bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic-Field Modification by a Vibrating Plate
Authors: Pernet David F. , Hruska G. R.
Published: September 2005

The object of the study was to investigate the sound field existing close to a plate that was free to vibrate and was exposed to an incident-sound field. Modification of the sound field was sought other than that due to diffraction. This would occur when sound is reradiated under conditions of plate resonance. A square, galvanized, aluminum plate, 12×12×0.020 in., clamped along all four edges, was selected for the study. A simple mode of vibration of the plate, for which a single nodal circle was observed, occurred at a frequency of 74 cps. The amplitude and phase of vibration of the plate relative to progressive plane wave excitation was determined at frequencies in the region of this plate resonance. Simultaneously the acoustic field both adjacent to and distant from the plate's surface was determined. Significant modifications to the incident sound field, as large as 10 dB, were observed. An analysis was developed that, given knowledge of the plate's vibration, accurately predicted this sound-field modification. [This study was supported in part by the U. S. Air Force.]
Sound Absorption in Electrolytes
Authors: Jackopin LeRoy , Stuehr John , Yeager Ernest
Published: September 2005

Further ultrasonic-absorption measurements have been made at 104–108 cps in a number of electrolytes including iodides, chlorides, acetates, acetic acid, and mixtures of electrolytes. A number of these electrolytes exhibit interesting relaxation effects, which have been interpreted quantitatively in terms of specific ion-ion and ion-solvent interactions. Reexamination of several systems for which ultrasonic relaxation effects have been reported by other workers, however, has failed to confirm these relaxation effects. These surprising findings reflect the need for greater acuracy in absorption measurements, particularly at frequencies below 5 Mc/sec, and the need for caution among acousticians to prevent overinterpretation of their data under conditions where statistical fluctuations as well as consistent errors are substantial. In addition, several instances are cited where relaxation effects reported in the literature have been confirmed but the explanations are not compatible with accepted concepts of electrolytes. New explanations are presented. [This research has been supported by the U. S. Office of Naval Research.]
Velocity of Sound in Single-Crystal Ice
Authors: Proctor T. M.
Published: September 2005

Only one of the previous measurements of the elastic constants in single-crystal ice has been extended below −30°C. Some of the elastic constants in ice have been measured by a variation of the sound-echo technique down to 50°K. The method and technique are described. The change in the constants with temperature is found to be large. Δc33/c33≈10−4/°C. Results are shown and compared to those of Zarembovitch and Kahane. Acoustic-coupling problems associated specifically with experiments on ice are discussed. [Work supported in part by U. S. Office of Naval Research.]
Effect of Localized Sound on an Electrode Reaction
Authors: Rowe W. E. , Nyborg Wesley L.
Published: September 2005

Ultrasound in the absence of cavitation was applied in a special manner to a process in which the sonic effect on a surface monolayer could be studied. The process selected [as in related work by Seegall (1960)] involved cyclic anodic and cathodic polarization of a platinum electrode in acid electrolyte. It was shown by Butler and others that in such a cycle adsorbed monolayers of oxygen and hydrogen are deposited and removed, as revealed by characteristic changes in recordings of the electrode potential E as a function of time t. In the present study, the test electrode used was a platinum sphere approximately 0.5 mm in diameter mounted on the tip of an 85-kc/sec Mason horn. Sound applied during selected parts of the cycle caused pronounced changes in recorded E vs t plots. The observed changes probably result from mass transport of dissolved gas and from stress on adsorbed layers, both transport and stress being associated with acoustic streaming. [Work sponsored in part by the U. S. Air Force Office of Scientific Research and by the National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
Viscoelastic Properties of Polystyrene Solutions
Authors: Lamb J.
Published: September 2005

Quartz crystals resonant in the fundamental torsional mode at frequencies of 40 and 73 kc/sec have been used to measure the viscoelastic properties of solutions of polystyrene in toluene, methylethylketone, and cyclohexane. A monodisperse polystyrene sample of molecular weight 2.39×105 was employed. The results have been compared with those of Harrison, Lamb, and Matheson (1964) for dilute solutions in toluene of a number of polystyrene samples of different molecular weight. In toluene, it is found that 25% of the contribution of the polymer to the viscosity of the solution is not able to take part in viscoelastic relaxation, and that the dynamic viscosity at high frequencies (the “Einstein viscosity”) is greater than the solvent viscosity. Under these conditions, the viscoelastic behavior of all time solutions of toluene of polystyrene samples of different molecular weights agrees with the predictions of the Rouse theory. From time value obtained for the Einstein viscosity of the solutions, it is shown that the radius of time equivalent hydrodynamic sphere is approximately proportional to the square root of the molecular weight of the polymer molecule. The viscoelastic behavior of the solution in methylethylketone is intermediate between the predictions of the Zimm and Rouse theories.
Theory of Damped Flexural Vibrations
Authors: Hoffman Ray D.
Published: September 2005

