bluuebunny/crossref_metadata_2025 huggingface dataset:
Shouting over Noise with a Megaphone
Authors: Pickett J. M. , Pollack Irwin
Published: September 2005

A small megaphone was tested for use in direct voice communication at high voice levels against backgrounds of noise. The voice transmission characteristics of the megaphone were measured. Intelligibility scores were determined for ten talkers, speaking with and without the megaphone, over a range of field voice levels of 70 to 100 db SPL (at 1 meter). A white noise and a low-frequency noise background were employed. Nearly the entire over-all acoustical gain produced by the megaphone was realized in improved intelligibility above both noise spectra. The acoustical gain of the megaphone permitted a lower voice level, and, hence, delayed the deterioration in intelligibility associated with distortions due to shouting. Frequency shifts in the voice spectrum were measured over a range of vocal efforts from conversational maximum shout. Control tests demonstrate that the voice-frequency shifts associated with shouting are not the primary factor in the deterioration of intelligibility; the frequency shifts appear to be only symptomatic of serious vocal distortions in shouting.
On the Scattering of Sound by Atmospheric Turbulence
Authors: Ingard Uno , Wiener Francis M.
Published: September 2005

Results of field measurements of scatter attenuation of sound in a turbulent atmosphere are reported. The observed attenuations are much smaller than might be expected from a scattering theory using the total scattering power of the turbulence in the calculation of the attenuation (Lighthill, 1952). That theory also predicts a strong dependence of the scatter attenuation on both mean wind speed and frequency. Again, this prediction is not supported by the experimental evidence. Attenuations calculated on the basis of backscattering alone are presented. They are in reasonable agreement with experiment. The backscattering is caused by eddies comparable in size to the wave length of the scattered sound. Consequently, the energy spectrum of the turbulence will affect the frequency dependence of the attenuation considerably. An extensive series of turbulence spectra has been obtained experimentally near the ground for different micrometeorological conditions. A discussion of these spectra and their dependence on mean wind speed and thermal gradients is presented. On the basis of the foregoing considerations, preliminary estimates of the attenuation of sound in the audio-frequency range by atmospheric turbulence are given.
Corrections to Small-Loss Approximations for Propagation Characteristics of Viscoelastic Materials
Authors: Fitzgerald James W. , Fitzgerald Edwin R.
Published: September 2005

The exact linear equations for propagation of a disturbance in a viscoelastic material are reviewed, together with the usual small-loss approximation. For tan δ⩽0.165 the approximate relations are within about 1%. Many plastic materials, however, have loss tangents considerably greater than 0.165 and appreciable errors result if the exact expressions are not used. A table of corrections to the small-loss approximate propagation constants is presented. The case of large-loss materials (tan δ > > 1) is also considered and approximate equation derived. For tan δ ⩾ 10 the large-loss approximate relations are within 5%. An interesting result from the large-loss approximation is that the product of the propagation velocity and attenuation is equal to 2 times the frequency (cα = ω). Some experimental data, both shear and longitudinal, for typical plastic material are given.
Measurement of the Adiabatic Elastic Moduli of Single Crystal Alpha Uranium
Authors: Fisher E. S. , McSkimin H. J.
Published: September 2005

The adiabatic elastic moduli at 25°C for single crystal alpha uranium are reported here as derived from ultrasonic wave velocities in the frequency range 30 to 180 mcps. Seven specimens grown by a grain coarsening method [E. S. Fisher, J. Metals 9, 882 (1957)] were used, with thickness dimensions of 2 to 4 mm and lateral dimensions of approximately 5 mm. Even though the sizes involved were small, the precision obtained was good, as evidenced by the numerous cross-checks afforded by the twenty-one free-space velocities determined. The method of measurement is briefly reviewed [refer to IRE Trans. on Ultrasonics Eng. PGUE-5, 25 (1957)], and the correlation of data to minimize uncertainties is discussed. In units of 1012 dynes/cm2 the elastic stiffness moduli are as follows (based on a density of 19.04 g/cc):

C 11  = 2.1474 ± 0.14% , C12 = 0.4649 ± 0.6%,

C 13  = 0.2177 ± 1.5% , C22 = 1.9857 ± 0.14%,

C 23  = 1.0791 ± 0.7% , C33 = 2.6711 ± 0.14%,

C 44  = 1.2444 ± 0.10% , C55 = 0.7342 ± 0.10%,

C 66  = 0.7433 ± 0.10% .

