bluuebunny/crossref_metadata_2025 huggingface dataset:
Auditory Acuity in Severe Aero-Otitis Media
Authors: Harris J. Donald
Published: September 2005

From personnel subjected to the Submarine Escape Training Tank at New London, a group was selected at random consisting of 90 men who were judged to have aero-otitis media of the severest, or No. 4, grade according to Dr. Teed's categories of otopathologic change. A brief description of the No. 4 category is given. Post-pressure audiograms at octaves 256 through 8,192 were compared with pre-pressure audiograms taken under almost identical conditions. Although a few cases exhibit a disabling loss, the mean drop for the whole group is surprisingly slight. It should be borne in mind that none of the cases reported here had been subjected to pressure more than once. Acuity seems not to drop markedly with perforation of the drumskin, bleeding from the drumskin or external meatus, or separation of the layers of the drumskin. It seems to be associated less with otopathology as such than with the extent to which the bulla is filled with blood. Thus the sharp drops in acuity which do occur may perhaps, at least in their early stages, be referred in large part to damping of the ossicles.
The Sound Spectrograph
Authors: Koenig W. , Dunn H. K. , Lacy L. Y.
Published: September 2005

The sound spectrograph is a wave analyzer which produces a permanent visual record showing the distribution of energy in both frequency and time. This paper describes the operation of this device and shows the mechanical arrangements and the electrical circuits in a particular model. Some of the problems encountered in this type of analysis are discussed, particularly those arising from the necessity for handling and portraying a wide range of component levels in a complex wave such as speech. Spectrograms are shown for a wide variety of sounds, including voice sounds, animal and bird sounds, music, frequency modulations, and miscellaneous familiar sounds.
Translators with External Phosphors
Authors: Dudley Homer , Gruenz Otto O.
Published: September 2005

Two translators are described which display instantaneously on a moving external phosphor the essential characteristics of sound waves, such as speech. There is thus presented to the eye a parade of speech patterns as though a printed line were passing by. The pattern of intensity vs. frequency vs. time remains in view long enough to permit the eye to observe pattern groups as an aid to speech interpretation. Typical applications are portraying the phonetics of speech and aiding the deaf to understand speech and to build up their own speech. The goal in the speech pattern portrayal is to show the stronger speech components simply but accurately as a function of frequency and time. The speech is equalized to bring out the stronger components over the frequency range. Next automatic volume control is applied to iron out level differences on a time basis. Then the 3500 cycle speech band is analyzed by twelve filters of about 300 cycles each and the resultant component powers applied to the excitation of a phosphor. The smaller translator employs twelve incandescent grain-of-wheat lamps for phosphor excitation, generating a pattern 1″ high and 5″ long and the larger translator sets up a pattern 7″ high and 47″ long. The patterns remain in the field of view for about two seconds.
The Portrayal of Visible Speech
Authors: Steinberg J. C. , French N. R.
Published: September 2005

This paper is concerned with the portrayal of speech in the form of visible patterns that one might learn to read as readily as one learns to understand spoken speech. The portrayal is to be accomplished automatically from the sound waves without a serious time lag between spoken word and visible patterns. In principle, the method attempts to perform a frequency-intensity-time analysis of the sound somewhat analogous to that performed by the ear, and to present the results in an orderly manner to the eye. The problem of obtaining legible patterns is one of choosing suitable frequency and time intervals in which to measure the intensity and suitable frequency, intensity, and time scales for the visual portrayal. The choice involves the characteristics of both the eye and the voice. The paper discusses objectives and requirements based on these characteristics, describes the patterns in current use and explores the possibilities and implications of certain modifications that might be made in the present portrayal.
The Propagation of an Acoustic Wave Along an Absorbing Boundary
Authors: Rudnick Isadore
Published: September 2005

The sound field of a point source near a plane boundary (complex impedance) cannot be obtained by an acoustic ray approach. In fact such an approach, which utilizes the reflection coefficient for plane waves leads often to completely contradictory results. The procedure which must be followed is exactly similar to that initiated by Sommerfeld to derive the electromagnetic field of a vertical dipole situated near a conducting plane. The results of such an analysis as applied to an acoustic point source are presented. The solution forms the basis for the explanation of hitherto anomalous results. For convenience further discussion will be restricted to cases in which the sound source is at the boundary although the solution is given for all source heights. The solution shows that when the bounding medium has a high real specific acoustic impedance, non-zero fields are obtained at all points along the boundary. For bounding media adequately described by simple porosity theory, the results are especially interesting in that they show that at reasonably large distances and at low frequencies the acoustic pressure at the boundary is inversely proportional to the square of the distance and the square of the frequency. Some calculations of the sound pressure as a function of height above an absorbing material (Quietone) show the presence of a minimum occurring some distance above the boundary.
Correlations Between Ultrasonic and Micrometeorological Phenomena
Authors: Drumheller Carl E. , Schilling Harold K. , Thorpe Howard A.
Published: September 2005