The theory of damped flexural vibrations is extended to higher overtones of the fundamental resonance. First, an explicit dependence of the amplitude of oscillation on frequency is found by binomial expansion and inversion by means of the Burmann series. Second, overtones are determined by application of boundary conditions. It is shown that the simplifying assumptions previously suggested in the literature cannot be used in the amplitude equation when damping is included, and the equation is extended to higher overtones. Using a computer program, the equation is solved for a wide range of damping values. The degree of shift of the overtone frequency is calculated and the number of overtones to be observed with a specific amount of damping is shown.
Dual-Phase Damping Material
Authors: Warnaka G. E. , Kerwin Edward M. , Carbonell Jaime R.
Published: September 2005

Small, overlapping platelets of structural material mixed in a matrix of viscoelastic damping material form a dual-phase damping material. This composite is an excellent extensional damping treatment because the viscoelastic damping material can be chosen for environmental resistance and high damping without regard for stiffness. The high extensional stiffness necessary in a good additive damping treatment can be obtained by incorporating the stiff platelets. Analysis of simplified, regularly oriented platelet configurations shows that, when the composite is deformed in extension, the platelets extend and the damping material between them shears. As a result of this type of deformation, the dual-phase material combines some of the better features of constrained and extensional damping treatments. The frequency range of the dual-phase material is broader than that obtained from constrained layer treatments while the damping of the treatment can be designed to be nearly as great as that of the viscoelastic matrix. The analysis presented agrees reasonably well with experimental data and has broad implications for filled materials.
Longitudinal Vibrations of a Drill String
Authors: Angona F. A.
Published: September 2005

When drilling an oil well with a rotary drill, the penetration rate often can be substantially increased by superimposing a vibratory motion on the rotating bit. In order to evaluate drilling methods that would include both rotary and vibratory action, a study has been made on the vibrational characteristics of long drill string. The resonant frequency of a drill string consisting of a length of drill pipe and a length of drill collars is determined by considering the string as a lumped-constant system and also as an acoustic transmission line. A frequency equation is derived by applying the wave equation to the system and satisfying the boundary conditions at the top and bottom of the string and also at the junction of the two sections. The frequency equation is solved graphically for a number of drill-string configurations and the results are compared with the measured frequencies.
Repetition and Recognition of Nonsense
Authors: Bastian Jarvis , Tanous Louise D.
Published: September 2005

A most important feature of the perceptual capacities contributing to the effective reception of linguistic events is that, even when the events are without lexical status for the listener, he can nonetheless assign a nonlexical, that is to say, phonemic identity to them. In order to examine the process of phonemic identification, particularly in the light of the articulatory reference conceptualization of this process posited by the Haskins group, CCVC syllables were developed that, although composed of only general American English phonemes, did not conform to the restrictions on English syllable formation. Carrier phrases were also developed for each syllable within which it was compliant with these restrictions, so that, for example, the carrier for /ŋziž/ was /ɡʌŋziz_ɔŋ/. Recordings of the syllables, both in and out of carriers, were presented to listeners for repetition. In addition, a recognition test was conducted in which the listeners were required to decide which, among systematic phonemic departures from them, were the events that they had previously repeated. The contingencies between repetition and recognition performances for the two sets of events are discussed.
Surface Waves in an Inhomogeneous Liquid Layer
Authors: DiNapoli F. R. , Middleton F. H.
Published: September 2005

The case of surface-wave propagation in a homogeneous layer embedded in a homogeneous medium has been reported in the literature. On the other hand, if the layer is inhomogeneous, the problem is considerably more complicated. In fact, only for a very few special cases does an exact solution exist. In this study, the inhomogeneity is introduced by allowing the sound velocity to have a layer depth dependence. A method is presented here that demonstrates the manner in which the variation of sound velocity affects the dispersive characteristics of the medium. The structure described is essentially an acoustic waveguide and normal-mode techniques are used to produce a mathematical model. The resulting modified Sturm-Liouville boundary-value problem is converted into a Fredholm integral equation through the use of the Green's-function technique. The kernel of this integral is quantized in such a fashion as to yield the relationship between the phase velocity of the surface wave and the layer depth. Dispersion curves for velocity profiles that could occur in the ocean are presented in the paper.
Sonic-Boom Pressure-Field Estimation Techniques
Authors: Carlson Harry W. , Mack Robert J. , Morris Odell A.
Published: September 2005

Current theoretical methods of estimating the flow field surrounding airplanes in supersonic flight are based on Whitham's solution for the flow about bodies of revolution and on other theoretical work that makes possible the representation of a complete airplane as an equivalent body of revolution. This paper presents a review of the fundamental theory and discusses the use of high-speed digital computers in providing rapid and reliable analysis of sonic-boom characteristics of complex airplane configurations. Application of the estimation techniques is illustrated in correlation with wind-tunnel and flight-test measurements.
Design Methods for Minimization of Sonic-Boom Pressure-Field Disturbances
Authors: McLean F. Edward , Shrout Barrett L.
Published: September 2005