(Part of this research was carried out under the auspices of the U. S. Atomic Energy Commission.)
Maintenance of Alertness by a Loud Auditory Signal
Authors: Knaff P. Robert , Pollack Irwin
Published: September 2005

Will a loud auditory signal help maintain a high level of alertness over a long period of visual monitoring? Apparently, yes. When the failure to detect a target is coupled with the occurrence of a loud signal, improved monitoring performance might be reasonably expected because the signal: (1) serves as an “alarm clock” to keep the subject awake; (2) serves to provide information that the target has not been detected; and (3) serves as a “punishment” for having failed to detect the target. Tests were conducted with 15 observers over six 90-min periods. The task of the observer was to detect a momentary change in the predicted course of the needle of a VU meter. The average frequency of targets was 0.8 target per min; the average probability of a target-occurrence was 0.027. After failure of target-detection, a truck horn placed near the ear was blasted. A substantial average gain in monitoring performance, relative to a control condition without the horn, was observed. The largest gain in monitoring performance was provided by the least proficient group of observers. Control tests suggest that the horn is effective primarily because it provides information and/or punishment, and not because it simply serves as an alarm to keep the observers awake.
Pressure Gradient-to-Pressure, Mechanical Sound Transducer
Authors: Embleton T. F. W. , Thiessen G. J.
Published: September 2005

In places of high ambient noise level there are situations where communication by electrical means is precluded. An aid to speech communication in these cases is a mechanical close-talking microphone which can be used in conjunction with ear defenders. This consists, on the outside of the ear cover, of a diaphragm (responding to the pressure gradient of the sound field), which is coupled mechanically to a second diaphragm on the inside of the cover. An acoustic filter system is associated with the air passage through the cover (necessary for the mechanical linkage) so that the attenuation provided by the cover is not impaired. Further improvement in the signal-to-noise ratio has been achieved by making the mechanical system resonant in the range of frequencies that are most important for speech intelligibility. Sentence intelligibility tests on 50 people showed, for example, that when the articulation index was zero for a nearby speech source the median subject obtained a score of 28% using ear covers alone and 84% with the sound transducer; the subjects with extreme scores improved from 0 to 14% and from 88 to 100%, respectively.
On the Strength Distribution of Noise Sources Along a Jet
Authors: Ribner H. S.
Published: September 2005

The spatial distribution of noise source strength along a jet is investigated theoretically. It is found, in particular, that a “slice” of jet (section between two adjacent planes normal to the axis) in the region of similar profiles downstream of the potential core contributes as x−7, where x is measured from a virtual origin near the nozzle. Because of this striking attenuation of strength with distance, the “fat” part of the jet may contribute much less to the total noise power than is commonly supposed on the basis of near-field measurements.
Distribution of Sound Sources in a Jet Stream
Authors: Dyer Ira
Published: September 2005

It is shown that the axial distribution of sound sources in a turbulent jet stream can be found in terms of (1) the spectrum of the total radiated sound power and (2) the frequency of the sources as a function of location along the jet axis. With the use of existing data on the sound power spectrum, and recently reported data on the frequency dependence of the most probable source location, an approximate axial distribution is derived. The derived distribution is in good agreement with calculations by Sanders based on turbulence measurements and Lighthill's theory. It is shown that the source distribution reaches a broad maximum at about 3 or 4 diam downstream of the nozzle, as expected. Beyond about 6 diam downstream of the nozzle the source distribution decreases very rapidly. Significant contributions to the total radiated power do not appear to originate further than about 10 diam downstream of the nozzle.
Method of Correlation between Sound Power Spectrum and Downstream Velocity Profiles of a Free Jet
Authors: Lee R. , Smith E. B.
Published: September 2005

Studies have been made to correlate the sound power spectrum of a free jet and its principal downstream aerodynamic parameter—the velocity profiles. Using the relationship established by NACA which describes the effective sound source locations, fd/U = a(x/d)−b, (1) where a and b are constants, d and U are exit diameter and exit mean velocity of the jet, f is frequency, and x is downstream distance from exit. Assuming that there is no turbulence noise generated in the potential core of the jet, it is found that the sound power at any frequency band may be approximately described by the following relationship: P (f) Kρ0c0−5 ∫ 0r(max) u8(r,x)rdr, (2) where u(r,x) represents the velocity profile across the axial-symmetric jet at some distance x downstream, and P(f) represents the sound power at some frequency f, which is uniquely related to x by Eq. (1). K, ρ0, and c0 have similar meanings as those terms found in Lighthill's equation. Theoretical justification and experimental confirmation of this method are discussed.
Noise Radiated by Jet Systems
Authors: Franken Peter A. , Dyer Ira
Published: September 2005

Measured values of over-all sound power radiated by turbulent jet systems can be presented in a very general way. A single curve results when the acoustic efficiency is plotted as a function of a ratio of velocities, densities, and temperatures (or molecular weights) of the jet and ambient fluids. This ratio can be derived from the well-known Lighthill theory, when heat and mass diffusion of the jet stream and the ambient fluid are considered. The approach correlates data taken on model air jets, helium jets, turbojets without and with afterburner, ram jets, and rockets. Special attention is paid to noise measurements on three large rocket engines. A predicted acoustic efficiency of approximately 10−2 is found to be in satisfactory agreement with measurements on both liquid and solid fuel rockets.
Nondestructive Testing by an Impedance Method
Authors: Arnold J. S. , Salmon V.
Published: September 2005

