bluuebunny/crossref_metadata_2025 huggingface dataset:
Classification of Marine Life Sounds, Using SCEPTRON
Authors: Balandis Leo S.
Published: September 2005

Typical sounds of several fish species have been uniquely recognized using an automatic spectrum-matching machine known as SCEPTRON® pattern recognizer. A variety of natural underwater sound recordings from different marine laboratories were used to obtain the samples of fish sounds and to evaluate the SCEPTRON device's capability in this application. The technique utilizes 2000 narrow-bandpass filters in the form of tiny resonant quartz fibers to provide a highly detailed memory of the sounds in a miniature size. The SCEPTRON memory is self-conforming, and extracts common spectral features from a signal group during the programming process. Operation is in real time, in the audiofrequency range. A description of the SCEPTRON apparatus is presented, together with data showing performance with marine-life sounds.
Axial Focusing in SOFAR Channel
Authors: Williams A. O. , Horne William
Published: September 2005

Ray and wave analyses predict repeated paraxial focal zones along the SOFAR axis from a point acoustic source on axis, given various roughly parabolic profiles of refractive index symmetric about this axis (quite unrealistic). Experimental corroboration is lacking. Wave analysis leads to focusing if propagation constants of successive normal modes display constant increments for a large subset of all modes. We examine this requirement with an index profile expressible near the axis in z2, z3, and z4, matching the standard Pekeris profile fairly well. Perturbation treatment of the quantum-mechanical anharmonic oscillator is applicable. The lowest 0.2 f modes (f, frequency in cps) approximate focusing requirements, but alternate ones, being nearly of odd parity, contribute little on axis. Interfocal separations are about 6 miles. Near calculated foci, these modes add almost coherently; all higher ones are assumed incoherent. “Enhancements” of energy in focal regions are then calculable. At 100 cps, enhancement is an undetectable few percent—in general agreement with Hirsch and Shear [J. Acoust. Soc. Am. 36, 1015 (A) (1964)]. [Work supported in part by the U. S. Office of Naval Research.]
Calculation of the Peak Amplitudes of SOFAR Signals
Authors: Hirsch Peter
Published: September 2005

The peak amplitudes of SOFAR signals have been estimated by considering particular mathematical models for the acoustic speed-versus-depth profile of the ocean and for the explosion waveform. The souud speed was assumed to vary as c2 = c02(1 − α2z2)−1, where c0 is the speed at the channel axis, z is the vertical distance from the axis, and α specifies the width of the channel. The source waveform was assumed to be a finite wavetrain, typically a 110-sec pulse of a 100-cps sinusoid. It is found that the range dependence of the peak of the received pressure amplitude is the product of two terms. The first is the expected cylindrical spreading loss. The second term oscillates with range. The amplitude of the oscillation depends on the source waveform and the range; for the typical 100-cps 110-sec pulse at 400 nm, the amplitude is about 12 dB. The distance between successive maxima of the oscillation is about 6 nm, and is independent of range and source waveform. [Work supported by the Bnreau of Ships, U. S. Navy.]
Langmuir Probe as an Acoustic Detector in an Ionized Gas
Authors: Gentle Kenneth W. , Ingard Uno
Published: September 2005

The possibility of using a Langmuir probe as a detector of sound waves in a weakly ionized gas is demonstrated by means of a simple experiment ill which an acoustic pulse transmitted through the plasma column of all argon discharge is detected by such a probe. Using this technique, the speed of sound and from it the neutral-gas temperature have been determined in all argon discharge as a function of gas flow, pressure, and discharge current. [Work supported in part by the [U. S. Army, U. S. Navy, and U. S. Air Force under contract DA 36-039-AMC-03200(E); in part by the U. S. Navy Office of Naval Research under contract Nonr-1841 (42); and in part by the U. S. Atomic Energy Commission under contract AT (30-1)-1842.]
Propagation of Acoustic Ion Waves in a Weakly Ionized Gas
Authors: Sessler G. M.
Published: September 2005

