bluuebunny/crossref_metadata_2025 huggingface dataset:
Contribution to the Theory of Radial Extensional Vibrations in Thin Disks
Authors: Moseley Donald S.
Published: September 2005

In a manner which parallels one derivation of the Rayleigh correction to longitudinal modes of a thin circular bar there is now derived a correction to the radial modes of a thin isotropic disk. This has been verified through the experimental use of disks of prepolarized barium titanate ceramic whose thickness-to-diameter ratios range from 0.0276 to 0.1171. Experimental work was performed with the aid of facilities of Brush Laboratories, Cleveland, Ohio.
Environmental Testing of Airborne Electronic Components at High Sound Intensities
Authors: Mintz F. , Levine M. B.
Published: September 2005

In an attempt to simulate for purposes of laboratory testing of electronic components the high-intensity sound fields encountered in the proximity of modern rocket and jet aircraft, the Armour Research Foundation has developed a convenient laboratory device, designated the “ARF High-Intensity Sound Chamber.” The ARF Chamber is simple to construct, calibrate, and operate. It utilizes readily obtainable components, including a small commercial loudspeaker driver, and is approximately 6 × 8 × 10 in., with a test chamber size of 6 × 6 × 6 in. It is estimated that a similar sound chamber could be constructed and instrumented for about $600. Calibrations have been made with audio-oscillator and “white noise” inputs; sound pressure levels in the order of 155 db are obtainable. Results of preliminary tests on electron tubes, sensitive relays, and pressure switches are included in the paper. This information is particularly interesting, as test results show some effects not obtained by vibration testing. Thus, it appears that high-intensity sound tests serve as a useful and valid supplement to vibration testing of airborne electronic components. The work was sponsored by WADC.
Variable Length Hydrophone
Authors: Mechler M. V.
Published: September 2005

The line hydrophone to be discussed provides a means for obtaining a variety of radiation patterns at a given frequency. The motor unit of the hydrophone is made up of 30 cylindrical BaTiO3 elements mounted end to end, and alteration of the transducer's beam pattern is effected by changing the number of adjacent BaTiO3 elements electrically incorporated in the line. Eight effective lengths of the transducer's motor unit are available, and therefore, at given frequency, any one of eight directivity patterns can be selected. A series of slides will be presented to show the directivity patterns associated with the various motor lengths. A comparison between measured and calculated patterns will also be presented. The elements of the transducer's motor unit are considered as a finite assembly of identical line segments which are uniformly separated and aligned along a common axis. Each of the segments is treated as a uniform line distribution of simple sources, and an expression for the transducer's directivity is approximated in terms of angular measure from the acoustic axis, the number of elements incorporated in the motor unit, and the spacing and length of the individual BaTiO3 elements.
Recent Developments in the Calibration of Microphones
Authors: Burkhard M. D. , Biagi F. , Cook R. K. , Corliss E. L. R. , Koidan W.
Published: September 2005

A method has been developed for measuring the acoustical impedance of a microphone's diaphragm at various frequencies. The impedance is derived from a series of voltage ratios and the known acoustical impedance of the coupler used for the measurements. In place of the usual reciprocity procedure of matching open-circuit microphone voltages, diaphragm motion is matched with the carrier-frequency detection system described elsewhere in this program. Combination of the acoustical impedance with other known parameters of the microphone permits accurate sound pressure measurements with carrier-frequency microphones. Calibrations of condenser microphones have been extended to very low frequencies, near 1 c/sec, by taking account of the cooling effects of the walls on the acoustical impedance of conventional cylindrical couplers. Analytical expressions for the temperature distribution in cyindrical enclosures have been obtained, and computations of the effect on the impedance are given in the form of plotted correction factors. The results of calibrations of condenser microphones at very low frequencies will be presented.
The Dynamic Magnetostrictive Properties of Alfenol
Authors: Davis C. M. , Robey I. L. , Ferebee S. F.
Published: September 2005

The magnetostrictive properties of Alfenol, a cold-rolled Fe-Al alloy, for use as the active element in electromechanical transducers were compared with those of nickel. The aluminum content of the Alfenol was varied from ten to sixteen percent. After a suitable heat treatment a maximum effective electromechanical coupling coefficient of 0.31 was obtained with 12-Alfenol biased to four oersteds. The maximum effective coupling coefficient of 13-Alfenol was observed to be approximately the same as that of nickel, 0.27. While the effective coupling coefficient of 13-Alfenol is smaller than that of 12-Alfenol, the product of the characteristic frequency times the thickness squared for 13-Alfenol biased to twelve oersteds was twice that of 12-Alfenol biased to four oersteds and four times that of nickel biased to thirteen oersteds. Performance is given for similarly constructed Alfenol and nickel transducers.
The Use of Flat Splitter Construction in Aviation Test Cell Silencing
Authors: Hirschorn Martin
Published: September 2005

