bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimum and Suboptimum Bearing Estimation for Deterministic and Random Signals in Normal Noise Fields
Authors: Middleton David
Published: November 2005

A general theory of maximum likelihood estimation (MLE) of bearing angle and associated measures of the location of signal sources by passive reception is constructed for arbitrary arrays and normal noise fields, extending earlier work. We distinguish two important classes of input signal: known and unknown signal waveforms. Explicit results are obtained for (unconditional) maximum likelihood estimators (UMLE's) of signal amplitude and waveform, and for the (log) likelihood functionals which must be further maximized by choice of bearing-angle parameters (through search procedures) for a priori distributions of parameters. Performance of the optimum bearing estimator (OBE) is measured in terms of the variance of the estimates, involving a matrix of order appropriate to the number of parameters to be estimated. For threshold cases where noise processes can be regarded as stationary, with sample-size large and array elements treated as point sensors, further results are obtained. Examples illustrating the critical role of a priori probabilities are provided, and comparison of the OBE with a suboptimum system (BDI) is made.
Effect of a Negative Capacitance Termination on Hydrophone Sensitivity
Authors: Stelting Raymond
Published: November 2005

The frequency response of piezoelectric hydrophones is determined to some extent by the electrical termination impedance. The effect of passive termination impedances such as shunt or series inductance on hydrophone frequency response is well known. This paper considers the effect of a negative capacitance termination on the sensitivity of piezoelectric hydrophones. The effect of the negative capacitance termination on the sensitivity was calculated for two analog circuits. Theoretical calculations indicate that the sensitivity should be greater than open circuit sensitivity and that the resonant frequency may be increased when the hydrophone is terminated in a negative capacitance. A negative capacitance circuit was designed, constructed, and used to verify the theoretical results experimentally. Three single-element hydrophones were used in the experiment. In each case, the sensitivity of the hydrophone terminated in a negative capacitance was compared to sensitivity with a high resistance termination. It was found that at frequencies below the first resonance the sensitivity increased by more than 3 dB. Increases of more than 10 dB were obtained at the resonant frequencies. The predicted increase in the resonant frequency was also observed. In one case, the resonant frequency changed from 47.5 to 52 kHz when the hydrophone was terminated in a negative capacitance. [This work was sponsored by the U. S. Naval Ship Systems Command.]
Acoustical Negative Resistance
Authors: Neustadt Herbert M.
Published: November 2005

The concept of acoustical negative resistance is a powerful tool for analysis of acoustical oscillating systems. An acoustical negative resistance is always either pressure-controlled or else current-controlled. An actual negative-resistance device always has some time lag in its response, and this lag may be of crucial importance. The lag usually can be represented by a reactance associated with the negative resistance, and a prediction can thus be made as to whether the frequency of an oscillator will be slightly above or slightly below a zero-reactance frequency of the oscillator's resonator. To show how the negative-resistance concept unifies the analysis of all acoustical oscillators, a negative-resistance explanation will be given for some of the operating characteristics of reed and brass musical instruments, the edge tone, and jet-edge resonators. [Experimental verification supported by U. S. Office of Naval Research, and U. S. Naval Academy.]
Passive End Correction of Pipes and Resonators
Authors: Elder S. A.
Published: November 2005

The usual assumption of an “inside” as well as “outside” end correction is shown to be incorrect. The size of the outside end correction at the mouth of an organ pipe depends upon whether it is referred to the area of the mouth or to the internal pipe cross section. In the former case, it is identical with the so-called “Helmholtz resonator” end correction. For large pipe-to-mouth area ratios, the end correction referred to the pipe must approach λ/4. The natural frequencies of an ideal closed pipe are given by solutions of cot kL=tan kΔL, where k=2π/λ, L is the length of the pipe, and ΔL is the end correction, =k−1 tan 1IS/σ[ε+0.6(σ/π)12], where I is image factor, S is pipe cross section; σ, mouth area; and ε, effective mouth depth. Complications due to annular effect, nonlinear reactance, jet-induced reactance, and orifice shape may explain why the present considerations were overlooked in the past. Experimental data are presented. [Work supported by the Office of Naval Research.]
Instrumentation and Techniques for Recording Aircraft-Flyover Noise
Authors: Zwieback Edgar L.
Published: November 2005

The introduction and widespread operation of turbofan-engine-powered aircraft of all sizes has resulted in increased emphasis on research into compressor-fan noise. Recording flyover noise of current aircraft for research requires test equipment and techniques designed for this purpose. Recent advances in electronics and electromechanics have resulted in the general availability of such new types of test equipment. These equipments, when suitably modified, meet the accuracy, calibration, and dynamic-range-data requirements and the reliability, portability, and simplicity-of-operation considerations necessary for efficient data gathering. The flyover-noise recording system includes the microphone, its mounting provisions, electronics and attenuator; the tape recorder; the system calibrators; the aircraft-distance-determining camera; the flyover-noise-aircraft position-correlation system; and the instruments to measure atmospheric conditions. A specific set of instrumentation, associated equipment, and test techniques that have been developed, evaluated, and utilized in several recent flyover-noise research programs are described. The system performance, in terms of accuracy and repeatability, has been determined along with the recording limitations based on the flyover noise of current turbofan-engine-powered aircraft.
Detection of Increments and Decrements in Continuous White-Noise Background
Authors: Anderson S. R.
Published: November 2005

