bluuebunny/crossref_metadata_2025 huggingface dataset:
Soliloquy on Wire Recorder Wow
Authors: Sear Arthur W.
Published: September 2005

A practical and mathematical consideration of several sources of wow in a wire recorder drive unit. The problems of driving an elastic recording medium at a constant velocity with a spool or capstan type of drive are considered and the limitations and requirements of the drives are discussed in some detail.
The Connsonata
Authors: Kent Earle L.
Published: September 2005

A newly developed electronic musical instrument is described, and the objectives and practical problems involved in its design are discussed. A program of organ music demonstrating the capabilities of the instrument will be given by Mr. Robert G. Campbell.
Directional Patterns of a Symmetrical Distribution of Sound Sources in a Plane
Authors: Camp Leon
Published: September 2005

A method of building up a directional sound source by the distribution in a plane of piston sources is described. The theory is developed on the assumption that along a line of these sources, the amplitude changes abruptly from one piston to the next, if amplitude variation is used to control the pattern. It is shown that for patterns commonly used, only elementary mathematical processes are necessary for determining the pattern of a given source. The measured patterns of several sound sources are compared with those predicted by theory.
The Propagation of an Acoustic Wave Along a Boundary—Experimental
Authors: Rudnick I. , Laird Donald
Published: September 2005

In a paper delivered at the Spring meeting of the Acoustical Society of America and soon to be published in the Journal of this Society the acoustic field produced by a point source of sound located at the boundary of separation of two media was derived. The approximate solution indicates that when one of the media is absorbing and the other medium is air, the field at the boundary decreases more rapidly than as the inverse square of the distance. Also there is a reduced phase velocity. Experiments were performed in a 2-meter cubical dead room to check these and other predictions. The results are in considerable agreement with theory.
Instrumentation for the Measurement of Sound Pressure Level with the Western Electric 640-AA Microphone
Authors: Veneklasen Paul S.
Published: September 2005

Fundamental to Acoustical Research is the measurement of sound pressure level. The W.E. 640-AA Microphone was used at the Electro-Acoustic Laboratory not only as a reference standard for the calibration of other types of microphone, but also for routine laboratory measurements. Given the pressure calibration of the microphone certain instrumentation and complementary calibrations are needed for the convenient use of this microphone under the various conditions encountered during research work. The following aspects of this subject are discussed: (1) Considerations regarding the effect of preamplifier input impedance on the frequency response and noise threshold of a condenser microphone. (2) An a.c. operated, cathode-follower type preamplifier and associated circuits. (3) A flexible extension for use with the preamplifier. (4) The use of small probe tubes. (5) Random incidence calibration and collected free field calibrations. (6) A “supercharged” cathode follower circuit and its application as a preamplifier.
Acoustic Determination of the Physical Constants of Rubber-Like Materials
Authors: Nolle A. W.
Published: September 2005

The elastic and viscous constants of rubber-like materials may be determined, under conditions of very small strain, through measurements of acoustic phase velocity and acoustic attenuation. The attenuation in such materials is usually high, with the result that the elastic and viscous constants must be computed by means of rigorous relations involving attenuation and velocity, rather than the approximate relations which are usually employed. The necessary relations are presented for the case of longitudinal waves in thin strips. An experimental method is described which has been used to measure acoustic phase velocity and attenuation in thin narrow strips in the frequency range from one to 26 kilocycles. One end of the sample strip is driven by a vibration generator. The phase and amplitude of the signal received by a moving detector are plotted automatically as a function of distance along the strip. On a particular sample the r.m.s. error in a series of measurements of velocity and attenuation ranged from 2 to 9 percent and 6 to 12 percent, respectively, over the frequency range. Sample acoustic data and the computed elastic and viscous coefficients are given for a carbon-black buna-N cement.
Identification of Musical Instruments When Heard Directly and Over a Public Address System
Authors: Eagleson Halson V. , Eagleson Oran W.
Published: September 2005

The problem in this study was to determine and compare the success of two groups of musicians and a group of non-musicians in their efforts to identify nine different musical instruments by tone quality alone when each instrument was heard directly and indirectly over a public-address system. An effort was made to use instruments that were representative of the strings, brass, wood-winds, reeds, and percussion groups. In order to make tone quality the principal factor in identification, an effort was made to use a tone whose frequency was as nearly common to all of the instruments as was possible. The tone agreed upon was middle C or its octave. The instruments were presented in a definite order with rest periods between each presentation. The data show that some of the instruments were recognized with greater ease and more certainty than others. In general, the percent of correct identifications was lower for each of the three groups when the tones were heard over a public address system than when heard directly. Statistical examination of the reliability of the difference between the means for each of the three groups, however, revealed that only the difference found for the members of the first group of musicians was large enough to meet Fisher's test for significance at the five percent level.
Mechano-Electronic Transducer
Authors: Olson Harry F.
Published: September 2005

