bluuebunny/crossref_metadata_2025 huggingface dataset:
Binaural Effects in Remote Masking
Authors: Hirsh Ira J. , Burgeat Michel
Published: September 2005

A first experiment has confirmed the findings of Hirsh and of Jeffress with respect to the effects of changes in the interaural phase difference for both noise and tone on the masked binaural threshold. The threshold for a low-frequency tone is some 12 db higher when both tone and noise are in phase at the two ears, than when either one is 180°. A second experiment utilized a high-frequency band of noise at a high level to produce “remote masking” for the same low tones in order to determine whether or not this other kind of masking would be similarly affected by changes in interaural phase. With the noise band in phase, a 180° change in the phase of the low-frequency tone produces a change in threshold of only slightly less than 12 db. But a similar change in the phase of the noise band produces no change in masking, except for a slight shift that can be predicted from the time shift at low frequency that would correspond to a half-wave in the high-frequency band.
Resonant Frequencies of Air Bubbles Generated in Open-Ended Pipes
Authors: Devin Charles
Published: September 2005

The natural frequency of volume pulsations of an air bubble at the center of a short open-ended rigid tube should be lower than that of a bubble of equal size in a free field. Air bubbles were generated at nozzles submerged in water in a o free field and, alternately, surrounded by short sections of brass tubing. The frequency of oscillations was determined through measurement of the radiated sound pressure. The effect of the tube on the resonant frequency agreed with that computed on the basis of simple potential theory.
Response of a String Imbedded in an Infinite Membrane
Authors: Lamb G.
Published: September 2005

An investigation has been initiated to determine the rigorous solution to some basic problems in structure-borne sound. As the first step in such a study, the propagation of flexural waves in an infinitely extended thin elastic plate supported by a single elastic beam has been considered. Since the main features of the wave propagation in such a coupled system are more simply exhibited in the case of a taut string embedded in a stretched membrane, the solution of this problem has been initially exploited. In particular the response of a string-membrane system to a harmonic driving force applied at a single point on the string has been investigated. The frequency dependence of the input impedance to the system, along with other features of the problem, will be presented and discussed. It is shown that the input impedance approaches the membrane impedance at low frequencies and the string impedance at high frequencies, while at intermediate frequencies the impedance depends upon the properties of both the string and the membrane. [Supported by Office of Naval Research, Contract No. Nonr 2322(00).]
Gravest Contour Vibration of Thin Anisotropic Circular Plates
Authors: Onoe Morio
Published: September 2005

In a previous paper [J. Acoust. Soc. Am. 28, 1158 (1956)], it was shown that the gravest mode of contour vibration of an isotropic thin circular plate has the circumferential order of two and is mostly equivoluminal in nature. Although the exact expression of the displacements includes Bessel functions, it can be reasonably approximated by a simple combination of trigonometric functions, which makes it possible to handle the anisotropic case. Since the mode is the gravest, Rayleigh's principle is applied in a procedure of approximation, taking an angle of rotation and a wave number as adjusting parameters. The results are compared with experiments of quartz vibrators. Calculated frequencies show agreement better than 1% with an exact value for isotropic plates and an observed value for a rotated Y-cut of quartz, which has a limited anisotropy. The accuracy decreases as the degree of anisotropy increases. For the X-cut of quartz, the calculated value is 4.7% higher than an observed value. One of the significant characteristics of the mode of vibration of an anisotropic plate is the fact that the direction of maximum displacement makes a certain angle with a crystallographic axis. The calculated value of this angle agrees exactly with the observed angle for the rotated Y-cut of quartz and within a few degrees for the case of the X-cut of quartz. Equivalent electric circuit constants and surface patterns of piezoelectrically induced charges are also calculated and compared with experiments.
Message Reception and Message Uncertainty
Authors: Pollack Irwin
Published: September 2005

A basic principle of language engineering is that the accuracy of message reception in noise is determined by the number of alternative messages that might be communicated. However, it is not clear whether the number of alternative messages available for presentation or the number of possible message-responses is the critical determinant of performance. We attempted to resolve this question in experiments in which trained listeners first memorized various sets of n spondee words (n varied from 2 to 64). Words, chosen at random from the set of n words, were then read, one at a time, over a noisy communications channel. Shortly after the word was read, the listener was instructed that the presented word was one of k possible words, where k⩽n. Accuracy of message-reception was found to be practically independent of the size of the message class (n), for a constant number of possible response alternatives (k). Furthermore, the number of necessary response distinctions—rather than response-uncertainty per se—appears to be the critical determinant of accuracy of communications.
Pulse Propagation in Rods
Authors: Krautkopf D. W. , Skudrzyk Eugen J.
Published: September 2005