In the atmosphere, within ten feet of the earth's surface, there are often intense temperature and wind gradients. Such gradients, as well as their fluctuations in time have been measured by sensitive micrometeorological instruments, and their effects upon ultrasonic propagation investigated, both in and out of dense forests in Panama and in Pennsylvania, over different types of ground coverings, under various weather conditions, both day and night. These studies have revealed definite correlations between micrometeorological and ultrasonic phenomena and their relation to large scale meteorological conditions, and to the terrain.
Auditory Factors in Radio Range Reception
Authors: Newman E. B. , Flynn John
Published: September 2005

The use of the conventional radio range in blind flying depends fundamentally upon an auditory discrimination. The off-course signal is heard only when the pilot can discriminate between the signals in the overlapping sectors. Any factor adversely affecting the pilot's auditory discrimination widens the beam. Interfering noise, such as set noise or atmospheric static, is shown markedly to reduce the ability to perform the necessary discrimination. Under special circumstances filters will offset some of this loss. The pitch of the signal, on the other hand, has little effect over a moderate range of frequencies. Some patterns of signals are discriminated better than others. Finally, the possibility of fatigue will be discussed.
The Pressure Distribution in the Auditory Canal in a Progressive Sound Field
Authors: Wiener Francis M. , Ross Douglas A.
Published: September 2005

The variation of the sound pressure along the auditory canal was determined experimentally on a number of subjects, male and female, placed in a progressive sound field. This was accomplished by insertion of a small flexible probe microphone at various positions along the length of the auditory canal. The subjects were placed in the sound field of a loudspeaker in a room free from acoustic wall reflections. The measurements were carried out over the significant range of audio-frequencies at various orientations in azimuth of the subjects with respect to the sound source. The free-field sound pressure was also determined at the subjects' location. The sound pressure at the eardrum is greater than the free-field pressure. The average ratio of these two quantities is a function of frequency and reaches values of about 20 db in the vicinity of 3000 c.p.s. The human ear is thus an effective acoustic “amplifier.” This amplification is a combination effect of diffraction around the head and pinna and resonance in the auditory canal. The measurements of the sound pressure at some of the other positions along the auditory canal serve to separate these two phenomena to a certain extent and to furnish additional information about the pressure distribution in the auditory canal.
Incremental Musical Scales
Authors: Gwynn M. H.
Published: September 2005

The equation V/T = 2sN represents a family of preferred number series. Each series is a train of scales of increasing and integer scale number, S. The note number, N, of all terms within each scale also consists of a series of integers. Hence the values for N or V within each scale consist of a rational arithmetic series. Sonically applied, V/T is a frequency, e.g., cycles per second. One particular type series, which is incremental, is defined by the following value for any note number, N = S + K + N, where K is an integer constant for each series of the type, and N is the tone number within any single scale, viz., the integer series, 0, 1, 2, ⋯, S + K − 1, S + K. Each incremental scale possesses S + K + 1 notes, one more note or tone than the preceding scale. Each lowest numbered tone, N = 0, is the coupling tone of a pair of finite incremental scales. The frequency of the highest note is double that of the lowest note, so that the octave is completed within each finite incremental scale. Trains of finite incremental scales may find application in a new pure tone music, rich in harmonic partials and tonal possibilities. The number of incremental notes chosen to span seven octaves may vary from 18 upward. A train of incremental scales is an homology of scales, with new effects introduced in each higher scale. Composition and rendition should be relatively simple, since incremental bass scales contain comparatively few notes conforming to the fact that aural sensitivity to pitch progresses with frequency through most of the sonic range.
Visible Sound
Authors: Potter Ralph K.
Published: September 2005

This is a demonstration-lecture concerning the portrayal of sound. New ways of picturing sounds in black and white and color and the relationships between movement in audible and visible sound will be discussed and illustrated. Also the legibility of speech patterns will be demonstrated by two-way telephone conversations in which the speech is seen rather than heard.
The Effect of Plugging the Ears on the Intelligibility of Speech in Noise
Authors: Kryter K. D.
Published: September 2005

This study evaluates by means of articulation testing methods the effect of wearing earplugs (Ear Wardens type V-51R) on communication with a public-address system, in person-to-person conversation, and with headphones. The articulation tests were conducted in the quiet and under various noise conditions. Two types of electronically generated noise were used at various intensity levels: one simulating “engine room” noise and the other simulating the frequency spectrum found in airplanes. For the tests with the public-address system the intensity of the speech was varied from 35 to 120 db. The results of the articulation tests reveal that in noises above 75 db listeners wearing Ear Wardens can understand speech better than listeners not wearing Ear Wardens. In the presence of airplane noise, Ear Wardens worn under various earphones slightly improve the reception of speech over military interphones operating at normal amplifier gain. It is concluded that in many situations where high noise levels are present, the use of Ear Wardens (or a similar, suitable device) would probably improve the intelligibility of speech, prevent possible hearing losses and reduce the annoyance and fatigue commonly attributed to noise.
Effects of Amplitude Distortion upon the Intelligibility of Speech
Authors: Licklider J. C. R.
Published: September 2005

