bluuebunny/crossref_metadata_2025 huggingface dataset:
Rocket-Engine-Noise Problems Associated with the Design of Ground Electronic-Equipment Rooms for Multimillion-Pound-Thrust Space-Booster Launch Facilities
Authors: Peverley Richard W. , Baratono John R.
Published: November 2005

Ground electronic checkout equipment for multimillion-pound boosters, such as TITAN III and SATURN V has been located in the close proximity of the vehicle, thus placing this equipment in the intense nearfield rocket-engine noise. Since ground electronic equipment is generally more sensitive to acoustic and vibration excitation than its airborne counterpart, the structural design of equipment rooms must provide sufficient noise reduction to assure good reliability and structural integrity during a launch. This paper contains a description of these problems. In addition, case histories of existing designs are included and a general approach to the problem is offered The problem is divided into three areas: noise-level prediction, equipment-fragility estimates, and equipment-room design. The different problems associated with fixed installations and transporters, where weight is a critical factor, are also discussed. Measured data are offered to substantiate calculations in some cases. This paper shows how approximate solutions are satisfactory for most designs and where more exact solutions are required for other cases.
Effect of Sensorineural Damage upon the Cat's Intensity-Difference Threshold
Authors: Elliott Donald N.
Published: November 2005

Eleven cats were exposed to pure-tone stimulation intended to produce moderate hair-cell damage. Behaviorally defined pre- and post-stimulation intensity-difference thresholds were then compared to see whether recruitment would be evident. Following this, the animals were sacrificed and their ears sectioned and examined to determine the extent of the damage. While varying degrees of damage were evident from the animals' behavioral audiogram and from the histopathological data, there was no evidence of a decrement in their intensity-difference thresholds. This lack of relationship between the discrimination and the histopathological data is discussed.
Evolution of Vertebrate Hearing
Authors: van Bergeijk Willem A.
Published: November 2005

The morphological kinship of the lateral-line organ and the various maculae of the inner ear has long been recognized. Recent investigations of the ultrastructure of the sensory cells in the organs and maculae have strongly reinforced the belief that the acoustico-lateralis system should be considered a unitary sensory system. Its several subsystems have special peripheral adaptations to deal with particular forms of mechanical stimulation, but use the same fundamental sense cell, the hair cell. Since the lateral line has been shown to be a displacement detector that responds to acoustic stimulation in the near field only, the question arises how the farfield, pressure-sensitive ear has evolved. It is proposed that the middle ear be regarded as a pressure-to-displacement transformer. Its earliest evolutionary form is the fish's swimbladder, which generates a local near field inside the fish in response to pressure waves. This local near field is then transmitted to the inner ear, through the body tissues in primitive forms, or via special links in higher forms. In terrestrial vertebrates, the eardrum evolves; it is always linked by special ossicles to the inner ear. In frogs, both forms of the middle ear are found in the tadpole and adult stages, respectively; in metamorphosis, the aquatic middle ear (lung) is replaced by the terrestrial form (drum membrane).
Cavitation Thresholds of Superfluid Helium
Authors: Finch R. D. , Kagiwada R. , Barmatz M. , Rudnick I.
Published: November 2005

The superfluid properties and the restrictions on possible types of nuclei make liquid helium especially interesting for cavitation studies. Previous measurements of the tensile strength of liquid helium, using static techniques, have led to values of 0.1 to 0.3 atm, which are considerably lower than theoretical estimates, as made for instance from the Van der Waals equation. This paper reports the production of ultrasonic cavitation in liquid helium over the temperature range 1.2° to 2.3°K. Visible bubbles were observed only at power levels much greater than threshold. A pair of identical transducers, resonant at 90 kc/sec, were used to generate cavitation, listen to the accompanying noise, and simultaneously measure the threshold of acoustic pressure, using a reciprocity technique. The onset of noise was used as a criterion of the threshold. Determined this way, the threshold is even lower than indicated by the static techniques, being very close to the liquid pressure head, except near the λ point where it rises sharply to values not exceeding 0.01 atm. This λ-point behavior is similar to that of other properties of the superfluid, such as the specific heat, with which it is possible that some correlation exists. [Work supported by the U. S. Office of Naval Research.]
Experiments on the Rijke-Tube Phenomenon
Authors: Friedlander Melvin M. , Smith T. J. B. , Powell Alan
Published: November 2005

Experimental investigations of the Rijke-tube phenomenon have used the same basic apparatus as that used by its discoverer in 1859—an open-ended vertical pipe containing a heated gauze in its lower half. Difficulties arise when this configuration is used for quantitative tests since the standing-wave distributions of the tube and its environment interact unless elaborate precautions are taken; consequently, the acoustic output of an experimental assembly of this form varies with its location. To vitiate this acoustic coupling, an inversion of the classical configuration was designed in which a water-cooled horizontal tube containing an electrically heated grid was terminated at each end by sliding pistons. A metered airstream passed through narrow annular ports in the piston heads, one of which housed a calibrated microphone. Thus, an assembly was obtained in which all the parameters connected with this thermoacoustic phenomenon could be continuously varied with no interruption of the test procedure. Maximum and minimum limiting airflows and thermal inputs for the resonant condition were established for all heater locations. Measurements were made of the oscillation amplitude and the data are shown to be consistent with existing theories, within the scope of necessary assumptions relating to the heat-transfer mechanism at the grid.
Acoustical Behavior of Segmented Ceilings
Authors: Veneklasen Paul S.
Published: November 2005