The propagation of sound pulses in rods is extremely complex. At very low frequencies Young's modulus determines the sound phenomenon. As the frequency increases shear waves are generated simultaneously and are generated, whenever a sound pulse is reflected at the end of the rod. At still higher frequencies dilatational modes of different phase and group velocities can be distinguished. The order of the energy carrying modes increases as the frequency increases and the losses in the rod are due to the losses in the shear and the dilatation moduli, the ratio between the two kinds of losses varying with the frequency. Finally, at high frequencies only high-order modes seem to be excited and the propagation velocity of pulses approaches the sound velocity of the infinite medium. An evaluation of sound velocity and attenuation measurements at high frequencies is therefore a very difficult task. The theory is illustrated by experimental results.
On the Propagation of Sound at Low Frequencies in an Inhomogeneous Atmosphere
Authors: Harris Cyril M. , Kirvida Leonard B.
Published: September 2005

The object of this experimental study was to obtain some indication of the characteristics of phase fluctuations, which result from the propagation of low-frequency sound through an inhomogeneous atmosphere. Sound from a 45-cps pure tone source (located on the ground) was transmitted to two distant microphones at ground level. Both microphones were approximately equidistant from the source. The acoustic signals received at each of the microphones were simultaneously recorded on a magnetic tape for microphone spacings, which varied from λ/6 to 9λ/2, under various atmospheric conditions, for different distances between the sound source and the microphones. From these records, the following information was obtained. (1) The instantaneous phase difference between the acoustic signals received at the two microphones. These phase differences were measured at two-second intervals throughout a 50-sec recording period and plotted about their mean value. (2) The means square value of the phase differences about the mean value. (3) The autocorrelation function for each of the graphs in (1). (This work was supported under Project Michigan, U. S. Signal Corps Contract DA-36-039-sc-52654.)
In-Flight Noise Suppressor Development Report
Authors: Gibbs R. M.
Published: September 2005

This is a report of BAC progress in the development of jet engine in-flight noise suppressors. The importance of model testing, full-scale ground testing and flight testing is emphasized. A relatively economical flight test method is presented which allows accurate flight noise data to be predicted without resort to take-off maneuvers at specific gross weights. The results of such flight tests have been summarized in a family of fixed altitude curves which relate over-all sound levels beneath the flight path to net thrust per engine. These curves together with Model 707-120 take-off performance data may be used to determine sound levels beneath the flight path for various take-off procedures at any gross weight.
Noise Control Measures for the Convair Jet-Liners
Authors: Koenig R. J.
Published: September 2005

Noise considerations have influenced the design of the Convair jet-liner since the beginning of the development program. This paper discusses the jet engine noise source and noise levels during operational use of the Convair 880 and 600 aircraft. Considerations involved in the selection of the suppressor for the General Electrical CJ 805 engine which powers the 880 are reviewed and noise characteristics of the engine with suppressor presented. The concentric jet aft-fan model of the CJ 805 engine, which powers the 600, is discussed. The effect of take-off flight path and engine power on community noise is shown.
Subjective Reaction to Airplane Noise
Authors: Watson Warren
Published: September 2005

Much has been said in the past several years about subjective reactions to airplane noise. Perhaps less has been said about actual experimental data in this area. This paper will report the results of experimental measurements made in the field with airplanes as well as data taken in the laboratory at the University of Washington. Some suggestions are made regarding the hazards of generalizing beyond the scope of the data.
Terminal Noise
Authors: Callaway Vern
Published: September 2005

The terminal handling characteristics of the Model 707-120 airplane has been studied in detail. Measurements of blast velocities, temperatures, and sound levels are presented. Sound levels inside and outside a simulated terminal at passenger loading areas are discussed for various approach and departure techniques.
Digital Computer Simulation for Speech Experiments
Authors: David E. E. , Mathews Max V. , McDonald H. S.
Published: September 2005

Speech research has been characterized by the need for building extensive experimental apparatus. As transmission systems using information theoretic codings and automatic recognition schemes have come under study, such apparatus has required large memory capacity and intricate logical structure. Simulation of equipment with digital computers results in reduction of the time and cost of experimentation, and more important, achieves a gross expansion of the ideas which can be considered. Whereas, previously instrumentation was an omnipresent limitation in all proposals, now the imagination of the researcher is the principal restriction. Digital simulation requires an input-output device to convert speech signals to series of numbers in a form acceptable to the computer and to translate the digital output of the computer to an audio signal. Such a device for sampling, quantizing, and recording speech-type signals on IBM 704 digital magnetic tape and for performing the inverse operation is described. Methods for grouping the data on the tape to meet the computer requirements are discussed. The computer speed and memory size to carry ont practical simulations are outlined. Simulation studies have been effectively applied to problems concerned both with coders for transmission systems and with phases of automatic recognition schemes.
Extremal Coding for Speech Transmission
Authors: Mathews Max V.
Published: September 2005