Experiences in the use of flat splitters in silencing arrangements for large air ducts, with special reference to aviation test cell silencing, will be discussed. Various splitter systems will be analyzed in comparison with the recently developed “Acou-Stack” system. This system resulted from model studies undertaken for the purpose of developing a silencing arrangement suitable for present-day aviation test cells. The importance of three design factors—(1) noise reduction; (2) strength of materials; and (3) pressure drop—will be stressed. The model test cell stack was constructed to a one-eighth scale based on a typical existing vertical sixteen-foot square jet-engine test cell. Extensive acoustic performance testing of subsequent full scale installations presents a very interesting comparison with scale model results. Agreement in the first three octave bands is very close whereas in the higher bands the full scale readings are 9 and 11 decibels better. This is attributed to higher sound-absorption coefficients for the full scale splitters. Scaling factors are more accurate for low frequencies because they are the result of volumetric configurations.
Recent Developments in Soundproof Doors
Authors: Munchhausen H. V.
Published: September 2005

A brief history of the development of soundproof doors over the last few decades is presented. Various approaches to the solution of this problem are reviewed and their effectiveness discussed. A new solution which has proved effective has been applied in the Munchhausen Door, details of the design of which will be shown. Among the data to be presented will be measurements of sound transmission loss at the standard frequencies.
On the Attenuation of Sound Passing over an Audience
Authors: Subrahmanyam D. L. , Bolt R. H.
Published: September 2005

The level of the direct (source to listener) sound in auditoria may be influenced considerably by attenuation owing to the audience. The analysis of echo effects, in particular, may be seriously in error if no allowance is made for the attenuation of the direct sound relative to the reflected. Measurements of the attenuation, using a one-fifth scale model of a seated audience in an anechoic space, have been made at several frequencies and with several heights of the source above the plane of the audience. The results are in reasonable agreement with those reported in 1934 by Bekesy for an actual audience; but the present results cover a wider range of conditions met in practice and they are systematized for engineering application
Heat Generation in Acoustic Boundary Layers?
Authors: Mawardi Osman K.
Published: September 2005

The conventional investigations of the propagation of sound waves in conduits, when taking into account the effect of dissipation through friction and conduction of heat through the walls, assume the fluctuating part of the temperature of the gas to vanish at the boundaries. This is in essence a first-order approximation. Very different effects, however, are expected when second-order terms are considered. The purpose of the present paper is to discuss in detail the nature of the solution obtained from a second-order approximation.
Spatial Fluctuations in the Backward Scattering of Sound from an Acoustically Rough Medium
Authors: Nolle A. W.
Published: September 2005

The experimental basis for the problem is as follows: Apparatus is arranged to detect the backward scattered signal resulting from a collimated ultrasonic beam (pulsed) which strikes an underwater sand surface at a specified angle. As the apparatus is translated so as to sample different portions of the surface, random fluctuations averaging two or three decibels are observed in the scattered signal. It is desired to know whether variations in the average acoustical properties of the scattering medium must be postulated to explain the effect. In the present work a calculation is made of the fluctuation properties of a model in which the phase of scattering from each pair of Fresnel zones is random, and in which the amplitude of scattering from each pair is governed by a Gaussian function. The results obtained from this model are in substantial agreement with experiment as regards both the magnitude of the fluctuations and the autocorrelation properties of the fluctuation function. Therefore the observed effect appears to be a necessary consequence of the acoustic randomness or roughness which is responsible for backward scattering, and it is not necessary to introduce spatial variations of average acoustical properties to explain the effect.
Effect of Pressure on Sound Absorption in Water
Authors: Litovitz T. A. , Carnevale E. H.
Published: September 2005

The pressure dependence of sound absorption allows further investigation of the relationship between shear and compressional viscosity. The need for this information in associated liquids is emphasized by the fact that the temperature dependencies of the two viscosities are quite similar and therefore offer little chance of distinguishing differences between these viscous processes. Measurements of absorption in water at 0°C and 30°C, at 45 mc up to pressures of 2000 kg/cm2 were made using a pulse technique. The absorption data at 30°C show that αobs/αshear decreases from 3.0 to 2.7 with increased pressure indicating that the compressional viscosity has fallen about 10 percent as the shear viscosity rises 10 percent. At 0°C the shear viscosity exhibits a minimum as the pressure increases. In the same pressure range αobs/αshear exhibits a maximum rising from 3.4 to 3.7 and then falling to 3.2. These results indicate that in water the pressure coefficient of compressional viscosity is opposite in sign to that of the shear viscosity.
The Computation of Intensity in Ray Acoustics with Application to Stratified Media Containing an Extremal of Velocity
Authors: Heller Gerald S.
Published: September 2005

