bluuebunny/crossref_metadata_2025 huggingface dataset:
Cavitation Streamers and Surface Wave Phenomena
Authors: Nyborg W. L. , Rogers A. , Hughes D. E.
Published: September 2005

Consecutive frames of motion pictures (4 sound cycles/frame) of cavitation streamers on the face of a vibrating probe (20 kc/sec) frequently show the continuous growth of bubbles to an apparently critical size, followed by a rapid shrinking or sudden disappearance. A faint cloud is often seen in the place of the large bubble, as if the latter had suddenly subdivided into a large number of bubbles of microscopic size. One is reminded of Willards' demonstration that a cloud of microbubbles is formed when a resonant bubble executes vigorous surface oscillations. Detailed information on events similar to the Willard phenomena has been obtained by study of a low-frequency device. A rectangular tube with transparent walls is mounted with axis vertical, partially filled with liquid, and tightly capped. It is set into vertical oscillation at 50- to 150-cps frequency and 0- to 3-mm peak-to-peak amplitude. Motion pictures will be shown, in which one sees the onset of surface waves, the development of crests into long liquid filaments which pinch off into droplets, and the encapsulation of air by arching over of the crests. Relevant theory has been given by Benjamin and Ursell and by G. I. Taylor. (Supported in part by the U. S. Public Health Service.)
Effect of a Plane Boundary on Sound Propagation in a Turbulent Medium
Authors: Maling George C. , Ingard Uno
Published: September 2005

The magnitude of the fluctuations in sound pressure which occur when a source is placed in a turbulent medium depend strongly upon the presence of reflecting boundaries in the medium. In this study, a slowly moving turbulent air stream was made to pass over a plane boundary. The fluctuations in sound-pressure level were measured as a function of the distance from a small source located at a fixed point above the boundary. The fluctuations in the phase difference between the direct and reflected pressures calculated from the statistical properties of the turbulence have been found to be sufficient to explain the observed results. (This work was supported in part by the U. S. Army Signal Corps, the Air Force Office of Scientific Research, and the Office of Naval Research.)
Measurement of Elastic Moduli by Means of Ultrasonic Waves in the Frequency Range 100 to 500 Mc/sec
Authors: McSkimin H. J.
Published: September 2005

Apparatus for measuring ultrasonic wave velocities and hence elastic moduli by means of phase comparison methods at frequencies as high as 500 Mc/sec is described. Gated harmonic generators for providing pulse modulated rf of accurately known carrier frequency and circuits for electrical coupling to resonant quartz crystal transducers are discussed. Application to measurements on small specimens, with illustrative data for cadmium telluride, is made.
Ultrasonic Absorption in Cyanide Solutions
Authors: Stuehr John , Yeager Ernest , Sachs Thomas , Hovorka Frank
Published: September 2005

Ultrasonic absorption measurements have been made in aqueous potassium cyanide solutions by the spherical resonator, statistical reverberation, and pulse-reflector techniques at frequencies from 40 kc to 25 Mc. Only one relaxation frequency has been found in this range. For a KCN concentration of 0.05 mole/liter at 25°C, the relaxation frequency is 900 kc with an excess absorption per wave length (αλ) at this frequency equal to 9.0×10−5. The dependence of the absorption on concentration also has been measured. The experimental data support the conclusion that an hydrolysis reaction involving the reaction of the cyanide ion with water is responsible for the abnormal absorption. The relaxation data have been used to calculate the rate constants for this hydrolysis reaction. (This research has been supported by the Office of Naval Research.)
Absorption in Fractionated Silicones
Authors: Hunter J. L. , Carome E. F. , Gutowski F. A.
Published: September 2005

Absorption and velocity measurements have been made in several fractionated silicone fluids in chain lengths of 2 to 11 siloxane groups per molecule. The viscosity range is from 0.63 to 6.04 centistokes, at 25°C. Absorption in general is only slightly greater than the Stokes low-frequency value. The lighter fluids give practically constant α/v2 in the frequency range employed (10–130 Mc), whereas the heavier fluids give a definite fall-off. As an example, assuming a single relaxation, a relaxation frequency of 55 Mc was obtained at 30°C in the fluid containing 10 siloxane groups. (This work was supported in part by the Office of Naval Research.)
Sound Velocity in Slightly Ionized Gases
Authors: Sessler G. M. , Schroeder M. R.
Published: September 2005

Measurements of the sound velocity in slightly ionized gases have been performed at gas pressures of about 1 mm Hg and at frequencies between 10 and 100 kc/sec. Ionization of the gas is effected by a dc discharge, the degree of ionization being of the order of 10−6 electrons and ions per molecule. The measurements have been taken with an acoustic interferometer, using electrostatic transducers with solid dielectric. The measurements show—besides an increase in the sound velocity which is due to a rise in temperature of the partially ionized gas—a dispersion of the sound velocity. This dispersion seems to be attributable to a resonance of the charged particles.
Measurement of Sound-Pressure Amplitude in Transparent Solids
Authors: Achyuthan K. , Breazeale M. A.
Published: September 2005