The effect of coupling a workpiece to a reversible electromechanical transducer will appear in an altered motional impedance. If the transducer has a strong isolated mechanical resonance and the load is light, the principal effect on the electrical impedance vs frequency curve about the resonance will be a perturbation in position and shape from the value without a load. An instrument to exploit this effect has been constructed, and has been named the STUB (STanford Ultrasonic Bond) meter. The device employs ferroelectric transducers ordinarily operating in the range of 100 kcps to 1 Mcps. It has been established empirically that when the load is an adhesively-bonded laminate or sandwich of the types employed in missiles or manned high-speed aircraft, the instrument is able to detect imperfections in the glue line. With the active participation of some 11 aircraft manufacturers and 3 other interested groups, a program has been set up and accomplished for comparing nondestructive STUB-meter data with that from a destructive test performed later on the same sample. Some 8000 data points were obtained. In a variety of useful test situations these data indicate correlation coefficients of 60 to 80% between the two types of tests. The STUB-meter principle has also been used with success on brazed and welded joints. [The research was supported by the Materials Laboratory, Wright Air Development Center, under Contract AF 33 (616)-3833.]
Effect or Ultrasonic Vibration of the Cutting Tool in Machining Metal
Authors: Frederick Julian R.
Published: September 2005

An investigation has been made of the effect of ultrasonic vibration of single-point cutting tools in machining various aluminum alloys. Conventional magnetostriction vibrators were used. The forces required to cut the metal are reduced; in some cases this reduction amounts to a factor of ten. In the cutting of soft ductile material there is less tearing and a consequent improvement in the surface finish as a result of vibrating the tool.
Effects of Acoustic Streaming on the Photographic Process
Authors: Jackson F. J. , Nyborg W. L. , Adams C. E.
Published: September 2005

It has been known for some time that ultrasonic irradiation of a photographic plate immersed in a liquid causes differential darkening of the emulsion. It was observed by some investigators that suppression of cavitation either entirely eliminated or greatly reduced the darkening action. Because of the complex and erratic nature of typical cavitation, it is difficult to determine which of its many aspects may be responsible for the observed darkening. In experiments to be reported here, it is found that small scale acoustic streaming in the vicinity of the emulsion will cause a darkening effect whether cavitation is present or not. Special experimental arrangements are utilized; by use of moderate sonic amplitudes, cavitation is either entirely supressed or else carefully controlled. Controlled “cavitation” is effected by allowing a single bubble of appropriate size to be present at the emulsion-liquid interface. Photographs of emulsions irradiated under various conditions (frequencies 10–50 kc) will be shown; density distributions will be compared with those which might be expected on the basis of known characteristics of the acoustic streaming. [The work reported here was sponsored in part by the National Institute of Health (Biophysics section) and in part by the U. S. Air Force Office of Scientific Research, Contract AF 18(603)-54.]
Recent Experiences with Soundproof Openings
Authors: Munchhausen H. V.
Published: September 2005

A number of cases of recent field work is described which show how it is possible to solve, simply and without sound, locks, feedback, and other noise problems which arise at doors and windows, particularly in studios and homes. Slides depicting field conditions will be shown.
Aerodynamic Sound Radiated from a Turbulent Boundary Layer
Authors: Phillips O. M.
Published: September 2005

It is predicted, using two different types of simple argument, that the fluctuations in pressure upon a rigid plane boundary produce no contribution to the radiated sound field. The first is an acoustical argument involving the reflection of normal dipoles in the surface, and the second, concerned with the dynamics of the turbulent flow, suggests that the integrated correlation of the pressure fluctuations vanishes. Recent wind tunnel experiments by Harrison, however, offer little indication of support to the latter result (derived for a semi-infinite flow region), and some tentative suggestions are made concerning the resolution of this apparent paradox. An estimate is found for the acoustical energy radiated by the fluctuating shear stresses on a semi-infinite flat plate, along which a turbulent boundary layer is developing, and this is compared with the quadrupole radiation from the turbulence itself. It is found that the aerodynamic surface sound is relatively unimportant, indicating that, in the flow past an aerofoil, the principal source of sound radiation may lie in the fluctuations in net lift per unit length on the aerofoil as a whole.
Observations on the Acoustical and Mechanical Properties of the Vocal Cords
Authors: Fink B. Raymond , Kirschner Francis G.
Published: September 2005

The geometrical configuration of laryngeal structures during phonation was studied by x-rays and the Bell Laboratory high speed motion pictures. The geometry of internal surfaces appears to act as an impedance matching device reducing the losses during transmission of energy from the infraglottic to the supraglottic cavities. The shape of the surface favorably affects the flow and the wave form of the acoustic pulses, and hence the harmonic content of the pulsations transmitted to higher cavities. The x-ray observations in vocal cords paralysis support this interpretation.
Vocal Virilization
Authors: Licklider J. C. R.
Published: September 2005