A new digital coding scheme for transmitting speech is described. The transmitted information consists of the amplitude of the speech wave at its extremes (relative maxima and minima) and the time intervals between extremes. The coding is related to clipped speech encoding which effectively transmits only the times of the extremes. The decoding process consists of interpolating a function between extremes so as to connect them smoothly and to preserve the extremes of the original speech in the reconstructed speech. The properties of the coding have been studied by digital simulation on an IBM 704 computer. Speech samples for subjective evaluation were generated and the information rate and distribution of extremes computed. The coding has a minimum information rate of about 15 000 bits per sec, good intelligibility, and a quality below that of commercial telephones. Subjective comparison with companded indicates that the quality is comparable to that of 30 000 to 40 000 bits per second PCM. The buffer size necessary to receive the randomly occurring extremes and transmit extremal information at a uniform rate is about 30 000 bits. Thus, the buffer introduces a two-second delay in a single-channel communication link.
Choice of Base Signals in Speech Communication
Authors: Dolansky Ladislav
Published: September 2005

Traditionally, the more complicated communication signals were most often expressed as Fourier series, or time functions specified at a considerable number of points. Such approaches are usually mathematically complete and may be useful in many respects; however, for good insight and for simplicity of any associated experimental equipment, they are usually inferior to expressions using parameters directly related to the process which generates the particular class of signals studied. Using an orthonormal set of decaying oscillatory functions, the problem of expressing voiced speech sounds by means of these functions, and of obtaining pertinent coefficients of these functions by measurement, has been studied. Experimental results will be presented.
Point Excitation of a Cylindrical Shell
Authors: Franken Peter A.
Published: September 2005

A thin cylindrical shell forced at a point comprises a useful model for studying the motion of a submarine hull set into vibration by mounted mechanical equipment. The formal solution for point excitation is readily derived in a modal expansion, and the Fourier inversion is performed. The known solutions of flat plate motion must apply when the forcing frequency exceeds the radial resonance, therefore the low-frequency case is generally of more interest. The behavior of the various angular modes of motion, the effects of water loading, and the radiation of sound by the vibrating shell, are considered. [Supported by Office of Naval Research, Contract No. Nonr-2322 (00).]
Effect of a Plane on the Power Output of a Monopole
Authors: Maling George C.
Published: September 2005

The presence of a plane boundary is known to affect the power output of a sound source, and the effect is most conveniently expressed as a “power amplification factor (W/W0)” which will in general depend on type of sound source, distance from plane, and boundary admittance. For a constant strength monopole near a plane with specified normal admittance (real), the power amplification factor can be calculated rigorously in terms of tabulated functions using existing theory on the reflection of a spherical wave from an infinite plane specified by impedance boundary conditions [U. Ingard, J. Acoust. Soc. Am. 23, 329 (1951)]. Plots of W/W0 as a function of source height are presented for several values of normal admittance including β = 1. [.This work was supported in part by the U. S. Army (Signal Corps), the U. S. Air Force (Air Research and Development Command), and the U. S. Navy (Office of Naval Research).]
Method for Predicting In-Flight Noise on Jet Aircraft Structure
Authors: Cho Alfred C. F.
Published: September 2005

The principal noise sources from jet aircraft can be summarized as jet noise, boundary layer noise, and the shock wave-turbulence interaction. The noise production of jet aircraft during the in-flight condition is different from the ground static operation due to changes in relative jet velocity, aerodynamic background, and the distribution of sound waves. Basically the in-flight sound pressure levels on a jet aircraft structure are derived from the ground static levels by adding corrections under various in-flight conditions. The directional distribution correction is due to a lateral acoustic quadrupole in motion at various Mach numbers. The relative velocity correction takes into consideration the moving air as a result of an airplane in motion. The altitude correction accounts for the changes in the density of air and the speed of sound at different altitude. All the corrections are expressed in decibels relative to sea level static condition. Boundary layer noise correction is applied in cases where such noise is comparable to or dominates other noises. After the corrections are applied to a number of positions on the aircraft structure, new contours of equal sound pressure level are drawn to represent the in-flight condition.
Exhaust Muffler Design for Two-Cycle Engines
Authors: Watters B. G. , Hoover R. M. , Franken Peter A.
Published: September 2005

Specification of insertion loss, or some other measure of muffler attenuation, is without much meaning to the muffler user unless it is accompanied by estimates of the change in engine performance brought about by the muffler. This paper describes a study of both the acoustical and mechanical characteristics of a reactive muffler for a two-cycle engine exhaust. The muffler consists of an expansion chamber and a tailpipe open to the atmosphere. Analog analysis of the muffler can exhibit the “lumped circuit” resonance behavior and the “distributed circuit” standing wave effects. The average back pressure due to the muffler is found to depend on the alternating component of the particle velocity in the tailpipe as well as on the steady flow through the muffler. The total pressure reacting against the exhaust port while it is open is the sum of the average back pressure and (primarily) the fundamental alternating pressure component. Dynamometer tests give the relation of total back pressure to horsepower loss. These results lead to design charts which indicate appropriate ranges of muffler dimensions for obtaining acceptable engine performance.
Mechanical Noise Sources as Calibrated Noise Standards
Authors: Hardy Howard C.
Published: September 2005

