bluuebunny/crossref_metadata_2025 huggingface dataset:
Sequential Dependence in Signal Detection, and Parameter Estimation by Sequential Tracking (PEST)
Authors: Taylor M. M. , Forbes S. M. , Creelman C. D.
Published: November 2005

The PEST psychophysical method [Taylor and Creelman, J. Acoust. Soc. Am. (to be published)] was used to determine the signal burst intensity giving 80% correct responses in a 2AFC detection task. Each PEST run was immediately followed by fixed level trials at that level. For the fixed level trials, P(C) averaged only 0.75. However, the probability of a correct response conditional on a correct preceding response, P(C/C−1), averaged 0.765. Assuming the apparent correlation to result from averaging results over periods of good and poor detection, the worst possible performance during “good” periods is about 0.80. These results suggest that PEST may be more accurate than are the conventional fixed level methods. PEST makes the task easier when the subject “loses track” of what he is trying to detect; whereas in a fixed level experiment the subject has little opportunity to refresh his memory for the signal to be detected. In computer simulation, PEST has proved to be quick and unbiased.
Sound Radiation of Complex Vibrators
Authors: Skudrzyk Eugen J.
Published: November 2005

The simplest type of vibrators are point and line sources. The sound fields of such vibrators are uncorrelated over space and their energies add, if they are separated by a distance greater than about 14 wavelength. Vibrators with nodal lines radiate as if their radiation impedance were ρc if the distance between the nodal lines is greater than half a sound wavelength. If their distance is smaller, they generate sound because of the distortion of the natural mode patterns by the driving force and because of the discontinuity of the vibration pattern near the edges of the vibrator. Both types of sound radiation turn out to be predictable in a very simple manner by a kind of Huygen's principle. Because ribs also distort the vibration field, they lead to increased sound radiation. [Work sponsored by the Office of Naval Research, Washington, D. C.]
Comparison of Methods of Farfield Prediction:
Authors: Murphy Donald A.
Published: November 2005

All farfield prediction methods utilizing nearfield measurements on a closed surface are describable as applications of a Green's integral formula. For truncated measuring surfaces, however, the corrections that must be made to the weighting functions derived from the Green's integral formula can severely limit their usefulness. For the case of spherical and cylindrical measuring surfaces, the corrections for truncated surfaces do not appear to be necessary; but for truncated planar surfaces they are dominant. The broadband “Green's transfer” functions used in farfield prediction for spherical surfaces have been described in a previous paper [J. Acoust. Soc. Am. 39, 1222(A) (1966)]. The Green's transfer functions for a cylindrical surface have been calculated and farfield predictions made on the digital computer. They are very similar to those for the spherical surface having the same weighting and phasing, although calculated from an altogether different mathematical expression. This expression will be compared to that used by Baker (Univ. of Texas Defense Res. Lab. Acoust. Rept. 196 (15 March 1962) for single-frequency measurements on a cylindrical surface.
Radiation Characteristics of a Circular Transducer Surrounded by a Nonconcentric Circular Shell
Authors: Moyer W. C. , Hamilton K. B.
Published: November 2005

An analytical solution is derived for the sound pressure field produced by a cylindrical transducer surrounded by a nonconcentric, circular, shell-type dome. This model represents an improvement over concentric circular dome models previously reported since transmit beams nonsymmetrically incident on the dome can be analyzed. Numerical results indicate two features, (1) the minor lobe structure of the farfield beam patterns is not symmetric relative to the beam axis and is dependent on the eccentricity of the dome and transducer; and (2) oblique incidence of the beam on the dome does not produce beam steering errors, i.e., the maximum response of the beam pattern agrees with the steered direction.
Automatic Evaluation of Time-Varying Communication Systems
Authors: Hecker Michael H. L. , von Bismarck Gottfried , Williams Carl E.
Published: November 2005

Many types of speech-communication systems may be readily evaluated with available electronic devices which employ the concept of the Articulation Index (AI) (e.g., the Speech Communication Index Meter). To study the feasibility of using such devices to evaluate time-varying systems, recordings were made of the transmission characteristics of a troposphere scatter system. At many specific points in time in these recordings, AI's were calculated and intelligibility scores were obtained from listeners with the aid of a special test procedure. For most points, the intelligibility score could be reasonably well predicted from the AI. This finding was interpreted as indicating that the existing devices are potentially capable of evaluating time-varying systems.
Evaluation of Underwater Speech Communicators
Authors: Hollien Harry , Coleman Robert F. , Thompson Carl L.
Published: November 2005