This paper reviews theoretically-based techniques for minimization of sonic-boom pressure-field energy and overpressures through detailed consideration of airplane configuration. The discussion includes consideration of the recently discovered potential for overpressure minimization for large, slender airplanes with extended nearfield characteristics. Use of the optimization methods is illustrated in correlations of theory with wind-tunnel measurements. Illustrations of the possible use of these methods in reducing overpressure for future airplanes such as the supersonic transport are given.
Some Effects of the Nonuniform Atmosphere on the Propagation of Sonic Booms
Authors: Kane E. J.
Published: September 2005

A recent theoretical development to describe the propagation of weak shock waves through a nonuniform media has been used to investigate the effect of stratified atmospheric models on the sonic boom generated by an airplane in steady level flight. The effects of variations in temperature, pressure, and winds with altitude on the strength, lateral distribution, and extent of the shock waves on the ground are discussed. Some comparisons of the theoretical results with flight-test data are presented, and areas that warrant future investigations are suggested.
Some Effects of Airplane Operations and the Atmosphere on Sonic-Boom Signatures
Authors: Maglieri Domenic J.
Published: September 2005

Data from flight experiments illustrate the nature of variations in the ground-pressure distribution patterns due to aircraft accelerations and atmospheric effects. The phenomena of superboom generation during the transonic flight, atmospheric refraction, grazing incidence-wave impingement, and the interaction of shock waves with atmospheric turbulence and temperature anomalies are described, along with their significance regarding community response.
Detection Theory: Uncertain Signal-Arrival Times
Authors: Nolte L. W.
Published: September 2005

The design, in block-diagram form, and performance of the optimum adaptive receiver is presented for a signal with synchronous Poisson arrival times. This receiver was evaluated experimentally on a digital computer for various values of duty factor, signal-to-noise ratio, and time. The receiver performance, presented in terms of the receiver operating characteristic (ROC), shows the effect of uncertain arrival times on detectability.
Effects of Sonic Boom on People: Review and Outlook
Authors: von Gierke Henning E.
Published: September 2005

This introduction to the second part of the sonic-boom symposium reviews the history of observations on human reactions to the sonic boom from the time when the boom was a demonstration curiosity to the present day where reaction of the population to the sonic boom is a scientific problem of technical, economic, social, and political consequences at the national and international level. The field programs conducted by the USAF and NASA over the last 15 years and over the last 5 years by the FAA were all of limited scope with respect to exploring direct and indirect physiological and psychological human reactions to sonic booms of different intensity and exposure frequency. Although the data accumulated might be adequate to decide on preliminary stopgap exposure criteria, it is obvious that a broader approach to the problem is required. Laboratory work in support of these questions has hardly been started. Neither conventional acoustic and vibration generators for boom-type stimulation nor special equipment for high-fidelity sonic-boom simulation have been fully utilized. Some of the open questions and possible approaches are discussed as part of a broad, long-range research program required to come up with scientific data as bases for operational sonic-boom exposure criteria.
Sonic-Boom Research and Design Considerations in the Development of a Commercial Supersonic Transport (SST)
Authors: Higgins T. H.
Published: September 2005

This paper presents a short history of sonic-boom research and related operational considerations in the development of a commercial supersonic transport (SST). The most intensive public-reaction research program to date was conducted at Oklahoma City, Oklahoma. An intensive research program to determine structural reaction to sonic booms was conducted at the White Sands Missile Range. These two programs are discussed and a brief summary of the findings off the programs is presented. The paper concludes that, although much has been learned about the sonic-boom phenomena through past flight and research activities, additional research and theoretical studies are warranted.
Response of Buildings to Sonic Booms
Authors: Weinroth Donald M.
Published: September 2005

If supersonic overflights must create ground-level shock waves, then the evaluation of the potential effects of these overflights as an inventory of buildings and structures that may exist when a supersonic transport becomes operational in the next decade depends on (1) resolution of the nature of the sonic-boom phenomenon and of the structural response to it, (2) definition of the environmental conditions to which the sonic-boom loading will be additive, and (3) assessment of the future inventory of buildings and structures. This paper is a summary of the present state of knowledge in the foregoing categories of questions and includes suggestions for future research programs.
Laboratory Tests of Physiological-Psychological Reactions to Sonic Booms
Authors: Kryter K. D.
Published: September 2005

Investigations of the physiological-psychological responses to sonic booms at the intensities anticipated from commercial supersonic aircraft can be conducted in the laboratory. Studies that would be of interest include (a) sleeping (degree of arousal as measured by electroencephalograph); (b) the reactions of people to booms as an auditory experience (subjective rating of booms vs other acoustical stimuli); and (c) the relative subjective noisiness of booms having different waveforms. A discussion of methods and results obtained in previous laboratory experiments of physiological-psychological responses to sonic booms and methods that might be used for additional research is presented.
Synthesis of Simple Shock Isolator
Authors: Fox Richard L.
Published: September 2005