Observers were presented with a two-alternative forced-choice (2AFC) task in which, in separate experimental runs, the signal consisted of either increments or decrements in a continuous white-noise background. Stimulus intensity differences that would yield a level of 75% correct response were determined for six naive observors by the PEST Technique (Parameter Estimation by Sequential Testing). Initially, decrements are more difficult to detect than are increments. With practice, however, detection of decrements improves more rapidly than does detection of increments, and initial differences tend to disappear. [Supported by National Research Council, Canada.]
Transient Overshoot in Linear Time-Invariant Systems
Authors: Green David M.
Published: November 2005

For a variety of maskers, the signal is more difficult to hear near masker onset than a few milliseconds later. Zwicker (1965) has called this phenomenon “overshoot.” Scholl (1962) has interpreted this fact as indicating that the critical band is wider at masker onset than it is 10–50 msec later in time. While this interpretation may, in part, be correct, it is also true that some linear, time-invariant systems show initial transients reminiscent of the overshoot phenomenon. The conditions needed to generate an initial overshoot in the response of a linear, time-invariant system are given and their implications for psychoacoustic data are discussed. [This research was supported in part by the National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare.]
Masking of Tones before, during, and after Brief Silent Periods in Noise
Authors: Elliott Lois L.
Published: November 2005

Thresholds were measured for a 5-msec tone which occurred at a number of different times before, during, and after a silent period of 25, 50, 200, or 500 msec duration in an otherwise continuous 70-dB-SPL (sound-pressure level) masking noise. When a 1900-Hz tone was masked by wide-band noise or by a narrow band of higher frequencies, threshold levels for signals occurring soon after the end of the silent period were elevated by as much as 15 dB compared with thresholds 250 msec after the noise began. This threshold elevation (previously termed “overshoot” when the noise burst followed an “infinite” silence) increased with the duration of the silent period. Smaller threshold elevations preceded the silent period. For a 2600-Hz tone centered in the narrow band of noise (a situation previously yielding no “overshoot” even for single bursts of noise), negligible threshold change occurred except during the silent period. Results are interpreted in terms of neural on effects and temporal development of auditory-frequency contours. [Supported by a program project grant of the National Institutes of Health, United States Department of Health, Education, and Welfare.]
Detectability of a Monaural Signal as a Function of Interaural-Noise Correlation
Authors: Dolan Terrence R. , Robinson Donald E.
Published: November 2005

The detectability of a monaurally presented, 500-cps signal was measured at each of several values of interaural correlation for a wide-band noise masker. The results, when expressed in terms of masking-level differences (MLD's), are in agreement with data reported by Wilbanks and show a function of similar form to that described by Robinson and Jeffress. The data are used to estimate parameters for a simple model which attempts to account for changes in detectability that occurs when a monaural signal is presented with binaural, correlated noise having an interaural level difference. The model suggests that, at low external noise levels, internal noise leads to a decrease in interaural-noise correlation. Predictions from the modal are in reasonable agreement with data reported previously by Egan and Dolan, et al. [Research partially supported by United Cerebral Palsy Research and Training Foundation and by Air Force Office of Scientific Research.]
Electrical Model for Binaural Detection
Authors: Jeffress Lloyd A. , Gaston Audley D.
Published: November 2005

An electrical model that takes a running average of interaural time differences yields results similar to human performance under several binaural conditions—N0Sπ, NπS0, and N0Sm—with continuous noise and gated signal. It shows a response to signal duration similar to that given by people. Previous models, such as the theta model and the E-C model, have no provision for handling the case of the continuous noise and gated signal and leave the effect of signal duration under these conditions unaccounted for. The device achieves its measurement of time difference by amplifying and clipping the inputs from the two channels, subtracting one from the other, and discarding differences of one sign while averaging those of the other. The voltage being averaged can be expressed by the equation E=Ei(et/RC−1)/(eT/RC−1), where t is the time that, say, the left ear leads the right, T is the period of the center frequency of the narrow-band noise, and Ei is the magnitude of the rectangular input voltage. [Work supported by a contract with the Naval Ship Systems Command, Department of the Navy, and through a grant from the National Aeronautics and Space Administration.]
Need for a New Acoustic Source
Authors: Craft William H.
Published: November 2005

Arguments are presented that develop the need for an acoustic-source arrangement which simulates convective-pressure fluctuations better than present methods. The type of source needed is described and a method for achieving such a source is proposed.
Transmission Phenomena in Slotted Acoustic Tubes
Authors: Rogers Joseph Wood
Published: November 2005