Evaluation of speech intelligibility—under optimum conditions—was carried out on a number of military and commercial underwater communicators. The site of the research was NRL's Underwater Sound Reference Division's Bugg Springs facility and the communicators evaluated were: (1) Aquaphone, (2) Aquasonics, (3) Bendix Watercom, (4) MAS (prototype), (5) PQC, and (6) Yack Yack (two configurations each were available for all units except Bendix and MAS). The group of talkers consisted of four Navy divers, four phoneticians and four women; however, slightly different groups were used for Bendix, PQC, and MAS. Divers descended 35 ft to DICORS and read PB-25 word lists equated for difficulty by Campbell. Recordings were made at the surface on an Ampex 601. Subsequently, intelligibility scores were obtained by playing the speech material to 12 listeners. Communicator intelligibility scores varied from levels close to zero to slightly over 50%. The poorest scores were obtained from the PQC and units utilizing throat microphones; the highest from the Aquasonics systems. [The project was supported by the Office of Naval Research.]
Reverberation Resolution Using Various Waveforms
Authors: Cobb A. Donn
Published: November 2005

This paper describes the results of an experiment conducted to determine the usefulness of various waveforms to resolve discrete reverberators. Returns from several topographic reverberators were obtained by using waveforms of essentially the same time duration. Continuous-wave (CW), hyperbolic frequency modulation, and pseudorandom noise were transmitted in an ocean basin and their reverberant returns recorded at the output of matched filters. The comparison is made on the basis of the resolving power of the waveforms used. In general, the results indicate that at short range, where many reverberant returns are received, the coded waveforms are more effective than CW. Conversely, at long range for discrete returns, it appears that CW is more effective, since the in-phase summing is less affected by the temporal and spatial stability of the wavefront.
Born Approximation in One-Dimensional Scattering Problems
Authors: Soodak Charles , Harrison Mark
Published: November 2005

If one attempts to find the transmission of sound through an arbitrary scattering layer by the use of standard integral equation techniques, an unexpected difficulty with the Born approximation is encountered. The first Born approximation, i.e., the unperturbed plane wave, gives a transmission coefficient greater than unity for all scattering layers. This is clearly incorrect. In this paper, a technique is presented for resolving these difficulties. It is shown that a scattering layer, whose index of refraction varies as a function of the coordinates in a complicated fashion, can be approximated by a series of layers with constant index of refraction provided that one considers only wavelength large in comparison to the extent of each layer. These approximation give the needed correlation to the first Born approximation. This second Born approximation is found to give correct answers for the transmission of sound. Some calculated result for typical scattering layers that might be encountered in the ocean are presented. The results are compared with exact answers obtained by partial-wave methods.
Estimate of Volume Scattering Strength from Biological Samples
Authors: Fessenden Frederic P.
Published: November 2005

Biological samples of marine organisms obtained from an area in the Western North Atlantic south of New England in August 1966 have been used to estimate the volume scattering strength of the deep scattering layer. Specimens were collected by the deep submersible STAR III on six different occasions; each of three conditions of the deep scattering layer (descending, ascending, and surface layers) was examined twice. For each case the acoustic cross section and the animal concentration were used to determine the scattering strength values were obtained. Scattering strengths are presented for single frequencies of 4 kHz and 12 kHz as well as for several frequency bands, using the theory of Mohammed [(J. Acoust. Soc. Am. 41, 177–181 (1967)] for calculating average backscattering coefficients. At 4 kHz scattering, strength values ranged from −46 to −84 dB; at 12 kHz values ranged from −50 to −59 dB. A comparison of these result with experimental values obtained in similar areas shows reasonable agreement for frequencies near 4 kHz are lower than those of other investigations.
Volume Reverberation Measurements between Bermuda and Puerto Rico
Authors: Adlington R. H.
Published: November 2005

Measurements of volume reverberation were made at 11 stations spaced approximately 75 miles apart on a line between Bermuda and Puerto Rico. The sound source was a 1-1b TNT charge exploded 18 in. below the surface and the receiver was an omnidirectional hydrophone suspended at 30 ft below the surface. The data have been analyzed in octave bands from 1.6 to 25.6 kHz. The octave-band scattering strength of the water column drops sharply south of Bermuda but experiences a slight recovery near Puerto Rico. These measurements are in substantial agreement with those made by other observers.
Sea Noise Statistics
Authors: Arase Elizabeth M. , Arase T.
Published: November 2005

The statistics of ambient noise in the ocean have been investigated for single receivers and a closely spaced vertical array in the frequency range from 200 to 1600 Hz in 12 oct bands. Amplitude samples were taken at 20 msec intervals and were recorded digitally. The data were analyzed in blocks of 500, 1000, and 2000 data points. Distribution functions and moments up to the fourth order were computed and the samples were tested as to their normality and stationarity. A greater percentage of the smaller samples, i.e., 500 points, fall within the 95% acceptance intervals for normality than the longer samples, thus confirming the nonstationarity of ambient noise in the ocean. [Hudson Laboratories of Columbia University Informal Documentation No. 145. This work was supported by the U. S. Office of Naval Research.]
Modal Energy Division in Semi-Infinite Plates
Authors: Torvik Peter J. , McClatchey Jay J.
Published: November 2005