In a large number of industrial applications the most convenient method of obtaining sound power ratings is by comparison with an acoustically calibrated mechanical noise source. The sound power outputs are compared in a random incidence (reverberant) sound field with standardized and relatively inexpensive electronic equipment which does not need to be calibrated. The acoustical absorption also does not need to be measured, provided it does not change appreciably during a test. This paper will describe two types of mechanical noise sources which are very stable. One of these operates from a compressed air supply. A group of these units have been calibrated by the Geiger-Hamme Laboratories and have become the standard sources for the trade association called the Compressed Air and Gas Institute. Another aerodynamic source operated by an electric motor gives a very uniform broad-band spectrum over eight octaves. This latter source has been calibrated by the Armour Research Foundation and is being used by many laboratories in the air motion industry. Both sources will be demonstrated. Some of the technical requirements and precautions for using this equipment for secondary sound power calibrations will be described.
Effect of Partitions on the Noise Propagation in Offices
Authors: Hardy Howard C.
Published: September 2005

A field study has been made of noise propagation in a large number of geometrical arrangements of offices of different uses, such as executive, supervisory, clerical, accounting, including large open areas. It is possible to rate these offices quantitatively in loudness categories. In the open office with an acoustically treated ceiling, sound was found to drop off with distance very close to the inverse square law, for distances of 50 ft or greater with some dependence on acoustical absorption efficiency. The effect of the 5.5-ft high partitioned cubicles is to cause the sound to drop off in 6- to 9-db increments and to allow closer spacing of personnel for the same amount of isolation. In higher partitions, the most important parameter is the acoustical absorption efficiency of the ceiling, and an approximate working equation has been tested which allows one to compute the amount of sound passing over such a barrier. The other important noise paths are doors, ventilating openings, and ceiling plenums, sometimes separated by only a porous acoustical barrier. In no case was the sound transmission loss of a full permanent or portable partition found to be equal to its rated value, chiefly because energy was conducted by flanking paths.
The Problems Presented in the Use of Acoustical Plasters
Authors: Fitzroy Dariel
Published: September 2005

Wide variation in absorptive coefficients, as reported from laboratory measurements, and those actually measured in the field, when acoustical plaster is used, indicates a serious problem in achieving desired results. Although laboratory tests seem accurate, many factors apparently conspire to defeat expected results. Some of these factors are discussed, based on field experience.
Application and Performance of Liquid Jet Transducers
Authors: Cottell E. C.
Published: September 2005

Six years ago, a commercial liquid whistle was first introduced in England, and since then has found a wide field of application in emulsification, dispersion, and mixing This whistle and other types are discussed. Established industrial applications of the liquid whistle are reviewed. Analysis of the high efficiency obtained with liquid whistles in liquid-liquid and liquid-solid processing. Comparison of results obtained with the liquid whistle with conventional emulsifying equipment and piezo electric transducer. The effect of cavitation on particle size in emulsions and possible reasons for better stability in eradiated emulsions in spite of random particle size compared with more homogenous systems.
Ultrasonic Vibration Potentials in Polyelectrolytes
Authors: Booker Ionathan , Yeager Ernest , Hovorka Frank
Published: September 2005

When ultrasonic waves are propagated through aqueous solutions of polyelectrolytes, alternating potential differences are generated between points separated by a phase distance other than an integral multiple of the wavelength. This effect is somewhat similar to the ionic and colloidal vibration potentials reported previously [J. Acoust. Soc. Am. 25, 456 (1953)] and occurs because of differences in the dynamic reactions of the large polymeric ions, the simple ions, and the solvent molecules to the material waves. In the absence of sound waves, the charge distribution associated with each polyelectrolyte particle is statistically symmetrical. In the sound field, each polyelectrolyte particle and its ionic atmosphere act as an oscillating dipole. This effect has been examined in polyacrylic acid solutions as a function of concentration and percent neutralization of the polyelectrolyte. Pulse-modulated ultrasonic waves have been used for the measurements at frequencies from 200 to 1000 kc/sec. The observed amplitude is in the range 10−5 to 10−4 v per unit velocity amplitude (cm/sec). This effect is expected to prove useful in establishing the state of coiling of polyelectrolytes. [This research has been supported by the Office of Naval Research under Contract No. 1439(04).]
Acoustical Design of the First Presbyterian Church Stamford, Connecticut
Authors: Klepper David
Published: September 2005

This church, designed by Harrison and Abramovitz, Architects, is unusual in that the basic architectural shape provides the desired acoustical environment, requiring no “applied” sound-absorbing material. Hearing conditions are highly satisfactory for both speech and music. The reverberation time characteristic is discussed along with the “gain” provided by the pulpit canopy. A tape recording will be presented and slides will be shown.
Acoustical Problems in Two Round Churches
Authors: Mikeska E. E. , Lane R. N. , Boner  , Lane
Published: September 2005