Two idealized single-degree-of-freedom shock-isolator optimization problems are considered. The first is a conventional system consisting of a linear spring and viscous damper; the design variables are thus the spring stiffness and damping coefficient. These are to be chosen so that when the unit is subjected to any of a known set of environmental shocks, alternatively (1) the maximum absolute acceleration experienced by the package is minimized subject to a limitation on the maximum relative displacement, or (2) the maximum relative displacement is minimized subject to a limitation on the maximum absolute acceleration. The second problem is the same optimization problem, but the isolation system consists of a bilinear spring and a viscous damper with a time-variable damping coefficient. The spring requires three design variables to describe it and the damper six. The first problem is solved using a simple numerical search method, the second using a more refined mathematical programming technique. Numerical examples are presented that, though not particularly significant in themselves, support the conclusion that such methods are useful additions to the “bag of tricks” for use when the problem is such that the more-classical methods are inapplicable.
Optimal Shock Isolator and Absorber Synthesis
Authors: Liber Theodore , Barnett Ralph L.
Published: September 2005

Methods are presented for constructing the optimum resisting function for a single-degree-of-freedom shock isolator in the sense that, of all possible functions, the optimum minimizes the mass acceleration for a specified relative displacement, or conversely. Using this capability, the optimum systems are characterized by displaying a tradeoff-limit relationship between their mass accelerations and relative displacements for all values of either quantity. The resulting optimal tradeoff-limit curve can be used to establish the existence of isolators for any shock input and bounds on mass acceleration and rattlespace (relative displacement). Furthermore, the curve acts as a yardstick for measuring the efficiency of proposed isolators, e.g., the best linear isolator. A similar treatment is given for the shock absorber where the mass acceleration and force transmissibility are taken as the tradeoff-limit quantities.
Optimum Distributed Damping for Structural Frames
Authors: McMunn John C. , Plunkett Robert
Published: September 2005

A method is presented for finding the damping required to optimize the steady-state vibration response of a portal frame. In this application, the optimum configuration is defined as that which minimizes the maximum transfer impedance over a frequency band subject to a given internal impedance of the driving machine and a given input impedance at the base of the frame. The portal frame is analyzed as a distributed system with distributed damping. The optimalization technique used is a modified steepest-ascent method to find the values of the damping parameters at local minimax values of the function. Some numerical results are given by way of example. [Work supported by the Bureau of Ships, U. S. Navy.]
Ultrasonic Temperature Determinations in a Shock Tube
Authors: Carnevale E. H. , Carey C. A. , Wolnik S. J.
Published: September 2005

An ultrasonic (Mc/sec) pulse technique has been used in determining the temperature of shock-heated gases. The gases studied were argon, neon, and nitrogen. The temperature range was from about 3000° to 9000°K. The temperatures have been compared with calculated values based upon shock-speed measurements. In the case of neon, the temperatures have also been compared with a simultaneous line-reversal temperature measurement. A discussion of the experimental apparatus, method of measurement, and experimental results is presented. [Research supported by the U. S. Air Force Office of Aerospace Research and the Air Force Materials Laboratory, Research and Technology Division, U. S. Air Force Systems Command.]
Measurement of Propagation Constants for Shear Waves in Dilute Macromolecular Solutions
Authors: Thurston G. B.
Published: September 2005

Direct quantitative measurements of the progression of a shear wave can be carried out in liquids that exhibit shear birefringence [G. B. Thurston and J. L. Schrag, J. Appl. Phys. 35, 144 (1964)]. From measurements of the amplitude and phase of the optical effect versus propagation distance, values of the attenuation and phase constants of the medium are obtained and a complex coefficient of viscosity is determined. An improved optical detection scheme permits measurements as near to the wave-generating surface of 0.1 mm, with a resolution of approximately 0.01 mm. By this means, measurements can be made for liquids of viscosity near that of water. Measured values have been obtained as a function of frequency and temperature for dilute solutions of Baymal and of polyethylene oxide in water. [Work supported by Acoustics Programs, Office of Naval Research, U. S. Navy.]
Model for Spontaneous and Synchronous Activity in Single Neurons
Authors: Kletsky Earl J. , Adams William B. , Zwislocki Jozef J.
Published: September 2005

Two response characteristics frequently observed in single neurons of the auditory system are spontaneous activity and quasisynchronous firing to periodic stimuli. These characteristics have been reproduced with a real-time electronic neuron model incorporating a randomly fluctuating threshold and both absolute and relative refractory periods. A wide variety of responses that bracket physiological results can be generated by manipulating noise spectrum and the ratios between either rms noise voltage or stimulus level to resting threshold. “Burst firing” during spontaneous activity is present for low-pass noise when the bandwidth is about 5 cps. Spontaneous interval distributions become more peaked at shorter intervals when either the bandwidth or the noise to threshold ratio is increased. When periodic stimuli are applied, interval histograms are generated that show quasisynchronous firing patterns. Only the details of these histograms depend on stimulus waveshape. The results suggest that the observed quasisynchronous firings are not restricted to auditory neurons, but may occur in any neuron having the above properties.
Some Consequences of a Hypothesis concerning Neuron Logic in the Ear
Authors: Karplus Henry B.
Published: September 2005