A mechano-electronic transducer is a system in which a voltage is developed by the motion of one or more of the elements in a diode, triode or other multielement electron tube. The electronic transducer possesses the following fundamental advantages; the vibrating element in the electronic transducer can be made very small with a resultant low mechanical impedance, the electrical power is not derived from the actuating system, therefore, the reaction into the actuating system is negligible, and there are innumerable possibilities in mixing, etc., in complex transducers. An electronic transducer has been developed which is suitable for the generating element in microphones, phonograph pick-ups, vibration pick-ups, etc. Phonograph pick-ups have been developed employing electronic transducers. The advantages are, high output, relatively low electrical resistive impedance, low acoustical noise, light stylus pressure with resultant low record wear, and stability under temperature and humidity changes. Microphones have been developed using the electronic transducer in which the output is comparable to carbon microphones.
Observation of Cochlear Structures During the Process of Hearing
Authors: Kobrak H. G.
Published: September 2005

The chief objection against the Helmholtz theory of hearing or against any hearing theory is that they are theories. It is the task of investigative work in physiological acoustics to make direct observations of the ear during the process of hearing and to replace theoretical deductions by experimental evidence. Two approaches are discussed in this paper. (1) Direct observation of the acoustic vibrations in the ear. (2) Experimental determination of the physical characteristics of the anatomical structures in the middle and inner ear. This paper is confined to the application of these two methods to the cochlear windows. Anatomical specimens of the oval and round window are demonstrated (lantern slides) and the acoustic vibrations during the process of sound conduction shown (motion picture film). The basilar membrane as observed through the round window membrane (round window membrane made transparent by special method) is demonstrated. The movement of the fluid in the cochlea is shown in motion picture recordings. The phase difference between stapes and round window membrane is demonstrated under stroboscopic illumination. Methods for estimating the elastic properties of the round window membrane are discussed.
A Cavity-Pressure Method for Measuring the Gain of Hearing Aids
Authors: Corliss E. L. R. , Cook G. S.
Published: September 2005

A cavity-pressure method for measuring the gain of hearing aids has been developed. It has the advantage of requiring no dead room, allowing a compact set-up. The method has been investigated as to its validity and the degree to which diffraction effects are avoided. Comparisons with free-field data are made. The applicability of results obtained by this method to the specification of gain characteristics for hearing aids will be discussed.
Long-range low-frequency CW propagation in the deep ocean: Antigua-Newfoundland
Authors: Guthrie A. N. , Fitzgerald R. M. , Nutile D. A. , Shaffer J. D.
Published: October 2005

The acoustic fields of shallow sources operating at 13.89 and 111.1 Hz were measured on a deep sound-channel hydrophone located near Antigua, W. I. The sources were towed away from the receiver along a great circle track to a maximum range of 2800 km. Convergence zones were observed at long range, and their positions were found to be frequency dependent. The average rate of increase of transmission loss with increasing range was less than that for cylindrical spreading. The propagation characteristics are explained in terms of the measured oceanographic features.
Pinna reflections as cues for localization
Authors: Wright Donald , Hebrank John H. , Wilson Blake
Published: October 2005

For monaural localization, the time delay between direct and pinna-reflected sound is the dominant feature of sound entering the external ear canal. Experiments measuring the human threshold of delay-time detection and the just noticeable difference of delay time were conducted employing white noise summed with a delay of itself. Threshold results show that delay times of 20 μsec are easily recognizable when the amplitude ratio of the delayed signal to the leading signal is greater than 0.67. Just noticeable difference results agree with measurements of the minimum audible angle for monaural localization. Results further demonstrate correspondence between human detection of a delay-summing process and an equivalent spectral filter.
Ray trace acoustics in unsteady inhomogeneous flow
Authors: Engelke Ray
Published: October 2005

The differential equations governing acoustic ray trajectories for space- and time-dependent flow are derived. The derivation requires only a generalized Huygens's principle and geometrical constraints. The Huygens's principle states that a ray's velocity is the vector sum of the sound speed along the wave normal and the particle velocity vector. It is found that the ray differential equations for unsteady flow have the same general form as those for steady flow. Earlier work is briefly reviewed.
Influence of rotation on the Kelvin-Helmholtz instability
Authors: Gedzelman Stanley D.
Published: October 2005

A two-layer fluid which is inviscid and which has no conduction is considered. Once rotation is included in the perturbation equations, cubic equation for the square of the wave speeds of two-dimensional waves results. Two of the roots can be closely approximated in rather simple analytic form. These roots are generally more unstable than the nonrotating waves. The root which is not degenerate as rotation approaches zero owes its greater instability under the presence of rotation to the fact that the fluid interface is tilted with respect to the gravity vector and the stabilizing role of the stratification is thereby reduced.
Ultrasonic Solid Delay Lines
Authors: Arenberg David L.
Published: September 2005