Acoustical measurements and design considerations are discussed for two churches with circular floor plans. One was carefully planned with the acoustics in mind and has proved successful. The other was built with a parabolic concrete dome; a thin sprayed absorbent lining inside the dome was counted on to eliminate the sound focusing effects. Echograms taken at various positions inside the church illustrate the resulting severe echo problems.
Acoustoelectronic Auditorium
Authors: Olson Harry F.
Published: September 2005

The term “acoustoelectronic auditorium” is used to designate an auditorium complex incorporating an integrated design of the room acoustics with the sound reinforcing apparatus. Under these conditions, the acoustic characteristics of the electronic sound system are coordinated and correlated with the acoustics of the enclosure. The features of the acoustoelectronic auditorium are as follows: an enclosure providing a large stage, a low ceiling, and a seating capacity of 300; sound reinforcing apparatus consisting of the following features: concealed and fixed stage microphones, concealed and fixed auditorium loudspeakers, and a delay system.
Just Noticeable Differences for Changes of Interaural Time Differences as a Function of Interaural Time Differences
Authors: Campbell Richard A.
Published: September 2005

The just noticeable differences for changes of interaural time differences between two bursts of noise were investigated as a function of the interaural time difference of the first (reference) burst. Four normal hearing subjects listened through earphones to time differences between ears which were varied by electrical means. The noise went through a low-pass filter set at 1300 cps and had an intensity of 70 db SPL. The bursts were 0.85 second in duration. Interaural time differences for the reference bursts were between 0 and 600 μsec, with just noticeable differences increasing from 12 to 21 μsec, respectively, in an exponentially increasing manner. These just noticeable differences correspond to 75% correct judgements in the symmetrical two-choice tests. Group and individual thresholds and their distributions are presented. [This paper represents a report of a Master's thesis submitted to Western Reserve University, Cleveland, Ohio (January, 1958). The author is indebted to Professor Earl D. Schubert, Coordinator of Research of the Cleveland Hearing and Speech Center, for generous guidance.]
Effects of Noise Plus an O2-CO2 Gas on the Human Auditory Threshold
Authors: Spieth Walter
Published: September 2005

Misrahy and co-workers demonstrated that either intense sound or inspiration of oxygen-deficient air lowers the endolymphatic oxygen tension in the guinea pig, while inspiration of oxygen plus rich CO2 raises it. Also, Tonndorf showed that exposure to loud sound plus gas poor in oxygen produces more temporary threshold elevation than does the sound alone. These results led us to speculate that if human subjects breathed a mixture of oxygen plus rich (6.7%) CO2 before and during exposure to loud noise, the resulting temporary threshold elevations would be less than those following noise plus normal air. Fourteen ears were exposed to 6 min of thermal noise of 118 db SPL with normal air and again when the O2-CO2 mixture was breathed during and for 2 min preceding the noise. Before-and-after thresholds were obtained for a 4- and a 6-kcps tone. The noise-plus-gas treatment produced not quite one decibel less average threshold elevation than did the noise treatment. This difference is not statistically significant, and it is concluded that the “true” effect of breathing this O2-CO2 gas, during this noise exposure is negligible.
Beats in Cochlear Models
Authors: Tonndorf Juergen
Published: September 2005

Particle motion within the fluids of cochlear models occurs in elliptical orbits which are essentially Lissajou figures caused by interaction between the (forced) stapedial motion and the (induced) motion of the cochlear partition [J. Acoust. Soc. Am. 29, 558 (1957)]. In response to beats these orbits were found to wax and wane synchronously with the beat frequency. However, the alternating waxing and waning was not symmetrically centered about the orbital midpoints. In scala vestibuli, the orbits invariably expanded farther in the apical than in the fenestral direction. In scala tympani, the directions were reversed. Thus a partial rectification occurred within the cochlear fluids which, being synchronized with the beat rate, was of opposite direction in both perilymphatic scalae. This manifestation of energy at the beat frequency had to be due to some nonlinear property of the model, since no energy occurs at this frequency in linear systems. The nonlinear property was finally identified as the stiffness gradient of the cochlear partition. The resulting beat amplitude (re particle amplitude of a given set of primaries) was directly related to the steepness of the stiffness gradient. Furthermore, the beat amplitude reflected upon the shape of the gradient at various locations along the partition when beats (of a constant rate) were produced by different sets of primaries. [This research was supported in full by the U. S. Air Force under contract number AF 41 (657)-148, monitored by the School of Aviation Medicine, U. S. Air Force, Randolph Air Force Base, Texas.]
Velocity of Transient Traveling Waves on the Basilar Membrane
Authors: Elpern Barry S. , Schubert Earl D.
Published: September 2005