The hypothesis described at the 65th meeting [J. Acoust. Soc. Am. 35, 809(A) (1963)] postulates interaction of neuron groups on the basis of stimulation of members of the group at fixed delays with respect to each other. Computations have been undertaken to examine the effect of such postulated neuron logic in conjunction with basilar membrane analogs. Both Flanagan's model [Bell System Tech. J. 41, 959 (1962)] and Stewart's model (AMRL-TDR-63-60) have been examined. Results indicate that such a mechanism could explain fine frequency discrimination. Furthermore, the characteristics of formants in sounds show how formant frequency and fundamental (or residue) might be obtained without postulating nonlinear distortion.
Tonal Interference in Cochlear Microphonics
Authors: Eldredge Donald H.
Published: September 2005

The interference effect or reduction in magnitude of cochlear microphonics (CM) for one tone in the presence of a second tone presented at levels above its own limits of linearity was described by Wever, Bray, and Lawrence [J. Acoust. Soc. Am. 12, 268–280 (1940)]. Their findings are confirmed for CM recorded differentially from any cochlear turn if traveling waves for both tones reach the electrodes. During interference, the input-output function is shifted toward fewer microvolts per microbar, harmonic distortion is decreased relatively more, and the limit of linearity is shifted to higher sound pressures. A change in the transfer function for transformation of basilar membrane displacement to CM is inferred. The frequent coexistence of the classical negative summating potential (SP) and interference suggests that SP may be an electrical sign of the mechanical change. However, interference may occur without SP; dc potentials related to asymmetrical transfer functions for electronic gates, for the middle ear, or for CM are often present; and maximum voltages for CM constitute boundary conditions for all input combinations. [Work supported by the National Institutes of Health, Public Health Service, U. S. Department of Health. Education, and Welfare, and by the U. S. Office of Naval Research.]
Time Histograms of Cochlear-Microphonic Response to Low-Pass Noise
Authors: Teas Donald C.
Published: September 2005

Cochlear microphonic (CM) response to steady-state noise, low-passed at 5 kc/sec, has been sampled at turn I and turn III in the cochlea (guinea pig). The steady-state activity is recorded on magnetic tape for off-line processing with the HAVOC computer. Time histograms utilizing a recurrent trigger—i.e., temporally unrelated—and a synchronized trigger derived from the input waveform have been computed at several criterion levels that are specified in terms of the rms of the CM. The effect of sampling time is also estimated. Bandwidth for the two electrode sites differs as expected. The curves describing number of events as a function of criterion level appear to be the sum of two subsets of events.
Middle-Ear-Muscle Effects on Low-Intensity Sounds
Authors: Price G. Richard
Published: September 2005

There is some interest in knowing what effect a middle-ear-muscle contraction elicited by contralateral stimulation has on tones of low to moderate intensity. Loudness judgments probably involve both central and peripheral factors. In order to evaluate the peripheral factors, cochlear-potential measures were made on 12 lightly anesthetized cats. Changes in the cochlear potential to pure tones in one ear (ranging in frequency from 0.2 to 10 kc/sec) resulting from middle-ear-muscle activity elicited by contralateral 2-sec pure-tone bursts (ranging from 0.65 to 5 kc/sec) were noted as the measured tones were varied in intensity. As the intensity of the tone being measured was varied, the size of the effect (in dB) remained constant.
Reliability of Acoustic Reflex Responses Obtained by a Relative Measurement Method
Authors: Peterson John L. , Lamb Lloyd E. , Hansen Sven
Published: September 2005

Auditory thresholds and measures of stapedius-muscle reflex activity were obtained from one ear each of ten normal hearing adults. Levels at which reflex responses occurred were measured by a relative method (Madsen acoustic impedance meter, model Z061) at 250, 1000, and 4000 cps, and were compared with hearing thresholds at each of these frequencies. Both auditory and reflex responses were measured ten times per subject for each test frequency, using the psychophysical method known as the up-and-down method. The resulting data indicate that, in general, auditory thresholds are more stable between subjects than satpedius-muscle reflex responses, and that reflex responses are more variable at 250 and 4000 than at 1000 cps. The obtained data are interpreted in terms of response stability for clinical and experimental purposes. Inter- and intra-subject variability is examined, as are the kinds of diagnostic information that might be gained from this type of middle-ear-impedance measurement.
System for the Study of Underwater Acoustic Propagation
Authors: Kronengold M. , Loewenstein J.
Published: September 2005