Understanding the phenomena associated with segmented ceilings or arrays of panels will help the acoustical designer to avoid severe problems. A study is presented using acoustical- and optical-modelling techniques to disclose the following factors: (1) frequency discrimination of the individual panel; (2) frequency discrimination of an array of panels; (3) interference of sound reflected from the panel array with reflection from a solid surface above; (4) interference effects in stepped panel arrays; and (5) focusing of concave panels and arrays.
Subjective Responses to Nonexponential Reverberation and Delayed Low Frequencies in Concert Halls
Authors: Atal B. S. , Schroeder M. R.
Published: November 2005

This paper presents the results of subjective tests related to hearing in concert halls. The influence of nonexponential decay on the subjectively felt reverberation was investigated by comparing non-exponentially reverberated sound signals with exponentially reverberated ones with different reverberation times. Two types of nonexponential reverberation were investigated: (1) reveration with different initial and final decay rates and (2) reverberation with increased or decreased energies in the direct sound and early reflections. Subjects were asked, in paired-comparison tests, which stimulus in each pair sounded more reverberant. In another experiment, low frequencies (below 300 cps) were eliminated from the direct component in the test stimulus and added, with a delay, to the reverberation. The test stimuli were compared with reference stimuli whose low-frequency components were attenuated by specified amounts. The subjects were asked which of the two stimuli had more low frequencies. Speech and music were used as test signals. The different reverberators and filters used were simulated on a digital computer.
Synthesis of Directive Arrays: Realization
Authors: Lowenstein C. D.
Published: November 2005

The directional-response function of a linear array of uniformly spaced point sources is uniquely determined by the excitation coefficients of the array. The magnitude of the response function is a cosine series in the phase shift between signals from adjacent sources. In this paper, the converse problem—that of determining the excitation coefficients of an array so that the response of the array will be equal to a given cosine series—is examined. Not every cosine series can be realized as the response of an array, since the magnitude of the response function is nonnegative. Any nonnegative cosine series is factorable into a product of elementary cosine-series factors, each of which corresponds to a 2- or 3-element array. These simple arrays are then compounded into a multielement array having the specified response function. Although the response of the product array is not altered by a mirror-image reversal of one of its factors, the excitation coefficients are changed. Thus, there can be several arrays having the same magnitude of directional response but having different excitation coefficients. Criteria for choosing among these equal-but-different arrays, such as phase response and spread of excitation coefficients, are examined.
Experience with the Flextensional Transducer
Authors: Akervold O. L. , Fox C. C.
Published: November 2005

“Flextensional” is a contraction of flexural and extensional. A flextensional transducer comprises a flattened shell undergoing flexural vibration, driven from the inside by a column of piezoelectric ceramic that is undergoing longitudinal, or extensional, vibration. The first design methods for transducers of this type were due to W. J. Toulis. This paper discusses the measured and predicted performance of several small flextensional transducers and a 7-element line array of them. A vibrational-mode study of the shell flexture, its dependence upon the driving column, and its relation to the measured performance is presented.
Solion Linear Acoustic Detectors of the Polarized Cathode Type
Authors: Larkam C. W.
Published: November 2005

Solions are electrical components involving charge transport by solution ions as contrasted to electrons, holes, or gas ions. Four general types of solion acoustic transducers may be distinguished on the basis of mechanism underlying the transducer action. One of these, the polarized cathode type, offers a combination of advantages, which includes low threshold pressure, high power gain, stable zero, and direct-current transmission. Individually constructed models with a nominally linear pressure response have been used successfully in the study of infrasonic disturbances transmitted through the earth and atmospheres, as well as under water. Yet, design and construction methods have not been perfected to a degree that would insure wide usage. The relatively sluggish motion of the charge carriers in the electrolyte of the detector is at the same time a necessary condition for transducer action and a factor limiting the dynamic response. A theoretical analysis of the transducer action is presented to explain the observed behavior of existing devices of this type and to indicate what may be expected from detectors having the benefit of more refined fabrication techniques. [Work supported by the U. S. Office of Naval Research.]
Flat, Spiral, Direct Radiator Transducer
Authors: Rich Stanley R.
Published: November 2005