During the last few years, several experiments have emphasized the importance of “periodicity,” as distinguished from “place,” as a determiner of the subjective pitch of complex sounds. These experiments have dealt with synthetic sounds. The observations to be reported were made in order to test extrapolation of the conclusions to the sounds of speech and, particularly, singing. Perhaps the simplest way to alter the “periodicity” of the quasi-periodic segments of a recorded speech wave is to blank out every second fundamental period. This leaves a cycle of the vowel wave form, then a blank, then another cycle, another blank, and so on. With a little more pains, one can refill each blank with a slightly distorted form of the wave that was deleted. Either process doubles the period of approximate recurrence of the waveform. When the modified speech is reproduced, the subjective effect suggests as a generic term for the modification the phrase “vocal virilization.” The effect will be demonstrated, as will be the persistence of the reduction in pitch despite elimination by filters and despite masking by noise of the vocal fundamental.
On Vowel Intonation Contours
Authors: Lieberman Philip
Published: September 2005

Synthetic three formant vowels were recorded with thirty-two different intonation contours, by varying the fundamental frequency as a function of time. The perceptual effects of these variations were investigated in a test in which listeners were required to discriminate between different intonation patterns. The reliability of the discriminations was correlated with the direction in which the intonation contour shifted, the rate of the shift and its magnitude. The relevance of the results to the problem of English sentence intonation is briefly discussed. [This work was supported in part by the U. S. Army (Signal Corps), the U. S. Air Force (Office of Scientific Research, Air Research and Development Command), the U. S. Navy (Office of Naval Research), and the National Science Foundation.]
Anatomy of Unstressed Syllables
Authors: Lisker Leigh
Published: September 2005

In the CVC syllable as synthesized on the Pattern Playback the nucleus is generally a three-formant pattern composed of distinct segments; an initial transition, a steady-state part, and a final transition. The formant frequencies of the steady-state part are those characteristic of the vowel as produced in isolation, while the transitions involve shifts in these formant frequencies that are to be related to the neighboring consonants. This neat tripartite division, although not closely approximated by spectrograms of real speech, affects only negligibly the quality of the acoustic signal, while it facilitates the isolation and manipulation of subfeatures of the pattern. For the most part, syllables of the type described have been synthesized as isolated items rather than as constituents of longer sequences. When they are included in longer sequences it becomes necessary. if one wishes to reproduce the normal rhythm of English, to take account of the fact that spoken syllables vary greatly in their durations, in particular, that syllables in unstressed position are frequently of such brief durations that a division into steady-state and transitional parts cannot be meaningfully accomplished. Examination of spectrograms and experiments with synthetic speech both suggest that for many unstressed syllables—namely those containing the schwa vowel—the character of the second formant may be related primarily to the consonants preceding and following the vowel and not so much to a fixed formant frequency of the vowel itself, and that the first formant provides the major cue to the identification of the vowel. (This research was supported by the Veterans Administration under contract V1005 M1253.)
A Comparison of Mouth, Ear, and Contact Microphones
Authors: O'Neill John J.
Published: September 2005

Four microphones, including an ear transducer and a bone oscillator, were used experimentally in simultaneous recording with a noise-cancelling microphone serving as a control. Speakers recorded PB word lists under three recording conditions of quiet, 100-db noise, and 111-db noise for each microphone comparison. Recordings were played back to a panel of 10 trained listeners over headphones under conditions of quiet and with white noise introduced into the circuit at an S/N ratio of 0 db. In quiet playback the control microphone maintained a fairly stable score within each set condition. For the quiet playback the control microphone was superior or equal to the other microphones for all recording conditions, with the ear-transducer and bone oscillator also showing superiority in the quiet recording conditions and one of the throat microphones demonstrating superior performance at 111-db recording condition. In the noise playback the control microphone did not perform consistently within each set condition. The somewhat tenuous results of this part of the experiment indicate that the ear transducer is superior at all recording levels for listening in noise with the throat microphone also demonstrating superior performance at 100-db and 111-db noise recording levels. Testing of variations of the original microphones substantiated the superiority of the noise-canceling microphone in noise recording conditions with playback in quiet. Fairly reliable performance for the ear transducer suggests its development for use in special situations. [This research was carried out in connection with Contract AF 19(604)-1577, monitored by Operational Applications Laboratory, Air Research and Development Command, Bolling Air Force Base, Washington 25, D. C.]
Segmentation Techniques in Speech Synthesis
Authors: Peterson Gordon E. , Wang William S-Y. , Sivertsen Eva
Published: September 2005

A basic method of speech synthesis is discussed in which segments of recorded utterances are joined together to produce continuous speech. The segments are characterized as (A) containing parts of two phones with their mutual influence in the middle of the segment, and (B) beginning and ending at the phonetically most stable position of each phone. All segments containing the same articulatory sequence have been defined as a dyad. The method of synthesis described involves not only the articulatory phones, but also the intonation, stress, and durational aspects of speech. Various techniques of obtaining the segments for speech synthesis are discussed. The method is limited to a specific dialect, and practically it is limited to a single speaker. A large number of segments is required to synthesize any arbitrarily selected utterance within these restrictions of dialect and speaker.
Hydrophone Minor Lobes Produced by Volume Scattering
Authors: Bell Thaddeus G.
Published: September 2005

