bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Hydrostatic Pressure on Magnetostrictors
Authors: Karplus Henry B.
Published: November 2005

The output of a 32-kc/sec laminated nickel-bar magnetostrictor radiating from each end into long 0.275 i.d. oil-filled pipes was monitored with a Kistler 601 gauge, as a function of the hydrostatic pressure applied to the system. The output of the magnetostrictor increased monotonically over the pressure range: 0–150 atm. Corrections for medium density and impedance change were applied but proved to be small. Brass masses attached to the ends of the magnetostrictor were adjusted to minimize interaction with modes of vibration other than the desired fundamental longitudinal mode. These masses also acted as pistons fitting loosely in the ends of the pipes. [This work was sponsored by the U. S. Office of Naval Research.]
Vibration and Sonic Metal-Fatigue Control by Homogeneous Viscoelastic Damping-Material Layers
Authors: Kirschner Francis
Published: November 2005

Considerable increase in fatigue life of structures exposed to high noise levels has been obtained by the application of homogeneous layers of viscoelastic damping materials. Examples are shown on the exponential horns used in sonic-fatigue testing equipment, such as random-noise- and discrete-frequency generating sirens (up to 177 dB PWL) and aircraft structures. Noise-control uses of homogeneous viscoelastic damping layers are described. Examples of noise reduction obtained in industrial gas-transmission pipelines and residential pipelines are described for a broad frequency and temperature range.
Response of Laminates with Dissipative Skins
Authors: Warnaka Glenn E. , Desai Ramesh R.
Published: November 2005

Laminates made with plastic or reinforced plastic skins were sometimes found to have different damping characteristics than expected on the basis of conventional laminate theory. Investigation of the magnitude of damping of the plastic skins indicated that they had moderate internal damping. Laminates made with such skin materials can be considered as two-phase damping structures. The core contributes shear damping, and the skins add their own characteristic internal damping. Mathematical analyses of the effects of dissipative skins on the dynamic response of laminates are presented. Experimental verification is shown, and some practical design considerations are discussed.
Synthesis of Reactive Mechanical Circuits for Impact Loading
Authors: Carl E. , Becker H. , Conway H. D. , Vogel Stephen M.
Published: November 2005

High-speed operation of modern machines has emphasized the effects of high loading rates and impacts. With wide-frequency-band excitation, it becomes necessary to consider an extended range of structural resonances to determine dynamic response and to improve the effectiveness of structural damping. In this paper, synthesis techniques are applied to the design of simple undamped (i.e., reactive) structural elements. Synthesis of mechanical circuits is complicated by the characteristically large numbers of degrees of freedom, and by difficulties of response measurement over a wide frequency range. However, Cauer's method of ladder network synthesis is readily applied for more than 20 alternating zeros and poles arrayed in a wide variety of frequency patterns. Of particular interest for dissipative purposes is the equal frequency spacing of zeros and poles for the reactive structure. Examples are given of circuit synthesis for this zero-pole spacing in the derivation of dimensions for simple circuits, including 15 degree-of-freedom ladders, cantilever beams, and circular disks. Computed circuit characteristics are then verified by mechanical driving-point impedance measurements over a frequency range extending to 50 kc/sec.
Psychoacoustical Study of Some Factors Affecting Human Echolocation
Authors: Welch John R.
Published: November 2005

Echolocation systems similar to those employed by bats are often considered as possible mobility aids for the blind. Echo sound fields would probably provide abundant environmental information if the human auditory system could effectively detect and locate echolike sounds. The refractory nature of the auditory system, however, enables the direct sound from an echolocation sound source to mask the echoes. A series of experiments was designed to investigate this masking phenomenon. In these experiments, both the direct and echo sounds were simulated by binaural clicks presented through earphones. The results indicate that localization judgments are affected by echo-delay time, relative intensity of the echo pulse and the direct sound pulse, and interaural time delay in the direct sound pulse. Sound-intensity level and repetition rate have little effect. Localization errors produced by interaural time delay in the direct pulse indicate that the pulse generator should be positioned on the centerline of the subject's head. This provides an explanation for the failure of echolocation systems employing hand-held sources, and indicates that with a head-mounted sound source human echolocation may become feasible for blind guidance. [This work was supported in part by the U. S. Army, the U. S. Air Force Office of Scientific Research, and the U. S. Office of Naval Research; in part by the National Science Foundation (Grant G-16526); in part by the National Institutes of Health (Grant MH-04737-02).]
Independence of Tonal Volume and Density
Authors: Slawson A. Wayne , Stevens S. S.
Published: November 2005

Although several experiments have shown the independence of the tonal attributes, volume and density, it has sometimes been suggested that density may be the inverse of volume. In order to test this possibility, observers were asked to scale the inverse of volume, i.e., to judge the apparent “smallness” of tones. The observers' task was to assign numbers proportional to the apparent “smallness” of a series of tones that varied in both frequency and sound pressure. Although these inverse judgments proved more difficult than judgments of other tonal attributes, the geometric means of the numerical estimates describe a function that is decidedly different from the one that describes density. It turns out that the isophonic contours for smallness are the same as those for largeness (i.e., tonal volume) and are opposite in slope from the equal-density contours.
Spectra of Vocoder-Channel Signals
Authors: Rader Charles
Published: November 2005