A wide-range direct radiator reproducer is presented, comprising a flat, rectangular, spiral winding bonded to a thin membrane, situated in a flat, orthogonal magnetic field. Design of structure and choice of permanent magnet materials provide flux density above 1500 G, resulting in efficiency equal to present-day low-efficiency reproducing systems. Frequency response is free of major or minor resonant and antiresonant peaks and nulls from 100 to 9000 cps. Oscilloscope photographs demonstrating the faithfulness of acoustic-output response to single Gaussian-pulse inputs are presented. Equivalence to the electrostatic transducer is discussed. Choice of parameters that provide conventional impedance (6 to 10 Ω) is analyzed.
In Situ Calibration of Microphones
Authors: Van Houten John J.
Published: November 2005

In-place calibration of microphones flush mounted to vehicle structures presents a unique instrumentation requirement. Numerous devices have been designed for calibration at near-operational sound levels under field conditions. One configuration using an electrodynamically driven coupler has been designed for in-place calibration of microphones flush-mounted to space-vehicle structures. It provides sound levels in excess of 150 dB (re 0.0002 dyn/cm2) with a response that is uniform at frequencies from 5 to 500 cps. A control microphone housed in the coupler greatly simplifies the procedure and provides the precision required by the measurement situation. Systems with essentially a “push-button” calibration are desirable durng preflight checkout of aerospace vehicles. Voltage insertion betwen a cathode follower and a condenser microphone provides a system that is compatible with this on-site pre-calibration requirement. These calibrations may be readily performed at frequencies from 5 cps to 10 kc/sec at levels comparable to those expected during flight operations.
Large-Area Pneumatically Driven Bass Reproducer
Authors: Rich Stanley R.
Published: November 2005

A large-area, lightweight piston radiator is coupled pneumatically to a much smaller cone-type bass driver by means of a small volume of air trapped between radiator and driver. The piston radiator and the driver are not physically connected to one another. The piston radiator is so suspended that the resonance frequency of piston mass with suspension stiffness is below audibility. The radiator itself is designed and treated so that its own first self-resonance mode is above the bass-reproduction range in which it is employed. The basic design provides a considerable increase in radiation resistance per unit area, which results in improved bass reproduction. Theory and system equivalence to an ideal horn are discussed. Practical realizations and results are presented.
Long-Range Shallow-Water Transmission Measurements
Authors: Mackenzie K. V.
Published: November 2005

Recent measurements were made in 25-f (fathom) water with 15-min CW tones of 350-, 700-, and 1300-cps sound transmitted from an anchored ship. The sound was received on an anchored vertical string of 14 hydrophones spaced 10 ft apart. The measurements were made to a range of 80 kyd over selected paths for which the thickness of the subbottom had been previously surveyed acoustically. The mean signal level at each hydrophone can be determined with an estimated accuracy of 1 dB. These mean levels define the CW sound field accurately for the first time. They exhibit a definite significant dependence on hydrophone depth as could be expected from the normal-mode theory. The signal-level fluctuations and frequency spreading agreed with earlier measurements [J. Acoust. Soc. Am. 34, 67 (1962)]. The sound levels averaged from the surface to the bottom agree with the ray theory [J. Acoust. Soc. Am. 33, 1505 (1961)].
Acoustic Propagation in the Nova Scotian Sound Channel
Authors: Macpherson J. D. , Fothergill N. O.
Published: November 2005

Long-range acoustic-propagation measurements have been made in the Nova Scotian sound channel, using explosives as broad-band sources. This sound channel is of seasonal origin with its axis between 150–300 ft, depending upon the time of year. The over-all water depth is about 600 ft. The attenuation coefficients measured in these experiments have the same form of frequency dependence as those measured in the deep sound channel but are an order of magnitude larger at low frequencies. The mechanism producing these losses is thought to be the same in both cases; that is, scattering out of the channel by velocity inhomogeneities in the water and the differences in magnitude are ascribed to the smaller scale of the Nova Scotian sound channel.
Some Deep-Water Sound-Transmission Paths South of Cyprus
Authors: Baxter Lincoln , Brockhurst Robert , Hays Earl E.
Published: November 2005

Deep-water sound-transmission paths extending in range through two convergent zones in the Mediterranean Sea south of Cyprus have been recorded by a new method that permits high-resolution, nearly continuous observation of travel-time difference from a rapidly moving sound source as a function of elapsed time. Striking confirmation of travel-time relations discussed by previous authors [M. Ewing and J. L. Worzel, Geolog. Soc. Am., Mem. 27 (1948); C. B. Officer, Introduction to the Theory of Sound Transmission (McGraw-Hill Book Co., Inc., New York, 1958); T. Arase, J. Acoust. Soc. Am. 31, 588–595 (1959); F. E. Hale, ibid. 33, 45–464 (1961)] are presented. The paths near Cyprus differ from those in the Atlantic because the Mediterranean skip distance is about 20 miles and the axis of the deep sound channel is only about 1000 ft deep. A number of additional features of the bottom-reflected path are clearly indicated. [Work supported by the U. S. Office of Naval Research, contract No. 4029.]
On the Calculation of Focusing Zones along the SOFAR Axis
Authors: Hirsch Peter , Shear Marcia
Published: November 2005