Knowledge of the sound-pressure amplitude, and hence the energy density, in solids is useful, for example, in experiments in which one is determining the influence of ultrasonic vibration on nuclear magnetization. A method for determining this sound-pressure amplitude in transparent solids directly from measurements of light diffracted by the wave plus an auxiliary measurement with a Babinet compensator is discussed. An estimate of the accuracy to be expected is given. (This work supported by the Office of Naval Research and the National Science Foundation.)
Shallow Water Sound Propagation in the Arctic Ocean
Authors: Hunkins K. , Kutschale H. , Herron T.
Published: September 2005

Experiments on underwater sound propagation in the shallow water of the Arctic continental shelf were conducted at Fletcher's Ice Island (T-3) during April and May 1960. Shots were made along two profiles, 6.8 and 8.2 km long in water depths of 62 and 50 km, respectively. The records show a characteristic sequence of arrivals in all cases. These wave groups, in order of arrival, are identified as (1) a “leaking mode,” associated with the ice layer, which travels with a velocity of about 3 km/sec, (2) a “second mode” with a velocity about 2.2 km/sec and associated with the bottom sediments, (3) a “first mode” of large amplitude and low frequency, (4) a high-frequency water wave which is superimposed on the “first mode.” The identification of these wave groups is made on the basis of comparison between observed phase and group velocity dispersion with calculated dispersion curves. The agreement between theory and experiment, using phase and group velocity and the first and second mode, is good.
Statistical Properties of Multipath Signals
Authors: Maunsell C. D.
Published: September 2005

In undersea acoustic propagation experiments there are frequently two or more acoustic ray paths simultaneously possible between the source and receiver. The resultant signal received depends on the relative amplitudes and phases of the component signals. Rapid changes in the relative lengths of these paths cause the interference patterns to change thus producing fluctuations in the received signal. Frequently the mean signal varies appreciably before sufficient observations can be gathered to produce a meaningful distribution curve. In order to study the short period fluctuation it is then more satisfactory to examine the relationship between the standard deviation and mean of a large number of relatively small samples. These can then be compared with various theoretical models. It has been found that for a considerable number of experiments the results agree with the predictions from the hypothesis of a Rayleigh distribution for signals reflected from a rough surface. When such a reflected signal interferes with a directly transmitted signal a Rice distribution is more appropriate.
Application of the Wiener Filter Theory to the Design of Seismic Arrays
Authors: Burg J.
Published: September 2005

The Wiener least-mean square error criterion is used in the design of two dimensional seismic arrays. The purpose of the seismic array and its associated electrical filtering network is to discriminate between the seismic signal and noise on the basis of differences in frequency, wave length and direction of propagation. Assuming only linear operations in the seismic detection system, one point of view is that the seismic system is a three-dimensional linear filter operating on the frequency and two-dimensional vector wave number Fourier transform description of the ground motion. The extension of Wiener filter theory to three dimensions shows that the only required knowledge of the signal and noise is their power spectra in terms of frequency and vector wave number. Results obtained from a theoretical power spectra model will be shown. A second point of view is that the seismic system is a multi-channel system, since each seismometer is a source of signal and noise. Assuming that the signal and noise are uncorrelated, the application of Wiener filter theory to this situation requires only the auto- and cross-correlations of the signal and noise between the various seismometer outputs.
Ambient Noise under Old Shore-Fast Sea Ice
Authors: Milne A. R.
Published: September 2005

During April, 1961, ambient noise measurements were made in Prince Gustaf Adolph Sea in the Canadian Arctic Archipelago. The sea in the experimental area was covered with old, rough ice at least 12 ft thick, intermixed in places with 8 ft of young ice, all shore-fast. Simultaneous measurements were made of wind-velocity and background ice motion. Thermal cracking of the ice caused by radiation cooling toward evening increased the ambient noise markedly. As a result, smaller explosive charges could be used in seismic shooting during the morning and with cloud cover in the evening. (A magnetic tape recording of a noise sample will be played.)
Development of the Wide-Band Noise Siren
Authors: Cole J. N. , Oestreicher H. L. , Powell R. G. , von Gierke H. E.
Published: September 2005

The wide-band noise siren principle [J. Acoust. Soc. Am. 31, 116 (1959)] has been further evaluated in two different, experimental siren designs with various loading arrangements. Acoustic power output, efficiency, power spectrum, and amplitude distribution of the noise generated by the various models will be discussed as a function of the flow conditions. Although the over-all efficiency of the small models discussed here (power output approximately 5 kw) is still slightly below 10%, experimental separation of the losses involved suggests that for a siren without air leakage and otherwise similar parameters efficiencies of approximately 30% should be attainable. It appears that the efficiency of the wide-band noise siren could be close to the efficiency of a pure-tone siren and in the same range as the efficiency of a siren producing sinusoidal waveform with amplitude modulation. Wideband noise sirens with 20-kw output have been built at other places and a 50-kw siren is presently under development. The wide-band noise siren appears to fill the long-felt gap for economical, realistic, and high-intensity jet and rocket noise simulation.
Pure Tone Spectra of Axial Compressors
Authors: Thiessen G. J. , Embleton T. F. W.
Published: September 2005