This report describes some of the transmission phenomena in slotted acoustic tubes. Only round cylindrical tubes with uniform slots are considered. A graph with a family of curves illustrates the behavior of the attenuation and phase constants as they vary with frequency and slot width. The slotted tube is a high-pass filter. When all of the variables (including slot width, wavelength, phase, and attenuation constants) are properly normalized with respect to the radius of the tube, two curves are found to be sufficient to describe the complete variation of the two constants. These phenomena are explained in terms of the analogous electrical-transmission line loaded with shunt resistance and inductance.
Phase Variation of Sound in the Florida Straits
Authors: Steinberg John C.
Published: November 2005

In a three-month program of the measurement of variations in amplitude and phase of 420-Hz CW signals continuously transmitted across the Florida Straits, a high degree of phase stability, from a communications viewpoint, is being observed. Phase variations that do occur appear to be more directly related to environmental changes than do amplitude variations. Variations in phase having diurnal and semidiurnal periods arise primarily from tidally related temperature changes in the slope waters of the sound path. These periodicities show marked similarities to variations in Key West tide height, and in the Florida Current transport reported by G. K. Wertheim in 1954. Periodicities of weeks and months, evident in the phase versus time curves, show magnitudes several times greater than those of the diurnal variations. These longer periods are of interest, both acoustically and oceanographically, in the prediction of expected phase and environmental variations. The observations are based on the results of a 20-day continuous-test period. [This work is supported by Acoustics Programs, U. S. Navy Office of Naval Research.]
Ray Representation of Diffraction Effects in the Spit-Beam Sound Field
Authors: Murphy E. L.
Published: November 2005

A generalized WKB-type approximation has frequently been applied to potential barrier problems in quantum mechanics. An analogous acoustic problem is the propagation of sound in a layered medium with the sound-velocity profile having a local maximum (split-beam sound field). Unlike the ordinary WKB method, the generalized procedure is designed to give solutions that are continuous through turning point regions and is especially useful when turning points are close together. This technique was applied to the split-beam sound field to investigate diffraction effects associated with turning-point regions where the geometrical-optics approximation fails. In some regions where asymptotic expansions for the generalized WKB solutions are valid, ray representations can be developed for these diffraction effects. Limitations on the validity of the ray representation and the extent of the regions (including the geometric shadow) in which diffracted rays may be introduced are discussed. Quantitative results are presented for transmission and reflection coefficients connecting the amplitude and phase along diffracted rays with those of the geometrical rays. Simple geometric schemes can, under certain conditions, be introduced relating particular diffracted rays to corresponding geometrical rays.
Precision in situ Measurements of Temperature, Salinity, Pressure, and Sound Speed on DEEPSTAR Dives
Authors: Mackenzie K. V.
Published: November 2005

Dives were made from 13 June-10 December 1966 on DEEPSTAR DS-4000 using three ACF TR-4 and one TR-3 velocimeters. Temperatures were measured by three thermistors. Pressures were measured with vibrations. Salinity was measured with a Hytech model 6007 salinometer. Fjarle bottles with two protected, and two unprotected, thermometers each were tripped at equilibrium points. Data (in frequency) were recorded for the entire water column from the surface to the bottom on a multichannel tape recorder for automatic analysis ashore. Dives were stopped at equilibrium points and outputs of the sensors directly counted. After readings were obtained at each equilibrium point, a bottle was tripped to get a water sample for laboratory analysis and to obtain protected and unprotected temperatures. Four equilibrium points on each dive were—(1) DEEPSTAR 30 or 50 ft deep for measurements near the surface; (2) and (3) buoyed 100 and 200 ft above bottom; and (4) on bottom. The craft hovered ±2 ft when buoyed from a 25-lb weight on the bottom. The results of the series of dives will be presented and discussed.
Symmetrical Scanning of the Head with Ultrasound
Authors: Makow D. M. , McRae D. L.
Published: November 2005

The absolute position determination of reflecting targets in the brain is difficult because of the refraction of the ultrasonic beam and the different velocities in the bones of the skull and brain. Since many brain disorders distort the almost symmetrical brain structures, emphasis should be placed more on the detection of asymmetries rather than on faithful mapping of the brain. The asymmetry can be displayed with considerable precision by symmetrical scanning of the head simultaneously from both sides with two transducers. An ultrasonic immersion scanner that employs this technique will be described, and the results will be discussed.
Holographic Imaging with Ultrasound
Authors: Thurstone Fredrick L.
Published: November 2005

Ultrasound fields, having both spatial and temporal coherence, have been used to produce sonic holograms that can produce three-dimensional images in a visible light field. The sound field is detected by mechanically or electronically scanning a piezoelectric element and determining both magnitude and phase of the sonic field. The information thus obtained is processed sequentially by electronic, optical, and photographic techniques to produce a hologram transparency. The generation of the images by wavefront reconstruction is accomplished with the coherent light produced by a laser.
A Calibration Study of One Hundred Audiometers Currently Employed in Hearing Conservation Programs
Authors: Thomas W. G. , Preslar Mack J.
Published: November 2005