The present state of the theory of SOFAR propagation still leaves unanswered the question of whether or not there exist focusing zones along the channel axis. We have gained some insight by considering a continuous-wave point source located in an ocean in which the sound speed varies as c2=c02(1−α2z2)−1. Here, c0 is the sound speed on the axis, z is the vertical distance from the axis, and α specifies the width of the channel. It is known that in this model the near-axis rays focus at regular intervals. It is also known that the normal-mode solution is a slowly converging mode series, of which the sum of the lowest-order terms shows the same focusing intervals as the near-axis rays. We have summed the series on a digital computer and shown that, even though the sum of the low-order modes is a smooth function of range, with the expected regularly spaced focusing zones, the addition of the high-order modes to form the complete sum results in a violently varying function, with no discernible focusing zones. We use this and other, more-qualitative results to support the argument that the CW theory is inappropriate for predicting the amplitude of the SOFAR crescendo and that a transient analysis is required. [Work supported by the Bureau of Ships, U. S. Navy.]
Underwater-Sound Ray and Refractive-Anomaly Plots Made with an Analog Computer
Authors: Beam John P.
Published: November 2005

A computer program has been developed that traces sound rays and gives a continuous value for the refractive anomaly. The program uses the second derivative of the sound velocity with respect to depth as a description of the medium, and this quantity is developed by a function generator as a function of depth. Ray and anomaly plots have been made with a simulated projector located at various depths. The depths were chosen so that rays emitted by the projector would pass horizontally through depth layers where the second derivative is large and negative, large and positive, and zero. The plots show that divergence zones arise when rays travel horizontally for long distances in layers where the second derivative of the velocity with respect to depth is large and negative. Convergent effects occur when rays travel horizontally for long distances in layers where the second derivative of the velocity with respect to depth is large and positive. Refractive effects are small only when the rays encounter no regions of extreme values of the second derivative or when the influence of one extreme region is nullified by another.
Experimental Observations on a Negative dc Resting Potential in the Cochlea
Authors: Butler Robert A.
Published: November 2005

A dc resting potential found in the organ-of-Corti region was recorded in guinea pigs. The round-window membrane was removed and a glass pipette filled with Ringer's solution was inserted through the basilar membrane. A dc potential of −80 to −90 mV could be recorded. The diameter of the tip of the pipette was usually 1 or 2 μ. However, a resting potential could be recorded by using pipettes whose tip diameter was as large as 25 μ, which suggests that this is an extracellular potential. Increasing the K+ concentration in scala tympani served to reduce the potential, with potential change being a linear function of log K+ concentration. This potential, as well as the endocochlear potential and the cochlear microphonics, was recorded during prolonged asphyxia. The course followed by the cochlear microphonics during asphyxia was similar to that plotted for the algebraic difference between the two dc resting potentials. This difference is considered to represent the dc-potential gradient across the reticular lamina. The relation of this negative resting potential to other electrical events in the cochlea is discussed.
Vestibular Response to Sound: Single-Unit Recording from the Vestibular Nerve in Fenestrated Deaf Mice (Df/Df)
Authors: Mikaelian D. O.
Published: November 2005

Deaf mice of the Df/Df strain have degenerated cochleae but histologically-normal vestibular structures. After fenestration of the horizontal semicircular canal, tones and clicks were delivered to the fenestrated ear through the external auditory canal, using a closed sound system. Single units of the vestibular nerve were picked up by tungsten microelectrodes. Single-unit responses were obtained only in fenestrated animals and only for frequencies from 80 to 4200 cps. Threshold was best for 1500 cps, and was at 78 dB re 0.0002 dyn/cm2. Click responses were also obtained. Some units with spontaneous activity were driven by tone bursts; others were inhibited. Spontaneous activity was present in single units of nonfenestrated mice but was not altered by tones or clicks, and no units were driven by either type of sound stimulus. [Work supported by grants from the National Institute of Neurological Diseases and Blindness, National Institutes of Health, U. S. Department of Health, Education, and Welfare, and by the Alfred P. Sloan Foundation.]
Excitation and Inhibition of Primary Auditory Neurons in the Little Brown Bat
Authors: Frishkopf Lawrence S.
Published: November 2005

Single-unit activity has been recorded from a total of 80 primary auditory neurons within the internal meatus of the bat Myotis l. lucifugus. The frequency to which an individual unit was most sensitive (“best frequency” of the unit) was always found in the interval 10 to 85 kcps; the best frequencies of about 23 of the units lay between 40 and 80 kcps. Sensitivity of a unit was sharply dependent upon frequency. The rise in threshold for frequencies above the best frequency of the unit was abrupt (about 300 dB/octave), while for frequencies below the best frequency it was somewhat more gradual (about 100 dB/octave). In over 80% of the units tested, evoked activity could be inhibited by frequencies just above the excitatory range of the unit. Some units were inhibited by frequencies below, as well as above, the excitatory range, though this effect was more difficult to observe. The latencies of excitation and inhibition were sufficiently alike to suggest that inhibition of this type cannot be under efferent control. The proximity of excitatory and inhibitory frequencies suggests an inhibitory interaction between elements in adjacent portions of the cochlear partition. Such inhibition, occurring in a relatively broadly tuned mechanical structure, tends to narrow the range of frequencies with which a single unit can be excited.
Model of the Encoding Function of Primary Auditory Neurons
Authors: Mundie J. Ryland
Published: November 2005