The radiation efficiency of a linear array of sources with linear phase variation was discussed previously and applied to the noise of suction rolls [J. Acoust. Soc. Am. 30, 449 (1958)]. Figure 7 can be used directly to predict qualitatively the spectrum radiated from an axial compressor such as a jet engine. (The phase parameter α′ is now the difference in the number of blades between the rotor and stator divided by the number in the stator. The fundamental frequency is the rotor blade passage frequency.) The value of d/λ1 for α′ is still a critical value but the details of the curves in Fig. 3 are modified by the circular array. The hub of the rotor decreases the rate of efficiency drop beyond the value α′=d/λ1. The duct around the system further discriminates against those harmonic components that have their maximum in the directionality pattern at right angles to the axis. The analysis of Tyler and Soprin [Proc. Soc. Automotive Engrs. (April, 1961)] for rotor-stator interaction is in error resulting in a critical dependence of radiation on rotor speed which does not exist.
Model Jet Noise Study
Authors: Wells R. J. , Tatge R. B.
Published: September 2005

Correlations between air flow measurements and sound measurements are presented for two model nozzles of approximately equal area—a 4-in. diam conical, and a “Daisy” with 6-in. o.d. Pressure ratios varied from approximately 1.3 to in excess of 4. Total temperature varied from ambient to over 2000°R. The results are given in the form of equations which allow computation of jet noise sound power for both subsonic and choked cases. These equations represent an extension of the density-modified Lighthill parameter. Generalized methods of computing sound power spectra are described. Correlations between air flow and directivity are presented in the form of charts. (This work was under the sponsorship of the U. S. Navy, Bureau of Naval Weapons.)
Noise Levels due to Trains
Authors: Embleton T. F. W. , Thiessen G. J.
Published: September 2005

Some fifty freight and passenger trains were investigated at distances between 25 and 1000 ft. The decrease of sound-pressure levels with increasing distance indicates that whistles are to be considered as point sources, but engines and track noise are line sources out to distances comparable with the lengths of the source. All engines showed a pure tone in the region of 100 cps and freight engines a second tone at about 300 cps when pulling hard. Otherwise freight engines showed little change in level whatever the operating conditions. Noise from passenger engines showed marked changes in level since they operate with much more exaggerated changes in power than freight engines. Track noise depends on the rolling stock—freight cars and run-of-the-mill passenger cars have very similar noise spectra whereas the deluxe cars used on “prestige trains” have spectra lying 10 to 20 db lower in all frequency bands. All the cars have coil springs but the latter alone have hydraulic shock absorbers.
Some Effects of an Observer on the Readings of a Sound-Level Meter
Authors: Young R. W. , Bauer B. B.
Published: September 2005

Directional sensitivity patterns of a sound-level meter were measured both in an anechoic room and over a reflecting surface to find the disturbing effects of a nearby observer. The source was at a height of 1 m above the reflecting plane and the sound-level meter at a height of 1.2 m, the separation being 7.5 m. The tests indicate that, if the observer is to hold the sound-level meter in front of him, errors in readings due to his presence can be reduced by locating the source to his left or to his right. The most serious disturbances due to the observer occur at frequencies below 1000 cps. In one case, when the microphone was 56 cm in front of an observer facing the source, at 250 cps the observer reduced the reading by 4 db, whereas at 400 cps his presence increased the reading by 2 db. The disturbances can be reduced, at least for some directions and frequencies, if the observer wears an absorbent apron or overcoat. If measurements are to be made on sine-wave sounds with an accuracy of ±1 db and with a microphone at waist height, it appears that the observer must stand certainly more than 1 m away from the microphone. However, for a band of noise 13 octave wide a nearby observer has little effect unless he stands directly between the microphone and the source.
Formant Tracking by Self-Adjusting Inverse Filtering
Authors: Lawrence Walter
Published: September 2005

A method of formant tracking is described in which the speech wave is passed through an adjustable network whose transfer function approximates to the inverse of the vocal tract filter. From the output of this network it is possible to derive error signals which indicate the polarity of the unbalance for each formant frequency. These signals can be used for continuously improving the approximation so that the zeros in the inverse network continuously follow the poles, or formants, in the vocal tract filter. A test setup, using analog computer type elements, is described, and its performance examined both with synthetic input and with real speech input.
A Recognition Program for English Fricative Consonants
Authors: Forgie James W. , Forgie Carma D. , Dickey Emy P.
Published: September 2005