Lincoln Laboratory's experimental vocoder analyzer includes a bank of bandpass filters, each 120 cps wide from 180–3000 cps and 360 cps wide from 3000–4740 cps, respectively, and each followed by a detector and a lowpass filter. The outputs of the lowpass filters are to be transmitted over a digital channel. It is important to know the spectral properties of these outputs in order that they be sampled at the minimum rate for adequate reproduction. The outputs of vocoder-analyzing channels with bandpass filters in 18 different parts of the band from 180–4740 cps were subjected to Fourier analysis, using the TX-2 digital computer as a flexible spectrum analyzer. The inputs were sentences 2 sec long, uttered by four different speakers, 20 sentences in all. The results were averaged over all the sentences and speakers, producing an average spectrum for each of the vocoder channels. The results indicate that 99% of the energy of the channel signals lies below 25 cps for almost all channels; hence, approximately 50 samples per second are necessary to adequately reproduce the lowpass signals.
Channel Vocoder with Digital-Pitch Extraction
Authors: Tierney Joseph
Published: November 2005

The channel vocoder is a speech processor that provides a moderate amount of band compression. Unfortunately, this compression is generally accompanied by a severe degradation in quality and intelligibility. The degradation is usually attributed to both inadequate pitch extraction and poor spectrum reproduction. Work at Lincoln Laboratory during the past two years has resulted in a digitized channel vocoder with acceptable output-speech quality and compression on the order of six or seven to one (5000–6000 bits/sec). This is due primarily to the use of a sophisticated digital pitch extractor at the vocoder analyzer and flattening of the excitation spectrum at the synthesizer. The pitch extractor is of a novel design, utilizing six elementary analog pitch extractors as inputs to a real-time digital processor that chooses the correct pitch period with high accuracy. The excitation spectrum is flattened before modulation at the synthesizer with a filter-bank and limiter-bank combination. Output speech is demonstrated.
Polymodal Vocoder: A New Approach to Versatile and Reliable Voice Communications
Authors: Yaggi L. A. , Mason A. E.
Published: November 2005

A polymodal vocoder was developed, based on a concept of flexibility for present and future data channels and data-handling equipment for digital-speech communication. The polymodal feature provides a user with a choice of three primary modes of vocoder operation, consisting of three digital-transmission rates with speech intelligibility, quality, and ability to recognize voices scaled in accordance with the data rate utilized. The minimal rate (1200 bits per second) is a 14-channel vocoder configuration; the conventional mode (2400 bits per second) is an 18-channel configuration, while the voice-excited vocoder mode (9600 bits per second) has two arrangements, one utilizing an 800-cps baseband and another with a 950-cps baseband. Spectrum-pattern data are normalized with respect to speech amplitude, for compatibility of the polymodal vocoder with an auxiliary processor for spectrum-pattern matching to further reduce the data-rate requirement and provide additional data rates. The polymodal system also lends itself to a concept of a fully adaptive system, self-adjusting to match available channel capacity. Design features of the polymodal vocoder are discussed, and recordings of the various modes presented. [This program was supported by Air Force Cambridge Research Laboratories (OAR) under contract AF19(628)-302].
Real-Time Adaptive Speech-Recognition System
Authors: Talbert L. R. , Groner G. F. , Koford J. S.
Published: November 2005

This paper describes a real-time speech-recognition system employing adaptive threshold logic elements called “Adalines.” Time-normalized digital patterns representing the time-frequency spectrum are obtained from amplitude-normalized outputs of 8 bandpass filters. Adaline networks that perform the speech-pattern classification are simulated in an IBM-1620 computer. In a recent experiment, the Adalines were trained on 8 samples each of a group of 16 phonetically balanced words. After correct classification of these samples, different samples, spoken by the same speaker, were correctly identified 112 times without error. When tested on new voices of the same sex, the machine achieved an average recognition rate of 90%; however, substantial improvement is realized by including the new speaker(s) in the training group. The use of adaptive networks as pattern classifiers has achieved enormous system flexibility, since complete redesign of the classification system can be accomplished by a training process. The system has successfully carried out many speech-recognition tasks, among them recognition of the 10 digits spoken in 4 different languages and identification of different speakers saying the same spoken words.
Computer Program to Aid in the Selection and Evaluation of Vocabularies for Word Recognizers
Authors: Forgie C. D. , Forgie J. W.
Published: November 2005