A model of the encoding function of primary auditory neurons has evolved from analysis of electrophysiological data. The model assumes that a primary neuron is exposed to cyclical inflections of a small length of the basilar membrane and that the neuron possesses a thresholding property that interacts with these inflections. It is also assumed that the neuron responds to inflections in one direction only and, therefore, possesses some degree of phase locking. The threshold of the neuron is not time-constant, but has the general shape of a decaying exponential of the form e−kt (t=0 indicates time of last firing of this neuron). The value of k is “noisy,” fluctuating from one discharge to the next, but maintains some average value. The average value of k determines whether the neuron encodes frequency, amplitude, or a combination of both. The average value of k is influenced by the immediately preceding average-pulse-rate output of the neuron, which gives to the neuron some of the properties of a feedback system. Equally important is the concept that a single neuron must function as a part of a population and that accurate retrieval of information is accomplished by spatial averaging of the population. Response of the model to auditory signals is quantitatively compared to electrophysiological data.
Studies of the Vortex-Whistle Periodic Flow
Authors: Chanaud R. C.
Published: November 2005

Experimental studies of the periodic motion associated with the vortex whistle were made in both air and water. It was found that the motion is a result of the hydrodynamic instability of the swirling flow. The critical Reynolds number was approximately 300, well into the laminar-flow regime. This critical Reynolds number depended primarily on the ratio of tangential to axial velocities, which may be characterized by a Strouhal number. The periodic motion, once established, can be described in terms of a tuned amplifier oscillator and appears to have several features in common with the vortex-shedding behind cylinders. Some studies were made of the periodic motion found in cyclone dust collectors and it was observed to be quite similar to that in the vortex whistle. Comparison was made with the unsteady motion associated with vortex-bursting on delta wings and the remarkable similarity of flow patterns suggests that this motion is also the same.
Revised Grain-Scattering Formulas and Tables
Authors: Papadakis Emmanuel P.
Published: November 2005

The current theory of Rayleigh and stochastic phase scattering of ultrasound in polycrystalline materials is reviewed and compared with (1) former theory and (2) experiment. It is found that, when the grain size is evaluated properly, the current theory accounts rather well for the scattering component of the ultrasonic attenuation of polycrystalline materials. A tabulation is made of the coefficients of attenuation caused by scattering for various materials. These coefficients multiplied by a factor involving the grain size and a factor involving a power of the ultrasonic frequency give the attenuation.
Vibration-Data Analysis. Part II. Engineering Applications
Authors: Bendat Julius S.
Published: November 2005

Various engineering applications for vibration-data analysis are discussed. Included will be input-output relations through linear systems, prediction of extreme properties, and generation of vibration-test specifications.
Numerical Procedure for Shock and Fourier Analysis
Authors: O'Hare George J.
Published: November 2005

This paper describes and derives a numerical integration technique presently being used at the U. S. Naval Research Laboratory for problems in structural dynamics. The method is capable of computing damped and undamped shock spectra, Fourier sine, cosine, and regular Fourier integrals, and the inversion of the Fourier integrals. It can also be used to calculate Fourier-series coefficients, and has been extended to nonlinear differential equations.
Forced Vibration of a Two-Degree-of-Freedom System with Combined Coulomb and Viscous Damping
Authors: Yeh Gordon C. K.
Published: November 2005

An exact solution for steady forced vibration of a two-degree-of-freedom system with two viscous dampers and one Coulomb damper subjected to a simple harmonic ground excitation is presented. The solution is valid for motions without standstill. The results are expressed in terms of nondimensional parameters that allow evaluations of response amplitudes and phase angles for various frequency ratios, mass ratios, and amounts of viscous and Coulomb damping. In the limits, the resulting expressions agree properly with those for a system without the Coulomb damper and with Den Hartog's expressions for a single-degree-of-freedom system with a Coulomb damper. Formulations for the special case of a two-degree-of-freedom system with a Coulomb damper (without viscous dampers) are also obtained. Numerical results are presented to compare the exact and approximate solutions for a single-degree-of-freedom system with combined Coulomb and viscous damping. The exact solution obtained in this paper can be used to estimate the accuracy of approximate methods for analyzing more-complex systems containing Coulomb damping.
Balancing Flexible Rotors
Authors: Eubanks R. A. , Muster Douglas
Published: November 2005