In order to study the effects of amplitude distortion upon the intelligibility of speech, articulation tests were conducted with non-linear circuits introduced into otherwise high-quality audio systems. The non-linear circuits represented basic types of amplitude distortion and provided controlled amounts of each type. The test results indicated that: (1) Non-linear distortion of the kind commonly introduced when audio amplifiers are overdriven has very little detrimental effect upon intelligibility. Speech which has been subjected to sharp symmetrical overload—peak clipping—is almost perfectly intelligible, even if it has been stripped down to one-tenth of the amplitude it would have had with linear amplification. (2) The extreme tolerance for peak clipping is matched by an equally marked intolerance for center clipping. Cutting out even a small fraction of the part of the speech wave nearest the time axis impairs intelligibility. (3) Insofar as the severity of their effects upon intelligibility is concerned, other types of non-linear distortion are intermediate between peak clipping and center clipping. (4) Amplitude distortion causes greater impairment of intelligibility when noise is mixed with the speech than when the signal is noise-free. Noise which passes with the speech through the non-linear circuit is especially harmful—unless the non-linear circuit is a peak clipper and the noise consists of pulses, in which case the clipper acts as a noise limiter and reduces the adverse effect of the noise.
Effects of Frequency Distortion upon the Intelligibility of Speech
Authors: Egan James P. , Wiener Francis M.
Published: September 2005

The effects of frequency distortion upon the intelligibility of speech were investigated by means of controlled articulation tests. A large number of systems having band widths ranging from about one-half octave to a system covering the entire range of speech frequencies was investigated. The responses of these systems were linear and approximately uniform over the pass band, with sharp cut-offs at either end. The acoustic gain of the systems was expressed relative to the transmission of speech through one meter of air between talker and listener. Two spectra of masking noise were used, and each system was tested over a wide range of speech-to-noise ratios. In one experiment the speech was filtered before mixing with noise and in the other experiment both the speech and the noise were passed through the same filter. The results show that as the width of the band of speech frequencies is decreased the slopes of the ‘gain functions’ relating articulation to level of received speech also decrease. For constant levels of received speech, the articulation obtained with wide bands of speech is always higher than that obtained with narrow bands. When the masking noise has a uniform spectrum level, the articulation scores obtained by passing both the noise and the speech through the same band-pass filter are only slightly higher than those yielded by filtering the speech alone. However, if the spectrum level of the noise falls rapidly as a function of frequency, a considerable improvement in articulation results from filtering the noise as well as the speech.
The Masking of Speech by Sine Waves, Square Waves, and Regular and Randomized Pulses
Authors: Stevens S. S. , Miller Joseph , Truscott Ida
Published: September 2005

The ability of three standard wave forms to mask speech, by raising its threshold of perceptibility, was measured as a function of the intensity and frequency of the masking signal. Depending on the other parameters of the interfering signal, optimal masking is produced when the fundamental frequency lies in the range 100 to 500 c.p.s. Intense sine waves mask best when their frequency is about 300 c.p.s., whereas for weaker sine waves the most effective frequency is about 500 c.p.s. Square waves are less critical as to frequency and intensity; fundamental frequencies between about 80 and 400 c.p.s. mask with approximately equal effectiveness. Pulses of 10-microsecond duration are most effective at a PRF of about 200 p.p.s. When the time interval between successive pulses is made irregular (random interval-modulation), their ability to mask speech is dramatically increased. The increase in masking is a function of the original PRF, the rate of modulation (determined by the spectrum of the modulating voltage), and the range of modulation. By a proper adjustment of the parameters of its random interval-modulation the train of pulses can be made to sound like a band of white noise.
Problems of High Altitude Communication
Authors: Weichbrod J.
Published: September 2005

The use by the Army Air Forces of high altitude for strategic bombing made the long standing and complex problem of voice communications at these high altitudes a matter of considerable urgency. The problems of high altitude communication and solutions thereto dealing with the various components in the system, namely, the microphone, interphone amplifier, and headset receivers are discussed in a general way.
High Frequency Radiation from a Cylinder of Arbitrary Cross Section
Authors: Lax M. , Feshbach H.
Published: September 2005