The performance of a word recognizer depends upon the vocabulary that it attempts to recognize. A computer program has been written to aid in the selection and evaluation of vocabularies for word recognizers. The program operates by predicting the performance of a given recognizer on a given vocabulary. The words in the vocabulary are treated as strings of phonemes, and it is assumed that the word recognizer being evaluated operates in terms of such strings. The program searches the vocabulary for word pairs that would be confused with each other if the recognizer were unable to make certain discriminations. When a confusable pair is found, it may be added to a list of confusions for later printing, or one word of the pair may be deleted from the vocabulary. The latter mode of operation results in a reduced vocabulary on which the recognizer should perform well. Results are presented for a vocabulary of about 1000 common words.
Message Probability and Message Reception
Authors: Pollack Irwin
Published: November 2005

Are words which occur more frequently “easier to hear” than words that occur less frequently? The conventional intelligibility analysis is biased to give an affirmative answer to this question. It is shown that unbiased analyses, however, also give an affirmative answer for words derived from small, known message sets differing in relative frequency of occurrence.
European Experience with the Application of Insulation Requirements
Authors: Brandt Ove
Published: November 2005

As an introduction, a brief survey of existing insulation requirements in Europe is given. Further, it is shown that such requirements are defined in slightly different ways. The advantages and disadvantages of the different definitions are demonstrated. It is proposed to have an international definition of insulation requirements in close relation with the international agreement on insulation measurements to be used in the laboratory and in the field. Finally, some practical experience with field requirements is given.
Linear Dimension in Vibrotactile Sensitivity
Authors: Verrillo Ronald T.
Published: November 2005

Sensitivity to vibration on the hand was determined as a function of frequency and contactor configuration. Earlier studies had determined that a contactor in the form of an annulus yielded a slightly lower threshold than a solid contactor having the same circumference. The present study verified this result. In addition, a contactor consisting of a sharp straight edge equal in length to the circumference of the solid and annulus was tested. The straight edge yielded data that closely parallel those of the annulus. Results indicate that the important parameters in vibrotactile sensitivity may be associated with the linear dimension of the skin displacement rather than area or contactor configuration. The result has theoretical implications concerning the mode of excitation.
Activation of the Efferent Cochlear Bundle in the Pigeon
Authors: Desmedt J. E. , Delwaide P.
Published: November 2005

An efferent cochlear bundle was demonstrated anatomically in the pigeon [Boord, Exptl. Neurol. 3, 225 (1961)]. We have developed techniques for stereotaxic stimulation thereof in pigeons prepared under Fluothane anesthesia and immobilized by transection of cervical spinal cord plus injection of Flaxedil. Responses to tone pips or clicks were recorded oscillographically from the exposed round window. When the testing sounds are preceded by delivery of, say, 30 shocks at 300/sec to the region of the efferent cochlear bundle close to the midline (histologically controlled), the cochlear microphonic (CM) potential is potentiated while the neural (N1) spike is reduced. These effects were titrated as equivalent dB changes in sound energy [cf., Desmedt, J. Acoust. Soc. Am. 34, 1478 (1962)] and they have not exceeded +6 dB equivalents for CM and −6 dB equivalents for N1. Corresponding figures for the cat's olivocochlear bundle are +4 dB equivalents for CM and −25 dB equivalents for N1 (Desmedt, loc. cit). The marked contrast in potency for gating out neural responses evoked by sound in these two species raises questions about (1) behavioral significance of efferent bundle in birds, and (2) mode of action on the inner ear. [This work was supported by Office of Aerospace Research, USAF, and by the National Institute of Neurological Diseases and Blindness, National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare.]
Acoustic Probe for Intraocular Pressure
Authors: Roth Wilfred , Blake Dale G.
Published: November 2005

A novel acoustic-stiffness meter to measure intraocular pressure is described. A light mass contacts the cornea and resonates with eye stiffness. Stiffness and resonant frequency vary with intraocular pressure. Pressure range for human eyes produces frequencies from 50–300 cps. Theory and experimental data are presented.
Arterial Supply of the Cochlea in the Domestic Cat
Authors: Reddy John B.
Published: November 2005

Despite the previous investigations of Nabeya, Batson, Schambaugh, and others, the basilar-vertebral circulation of the cat's cochlea is not well-documented. The variations of the anatomy of the anterior-inferior cerebellar artery in cats and humans are discussed. A perfusion method utilizing radioopaque material in cats is described and may eventually be utilized in the study of the dynamic circulation of the cochlea. This arterial supply should be well-understood before significant neurophysiologic recordings are reported in this laboratory animal.
Correlational Analysis of Evoked Responses
Authors: Gerken George M.
Published: November 2005

In a previous study, electrodes were implanted permanently in auditory cortex in 6 cats, and the cortical responses evoked by acoustic stimulation were recorded daily over a period of several weeks. Recordings were made simultaneously from the 4 pairs of electrodes in each animal. The evoked response was typically recorded as a complex potential of characteristic form consisting of several surface-positive and surface-negative deflections. These deflections were measured by an arbitrary but standardized procedure, the measurements being referred to as components of the evoked response. The purpose of the present analysis was to determine the relationships among 4 components of the evoked response and, hence, to see if there was some empirical basis for regarding the evoked response as a unitary phenomenon. To accomplish this the product-moment correlation coefficient r was utilized and for each electrode pair 6 correlation coefficients, representing the interrelations among the sets of data for the 4 components, were computed. Although the computed correlation coefficients were usually positive and sometimes of appreciable magnitude, it is concluded that the evoked response is best regarded as several interrelated responses.
Pseudorandom Signal-Correlation Methods of Underwater Acoustic Research
Authors: Stewart James L. , Allen Willard B.
Published: November 2005