The computation of intensity in ray acoustics will be discussed and the results applied to the computation of acoustic intensity due to a point source located at an extremal of velocity. Near a maximum velocity the intensity falls off exponentially at large distances from the source with an attenuation coefficient proportional to the curvature of the velocity profile at the maximum. In the case of a velocity minimum a series of focal points located at the level of minimum velocity is predicted. The distance between the focal points is proportional to the radius of curvature of the velocity profile. The entire acoustic field due to particular velocity profiles will be presented.
A Nonreflecting Wall Lining for Underwater Sound Studies
Authors: Tamarkin Paul , Eby R. K.
Published: September 2005

In various underwater sound propagation studies being carried out in these laboratories, there has developed a need for a wall lining which eliminates sound reflections from the walls of the tanks used. Besides reducing the reflected sound level sufficiently, the lining had to satisfy the additional requirements of being inexpensive, easy to prepare, and simple to install. We have found that sheets of rubberized horsehair upholstery batting, when properly treated chemically, satisfy these requirements. This material reduces the wall reflection at normal incidence to a level approximately 20 db below that obtained from the water-steel interface. The chief disadvantage of this material is that prolonged immersion of more than 16–20 hours incapacitates it progressively. We will present the results of measurements on the frequency dependence of absorptivity and reflectivity, as well as the dependence of these parameters on angle of incidence. A hypothesis as to the mode of action of this material will be advanced.
Underwater Sound Scattering from a Rough Surface
Authors: LaCasce E. O. , Tamarkin Paul
Published: September 2005

An approach to the study of scattering of underwater sound from a rough sea surface has been undertaken by the use of scaled model experiments. These experiments have been performd in a tank of water, 4 × 4 × 10 ft. Steady-state conditions are imposed, although a pulsed carrier is employed to eliminate interference from wall reflections. The model rough surface studied is a corrugated one of cork sheet (which provides a free surface) mounted on plywood, the corrugations being essentially sinusoidal. A directional receiver is used to scan the scattered radiation. The acoustic wavelengths used vary from 1.5 cm to 0.6 cm. The surface wavelength and amplitude are 0.95 cm and 0.3 cm, respectively. Measurements on the distribution in angle of the scattered radiation as a function of angle of incidence, surface parameters, and acoustic wavelengths will be presented and compared with some existing approximate theories.
Phase and Intensity Relationships in the Interference of Bone- and Air-Conducted Sound
Authors: Dolch John P.
Published: September 2005

The sensation caused by a bone-conducted tone can be made to disappear completely by appropriate adjustment of the phase and amplitude of a simultaneously presented air-conducted tone of the same frequency. To explore some phase and intensity relationships of this interference phenomenon an apparatus was constructed that provides three separate pure tone channels of exactly the same audio frequency with independent phase and amplitude controls in two of the channels. A unique method of audio phase shifting is described that provides continuously variable phase shifts of 360 degrees with substantially no variation in the amplitude of the audio signal output. This method allows a single calibration of the phase shifter for any desired audio frequency output. Theoretical curves are presented of the resulting sensation level expected if the phase or intensity relationships between interfering air- and bone-conducted tones are varied about the condition of maximum interference that results in the subjective experience of silence. The method and results of the empirical verification of these curves are presented. The possibilities of utilizing air and bone conduction interference to improve interphone communication and afford ear protection in high-level ambient noises are briefly discussed.
Qualitative Descriptions of Short Bursts of Sound
Authors: Pepinsky Abe
Published: September 2005

Serious attempts have been made to choose adjectives which might adequately describe the quality of complex notes. Such studies have dealt largely with musical sounds of considerable duration. However, short bursts of sound, of the order of magnitude of a few milliseconds, offer new problems because of frequency side bands of energy. The form of the intensity gradient is found to be an important factor characterizing the sound. Oscilloscopic examination of such bursts of sound presents envelopes whose shapes correlate well with the definition of quality. Although permissive utilization of adjectives seems to depend mainly on the individual's interests and experience, a list of adjectives was finally agreed upon which serve quite well in differenciating the various qualities.
Acoustic Properties of Hemoglobin Solutions
Authors: Carstensen Edwin L.
Published: September 2005

Difference methods have been used to measure both the absorption and the velocity of sound in solutions of hemoglobin in the range from 0.3 to 10 Mc, and for various temperatures and concentrations. The absorption varies as a linear function of frequency over a large part of the range covered. Measurements show marked dispersion in the velocity of sound over the entire frequency range.
Acoustic Irritation Threshold of Ring-Billed Gulls
Authors: Thiessen G. J. , Shaw E. A. G.
Published: September 2005

Using the cringing reaction (which became noticeable at the age of about four months) as a criterion, the acoustic irritation threshold of six gulls aged six to ten months has been determined. The minimum value of about 85 db occurred at about 500 cps during the age period of six to seven months. At nine months the threshold had shifted upward about 15 db and was apparently still rising. An additional reaction consisting of dipping the tail occurred at this time. Measurement of the change in heart rate due to the sound also lends itself to a determination of the threshold and this agrees approximately with the cringing threshold for 1000 cps. The threshold of hearing measured for a single bird is about 30 db above the human threshold at 1000 cps but could not be measured too accurately due to the considerable activity of the bird and the consequent high ambient noise.
Utilization of the Intratympanic Muscle Reflex for Objective Determination of Cochlear Function
Authors: Kobrak H. G. , Whitman John M.
Published: September 2005