Directional hydrophones on naval vessels are often limited in listening performance by acoustic interference arising from discrete sources such as propellers, pumps, or discharges. While a directional hydrophone may achieve some discrimination against such sources, the effectiveness of this discrimination is limited by the minor-lobe response in the direction of the source of interference. In an ideally homogeneous, unbounded medium, the minor-lobe characteristics of a directional hydrophone would be determined completely by the characteristics of the hydrophone and any associated baffle structure. In the ocean, however, backscattering from various discontinuities contributes significantly to the in situ minor-lobe structure. One type of practical discontinuity in the ocean is that caused by volume scatterers. It is of interest to examine theoretically the seriousness of volume scattering as a contribution to minor-lobe level, since it would appear to impose a practical limit to what can be achieved by minor-lobe-suppression techniques in hydrophone design. Quantitative deductions concerning this phenomenon may be made regarding the effects of such factors as volume-scattering coefficient, direction of source, distance to source, directivity index of hydrophone, and attenuation constant of the medium.
Sound Velocity vs Temperature in Water-Saturated Sediments
Authors: Shumway George
Published: September 2005

Sound velocity vs temperature was measured in a continental shelf silt, a calcareous ooze, a deep-sea red clay, a continental slope clay, and a quartz sand using a resonant chamber technique. The temperature effect on these water-saturated sediments was approximately the same as for water alone. This similarity to water behavior would be expected inasmuch as the compressibility of a water-sediment mixture is dominantly due to the relatively large water compressibility. Theoretical velocity-temperature curves were computed from handbook data on density and compressibility of water and mineral constituents as a function of temperature, and these curves fit the experimental data reasonably well.
Fluctuations of a Continuous Wave Signal
Authors: Baker H. H. , Berman A. , Clay C. S.
Published: September 2005

Fluctuations in the phase of CW signals were measured as a function of distance traveled in water. The data were compared with two theories. First, the phase fluctuations were assumed to be due to fluctuations of the travel times of the acoustic waves. Second, the fluctuations were assumed to be caused by the addition of background noise. The results of these experiments gave an upper limit to the magnitude of acoustic path fluctuations.
Acoustic Response of Vibration Pickups
Authors: Jones Earle , Edelman Seymour , Smith Ernest R.
Published: September 2005

Vibration pickups respond to air-borne sound. Separation of the signal owing to this acoustic excitation from the signal arising from vibration of the base of the pickup is difficult. This paper reports preliminary experiments in which the vibration pickup whose response is being measured is mounted back to back with a standard pickup. Both pickups experience the same vibration but only the pickup being measured is exposed to the sound field.
High-Frequency Strain Gauge and Accelerometer Calibration
Authors: Nisbet J. S. , Brennan J. N. , Tarpley H. I.
Published: September 2005

A method and apparatus are described for calibrating bonded wire resistance strain gauges in the frequency range from 2 kc to 20 kc. The gauges are mounted on an electromagnetically excited, longitudinally resonant bar whose amplitude of vibration is measured by an interferometer. Factors affecting the frequency sensitivity relationship of bonded wire strain gauges are discussed and a typical calibration is given. Application of strain gauge assemblies calibrated in this manner as secondary standards for accelerometer calibration is discussed. (The work described herein was accomplished under sponsorship of the Quartermaster Corps, U. S. Army.)
Impact Type Accelerometer Calibrator
Authors: Conrad R. W. , Clements E. W. , Vigness Irwin
Published: September 2005

A drop-tester type accelerometer calibrator has been developed, consisting of a falling weight (12 lb) which impacts on one of several anvil surfaces. Three basic anvil surfaces have been investigated, yielding peak accelerations over the ranges of 10–50 g, 25–150 g, and 100–700 g with pulse lengths of 30, 12, and 3 msec, respectively. Pulse wave forms are approximately half-sinusoidal. Accelerometer outputs are presented to a peak-reading integrating circuit which maintains its maximum reading for about 10 sec and then resets automatically, being insensitive to inputs resulting from bouncing of the falling weight during the period of indication. The calibrator is of a comparison type, since the output of the subject accelerometer is compared with that of an adjacently mounted standard accelerometer. By a separate determination of the velocity-change involved in the impact the method can be converted to an absolute method of calibration.
Method of Improving Acoustic Transmission in Folded Horns
Authors: Carlisle Richard W.
Published: September 2005

A novel principle has been developed, applicable to folded horns, for improving the acoustic transmission around bends having a radius greater than one quarter wavelength. This consists of the use of a conoidal reflecting-type surface in the outer half of the fold. It is beneficial in the frequency-spatial region intermediate between normal horn refraction action and specular or optical-type reflection. A practical application is described.
Localization of Aural Harmonics Along the Basilar Membrane of Guinea Pigs
Authors: Tonndorf Juergen
Published: September 2005