New methods of underwater-acoustic-propagation research have been developed in which noiselike or pseudorandom signals, generated by shift-register encoders, are detected by correlation techniques. Three classes of experiments are described: (1) the signal received is crosscorrelated with a time-delayed and time-compressed replica of the transmitted signal; (2) two received signals are crosscorrelated and studied as a function of hydrophone separation; (3) the received signal is correlated with that received from a later repetition of the transmitted signal. It will be demonstrated both theoretically and experimentally that the results of the first class of experiments are different from and unpredictable from those obtained by employing the usual filtering and detection of impulsive or single-frequency signals. The problems arising from multipath interference, which are different for the first and second classes of experiments, are discussed and some solutions proposed. A heterodyned clipped Deltic correlator for field use, which searches simultaneously for the signals in range and Doppler, is described.
Acoustic Scattering from the Ocean Bottom
Authors: Thompson Kingsley P. , Hurdle Burton G.
Published: November 2005

An experiment has been conducted to obtain the intensity field of sound scattered from a relatively rough region of the ocean bottom. Pulsed 19.5-kc/sec transmissions, directed towards the bottom, were made from a ship as it approached and passed a special radio sonobuoy. Sets of data were taken with the beam incident on the bottom at grazing angles between 30 and 90 degrees. Bottom-scatter returns in the monostatic direction were received on the source transducer, while reception in other directions was made by the buoy. The source was a tiltable piston transducer with a beam width of approximately 8°. The buoy hydrophone was omnidirectional in the horizontal plane with a rejection of surface-reflected signals in the vertical plane. The data were analyzed on the basis of an isotropic-scatter model, taking the velocity gradient into consideration. Results are presented in the form of polar plots of bottom scattering strength These intensity fields have been obtained from areas east of Bermuda for two bottom types, mudcoral and ooze, in water depths of approximately 750 and 1250 fathoms, respectively. Implications of the characteristics of these fields, along with results of other aspects of the data, are discussed in paper BB6.
Computer Study of the Pressure-Equalized Barrel-Stage Transducer
Authors: Middleton Foster H. , Haas Robert S.
Published: November 2005

In order to explain certain experimental phenomena of the pressure-equalized barrel-stave transducer, a spherical model is postulated. A digital computer program has been written that is used to determine the farfield radiation pattern in terms of a known or assumed surface-velocity distribution. Several different velocity functions are employed to explain sensitivity reductions at certain frequencies and notches in the radiation pattern. Once these explanations are available, new designs may be improved and existing transducers can be changed as appropriate. The velocity distributions used in this work correspond to complex modal vibrations of the radiator, and were suggested, in part, by experimental data on a particular transducer. The principal advantage of the computer approach is the speed with which any desired velocity distribution may be altered and the resulting farfield quantities recalculated. The method holds promise for the future development of design procedures. The computer program with an explanatory narration is included with this paper, as are samples of experimental and computer-produced radiation patterns.
Vertical Directionality of Ambient Noise in the Ocean
Authors: Fox G. R.
Published: November 2005

Measurements have been made of the vertically directional distributions of ambient noise in the deep ocean in the frequency range 200–1500 cps. The measurement equipment consisted of an experimental 300-ft vertical linear array of 40 hydrophones several hundred feet above the ocean bottom, at a depth of about 15 000 feet. Results are based on average levels received on the beams of the array steered from horizontal to vertical and on levels measured with omnidirectional hydrophones. The effects of local weather conditions on the vertical noise distributions are discussed. [This work was supported by the Bureau of Ships, U. S. Navy.]
Acoustical Isolation from Animal Sounds
Authors: Hirtle P. W. , Farrell W. R.
Published: November 2005

Research and veterinary facilities almost always require outdoor areas for housing animals. In the design of such facilities, it is important to consider potential neighborhood annoyance due to animal noises. Acoustical analyses of two animal research centers are presented. The analyses take into account such factors as spectra of animal sounds, location and orientation of facilities, sound propagation out of doors, neighborhood reactions to noise, etc. Included are measured spectra for some animal sounds (those of dogs and monkeys). These spectra peak sharply in the 600- to 1200-cps region, and, as a result, this frequency region will usually be most critical in determining neighborhood reactions.
On the Introduction of Prior Information into a Computer-Programmed Speech-Recognition Scheme
Authors: Hughes G. W.
Published: November 2005