In the animal experiment in which exposures of the middle ear are possible it is readily seen that contractions of the two middle ear muscles occur when a sound of sufficient strength and frequency impinges on the ear. Using magnification up to seventy times no visible movements of the eardrum can be seen during contractions. It can be shown that the acoustic vibrations of the eardrum diminish when the muscles contract. In man the physiological conditions differ from the animal experiment in that no diminution of acoustic or semistatic eardrum vibrations occur during acoustic stimulation. However, by using a small, light reflecting surface on the eardrum (mirror in umbo area) rotation of the malleus tip of about 10 minutes can be demonstrated on acoustic stimulation. This reflex acts as proof that the cochlea has received and utilized the acoustic stimulus. The reflex is an objective observation of cochlear stimulation. Slides and a motion picture are shown to demonstrate the experimental results.
The Effect of Large Interaural Time Differences upon the Judgment of Sidedness
Authors: Wilbanks W. A. , Blodgett Hugh C. , Jeffress Lloyd A.
Published: September 2005

Bands of noise presented to the two ears via earphones are perceived as lying to one side when that side leads in time. Roy Klumpp has shown that interaural time differences as small as ten microseconds can be detected. The present study is concerned with the other extreme—the largest time differences that can be heard as “sided.” The interaural time delay in the present experiments was obtained by displacing one head of a binaural tape reproducer carrying the noise. A slow acting gate turning the signal on in both channels simultaneously was used to prevent the subject's getting a cue from the onset of the signal. Results will be presented showing the effects on the threshold for sidedness, of level imbalance, of the band width and the frequency of the noise, and of individual differences. The thresholds varied from a fraction of a millisecond to about 20 milliseconds depending upon the parameters involved.
Scattering of Sound by Isotropic Turbulence
Authors: Horiuchi Isaburo
Published: September 2005

Existing information concerning the characteristics of atmospheric turbulence is analyzed, and some representative figures on the resulting scattering of sound to be expected are obtained. The nature of such turbulence, the extent and causes of the anisotropy near the ground, the variation in its character with altitude, and the extent to which approximation of isotropy are valid are discussed. Other micrometeorological parameters are considered and their effects on sound propagation in comparison to those caused by velocity fluctuation estimated. A reasonable spectral function for isotropic turbulence is applied to a scattering cross-section expression derived by Kraichnan to obtain numerical results for the scattering. These are compared with recent experimental data.
An Automatic Data Reduction System
Authors: Watters Bill G. , Baruch Jordan J. , Kamperman George W.
Published: September 2005

The problems involved in manually reducing acoustical data obtained on extensive field noise surveys make this phase of the job an exceedingly tedious one. Instrumentation has been developed to perform the reduction techniques automatically from tape-recorded field data. Once the correction numbers for the recording system have been inserted, the system will plot a narrow band analysis, a 13 octave band analysis, or an octave band analysis of a sample of the noise. The ordinate may be either peak pressure level, rms pressure level, or average pressure level. Facilities have been provided for taking samples from several points (such as the equal area points on a grid) and averaging the squares of the pressures, thus yielding an average intensity over the grid. For the case where the areas are not equal, weighting functions may be introduced.
Time Distortion in Magnetic Recording
Authors: Mansfield Young F.
Published: September 2005

Time distortion introduced by the magnetic recording process is studied theoretically and experimentally. Problems of discriminating between actual time fluctuations and effects of noise are treated. Both recorder and tape are responsible for observed fluctuations. Measurements of the components due to tape alone are in excellent agreement with theoretical results obtained from a statistical model of the tape.
An Electronic Distribution Analyzer
Authors: Young F. Mansfield
Published: September 2005

A direct indicating instrument for the measurement of the unconditional probability density function of an input signal has been developed. Either statistically stationary or repetitive inputs can be analyzed. Integration times up to 1000 seconds are available. Examples of measured distribution functions of speech and music will be shown.
Hydrodynamic Feedback Oscillators
Authors: Bouyoucos John V.
Published: September 2005

The conversion of fluid-flow energy to acoustic energy by means of a controlled, variable-area orifice is described. Such an orifice acts as a variable flow-impedance device, and it is shown that for small variations of area a simple circuit representation may be obtained which involves an acoustic pressure or volume velocity “source” of finite internal impedance. Although such a mechanism is actually a “displacement-controlled” device, the area-variation can be “sound pressure-actuated.” Thus the network representation of the system can have the form of a four-terminal, unilateral, acoustic transducer which is, in many respects, similar to the vacuum tube. Acoustic feedback may be employed between these terminal pairs to originate and sustain the energy conversion process, thus giving rise to self-excited oscillations. Most of this converted energy is available to be dissipated in an acoustic load, since only a small fraction must be returned to the system to maintain the excitation. A number of oscillator configurations are illustrated, some of which are analogous to common vacuum-tube systems. (This research has been aided by funds made available under a contract with the U.S. Office of Naval Research.)
An Improved Ear Defender Cushion
Authors: Shaw E. A. G. , Thiessen G. J.
Published: September 2005