The radiation from a cylinder of arbitrary cross section is expressed in terms of a superposition of plane waves. This makes it possible to compute a pressure or velocity distribution at the surface of the cylinder which will produce a desired pressure distribution at large distances. The converse problem of finding the pressure at large distances from the pressure or velocity at the surface is solved by an approximate method valid at sufficiently high frequencies. For a circular cylinder this method leads, in first order to the well-known result that each point on the surface radiates normally to itself. For non-circular cylinders this simple result continues to hold. The approximation is extended to second order, and the procedure is found to be valid when the surface itself and the pressure at the surface are smooth functions of angle. The method developed here can be used to compute the radiation impedance at the surface. It can also be applied to the problem of scattering by cylinders of arbitrary cross section.
Transmission, Reflection, and Guiding of an Exponential Pulse by a Steel Plate in Water. II Experiment
Authors: Osborne M. F. M. , Hart S. D.
Published: September 2005

In this paper are given the results of an experimental study of the interaction of an explosion wave with a water-backed steel plate. Data are given showing the dependence of the transmitted and reflected wave on the angle of incidence, and of the diffracted wave on position behind the plate. These data are illustrative of the use of the explosion wave in acoustical research. The plate acts as a filter, removing the high frequencies from the transmitted wave and the low frequencies from the reflected wave. The reflected wave is approximately constant in shape, or time scale, with angle of incidence. Its amplitude has a broad maximum at normal incidence. In addition to the reflected, diffracted, and transmitted wave, waves can travel along the plate, in which case the plate can act as a wave guide. As a consequence of dispersion in the guided waves a precursor precedes the explosion wave as it travels along the plate. The dependence of the frequency, length, and amplitude of this precursor upon orientation of the plate, position, and time has been determined.
The Attenuation of Sound Waves in Water by a Reverberation Method
Authors: Leonard R. W.
Published: September 2005

Sound waves are set up in a spherical tank by a crystal driver attached to the tank wall. The pressure level is obtained by a crystal hydrophone mounted flush in the tank wall. The output of the hydrophone is amplified and applied to a high speed level recorder. Decay curves are obtained by stopping the source. The crystal source is energized by a band of thermal noise insuring that a number of modes of vibration will be excited simultaneously. The spherical enclosure minimizes the shear losses at the wall for radial modes of vibration. The air radiation losses are readily computed for these modes. The mass reactance of the tank wall greatly reduces the air radiation losses at 25 kilocycles. On the basis of preliminary data to be presented at the meeting, the method may prove of considerable value in the study of the effects of hydrosols on the attenuation of sound waves in water.
A Hundred-Element Tone Synthesizer
Authors: Wente E. C. , Lovell C. A. , Muller J. F.
Published: September 2005

With the instrument to be described a complex electric current is generated by a combination of sine-wave currents derived from magnetic records. There are a hundred of these records placed side by side on a rotating drum. The components are independently controllable in amplitude. The higher harmonics in each component are at least 40 db and in most cases more than 50 db below the fundamental. The spectral composition of the synthesized tone is automatically displayed on a vertical chart. The instrument is provided with special circuits whereby the build-up and decay rates of groups of components may be adjusted to simulate the characteristics of various musical instruments.
Refinements in Supersonic Reflectoscopy
Authors: Firestone Floyd A. , Frederick Julian R.
Published: September 2005

A simple circuit for generating the high frequency voltage trains for energizing the crystal of a supersonic reflectoscope, is described. The reflectoscope can be adapted to the technique of measuring the thickness of metal plates by obtaining thickness resonance either with longitudinal or shear waves. Means for radiating shear and Rayleigh waves will be discussed. With shear waves experiments similar to those with polarized light can be performed on materials which possess elastic aeolotropy.
Magnetic Throat Microphones of High Sensitivity
Authors: Martin Daniel W.
Published: September 2005

An analysis is made of the problem of intelligence pick-up from anatomical vibration. Methods for measuring the actual and the effective response-frequency characteristics of the throat are described. Measurements on the variation of effective sensitivity among different subjects are discussed in connection with the concept of “vocal efficiency.” Design and performance data are given for several magnetic throat microphones of relatively high sensitivity.
Mechanical Impedance Bridge
Authors: Chrzanowski Peter
Published: September 2005

A mechanical impedance bridge based on the mechanical analog of Flanders method for measurement of acoustic impedance is described. The unknown impedance is attached to a bar rigidly connected to the voice coils of two dynamic loudspeaker driving units. One coil acts as the driver; the other serves as a detector. The unknown impedance is obtained in terms of three balances of an a.c. potentiometer connected across the coils. Two of the balances are for known mechanical impedances attached to the bar. Results of measurements of the mechanical impedance of phonograph needles are presented.
A New Method of Measuring Mach Number and True Air Speed of High Velocity Aircraft
Authors: Weinbaum Sidney , Corey Victor B.
Published: September 2005