An extension of a method originally employed by Békésy in 1933 was used to estimate the velocity of the traveling wave at several points along the cochlear partition. The method consists of masking different portions of the basilar membrane at the two ears so that the wave produced by a simultaneous click at the two ears would emerge from the masked portion of one ear sooner than from the other. As a result, the click appears to lateralize toward the side which emerges sooner. Now, if one delays the click delivered to the “leading” side by an amount sufficient to “center” the subjective click, the amount of delay introduced gives an estimate of the original difference in time of emerging and hence of the time taken to travel the portion of the membrane represented by the difference in cutoff frequency of the two masking noises. Such measurements were taken for 14 overlapping half-octave segments of the basilar membrane on seven subjects. Measurement was not possible below 1000 cy; hence, direct comparison with Békésy's stroboscopic observation on transient traveling waves is possible only at one point. Velocity measurements are compared with other available estimates.
On the Conceptual Necessity and Use of Perfect Couplers in Schematic Diagrams
Authors: Trent Horace M.
Published: September 2005

If the criterion is adopted that a schematic diagram of a system must give a complete representation of all the physical or engineering principles involved including a specification of the characteristics of each part and how the various parts are joined to form the system, it follows that perfect couplers must be included in the list of items available to anyone creating schematic diagrams. It is shown by examples that perfect couplers produce their action by the imposition of constraints and that the set of constraints for a given coupler imposes the condition of no power loss or gain. Conversely, if a conceptual device is known to be a perfect coupler and some constraints are known, then the remaining ones can be deduced. It is shown that perfect couplers may be of two types and that examples of each type are common. It is further pointed out that perfect couplers present no problem if an investigator is always aware of their possible existence. The discussion closes by showing that couplers can be dealt with mathematically in a systematic manner.
Comparison of Stress Response and Fatigue Test Results under Random and Sinusoidal Acoustic Loading
Authors: Belcher Peter M. , Eshleman Arthur L. , Van Dyke Joseph D.
Published: September 2005

For several configurations of aircraft structure, measured values of stress response under random loading are compared to those computed from sinusoidal stress response data. Predictions of long-life allowable random loads are made from fatigue test data obtained under sinusoidal loading. These predictions are compared with those inferred from failures in accelerated tests under random forcing. It is concluded that the convenient and relatively inexpensive sinusoidal test provides a simulation of random loading of sufficient accuracy for use in the design of structural components.
Experimental Use of Electrical Network Theory in Complex Linear Mechanical Structures
Authors: Stewart David A.
Published: September 2005

Linear mechanical systems may be analyzed according to electrical network theory. The analysis may proceed from empirical mechanical impedance data without detailed knowledge of the masses, dampers, and springs involved. The analysis can then predict reduction of vibrational response due to certain experimental changes such as the addition of a tuned, damped vibration absorber. This discussion also describes how the mechanical impedance of a tuned, damped vibration absorber may be calculated using four-pole parameters.
Graphical Method of Determining the Ratings of Shaker-Amplifier Systems for Sine Wave and Random Noise Vibration Testing
Authors: Tillou F. M. , Metzgar K. J.
Published: September 2005

A graphical representation of audio amplifier power capabilities is developed which enables the quick determination of the maximum sine wave or random volt-amperes which can be delivered to a complex impedance load. Amplifiers considered are class AB1 triode, class AB2 triode, and class AB1 tetrode types. The amplifier chart is of such form that load voltampere requirements may be superimposed on it to determine performance. The effects and use of series swamping resistance for decreasing amplifier plate dissipation limitations are discussed. Typical sine wave and random noise shaker power requirements are presented and methods of plotting them on the amplifier chart are developed which enable determination of maximum shaker-amplifier system ratings.
Phenomenal Tonal Memory Covering Retention between 64 and 3072 cps
Authors: O'Brien Cyril C.
Published: September 2005

By a process of screening 114 music students with superior ability for tonal memory, 24 were found to possess a tonal memory span greater than 6 tones on a test of 30 paired non-melodic tonal patterns specially designed by the author for measuring a 7 to 12 span retention. Only 2 had a 12-tone memory span for each of the three areas of the piano, namely, 64 to 192 cps, 256 to 768 cps, and 1024 to 3072 cps. Two of the students possessed a 12 tone memory span, but for only one of the three areas. The maximum span given in the test was double the 6 tone upper limit span of the Seashore—Series B Tonal Memory Test. Statistically speaking, the 4 with the 12-tonal memory span are 3 sigmas or more beyond the mean. The findings of this experiment indicate that unusual tonal memory is not necessarily the same in extent for all pitch areas of the piano.
Mechanisms of Frequency Response Extension
Authors: Creelman C. Douglas
Published: September 2005