A fixed underwater acoustic range between Miami and Bimini, Bahamas, was instrumented for the study on a continuous basis of propagation characteristics in relation to significant environmental factors. Precision oscillators at the transmitting and receiving sites provide signals for transmission and time referencing. The phase difference between oscillators is held to a few degrees by periodic comparison with WWVB. A bottom-mounted sound source off Miami produces a level of 120 db μb at 1 yd in a 100-cycle band centered at 420 Hz. CW signals received at Bimini on bottom-mounted hydrophones are processed in real time with a phase-coherent demodulator. Pseudorandom sequences are tape-recorded with a signal from the reference oscillator for studies at The University of Michigan, a participant in the program. [Research supported by the U. S. Office of Naval Research.]
Pulse Distortion in the Underwater Sound Channel
Authors: Hirsch Peter
Published: September 2005

The underwater sound channel affords an interesting opportunity to study the distortion of a propagating acoustic pulse after multiple total internal reflections. Using c2=c02(1−α2z2)−1 as a model for the channel (c is the sound speed, c0 is the speed at the channel axis, z is depth, and α specifies the channel width), and f(t)=t exp {−At} as a model for the source waveform (t is time and A is the time constant), it is shown that after an even number of reflections the pulse appears essentially undistorted. However, after an odd number of reflections the calculation predicts a pronounced change in the pulse shape. The difference between arrivals that have been reflected an even and odd number of times may be discernible on existing sofar records. [Work supported by the Bureau of Ships, U. S. Navy.]
Talking Levels for a Number of Assigned Communication Tasks
Authors: Gardner Mark B.
Published: September 2005

This paper primarily concerns talking levels employed by participants who communicated in pairs over a two-way high-quality loudspeaker system. Tests were conducted in the presence of noise, adjusted over a level range from NC-23 (a very quiet conference room location) to NC-60, with circuit gains adjusted in turn from −40 to +10 dB re unity. Test material consisted of prepared text, conversation, and a problem-solving situation. Participants rated the communication achieved for each test condition as acceptable or as not acceptable and as excellent, good, fair, poor, or very poor. Results showed that, while talking level always increased with increasing noise level, it remained relatively unaffected by system gain over a rather wide midrange adjustment of the latter. Approximately, “unity gain” received the highest average rating over most of the noise range employed. The study also included face-to-face communication for a number of related test conditions. Here, the talking levels employed were influenced somewhat more by environment and assigned task than were those used with the loudspeaker system.
Development of Tests for Evaluating the Performance of Hearing Aids
Authors: Corliss Edith L. R. , Burnett E. D. , Priestley J. T.
Published: September 2005

This paper summarizes the results of recent research relevant to the Veterans' Administration hearing-aid program. For prediction of the behavior of hearing aids, two properties—intermodulation and ringing (“hangover”)—have been found critical, and at least as important as conventional tests for gain, frequency response, harmonic distortion, and internal noise. Both intermodulation and ringing reduce the perceived signal-to-noise ratio; their effect is more serious for persons with hearing loss than for persons with normal hearing. By using a noiselike signal having a number of specific frequencies omitted, a test has been devised to detect the spurious frequencies generated by intermodulation; appearance of the missing frequencies in the hearing-aid output indicates intermodulation. To establish the clinical significance of this test, we have developed a method for generating speech-test tapes containing varied known combinations of harmonic and intermodulation distortion. Ringing in a hearing aid introduces noise that persists after cessation of the signal, and the principal response to impulsive sounds occurs at the dominant frequency of ringing. To evaluate ringing, it was necessary to design a loudspeaker itself essentially free of ringing and to develop techniques for measuring power distributions of speech and noise.
Subtractive Hearing Loss, Loudness Recruitment, and Decruitment
Authors: Davis Hallowell , Goodman Allan C.
Published: September 2005

The normal relation of subjective loudness to intensity is regular, smooth, and lawful. The most frequently recognized abnormality of the loudness function is a more-rapid-than-normal growth of loudness with increase of intensity: namely, loudness recruitment. A hypothesis is presented to the effect that a random loss of sensory units (“sensory unit” is defined as a nerve fiber of the auditory nerve and the sensory cells of the organ of Corti that excite it) may result in a reduction of the maximum subjective loudness. Several cases of neural and central lesions are presented, some with normal thresholds. These illustrate a less-rapid-than-normal growth of loudness with intensity, which may be attributed to such a loss or block of sensory units. The condition is referred to as “decruitment.” The cases are illustrative. More observations are necessary to establish the incidence and possible localizing value of the symptom.
Discrimination of Spectral Cutoff Frequency in Residual Hearing and in Normal Hearing
Authors: Pickett J. M. , Daly Robert L. , Brand Susan L.
Published: September 2005

Subjects were selected who had severe cochlear signs in differential audiometric tests and who retained speech discrimination at low levels of proficiency. Subjects with normal hearing were also used. The discrimination-test stimuli were formed from a broad-band random noise shaped by low-pass filters set for cutoff at five frequency positions: 250, 500, 1000, 1500, and 2000 cps. At each frequency position, discrimination for a difference in cutoff frequency was tested using a series of discrimination tests. An AX procedure was used with constant-stimulus differences, but no difference on half the trials. Discrimination performance was expressed as the threshold difference in cutoff frequency divided by the frequency position. For the normal listeners, this fraction was 0.12 at 250 cps and, above that, it ranged from 0.03 to 0.05. For the cochlear listeners, the discrimination fraction was close to normal, 0.15, at 250 cps but progressively larger—i.e., less sensitive—at successively higher frequencies. [Research supported by National Institute of Neurological Diseases and Blindness, National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare.]
Amplitude of Békésy Tracings with Different Attenuation Rates
Authors: Harbert F. , Young I. M.
Published: September 2005