Every speech-recognition scheme, proposed or built, incorporates a great deal of information concerning the nature of the “unknown” utterance. Language structure, articulatory constraints, speaker characteristics, statistically derived acoustic patterns, and special or limited input vocabularies are categories of prior information whose use causes some of the disparities in the types of systems being attempted today. The amount of information introduced and the consequences on the identification procedures and results are often overlooked; these are discussed. Some experiments are presented that attempt to assess the role of speaker peculiarities in automatic recognition. In particular, a measure of the latitude of individual speakers in fixing the acoustic correlates of the distinctive feature tense-lax is sought. [The research reported in this paper was sponsored by the U. S. Air Force Cambridge Research Laboratories, Office of Aerospace Research, under contract AF 19(628)-305.]
Acoustic Parameters of Vocal Pitch
Authors: Speaks Charles E. , Schultz Martin C.
Published: November 2005

Recent perceptual studies employing analysis of natural vowels and synthesized complex waves have suggested that spectral parameters other than fundamental frequency may be operative in pitch perception. The present study was designed to investigate the extent to which high-pitched male subjects and males with normal vocal pitch could be distinguished by characteristic resonant frequencies and amplitudes, as well as fundamental frequency. Pitch judgments scaled by the pair-comparison techniques were related to spectral parameters. Data were collected from 1500-msec midvocalic segments of /i/ vowels produced by 25 subjects. The data suggested that some form of physiologic changes are manifest for the two groups such that the characteristics of the acoustic resonators are different for males with abnormally high-pitched voices. These subjects utilized a resonating system wherein the second formant was approximately 200 cps higher than was apparent for persons of normal vocal pitch. No differences in formant amplitudes were found. Inconsistencies in the fundamental frequencies and listener pitch-judgment data demonstrated the need for expanded knowledge of the relation of listener perception of pitch to parameters of the acoustic signal.
Identification from Voice: Techniques for the Reduction of Trial-Retrial Variability
Authors: Kurtzberg Richard L. , Alpert Murray , Friedhoff Arnold J.
Published: November 2005

The use of the voice as a means for identifying an individual is limited to a great extent by marked variability of trial-retrial responses. This paper discusses several techniques designed to reduce this variability. A spectral analysis series of 10 measurement points in the frequency range from 500 to 2000 cps with passbands 1 cps in width is employed for the vocal analysis. Data are presented from a series of 5 experiments with 70 subjects. Results of these studies are presented: (1) Frequencies below 500 cps are highly labile. They are shown to vary as a function of mild stress, time, and simple stimuli. (2) The energy distribution above 2000 cps depends more upon the spoken sound than upon the individual characteristics of the speaker. (3) Subjects were instructed to match the fundamental frequency to a standard tone (125 cps for males, 250 cps for females). (4) Each subject matched the intensity of his voice to a standard. Thus, fundamental frequency and intensity of the voice sample can be controlled. These techniques eliminate the major sources of variability in intrasubject vocal analysis. The extent to which these techniques permit discriminations among individuals on the basis of their speech is discussed.
RCA Victor “Dynagroove” System
Authors: Olson Harry F.
Published: November 2005

The RCA Victor “DYNAGROOVE” system is a planned evolution of improvements in all aspects and elements of sound recording by means of disk records. The main objective has been to provide a distinct improvement in performance by the development of a new cohesive and integrated system from the artist's conception of the music to the reproduction of the sound as perceived by the listener.
Radiation Impedances of Plane-Array Elements
Authors: Martin Gordon E.
Published: November 2005

This paper considers the radiation impedances of various sizes of elements forming a plane array. The mutual-interaction impedance for various shapes of radiators and types of baffles is discussed in order to form a basis for computation of the total interaction impedances. Erroneous results can be obtained if the wrong theoretical model is used for the element; specific limitations of the circular piston and the pulsating hemisphere are described. Suitable techniques are discussed and results are compared with those of Stenzel and Pritchard. It is shown that the radiation impedances reported at the November 1962 Meeting were erroneous. The general behavior of radiation impedance is summarized.
Velocity Control of Transducer Arrays
Authors: Martin Gordon E.
Published: November 2005

The trend in underwater acoustics toward lower frequencies requires that transducers consist of large arrays of many elements. The element's dimensions are often small as compared to the wavelength. In some cases, it is possible for element radiation interactions in arrays to result in a mechanically unstable system wherein the velocity distribution over the array becomes uncontrolled. This paper reviews the developments of this problem, including the favorable solution for velocity control. Early work in the field of radiation impedance of arrays is reviewed. The author's calculations and experiments of 1956–1957 are described as an illustration of uncontrolled-velocity distribution. Study of this problem proceeded at this Laboratory and Carson published a cure for the trouble, which was derived for a magnetic-type transducer with one mechanical degree of freedom. He obtained a velocity-control technique for piezoelectric transducers by duality. Another method of analysis involving network theory is described that greatly simplifies the explanation of velocity control. Three new array velocity-control criteria are discussed. Elementary examples are described, including mechanical systems having one and two degrees of freedom. These examples are used to show the correct method of choice of the velocity-control reactor.
Solion Infrasonic Microphone
Authors: Collins Joseph L. , Richie William C. , English G. Earle
Published: November 2005