Measurements of the velocity and attenuation of electrostatic ion waves in weakly ionized nitrogen were performed at gas pressures of a few microns and at frequencies between 0.1 and 1 Mc/sec. Ionization of the gas is produced by an rf discharge, the degree of ionization being about 0.01%. The ion waves are excited by application of pulse-modulated signals to a grid arrangement that is immersed in the plasma. Velocity and attenuation are measured with an electrostatic probe that is movable parallel to the direction of wave propagation. The results show that the phase velocity of ion waves under these conditions is of the order of 105 cm/sec and increases slightly with increasing frequency. The attenuation constant is of the order of 1 cm−1. The attenuation can be explained by viscous absorption due to the viscosities of the ion and electron gases. Attenuation due to collisions of ions with neutral particles and dne to collisionless (Landau) damping seems to be relatively small in the frequency and pressure ranges under consideration.
Interference Patterns in Reverberant Sound Fields, II
Authors: Waterhouse Richard V. , Cook Richard K.
Published: September 2005

Contour charts are given of the sound fields near one, two, or three reflecting surfaces at right angles, for random sound incidence. The charts show contours of the mean-squared pressure in decibels as a function of position in the region within 2 wavelengths of the boundary surfaces. The boundary conditions at the reflecting planes are pressure reflecting (normal velocity equal to zero) or pressure release (pressure equal to zero). By reciprocity, the charts also give the radiation resistance of a point source as a function of position near such reflectors. The formulas used are tabulated; they extend and in some places correct formulas given in an earlier paper [J. Acoust. Soc. Am. 27, 247–258 (1955)]. The features of the sound fields near the reflectors are discussed, and some applications to acoustics measurements in reverberant sound fields are considered. [Work partly supported by the U. S. Office of Naval Research.]
Measurement of High-Q Resonances in Liquid-Filled Spheres
Authors: Simon Murray
Published: September 2005

One of the most important and difficult to measure elastic constants is the bulk modulus and its Q factor. In order to measure the Q factor of a small solid specimen, a high-Q liquid-filled system must be obtained. For the past year, an attempt has been made to excite the radial modes of a water-filled sphere suspended in a vacuum. At first, excitation at the wall was tried and proved unsuccessful, since it put energy into many of the shell resonances and produced a highly complex resonance pattern. In the past few months, a successful method was found. A small barium titanate crystal was cemented to the end of a brass tube and placed at the center of the sphere. Using this crystal for both driving and receiving, Q's as high as 72 000 have been obtained for several resonances, in two water-filled spheres of different wall thickness and diameter. Small samples were placed at the center and changes in the Q were measured. [Work supported by the U. S. Air Force Office of Scientific Research (AF-AFOSR-43-63).]
Pulse Propagation in Cylinders at the Lower Ultrasonic Frequencies
Authors: Lange James N.
Published: September 2005

The theoretical treatment of wave propagation in cylinders has progressed rapidly in recent years with the use of computers and the development of simplified theories for long wavelengths. There are, however, a number of phenomena that have not been adequately explained. In particular, the presence of mode conversion at the lower ultrasonic frequencies (when the diameter of the cylinder is less than 110 of a wavelength) is not yet understood. This paper discusses the origin of mode conversion and its relation to the “end resonances” as derived by McNiven. The roots of the Pochhammer-Chree frequency equation are reviewed critically with these phenomena. [Work supported by the U. S. Air Force Office of Scientific Research under grant No. 43-63.]
Some Modifications to the General Dynamics/Electronics Formant Vocoder
Authors: Houde R. A. , Larkin W. D. , Stewart L. C.
Published: September 2005

At the last Fall Meeting, we reported on a method of formant analysis using a partial spectrum-pattern-matching technique that was demonstrated in an experimental model formant vocoder [J. Acoust. Soc. Am. 35, 1912 (A) (1963)]. At the same time, the first tentative results of a brief critical study of the system performance were also given. Since that time, a much more detailed investigation of the errors made by that system has been conducted. As a result of this study, certain modifications to that system have been proposed to improve the intelligibility and quality of the General Dynamics/Electronics formant vocoder. Some of these improvements have been simulated with a computer. This paper presents the results of this study and demonstrates the improvement noted in the computer simulation of some of the modifications suggested. [Work supported by the U. S. Army Electronics Research and Development Laboratory, Ft. Monmouth, N. J., and General Dynamics/Electronics.]
Differing Pharynx Shapes and Sizes for Vowels
Authors: Truby H. M.
Published: September 2005