The stress and displacements within a semi-infinite elastic plate resulting from a time-varying (sinusoidal) edge loading are determined in terms of the modes of the infinite plate. A uniform normal stress with zero shear stress was supplied at the edge. The coefficients in the expansion are determined by a method given previously [J. Acoust. Soc. Am. 41, 346–353 (1967)]. Frequencies up to the frequency where five propagating modes are present are considered and the fraction of the supplied energy going into each of the modes determined. In the frequency range considered, the dominant mode changes from the first to the second and then to the third. A method for predicting the dominant mode requiring only a knowledge of the real roots of the Rayleigh-Lamb equation is suggested.
On the Response of Linear Structures to Classes of Pressure Fields
Authors: Cottis Milt G.
Published: November 2005

With the use of a general expression for the Green's function appropriate to a homogeneous, linear structure of finite extent and constant damping, the response integral representation is transformed to the wavenumber (k) and frequency (ω) spaces. Instead of specifying particular functions for the pressure field, general analytic properties of its spectra in the complex k and ω planes are assumed and the appropriate integrations are carried out with the use of residue theory. Response solutions are obtained for the important class of pressure fields whose spectral representations have poles of any order, including essential singularities. The field itself may be random or deterministic (truncated in space, time, or both), stationary or convecting. It is shown that the general behavior and physical properties of the response to any given load can be predicted with no computation on the basis of the analytic properties of the field in the complex k and ω planes. Application of this new formalism to a particular class of fields and to the question of pressure field simulation is discussed.
Matrix Analysis of Linear Structures Subject to Stationary and Correlated Random Inputs
Authors: Kouskoulas V. J. , Hurty W. C.
Published: November 2005

On the basis of correlation and spectral theories of complex random functions, this paper presents a unified matrix theory for the response of linear time invariant structures to stationary and statistically correlated random inputs. This theory is applicable to any structure whether it is a beam plate or shell, provided that its influence coefficients may be established. Various properties of the Input-output statistical matrices are exposed and formally proved for the simplifications they introduce in practical applications. The idea that the random response of a structure need not be based on its response to some deterministic input is fully employed. Indeed, no deterministic response is assumed and the Admittance matrix is established for nonproportional and proportional damping.
Comparison of Estimated and Measured LM Acoustically Induced Vibration
Authors: Bernstein M. , Pulgrano L.
Published: November 2005

The launch vibration levels induced during an acoustical test of the Lunar Module on several items are compared with estimates made by extrapolating statistically analyzed measured data. Procedures and data adapted from work by Mahaffey and Smith and by Barrett were used. Both methods were generally conservative. Estimates for a densely arranged 12 ton electronic equipment rack were particularly high. The use of component and support structure weights as attenuation factors is described to demonstrate the necessarily large reliance on engineering judgment in these procedures. The acoustical test, in which a representation of the entire Apollo system is excited through contiguous external ducts, is described briefly. An envelope of measurements of 282 accelerometer locations on the ascent stage considered as measuring equipment response is compared with 75 locations considered “primary” structure motion to demonstrate that specifying an envelope over the latter can be very conservative.
Acoustical Qualification of Saturn S-IC Fin Structures
Authors: Kennedy David R. , Beck Clark J.
Published: November 2005

The four aerodynamic fins, which are located close to the F-1 engines on the S-IC stage of the Saturn V vehicle, will be subjected to very high noise levels during both launch and flight. High-level acoustic energy is recognized as a potential cause of structural failure; hence, acoustic qualification tests were carried out on four fin specimens in a progressive wave chamber. Under identical test conditions (163 dB for 20 min), two of the specimens failed while two survived with no fatigue cracks detectable. This difference between the test results is attributed to the use of a thin layer of fiber glass tape in the construction of the two fins that did not fail. This tape was primarily used to separate the dissimilar metals of the ribs and skin. This paper describes the tests and presents data which show the reduction in strain levels produced by this thin layer of tape. [This work has been supported by the National Aeronautics and Space Administration.]
A Broad-Band Versus Narrow-Band Measure of Spectral Peaks in Vibration Data
Authors: Trummel Marc C. , Wiksten David B.
Published: November 2005

Spacecraft vibration caused by wide-band excitations may be subdivided into structurally related zones and presented a space average spectrum levels percentile spectrum levels, maximum envelopes, etc. In many cases, it is desirable or actually required to use frequency smoothed data such as the 13-oct band format. This requirement arises when predicting vibration levels on new spacecraft or structures by extrapolation from previous data or by analytic methods. Other applications occur in certain acoustic testing or case where only 13-oct data is available. As a final step in using broad-band frequency data, a peaking factor is required to estimate the narrow-band peaks to be expected. Empirical estimates of peaking factors are derived by analysis of vibration data from tests of two structurally dissimilar spacecraft: the MARINER and SURVEYOR. Data are analyzed and manipulated in 13-oct and narrow-band formats. Peaking factors are derived for: (1) a direct comparison of 13-oct and narrow-band data, (2) space averages of both types of data and, 3) 95th percentiles from sets of both types of data.
Use of Acceleration Feedback in Active Shock and Vibration Isolation
Authors: Calcaterra Peter C. , Schubert Dale W. , Ezekiel Frederick E.
Published: November 2005