Harmonic distortion resulting from cochlear overload is caused by Békésy's “eddies,” according to experiments on cochlear models [J. Acoust. Soc. Am. 29, 1249 (1957)]. This hydrodynamical distortion (1) does not affect the mechanical response of the round window and (2) is resolved along the cochlear partition in accordance with the place principle of frequency localization. Wever and Lawrence, however, had concluded that intra-cochlear distortion occurs at the haircell level [Physiol. Acoustics (Princeton, 1954)]. In this latter case resolution should not be in accordance with the place principle. Tasaki et al. [J. Acoust. Soc. Am. 24, 502 (1952)] have demonstrated (by use of differentiating electrodes inserted at several points along the cochlea) phase variations of cochlear microphonics in accordance with the traveling wave concept of Békésy. This latter method was adopted for purpose of the present study. Two alternatives were visualized. The haircell hypothesis would be supported if the complex wave forms resulting from cochlear overload would look identical (except for differences in amplitude) when being picked up at various points along the basilar membrane. The hydrodynamical hypothesis would be supported if wave forms at various pickup points would differ in (a) amplitude, (b) harmonic content, and/or (c) phase relation among harmonics. The results to be presented are in favor of the second alternative. [This research was supported by the United States Air Force under contract number AF 41 (657)-148, monitored by the School of Aviation Medicine, USAF, Randolph Air Force Base, Texas.]
Mapping of the Electrical Response of the Cat's Auditory Cortex to Some Amplitude Modulated Signals
Authors: Small Arnold M.
Published: September 2005

In view of recent interest in the perception of periodicity, the following study was undertaken in order to determine whether an electrophysiological correlate of periodicity existed in the cerebral cortex of the cat. Anesthetized cats were presented with certain repetitive signals including both bursts of tone and bursts of noise. For these AM signals the rise-time of the individual bursts was varied. In addition, responses were recorded at each cortical point for wide-band noise and pure tones corresponding to the repetition rate and to the carrier frequency of the AM signals. On each cat electrical responses were recorded from approximately twenty-five cortical points by means of microelectrodes (5 μ) and gross platinum electrodes. Responses were analyzed with regard to latency, amplitude, and wave form. The results seem to indicate that the spacial coding of the anesthetized cat's auditory cortex is in terms of Fourier frequency. No response corresponding to envelope periodicity is readily detected. An attempt will be made to relate response characteristics to the effective band width of the signals.
Vibratory Energy and the Biochemistry of the Acoustic Nerve
Authors: Angeluscheff Z. D.
Published: September 2005

“We do not know how the nerve responds to incoming vibrations” (v. Békésy, 1956). The mechanical solution of the phenomenon of hearing has failed and directs our search in new directions. The ear is conditioned to sense as sound vibratory energy of Herzian range. Ultrasonic waves not sensed subjectively act, nevertheless, objectively upon the hearing apparatus and cause chemical changes in the proteins. Chemical changes start with migration of ions. 1016 microwatt/sq cm, an infinitesimal intensity, initiates migration of ions and hearing in man. A drop of water grooves a stone not by force (intensity), but by its frequency of falling (frequency). Frequencies set structures in resonance. The atom is an organized unit; so is the organic cell. The movement of electrons is the dynamic stimulus of organized living units of organic matter. The potassium (K) bound to protein molecule, by emission of beta and gamma particles, is the motor of the living cell. The study of nuclear resonance in crystals of potassium has demonstrated its spinning. The electron spin resonance of nitrogen in organic compounds has been recorded at 900 Mc. An atom in excited states (overtones) emits particles. Vibratory energy induces cytochemical changes in the nerve cells and depletes them of desoxyribonucleic acids which are responsible for protein synthesis. Vibratory energy depletes nerve cells of potassium, the most essential electrolyte for conducting stimuli. Depleted of potassium, the nerve ceases to respond to incoming vibration and results in nerve deafness.
Protection of Electronic Equipment from Aircraft Vibrational Environments
Authors: Molloy C. T.
Published: September 2005

A few years ago the Society of Automotive Engineers organized a Committee whose objective was to develop design procedures for vibration, shock, and random excitation isolation of electronic equipment on aircraft. The work of this group is still in progress but a considerable amount of technical information has been developed, and it appears worthwhile to present this information to the Acoustical Society membership in order to take advantage of the resulting interchange of ideas. The S-12 Committee work has been organized into four major categories, and a subcommittee covers each. These subcommittees are: (1) Vibration Sources, (2) Vibration Isolation Systems, (3) Receivers—(The Protected Electronic Equipment), and (4) Complex Wave Excitation. A summary of the work accomplished in each of the above categories will be presented. It is, of course, understood that the author of this paper is merely a spokesman for the SAE group and as such is presenting the results of the efforts of the group.
Data Reduction Techniques for Flight Vibration Measurements
Authors: Kennard D. C. , Thomas C. E.
Published: September 2005