It is an acoustic commonplace that sound derives from motion, and it is clear that the sounds of speech derive from the act of speech. Physiologically speaking, then, speech is pattern-conditioned articulatory modification of physically generated vocal-tract-amplified sound. One of the byproducts of pattern-conditioned articulation is inherent involuntary action interrelated with the projected voluntary action, including muscular and other motor preadjustments anticipatory to segmental speech-sound-nucleus phenomena. Both cinéradiographic and sound spectrographic analysis demonstrate these anticipative adjustments, and cinéradiography, by revealing normally inaccessible dimensions defining the physical state of the vocal-tract cavities, clarifies spectral shapes apparent on sound spectrograms but not always deducible from the referent perceived speech signal. An x-ray motion film of the production of 15 isolated General American vowels discloses the drastically varying cavity sizes and contours from vowel to vowel and thus divulges formant-cavity information critical for reliable automated speech-simulation and -detection research.
Reflection and Scattering of Sound by the Sea Bottom. Part II. Field Data
Authors: Bell T. G.
Published: September 2005

This paper is Pt. II of a trilogy [Pt. I: H. W. Marsh, “Theory.” Paper K1, this meeting. Pt. III: C. W. Horton, “Model Studies.” Paper K3, this meeting]. A review is made of experiments in both shallows- and deep-water ocean areas, illustrating frequency- and angle-dependent reflection effects. Interpretations of these measurements are made in the light of knowledge of the geological character of the regions involved.
Reflection and Scattering of Sound by the Sea Bottom. Part III: Model Studies
Authors: Horton C. W.
Published: September 2005

This paper is Pt. III of a trilogy [Pt. I: H. W. Marsh, “Theory.” Paper K1, this meeting. Pt. II: T. G. Bell, “Field Data.” Paper K2, this meeting]. Selected experiments performed in the laboratory and in Lake Travis are reported that are valuable in interpreting or predicting effects observed in the field. The models illustrate the effects of layered media, backscattering, and absorbing (porous) materials.
Results of the Mechanical-Impedance Round-Robin Measurements
Authors: Belsheim R. O. , Remmers G. M.
Published: September 2005

Several years ago, a mechanical-impedance “round-robin” measurement project was initiated by the ASA Shock and Vibration Committee to determine by actual comparison measurements whether the state of the art is sufficiently advanced to yield reliable and repeatable results when measurements are made by different teams and equipment. Comparisons of these data are presented. Details of the test fixtures, procedures used in gathering the data, and the methods of comparison are discussed. The significance of the results are probed and recommendations made.
Wave Effects in Rubber Antivibration Mountings
Authors: Snowdon J. C.
Published: September 2005

A guide to the character of wave effects in antivibration mountings has been obtained from an approximate theory of rod vibration given by Love, in which a lateral-inertia correction is introduced. Thus, the longitudinal vibration of uniform mass-loaded rods that possess a finite length-to-diameter ratio has been determined from the Love theory. Further, into this theory has been inserted the observed frequency dependence of the mechanical properties of both low- and high-damping rubbers. Representative computations of transmissibility made from the Love theory have been compared with results obtained, for the same rubbers, from the simple one-degree-of-freedom theory in which wave effects are disregarded. For rubbers with low damping, the effectiveness of the mountings at high frequencies is overestimated by the simple theory, although the transmissibility of the mountings will normally remain a small quantity. For high-damping rubbers, however, the simple and more-complex theories are found to be in relatively close agreement.
Investigation of Structure-Borne Active Vibration Dampers
Authors: Rockwell T. H.
Published: September 2005

The use of active feedback elements to produce damping of multiresonant structures has been extended to include the case where the damping-force generator is supported by the structure being damped instead of by a rigid external base as previously reported. The theoretical damping equation and a design procedure for the structure-borne active damper are presented. Agreement between theory and experiment for the particular case of a 48-in.-long uniform beam is quite good. A simultaneous reduction in resonant mobilities of all resonances lying below 10 kc/sec has been demonstrated. The reduction obtained was equivalent to that achieved for the previously reported case in which the damping-force generator was supported by a rigid (external) base. At some high-Q modes, the reduction was as much as 30 dB.
Flexural-Wave Transmission Properties of Plate-Joint Systems
Authors: Pallett David S.
Published: September 2005

Simple plate-joint and rod-joint systems are in general characterized by single and often multiple passing and stopping bands for flexural waves incident upon the joint. Joint width or “clamping length” and polar moment of inertia are of considerable significance in determining the position of the zeroes of transmission. Experimental studies on plate-joint systems have included the use of joints for which the clamping length and polar moment of inertia can be varied independently of other parameters. Measurements have included the use of an isolating box that totally encloses one plate segment in order to reduce the possibility of excitation of this segment by the acoustic radiation from another portion of the system. Theoretical studies of the transmission characteristics for finite-width rod-joints based on centroid displacement, pure rotation, and rotation and displacement models are discussed.
Sound and Vibration Transmission through a Rectangular Double Wall by Statistical Methods: Theory and Experiment
Authors: White Pritchard H. , Powell Alan
Published: September 2005