In designing ear defenders of the cover type for protection against sound the cushion presents a serious problem. To provide an airtight seal against an irregular object like the side of the head, the cushion is usually made quite soft. This, however, contradicts the requirement of a cushion with a high spring constant which is necessary to prevent the cup from vibrating at low frequencies. This contradiction is resolved by the use of an annular sheath which is filled with a liquid or semisolid. The high bulk modulus of the liquid prevents appreciable volume changes of the cushion due to the sound pressure while the high Young's modulus of the sheath prevents area change. The vibration of the cup is greatly reduced while the thin sheath offers no great rigidity to impede fitting the head. Low frequency attenuations as high as 34 db have been obtained when a solid material is substituted for the head. This is much higher than the limit set by the compliance of the skin and flesh on the head.
Mean Reactions in Vibrating Systems
Authors: Greenspan Martin
Published: September 2005

The time average forces exerted by the constraints in a vibrating system (radiation pressure, mean tension in a vibrating string, etc.) are easily computed from the “adiabatic law” of Boltzmann and Ehrenfest (Brillouin, Les Tenseurs). The usual derivation from the principle of varying action is difficult. An equivalent principle, which however gives the time dependence as well, will be derived in simple fashion from Lagrange's equations. It will be shown how similar results can be got from the solutions of linear differential equations with slightly variable coefficients.
An End-Fire Source
Authors: Junger Miguel C.
Published: September 2005

A radially pulsating cylindrical sound source gives rise to broadside radiation if all its elements move in phase. On the other hand, when a progressive phase shift between elements along the cylinder is introduced (by means of waves propagating along the cylinder, or of standing waves), the radiation can be “steered.” When the phase velocity of these waves is equal to the sound velocity in the surrounding medium, the source produces a radiation pattern which resembles that of an end-fire directive array of point sources. The high directivity thus achieved is independent of the ratio of source diameter to wavelength. This source may be in the form of a fluid-filled hose, or of an elastic rod or shell. In order to produce a design embodying the required characteristics, the dynamic phenomena in the surrounding medium and in the cylindrical column must be analyzed simultaneously. Since the surface area of this source can be conveniently made much larger than that of a piston-type source, large amounts of energy can be radiated. The results of an analytical and experimental investigation of this source are presented.
Sound Scattering by a Cylindrical Vortex
Authors: Dyer Ira
Published: September 2005

The equations of motion appropriate for waves in moving and inhomogeneous media are reduced to two coupled equations in the scalar and vector potentials of the sound particle velocity. The coupled equations are applied to an ideal vortex by approximately evaluating the vector potential in terms of the scalar potential; the vector potential obtained here was first obtained by Obukhov. The resulting equations are solved by integral equation approximations, yielding expressions for the scattered field and the cross section. The calculations show that sound scattering from a vortex is important when the core circumference is greater than the wavelength times the square root of the ratio of the sound to vortex frequency. Scattering from the core is shown to be an important effect compared to the effect of the irrotational motion outside the core.
Acoustic Streaming in the Vicinity of a Cylinder
Authors: Raney W. P. , Corelli J. C. , Westervelt P. J.
Published: September 2005

Combined theoretical and experimental studies have been carried out on the steady streaming velocity generated in the vicinity of a rigid cylinder oscillating to and fro in a viscous, incompressible fluid. The experimental results were found to be explained by first-order perturbation theory as long as the oscillation amplitudes did not exceed the radius of the oscillating cylinder. The results were confirmed experimentally with solutions of glycerin and water for a range of kinematic viscosity extending from 0.0086 cm2/sec to 0.4026 cm2/sec. Cylinder radii of 0.066 cm to 0.20 cm were employed and the frequency of oscillation varied from 80 cps to 160 cps. An outer cylindrical boundary of radius 2.23 cm or 4.1 cm was placed coaxially with the mean position of the oscillating cylinder. The theory, confirmed by experiment, indicates that the dimensionless dc boundary-layer thickness δdc/a (δdc = thickness of the steady inner circulation, a = radius of cylinder) is a universal function of the dimensionless acoustic boundary layer thickness δac/a. It has previously been proved that the streaming generated by the interaction of a small amplitude sound wave with a fixed cylinder should give identical results as long as the wavelength of the sound is large compared with the radius of the cylinder. This proof has been experimentally verified by showing that the values of the dc boundary-layer thickness obtained by Holtsmark et al. in their acoustic experiment in air agree within experimental error with our experimentally determined universal curve for the dimensionless boundary-layer thickness. It is concluded that the first-order perturbation theory of Schlichting, and its subsequent refinement by Holtsmark et al., adequately explains the observed phenomena so long as the amplitude of oscillation is sufficiently small. Some observers have reported that the streaming configuration is altered with increasing amplitude of oscillation. This alteration may result in apparent reversal of flow. As has been previously pointed out this flow, which is observed at higher intensities, cannot be explained by any first-order theory such as that of Schlichting.
Anisotropy of Polarized Polycrystalline Barium Titanate
Authors: Moseley Donald S.
Published: September 2005

