almost zero near the boiling point. The value of the parameter α/ν2 (α is the amplitude absorption coefficient, ν the frequency) is 5480 10−17 sec2/cm at 20°C, in good agreement with other results showing dispersion in carbon disulfide in the frequency range 1–100 Mc/sec.
Surface Vibration Patterns of Piezoelectric Radiators. II
Authors: Nixon J. D. , Rhodes R. A. , Williams A. O.
Published: September 2005

This is a continuation of work previously reported. The technique has been modified to use multiple-beam interferometry with an X-cut quartz crystal polished and silvered on both faces (80 percent reflectance). Use of auxiliary optical flats produces separate fringe patterns from the two quartz faces. These patterns are superimposed in the field of view and are visible simultaneously. Since the fringes cross each other, the two patterns are distinguishable. When the quartz radiates acoustically into air, strong vibration of any part of either face is detected by disappearance of part of the associated fringe system. Visual observation and photographs show strong localized disturbances to be the rule; the disturbances on directly opposite portions of the quartz faces do not necessarily coincide.
Spectrum Analysis by Time-Limited Fourier Transforms
Authors: Di Toro M. J.
Published: September 2005

The usual frequency spectrum of a wave form, as determined by its direct fourier transform, is a time invariant function useful for some applications, as for example in network design. However, the time invariant fourier spectra of audible wave forms have little in common with what is heard. This is because the type of spectral analysis in the ear is one which preserves the temporal pattern of the sounds; i.e., it results in a spectrum which changes with time. It is shown that such time varying spectra, or temporal spectra, may be obtained mathematically simply by taking the usual direct fourier transforms of the wave forms and limiting the integration to a finite, rather than infinite, interval of time. The results of such an analysis indicate that temporal fourier transforms are analogous to the response of a bank of tuned reeds of finite pass bands. It is also shown that, as one attempts to determine with greater accuracy the epoch of a wave form in time, its spectrum is determined with less accuracy. This is close to the indeterminacy principle indicated by Gabor. For simplicity of mathematical analysis, probability-shaped wave forms are used.
Reflection of Acoustic Waves from an Inhomogeneous Medium
Authors: Heller G. S.
Published: September 2005

The reflection coefficient has been calculated for a plane acoustic wave starting out in a homogeneous medium and encountering a medium in which the velocity varies exponentially with distance. The coefficient is derived from an exact solution of the wave equation for oblique incidence. For an exponential decrease, numerical results have been found for values of ω/g = 10 and 100, where ω is the angular frequency and g is the velocity gradient at the start of the exponential variation. These values compare well with those calculated from an approximate formula utilizing the W.K.B. method given earlier by the author. The W.K.B. solution is fairly accurate for angles of incidence up to 60° if ω/g = 100, and up to 45° if ω/g = 10.
Instrumentation for the Study of Impact Sound
Authors: London Albert , Boesch Philip W.
Published: September 2005

Instrumentation will be described for the measurement of the relation between the total acoustic energy emitted by a floor when subjected to a mechanical impact and the striking velocity of the impact hammer. In addition, the mechanical force generated during the impact is measured. Some experimental results on a wooden floor and steel plate will be described. The relation between these measurements and the problem of standardizing routine impact sound measurements on floors will be discussed.
The Intervalgram as a Visual Presentation of Speech Sounds
Authors: Chang Sze-Hou , Pihl George E. , Wiren Jacob
Published: September 2005

The points of zero crossing and the points of zero slope of the oscillograms of speech sounds are considered to contain the essential information for intelligibility. The intervals between zero crossings θ0, and the intervals between zero slopes θm, are plotted as points in rectangular coordinates. The ordinate of the dot is a function of θ(θ0 or θm), and the abscissa is a function of the time of occurrence t of the particular θ. The choice of these functions depends upon the types of portrayal needed for a specific analysis of speech sounds. The resulting intervalgram gives a halftone picture (consisting of dots) of speech sounds. The patterns may be proportioned to show either a detailed or general representation of the variation of the interval distribution. One type of pattern portrayed at the speech rate on a cathode-ray oscilloscope with a screen of long persistence has been found quite similar in certain respects to the patterns obtainable by the sound spectrograph as described in the book Visible Speech by Potter, Kopp, and Green. The equipment involved in obtaining the intervalgram, however, is much simpler.
Difference Limens for Complex Frequencies
Authors: Stevens K. N.
Published: September 2005

Most of the stimuli that are commonly experienced by the ear, especially in the perception of speech, are transient sounds of a more complex nature than the pure tones and clicks usually studied in psychoacoustics. A natural building block for such complex sounds is the damped sinusoid of the form e−σt cosωt, since this is a basic component of the response obtained when any linear system with resonances undergoes transient excitation. As an introduction to a study of the perception of waves with such “complex” frequencies, difference limens in frequency have been measured for single stimuli of this form, over a range of values of the parameters σ and ω. For small values of the damping σ the DL is close to the value for pure tones, but as the damping increases, discriminability deteriorates rapidly. In the range of σ between 150 and 500 sec−1 (bandwidth between 50 and 160 cps), the variation of DL with frequency exhibits a minimum between 500 and 1000 cps. A similar investigation of the same DL's has been made for series of these stimuli repeated at a frequency comparable with the fundamental pitch in vowel sounds. The results of these experiments are used to estimate the degree of precision that is possible in the perception of the formants that characterize speech sounds.
Recovery of the Audibility of Clicks after Exposure to Pure Tones and Noise
Authors: Hirsh I. J. , Ward W. D.
Published: September 2005