This study describes results based on the calibration of 100 audiometers over a 3-yr period. The audiometers tested were in current general use from 11 different agencies or individuals, and represented 30 different models from eight manufacturers. The audiometers were calibrated with high-quality laboratory-standard equipment under the most careful conditions. Sound-pressure output levels of the earphones were recorded for each frequency and attenuator setting from maximum output to 20-dB hearing loss (HL). Some difficulty was encountered with acoustic measurements below 30-dB HL using ISO standards. Below this level, terminal voltage readings were used. Only two audiometers could be judged in calibration when strict compliance with the standards was observed. The most frequent problem found was incorrect sound-pressure output of the earphone. Eighty-nine of the 100 audiometers failed to meet this specification. The second most common problem involved excessive rise time. The third most common problem was frequency outside the tolerance limit. This was followed in order by failure to meet specifications for hearing-loss interval and hearing-loss range, instability of SPL output with ac line voltage variations, excessive harmonic distortion, and excessive shock hazard. [Work supported in part by U. S. PHS National Center for Chronic Disease Control.]
Influence of Polarity of Acoustic Stimulus on Psychophysical Threshold
Authors: Hall J. L.
Published: November 2005

A 3-msec burst of a 1-kHz tone was added to every eighth cycle of a continuous 50-Hz tone and presented monaurally through a TDH-49 earphone. The threshold intensity of the high-frequency burst was determined as a function of two parameters [Deatherage et al., J. Acoust. Soc. Am. 38 (1965)]: (a) intensity of the low-frequency tone (110, 100, 90, and 80 dB re 0.0002 dyn/cm2, and low-frequency tone absent); and (b) phase of the low-frequency tone at which the high-frequency burst occurred (increments of 45°). At the three highest intensities, changes in phase produced appreciable threshold shifts, repeatable from subject to subject. The results are interpreted in terms of the relationship between polarity of displacement of the basilar membrane and initiation of activity in the auditory nerve (Kiang et al.)
The Effect of Depth and Content of the Middle Ear Cavity on Underwater Hearing Thresholds
Authors: Brandt John F.
Published: November 2005

The audibility threshold performance of the human ear submerged in water at ear depths of 12, 35, 70, and 105 ft is compared to its performance in air. Threshold SPL's at 125, 250, 1000, 2000, and 8000 Hz from six divers wearing open circuit, air breathing SCUBA equipment were obtained by the Békésy technique. Differences between water and air conduction thresholds ranged from about 30 dB SPL re 0.0002 μ at 250 Hz to 60 dB at 2000 Hz. Water conduction thresholds that are generally independent of test frequency require about 71 dB SPL. No significant effect upon threshold was provided by ear depth. Thresholds were also obtained from three divers at 105 ft breathing compressed air and, in another condition, breathing a mixture of helium and oxygen. Significantly higher thresholds (about 5 dB) at all frequencies were obtained with the helium-oxygen mixture in the middle-ear cavity. [Research supported in part by Office of Naval Research and National Institutes of Health.]
Sound-Shadow Effect in Impulse Noise
Authors: Hodge David C. , McCommons R. Bruce
Published: November 2005

The sound-shadow effect of the human head in an impulse-noise field was studied by exposing 27 subjects to gunfire noise so their left ears were normal to the oncoming shock wave (near ear) and their right ears were protected by the shadow of the head (far ear). Noise exposure was continued until the subject's near ear demonstrated 15 dB TTS and the postexposure TTS in near and far ears was compared. Peak pressure level at the entrance of the far-ear canal was less than one-half that found at the near ear (153 vs 161 dB re 0.0002 μbar). Mean TTS was significantly smaller in the far ears than in the near ears. The mean “protection” afforded the far ear by the head's shadow ranged from 3 dB at 1 kHz to 12 dB at 6 kHz. The implications of the findings for the protection of weapon crewmen and others is discussed.
Threshold Shift in Hearing as a Function of Bandwidth and Mode of Noise Exposure
Authors: Cohen Alexander , Jackson Emanuel
Published: November 2005

Fifteen subjects were each given separate 15-min exposures to three bandwidths of fatiguing sound (whole octave band and 13-oct band centered at 1000 Hz, pure tone of 1000 Hz) presented in three modes (constant level, variable level, and intermittent). The 13-oct band SPL were 5 dB below the whole octave-band levels for the various exposure conditions that, according to the CHABA criteria, should have yielded equivalent threshold shifts (TTS). The pure-tone SPL's equaled the 13-oct band levels for one set of exposures, and were 3 dB lower in another set. These latter conditions were intended to verify the increased noxiousness of pure-tone versus narrow-band noise stimulation, also specified in the CHABA criteria. Comparisons of the TTS produced by the different bandwidths and modes of noise presentation suggested that the CHABA criteria may error on the conservative side, especially in rating the hazards to hearing of 13-oct band and variable types of noise exposure. Implications of these findings as regards critical-band-TTS notions and the action of the acoustic reflex are noted.
Theoretical Analysis of Compressor Noise
Authors: Lowson M. V.
Published: November 2005