Amplitude measurements of threshold fixed-frequency Békésy tracings were made for interrupted and continuous tones on normal and pathological ears. Comparison of four attenuation rates (1, 2, 4, and 8 dB/sec) on the same subjects indicates that bottoms of spikes were similar for different attenuation rates both for interrupted and continuous tones, while the tops and midpoint of spikes were significantly different as attenuation rate varied. Standard audiometry thresholds showed either equivalent or greater hearing loss of less than 5 dB as compared with bottoms of interrupted-tone spikes. Doubling the attenuation rate changes amplitude in the ratio of about 1 to 1.6 and increases pen reversals per unit time in the ratio of approximately 1 to 1.2. This is true for both interrupted- and continuous-tone tracings. Separation between interrupted- and continuous-tone tracings in pathological ears is not significantly different for various attenuation rates. Subject acceptability and test-retest reliability of different attenuation rates are discussed. [Work supported by the National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare.]
Experimental High-Frequency Audiometer and Some Testing Results
Authors: Skee Vincent J.
Published: September 2005

Conventional audiometry seeks to relate hearing loss, damage, and variations in sensitivity in degrees of conformity over a range of frequencies up to 8000 cps. The frequencies above 8000 cps should be of clinical and general interest owing to increasing wide-band noise by-products, and their effects upon general hearing. A series of air-conduction sensitivity tests in the range between 10 000 and 24 000 cps was started by Dr. Samuel Rosen of New York. Tests were made at various locations with different degrees of civilization, thus at different levels of technology. Preliminary findings seem to show that young ears worldwide show closely similar sensitivity to high frequencies, but that after puberty marked loss of sensitivity appears and degradation is progressively larger in populations that are exposed to advanced technology. The experimental model HFA 2 and HFA 3 audiometers used in testing between 10 000 and 24 000 cps are described in development, construction, nearfield coupling techniques, and calibration. A brief summary of statistics and controlled variables is given, with a description of clinical work in progress. High-frequency test results are shown to be mainly independent of locale and equipments. The need for extensive further research is emphasized, to form conclusive associations and possible diagnostic-tool values.
Effect of High- and Low-Filtered Noise on Intelligibility of Filtered Speech
Authors: Singh Sadanand , Brokaw Sonia P. , Fricke James E.
Published: September 2005

Intelligibility of filtered speech, as well as the effect on speech perception of filtered noise, have both been investigated. In this study, the frequency spectrum of both noise and speech was divided into four “equally contributing” bands: 300–760, 760–1450, 1450–2550, and 2550–7000 cps. In one condition, the noise was presented in the 300- to 760-cps band, while the speech (PB words) was presented through each of the four bands individually. In the other condition, the noise was presented in the 2550- to 7000-cps band, while the speech was filtered through the other four bands. Three S/N ratios were used in both conditions. Two speakers recorded the words, attempting to equate the level of loudness for all words. The results demonstrated that, when the noise was filtered through the low-frequency band, the intelligibility for the words increased as the frequency separation between noise and speech became greater. At one point, the intelligibility of the PB words was greater, with noise being presented simultaneously in the low-frequency band, than when the words were heard with no noise—the control condition. When noise was filtered through the high-frequency band, a similar effect was seen. In both conditions, the progressiveness of the intelligibility scores was not linear.
Reduction of the Resonant Response of Lumped- and Distributed-Parameter Systems by the Application of Dual Dynamic Absorbers
Authors: Snowdon J. C.
Published: September 2005

The simultaneous application of two dynamic absorbers to an undamped single-degree-of-freedom system or to an undamped cantilever beam is discussed theoretically. The dynamic absorbers possess viscous damping. They are tuned and damped in the so-called optimum manner for which it is possible to suppress the resonance of the simple oscillator or the resonances of the beam in a uniform and symmetrical manner. The beam is excited by a sinusoidally varying force situated either at its free end or at its midpoint. It is to these locations that the dynamic absorbers are attached. The absorbers are tuned to the first and second resonant frequencies of the beam, the optimum values of absorber tuning and damping depending upon the location of the absorbers and upon the beam resonance that is of concern. In addition to the rôle of the absorbers in suppressing the first and second beam resonances, excitation of the third resonance is essentially avoided when the driving force is situated at the midpoint of the beam because a nodal point of the third mode occurs very near to the beam center. [Sponsored by U. S. Bureau of Naval Weapons, U. S. Bureau of Ships, and U. S. Office of Naval Research.]
Natural Modes and Frequencies of Vertical Vibration of a Beam with an Attached Sprung Mass
Authors: Leibowitz Ralph C.
Published: September 2005