Exposure to an intense noise or tone produces a temporary elevation of the threshold for brief acoustic clicks. The course of recovery from such auditory fatigue has been measured as a function of the frequency, intensity and duration of the noise or tones. A battery of four clicks, each of which is 3 db more intense than its predecessor, is presented every 3 seconds so that an estimate of the click threshold may be made every 3 seconds. Extensive individual differences tend to obscure, only partially, a general course of recovery. A Békésy-type audiometer permits a continuous-frequency audiogram to be made both before and after exposure, so that variations in the recovery of clicks among individuals may be compared with differences in their audiograms. When the energy in the stimulating tone or noise is concentrated in the region below 1000 cps, recovery to normal (and sometimes better than normal) occurs in about 40 seconds. But this rapid recovery is followed by a second elevation in the threshold that reaches a maximum between 100 and 150 seconds after cessation of the stimulating sound. When the energy is concentrated above 1000 cps, the final recovery (after 150 sec) is considerably delayed, indicating a more persistent auditory fatigue from high frequencies than from low. (Differences among individuals are especially great for high-frequency stimulation.)
Measurements of the Acoustic Radiation Pressure on a Sphere in a Standing Wave Field
Authors: Rudnick I.
Published: September 2005

A 1-mm radius cork sphere was suspended by a fine vertical thread in a standing wave field whose axis of symmetry was horizontal. The force on the sphere was determined by the deflection from the vertical position. This force was determined as a function of axial position at a single frequency, and the dependence of the force, at a point halfway between the pressure node and antinode (the force is maximum at this point), on the acoustic amplitude was measured at several frequencies in the range 400 cps to 2800 cps. The maximum acoustic displacement amplitude used was less than the radius of the sphere but was of the same order of magnitude. The results are found to be in good quantitative agreement with the theory of L. V. King.
A Theory of Edge Tone Production
Authors: Nyborg W. L.
Published: September 2005

A jet-edge (JE) system is an arrangement for projecting a thin blade of air from an orifice and against a knife edge; under appropriate conditions, edge tones result from a setup of this kind. It has been shown that knowledge of the characteristics of JE systems is important in understanding the behaviour of such sound generators as organ pipes and Galton-type whistles. Despite an abundance of literature on the subject of edge tones, little quantitative theory is available concerning the dynamics of a self-oscillating JE system. In this paper, a simplified model is proposed, for which the equation of motion is then deduced in terms of undetermined functions; the result is an integral equation of the form y(t) =  ∫ −∞τ−t g(t − τ)⋅φ[y(τ)]dr, where y(t) is the transverse displacement of the stream at the knife edge at any time t, and where g(t − τ), φ(y) are the above-mentioned undetermined functions. Self-oscillatory solutions have been obtained corresponding to special assumptions about g and φ; the latter are usually chosen to be nonlinear functions of their arguments, so that (1) then becomes a nonlinear integral equation. Certain self-oscillating electromechanical systems are governed by nonlinear integral equations of the form of (1); this suggests that these systems maybe regarded as analogs of the JE system.
Moving Sound Sources and Receivers
Authors: Oestreicher Hans L.
Published: September 2005

A general formula is derived for the field of an arbitrarily moving sound source of zero and first order (dipole), while a more detailed numerical discussion is given for the rectilinear motion. The directivity pattern and the radiated power of a source of zero order, a dipole, and a simple radiator group is computed for different velocities. Good agreement is found between the dipole field and measurements of vortex-sound of rotating rods. (See Wittern, Abstract J3.) The consideration of the motion of a sound receiver is much simpler. The combination of a moving source and a moving receiver leads to a generalized doppler-effect formula.
Accurate Prediction of Resonant Frequency of Water Loaded Transducers
Authors: Robey Donald H.
Published: September 2005

The resonant frequency of a crystal transducer may either increase or decrease when taken from air and immersed in water. A formula is derived which predicts the approximate resonance in either case. In general, it is found that the reactive component of the radiation impedance tends to lower the frequency while the resistive component tends to raise the resonant frequency by effectively diminishing the Rayleigh “finite width” correction. The resultant frequency cannot, of course, exceed the “thin bar” resonance.
Variable Resonant Frequency Crystal Transducer
Authors: Robey Donald H.
Published: September 2005

The resonant frequency of a crystal and backing plate combination can be controlled by means of a magnetic field applied to the backing plate. A change in frequency of one-half an octave can be attained. The “Q” of the combination remains almost constant with the small changes in the magnetic field associated with the frequency change.