The theory has been developed for an acoustical method which promises to be useful for accurately determining both the Mach number (v/c) and the true air speed (v) of an aircraft even though sonic speed (c) is approached or exceeded. Necessary to the operation of this method are a small sound emitter which radiates into the medium through which the aircraft moves, and two small sound receivers so placed with respect to the emitter that normal motion of the aircraft through the medium affects differently the two acoustic transit times t1 and t2. Arrangements with one receiver ahead of the sound emitter (in the direction of motion) may be used up to Mach unity, while for higher speeds both receivers must lie behind a plane through the emitter normal to the motion. Even then, limiting or “cut-off” velocities may exist. The expression for Mach number, necessarily a function of transit time ratio, is reduced to comparatively simple form by judicious positioning of the sound receivers with respect to the emitter. Although the expression for true air speed must involve one of the transit times explicitly, the building of direct reading electronic instruments for either true air speed or Mach number is feasible. Apparatus required for these measurements may be confined entirely to the aircraft under test, freeing pilot and plane from the dangers and difficulties attending low altitude speed tests over measured courses.
A Micro-Displacement Meter
Authors: Post R. F. , Howard R. L.
Published: September 2005

This paper deals with an equipment capable of detecting and measuring the amplitude of vibration of small surfaces (such as the vibrating faces of ultrasonic piezoelectric crystal assemblies) when the displacements are less than one micro-inch, with the introduction of negligible acoustic loading. The usable frequency range is 100 c.p.s. to 100 kc. The operation of the micro-displacement meter is based on the frequency-modulation technique of measurement, previously described. The method consists of determining the amount of frequency modulation produced in a vacuum-tube oscillator circuit which is coupled electro-mechanically to the vibrating system under measurement. The equipment employs a frequency-modulated oscillator or simple construction, so designed that the vibrating system is electromagnetically at the open end of a quarter-wave line—a point of very high impedance. Thus the vibrations produce a change in the terminating impedance of the resonent line, which in turn results in a large change in the oscillator frequency. The sensitivity of the system is also enhanced by the relatively high oscillator frequency (500 megacycles) which is used. At this frequency small percentage frequency variations correspond to sizeable absolute variations in frequency. The design is applicable for use in many related problems, such as the measurement of shock waves, the “probing” of acoustic fields, and employment in an extremely lightweight phonograph pick-up.
The Underwater Sound Calibration Station of the Ordnance Research Laboratory, The Pennsylvania State College
Authors: Ebaugh Paul
Published: September 2005

A field station for the testing and calibration of underwater sound devices under free field conditions is a necessity for any laboratory engaged in underwater sound research. The Black Moshannon Calibration Station, located in Black Moshannon State Park, fulfills such a need for The Ordnance Research Laboratory. This station was located on the Black Moshannon Dam principally because of its proximity to State College and because of the natural conditions existing which make it an ideal location for the carrying-out of such work. The laboratory building, in keeping with the surroundings, is of rustic architecture, built on pilings out over the water. It is totally enclosed and is provided with central heating to permit year-round operation. Maximum water depth under the building is fifteen feet, the bottom being dredged into a smooth contour which meets natural existing depths about fifty feet out from the building in all directions. Within the laboratory are occasional living quarters, lavatory and shower, an office, store rooms, shop, control room, and general operating room. The operating room contains two open wells which provide access to the water below. On the wells are mounted handling gear for suspending devices up to one-ton weight and four-foot diameter below the surface of the water. Beside the wells are relay racks containing controls for the hoist trains, power sources, and receiving preamplifiers. The major portion of the measurement apparatus is mounted in a console within the control room. From this position an operator can control the complete measuring circuits as well as the rotating hoist trains. The electronic apparatus is capable of either random noise or pure tone measurements over a frequency range of 2 to 100 kc. In addition, apparatus is available for such work as requires pulsing techniques. Frequency accuracy is maintained by constant monitoring against WWV while voltage and current measurements are compared to an Eppley Standard Cell. Standard hydrophones of the pressure gradient, magnetostriction, and crystal types are used in performing comparison measurements. The calibration of these hydrophones is maintained by reciprocity methods and cross-calibrations with other laboratories. Preliminary analysis of the average probable error of measurements made to date shows it to be less than 0.5 decibel.
Measurement Conditions Influencing the Front-To-Back Discrimination of an Underwater Hydrophone
Authors: Miller Laymon N.
Published: September 2005

In almost every application of an underwater listening unit it is necessary to listen by means of some predetermined scanning or searching technique for some external noise source in the presence of a nearer noise source caused by the propulsion mechanism of the carrier vessel. In order to listen more advantageously for external sources, it is general practice to locate the listening hydrophone in the forward part of the vessel, so as to remove it as far as possible from the so-called “self-noise” source in the aft part of the vessel. In order to reduce further the reception of this unwanted self-noise, it is desirable to design the listening hydrophone to discriminate against such noise coming in from the rear, without materially affecting the front-side sensitivity. The term “front-to-back discrimination” is used to describe this particular quality of a hydrophone. It is the purpose of this report to discuss a few of the measurement conditions which influence the value of the “front-to-back ratio” of a hydrophone. Emphasis is placed on those factors involved in any measurement which are external to the hydrophone itself; for example, the conditions of the medium and the surrounding region, the mounting conditions and the acoustic baffling of the hydrophone, the directionality characteristics of the transmitting transducer, or projector, with which the hydrophone is measured, and the distance separating the hydrophone and the projector. The data here presented were made with various types of hydrophones under various sets of conditions at the Harvard Underwater Sound Laboratory measurement station at Spy Pond during the last two or three years of the war.
Ultrasonic Measurement of Wall Thickness in Diesel Cylinder Liner
Authors: Struthers Francis W. , Trent Horace M.
Published: September 2005