A computer program has been developed to classify English fricative phonemes. Input to the computer is sampled, quantized spectral data (8-bit samples from 35 frequency channels scanned every 5.5 msec). The data are first processed by a segmentation program which marks intervals of time according to type of phoneme (e.g., fricative, nasal, vowel, stop). The fricative classification program treats segments already labeled fricative and decides which phoneme the segment represents. The program operates by computing measurements of a number of properties of the spectrum of the fricative segment and by tracking the first three formants in adjacent vocalic segments. A simple statistical procedure is used to derive weighting functions which transform the measurements into a set of scores. The phoneme corresponding to the highest score is selected as the label for the fricative. (Lincoln Laboratory operated with support from the U. S. Army, Navy, and Air Force.)
Speech Compression by Means of Orthonormal Function Expansions
Authors: Manley Harold J. , Brick Donald B.
Published: September 2005

Speech compression systems are described which make use of orthonormal function expansions of either the speech waveform itself or the short-time autocorrelation function of the speech waveform. A system of this type theoretically can be optimized so that a minimum number of independent, slowly varying parameters are transmitted for a given level of desired performance. In both types of systems, the compression in data rate is obtained through the optimization of the expansion series, the truncation of the series, and by averaging the coefficients of the expansion over several pitch periods. In addition, the phase spectrum of the speech signal can be eliminated in a systematic manner in both the system wherein the waveform is analyzed and the systems where the autocorrelation function is analyzed.
An Acoustic Description of Dysarthric Speech
Authors: Lehiste Ilse , Tikofsky Ronald S. , Tikofsky Rita P.
Published: September 2005

The paper reports the results of a spectrographic study of the speech of ten dysarthric subjects. The material recorded by each subject and analyzed spectrographically consists of a set of 50 CNC words, 60 words incorporating initial and final consonant clusters, and 50 spondees. The patterns associated with dysarthric speech were compared with spectrograms made of the speech of a normal speaker who pronounced the same set of test words, as well as with a considerable number of spectrograms of utterances by various other normal speakers of the same dialect, recorded and analyzed in the course of research in acoustic phonetics at the Communication Sciences Laboratory of The University of Michigan. Acoustic patterns characteristic of the speech of the individual dysarthric subjects are described; general symptoms associated with the speech of all subjects are presented and discussed. (This research was supported by a grant from the National Institutes of Health.)
A Study of the Intelligibility of Dysarthric Speech
Authors: Tikofsky Ronald S. , Lehiste Ilse , Tikofsky Rita P.
Published: September 2005

This paper reports an investigation of the intelligibility of dysarthric speech. Dysarthric and normal speakers recorded sets of CNC words, spondees, and words involving consonant clusters. Three listening tapes were made from each recording, in which the order of presentation was varied so that each list occurred in each position only once. Listeners from the Speech Department of The University of Michigan were required to listen to one tape and record the word they thought they heard in English spelling. Ten listeners were used for each of the three listening tapes for the dysarthric and normal speakers. The results of the intelligibility studies showed that the order of presentation does not affect the listener's judgment. A comparison of the results obtained from the listeners with results obtained from an acoustic phonetic analysis of the dysarthric speech will be presented. (This research was supported by a grant from the National Institutes of Health.)
Perceptual Criteria of Speaker Identity
Authors: Voiers William D.
Published: September 2005

An experiment was designed to determine the nature and number of basically different ways in which, or dimensions in terms of which, a given voice may be perceived to differ from another voice or voices; to determine, in effect, the nature and number of independent channels potentially available to a listener for information as to speaker identity. Tentative identification of these perceptual channels was accomplished by a factor analysis of 32 listeners' perceptual responses (on a 49 scale modified semantic differential rating form) to 16 speakers' voices under systematically varied listening conditions. Seven well-defined factors and several tentative factors were revealed by the analysis. Following the computation of “factor scores” for each of the 512 listener-speaker “intersections,” analyses of variance with factoral design were employed to determine the relative contributions of speakers, listeners, conditions, and their interactions to variation in each dimension of the perceptual factor space. Based on the results of these analyses, a simplified, pure-factor voice-rating form was constructed and used in additional experiments designed to estimate the amounts of speaker identity information potentially communicable to a listener via each of the perceptual channels in question.
Instrument for Measuring Density of Homogeneous Liquids Using Vibrations in a Rotor
Authors: Olson N. , Thiessen G. J.
Published: September 2005

At the May, 1959 meeting of the Acoustical Society, an instrument for measuring pulp content of dilute pulp suspensions was described. Also mentioned was a continuous flow instrument for measuring density of homogeneous liquids. The liquid container forms a part of an unbalanced rotor, and the amplitude of vibration of the upper flexibly mounted bearing becomes a measure of the density of the liquid. Over a narrow range of densities (about one part per 1000) the measurements could be made to a part in 105. The present instrument is a further development designed to accommodate a much larger range of density. Two balancing arms, pivoted about the axis of the rotor, take up stable positions when the center of gravity of the system falls on the pivotal axis. The angular separation of the balancing arms becomes the principal variable in the density expression, and is measured with an electronic counter, i.e., in terms of time. Due to friction in the pivot bearings, perfect balance is in general not achieved, so that a residual vibration remains as a second variable in the density expression. By a slight offset of the upper bearing which supports the vibration pickup, a deliberate “bias” vibration is introduced to eliminate ambiguity of phase. Continuous density measurements to a part in 101 appear feasible.
Ultrasonic Grinding Techniques for Mild Steel
Authors: Fernald O. H. , Semmelink A.
Published: September 2005