The effects of flexibility on balancing may be small for many rotors that operate well below their first critical speed. The effects, however, are always present and, when very small balancing errors are required to produce an acceptable noise level, even small effects can become important. As a result of these considerations, it is apparent that the need exists for the development of rotor-balancing methods that take into account the inherent flexibility of the rotating devices involved, and that can be used to mitigate the undesirable effects introduced through this flexibility. The resulting operations are called “flexible balancing.” The procedures are not intended to completely eliminate the distributed unbalance in the shaft; they are instead pointed toward the reduction of deleterious effects within the speed range to be experienced by the rotor. Several proposed procedures are presented and discussed. The results of experimental and analytical evaluation are reported and compared.
Mechanical-Impedance Measurements on the Human Body and Their Use in Biodynamics
Authors: von Gierke Henning E.
Published: November 2005

This lecture reviews some of the mechanodynamic properties of human body tissue and of the whole body structure and the measurement methods applied in this research area. Impedance data calculated recently from measurements made in the transient acceleration environment are compared to impedance results obtained during steady-state vibrations. Application of these results to a better understanding of the body's physical and physiological and behavioral response to vibration and impact loads is discussed, and their importance to protection-system engineering is stressed.
Simulation of Aerospace Flight-Acceleration Environments for Biodynamics Research
Authors: Clarke Neville P. , Wolff Walter M. , von Gierke H. E.
Published: November 2005

The operational acceleration environments generated by flight in aerospace vehicles range from prolonged periods of weightlessness to extremely brief high-magnitude impact forces resulting from ground landing. Complex linear and angular vibrations are produced either singly or in combination and may be superimposed on sustained accelerations, such as those produced by booster rockets. In the past, laboratory simulators have, because of technical limitations, usually tended to reproduce isolated segments of the operational environment. The next generation of simulators will provide the ability to create the high magnitude complex accelerations of operational environments for exploration of the physiologic, biomechanic, and performance changes resulting from exposure of humans and animals to these environments. In this laboratory, the SIXMODE (six-degree-of-motion device) and the dynamic escape simulator, a sophisticated centrifuge, are under construction. The HICODE (high-amplitude complex decelerator) and the landing impact simulator are being designed. The specific design characteristics and performance range of these devices are presented and discussed.
Self-Synchronized Vocoder Digital-Transmission Systems
Authors: Dumanian J. A.
Published: November 2005

Energy in the spectrum channels of the Lincoln Laboratory channel vocoder is sequentially sampled and converted to a logarithmic digital representation and is interspersed with a linear-pitch digital representation. This digital format is transmitted over a single wire channel to the vocoder synthesizer where the digital data are reconverted. On receiving the serial stream of binary data, the demultiplexer performs a bit synchronization and a word synchronization, at the cost of no extra bits. After synchronization, the demultiplexer converts the pitch bits into a pitch pulse train, detects buzz or hiss condition, and makes a digital-to-analog conversion of the spectrum-channel data. The transmission rates for the digital-transmission systems are 4800 and 2400 bits/sec. A magnetic-tape recording of synthesized speech at these rates is played. An analysis of the probability of losing synchronization and average times of reacquisition of synchronization at various error rates is presented.
Some Work on Channel-Vocoder Excitation
Authors: Tierney Joseph
Published: November 2005

High-quality microphone speech processed by the Lincoln Laboratory channel vocoder used in both pitch-excited and voice-excited modes was the basis for a subjective comparison test. The pitch-excited mode used the digital pitch extractor described by B. Gold at the Fourth International Congress on Acoustics, Copenhagen, 1962. The voice excitation was obtained with a band of speech from 180 to 900 cps., half-wave rectified, and then differentiated. The results of the test indicate the two excitation signals to be equally effective in producing good synthetic speech. Listener acceptance was about equally divided between the two speech signals. Differences in the two synthesized outputs can be attributed to differences in excitation phase structure as well as differences in the location of excitation spectral energy. Some work is also reported on subjective evaluation of vocoder speech produced with smoothed pitch excitation.
Sound-Reduction Closures
Authors: Munchhausen H. V.
Published: November 2005

Conventional closures (doors or windows) yield STL averages in the 20-dB range. Field need for sound insulation may be as low as 25 dB; or, in an extreme case, it may exceed 60. The great majority of applications call for an actual TL of the field installation from 35 to 45 dB. The methods now in use to achieve the required STL are discussed in brief. As the requirement grows, not only does the panel itself need to be a more efficient interceptor throughout the audio range; provisions to reduce sound leaks at the panel periphery, always important, become crucial; and as the needed TL goes up so does the necessity of avoiding flanking paths, through or around the stationary construction. Photos and diagrams are presented as slides to illustrate good solutions for given requirements.
Comparison of the Acoustical and Constructional Parameters of the Conventional 16 to 17-in. Viola and the New 20-in. Vertical Viola
Authors: Hutchins Carleen M.
Published: November 2005