This paper discusses the theoretical, as well as the practical aspects of using acceleration feedback in conjunction with an electrohydraulic closed loop control system to achieve shock and vibration isolation. The payload to be isolated is mounted on a hydraulic cylinder which is driven by a servo-valve. The signal from an accelerometer mounted on the object serves as the principal controlling signal to the servo loop. By striving to maintain zero acceleration the payload is thus isolated from disturbing base motions. A position feedback signal maintains the payload at fixed position within the cylinder even in the presence of steady base acceleration. The advantage of such a system is to provide isolation at frequencies below 1 Hz with minimal space and deflection requirements. In addition to rejecting base disturbances, the system is nearly insensitive to external forces applied to the isolated payload. A laboratory test model was designed and built to provide isolation against vertical dynamic excitations experienced by pilots during low-altitude high-speed flights. Analytical and experimental results are shown for the response of the model in the frequency and time domains.
Establishment of Objective Criteria Reflecting Subjective Response to Roller Bearing Noise
Authors: Lucht R. F. , Scanlan R. H.
Published: November 2005

In recent years, the question of noise generated by rolling element bearings has been given considerable attention. That a certain irreducible “minimum” noise will be created by a properly functioning bearing has been pointed out in earlier work. Acceptable roller-bearing noise levels above this minimum are regarded, in this paper, as being of necessity set by subjective standards. The paper addresses itself first to the validity or consistency of certain subjective evaluations of bearing noise made by a group of observers in representative circumstances. Next, the question is examined of what quantitative objective measurements are to be made in order accurately to reflect the character of the subjective evaluations. Finally, correlations between objective and subjective data are shown to be good. A representative method is thus defined for providing objective criteria that reflect subjective appraisal in this type of problem.
Responses of Single Fibers in the Auditory Nerve of the Squirrel Monkey to Paired Phase-Locked Low-Frequency Tones
Authors: Brugge John F. , Anderson David J. , Hind Joseph E. , Rose Jerzy E.
Published: November 2005

Data were analyzed on-line and from analog tape using a LINC computer. Stimuli were 10-sec complex sounds generated by summing two phase-locked low-frequency sinusoids. Both frequencies were within the response area of the unit and were related in ratios of small integers. Periodograms, i.e., distributions of unit responses over one period of the complex waveform summed for all repetitions of the waveform stimulus, were studied. The findings suggest that units discharge preferentially at times when the displacements in one direction of the cochlear partition are at or near maximal values. When intensity or phase of either stimulus component is varied with a resulting change in the complex waveform, there is a corresponding change in the periodogram. Concurrently, interspike intervals are grouped around values which are integral multiples of the time between the peaks of the periodogram, and the frequency of occurrence of such intervals is a function of the amplitude of these peaks (NB-06225).
Discharge Rates of Auditory-Nerve Fibers in Response to Electric and Acoustic Stimuli
Authors: Moxon E. C. , Kiang N. Y. S.
Published: November 2005

Responses of single auditory-nerve fibers in anesthetized cats were studied using electric and acoustic stimuli. Shocks a few decibels above threshold delivered through stimulating electrodes placed on or in the cochlea elicit responses with latencies that are both short (0.5 msec) and stable as compared with responses to acoustic clicks. For sufficiently high shock levels a one-to-one ratio of spikes to shocks can be maintained for several minutes at rates as high as 500/sec. The responses of single fibers to tones at the characteristic frequency (CF) cannot be maintained at rates higher than about 200/sec even at maximally effective stimulus levels. These results indicate that the maximum maintained rate of discharge under acoustic stimulation is not limited by the capabilities of the axon. [Work supported by NIH grants, the Joint Service Electronics Program, and a NASA grant.]
Peripheral Inhibition in Frog Primary Auditory Fibers
Authors: Liff Harold J.
Published: November 2005

The responses of complex units in frog eighth nerve can be inhibited by adding an inhibitory tone to the excitatory stimulus. The best inhibitory frequency is greater than the unit's characteristic frequency, and outside of its tuning curve. Units do not adapt to an excitatory stimulus during inhibition and if previously adapted they show a rebound in firing rate following termination of the inhibitory tone. The effect of an inhibitory tone is as strong after several minutes as at its onset. The dynamic range of rate of firing is not reduced by adding an inhibitory tone. Tones in a certain frequency range can excite a unit while simultaneously inhibiting its response to a second stimulus. This excitation appears to be independent of whether or not the second stimulus is present [Work supported in part by the Air Force Office of Scientific Research under contract AF 49(638), and in part by the Public Health Service, U. S. Department of Health, Education, and Welfare.]
Binaural Interaction in the Cat Superior Olive S Segment
Authors: Boudreau James C. , Tsuchitani Chiyeko
Published: November 2005