The modifications that have been developed in order to adapt the Sonigage to the quick inspection of Diesel cylinder liners are described. A method of introducing ultrasonic vibrations from a conventional flat-crystal probe into a curve surface and an adaptor for determining thickness by interpreting the harmonic responses have proven to be valuable in expediting this type of work. In the hands of an experienced operator the technique can be made to yield much valuable information concerning the relative homogeneities of the castings.
The Detection of Internal Leaks in Aircraft Hydraulic Systems
Authors: Nuckolls Richard G. , Trent Horace M.
Published: September 2005

The problem of locating defective valves which cause excessive internal leaks in aircraft hydraulic systems has been successfully solved by the development of an acoustic device called the Hydraulic Leak Detector. In principle, the device monitors the ultrasonic vibrations produced in the system by the leaking valve, which vibrations are most intense at the defective element. A recording of the characteristic sounds heard in the hydraulic leak detector is presented and discussed.
An Acoustic Lens for Underwater Sound
Authors: Herr Robert
Published: September 2005

In order to meet a demand for plane or converging waves in underwater acoustic measurements an acoustic lens has been developed. The lens employs carbon tetrachloride contained in a metal form. The curved surfaces of the lens are spun to the desired curvature from 0.026-in. aluminum sheet, and these are assembled with a brass frame. Two experimental models of 12.1-in. diameter and 36-in.-focal length have been built for operation at 60 kc and perform satisfactorily. The chief aberrations are caused by diffraction at the edges and irregular transmission characteristics of the rim of the lens where brass and rubber gaskets are present. With the source at the focal length, measurements were made of phase and amplitude along straight lines perpendicular to and through the axis of the system, at various distances behind the lens, and for various frequencies in the range 28 to 62 kc. At 62 kc the phase is constant within ±7°, 3 in. behind the lens, or ±23°, 12 in. behind the lens, over a 5-in. radius. Within this same radius the amplitude is constant within 1 db at 3 in. and 2 db at 12 in. behind the lens. Behavior is poorer at lower frequencies as the diffraction effects became serious. Transmission loss has not been accurately measured but is much less than 1 db. Two lenses together have been used to focus sound of various frequencies.
Ultrasonic Lenses and Transmission Plates
Authors: Ernst Paul J.
Published: September 2005

Boyle and Rawlinson's formula is applied to the design of low loss ultrasonic lenses of plastics, metals, and other solids. Plano-spherical or plano-cylindrical ultrasonic lenses are used in direct contact with the generating crystal as well and called “ultrasonic contact lenses” in analogy with the corresponding devices for the human eye. To reduce the loss of energy by reflection of ultrasonics at the boundary between two media of different acoustic resistivities plane parallel plates are employed, named “transmission plates.” They are analogs of the coatings used to extinguish reflection of light from glass. The high efficiency of the devices described above is recorded in various ways. The usual optical methods are simplified and improved by the application of the concentrated-arc lamp. Eventually the possibilities of further developments are discussed and some problems awaiting solution.
Reflection of Sound from the Sea Surface
Authors: Liebermann Leonard N.
Published: September 2005

Problems arising in the analysis of echo ranges are contingent for their solution on a thorough understanding of the way sound is reflected from a rough sea surface. Information on surface reflectivity has been obtained by means of a special experiment carried out under controlled conditions. The method consists of controlling the geometry by mounting projector and hydrophone on vertical steel towers embedded in the ocean bottom, and sending a very short frequency-modulated pulse from projector to hydrophone. Each such frequency sweep yielded an interference pattern, since the path difference between direct and reflected sound was fixed while the sound frequency was changing; from an examination of the interference patterns of many successive pulses, it is possible to obtain (1) the instantaneous reflectivity, (2) the time structure of changes in reflectivity, (3) the probability distribution of the amplitude reflection coefficient. It is found that the reflectivity at any one frequency changes negligibly in a time interval as small as 1/30 of a second, but may change appreciably in the course of a few seconds. The reflection coefficient at any one instant is frequency-dependent, in a manner depending on the instantaneous geometry of the surface. With all surface wave heights up to one foot, the instantaneous reflection coefficient was found to vary between 0 and 2.5, with median values near unity. At least 10 percent of the time on each day the amplitude reflection coefficient was above 100 percent. These results indicate that the sea surface reflects sound as if it were a collection of many separated distinct small mirrors oriented at the right direction to deliver sound to the hydrophone.
Attenuation of Sound in Water
Authors: Wilson Donald A. , Liebermann Leonard N.
Published: September 2005