The solion infrasonic microphone is an electrochemical pressure transducer designed for the measurement of atmospheric-pressure variations. An over-all transducer frequency response from 0.01 to 50 cps and a dynamic range from 0.1 to 1000 dyn/cm2 has been obtained with the design described. Stability, sensitivity, low power consumption, and remote-operation capability are the inherent features of this new acoustic tool. A description of the solion transducer, of the infrasonic microphone, and the over-all response of the system is presented.
Study of Arrival Angles for “RSR-Type” Energy Received on a Model Sloping Ocean Bottom
Authors: Murphy D. A.
Published: November 2005

Energy originating near the surface that propagates over long distances in the deep ocean is primarily confined to the refracted-surface-reflected (RSR) mode. An ocean model using two straight lines to represent a horizontal bottom and inclined slope was employed to study angles of arrival of “RSR-type” energy. An 11-layer velocity profile was used to calculate ray paths for three receiver depths located on the slope. Three discrete arrival angles were observed for RSR energy reflected once or less from the slope. Range-angle plots were used to illustrate the effects of the slope on the arrival angles. A steeper slope causes the slope-reflected rays to be separated more in arrival angle from directly received rays. Deepening the receiver causes merging and eventual elimination of the two slope-reflected rays; thus, it is possible to eliminate unwanted “RSR-type” energy by choosing a suitable receiver depth. [This work was sponsored by the U. S. Office of Naval Research.]
Model Studies of a Single Surface-Bounce, Underwater, Acoustic-Communication Channel
Authors: D'Antonio R. A. , Hill R. F.
Published: November 2005

Underwater acoustic-communication experiments are being conducted in a 12×4×4-ft model tank equipped with a remote-controlled transducer-positioning system and a “sea-state” generator. The statistics of the various sea states are obtained by utilizing two waveheight indications. The output of these devices is instantaneous profiles of the surface at particular locations. The output of the waveheight indicators is digitized, recorded onto IBM magnetic tape, and analyzed on an IBM-1620 computer. Auto- and cross-correlation functions as a function of position are obtained for various modeled sea states. An advantage of the model tank is that it is possible to investigate any individual acoustic path desired without the confusion of multipaths that occur in typical real ocean channels. The path that we are investigating at this time is the single surface bounce. A train of constant-amplitude pulses, amplitude-modulating a 1-Mc/sec carrier, is reflected off the surface and the received wave is recorded. Using the same data-processing equipment described above, the correlation functions for the transmitted and received pulse trains are obtained for various “sea states.”
Some Intense, Low-Frequency, Underwater Sounds of Wide Geographic Distribution, Apparently of Biological Origin
Authors: Walker R. A.
Published: November 2005

A certain intense, underwater, transient sound has been observed over extended areas of the Atlantic and Pacific Oceans. The power spectrum for a single pulse of this sound is strongly peaked, energy being confined to a narrow band centered in the vicinity of 20 cps; the sounds accordingly have been named twenty-cycle pulses. A single pulse typically lasts about one second; the pulses normally occur in trains, or groups, characterized by remarkably regular repetition rates. A common rate is one pulse approximately every 10 sec, although others are observed. A typical pulse train is of several minutes' duration; separated by silent periods two to three minutes in length, pulse trains often repeat for many hours. On the continental shelf south of New England, the positions of scores of sources of this sound have been determined by remote acoustic ranging; the sources are found to move. Speeds are typically a few knots. Radiated sound levels are so high that the sources are detectable tens of miles away. Source densities of only one in several hundred square miles are most common. Movements appear random, suggesting that the source is biological. The low areal density, the high source level, and speeds of a few knots that are sustained for hours suggest a large animal. Characteristics possibly correlated with the sounding cycles of whales are apparent. The hypothesis that the sounds originate from the heartbeats of whales appears credible on several counts.
Temporary Threshold Shift in Successive Sessions for Subjects Exposed to Continuous and Periodic Intermittent Noise
Authors: Fletcher J. L. , Loeb M.
Published: November 2005

Eight young men and eight young women were exposed for 10 min in five successive sessions to 110-dB (SPL), 1200- to 2400-cps continuous noise; an equal number were exposed similarly to 1200- to 2400-cps, 120-bB (SPL) intermittent noise, alternately switched on and off for 1 sec over 20-min sessions. Continuous threshold tracings were obtained at 4000 cps for 2 min preceding and 1 min following exposure. For the intermittent noise, there was a tendency for temporary threshold shift (TTS) to decrease in successive sessions; for the continuous noise, TTS remained fairly constant in successive sessions. Significance of the findings and possible underlying mechanisms are discussed.
TTS Produced by Low-Level Tones and the Effects of Testing on Recovery
Authors: Bell Donald W. , Fairbanks Grant
Published: November 2005