The existence of a great many modes in a randomly excited complex system makes a detailed classical modal analysis almost intractable. However, the existence of groups of similarly excited modes allows certain averages of the response to be found, as for response of a cylindrical shell to jet noise [A. Powell, in Random Vibration, S. H, Crandall, Ed. (Technology Press, Cambridge, Mass.), Chap. 8], and for the excitation of a structure by a reverberant acoustic field [R. H. Lyon and G. Maidanik, J. Acoust. Soc. Am. 34, 623–639 (1962)]. For sound transmission through a rectangular double wall, this technique gives results that agree within experimental error of measured transmission loss: much better than conventional loss estimates. Experiments have confirmed that the product of modal “density” and average joint acceptance of the first panel is the most important quantity in determining the transmission characteristics of the wall. [Partial support by the U. S. Office of Naval Research.]
Experimental Liquid-Filled Transducer Array for Deep-Ocean Operation
Authors: Kendig Paul M. , Clarke Hugh J.
Published: September 2005

A small experimental transducer array was designed, constructed, and tested to demonstrate the feasibility of enclosing the elements in a liquid-filled housing that requires no pressure-release materials. The transducer consists of four dumbbell-type lead zirconate titanate transducer elements that are set in close-fitting cavities in a high ρc metal block. The entire housing is filled with a silicone fluid and provision is made to maintain the inside pressure equal to the pressure on the outside at all times. Presentation of frequency-response curves, electrical input impedances, and efficiencies demonstrates that the transducer characteristics are relatively insensitive to ambient pressures up to 1000 psi, the maximum pressure available for test. The transducer is further characterized by high power capability, good efficiency, a low Q, and a high effective electromechanical-coupling coefficient. [Research sponsored by the USN Bureau of Naval Weapons.]
Unidirectional Resonance Characteristics of Split Cylinders
Authors: Devine John A. , West Herbert L.
Published: September 2005

Unidirectional characteristics can be generated in cylindrical piezoelectric-effect transducers by splitting the elements parallel to their longitudinal axes. These characteristics, which have been called directional resonance effects, are being investigated at the U. S. Naval Air Development Center under its Foundational Research Program. It was observed that line transducers made of cylindrical elements showed deviations from uniformity in response patterns when elements were damaged by cracking. A working hypothesis for such behavior was formulated and applied to transducer design. Line transducers that provide unidirectional patterns at certain frequencies have been designed. For example, a 12-in. line made up of cylinders having a diameter of 112 in. when used without any reflector gave a unidirectional response pattern having a front-to-back ratio of approximately 10 dB at a frequency of 10 kc/sec. The hypothesis indicates that patterns occur at a series of frequencies. The presence of such patterns has been verified experimentally and the front-to-back ratio exceeded 30 dB. The hypothesis used, transducers designed, and the results obtained are shown.
Novel Formulation of the Helmholtz Integral for Calculating the Acoustic Field of Slender Axisymmetric Radiators
Authors: Copley Lawrence G.
Published: September 2005

The usual form of the Helmholtz integral expresses the sound pressure radiated by a vibrating body immersed in an acoustic fluid as an integral over the vibrating surface involving both normal velocity and surface pressure. These two quantities are interdependent owing to the acoustical behavior of the fluid. If the normal velocity is assumed prescribed, the surface pressure is generally unknown. The present method calculates the surface pressure, using an integral equation derived from the Helmholtz integral by restricting the “field” point to lie inside the radiator. It then uses the Helmholtz integral to compute the acoustic field. The integral equation has a regular kernel and a line domain. (Related integral equations used previously by others have singular kernels and surface domains.) A numerical iteration has been developed for solving the integral equation by desk computation. Ranges of frequency and slenderness for which the iteration converges have been determined. Extension of the method to elastic-acoustic interaction problems appears feasible. [Work performed under U. S. Office of Naval Research contract Nonr-3845(00)(X) with the David Taylor Model Basin.]
Energy Spectra of Small Explosions at Great Depths
Authors: Christian Ermine A. , Blaik Maurice
Published: September 2005