The attenuation of sound in water in the frequency range 16–22 kc has been measured by noting the time of decay of sound in a container. This method was first used by Knudsen for the study of attenuation of sound in gases. The decay time is dependent on the loss of sound through the walls as well as the absorption in the water. The loss through the walls was minimized by using a specially constructed hollow bronze sphere, two feet in diameter, whose wall thickness, 1.5 inches, constituted approximately one-quarter wave-length at 22 kc. The measured attenuation was found to be strongly dependent, as acoustic theory predicts, on the presence of bubbles formed during the process of filling the container. Since these bubbles may adhere to the walls for periods of several days, special precautions were taken in introducing the water to prevent their formation. The attenuation of bubble-free water was found to be no greater than 2.0±0.1 db/kyd at 16 kc and no greater than 3.0±0.1 db/kyd at 22 kc. The attenuation for natural bubble-free sea water was found to be no greater than 4.1±0.1 db/kyd at 16 kc and 6.0±0.1 db/kyd at 22 kc. A theory will be presented to account for the increase in attenuation in salt water over plain water.
Image Interference in the Presence of Refraction
Authors: Young Robert W.
Published: September 2005

Underwater sound transmission has been studied as a function of range at frequencies of 0.2, 0.6, 1.8, 7.5, and 22.5 kc, under a variety of thermal conditions. At the three lower frequencies marked inteference patterns are observed. These result from the combination of surface reflected sound (as from an image source) and directly transmitted sound. Refraction modifies the interference pattern. When the sound velocity increases with increasing depth the interference pattern is contracted; when the velocity increases with depth the pattern is extended. An easily used formula is developed to predict this influence of refraction on the propagation of sound emitted from a point source adjacent to a reflecting plane. The theory is in good agreement with the experimental data obtained with the source at a depth of 14 feet from the surface and the receiver as deep as 300 feet.
On Fluctuations of Ultrasonic Intensities Outdoors
Authors: Schilling H. K. , Nyborg W. L. , Thorpe H. A.
Published: September 2005

The phenomenon of ultrasonic intensity fluctuations has been studied experimentally outdoors under various kinds of weather conditions. There seem to be three types of fluctuations. Their causes are suggested by correlations of ultrasonic data with simultaneous micrometeorological observations. Two types of fluctuations are of the mean intensity. Those of the first are usually fairly slow with a period of several minutes and with a range of intensity variation of 10 to 30 db. Apparently they are observed only near boundaries of “shadow zones” and are caused by the motions of the “shadows” as the vertical gradients of the velocity of sound change. The second type is ordinarily faster, with a frequency of 2 or 3 per minute, and an intensity range of only 2 to 5 db. They are observed at a distance from shadow boundaries where the fluctuations of gradients can produce only changes in the convergence and divergence of rays with consequent variations in intensity. Third type fluctuations are usually extremely rapid, as frequent as several times per second, with an amplitude of variation of several db, and there is evidence that they are caused by the random motion, between source and receiver, of inhomogeneities or discrete bodies of air in the atmosphere. Typical diurnal cycles of ultrasonic fluctuations and of related weather conditions, as well as of micrometeorological phenomena, have been observed.
Absorption Frequency Characteristic of Cylindrical Plywood
Authors: Boner C. P. , Rutherford C. R. , Seay C. F.
Published: September 2005

Incomplete pre-war data on absorption of plywood in cylindrical forms are presented as a tentative guide for use in studio and auditorium design. Methods of cylinder construction are discussed, and preliminary observations are made concerning the effect of multi-layer construction on absorption. The major advantages of this type of design are felt to be the flat frequency characteristic and the marked reduction in flutter obtainable. Certain obvious limitations of live-room diffusive designs are pointed out.
Disk Recording Studio Acoustics
Authors: Dunbar J. Y. , Green Lonsdale
Published: September 2005

A report on several well-known recording studios, giving the measured acoustic properties of each, might be helpful in suggesting a trend to future construction and treatment. This paper covers recording studios of WOR, Decca Records, World Broadcasting and Empire Broadcasting Corporation. Measurements were made of reverberation decay times at six frequencies from 150 to 4800 c.p.s. Some studios show measurements made before and after treatment.
Review of Criteria for Studio Design
Authors: Nixon George M. , Gurin Herman M.
Published: September 2005

The significance of volume, reverberation, and diffusion are reviewed and the methods in achieving the most desirable combination are developed. Experience is drawn from some new studios recently designed and built and the results discussed.
An Acoustic Constant of Enclosed Spaces Correlatable with their Apparent Liveness
Authors: Maxfield J. P. , Albersheim W. J.
Published: September 2005