A study was made of the vibration characteristics of a beam with an attached sprung mass. Analytical and electrical-analog methods are devised to determine the natural frequencies of the system. These methods are first used to determine the natural frequencies of a uniform beam with a sprung mass and it is shown that the two methods give results that differ by 1% in the lower mode and by 10% in the highest (fifth) mode. Then, for the nonuniform beam-sprung-mass system, the natural frequencies and mode shapes are determined by means of the electrical analog only. General conclusions are drawn on the effects of a sprung mass on the frequencies and modes of vibration of the beam to which it is attached. Of particular interest is the repulsion of the original beam frequencies and the occurrence of two modes with the same number of nodes for the combined beam-sprung-mass system.
Mechanism of Vibratory-Energy Dissipation at Joints in Thin Metal Structures
Authors: Ungar Eric E. , Carbonell Jaime R.
Published: September 2005

Experimental results are summarized that indicate that the dissipation of vibratory energy at multipoint-fastened (bolted, riveted, or spot-welded) joints connecting panels to stiffeners or to other panels, at frequencies considerably above the panel fundamental, is not associated with interface slip or friction. It is shown that this energy dissipation rather is primarily due to the “pumping” of air produced as adjacent surfaces between fasteners move away from and toward each other. Some implications of these results are pointed out; particular reference is made to the fact that tests at ground-level atmospheric pressures may lead to underestimates of the vibrations of flight structural components at altitude. [Research sponsored by Air Force Flight Dynamics Laboratory, Research and Technology Division, Air Force Systems Command, U. S. Air Force.]
Response of a Linear System to Impulsive-Noise Forcing
Authors: Janssen Raymond A. , Smits Talivaldis I.
Published: September 2005

In view of the increased importance of the effects of impulsive-noise excitation, certain response statistics of a linear single-degree-of-freedom system are experimentally and analytically investigated for such non-Gaussian loading. Of main interest in these response studies are the crest (level crossing) statistics and the first-order probability density. Analytic development, using a Poisson process impulsive-noise model, provides an approach to the response probability density and also to the response crest statistics for low impulse frequencies. The former study utilizes a recursion relationship between the moments and the semiinvariants of the response, while the latter, as a secondary result, gives the probability density of the response envelope. An impulsive-noise generator, developed for experimental simulation of the Poisson model, is discussed, and results of response crest and probability-density measurements on a mass-loaded cantilever beam driven by this generator are presented. [Work supported by the U. S. Air Force.]
Designing an Acoustic-Isolation Enclosure for a Microwave Echo Box
Authors: Putukian John H.
Published: September 2005

Experimental effort to evaluate the frequency sensitivity of a microwave echo box to an acoustic environment is described. The problem is shown to be that of providing low-frequency mechanical-vibration isolation at the echo-box mounting points and of designing an echo-box enclosure with emphasis on attenuation of low-frequency acoustic transmission. The difficulty of defining the required noise reduction to ensure satisfactory performance of the echo box is discussed.
Harmonic Generation in Solids Effect of Dislocations
Authors: Elbaum C.
Published: September 2005

Two causes of anharmonicity in solids, with the resulting generation of higher harmonics of a propagating wave, are discussed. One of these causes is lattice anharmonicity, which is characteristic of all solids. The other is the nonlinear stress-strain relation for dislocation motion; the latter cause applies to all solids in which glide motion of dislocations is produced by small stresses. In the case of the second harmonic, a lattice term, a dislocation term, and a crossterm contribute to the amplitude, and all three terms can be of comparable magnitude. Except in special circumstances, it is difficult to separate experimentally the three terms that contribute to the amplitude of the second harmonic. In the case of the third harmonic, the lattice contribution is usually much smaller than the dislocation contribution, when a reasonable density of dislocations is present, and the separation of the two effects is more easily accomplished. The relation of the amplitudes of the harmonics to higher-order elastic constants is also discussed.
In Situ Observation of Insonated Crystalline Objects in the Siemens Elmiskop
Authors: Lagenecker I. B.
Published: September 2005

A new experimental technique is presented that combines electron microscopy of dislocation structures in metal crystals with the application of high-amplitude ultrasonic stress waves at energy densities between 105 and 1010 erg/cm3 at a nominal frequency of 40 kc/sec [B. Langenecker, AIAA J. 1, 80 (1963)]. The acoustic field is produced by a piezoelectric transducer and an ultrasonic-velocity transformer [E. A. Neppiras, Brit. J. Appl. Phys. 11, 143 (1960)]; it is observed by a very small magnetostrictive probe [B. Langenecker, J. Acoust. Soc. Am. 38, 234–238 (1965).] High-amplitude ultrasound is used to cause changes in dislocation structures, and the damping of the sound waves is measured as these structural changes occur. Preliminary results from these in situ observations carried out in a Siemens Elmiskop I are discussed in the light of present theories on internal friction in metal crystals.