Techniques of ultrasonic impact grinding in common use have been applied primarily to brittle materials. In previous investigations, it was found to be extremely difficult to cut soft and ductile materials because the resilience of the material absorbs the impact without fracture. A recent investigation was successful in developing means for rapid cutting of deep holes in relatively soft steel by ultrasonic drilling techniques. Problems of achieving slurry feed and particle removal, optimum amplitudes and directions of motion, optimum particle diameters of the slurry are discussed in this paper. Reasonably rapid cutting rates were achieved only when a suitable diagonal direction of cutting was used. This required the design of the cutting tool to have a suitable torsional resonance adequately coupled to the normal longitudinal resonance. The final cutting rates achieved of 0.040–0.050 in./min for depths of 12 in. compare quite favorably with those previously achieved for brittle materials. (This work was supported by the Bureau of Naval Weapons.)
Ultrasonic Velocity Measurements at Solid-Liquid Interfaces
Authors: Mayer Walter G. , Kelsey John F.
Published: September 2005

An optical method is described with which the energy ratio of incident to reflected ultrasonic waves at a solid-liquid boundary can be measured for various angles of incidence. The method consists of comparing the light intensity distribution in the diffraction patterns produced by the incident and the reflected waves. The ultrasonic velocity in the solid is calculated from these measurements using the technique of locating the angles of maximum reflection in the liquid [W. G. Mayer, J. Acoust. Soc. Am. 32, 1213 (1960)]. Results are given for some solids. (This work supported by the Office of Naval Research, U. S. Navy, and by the National Science Foundation.)
Reciprocity Calibration in the Near Field
Authors: Martin Gordon E.
Published: September 2005

The reciprocity behavior of electroacoustic transducers is investigated theoretically and experimentally in the near field. The work of Foldy and Primakoff is extended to include two radiators of arbitrary size in the field. The experimental study is based upon a bizonally shaded rectangular transducer for which the near field extends to separations of approximately 10 m. The reciprocal behavior of two acoustically coupled transducers is described theoretically and experimentally. It is shown that units are reciprocal to separations which are so small that 5-db standing waves exist. The three-transducer reciprocity calibration technique is described theoretically and experimentally. Contrary to many published opinions, it is proved that spherical or quasi-spherical waves are not necessary. The results include the calibration of a transducer in its near field and the calibration of a transducer in the near field of a reciprocal transducer.
Precise Ultrasonic Measurements for Microbubbles Research
Authors: Turner William R.
Published: September 2005

New instrumentation, recently completed for research into the physics of microbubbles, provides measurement of relative velocity and relative attenuation at 1.64, 4.93, and 8.22 Mc, using a single quartz transducer and a reflector mounted in a cage that can be transferred readily between reference and test water bodies. Additionally, a separate transducer and reflector provide a measurement of relative velocity only at 100 kc/sec. Relative velocity is accurate to 0.05 m/sec, and relative attenuation to 0.1 db. A precise detection of the relative attenuation is obtained by electronically switching the signal source between the transducer and a calibrated electrical attenuator, and then mixing the echo, delayed in time, with the attenuator signal to produce a sensitive null at balance, after a signal frequency adjustment to produce phase opposition. Velocity is determined by measuring the frequency interval between successive nulls. (This work supported by the Office of Naval Research.)
Response of a Fluid-Filled Bore Hole to a centered Point Source
Authors: Ingram John I.
Published: September 2005

The problem considered in this study is that of a point source on the axis of a fluid-filled cylinder which is surrounded by an infinite elastic solid. The source taken is of the type used by Sommerfield. Solutions of the wave equation are developed in terms of Fourier integrals. The singularities in these integrals are circumvented by contour integration. Specific numerical examples are calculated to define the axial, radial, and frequency dependence of the fluid potential.
Sonar Equations for Short Transients
Authors: Urick R. J.
Published: September 2005

In dealing with short transients, such as explosive waves, in underwater sound, the ordinary formulation of the sonar equations is inadequate. The reason lies in the fact that it has become customary to use intensity—or the rate of acoustic energy flow—as the basic unit for the formulation. However, when dealing with transients of irregular and undeterminable wave shape, intensity has no significant practical meaning. Instead, it is postulated that the energy of the transient, or the time integral of its intensity, is a conservative quantity having usefulness in prediction, to which the ordinary steady-state sonar parameters may be applied. In this paper the energy form of the sonar equations is indicated, and expressions for predicting the intensity level of reverberation in terms of the energy of the source is derived. Some comparisons with observations using explosive sound sources will be given.
Underwater Acoustic Telemetry
Authors: Campbell D. E. , Cyr R. J. , Crosier C. P.
Published: September 2005