The development of an ultrasonic delay line for the storage of pulses 1 microsecond long for periods up to 2000 microseconds is discussed. Theoretical considerations of the piezoelectric transducer involving the quartz crystals and acoustical constants of the medium developed by Emslie, Huntington, and Benfield, are applied to determine the band width and power loss of the delay line. Problems, peculiar to the use of solids because of the presence of more than one mode of propagation and the distribution of energy between the different modes on reflection from an air surface, are evaluated for a wide range of Poisson ratios. Measurements of velocity and attenuation in some polycrystalline metals, single crystals, and glasses are given. Fused quartz was found to be the most promising material.

Delay lines constructed using a light source and photo-elastic pick-up were not completely developed, but several types using crystal pick-up as well as transmitter were satisfactory. For delay times longer than 300 microseconds, multiple reflection paths in two and three dimensions were used and their preparation from fused quartz discussed.
Simplified Porosity Measurements
Authors: Leonard R. W.
Published: September 2005

With the increasing importance of acoustical impedance and its relation to flow resistance and porosity in homogeneous porous materials, a simplification in the technique of porosity measurement seems in order. It is the purpose of this paper to describe a dynamic method of measuring porosity. The essential feature of the dynamic method is the use of the compliance of the air in the pores of the material to control the period of the free damped oscillation of a mechanical system. The dynamic method has the advantage of small temperature dependence and minimal time for a single measurement.
Monaural and Binaural Threshold Sensitivity for Tones and for White Noise
Authors: Pollack Irwin
Published: September 2005

Monaural and binaural thresholds of ten listeners were determined for a 1000-cycle tone and for a white noise. For each of the observers, the binaural threshold was found to be significantly lower than the monaural threshold when the two ears were “equated” in sensitivity, i.e. when the difference in sensitivity between the ears of a given observer was effectively canceled by experimental procedures. Furthermore, the difference between the monaural and binaural thresholds was found to be significantly greater for the pure tone than the corresponding difference for the noise.

Monaural and binaural thresholds were also determined with the two ears “equated” in sensitivity and with the two ears “mismatched” in sensitivity by fixed ratios. It was found that the difference between the binaural threshold and the threshold of the better ear decreased as the difference in the effective stimulation at the two ears was increased. The difference between the binaural threshold and the threshold of the better ear was found to be not statistically significant when the two ears were stimulated at sensation levels more than 6 db apart.

The results of the present study fail to confirm the hypothesis that the auditory threshold is constant and equal to the sum of the effective acoustic powers at the two ears. For most of the observers, the difference between the monaural and binaural thresholds was found to be significantly less than would be predicted by this hypothesis.
Some Biological Effects of Intense High Frequency Airborne Sound
Authors: Allen C. H. , Frings H. , Rudnick I.
Published: September 2005

Some experiments have been conducted to determine the effect of intense high frequency airborne sound on mice and a variety of insects. The sound source was a high frequency siren. The frequency used was about 20 kc and its acoustic level, in the region where the subjects were placed, was between 160 and 165 db (relative to 10−16 watts/cm2). With sufficient exposure—from 10 seconds for flies and mosquitoes to 3 or 4 minutes for roaches and caterpillars—the sound proved lethal in all cases. More detailed work was performed on mice and the roach, Periplaneta americana. In both cases it was definitely established that the heating produced by sound absorption was sufficient to cause death. In addition to the heating there are other effects, notably tissue rupture, as evidenced by the almost complete destruction of the wings on flies and mosquitoes and the rapid deterioration and final disappearance of the external pinna of a mouse which had received a sub-lethal dose. During observations it has been impossible to completely avoid personal exposure to the sound field and some of the effects observed under these conditions will be described. These include momentary dizziness, and heating of exposed parts of the hand.
Absorption and Scattering for Impedance Boundary Conditions on Spheres and Circular Cylinders
Authors: Lax M. , Feshbach H.
Published: September 2005

The phase shift analysis is applied to the absorption and scattering of plane waves by spherical and circular cylinder regions. The boundary condition on the surface of these regions is expressed in terms of an impedance. A method of calculating the required phase shifts and corresponding scattering and absorption cross sections is presented together with the necessary tables. It is found that when the reactive part of the impedance is capacitative, resonance phenomena can occur. Approximate cross sections for low and high frequencies are given. It is shown that at low frequencies, acoustic treatment of scattering surfaces will, in general, increase the scattering and, therefore, their ability to increase the diffusion of sound in a room.
Construction Material of the Sound Conduction System of the Human Ear
Authors: Kobrak H. G.
Published: September 2005

The behavior of the living elastic bodies in the ear must be studied for a full understanding of the ear as sound conductor. Two elementary structural elements possessing restoring forces are the collagen fiber and the elastic fiber. These two tissue elements form membranes, ligaments, tendons, and articulations in the ear.