There is considerable evidence that subjects in a traditional psychophysical experiment act as narrow-band receivers tuned to the frequency of a known sine-wave stimulus. Obviously wave forms in real life are complex rather than simple, and the wave forms we hear can seldom be predicted exactly. A series of experiments was conducted attempting to arrive at a model for hearing when the sine-wave signal to be presented is not absolutely predictable, but might be one of two alternative frequencies. For each experimental run of 100 trials, one of two possible tones was randomly selected for presentation on each trial in a two-alternative forced-choice detection situation: one of the tones was always 1000 cy and the other had a frequency difference of 20, 100, 200, or 500 cy above or below, giving eight pairs of tones investigated. The intensities of the tones were equated for detectability in a standard single tone preliminary detection experiment. All eight pairs were run at two different levels of background noise using different signal intensities. Under these conditions differential predictions of observers' behavior with an uncertain signal can be made within the framework of the theory of signal detectability for a number of alternative models calculated to account for the extension of frequency sensitivity. The data are compared to predictions from a scanning model, a multiplex model, a threshold model, and a variable band model. (This research was carried out under sponsorship of the Operational Applications Laboratory, Air Force Cambridge Research Center and Evans Signal Laboratory, Signal Corps Engineering Laboratories, Fort Monmouth, New Jersey.)
Backward Masking by an Intense Burst of Noise
Authors: Pickett J. M.
Published: September 2005

An experiment was carried out to measure the auditory masking effect of an intense noise burst on a preceding weak stimulus. A short 1000-cycle tone preceded a burst of white noise by a variable silent interval. The threshold intensity level of the tone was taken as a measure of the masking provided by the noise burst. The effects were examined of combinations of the following conditions: tone-durations of 5, 10, 25, and 50 msec; silent intervals of 0, 2, 5, 10, 25, and 100 msec; and noise burst levels of 75, 95, 105, 115, and 125 db SPL. Appreciable elevations of tone threshold were observed for tone-duration less than 25 msec, with silent intervals less than 25 msec, and at noise burst levels above 95 db. Threshold elevations increased progressively as noise burst level was increased. The latter effect increased with shorter tones and with shorter silent intervals.
Binaural Masking of Noise by Noise
Authors: Tobias Jerry V. , Curtis Jack F.
Published: September 2005

Studies of binaural signal selection for various contextual stimuli have been reported by a number of investigators. It is necessary to know, in an eventual complete analysis of the auditory system, whether binaural selection mechanisms operate differently on noncontextual signals. As a first approach, two broad-band noises (N1 and N2) were presented binaurally such that one-second segments of N2 were immersed in N1, which was much longer. N1 was identical at the two ears. N2, however, could be presented in several ways: in phase at the two ears, 180° out of phase, with an interaural time disparity of 500 μsec, or heterophasic. Subjects responded when they heard any change in the character of the signal, and from these responses, masked thresholds of N2 were plotted as a function of N1/N2. Results for the in-phase condition compare predictably with the monaural results reported by Miller (1947). Selection ability for all the various conditions of noncontextual signals is compared with that for spondees under similar conditions. (Part of this research was supported by funds from the National Science Foundation.)
Experiments on the Bone-Conduction Threshold in a Free Sound Field
Authors: von Gierke H. E. , Nixon Charles W.
Published: September 2005

Earlier investigators of the free-field bone-conduction threshold occluded the auditory meatus with plugs and muffs and reasoned by various arguments that the real-ear attenuation obtained was less than the attenuation provided for air-conducted sound. The conclusion was that the sound perceived reaches the auditory system via bone conduction, i.e., not through the auditory meatus. The present experiments are a check on these conclusions for the higher frequencies. With the auditory canal occluded, the whole skull or sections of it, excluding the muffs, was covered with a 2-in. layer of absorbent cotton. A higher free-field threshold with the cotton indicated that without cotton the sound was reaching the ear via bone. (The SPL over the muffs was not altered by the cotton.) Cotton over the face and back of head raised the bone-conduction threshold by 10 to 18 db (2000 to 8000 cps). Bone conduction thresholds measured previously were confirmed from 1000 to 8000 cps. Front and back of the head were approximately of equal sensitivity with respect to bone conduction. Covering only the side of the head facing the sound source raised the threshold more than covering the “shadow” side alone. The results suggest a possible method for improving the effectiveness of special noise attenuating devices.
Intensive Differential Thresholds for Octave Band Noise
Authors: Small Arnold M. , Bacon W. Edward , Fozard James L.
Published: September 2005

This study investigated intensive differential sensitivity for bands of noise as a function of center frequency of the band and sensation level. Eleven untrained subjects and three trained subjects participated, using the method of limits. Results showed that differential thresholds for the low octave band (127–255 cps) of noise were larger than those for a middle octave band (1040–2080 cps) and high octave band (4080–8160 cps) of noise. The middle and high bands in turn yielded differential thresholds that were larger than those for a wide band noise. Increasing the sensation level served to increase differential sensitivity for all bands, especially at low sensation levels. The size of the differential thresholds for the octave noise bands were similar to those obtained for pure tones whose frequencies approximated the center frequency of the noise band. Comparison of the differential thresholds for wide band noise to those obtained by other investigators showed close agreement.
Noise-Reducing Line Microphone for Frequencies below 1 cps
Authors: Daniels Fred B.
Published: September 2005