The development of the small viola as an instrument comfortable to play under the chin has given rise to a special tone quality, but at the same time has produced an instrument with definite problems, which viola players are continually striving to overcome. The 20-in. viola has been developed as the result of applying the theory of violin-type resonances to an instrument tuned in the viola range. Problems of scaling, patterns, and arching designs in relation to resonant placement and tone quality are discussed and demonstrated. [Work supported by the John Simon Guggneheim Memorial Foundation.]
Iteration Techniques in Computer Study of Flooded Cylindrical Radiators
Authors: Haas R. S. , Middleton F. H.
Published: November 2005

The computer study reported at the 65th Meeting of the ASA has been successful in explaining some of the behavior of large, flooded, barrel-stave transducers. This approach has a fundamental weakness in that one does not know a priori the correct source surface-velocity distribution to feed into the computer program. By the time these data are available in a specific design case, it is too late for the computer study to be of value to the designer in the prediction of general behavior. An iteration procedure has been developed, which solves this difficulty by successively modifying the velocity distribution. This is done in such a way that the prescribed source velocity of the active region of the transducer is maintained constant while the inactive region of the model is given nearly any surface shape that is convenient. In general, the result of this procedure is a set of boundary conditions that fails to satisfy the physical requirements. These inconsistencies are used to produce a more reasonable source velocity distribution, which serves as an improved input for a second solution. This process is repeated, each time giving boundary conditions that are more physically acceptable. Program results are compared with experimental model measurements. [Work supported by U. S. Office of Naval Research, Acoustic Programs.]
Increased Bandwidth for Deep-Submergence Transducers
Authors: Martin Joseph E.
Published: November 2005

A technique is described for eliminating the bandwidth degradation usually associated with piezoelectric cylindrical radiators that have been liquid filled for hydrostatic-pressure compensation. This technique utilizes an acoustically stiff internal structure to control the impedance presented to the vibrator at the internal ceramic-liquid interface. By controlling this interface impedance, it is possible to eliminate the effective mass contribution from the pressure compensating fluid. A comparison between theoretical and experimental data is presented for several units utilizing this technique. One of the units discussed is a cylindrical line transducer resonant at 2.5 kc/sec with a bandwidth greater than 1600 cps and an efficiency greater than 60%. The unit is pressure-compensated for deep-submergence operation with no degradation in performance.
Power-Output Capability of a Piezoelectrically Driven Tonpilz Transducer
Authors: Lubell A. H.
Published: November 2005

The analysis of a piezoelectric ceramic-driven transducer using compliance loading, given in a previous paper for a symmetrical configuration [A. H. Lubell, “Use of Compliance Loading as a Transducer-Design Technique,” J. Acoust. Soc. Am. 35, 1903 (A) (1963)], is extended to the asymmetrical case. It is shown that for any Tonpilz configuration, the use of compliance loading will increase the power output whenever the mechanical Q of the transducer exceeds the optimum Q of the piezoelectric ceramic. Several forms of power-output expression are presented in terms of volume of ceramic, internal transducer volume, and radiating area. It is shown that for a given internal transducer volume, it is possible to trade bandwidth for power output when compliance loading is employed. It is also shown that the power output per unit volume of ceramic is independent of the mass ratio. Hence, the expressions developed for power output can be used as an absolute measure of the quality of available ceramic compositions for use in the construction of underwater acoustic transducers having the Tonpilz configuration.
Technique for Curing Polyurethane Coatings on Piezoelectric Transducers
Authors: Fabian R. W. , Long L. E. , Repici D. J.
Published: November 2005

Polyurethane coatings on transducers commonly had (or developed) a fishscale-type appearance due to fissures, contained entrapped bubbles, and exhibited poor adhesion to the silvered electrodes of piezoelectric-ceramic elements in all cases tried when the material was cured at 150°F beginning sequentially after pouring. These defects, which caused loss of watertight integrity or anomalous acoustic characteristics, were eliminated when the 150°F cure was preceded by a 24-hr room-temperature (75°±5°F) cure. No difficulties were encountered in potting small (112 in. diam×112 in. long) cylindrical ceramic, or in encapsulating large (6 in. diam×24 in. long) cylindrical assemblies. Use of the 2-step curing process permitted simplification of shop practice in that the mold was not placed in the oven until after the polyurethane had achieved its initial set. Hence, mold-handling was facilitated. All transducers that have been potted in transparent polyurethane and cured using the technique described have met the required standards of acoustic behavior and have remained watertight at pressures up to 1500 psig. Since many of the defects noted above would have been invisible in opaque polyurethane potting compounds, the periodic use of a transparent formulation to check the efficacy of the curing process and/or raw materials being used was indicated.
Pitch of Periodically Interrupted Tones
Authors: Swigart Elsa
Published: November 2005