The physical behavior of these two fiber systems is described. Three areas in the ear are distinguished according to their construction material. Methods of measuring the physical characteristics of the ear structures are described. The linear displacement of the center of the ear drum as a function of static pressure changes in the outer ear canal is given. Static movements of the stapes footplate due to reflectoric muscle contractions were used to calculate the elongation of the stapes ringband in vivo.
A Cavity Pressure Method for Measuring the Gain of Hearing Aids
Authors: Corliss Edith L. R. , Cook G. S.
Published: September 2005

A cavity pressure method for measuring the gain of hearing aids has been developed. It has the advantage of requiring no dead room, allowing a compact set-up. The method has been investigated as to its validity and the degree to which diffraction effects are avoided. Comparisons with free field data are made. The applicability of results obtained by this method to the specification of gain characteristics for hearing aids is discussed.
A Sheet of Air Bubbles as an Acoustic Screen for Underwater Noise
Authors: Loye Donald P. , Arndt Wm. Fred
Published: September 2005

In Pearl Harbor, where there often were eight hundred ships of all kinds, the underwater noise level was high. No place was found where noise measurements could be made satisfactorily, and therefore it was decided that the best arrangement would be to insulate Auxiliary Repair Docks, and measure the noise of submarines while they were in the docks. This was done by the development of a suitable air bubble screen across the open end of the dock. Such an acoustic barrier was comparatively easy to install, did not interfere with submarines entering and leaving, kept ocean surface oil out of the dock, insulated against low as well as high frequency noises as was required, and, after extensive experimentation, the noise of the screen was reduced to a level that did not interfere with the noise measurements. The insulation of the screen upon the noise of a nearby submarine charging batteries is illustrated by a phonograph recording.
Acoustic Treatment of Liquids in Thin Laminae
Authors: Horsley Caperton B. , Jones R. Clark , Smith Alan A.
Published: September 2005

Very large amplitudes of the velocity and acceleration produced by a sound wave in water may be evoked by exposing thin laminae of the liquid to an airborne sound wave. In the case of water and air at atmospheric pressure and at a frequency of 10,000 c.p.s., the power advantage is shown to be a factor of about 3600 when the thickness of the lamina is small compared with 14 microns. On the other hand, the use of liquid laminae is ineffective when the effects desired depend on the pressure amplitude of the sound wave, as distinct from the velocity or acceleration. Sketches of an experimental arrangement are shown.
Compressional Wave Front Propagation through a Simple Vortex
Authors: Lindsay R. B.
Published: September 2005

The equations of propagation of a compressional wave through a moving medium are developed in vector notation. Application is made to the special case of a linear vortex of constant strength m in which the motion is irrotational. Differential equations are set up in general form for the wave fronts and rays. A simple approximation is derived for the distortion produced in an originally plane wave front by transmission through the vortex. The results are in general agreement with observed fluctuation phenomena in acoustic propagation in air.
Acoustic Impedance from Motional Impedance Diagrams
Authors: Fay R. D. , White J. E.
Published: September 2005

When an acoustic load is coupled to an electromagnetic transducer through a length of air column, there is a critical length at which an increment in acoustic load produces a maximum increment in electrical impedance. The method described makes use of this critical coupling to obtain an optimum precision in determining an acoustical impedance. It is noteworthy that the value of the characteristic impedance of the air column is not assumed but is directly measured.
The Comparative Performance of an Experimental Hearing Aid and Two Commercial Instruments
Authors: Hudgins C. V. , Marquis R. J. , Nichols R. H. , Peterson G. E. , Ross D. A.
Published: September 2005

An experimental hearing aid, two representative commercial models, and a high fidelity audio-amplification system were explored in a series of systematic articulation tests with hard-of-hearing subjects as listeners. The experimental hearing aid was designed to determine to what extent certain desirable design objectives could be incorporated in a portable hearing aid. A technical description of the experimental instrument is given in an appendix. The paper describes the experimental methods and testing equipment employed and summarizes the results in the form of articulation curves obtained from six hard-of-hearing listeners. The method adequately brings out performance differences in the four instruments and shows the superiority of the experimental hearing aid over the commercial instruments for most subjects.
Secondary Pressure Pulses Due to Gas Globe Oscillation in Underwater Explosions. II. Selection of Adiabatic Parameters in the Theory of Oscillation
Authors: Arons A. B.
Published: September 2005

A summary is given of the theory of pulsation of a stationary gas globe in an infinite incompressible fluid. If three parameters appearing in the formulation are selected by fitting the equations to three independent experimental results, it is shown that the theory fits the remaining experimental results and can be used to predict bubble pulse properties over wide ranges of the independent variables.
A Hydrophone Suspension System
Authors: Garland David C. , Tindal Charles H.
Published: September 2005