Equipment developed for test and use in a feasibility study of an acoustic FM/FM telemetering system is described. The system employs two standard subcarrier oscillators at 0.96- and 1.3-kc frequency modulating a 40-kc carrier to provide channels of continuous information. The objective has been to determine the effect on recovered data of such underwater acoustic phenomena as multipath transmission, Doppler, amplitude modulations and phase modulations. The various sea tests and their results are discussed. The quality of recovered data under favorable conditions are comparable to that of conventional radio frequency FM/FM telemetry. Interference when present appears to evolve about time variation of propagation loss which results as a very low frequency amplitude modulation of the carrier, AM of 5 to 100% has been noted. Operation in shallow water 50–150 ft presents greatest challenge. Range and data recovery agree with calculated performance. It was found that the transducer can be operated at resonance with a frequency deviation of ±15%. With variation in Q of 2 to 20, a comparison of recovered data indicates no appreciable deterioration.
Broad-Band Highly Sensitive Hydrophone for Deep-Water Applications
Authors: Moose P. H. , Ellis R. M.
Published: September 2005

A recent investigation of this laboratory has led to the development of a deep-water broad-band sensitive hydrophone-preamplifier assembly having a listening threshold of 5 db below sea-state zero from 5 cps to 10 kc. We have achieved this capability by combining a hybrid preamplifier having extremely low self-noise and high input impedance with an active element composed of a stack of ceramic disks polarized and active in the thickness mode. The unit has a frequency response of 5 cps to 100 kc and a basic sensitivity of −89 db. The compact preamplifier was designed for a large feedback, which gives it a high degree of stability. It has a flat response over a wide band, a gain of 50 db, a dynamic response range of 80 db, and an output driving impedance of 150 ohms, which permits its use with long lengths of cable.
Filters for Near-Field Noise
Authors: Parvulescu Antares
Published: September 2005

It is well known that an array can be designed to reject noise arriving from one (or several discrete) fixed directions, by adjusting the nulls of its pattern to coincide with the unwanted directions. It is not possible to design an array to accept only discrete directions; nor is it possible to design it to reject an entire solid angle of noise. In these properties the array (or space-frequency filter) is entirely analogous to the ordinary time-frequency filter. We show here that a similar property exists for the radial coordinate. A source of noise in the vicinity of a receiving station may have a small power output and yet greatly interfere with the reception of distant signals. It is possible to eliminate entirely the noise due to a point source by suitably combining the outputs of two transducers located at the receiving point. Such a filter operates by virtue of the sphericity of the noise wave front, and is effective over a broad band of frequencies. The technique can be immediately extended to the case of several discrete noise sources. In the general case of a continuum of noise sources, it is no longer possible to remove all the noise, but an “optimum radial filter,” in either the rms or the absolute-value sense, must be designed on the basis of the “radial spectrum” of the noise. (This work was supported by the Office of Naval Research.)
Vibration and Acoustic Tests of Missile Structure
Authors: Rader W. P.
Published: September 2005

The results of vibration and acoustic tests of a missile structure are presented. Sinusoidal vibration surveys, low-level acoustic tests using a random siren as the noise source, and high-intensity random-noise tests to determine the probability of acoustically induced structural failures during underground launch operations were conducted. Resonance frequencies, mode shapes, and damping ratios were determined, and the absolute value of the driving point impedance as a function of frequency was calculated. The correlation between localized excitation (random siren) and excitation of the entire structure during an in-silo launch was investigated. The linearity of acceleration response of skin panels, stringers, and ring frames was determined from 13-octave band analysis of the output signals of accelerometers and of microphones over a range of over-all sound-pressure levels from 140 to 165 db.
Preliminary Criteria for the Avoidance of Sound-Induced Damage to Building Structures
Authors: Dyer Ira , Wiener Francis M.
Published: September 2005

Intense low-frequency sound generated by powerful space vehicle boosters may cause damage to building structures. Quantitative information on the damage problem is still fragmentary, but the general outlines of the problem can be sketched. Several case histories have come to our attention which provide some rough bounds on the damage problem. A simple theoretical analysis is used to derive preliminary criteria for the avoidance of building damage; these criteria are consistent with the case histories available. The octave-band sound-pressure levels not to be exceeded are shown to increase 6 db/frequency octave, indicating that the damage potential is greatest at low frequencies. Because of the limited number of case histories available and the simplifying assumptions used in the analysis, these criteria must be regarded as preliminary. (This work was supported by NASA, Marshall Space Flight Center.)
Comparison of the Effects of Linear and Logarithmic-Sweep-Frequency Vibration-Test Procedures
Authors: Gertel Maurice
Published: September 2005

In qualification acceptance tests of equipment for military service it is standard procedure to perform both resonant-frequency and sweep-frequency vibration tests to verify that the equipment has adequate endurance strength. Resonance testing is defined in a reasonably explicit manner; however, in contrast, sweep-frequency procedures are vaguely specified as linear or logarithmic sweeps. This paper presents a comparison of the responses of simple systems to a linear sweep rate df/dt = const and logarithmic sweep-frequency patterns df/dt = const × fn, where n = 1 and n = 2. Also included is a discussion of the environmental situations where each type of sweep test may be pertinent.
Some Measurements on the Vowel Sounds of Conversational Speech
Authors: Swaffield John , Shearme J. N. , Holmes J. N.
Published: September 2005