Two forms of an acoustic “constant” for enclosed spaces are derived, one of which is correlatable with the subjective “liveness” of the space. These two forms are: (1) The ratio of the instantaneous value of the energy density of the reverberant sound to the instantaneous value of energy density of the direct sound. (2) The ratio of a time integral of the energy density of the reverberant sound to the instantaneous value of the energy density of the direct sound. Data are presented to show that the second form of the constant is the one correlatable with the acoustic properties of the space and the distance from sound source to listener. A discussion of the characteristics of reproduced sound for various values of this constant indicates the nature of its possible connection with some of the fundamental attributes of hearing.
A System for Reducing Scratch in Record Reproduction
Authors: Carlisle Richard W.
Published: September 2005

The reduction of record scratch is shown to be possible by taking advantage of the masking characteristics of the ear. High frequency background noise can be masked only by high frequency sounds; therefore, to reduce scratch, the high frequency response should be suppressed except during the intervals when high frequency sounds are transmitted. Most typical high frequency sounds are instantaneously accompanied by related sounds of mid-range frequency. The control of high frequency response may be accomplished either as a function of the level of such mid-range signals, or of the level of high frequency signals. The former is preferable since the latter distinction may be obliterated by the great variation in the level of scratch. Electrical circuits are shown by which high frequency response is suppressed when no mid-range signals are present and instantly restored when such signals occur. These circuits must be arranged to provide substantially instantaneous restoration of highs, but the rate of suppression must be relatively slow in order to avoid interfering with the natural rhythm and accent of music or speech.
On the Absolute Calibration of Phonograph Test Records by Means of Light Patterns
Authors: Wathen-Dunn Weiant
Published: September 2005

That geometry of the record cutting process, necessary to an understanding of how light patterns are produced, is reviewed briefly; the method of producing light patterns on test records is described; and the salient experimental phenomena are noted. Reference is made to a solution of the problem by Richard Bierl in the Akustische Zeitschrift for May, 1940, and Bierl's results are put into a more useful form. A more general equation for the phenomenon, which reduces to Bierl's equation upon satisfying his conditions, is derived, and the accuracy of both formulae is examined.
General Principles of Optical Recording on Film
Authors: Maurer John A.
Published: September 2005

General information will be presented regarding the dynamic range, frequency response, and distortion which occurs in various types of film recording. Reference will be made to apparatus which is used at the present time, and such apparatus will be discussed briefly.
Distortions Peculiar to Sound Recording on Motion Picture Film
Authors: Ireland R. Paul
Published: September 2005

This paper presents a classification of distortions peculiar to sound recording on film. Sources of these distortions include imperfections of photographic reproductions, the optics of the system, the light modulator, and the photoelectric cell. The effects of these are considered on various types of variable density and variable area sound recording.
Some Factors Influencing the Choice of a Medium for Magnetic Recording
Authors: Holmes Lynn C.
Published: September 2005

No other single factor contributes so much to the ultimate performance of a magnetic recording system as the recording medium itself. Within the last three or four years, many papers have described the performance of magnetic recording systems but none has given much attention to the correlation between the magnetic properties of the recording medium and the performance of the system. It is the purpose of this paper to show how some of the performance characteristics of magnetic recording systems depend on the magnetic characteristics of the recording medium. The most important single magnetic characteristic of the medium for good high frequency response is high coercivity. High retentivity is necessary for high output voltage at the frequency of maximum response. However, low retentivity is desirable not only from the viewpoint of reducing crosstalk but also from that of improving the response at the higher audiofrequencies relative to the response at the frequency of maximum response. The ratio of coercivity to retentivity is proposed as a figure of merit for estimating or predicting the frequency response of a medium when used with a specific magnetic recording system. The limitations imposed by the magnetic properties of the medium on the design of magnetic heads and magnetic recording systems are also discussed. The problem of modulation noise and its relation to the Barkhausen effect is emphasized because this may impose a serious limitation on the use of certain magnetic recording media which seem to be excellent in all other respects.
Design Problems on Magnetic Recording Equipment
Authors: Begun S. J.
Published: September 2005

The development of powder coated materials as recording media had a profound influence upon the design of magnetic recording equipment. The principal features of a magnetic recorder which uses 14″ coated paper tape as a recording medium are described. Even though the recording speed of the paper tape is only 7.5″ per second, the instrument will handle frequencies up to 5000 c.p.s. Since the thickness of the recording medium is less than 0.0022″, and its motion is slow, approximately half an hour of recording time can be accommodated on a standard 8 mm motion picture reel with a diameter of 7″. A voice recorder will be described which uses a coated paper disk as a recording medium. The sound track is helically recorded, 40 lines per inch, from an inner diameter of slightly more than 5″ to an outer diameter of approximately 9″. A novel design of a wire recorder is briefly described. This device has for a recording medium a non-magnetic wire plated with a cobalt-nickel alloy.