A description of apparatus for suspending two transducers in a tank of water is given. The design is such that the positions and orientations of the transducers may be easily adjusted for a variety of arrangements.
Characteristics of Stepped-Frequency Transducer Elements
Authors: Bundy F. P.
Published: September 2005

A common method of making transducers with broad frequency responses is to use ensembles of resonant subelements of slightly different frequencies. The theory, design, construction, and tests of a transducer of this type are presented in this paper. Six subelements of three different natural frequencies about 6 percent apart were used. The subelements consisted of magnetostrictive laminated nickel stacks, which were mechanically isolated from each other but linked by a common electrical winding. The relationships between the amplitude and phase responses of the unit as functions of frequency were determined experimentally and compared with the theory. The efficiency of transformation of energy was determined for the frequencies of maximum response. All the characteristics of the stepped-frequency transducer are compared to those of a less resonant, single-frequency transducer of comparable breadth of frequency response. It is found that the stepped-frequency transducer can be no more efficient than its single-frequency equivalent, and that its amplitude and phase response characteristics average about the same as the single-frequency equivalent but are more irregular. In the stepped-frequency transducer there are two frequency intervals in which the phase may remain stationary or actually decrease with an increase in frequency, but these intervals occur at the amplitude response minima. It is concluded that in practical transducer design slightly resonant single-frequency elements are superior to those made of ensembles of more resonant subelements of several different frequencies.
Reflection of Sound from Coastal Sea Bottoms
Authors: Liebermann L. N.
Published: September 2005

An experimental method has been developed for measuring the reflection coefficient of the ocean bottom for supersonic sound at grazing incidence. In this method the geometry is controlled so that the resultant of the direct and reflected rays passes through consecutive maxima and minima at the hydrophone. The amplitude reflection coefficient is given by the expression (M − m)/(M + m), where M is the amplitude of a maximum and m is the amplitude of the following minimum. Using this method, with a grazing angle of nine degrees, the following values were obtained for the reflection coefficients at 17 stations near Woods Hole: mud—0 to 0.20, mud-sand—0.20 to 0.40, sand-mud—0.40 to 0.60, sand—0.40 to 0.85, stony—0.50 to 0.85. It is observed that the reflection coefficient depends not only on the median size of the particles making up the bottom, but also on the sorting of the particles and on the bottom topography.
Acoustical Methods in Supersonic Aerodynamics
Authors: Miles John W.
Published: September 2005

The paper illustrates certain techniques common to acoustics and supersonic aerodynamics. The basic equations describing hydrodynamical phenomena taking place in a supersonic, inviscid stream are developed. After linearization, the equations are solved for the velocity potential resulting from an arbitrary source distribution in the plane z − 0. The integration of the results for two-dimensional flow is carried out, and the application to various aerodynamic problems is cited. As a second illustration, an analogy, attributable to von Kármán, between two-dimensional flow caused by a distribution of acoustic oscillators along a line having arbitrary time histories and the steady three-dimensional flow about a thin wing is described. Using the techniques of Fourier integrals, this analogy is used to compute the wave drag caused by a symmetrical wing at zero lift.
Elastic Impact of Pianoforte Hammer
Authors: Ghosh R. N.
Published: September 2005

This paper discusses the dynamical theory of the impact of a felt hammer upon a string at a distance α from one fixed end such that the reflected wave from the other distant fixed end does not reach the striking point during the time the hammer is in contact with the string. The Heaviside operational method leads to a solution in the form of a series consisting of incommensurable terms with damping coefficients increasing with the order of the term and tending to a limiting value. In the case of a hard hammer the damping coefficients decrease, and the terms are very much less incommensurable. These are the essential differences between the two cases that lead to smoothening down of the pressure and time curve between the hammer and the string in the case of a felt hammer.
The Directional Characteristics of a Clamped-Edge Disk
Authors: Merrill Lynn L. , Slaymaker Frank H.
Published: September 2005

It is well known that to obtain very small side lobe radiation the amplitude distribution across a radiating surface should be such that the maximum amplitude is at the center and the minimum at the edges. The Gaussian distribution gives no side lobes, but requires an infinitely large radiator. This paper gives the analysis of the clamped-edge disk, vibrating in its first normal mode. It shows that the dynamic curve approximates the Gaussian form and that the sound pressure distribution has very small side lobes, the amplitude of the first side lobe being 33 decibels below that of the axial lobe.