The noise radiated by rotor-stator and stator-rotor interactions in a duct of negligible length has been analyzed with the aid of the author's general theory. Explicit analytic results for rotating fluctuating source patterns have been found, which reduce to the case of Gutin for the steady propeller case with no axial velocity, and to Garrick and Watkins' results for the propeller problem with axial velocity. Computed results of over-all power and directionality will be presented for several basic cases, and the practical implication of these theoretical results will be discussed. [This work has been supported by the National Aeronautics and Space Administration under contract.]
Rotor-Stator Interaction in an Axial Flow Blower
Authors: Embleton T. F. W.
Published: November 2005

Measurements have been made on a ducted, single-stage blower, 12 in. in diameter, rotating at 4500 rpm. The duct includes a venturi, enabling mechanical prover and efficiency to be measured simultaneously with SPL's. Recently, Lowson [“Reduction of Compressor-Noise Radiation,” J. Acoust. Soc. Am. 40, 1248(A) (1966)] surveyed various possible noise-reduction methods. The experiments support qualitatively some of his estimates, though some quantitative differences also occur. As a function of axial spacing between rotor and stator, the SPL (both the pure-tone spectrum at the blade-passage frequency, and broad-band noise with the pure tones removed) shows a break in slope at a spacing rougly equal to the chord of a rotor blade. At smaller spacing the slope lies between 3 and 10 dB per doubling of spacing—depending on stator blade pitch, number of stator blades, and other parameters—while at larger spacing the sound levels decrease between 0 and 2 dB per doubling of spacing. Mechanical efficiency is independent of spacing up to about one chord length; at greater spacings it usually decreases slightly—typically it is reduced 2%–3% at a spacing of three or four chord lengths.
Predicting Hearing Impairment from A-Weighted Sound Levels
Authors: Botsford James H.
Published: November 2005

The hearing deficiency of a group may be described in terms of the percentage having impaired hearing in order to focus attention on the abnormalities of medical significance. The prevalence of hearing impairment for speech as defined by the medical profession was determined for various populations using published hearing survey data. The incidence of hearing impairment was found to increase with age in all populations and also with A-weighted sound levels in the groups exposed to harmful noise at work. The effect of harmful noise exposure at work is to increase the incidence of hearing impairment above that found in unexposed populations of the same age. Curves were drawn for predicting the net increase in incidence of hearing impairment resulting from exposure to various A-weighted sound levels at work. The increased impairment predicted for noise exposures that do not exceed the limits currently recommended was found to be acceptably small.
Predicting Speech Interference and Annoyance from A-Weighted Sound Levels
Authors: Botsford James H.
Published: November 2005

A sample of 741 noises measured in factories and in construction equipment was used to relate speech interference levels to A-weighted sound levels. A mathematical formula was developed which predicts the speech interference level from the A-weighted sound level with little error. A graph was drawn for use in predicting speech interference effects directly from A-weighted sound levels. Another sample of 235 noises measured along industrial plant boundaries was used to relate A-weighted sound levels to the level rank used for rating annoyance. A method was developed for predicting the level rank from the A-weighted sound level with satisfactory accuracy. A graph was drawn for predicting the degree of annoyance directly from the A-weighted sound level. The methods developed for predicting speech interference and annoyance effects directly from A-weighted sound levels are believed to be as accurate as the methods utilizing octave-band sound-pressure levels on which they are based.
Category Scaling Judgment Tests on Motor Vehicle and Aircraft Noise
Authors: Pearsons Karl S.
Published: November 2005

Tests have been conducted in which subjects were asked to rate the sounds produced by aircraft flyovers and motor vehicle drivebys on a category scale. Recorded sounds were rated by college students in an anechoic chamber; “real-life” sounds were rated by college students and community residents at locations near a highway and two airports. The subjective ratings were correlated with the calculated perceived noise levels of the sound. In the laboratory and field environments, the results indicate little difference in the ratings as a function of perceived noise levels. In addition, the relationship between noisiness rating and perceived noise level is quite similar among the various noise types tested. [Work supported by the Aircraft Development Service, Federal Aviation Administration.]
Cross-Spectral Density of the Noise on a Baffle Beneath a Plane Covering Layer
Authors: Gardner S.
Published: November 2005

Analytical results have been obtained for the cross-spectral density of the noise pressure on an infinite plane baffle located beneath a fluid layer, when random pressure fluctuations present on the upper surface of the layer have spatial scales that are small in comparison with an acoustic wavelength, and the baffle acts as a “locally reacting” surface. (1) If the layer thickness is small in comparison with an acoustic wavelength, and large in comparison with the length scales of the surface pressure, the pressure spectral density on the baffle is inversely proportional to the layer thickness. The random pressure on the baffle is isotropic, with correlation lengths proportional to the layer thickness. (2) If the layer thickness is large in comparison with an acoustic wavelength, the pressure spectral density on the baffle is independent of the layer thickness. The random pressure on the baffle is isotropic, with correlation lengths proportional to the acoustic wavelength. [Work supported by the Office of Naval Research, Code 468.]
Propagation of Unstable Finite-Amplitude Waves
Authors: Van Buren A. L.
Published: November 2005