With the exception of low-frequency characteristic frequency (CF) units, the ipsilaterally evoked discharge of the majority of S-segment cells can be inhibited with simultaneous stimulation of the contralateral ear. The contralateral inhibitory CF is usually identical to the ipsilateral excitatory CF. The width of the contralateral inhibitory tuning curve is similar to the width of the ipsilateral excitatory tuning curve. Partial inhibition of the ipsilaterally evoked discharge increases the interspike intervals and increases the variability of the discharge. Inhibition, like excitation, is tonically acting. The contralateral inhibitory input with equally intense tones (measured in terms of decibels above threshold) is either about as effective as the excitatory input or less effective, rarely more effective. The primary factor determining the spike output from S-segment cells is not the absolute intensity level of the stimulus but rather the relative intensity difference of the stimulus at the two ears. [Work supported in part by National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
Dynamic Constraints in the Variation of Subglottal Pressure
Authors: Rothenberg M.
Published: November 2005

Using a circuit-type model for the subglottal system similar to that originally proposed by van den Berg [Acta Physiol. Pharm. Neerl. 9, 361–385 (1960)], it is shown that the physical dynamic constraints of the subglottal system do not significantly limit the ability of the respiratory musculature to produce changes in subglottal pressure. The primary limitations appear to come from the dynamic limitations inherent in the mechanism of muscle contraction, with the physical system between the muscles and the pressure in the trachea adding a delay of about 15 msec. The model discussed can also be used to predict the variations of subglottal pressure resulting from changes in glottal-supraglottal air flow resistance.
Glottal Wave Periods in VCV Environments
Authors: Wendahl Ronald W. , Page L. Dennis
Published: November 2005

Current interest has centered on the effects of vocal tract impedance changes upon glottal function. The present study was designed to determine fundamental frequency changes between vowels and consonants in simple VCV syllables. Thirteen vocally normal male subjects were asked to phonate the syllables /ava/and /ivi/ at two fundamental frequencies. Their phonations were analyzed by visicorder-caliper methods. The results demonstrated that the consonant in each series typically and significantly lowered the fundamental frequency from 4% to 15%. Although the results were confounded in some subjects by inflectional and erratic behavior beyond our calibrated 0.2% measurement error, the results substantiated the reports of other investigators regarding the importance of mechanical coupling between glottis and vocal cavities.
Observation of the Larynx by a Fiberscope Inserted through the Nose
Authors: Sawashima Masayuki , Hirose Hajime , Fujimura Osamu
Published: November 2005

A specially devised fiberscope by use of a thin flexible fiber-optics cable was inserted through the nose in order to observe the laryngeal conditions in the course of unperturbed speech utterances. Glottal conditions during various phonatory and articulatory activities have been visually inspected and photographed. The flexible optical cable with its tip is 5.6 mm in diameter. The hard tip, 15 mm in length, houses inside an objective lens designed for a straightforward view. Glass fibers of 15 μ are used for an image guide, and the size of the image on the photographic film is 5.6×5.6 mm2. The insertion of the optical cable does not cause any discomfort unless the nasal cavity of the subject is particularly narrow. When the scope reaches near the level of the epiglottis, the larynx is readily visible and the scope can be kept in position with a good stability. Cinefilm of the larynx obtained by this fiberscope with simultaneous sound recording will be shown at the meeting.
An Experimental Investigation of Pitch Change in Speech
Authors: Ohala John , Hirano Minoru
Published: November 2005

Electromyographic recordings of the activity during speech of selected intrinsic and extrinsic laryngeal muscles were made using three American English-speaking subjects. On all three subjects, the activity of the lateral crico-arytenoid, the crico-thyroid and the sterno-hyoid muscles were sampled; on one of the three, records of the vocalis and interarytenoid muscles were also obtained plus direct recordings of the subglottal pressure. The data provided no confirmation of a recent hypothesis by Lieberman [Intonation, Perception, and Language (MIT Press Cambridge, Mass., 1967)] that, for American English, during other than YES-NO questions, the laryngeal tension remains relatively steady and that pitch variation is a function of the subglottal air pressure. On the contrary, the muscles studied participated actively in pitch control, and variations in subglottal pressure could account for but a fraction of the observed pitch changes. The crico-thyroid and lateral crico-arytenoid assist in raising pitch, and the sterno-hyoid assists in lowering pitch. [Work supported by National Institutes of Health, U. S. Department of Health, Education, and Welfare, and the Office of Naval Research.]
Electronic Measurement of Nasality: A Study of Normal-Speaking Adults
Authors: Bensen Jack F. , White Frazer D.
Published: November 2005

Electronic measurement of nasality, desirable in clinical and medical services dealing with the speech defective, has been shown possible using the voice systems nasality meter. Previous studies indicate that the circuit, measuring phase shift of the second formant, has the potential of recognizing nasal components of the human vocal utterance. The authors developed a clinically useful test in a preliminary study. Using this on 200 normal-speaking college age adults, this report presents norms on this population. The meter measures phase shift two ways, either comparing amounts of energy stored in two separate circuits or by balancing the two circuits using a calibration dial. By the first method, males showed a mean difference of 1.2, a range from −1.0 to 3.1. Females had an average difference of 1.4, a range from −4.0 to 0.4. Using the calibration meter (reading from 0.0 to 99.9), males scored an average of 41.9, a range of 16.0 to 75.0, a standard deviation of 12.5 Females scored an average of 16.7, a range of 1.0 to 33.0, a standard deviation of 6.9. This difference was significant at the 0.002 level of confidence. Possible reasons for this difference are suggested.
Coherence of Convergence Zone Sound
Authors: Lund G. R. , Urick R. J.
Published: November 2005