Bars of polycrystalline barium titanate were prepared as twins identical in every way save the direction of polarization. The first step was the application of that polarization which gave minimum electromechanical activity as detected by an ac bridge, and this was taken to represent the unpolarized isotropic state (s11 = S33). Secondly, large scale polarization was then produced, and the resulting split into constant E and constant D compliances, and the ratios of s33 to s11 at constant E and constant D of the polarized material were obtained. Time dependence of the order of a few days was noted. Facilities were made available through the cooperation of Brush Laboratories, Cleveland, Ohio.
The Interaction of Acoustical Waves with Concentration Gradients
Authors: Penn Robert , Yeager Ernest , Hovorka Frank
Published: September 2005

The interaction of ultrasonic waves with concentration gradients in solutions has been studied quantitatively with schlieren techniques having a resolution of the order of 10−4 cm. Although the gradients have been produced electrochemically at anodes and cathodes in copper sulfate solutions, the conclusions have been extended to concentration gradients in solutions in general. Moderately intense ultrasonic waves (e.g., 1 watt/cm2) are more effective than conventional agitation in disrupting these concentration gradients primarily because of the micro agitation associated with cavitation at or near the interface. Streaming effects in the ultrasonic field augment cavitation. The effective dimensions of the concentration gradients are reduced to a value approaching 10−4 cm as compared with 10−3 cm for ordinary directional flow. This accounts in good part for the increments produced by ultrasonic waves in the rates of various physical and chemical processes involving two or more phases. In a standing wave of low intensity with the wave front perpendicular to the phase boundary, the concentration gradients become localized at the displacement nodes or loops depending on whether there is a deficit or excess of solute at the interface.
Measurement of the Breaking Stress of Materials by Use of a Barium Titanate Transducer
Authors: Wick R. F.
Published: September 2005

The breaking stress of certain plastics and some metals has been measured by use of a barium titanate transducer with attached horn, resonating at 18 kc. The horn is made in two sections, a metal part which is permanently connected to the barium titanate, and a removable part made of the material to be tested. The stress is calculated from the amplitude of motion of the small end of the horn. Pulse technique is used in an attempt to avoid heating of the sample.
Absorption of Sound in Air and Mixtures of Nitrogen and Oxygen at Low Pressures
Authors: Stavseth Richard M.
Published: September 2005

The amplitude coefficient a for pulsed sound waves has previously been measured for pure nitrogen and oxygen. These measurements which were made in the frequency range of 60 to 70 kc, and pressure range of 1- to 10-mm Hg gave values for (pα/f2)107 (cgs units) of 1.64 for N2 and 1.92 for O2. Measurements subsequently made in air gave values significantly lower than either of these two values, the result being 1.52. Measurements were then taken in mixtures of N2 and O2 for the proportions 80 percent N2 − 20 percent O2, 50 percent N2 − 50 percent O2, and 20 percent N2 − 80 percent O2; these gave the values 1.54, 1.57, and 1.73. The ratio r of the experimental value of α to the classical value then becomes 1.25, 1.12, 1.08, 1.12, and 1.19 (rms deviation of no more than 0.05), running from pure N2 to pure O2. Other workers have reported much larger values for the ratio r, in some cases as high as 2.5. Assuming a relaxation mechanism whose relaxation time τ is small compared to the period of the sound wave, the Kneser-Rice-Herzfeld theory indicates that (r − 1) is proportional to τ. The lowest value of τ obtained from this data is of the order of the mean time between molecular collisions.
Vowel Synthesis Using Resonant Circuits to Represent Formants
Authors: Weibel Erich S.
Published: September 2005

The amplitude spectrum of a vowel is a product of two factors, the spectrum of the wave generated by the vocal cords and the transfer impedance. The characteristics of a vowel, namely, position, width, and magnitude of the formants are given primarily by the transfer impedance. This transfer impedance may be expanded in a partial fraction series. The first three terms of this series, representing the first three formants of the vowel, are realized as parallel resonant impedances. A current proportional to the vocal cord wave is passed through these impedances. A voltage having the desired vowel spectrum is now obtained as the sum of the voltages developed across the resonant circuits. The position, width, and magnitude of the three formants are independently controllable. Three formants suffice for production of realistic vowels.
Identification of Speech Sounds from Analytical Records
Authors: Wente E. C.
Published: September 2005