When a finite-amplitude ultrasonic wave in water is reflected from an interface, a phase shift of the Fourier harmonic components can occur. The new phase relationship between the harmonics may cause the wave to be unstable. Depending on the phase shift, the amplitude of the harmonics may increase or decrease as the wave tends toward a stable configuration. A model that assumes that the reflection of these components is the same as if they were independent waves is used to calculate phases (and amplitudes) of these components as the wave propagates after reflection. These results are compared with experiment. (Stabilization distances are not sensitive to variatons in α0L, where α0 is the low-amplitude attenuation coefficient and L is the discontinuity distance. [Research sponsored by the Office of Naval Research.]
Gas Diffusion by Pulsating Bubbles in Sonic Fields
Authors: Gould Robert K.
Published: November 2005

A pulsating gas bubble is suspended by an acoustic radiation pressure force in a liquid. The bubble is far from all boundaries and virtually stationary. When the sound field is relatively weak and the liquid is undersaturated with the gas in question, the bubble shrinks under the influence of normal diffusion of gas into the liquid. When the liquid is saturated and the sound field relatively strong, the bubble may grow or shrink under the opposing influences of surface tension pressure and sonic pressure (rectified diffusion). Measurement of the diameter of the bubble as a function of time permits, in the first case, determination of the diffusion constant for the gas-liquid system, and, in the second case, experimental evaluation of current theories of sonically induced rectified diffusion. It is found that when a bubble breaks into surface oscillations, whichever process it is undergonig at the time, either growth or decay, is enhanced. [This work was supported in part by NIH grant while the author was on sabbatical leave during the academic year 1966–67 at the University of Vermont, Burlington, Vermont.]
Incipient and Desinent Threshold of Visible Cavitation in Helium
Authors: Beaubouef H. R. T. , Chu M. L. , Mosse A. , Finch R. D.
Published: November 2005

Measurements have been made of the incipient and desinent thresholds of visible cavitation in helium II, between 1.8°K and the λ point. It was found that the incipient voltage threshold for visible cavitation was at least twice as great as the desinent threshold. The desinent threshold at the lower temperatures was an order of magnitude higher than the audible threshold, but become comparable to the audible threshold close to the λ point. A qualitative explanation of the existence of incipient and desinent thresholds is advanced on the basis of Hsieh's theory of rectified internal convection [Contract Nonr-Rept. No. 85-33]. Further experimental observations of the sizes and motions of visible cavities and of the noise spectra of cavitation are discussed in relation to this theory. [This work was supported by NSF grant.]
Profile of Repeated Shock Waves in a Tube
Authors: McKittrick James L. , Blackstock David T. , Wright Wayne M.
Published: November 2005

Measurements of the waveform of a plane progressive sawtooth wave in a 2-in.-i.d. air-filled tube have been made with a wide-band condenser microphone mounted flush in the rigid end plate of the tube. The source, a horn driver at the other end of the tube, was excited with tone bursts to avoid standing waves. The frequency was 3.4 kHz and the sound-pressure level 154 dB. Under these conditions, the predicted shock formation distance is about 5 ft and the sawtooth distance about 8 ft. Measurements at 12 ft did not, however, confirm the expected perfect sawtooth shape. Although the bottom of each shock was sharp, the top was well rounded. Total delay between the bottom of the shock and the peak was about 25 μsec, i.e., about 10% of the wave period). At greater distances the delay was longer. The delay cannot be ascribed to poor microphone response. Tests with N waves in free space indicated a microphone rise time of less than 1 μsec. The rounding of the shock peaks apparently is caused by tube wall effects. [Work supported by NDEA, AFOSR, and ONR.]
Near Noise Field of the Transitional Ballistics Phase
Authors: Bixler O. C. , Dahlke H. E. , Kaplan R. E. , Van Houten J. J.
Published: November 2005

Transitional ballistics involves the events that occur at the muzzle of the weapon prior to, during, and immediately after the uncorking of the projectile. Shock waves precede and follow the projectile during this period of the ballistics cycle. Theoretical and experimental examination of this phase provides details regarding the near noise field associated with a weapon. Shadowgraphs of the nearfield shock waves and space-time diagrams for both supersonic and subsonic projectiles reveal the development of the acoustic and ballistic flow fields. The nonlinear nature of the near noise field is examined in detail by application of Whitham's theory of propagation in nonuniform channels. [Work supported by the Rock Island Arsenal, Illinois.]
Calculation of Underwater Sound Intensities by Numerical Integration Techniques
Authors: Miller Max K.
Published: November 2005