A novel type of line microphone is described that utilizes a distributed input primarily for the purpose of improving signal-to-wind-noise ratio. The input to the transducer takes place through a tapered pipe that is coupled to the atmosphere by means of acoustical resistances uniformly spaced along the length of the pipe. The relationship between the resistances of the openings and the longitudinal variation in the characteristic impedance of the pipe is so adjusted as to make the system nonreflecting. Microphones of this type have been constructed for use in the frequency range below 1 cps for the purpose of detecting atomic explosions at great distances. A prototype 1980 ft long with 100 openings is described, which gives an improvement in the signal-to-noise ratio of as much as 20 db under severe wind conditions.
Listener Reaction to Stereophonic Reproduction by Reflected Sound
Authors: Sioles George W. , Carlisle Richard W.
Published: September 2005

Comparisons were made by numerous observers of the stereophonic perception of direct versus reflected sound. For conventional direct sound, two loudspeakers having wide frequency response were used at spacings of from six to fifteen feet, directed toward the listeners. For reflected sound, equivalent dual sound sources were used placed back-to-back near the walls of a room in which it was desired to establish a stereo sound field. The frequency response of the latter system was equalized to have the same apparent response as the conventional system. Many of the tests were conducted behind a sound permeable screen. Listeners were mixed in their ability to identify the reflective systems and in their preference for one system over the other, although they reacted favorably to both systems.
Attenuation of Spherical Helmets
Authors: Raelson V. J. , Burkhard M. D. , Benson R. W.
Published: September 2005

The attenuation of jet noise obtained by the use of a complete enclosure helmet when worn by a human observer has been investigated. The measurements were made in the reverberant field of a synthetic jet noise source. Helmets were essentially spherical in shape with a diameter of 14 in., and were strapped to the body of the observer, together with a seal of foam rubber. A helmet constructed of clear lucite produced over-all attenuations of about 20 db for the frequency range 75 to 9600 cps. Results indicated that low-frequency noise entered the helmet through the seal at the shoulders. Liquid (water) seals increased the attenuation in the two lower octave bands by about 9 db. A minimum in the attenuation occurred in the 1200- to 2400-cps octave band. In this frequency range the wavelength of the sound is the order of 12 to 1 times the sphere diameter. For a stiffer sphere of thin gauge steel the band of minimum attenuation was one octave higher. The attenuation increased in the highest octave bands and could reach levels of 35 to 40 db in the highest two bands with absorbing material in the helmet. The same type of helmet, when sealed to a wooden form, molded to fit the shoulder piece was capable of an over-all attenuation of 28 db. Measurements of attenuation by both physical measurements and subjective threshold shift were in substantial agreement. (This research was supported in part by the U. S. Air Force, Wright Air Development Center, Wright-Patterson Air Force Base, Ohio.)
Model Experiments Relating to Sound Propagation in Shallow Seas
Authors: Wood A. B.
Published: September 2005

The object of model experiments on sound transmission in the sea is to supplement the somewhat empirical approach to the subject on a full scale. One serious difficulty in transmission research in the sea is that the conditions of the experiment are frequently not under our control—various perturbing factors are present which may mask the effect it is required to detect. The paper deals with the design of tanks, sound absorbers, transducers, etc., for small-scale work at frequencies of the order of 0.5 to l Mc/sec. This equipment has been used to record amplitude and phase of the received signal and to study the following factors influencing sound transmission: (1) nature of the bottom, (2) mean temperature and temperature gradients, (3) surface waves, and (4) depth of water. A study has also been made by visual observations of the sound distribution on the bottom and surface using (a) chemical methods, (b) abrasive methods, and (c) photography of “wedge” interference fringes on the water surface. These experiments reveal the complex nature of the interference phenomena occurring in the water. A new scanning technique has also been developed which gives a picture of a vertical section of the sound field (longitudinal or transverse) in the “model” tank. In this method the sound received is used to modulate the brightness of a cathode ray spot, and a “picture” record is made of the sound-intensity variations of the sound-field in the water. Comparisons have been made in this way between rocky and sand/mud bottoms.
Information Processing and Acoustic Systems
Authors: Loda Charles J.
Published: September 2005

This paper presents a summary of a survey of theoretical and experimental methods employed in the analysis and synthesis of acoustic systems. The work has been conducted under the sponsorship of the Office of Naval Research. Although primary emphasis has been placed on underwater acoustics, the survey has drawn heavily from related work in the fields of radar, optics, geophysics, radio astronomy, and electromagnetic communications. The conceptual model which has guided the program involves space-frequency-time interrelationships existing within information “fields.” Selection of analytical and experimental methods has been based on their relative utility and efficiency in specifying space-frequency-time interrelationships in order to (a) improve understanding of acoustic systems and processes and (b) improve capacity to perform specific functions. Morphological analyses of instrumentation which may be employed in exploring space-frequency-time parameters will be discussed.