The system used at the Wright Air Development Center for recording and analyzing flight vibration data, is described. It has made possible a significant increase in the quantities of raw data which can be acquired to define the vibration and sound environments in various aircraft. To reduce the large quantities of data to usable form, processing techniques have been evolved based upon the use of standard business machines and the ERA 1103 computer. These techniques are described and methods are illustrated for presenting data to define spectral and statistical qualities of the sound and vibration environment. A proposed system to provide still further automation of the data reduction process is described briefly. It is concluded that these recent advances in state of the art make possible the acquisition of sufficient data to eliminate eventually the “guess-work” in defining sound and vibration environments of aircraft and missiles.
Minimizing Damage from Random Vibration
Authors: Mains R. M.
Published: September 2005

The response of structures to random vibration is discussed in terms of the damage producing characteristics of the response. Various damage processes both in the structure and in components mounted on the structure are then considered, and means for alleviating the damage are discussed. This leads to some simple statements of criteria for minimum damage in different cases, and some practical suggestions on how this may be achieved.
Frequency Response Characteristics of Random Noise Systems
Authors: Maki Charles
Published: September 2005

Transfer function characteristics showing the ratio of vibration parameters to input voltage as a function of frequency for the electrodynamic vibration exciter operating under unloaded and loaded conditions are presented and explained in terms of the mobility analog. Actual table acceleration frequency responses of resonant systems mounted on the machine are shown, as well as the degree of flatness which can be achieved using proper means of equalization for purposes of random noise testing.
Statistical Evaluation of Near Field Sound Pressures Generated by Exhaust of a High Performance Jet Engine
Authors: Kamps Edwin C.
Published: September 2005

The operation of modern, high performance, turbojet engines creates an environment that promotes rapid structural fatigue in many areas in jet aircraft. To facilitate the simulation of a valid test environment and therefore enable fatigue resistant structure to be readily developed, the characteristics of the near field sound pressures created by the jet stream must be established. This study is concerned with the establishment of the level and the rate of occurrence of peak pressures in relation to the commonly measured rms level. A method is presented which enables the determination of these qualities from rms sound pressures recorded on magnetic tape. Also included are typical results obtained from near field sound pressures which were created by the jet exhaust of a General Electric CJ805 turbojet engine. Noted conclusions: (1) occurrence of peak pressures does not follow a Rayleigh distribution. (2) Peak pressure distribution is not altered by the physical position related to the jet stream nor does it appear to be a function of frequency. (3) A maximum ratio of peak to rms pressure is shown to exceed four, but a physical limit is not established.
Experimental Studies of Noise Intrusion into the Community Areas from Aircraft Flight Operations
Authors: Clark W. E. , Galloway W. J. , Pietrasanta A. C. , Stevens K. N.
Published: September 2005

Field studies have been performed to provide experimental data on noise intrusion into community areas from aircraft flight operations. Air traffic activity over selected community areas in the vicinity of two air bases was determined from analysis of air base flight movements and from field observations. Flight paths, pattern altitudes, climb profiles, and engine power changes were determined from aircraft tracking observations, from interrogation of flight and operations personnel, and from special logs prepared by crew members on aircraft in flight. Noise from flyovers observed at ground locations was recorded in synchronization with position data. Simplified prediction models were formulated from the experimental data, and these were used, together with previously developed procedures, to describe the noise intrusion. This paper describes the types of data obtained and discusses significant experimental findings on flight activity variations, flight path variations, and time patterns of sound pressure level observed on the ground for aircraft flyovers. Conclusions drawn from the experimental data on sound propagation from aircraft to ground and on the effects of jet aircraft speed on noise generation are also discussed. Several indices used in the description of aircraft noise intrusion are defined. [This work was supported in part by the U. S. Air Force under Contract Nos. AF 33(616)-3335 and AF 33(616)-3938.]
Comparison of the Take-Off Noise Characteristics of the Comet Jet Airliner and of Conventional Propeller-Driven Airliners
Authors: Miller Laymon N. , Beranek Leo L. , Hoover Robert M.
Published: September 2005

This paper presents noise data obtained during recent tests of the prototype of the British Comet 4 airliner in take-offs from the De Havilland plant at Hatfield, England. The data are analyzed in terms of noise levels, spectrum distribution, and noise duration and are compared with related data obtained from tests with several propeller-driven airliners. Measurement positions were located at points under the take-off path corresponding to residential areas near present-day airports. This work was sponsored by the Port of New York Authority.
Noise Characteristics of Some Commercial Jet Aircraft during Ground Operations
Authors: Miller Laymon N. , Hoover Robert M.
Published: September 2005

Measurements have been made of the noise of two commercial jet aircraft, the French Caravelle and the British Comet, during ground runup and take-off operations. Noise directivity measurements taken during the ground runup operations are presented as a function of engine power and number of operating engines. These results provide data on the noise of two commercial jet aircraft using engines with and without in-flight suppressors. From both the take-off noise data, measured to the side of the runway, and the static ground runup data, estimates are made of the average maximum noise levels that can be expected outside airport terminal buildings due to various operations of commercial jet aircraft.
Portable Sound Suppressor for Afterburner Operations
Authors: Kirchman E. J. , Owen Avery L.
Published: September 2005