Calculation of sound intensities in the ocean where the velocity profile is given at discrete values of water depth presents difficulties. Suitable functions must be used in order to fit the measured points, and then be integrated to give correct sound intensities. Overlooked is the fact that when the measured velocity is given at discrete points, calculations lend themselves naturally to numerical integration techniques. In this paper, Chebyshev quadratures and Simpson's one-third rule are used to calculate sound intensities by integrating expressions containing the velocity function. These methods avoid the problem of fitting the velocity profile with a function that can be integrated to yield meaningful results. The ocean is divided into several layers and integrations are done from interface to interface. For Chebyshev integration, three layers give good results and velocities are required at relatively few depths. Simpson's one-third rule requires equally spaced data and more points, but it is fast on digital computers. Intensities are compared with those calculated using piecewise linear profiles—known to give infinities in intensity calculations.
Comparative Measurements of Low-Frequency Attenuation in the Deep Ocean Employing Sinusoidal and Explosive Sources
Authors: Thorp William H.
Published: November 2005

This paper describes a deep-water propagation experiment involving the use of both explosive sources and towed sine-wave projectors in the SOFAR channel of the North Atlantic. It was conducted with the objective of narrowing the list of potential causes put forth to explain the well-documented, but unexpectedly large, attenuation coefficients that have been reported by determining whether the observed anomalies stem from fundamental differences in the sources employed or from mechanisms associated with the medium. The study initially considers the conformity of coefficients in the 354–3540-Hz region for the impulsive measurements in this instance with previously reported values. Thereafter results of the present regression analysis are compared with an identical treatment of simultaneous single-frequency data at 1900 and 3800 Hz, and the relative agreement is discussed in terms of the statistical confidence limits of each.
On the Sound-Pressure Transformation from Free Field to Eardrum of Chinchilla
Authors: von Bismarck Gottfried , Pfeiffer Russell R.
Published: November 2005

The sound pressure at the eardrum of anesthetized chinchillas was measured with a probe-tube microphone implanted into the external auditory meatus. The ratio of this pressure to the free-field pressure measured at a point corresponding to the center of the animal's head was determined as a function of frequency (sound pressure transformation function, SPTF). Two distinctly different types of SPTF's were found. They differed by as much as 15 dB in the frequency range 1–8 kHz. Several of the ears that exhibited one type of SPTF showed slight perforations in the tympanic membranes. It appeared that a static pressure difference across the eardrum was responsible for the other type of naturally occurring SPTF's. Both types of SPTF's could be artificially produced by either creating or by equalizing static middle-ear pressure. [This work was carried out at the Massachusetts Institute of Technology and supported in part by the National Institute of Health (Grant), the Joint Services Electronics Program, and NASA Grant.]
Temporary Threshold Shifts in Chinchillas
Authors: Ward W. Dixon , Nelson David A.
Published: November 2005

Detailed audiograms were determined for 20 chinchillas (conditioned avoidance technique). The animals were then exposed for 10 min to successively higher levels (70–110 dB SPL) of a noise specially filtered in an attempt to produce approximately equal values of temporary threshold shift (TTS) at 1, 2, 4, and 8 kc/sec. The observed growth of TTS with level is in essential agreement with results reported by Peters [J. Acoust. Soc. Am. 37, 831–833 (1965)] on two chinchillas, namely, that they are 10–15 dB more susceptible to TTS from noise than humans. That is, a noise of say 100 dB SPL that produces a certain value of TTS in men will produce the same value of TTS in chinchillas when its level is 85–90 dB SPL. Although group means are quite stable upon replication, within-animal test-retest variability is so great that it is difficult to assign indices of relative susceptibility to the chinchillas. Sources of variability will be discussed. [Research supported by Public Health Service.]
Distribution of Harmonics in the Cochlea
Authors: Dallos Peter , Sweetman Richard H.
Published: November 2005

While it is now clear that the primary source of harmonics is in the inner ear, there is no agreement on their mode of generation. To study this problem, microphonic potentials (CM) were recorded from guinea pig cochleas with differential electrodes situated in the first and third turns. The distribution of harmonic distortion components in the CM was studied by comparing the relative response magnitudes of the fundamentals, their harmonics, and of tones at the frequency of the harmonics. It is concluded from these experiments that harmonic components in CM are distributed as their fundamentals and not as pure tones corresponding to them in frequency. To study this problem further, we attempted to cancel any one distortion component in the CM with a bone conducted stimulus of the same frequency as the distortion product in question, and of controllable phase and magnitude. While it was a relatively easy task to cancel the CM response for any harmonic component in either turn of the cochlea, we never succeeded in eliminating the distortion in both turns simultaneously. These experiments indicate that internally generated signals (i.e., distortion components) do not generate the same types of traveling wave as do external stimuli. [This research was supported by grants from the National Institutes of Health.]
Noise from a Simplified Model of a Supersonic Turbulent Shear Layer
Authors: Ribner H. S.
Published: November 2005