For a disk of a given diameter the width eft the axial lobe may be decreased by raising the frequency of the first normal mode, which requires a corresponding increase in the disk thickness. At very high frequencies the disk thickness may become prohibitive. In such cases a thin disk can be forced to vibrate in the shape of the first normal mode by a proper radial distribution of the driving force.
The Diffraction of Sound by Circular Disks and Apertures
Authors: Spence R. D.
Published: September 2005

A rigorous theory of the diffraction of plane sound waves by circular disks and apertures is developed by use of oblate spheroidal coordinates. Numerical results for the cross section for scattering and transmission are given in graphical form.
Calculation of the Directivity Index for Various Types of Radiators
Authors: Molloy C. T.
Published: September 2005

This paper gives the derivations of the “directivity index” formulas for several types of sound radiators. The “directivity index” is defined as “the ratio of the total acoustic power output of the radiator to the acoustic power output of a point source producing the same pressure at the same point on the axis.” The utility of the directivity index concept is that it permits power calculations to be made for all radiators in the same manner as for point sources. Directivity index formulas, together with graphs covering practical cases, are given for the following types of radiators:

1. General plane piston in infinite baffle,

2. Circular plane pistion in infinite baffle,

3. Rectangular plane piston in infinite baffle,

4. Sectoral horn,

5. Multicellular horn,

6. Piston set in sphere.
Thickness-Shear Vibrations of Thin Anisotropic Plates
Authors: Hok Gunnar
Published: September 2005

The vibrational boundary conditions of a free, thin, rectangular, plane-parallel plate can be satisfied by the sum of an infinite series of plane wave components. When the ratios of the thickness to the length and width of the plate are small, this series converges rapidly enough to give a fair approximation with a reasonable number of terms.

Frequency spectra as well as standing-wave configurations are calculated approximately for AT and BT cut quartz plates. Some observed data are given for comparison.
On Ultrasonic Propagation through Mercury in Tubes
Authors: Huntington H. B.
Published: September 2005

Some measurements have been made of the attenuation of ultrasonic waves in mercury as a function of tube diameter and the inner surface of the tube. A pulse technique was employed and attenuation was measured at 10.6 Mc/sec. by comparing successive echoes of the initial pulse. The results with smooth glass tubes are in qualitative (although not quantitative) agreement with the predictions of the Helmholtz theory for tubes large compared with the wave-length.
Acoustic Impedance Measurement of Very Porous Screen
Authors: Harris Cyril M.
Published: September 2005

A new procedure is presented for the measurement of the normal specific acoustic impedance of extremely porous screen as a function of frequency. The method, restricted to this case, is based on a special application of the Transmission-Characteristic Method of impedance measurement and can be applied to screens having impedances even less than 1/100 the characteristic impedance of air. Relatively simple experimental equipment and computation is required. Measured values of the impedance for two samples of extremely porous screen, determined by this procedure, are given.
Sound Pressure Measurement Equipment for the Range 50 Cycles to 250 kc
Authors: Massa Frank
Published: September 2005

This paper describes a newly developed acoustic instrument that is now commercially available for making absolute sound pressure measurements over the frequency range 50 cycles to 250 kc. The microphone standard is only 18″ diameter, and is therefore completely free of diffraction errors throughout the entire audible spectrum to beyond 20 kc. In order to maintain constant phase shift between the generated voltage and the actuating pressure, the vibrating system is stiffness-controlled to beyond 250 kc, thus insuring accurate reproduction of pressure wave transients having extremely steep wave fronts. The tiny size of the microphone and its very high acoustic impedance will permit free field measurements throughout the entire audible range without diffraction errors, as well as making easily possible many special acoustic measurements extending well into the ultrasonic region, heretofore very difficult to make. A preamplifier and power supply unit makes the equipment readily portable.
Reverberation in the Sea
Authors: Eyring Carl F. , Christensen Ralph J. , Raitt Russell W.
Published: September 2005

The apparatus used to measure ocean reverberation at 24 kc consists essentially of a sound projector which sends a signal of adjustable duration into the water; a hydrophone which translates the backward scattered sound into electrical voltage; an amplifier which increases this voltage; a cathode-ray oscillograph which converts voltage fluctuations into spot movements; and finally a camera which records the movements on a moving film. Simple reverberation theory indicates (i) that reverberation level increases 10 db with a tenfold increase of pulse length; (ii) that volume reverberation level decreases 20 db for a tenfold increase in range; and (iii) that surface reverberation level decreases 30 db for a tenfold increase in range. At certain times and under certain conditions, presumably when ocean conditions are those postulated by theory, observed reverberation levels agree with theoretical values. Such agreement, however, is relatively uncommon. Under most conditions, deep scattering layers cause volume reverberation levels to depart markedly from simple theory; also, a combination of refraction, wind, and other factors causes a decrease in surface reverberation level with range which is too rapid to be in agreement with simple theory. When a sound beam is projected horizontally in deep water, both surface and volume reverberation might be expected. Under a rough sea and for ranges less than 500 yards, surface reverberation predominates over volume reverberation. Beyond 1000 yards, even under a rough sea, volume reverberation usually overshadows surface reverberation. Also, for such long ranges, attenuation enters as an important factor and causes the reverberation level to fall off more rapidly than the rate predicted by simple scattering. In shallow water, bottom reverberation (which depends for its intensity on whether the bottom is rock, sand, mud and sand, or mud) is the dominant part of the observed reverberation.
Absorbing Media for Underwater Sound Measuring Tanks and Baffles
Authors: Mason W. P. , Hibbard F. H.
Published: September 2005