With the apparatus described in paper number Q4, records were made of most of the principal speech sounds in different phonetic environments as spoken by each of four persons. In this paper the discussion will center around the identification from these records of the vowels and some of the consonants. Particular difficulties in the interpretation of certain classes of sounds will be pointed out.
Thermal Relaxation in Fluorine
Authors: Shields F. Douglas
Published: September 2005

Sound absorption and velocity measurements in fluorine at 28° and 102°C indicate vibrational relaxation times of 20.7 and 10.7 μsec for these two temperatures, respectively. The measurements were made inside a glass tube 1.73 cm in diameter using progressive waves. These results when combined with earlier results in the other halogens indicate certain changes which improve the accuracy of the Slawsky, Schwartz, and Herzfeld theory.
Optimum Signal Processing of Three-Dimensional Arrays Operating on Gaussian Signals and Noise
Authors: Bryn Finn
Published: September 2005

The essential function of the optimum detector is that of applying linear mean-square regression process to the output of the array and measuring the power in the residues thus formed. The elements required for instrumentation of the detector are deduced and numerical examples relating to specific array configurations are presented. At low frequencies the directivity pattern of the optimum detector is superdirective. There is strong evidence that this directivity pattern is the one having maximum directivity index.
Sound Sources and Probes for the Measurement of Pulsed Acoustical Waves in Water
Authors: Neubauer Werner G.
Published: September 2005

Acoustical pulses of variable length and repetition rate are generated by an electronic system composed of instruments which are commercially available, except for a gate unit. The system is designed to permit acoustic transmission and reflection experiments in a controlled water medium within the confines of a laboratory-size wooden tank. Pulses of sine wave between 60 kc and 1 Mc are used. An acoustical source constructed of a barium-titanate spherical cap generates an acoustical pressure field as high as 2.1×104 μbar (86.7 db re 1 μbar at 1 m) at 230 kc at a distance of 1 m which is sensed by miniature hydrophones with lead titanate-zirconate disk elements as small as 0.063 by 0.009 in. The ceramic is enclosed by metal to overcome problems encountered previously with waterproof coatings incapable of keeping water from the ceramic for long periods of immersion. Pressure sensitivity of the probe hydrophone with preamplifier (49.6-db gain) is 10.3×10−6 v/μbar (−99.8 db re 1 v/μbar) at 230 kc.
Scanned Line Hydrophone Method of Determining Angle of Arrival of Sound in Water
Authors: Pigott M. T. , Whitmarsh D. C. , Brown J. L.
Published: September 2005

A group of hydrophone elements uniformly and closely spaced along a straight line is used to measure the angle of arrival of sound waves. By sampling the outputs of these elements rapidly and in succession, one simulates single hydrophone moving relative to the sound waves. The signal measured at the output has a frequency given by the Doppler equation f=f0(1 +α cosθ), where f0 is the frequency of the sound in the water, α is the ratio of the scanning speed to the speed of sound, and θ is the bearing angle desired. The theoretical results expected along with the experimental measurements which confirm the theory and a description of the equipment used are included.

It was found that the scanned system simulates almost exactly a single moving point hydrophone, and the Doppler equation was found to hold. Pure tones and narrow-band noise signals are shifted in frequency. The angular resolution was found to be equal to the ratio of the wavelength of the sound to the component of the hydrophone length normal to the direction of sound propagation.
Reflection and Transmission of Sound by Elastic Spherical Shells
Authors: Goodman Ralph R. , Stern Raya
Published: September 2005

The sound fields resulting from a plane wave incident on a spherical elastic shell are found. Both the internal and external fields due to the shell are considered and compared with well-known results. The Rayleigh limit is discussed, and it is found that the external field is similar to that produced by a rigid sphere but with more complicated coefficients. The internal field is of a complicated nature but reasonable to consider for numerical computation. The sound fields for a hemispherical shell mounted on a rigid medium are obtained by the image method. Numerical results for the sound intensity at the center of the hemisphere are presented for various elastic materials.
Failure to Localize the Source Distance of an Unfamiliar Sound
Authors: Coleman Paul D.
Published: September 2005

The ability of subjects to judge the distance of the source of an unfamiliar sound was studied. It was found that distance judgments on the first trial were unrelated to actual distance. With further trials valid distance judgments became possible.
Low Resonant-Frequency Barium-Titanate Transducer
Authors: Dean L. Wallace , Ball N. Addison
Published: September 2005

A transducer consisting of a barium-titanate bilaminate-strip mass loaded at the ends was found to have a resonant frequency in range 200 to 1700 cps. Comments are made on some of the electrical and mechanical parameters of this composite transducer.
Generation of Infrasound by Ocean Waves
Authors: Daniels Fred B.
Published: September 2005

A summary is given of past observations of microbaroms, atmospheric pressure oscillations that have periods near 5 sec, and it is shown how the generation of these oscillations is explained by Nanda's theory of the origin of micro eisms.
Waveform of Finite Amplitude Derived from Equations of Hydrodynamics
Authors: Heaps H. S.
Published: September 2005