The vertical coherence of underwater sound in a convergence zone has been investigated by means of a vertical receiving array of six hydrophones spaced 212 ft apart and hung at a depth of 3800 ft from a surface ship. A second ship towed a 1120-Hz cw source outward in range from 28 to 43 miles. The outputs of the different hydrophones, when correlated, yield correlation coefficients equal to nearly unity when in the convergence half-zones at 30 and 38 miles, and show only a slow falloff with increasing separation. Between zones, where bottom-reflected paths occur, the correlation coefficient was much smaller and was found to fall off faster with increasing separation. It may therefore be concluded that a vertical array located in the convergence zone of a distant source will experience a higher signal-to-noise ratio as a result of two effects: an increased signal level due to convergence, amounting to 10 dB in our experiment, and an increased array gain due to the greater coherence of the received sound.
20-Hz Signals Observed in the Central Pacific
Authors: Northrop John , Cummings W. C. , Thompson P. O.
Published: November 2005

Twenty hertz signals, similar to those reported by other investigators from different locations, were recorded on hydrophones of the Pacific Missile Range at Midway, Wake, and Oahu Islands. Year-round recordings revealed the signals during the winter months with a peak in October at Midway, December at Oahu, and January at Wake. There was no daily pattern of occurrence. More signals were recorded at Midway than at the other locations. Signals appeared in pairs with members separated by 16 sec between Type I and Type II, and 20 sec between Type II and Type I. Both signals had maximum energy near 20 Hz and lasted about 1 sec. Type I ranged from 18–27 Hz; whereas Type II ranged from 18–44 Hz. Signal trains lasted 10–12 min, and they were separated by 1–3 min. Estimated source levels ranged from 85–120 dB re 1 μ (at 1 yd). Source movement was evident at stations where a series of signals was recorded at two or more hydrophones.
Sound Production of Migrating Gray Whales, Eschrichtius gibbosus Erxleben
Authors: Cummings W. C. , Thompson P. O. , Cook R. D.
Published: November 2005

Observations were made during two southward breeding migrations (1966, 1967) of gray whales. Bottom-mounted hydrophones and a moored ship were positioned off San Diego, in the path of about 230 whales. Sound sources were located using received levels and arrival time differences. Visual tracking corroborated sound data. Moans were, by far, most common of more than 200 whale sounds. Moans lasted 1.25 sec; their source level was about 120 dB re 0.0002 dyn/cm2 a at 1 yd; and they ranged 20–150 Hz. Whales moaned while submerged, day and night, under varied weather conditions. Blows (surface exhalations) lasted 1.5 sec and ranged 15–175 Hz. Infrequent bubble-type signals, lasting 0.7 sec, were about 112 dB re 0.0002 dyn/cm2 at 1 yd, and ranged 15–305 Hz. Average swimming speed of single whales was 5.5 knots, based on sound tracks. Whales migrated all night despite dense fog. Large bioluminescent areas around migrating whales were seen from the ship and from an airplane. No characteristic behavior could be associated with sound production.
A Test Tank for Independent Determination of Pressure and Velocity Thresholds of Small Fish
Authors: Siler William , Cahn Phyllis , Wodinsky Jerome , Fitzgerald James
Published: November 2005

A test tank is described which permits individual variation of pressure and velocity sound-wave components. Standing waves are generated by two J9 speakers with precisely controllable relative amplitude and phase. A velocity unit analogous to the microbar is proposed to be used for calibration, and a Bode-type plot is presented for relating test tank conditions to the spatial near or farfield of traveling waves. Use of the tank in fish threshold determination is described. Analysis of threshold test data is complicated by the “two-stimulus” problem, and a graphical analysis method is presented. Strengths and weaknesses of the prototype tank are discussed, and plans for approaching the general noise problem discussed. [Work supported by the National Science Foundation.]
Investigation of the Vibrational Properties of a J9 Transducer in Water by an Optical Interferometric Technique
Authors: Gilheany J. J. , Andrews F. A.
Published: November 2005

The magnitude and phase of the mechanical and radiation impedance of a USRL J9 transducer at nonresonant frequencies have been directly measured under free-field conditions by an optical interferometric technique. The requisite facility and technique (measurement of vibrational amplitude as a function of drive current) are described. The mode shape of the transducer in air and in water is also shown. [Work supported by Code 468 of the Office of Naval Research, U. S. Navy.]
A Finite Difference Analysis of the Vibrations of Solid Cylinders
Authors: McHahon G. W.
Published: November 2005