By using absorbing walls surrounding a small body of water, measuring tanks have been produced which will determine the directional properties of underwater sound instruments down to a level of 25 db below the direct beam. These absorbing media are constructed by inserting fine mesh screen or packed copper wadding in a viscous liquid such as castor oil. These obstructions result in an enhanced viscous action which is nearly independent of the frequency above 10 kilocycles. A six-inch wall can reduce the reflections by 20 db. Tanks using such absorbing media were used for testing transducers at the manufacturing plant and were used for determining the approximate characteristics of small sized instruments. Absorbing media were also used in the sound transparent dome housing the transducer and in the back of the QJB transducers.
The Time Integral Basic to Optimum Reverberation Time
Authors: Maxfield J. P.
Published: September 2005

Equations showing the relation between the volume, V, of an auditorium and its optimum reverberation time, T0, were published independently by MacNair and Lifschitz. MacNair's equation was derived from the following basic assumptions: ∫ 0T1 (logρ)dt = a const., E = const., where ρ=instantaneous value of the energy density of sound during decay,T1=time of decay to minimum audibility,E=rate of supply of energy during the steady state condition.

This paper shows that an equation, relating T0 and V, can be deduced which more nearly fits all the empirical facts by basing the derivation on the following assumptions: ∫ 0T1 ρ ⋅ dt = a const., E = GVn, where G=a constant,n=a constant which should be less than unity.

The resulting equation for n = 23 is T0 = 0.212 V1/6. This is in agreement with the empirical data and with the equation derived by Maxfield and Albersheim from acoustic “liveness” considerations.

The psychologists and physiologists studying the mechanism of hearing should be interested in these results, as they have a bearing on the manner in which the ear integrates the sound being perceived.
Reflection of Underwater Sound from the Sea Surface
Authors: Liebermann L. N.
Published: September 2005

Information on the instantaneous sea surface reflectivity for 30-kc sound has been obtained. The method required that the submerged source and receiver be rigidly mounted on towers resting on the sea bottom. Transmission of a frequency-modulated sound pulse results in an interference pattern at the receiver; interference occurs between the direct and reflected sound. Analysis of these interference patterns reveals the following: The average time of persistence of the pattern is five-hundredths of a second. Under the conditions of the experiment, surface reflectivity is highly frequency dependent. The median value for the reflection coefficient is near to unity. Approximately 10 percent of the time the sea surface focuses the sound, giving a a reflection coefficient greater than unity.
The Representation of Vowels and Their Movements
Authors: Potter Ralph K. , Peterson Gordon E.
Published: September 2005

It is shown that movement of the major resonances in the voiced sounds of speech may be represented by traces in a three-dimensional graph. Apparently a great deal can be learned about speech through investigation of such traces, and they suggest a new method for vowel designation that is particularly adaptable to quantitative analysis.
The Influence of Interaural Phase on Interaural Summation and Inhibition
Authors: Hirsh Ira J.
Published: September 2005

The difference between the binaural and monaural thresholds varies within fairly large limits. Although this binaural-monaural difference does not vary as a function of frequency when pure-tone thresholds are measured in the quiet, the difference does vary with frequency when pure tones are presented against a background of noise. Binaural summation, a term which has been used in the past to refer to the phenomenon in which the binaural threshold is lower than the monaural, obtains for masked thresholds only when the phase angles between the the two earphones are opposite for the tones and the noise. If the tones and the noise have the same interaural phase angle the binaural threshold is higher than the monaural. This phenomenon, called interaural inhibition, as well as its antipode, interaural summation, is most marked at low frequencies and increases as the intensity of the masking noise is increased. The discussion considers some implications of these findings for the theory of masking and of interaural summation.
Melodic Scales
Authors: Vermeulen R.
Published: September 2005

An attempt is made to give a derivation of musical scales on melodic rather than harmonic principles. Starting from the hypothesis that the scale shall contain, at most, two different intervals and shall contain a perfect fifth, all possible scales have been investigated. Only a few satisfy some rather obvious conditions. With three exceptions these can be recognized as existing scales. The intervals of the customary scale prove to be those of Pythagoras. It is pointed out that the differences between this scale and the equally tempered one are only slight while the latter one lies in between the Pythagorean and the just scales.
Ultrasonic Absorption in Water in the Temperature Range 0°–80°C
Authors: Smith Myron C. , Beyer Robert T.
Published: September 2005