Fairly well-defined and generally accepted regions of the (first formant frequency)—(second formant frequency) plane (referred to as the F1F2 plane) can be associated with each speech vowel sound. Delineation of the boundaries of these regions may be based on analysis of spoken vowels or on perception of synthesized vowels; in either case, the data are derived from the study of isolated vowels or monosyllables, and the resulting two sets of regions prove to be roughly the same. An alternative study, described in the paper, can be made, however, based instead on the vowel sounds occurring in “connected” or “conversational” speech. In this case the density of distribution of points within the F1F2 plane shows that there is little or no clustering of stationary points within the original (“monosyllable”) vowel regions and certainly permits neither identification of old, nor definition of new, regions. A set of tracks can be constructed, however, to correspond to the almost continuously moving F1F2 points and from these can be derived, by suitable processing, a new set of regions of simple shape, one region for each vowel sound as before. The differences between the set of regions for “monosyllable” vowels, i.e., the generally accepted set, and the set for “conversational” vowels, which may be reasonably regarded as the set in normal use, are striking. Two differences are (a) the set of vowel regions is now clustered very much more closely together than before and (b) for a given speaker the positions of “monosyllable” vowels do not even lie within the regions of the corresponding “conversational” vowels.
Properties of the 8th Nerve
Authors: Ruben Robert J. , Fish Hugo , Hudson William
Published: September 2005

There has been some debate as to whether or not the action potential of the 8th nerve as viewed at the round window, and N1 and N2, originate within the cochlear or in the nervous system. Several experiments have been undertaken in cat in which the 8th nerve was sectioned completely, leaving the blood supply intact. By recording from the severed distal stump and the round window, the N1 and N2 were found to be preserved up to 24 hr after sectioning. By using careful time studies, several properties of the 8th nerve were also noted. The latency of the N1 as recorded at the round window with the first potential recorded on the 8th nerve was carefully measured. A discrepancy in conduction time was found. The conduction time was based upon the fiber diameter which has been measured, and also direct studies. The knowledge gained from these experiments will be of great use in the interpreting of the cochlear response to click as recorded in the human round window. The locus of both the N1 and N2 has been shown to be peripheral to the cochlear nucleus. Time studies indicate that the origin of the N1 and N2 is at some point peripheral to the ganglion cells in the modiolus.
Acoustic Trauma: Concomitant Behavioral and Electrophysiological Measurements in the Cat
Authors: Beatty Dana , Simmons F. Blair
Published: September 2005

Cats with electrodes permanently implanted on the round window of the cochlea and previously trained to respond to threshold and supra-threshold tones in shuttle-box conditioning were exposed to traumatic sound (135 db at 1 kc for 2 hr). Serial concomitant measurements of both behavioral and electrophysiologic (CM and AP) responses were obtained before and after exposure at several frequencies. Temporary threshold shifts of 65 to 95 db were produced in the middle frequency range. Associated cochlear microphonic changes were considerably less (5 to 25 db) and in most cases returned to pre-exposure values long before behavioral indexes at varying degrees of permanent threshold shift.
Reverberation in the Ocean
Authors: Saxton Harold L.
Published: September 2005

The problems associated with acoustic reverberation in the ocean continue to be of prime importance in the use of active sonar. Even though a great amount of effort has been devoted to these problems, they are still not well understood and experimental evidence remains the prime source for an evaluation of the state-of-knowledge, in this field. This paper attempts to summarize the state-of-knowledge through the presentation of recognized fundamentals and results of pertinent experiments.
Observations of the Stability of a Normal Mode Sound Field in an Intermediate Scale Model
Authors: Scrimger J. A.
Published: September 2005

Spectra of sound pressure amplitude versus frequency in the range 1.1–2.4 kc have been obtained at regular intervals in shallow (10 ft) water during two periods of extended observation. The acoustical data have been presented in the form of contour diagrams of sound pressure amplitude versus frequency and time as coordinates and compared with water conditions. The form of the contour diagrams permits differentiation between field structure variation and variation in attenuation, although differentiation between the associated processes has not been possible. Temporal variation in the vertical sound velocity profile produced only small changes in the gross features of the field structure—as inferred from the contour diagram—for up to the first three modes of propagation. For frequencies above 1.6 kc (i.e., when three or four modes were stimulated) the variations in field structure were prominent. Attempts have been made, with little success, to explain periods when the received signal was strongly attenuated in terms of vertical sound velocity structure.
Measurement of Acoustic Coherence Coefficients in Deep Water
Authors: Robertson G. H.
Published: September 2005