A layer of two-dimensional square “eddies” separates a main flow Uj from fluid at rest; the eddies move at the mean (supersonic) speed Uj/2. The initially plane interfaces will ripple slightly, developing Mach waves to balance internal and external pressures. The Mach wave pressure pattern (noise) is readily calculable. The sound power from unit area of interface comes out to be P = e(peak eddy velocity)4 [(Uj/2c)2 − 1]12/16 Uj. In an example (simulated round rocket jet), the effective area is taken as 6π (diam)2, Uj/c = 6, peak eddy velocity = 0.1 √ Uj. The efficiency (noise power/flow power) comes out to be 0.17%, which is of the order of measured values for rocket noise. [This study was supported by a grant from the Air Force Office of Scientific Research.]
Boundary Layer Noise: The Relationship between Turbulent Shear Stress and the Turbulent Wall Pressure Field
Authors: Black Thomas
Published: November 2005

This paper presents a recently developed model of wall turbulence that provides a new interpretation of the turbulent wall pressure field and hence a new approach to related acoustical and vibrational problems. The theory suggests that the turbulent transfer of momentum is effected by a moving array of horse-shoe vortex structures that are generated and maintained by a spatio-temporal instability of the sublayer flow. As a result of the interaction between these vortex systems and the basic flow, a characteristic pressure signature is generated on the wall directly beneath each vortex structure, the shape and average strength of the signature being related to the local turbulent shear stress distribution. The turbulent wall pressure field is attributed to the motion of the resultant pattern of pressure signatures over the wall, and is seen as an integral and essential part of the turbulent shear stress mechanism. A new “pulse amplitude modulated” model of the pressure field is accordingly proposed in which the pressure at a fixed point on the wall is generated essentially at a single, characteristic frequency (related to local wall shear stress) by the regular or near regular passage of pressure pulses whose amplitudes vary randomly over a range determined by the ratio of boundary layer to sublayer thickness (i.e., over several orders of magnitude).
Acoustic Radiation from Turbulence near a Composite Flexible Boundary
Authors: Crighton D. G.
Published: November 2005

In an attempt to study diffraction phenomena within the context of aero-dynamic noise theory, the problem of radiation from turbulence near an infinite flexible panel is considered, in the case when the panel consists of two half-planes of differing impedances. The Kirchhoff-Powell radiation equations are reduced to a pair of singular integral equations, and a complete formal solution of these equations is given. Various acoustic sources distributed along the line separating the panels are identified and interpreted, and a great simplification of the complete solution is obtained in the high-frequency limit. In this limit, it is shown that, apart from the modification of the turbulent pressure field by a certain distribution of sources along the line of separation, the effect of the composite flexible boundary is merely to reflect rigidly the turbulence-generated sound field. [Research carried out under the Bureau of Ships and General Hydromechanics Research Program, administered by the David Taylor Model Basin, under contract.]
Toward an Acoustically Motivated Length Scale for Noise Environments beneath Disturbed Boundary Layers
Authors: Luksus E. J.
Published: November 2005

This paper deals with moderate noise disturbances associated with shock. It is hoped that this work constitutes a bridge between the well-predictable noise due to undisturbed boundary layers and the yet unpredictable noise due to intense shock-boundary layer interactions. Moderately disturbed data is extracted from work published by Speaker and Ailman [NASA CR-486 (1966)], that data being variously scaled to show that the high-frequency behavior is well handled by nondimensionalization according to momentum deficit thickness θ. The prominance of θ substantiates that wall noise originates close to the wall, which makes possible a modification of the displacement thickness δ*, creating what appears to be another satisfactory acoustic scale. The indication is that boundary-layer acoustic tests should be associated with aerodynamic measurements that emphasize the inner, stress-dominated portions of the boundary layer if information is to be obtained pertinent to the relations between flow disturbances and wall noise.
Acoustic Ion Waves in Gas Plasmas
Authors: Sessler G. M.
Published: November 2005

The generation of acoustic ion waves in gas plasmas is described, and the propagation characteristics of these waves in various ranges of frequency, plasma density, and neutral gas pressure are reviewed. The use of acoustic ion waves in plasma diagnostics is also discussed.
Effect of Dielectric Constant on Relaxation Frequency of MgSO4 Solutions
Authors: Fisher F. H.
Published: November 2005

Experimental ultrasonic absorption work by Bies (1955) for MgSO4 solutions shows that the primary relaxation frequency is increased to ∼200 kHz from 130 kHz as the dielectric constant is lowered from 78.5 to 67 using a water-dioxane mixture as a solvent. This relaxation frequency also increases as a function of concentration, and Fisher (1965) measured a relaxation frequency of around 200 kHz at 0.5 molar concentration. Measurements of the dielectric constant of solutions by Hasted, Ritson, and Collie (1948) indicate that the dielectric constant of a 0.5 molar MgSO4 solution is about 67. These results suggest that the lowering of solvent dielectric constant by adding dioxane is equivalent to the lowering of solution dielectric constant by increasing concentration. The acoustic relaxation frequency data of Bies and Fisher support the hypothesis that the two methods of lowering solution dielectric constant are additive. More accurate measurements should be made to verify previous results. Also, the work of Bies should be extended to lower dielectric constants (D = 45) where if the additivity assumption holds the relaxation frequency should show an increase to about 200 kHz based upon the 0.5 M work by Fisher for a solvent with D = 56.5.