It is shown that a prediction of the change of shape of a pressure pulse during its progression through a propagating medium may be deduced directly from the general equations of hydrodynamics. The distance at which a shock front forms may be determined as the radius of convergence of the solution. The effect of viscosity may be included.
Field Installation Acoustic Treatment of Air Conditioning Equipment
Authors: Becker Carl
Published: September 2005

Attainment of acceptable air conditioning noise levels results from (a) low vibration and noise output, and (b) acoustic enevironment at installation. Commercially available equipment requires extraneous acoustic treatment for 5 to 50% of domestic installations (depending on building construction) in order to eliminate annoyance. Acoustical surveys of site conditions prior to installation permit most economical application of acoustic treatment and constructions. Classification of installation features and identification of respective transmission paths facilitate prior analysis of site conditions and assessment of treatment requirements. The most important transmission paths are through (a) the foundations, (b) the air discharge and return openings and ducting, and (c) the equipment casings. Effective methods for blocking transmission along each path by means of field applied treatments are discussed.
Noise Reduction by Parallel Baffles for Random Incidence Sound Waves
Authors: Doelling Norman
Published: September 2005

The noise reduction afforded by ducts or parallel baffles depends not only on the physical properties of the duct and its lining, but also upon the angle of incidence of the sound waves impinging on the ducts. The noise reduction per duct width or per unit length provided by a duct for sound waves impinging at several angles of incidence is found to vary with the length of the duct. The variation of noise reduction per duct width decreases with increasing duct length. For sufficiently long ducts, however, the noise reduction per duct width approaches a constant value For a fairly wide range of duct lengths, the noise reduction can be expressed as a + bl, where b is the noise reduction per duct width, l is the length of the duct measured in duct widths, and a is a source distribution correction factor. Several sets of experimental data are presented to show that a may be comparable in size to bl for typical duct lengths. Several implications of a noise reduction of the form a + bl are discussed. Procedures are given for estimating the noise reduction for ducts of finite length by use of Morse's theory and the data presented here. Some unsolved problems are discussed. [Supported in part by the U. S. Air Force under Contract Nos. AF 33(616)-2151, AF 33(616)-3335, and AF 33(616)-3938.]
Transmission Loss of Some Common Partitions
Authors: Watters Bill G.
Published: September 2005

Field measurements have been made of the transmission loss of about a dozen commonly used partitions. The test conditions were exceptionally good so that the flanking problem was not serious. The test results can be summarized as follows: (1) For most of the partitions the measured transmission loss (TL) can be explained, in at least a qualitative way, in terms of the partition weight, stiffness and damping; the partition size; and the size and shape of the test rooms. (2) For most of the partitions the measured TL was appreciably less than the value one would predict if the wall stiffness is neglected. (3) For most of the partitions the measured TL was appreciably less than the values published by testing laboratories (which utilize the standard, ASTM E90-50S test method).
Acoustical Analysis of Speech
Authors: Stevens K. N.
Published: September 2005

The objectives of acoustical analyses of speech are generally to obtain economical descriptions of the important characteristics of speech sounds, together with the distributions of these characteristics. The relevant acoustical properties cannot be determined and quantified easily without reference to data on the processes of speech production and perception. An understanding of speech generation indicates the constraints that are imposed on the vocal output, whereas knowledge of the perception process suggests acoustical properties that are likely to be important for understanding speech, as well as the accuracy with which they should be specified. It is probable that relatively inaccurate measurements of several “unreliable” features are adequate to distinguish reliably a given speech sound from others of the same language, provided these features are selected properly. These remarks are illustrated by existing data on the acoustical properties of vowel and consonant sounds, and areas are noted where further data are needed. The possibilities of utilizing the high-speed digital computers in the analysis of speech are discussed.
A Real-Time Speech Input System for a Digital Computer
Authors: Forgie James W. , Hughes George W.
Published: September 2005

In order to take best advantage of the speed and flexibility of the digital computer as a research tool in speech analysis and recognition studies a real-time input system is needed. Such a system, which makes power-spectrum data directly available to the computer, has been constructed at the Lincoln Laboratory for use with the TX-0 and TX-2 computers. A speech signal is fed to 35 band-pass filters covering the range 100 to 10000 cps. The output of each filter is envelope-detected, and the envelopes are sampled periodically by a 128-position mercury commutator switch. The output of the commutator is converted to binary digital form and fed directly to the computer, At present the system is capable of making 7620 samples per second with a signal-to-noise ratio of over 40 db (7 bits). The filters, made up of high-pass and low-pass sections in cascade, can be connected to give a variety of band widths and center frequencies Patch-cord connections between envelope-detector outputs and commutator inputs permit some frequency channels to be sampled at higher rates than others when desired. Utilizing the maximum sampling rate of the input system and the full storage capacity of the computer, up to 20 sec of continuous speech may be read into the computer and held for analysis. [The research reported in this talk was supported jointly by the U. S. Army, Navy, and Air Force under contract with the Massachusetts Institute of Technology.]