Absorption of ultrasonic waves in water has been measured at temperatures from 0°C to 80°C at six frequencies between 12.25 megacycles and 40.50 megacycles. The experimental values are shown to agree within experimental error with the theoretical values calculated by L. H. Hall on the basis of a structural absorption.
Lamination Designs for Magnetostrictive Underwater Electroacoustic Transducers
Authors: Camp Leon
Published: September 2005

A theory is presented for the design of laminations to be used in the construction of transducers having a plane piston-like radiating face. Data is given to show how well the theory predicts the operating characteristics of these transducers.
Reflection of Sound From Submerged Plates
Authors: Finney W. J.
Published: September 2005

It has been found that an appreciable reflection occurs in the direction of the incident wave when high frequency underwater sound strikes a submerged steel plate at an oblique angle of incidence. The magnitude of this “non-specular” reflection, together with the associated transverse vibrations in the plate, has been studied experimentally as a function of frequency, plate dimensions and angle of incidence. Significant non-specular reflection occurs from bounded plates between about one-quarter inch and two inches thick, when the product of thickness in inches and frequency in kilocycles per second lies between about 20 and 60 in.-kc. Within this range, the angle of incidence for maximum non-specular reflection, η is described by the empirical relation: sinη = 2.16/(bf)13. This relation has been found to apply also to 0.002 inch plates at 15 megacycles.

The results of the present study are in agreement with a theoretical analysis by Fay, and with the experimental results obtained by Sanders at frequencies of several megacycles.
Electromechanical Feedback
Authors: de Boer Jan , Schenkel Gerrit
Published: September 2005

Obtaining a suitable mechanical resistance usually presents considerable difficulties when constructing electromechanical apparatus, such as microphones and loudspeakers. This article describes how a mechanical resistance—or, in general, a mechanical impedance—can be achieved in an electrical way. Special artifices such as compensation coils or bridge connection, which are required to overcome secondary difficulties, are illustrated by some practical applications.
The Coupling of a Cylindrical Tube to a Half-Infinite Space
Authors: Miles John W.
Published: September 2005

The radiation admittance of a semi-infinite space, as seen by a cylindrical tube through an aperture in an infinite plane, is computed. The pressure fields in the tube and half space are developed in terms of the axial velocity in the aperture, and an integral equation for this velocity is determined. It is shown that the velocity function which satisfies this integral equation makes the real and imaginary parts of the radiation admittance absolute minima. An asymptotic expression for the field at a distance from the aperture is developed, and reflection and transmission coefficients are determined in terms of the radiation admittance.

The general theory is applied to a circular tube and an infinite slot. Numerical results are given in the form of curves, and the results for the circular tube are compared with those obtained by Rayleigh.
On the Radiation of Sound into a Circular Tube, with an Application to Resonators
Authors: Ingård Uno
Published: September 2005

The radiation from a plane piston into a rigid circular tube is treated. Consideration is given to the propagation of higher order sound waves. Curves of radiation impedance and pressure distribution are given together with an analysis of the elements of the equivalent impedance circuits. In addition to the closer study for special values of the tube's end impedance, some outline of the general case is given. Simplified measurements verify the calculations in the case of a tube closed by a rigid wall. Finally, the resonance frequency of cylindrical resonators is discussed.
Radiation from a Diaphragm Struck Periodically by a Light Mass
Authors: Strasberg Murray
Published: September 2005

Expressions are obtained for the energy radiated by a clamped circular diaphragm excited by periodic impacts. The radiation consists of a line spectrum with intensity maxima in the neighborhood of the resonant frequencies of the various vibrational modes of the diaphragm. The energy in the spectrum lies almost entirely below a frequency equal to twice the reciprocal of the time of contact of the hammer with the diaphragm at each impact.

Expressions for the efficiency of the system as a converter of mechanicai energy into acoustical energy are derived, and the conditions resulting in maximum efficiency are determined. Curves are presented to assist the calculation for the case of a steel diaphragm in water.
The Massachusetts Hearing Test
Authors: Johnston P. W.
Published: September 2005

A combination speech-pure tone group test technique is described in which standard phonograph speech audiometer equipment is readily converted for dual test use through the addition of a commercial discrete frequency audiometer and an inexpensive coupling unit. The group pure tone section of the test is rapidly scored. The group pure tone section of the test is shown to possess a marked superiority over the phonograph record test in terms of correlation with individual pure tone test criteria.
Chroma Fixation at the Ends of the Musical Frequency Scale
Authors: Bachem A.
Published: September 2005

It is observed that tone chroma reaches a definite limit near the upper (and perhaps lower) end of the musical range, while tone height still increases (or decreases) perceptibly.