To evaluate TTS from exposure frequencies presented at low levels, and the effects of threshold testing on recovery, sensation levels of 10, 20, 40, and 60 dB and frequencies of 1, 2, and 4 kc/sec were presented for 60 sec, followed by 0, 15, 30, or 60 sec of silence before testing. Twenty audiometrically normal subjects were used. At all frequencies, TTS was found to be a monotonic function of level if measured within 5 sec after exposure. Recovery from TTS induced at 60 dB SL appeared faster than at 40 dB SL. Early recovery rate increased directly with level of exposure when recovery was measured by continuous tracing, and, with a few exceptions, the same relation was found when recovery was measured by testing after intervals of silence. At 40 and 60 dB SL, TTS varied directly with frequency when measured immediately after exposure. Continuous postexposure threshold testing significantly retarded recovery produced by all frequency-by-level combinations. Thirty sec after exposure, this retardation averaged about 3.5 dB. Recovery after 15 sec of silence was approximately equivalent to recovery after 60 sec of continuous testing. [This research was aided by National Institutes of Health research grant OH-00053, U. S. Department of Health, Education, and Welfare.]
Pitch Perception of Randomly Triggered Pulse Pairs
Authors: McCLellan Max E. , Small Arnold McC.
Published: November 2005

The precision with which listeners matched the pitch of a sinusoid to the pitch corresponding to the reciprocal of time separation between members of randomly triggered, dc pulse pairs was investigated. Six time separations were utilized under each of three rates of random “repetition.” In agreement with previous findings by the authors, the modal value of listener responses was, generally, found to be in close proximity to the reciprocal of time separation. A spectral analysis of the stimuli revealed peaks in the spectral envelope that appeared to be spaced by the frequency corresponding to the reciprocal of time separation. These findings suggest that information in the frequency domain may not be ruled out as important in the perception of time-separation pitch.
Ultrasonic Attenuation in Thin Films
Authors: Ghering Walter L.
Published: November 2005

The loss factor of a liquid is usually referred to an effective infinite medium to avoid the influence of surface-tension effects. For finite samples, the surface tension and configuration influences the effective loss factor of the sample and when the physical shape of the specimen approaches a thin film these effects predominate. The effective loss factor of a number of liquids and semi-solid substances was measured for various film thicknesses. The data show the effect of film thickness on the loss factor and the effectiveness of the substance for ultrasonic damping. The arrangement employed used parallel-mounted quartz crystals in tuned circuits. The system was excited to resonance by a pulse and the response and decay of the system were recorded. By means of energy considerations, the effective loss factor of the sample was determined. [This work was sponsored by the U. S. Air Force.]
Ultrasonic Waves of Finite Amplitude in Solids
Authors: Thompson D. O. , Breazeale M. A.
Published: November 2005

The distortion of an initially sinusoidal ultrasonic wave in solids has been experimentally observed. The dependence on pressure amplitude of the propagation characteristics of such waves is discussed, and the relationship between this phenomenon and third-order elastic constants used to describe anharmonicity of solids is pointed out.
Arrays for the Measurement of the Angular Distribution of Ambient Noise in the Ocean
Authors: Arase E. M. , Arase T.
Published: November 2005

Various models have been suggested to describe ambient noise in the ocean. For example, in terms of the angular distribution at a point, isotropic- or peaked-noise fields are assumed. In terms of the distribution of sources, a uniform distribution of surface sources is usually assumed. The experimental verification of such predictions requires linear arrays only, since all of the models assume cylindrical symmetry. The resolution and discrimination of such linear arrays are discussed for various spacings of the array elements and models of the noise field. Best results are obtained by separating the array elements by approximately 12 wavelength. For noise fields that are not cylindrically symmetric, planar or volume arrays are required. Characteristics of these arrays are also discussed. [Hudson Laboratories, Columbia University Informal Documentation No. 34. This work was supported by the U. S. Office of Naval Research.]
Spatial Resolution of Linear Arrays against Noise
Authors: Axelrod E. H.
Published: November 2005

Stone [J. Acoust. Soc. Am. 34, 328 (1962)] has shown that uniform linear arrays act as low-pass spatial-frequency filters against ambient noise, rejecting components of the noise field above a cutoff frequency sc. This work is extended to give an approximation to sc for linear arrays in general. It follows from the sampling theorem that measurements at steering-angle increments characterized by sc give all the information about the noise field obtainable with a particular array. The following implications are discussed: (1) Noise measurements at finer increments give rise to spurious detail or implausible oscillations in the computed noise field. (2) Apparently reasonable computations may yield physically impossible fields. In fact, an infinite set of noise fields exists that produces exactly the measured responses. These fields are shown to consist of a principal part with spatial frequencies below sc, together with one of an infinite set of fields with frequencies greater than sc, which produce zero response when scanned by the array. (3) This principal part may be determined by a convergent iterative procedure only for certain values of the Fourier transform of the array gain. Application of these results is made to a deep-water vertical research array. [This work was supported by the Bureau of Ships, U. S. Navy.]
Data Reduction for Directional Noise Fields
Authors: Schoomer B. Alva
Published: November 2005