The “Martin Cone” principle of noise reduction has been adapted to an afterburner configuration that requires no external sources of coolant. This muffler provides over 30 db attenuation of the maximum noise lobe and is still fairly effective at the inlet where it provides 10 db of attenuation. Test data, movies of the operation, and limitations of this system will be discussed.
Vibration and Acoustic Problems in Large Ballistic Missiles from a Designer's Viewpoint
Authors: Evans Jack
Published: September 2005

The problems encountered by the airframe designer in the selection of vibration isolators, the design of supporting structures, and equipment, as well as the probable expected vibratory inputs for large missiles, are presented.
Noise Investigation of Interfering Jets
Authors: Smith E. B. , Lee R.
Published: September 2005

Rectangular jets of various height-to-width ratios have been operated over a range of exit velocities in an anechoic chamber. Each of the jets had an exit area equal to one square inch and was tested in pairs of equal height-to-width ratios. The noise intensity and directivity pattern were measured and evaluated as a function of the separation distance of the jets, the height-to-width ratios, and the jet velocity. Noting the width of the jet as w, and separation distance as s, the s/w ratio was varied from zero to two and the value was noted where the generated noise was a minimum. This optimum s/w ratio was found constant with respect to the angle of radiation and the jet velocity for all height-to-width ratios. The effect of forcing air through the area between the jets by means of a third jet was also studied. Results of these studies in relation to rational design of jet noise suppressors are discussed.
Effect of External Sound Fields on Hearing Tests in Audiometric Booths
Authors: Ancell James E.
Published: September 2005

There has been some confusion in the past regarding the specifications and manufacturing claims for the sound attenuation of audiometric booths. It was therefore decided that for a particular model of audiometric booth, performance tests would be made by direct measurement of the threshold shift for normal hearing individuals caused by typical environmental sounds or noises. The particular booth used was the Burgess Manning Model 301 Acousti-Room, one of the light, portable variety. The booth was assembled in a relatively quiet room which was fairly “live” acoustically, with the back of the booth against the middle of the largest wall in the room. The simulated ambient environmental noise was generated with a professional quality tape recorder and loudspeaker unit playing tape loops upon which suitably shaped broadband noise spectra were recorded. Hearing tests were made on 25 young normal hearing subjects who occupied the booth while the ambient noises were reproduced at various levels. The audiometric phase of the tests was performed under the supervision of Dr. James Jerger. Audiometric tests were also performed on the same subjects in the minimum noise field obtainable at the test location. The data obtained were then analyzed by Dr. Jerger with regard to average thresholds and threshold shifts. From this analysis it was possible to predict the audiometric thresholds obtainable when such booths are used in environments having various subjective classifications ranging from noisy to quiet clinical offices. One example of the predictions derived shows that the environmental noise of a typical clinical office produces masking effects which would lead to erroneous average audiometric thresholds ranging from 10 to 20 db in the frequency range from 125 to 2000 cps. If this particular booth is used in such an environment, normal audiometric thresholds are predicted at all frequencies except 125 cps, where the false audiometric indication would be about 10 db.
Relations among Intensity, Time, and Temporary Threshold Shift
Authors: Ward W. D. , Glorig A. , Sklar D. L.
Published: September 2005

The results of a series of studies, using normal ears, on the effects of broad-band noise (equal energy in all octave bands from 75 to 10 000 cps) can be summarized by the equation TTS = 1.06R(S-85) (log10 T/1.7) (1–0.37 log10 t/2), where TTS is the threshold shift at 4000 cps in db, t minutes after cessation of a T-minute exposure to the noise; S is the sound-pressure level of the noise, and R is the fraction of time that the noise is on. This equation is shown to hold for 0<TTS<50 db, 85<S<110 db SPL, T>5 min, t>2 min, and all values of R provided that the noise pulses are 1 sec to 1 min long. Thus the relation between intensity and duration for constant TTS is much more complicated than predicted by the equation IT = K of classical psychophysics, or the I2T = k recently suggested, although both are approximately true in particular regions. Furthermore, it is evident that a noise on only part of the time is much less dangerous than one on continuously. (This research was supported in part by a grant from the National Institutes of Health.)
Auditory Adaptation in Noise
Authors: Wright H. N.
Published: September 2005

The initial rate, extent, and recovery from auditory adaptation (Hood's perstimulatory fatigue) were measured in both the presence and absence of noise in ten normal ears by the method of fixed intensity at 250, 1000, and 4000 cps. It was found that the initial rate and extent of adaptation in noise were excessive at 4000 cps, but not at either 250 or 1000 cps. Recovery from adaptation was found to be equivalent, but never complete, at each frequency in both noise and quiet. When the noise was sustained in one ear and a pure tone introduced over the noise at 1-min intervals, there was an apparent decline in the ear's response at 250 and 1000 cps, but not at 4000 cps. When the noise was not sustained, but followed the same periodic intervals as each pure tone, there was a decline in response at 4000 cps, but not at either 250 or 1000 cps.