A finite difference analysis has been used to study the free axially symmetric vibrations of solid isotropic elastic cylinders. A grid having up to 36 independent lattice points was used with simple central difference formulas to set up a system of homogeneous equations, whose determinant was solved to yield the resonance frequencies. The results have been compared with Rayleigh-type thickness corrections to the frequency equations for thin disks and slender rods, and with experimental observations on solid steel and aluminum cylinders. The results indicate an accuracy within 1% for the first longitudinally symmetric mode and within 4% for the second-symmetric and first- and second-antisymmetric modes over a height-to-radius ratio range of 0.8 to 3.5 and for Poisson's ratio up to 0.34.
A Family of Electrostatic Sensors for Hypervelocity Microparticle Impact Momentum Measurement
Authors: Meyer N. J. , Beavers B. R. , Powell J. G.
Published: November 2005

The basic transduction principles of the condenser microphone have been adapted to produce a suite of hypervelocity microparticle impact sensors. Two types of sensors have evolved from the basic condenser microphone geometry. First, a lumped parameter (rigid impact plate supported by a spring) device analogous to the ballistic pendulum, and second, a distributed parameter unit of maximum sensitivity that senses the capacitance variations produced by the particle impacts on an extremely thin plate. In the case of the lumped parameter design, laboratory tests have verified the theoretically predicted sensitivity. Variations on the basic lumped parameter design have permitted momentum measurements over a range of seven orders of magnitude, while the distributed parameter model has demonstrated a sensitivity at least two orders of magnitude better than any device yet reported. [This work, which has been partially supported by NASA Manned Spacecraft Center, is preparatory to the measurement of particle impacts on the lunar surface.]
Small, Low-Frequency Omnidirectional, Broad-Band Hydrophone
Authors: Solberg Ruell F. , Kreisle Leonardt F.
Published: November 2005

A small, low-frequency omnidirectional, broad-band hydrophone with relatively good sensitivity and capacitance has been designed, constructed, and tested. The design was of such nature that the hydrophone should withstand vibration and high-velocity shock in addition to meeting other particular requirements. A radially polarized, PZT-5H piezoelectric ceramic tube with end caps and an internal air cavity was cast in a polyurethane compound. This piezoelectric material has a high permitivity for maximum capacitance for permitted physical dimensions; however, two disadvantages are its low upper Curie point and its large variation of capacitance with temperature. A 1-in. outside diam, 18-in. wall thickness, and 1-in. length tube was used as the active part of the hydrophone. Properties of the hydrophone include a capacitance of 0.013 μF, sensitivity of about −95 dB, and omnidirectionality in all planes to about 5 kHz. [The work was partially supported by U. S. Naval Ordnance Laboratory.]
Penetration of a Sonic Boom into Water
Authors: Cook Richard K.
Published: November 2005

An aircraft in level flight at a supersonic speed over water produces a sonic-boom pressure on the water surface. Usually the N wave of the incident sound pressure moves across the surface at a subsonic speed, relative to the speed of sound in water. Therefore, the boom energy is totally reflected, and the sound pressure in the water falls off exponentially with depth below the surface. The penetration depth, comprising about 85% of the underwater energy, is of the same order as the N-waveform length on the surface. The analysis shows further that the underwater N wave has a weak precursor and a weak tail. The same is true of the wave reflected into the atmosphere. The N-wave pressure is an odd function of distance from the wave center, but the precursor and tail is an even function. This is a special case of reflection effects on a sonic boom. If small and brief (in time) perturbations occur at a reflecting surface, the perturbation pressures will be approximately the same function of distance from the trailing edge of the boom as they are from the leading edge.
An Experiment to Locate The Acoustic Sources in a High Speed Jet Exhaust Stream
Authors: Potter R. C. , Jones J. H.
Published: November 2005

A small high-speed (Mach 2.5) cold jet was operated with the exhaust stream passing through a hole in the wall of a 100 000 ft reverberation room. The reverberant SPL was measured to allow the total acoustic power generated by the flow inside the room to be determined. The jet nozzle was then progressively withdrawn so that a smaller amount of the mixing flow was retained within the room. The experiment was repeated with the jet inside the room, with the flow directed outwards and the jet nozzle moved back into the room. The resultant acoustic power curves were differentiated to give the acoustic power generated per unit length of the jet gas flow. The results are presented and experimental details reviewed. It is concluded that the flow near the supersonic core tip is responsible for the majority of the noise generated.
The Effect of Exhaust Temperature on Jet Noise Generation
Authors: Plumblee H. E.
Published: November 2005

An experimental study was made to determine the effects of jet engine exhaust temperature on jet noise generation. Noise data were taken at 70 points on a uniform grid in the nearfield and farfield of a 3.5 in. diam model jet. Jet efflux temperature was varied from 560°R to 3860°R and exhaust velocity ranged from 930 fps to 4660 fps. Based on existing theories, a semi-empirical relationship was derived for predicting the nearfield and farfield sound pressure levels. A computer program was subsequently developed which calculates and plots SPL contours for the over-all and octave bands, using exhaust temperature and Mach number as controlling parameters. In the farfield, a unique method is shown for reducing jet noise. The reduction is based on fixed exhaust velocity and thrust while varying temperature. A reduction of 5.5 dB has been noted for a 130% increase in jet efflux temperature, i. e., 560°R to 1290°R. This is a continuing research program and results of tests designed to further define the reduction phenomenon will be included, if available. [Portions of this research were sponsored by Air Force Contract AF33 (615)-2503.]
Influence of Airspeed on Noise Generated Within Various Fixed- and Rotary-Wing Aircraft
Authors: Gasaway Donald C.
Published: November 2005