Coherence measurements have been made relating sinusoidal signals simultaneously received at separated hydrophones. The definition of coherence advocated by Shapiro in the previous paper is used. The quantity measured is closely related to phase. Of interest is long term average phase as well as a measure of the fluctuations about this mean. Such measurements are useful as an aid in understanding the performance of complex hydrophone systems. The measurement is accomplished by cross multiplying and averaging stored five-second segments of information from each of two channels. This computation is carried out for a range of delays comprising several periods of the sinusoidal signal. A facsimile type recorder provides a pictorial display of how phase wanders as a function of time. Long term averages are obtained numerically from samples of the continuous display. Recently collected quantitative data are presented for several hydrophone spacings in deep water. The results show violent phase fluctuations and dramatically illustrate the statistical nature of acoustic transmission in the ocean. (This work was supported by the Bureau of Ships.)
Determination of Finite Amplitude Distortion by Light Diffraction
Authors: Cook B. D.
Published: September 2005

The theory of a new method of determining the harmonic structure of a finite amplitude wave by light diffraction has recently been given [B. D. Cook, J. Acoust. Soc. Am. 32, 336 (1960)]. This method allows the computation of the amplitudes of the harmonic components of the instantaneous pressure from the measurements of the light intensities of all of the diffraction orders. Preliminary measurements and computations indicate that this method will be a valuable tool in the study of finite amplitude distortion. (This work was supported by the Office of Ordnance Research, U. S. Army.)
Diffraction of Wide and Narrow Light Beams by Distorted Finite Amplitude Progressive Ultrasonic Waves
Authors: Hargrove L. E.
Published: September 2005

Results of an investigation of the diffraction of light passing through an ultrasonic wave of finite amplitude are given. A method is developed and used to determine the second harmonic component of the distorted ultrasonic wave at various distances from the transducer, while maintaining a constant local fundamental component. A wide light beam (giving discrete diffraction orders) is used for these determinations. It is then shown that the observed continuous light distribution (using a narrow light beam) is in good agreement with the theoretically predicted distribution. The effects of third and higher harmonics are neglected. These determinations of second harmonic are compared with values obtained from diffraction effects observed after passing the second harmonic component through an acoustic filter plate. Measurements were made at 3.0 Mc in water with approximately 23 of an atmosphere local ultrasonic pressure amplitude. (This work was supported by the Office of Ordnance Research, U. S. Army.)
The Scattering of Sound by a Thin Prolate Spheroidal Shell
Authors: Silbiger Alexander
Published: September 2005

This paper deals with the scattering of a plane wave incident on a prolate spheroidal shell along its axis of revolution. The procedure can be easily generalized to an arbitrary direction of incidence. Contrary to the case of spherical and cylindrical shells, the spheroidal wave functions in terms of which the incident and scattered waves are expressed, do not coincide with the normal modes of the shell. As a result, when the coefficients of the expression of the shell motion in the spheroidal functions are used as generalized coordinates, all the Lagrangian equations will be coupled. Expressions suitable for computer calculations are given, and an example is worked out in which the frequency of the incident wave is close to one of the natural frequencies of the shell. Under these conditions the scattering action of the shell differs strikingly from that of a rigid spheroid. (This paper is based on work sponsored by the Office of Naval Research.)
Measurement of Driving Point Impedance of Thin Plates
Authors: Thomas D. A. , Henriquez T. A.
Published: September 2005

The driving point impedance of thin plates as implied by the work of Zener and given explicitly by D. A. Thomas [J. Acoust. Soc. Am 30, 220 (1958)] was determined by measuring with a pulse method the complex force and velocity at the driving point. The plate was terminated in wet sand to simulate infinite plate conditions. At low frequencies, the measurements were limited by the physical dimensions of the plate. At high frequencies, compliance in the mounting of the accelerometer and driving coil caused inaccuracies in the measurements. Measurements were made on one aluminum plate and one steel plate. The data obtained agreed well with theory in the frequency range 300 cps to 3 kc.
Influence of Area and Mounting Conditions on the Transmission Loss of Single Walls
Authors: Heckl Manfred
Published: September 2005

Finite walls with small damping are subject to resonances that lead to amplitudes which are often much greater than the amplitudes calculated for infinite walls. These resonances are due to excitation of free waves at the wall boundaries. The free waves do not usually affect the TL of a limp wall because in this case the free waves are radiated only to a small extent. For a stiff wall, however, the free waves are very important. It will be shown that they are responsible for some effects that have been measured (see previous paper) but cannot be explained by theories that assume walls of infinite size. In particular, the influence of the area and of the bending wave transmission into adjacent structures will be discussed.
Some Field Measurements of Building Constructions Having High Sound Transmission Loss
Authors: McKay Ronald L.
Published: September 2005

Field measurements of the sound transmission loss provided by various complex building constructions are presented. The constructions are of the type frequently used in music schools and laboratory test facilities. Data are given on double masonry walls, on masonry walls with resiliently furred plaster, and on floating concrete floors. Some data are compared with similar measurements reported in the literature. Certain conclusions are drawn concerning practical design procedures.