This paper is a study of the effect of periodic interruptions on the pitch of 500, 1000, 2000, and 4000-cps tones. The interruptions, which were of the duration of one sinusoidal wave of the tone frequency, were regularly spaced to produce a series of pulses. In one testing condition, the pulses, if presented individually, would be of insufficient duration to permit pitch discrimination. In the other testing condition, the pulses, if presented individually, would be of sufficient duration to permit pitch discrimination. The 20 subjects attempted to adjust a pure tone to match the modulated tone. The deviations in cycles per second were recorded by the experimenter. A tone composed of pulses of insufficient duration to permit pitch discrimination was matched with a tone equal to the frequency of the actual number of cycles emitted from the earphones. A tone composed of pulses of sufficient duration to permit pitch discrimination was matched with a tone composed of the sum of the number of cycles omitted from the earphones plus those omitted in the process of modulation. It is evident that there is a relationship between the duration of the pulses of an amplitude-modulated tone and the pitch. The critical factor seems to be whether or not the individual pulses exceed the duration necessary to permit pitch discrimination.
Masking of the Pitch Related to the Time Delay between Two Pulse Trains
Authors: Small Arnold M. , Canahl Julius A.
Published: November 2005

If a repetitive train of dc or ac pulses is delayed with respect to itself, mixed with the original signal, and presented to a listener, a pitch will be perceived corresponding to the reciprocal of the delay between proximal pulses of the mixed pulse trains. The purpose of the present study was to ascertain whether there is a single component in the signal spectrum located at the reciprocal of the pulse delay that is responsible for the perception of this time-separation pitch (TSP). Low-pass noise with various cutoff frequencies was used as the masker. Masked thresholds were obtained by having each of the 6 listeners adjust the noise so that the pitch shift produced by a 5% change in pulse delay was just audible. dc pulse trains with 3 pulse separations were used and as control conditions 3 corresponding pure tones served as the signal. The results show that the noise-spectrum level for masking TSP decreases gradually by about 12 dB/octave as the noise cutoff frequency is raised. This is not the case with pure tones, where under similar circumstances the noise-spectrum level for masking decreases abruptly once the noise cutoff is above the signal frequency. Consequently, it seems as though no single spectral component is responsible for TSP.
Pulse Thresholds with Selective Masking
Authors: Lummis Robert C.
Published: November 2005

A masked-threshold measurement is described in which the perception of a pulsive signal near threshold is derived from a restricted segment of the basilar membrane. The signal to be detected is a pair of identical, short acoustic pulses presented monaurally over headphones. The click pairs are repeated at a rate of 10 sec−1. The interpulse interval is an experimental parameter and varies from 0 to 32 msec. The masking signal is high-passed noise. The threshold of the click pair is measured by the von Békésy technique while the noise level is held constant. It is hypothesized that the spectrum of the masking noise, in combination with the frequency sensitivity of the ear, confines the suprathreshold click activity to a small region of the basilar membrane. With this hypothesis, and with reasonable assumptions about neural transduction, the relation between time spacing and threshold for the click pair may be predicted from the impulse response of the membrane. The prediction exhibits a maximum at a time spacing of 1/(2F), where F is the natural frequency of the particular place on the membrane. The experiments described confirm the existence of this maximum, and the pulse spacing at which it occurs agrees quantitatively with the predicted value for a range of noise levels and cutoff frequencies.
Loudness is a Product of Density Times Volume
Authors: Stevens S. S. , Guirao Miguelina , Slawson A. Wayne
Published: November 2005

Experiments were designed to determine the relation between loudness and two other auditory attributes, volume (apparent size), and density (apparent compactness or concentration). Two sets of stimuli, quarter-octave bands of noise covering a wide range of center frequencies and SPL, were presented through earphones to observers who made magnitude estimations of one or another of the attributes. The loudness estimations were plotted against loudness level and found to agree with the sone scale. A plot of the estimations of loudness against the product of the estimations of volume times the estimations of density produced a slope of 1.0 in log-log coordinates. Loudness is, therefore, proportional to volume times density. This relation was confirmed by experiments involving magnitude estimations of the inverse attributes, softness, smallness, and diffuseness. These inverse attributes were found to be the reciprocals of their respective direct attributes. As predicted, softness turned out to be proportional to the product of smallness times diffuseness. Thus, magnitude estimations of both the attributes and their inverses established the proportionality between loudness and the product of volume times density.
Spectral Flattening and Its Application as a Synthesis Technique
Authors: Cassel Lawrence E.
Published: November 2005

During the past five years, many approaches to vocoder synthesis have been proposed. The use of the spectral-flattening technique in the voice-excited vocoder represents the first attempt to apply a synthesis process capable of operation in other vocoder systems, such as the channel vocoder. The use of this technique represents the first major variation in the basic channel-vocoder concept and certainly is worthy of a detailed theoretical and practical evaluation. Conflicts concerning the theoretical value of this technique are now prevalent. A detailed study of the use of spectral flattening (or dual-filter synthesis) in the channel vocoder has been completed and evaluations of various implementation of this technique have been performed. As a result of these studies and evaluations, some definite answers and comments on the theoretical and practical value of spectral flattening have been derived. Conclusions reached and theoretical considerations are presented. A tape demonstration follows. [A portion of this study supported under contract No. AF19(628)-586.]