The data reported in this study will assist human-factors engineers and aeromedical personnel in assessing noise exposures associated with the operation of aerospace vehicles. The influence of increased flight speeds on the level and character of noise generated within the cockpits of 148 fixed- and rotary-wing aircraft is described and illustrated. Stereotyped collateral effects resulting from increases in airspeed are categorized for different types of vehicles and the noise envelopes that evolved from this study are grouped into two main categories: fixed-wing and rotary-wing. Secondary noise envelopes are then illustrated for each of the two main groups according to the type of power plant mated to the vehicle. The envelopes derived from this study clearly illustrate differences in the character and level of noise generated within various aircraft due to increased airspeed. Also, and probably more important, the various envelopes verify that within similar types of aircraft the increased airspeed results in changes in noise levels and spectra that are stereotyped.
Laboratory Study of Jet Aircraft Noise Complaint Potential as Related to Context of the Noise
Authors: Mabry J. E. , Little J. W.
Published: November 2005

Previous studies using category scaling of jet aircraft flyby noise have emphasized scales of annoyance, objectionability, noisiness, intrusiveness, and so on. The present study related subjects' predictions of their complaint performance to acoustical characteristics of recorded flybys. In addition to the aim of obtaining a direct relationship between “expectation of making a complaint” and acoustical parameters, the study investigated predicted complaint performance as related to the immediate acoustical environment. For example, there were significant differences in complaint predictions for the same flyover when juxtaposed (both before and after) with different flyovers; also, the judgment that a particular flyover was more annoying than a comparison flyover increased significantly the probability of predicting a complaint for that flyover. This is laboratory data that nicely supports the “projection hypothesis” of the 1961 Farrborough experiments. Subjects' complaint predictions from the laboratory setting are also related to actual complaint performance obtained from sociological survey type investigations. Contrary to the findings of previous investigations, complaint predictions for males were significantly greater than for females.
Pitch of Pure Tones
Authors: Swigart Elca
Published: November 2005

In Part 1, university students enrolled as music majors served as subjects to determine discrepancies between frequencies of pure tones presented through either a bone oscillator or earphones (monaurally and binaurally) and the fundamental frequency of vocal limitations of pitches of the pure tones. All vocalizations were recorded on magnetic tape and analyzed to determine fundamental frequency. In Part II, pure tones were presented at one of two intensities through a bone oscillator placed on the mastoid bone and matched in pitch with a pure tone (variable in frequency by the subject) presented through earphones (monaurally and binaurally). Discrepancies of responses in hertz from the stimulus were recorded by the examiner. Results indicated minimal differences among responses to stimuli through the bone oscillator and monaurally and binaurally through earphones. However, an increase in intensity of the stimuli through the bone oscillator raised the matched frequency of pure tones through the earphones presented either monaurally or binaurally. An increase in intensity of stimuli presented binaurally through the earphones lowered the fundamental frequency of vocal limitations of those pitches. Analyses of pitch matching responses to other stimulus conditions were also computed.
Perception of Frequency Modulation
Authors: Takefuta Yukio
Published: November 2005

The purpose of this experiment was to plot equal pitch-modulation contours as statistical functions of duration, direction, and extent of frequency modulation. Twenty college students listened to 66 quasipure tones each of which was a combination of one of six durations (40–1000 msec) and one of 11 extents of modulation (−10 to +10 semitones). Duration and direction as well as extent of frequency modulation affected pitch modulation as evaluated by a method of magnitude estimation. A regression line was fitted to the listeners' responses plotted on a coordinate of pitch modulation (psychological) and frequency modulation (physical) for each combination of duration and direction. Expected mean values on the regression lines rather than the actual mean values were used to plot the contours for each extent, duration, and direction. The nearest but significantly different mean values from the expected mean of zero were used to determine the thresholds of pitch modulation. The distance between the threshold value and zero mean was determined by calculating confidence intervals for the expected mean values of zero by using the variance of the observed data.
A New Technique for Determination of Cross-Power Spectral Density with Damped Oscillators
Authors: Simon Wayne E. , Walter Louise A.
Published: November 2005

A new technique for computation of cross-power spectral density of random processes has been developed, programmed, and tested on a variety of constructed random and periodic signals of known characteristics. The technique is based on derived relationships between cross-power spectral density and the mean value of certain products of a random signal and the response of an oscillator driven by the random signal. In addition, a technique for discrimination between periodic and random signals has been developed that is based on comparison of the amplitude distribution of the signal and the amplitude distribution of the acceleration of an oscillator driven by the signal. Computations have been performed for a variety of signals with known characteristics with very satisfactory results.