Using the results presented in another paper [E. H. Axelrod, Paper G2, this meeting], a data-reduction procedure is derived for computing the vertical directionality of an ambient-noise field from the responses of a vertical array. The resulting equation produces the best noise field in the least-squares sense. The computational procedure involves (1) initial smoothing of the observed data; (2) selection of appropriate beam spacings, using the critical spatial frequency of the array; (3) calculation of the ambient-noise field as a function of angle from the vertical. Typical results are presented and their sensitivity to the procedure is discussed. The application of the results to an existing array is presented.
Effect of Ice Cover on Shallow-Water Ambient Noise
Authors: Payne F. A.
Published: November 2005

Shallow-water ambient-noise measurements in the frequency range 10–3000 cps have been made in the Gulf of St. Lawrence off the north coast of Prince Edward Island in open-sea conditions and with ice cover. The presence of ice is found to make a large difference both to the level and spectral distribution of the ambient noise. Results are presented that illustrate both the effect of ice cover on the ambient noise and the transition from the “open-water” to “ice-cover” conditions.
Noise under Shore-Fast, Winter Pack Ice
Authors: Ganton J. H. , Milne A. R.
Published: November 2005

Records of ambient noise under shore-fast, winter pack ice were obtained during the “dark” period in January and early February 1963. Four hydrophones, in a 122-m square array were mounted on the bottom in 92-m of water near Ellef Ringnes Island in the Arctic Archipelago. Thermal stresses in the surface of the ice, caused by changing air temperatures, governed the rms noise levels. In general, decreasing air temperatures caused tensile cracking at the surface of the ice, with a resultant increase in the impulsive noise detected in the water beneath. Simultaneous recordings of noise from more than one hydrophone permitted statistical measurements to be made on the directions of the sources of these impulses. In addition, recording during the dark period removed the influence of solar radiation on the surface stresses in the ice sheet.
TITAN II Noise-and-Vibration Test Programs
Authors: Bond D. A. , McGregor Howard N.
Published: November 2005

A brief summary of the background and special noise-and-vibration test programs utilized in the development of the TITAN II silo-launched ICBM is provided. The relative merits of the various types of test methods are critically evaluated with recommendations, based on the TITAN II program experience, for methods considered most promising for future ICBM and space-vehicle applications.
Some Studies of TITAN II Noise-and-Vibration Data
Authors: Franken Peter A. , Keast David N.
Published: November 2005

The use of noise-and-vibration data has played an important role in assessing the dynamic environment of the TITAN II vehicle. The results of this work have contributed to the current fund of engineering knowledge and also pointed out important areas of uncertainty. Three general topics are discussed in a review of the state of the art: (1) empirical and analytical methods for estimating rocket noise and structural response; (2) recent statistical-data studies, in which variations associated with measurement location, analysis bandwidth, etc., have been derived; and (3) unsolved problems.
Some Sonic-Boom-Induced Building Responses
Authors: Cawthorn Jimmy M.
Published: November 2005

Results are presented from a series of tests in which a building structure instrumented with microphones, strain gauges, and accelerometers was subjected to sonic booms. The significance of such variables as aircraft Mach number, altitude, and flight direction is discussed. Included for discussion are shock-wave pressure-loading time histories and the associated transient responses of various components of the building. The measured stress levels associated with the range of sonic-boom overpressures estimated for routine military and commercial operations are noted to be relatively small as compared to the design stresses of the building and may be of the same order of magnitude as those associated with such everyday occurrences as door slamming.
Effect of Signal Bandwidth on Measurements of Sound-Transmission Loss of Partitions
Authors: Huntley Ralph , Siekman William
Published: November 2005

A number of measurements of the sound-transmission loss of 14-in. glass made with different signals are compared. Signals used are one-, 12-, and 13-octave bands of white and pink noise and tones warbled ±20 cps from the center frequency 5 times/sec. It is concluded that the 112-octave signal bandwidths are too wide to give the detail needed and that absorption measurements made with these signals contribute inaccuracies greater than the precision otherwise possible. It is recommended that signal bandwidth be standardized at 13 octave and that measurements be made at contiguous 13-octave intervals at the American Standard Preferred Frequencies.
Effect of Receiving-Room Absorption on Transmission-Loss Measurements by AMA-1-II Method
Authors: Huggins Donald N.
Published: November 2005

The room-to-room test method designated AMA-1-II was designed to measure sound transmission through suspended acoustical ceilings by way of a common plenum, but has also been used to measure the transmission loss of the partition dividing the two rooms with the plenum path closed off. Tests have been conducted on a single partition under varying conditions of absorption and diffusion in the rooms on both sides. The results show that the value of transmission loss determined from the standard formula TL=L1−L2+10 log (S/a) is independent of receiving room absorption a over a wide range, including complete ceiling coverage with a material having an absorption coefficient greater than 0.80, provided a is measured by a steady-state method.