The total energy spectrum of a small explosive charge fired at great depths differs markedly from the smooth shock-wave spectra that have been demonstrated by Weston and others. The oscillations due to the interaction of shock-wave and bubble pulses are pronounced even at kilocycle-per-second frequencies, and the bubble contributes significant additional spectral energy at several harmonics of the bubble frequency (inverse of the bubble period). In a study of the effect of charge weight and depth on the acoustic signal from an explosive source, spectra were digitally computed from broadband pressure recordings made at the surface above small charges fired in the ocean. Charge weights varied by a factor of 150, depths by a factor of 25, and bubble frequencies ranged from about 50 to 1500 cps. Methods of estimating spectrum level using semi-empirical expressions for the pressure-pulse parameters are discussed.
Effects of Moderate Doses of Curare on Acoustic-Reflex Function
Authors: Loeb M. , Smith R. P. , Fletcher J. L.
Published: September 2005

It was hypothesized that the middle-ear muscles would be among the first affected by curare action, and this hypothesis is supported by a recent paper by Lehnhardt in which it was reported that a curarelike drug suppressed impedance changes attributable to acoustic-reflex action. If the procedure is feasible, it should be possible to determine the influence of the reflex on ipsi- and contra-lateral masking, fatigue, adaptation, and other auditory functions. Several volunteer subjects were given intravenous doses of d-tubocurare sufficient to produce ptosis and appreciable loss of grip strength. Acoustic-reflex action was monitored by a manometric technique similar to that recently described by Weiss, Mundie, Cashin, and Shinabarger. Reflex reductions were observed in some subjects but not all. While the technique has promise, it is possible that the dosage required for reflex abolition will be such as to make its application impractical.
Masking-Level Differences for Pulses
Authors: Rabiner Lawrence R. , Flanagan J. L. , David E. E.
Published: September 2005

The effects of interaural time upon the masked, binaural thresholds of periodic pulses were measured. Two interaural time conditions were considered: namely, zero and one-half the repetition period. Additional parameters were interaural phase of the masking noise (0 rad, π rad, and uncorrelated), noise level (approximately 40 and 60 dB sensation level), and pulse rate (10, 50, 250, and 1000 pps). Listening was via headphones in a sound booth. The thresholds were measured by a modified Békésy technique. At low pulse rates (10 and 50 pps), the results for correlated masking show small, if not negligible, masking-level differences. At the high pulse rates (250 and 1000 pps), masking-level differences comparable to those for pure tones are measured. Like the behavior for tones, the antiphasic conditions are more detectable and the homophasic conditions are less detectable. For both sensation levels, on the other hand, the uncorrelated noise condition shows a measurable masking-level difference at the low pulse rates. Ancillary experiments at low pulse rates, with interaural times of 2 and 6 msec, suggest that detectability is essentially independent of position of the sound image in phenomenological space. This result is one more fact with which any adequate theory of binaural hearing must deal.
Temporal Perception of Tone Pulses
Authors: Peters Robert W.
Published: September 2005

Observers adjusted the center pulse of a 3-tone/pulse series by either increasing or decreasing the frequency to achieve the criterion that the center pulse was heard to occur either first or last. At the beginning of each trial, the frequency of all three pulses was the same. The frequency increase or decrease necessary to achieve the temporal-order criterion was examined in the frequency range of 500–4000 cps, at pulse durations and intervals in the range from 10 to 80 msec, and for various SPL. The results indicated that the required change in frequency of the center pulse to alter perceived order increased as the test frequency increased and that the values were similar to those for critical bands. The phenomenon was also examined for two- and five-pulse series. For some observers, temporal perception different from actual order was reported. [Research supported by U. S. Aeronautical Systems Division, Wright-Patterson Air Force Base, under contract AF 33 (615)-1181.]
Detection of Auditory Signals in Reproducible Noise
Authors: Pfafflin Sheila M. , Mathews M. V. , Kohut J.
Published: September 2005

Twelve reproducible noises were used as stimuli in a 2-interval forced-choice signal-detection experiment. The noises were stored numerically in a PB250 computer that converted thein to sound during the experiment by means of a digital-to-analog converter. The 240 numbers specifying a noise were sampled at a rate of 2500 numbers/sec, generating a 96-msec stimulus. A sinusoidal signal with a period of 8 samples/cycle was added to one noise on half the trials. Spectral analyses were computed for all stimuli. On nonsignal trials, biases to particular noises were found that could be explained in part, but not entirely, by differences between the noise pairs in energy around the signal frequency. Performance on signal trials was related to the energy difference between the stimuli in the region near the signal frequency, but was not entirely accounted for by this variable. Special characteristics of certain noises appear to affect the subject's response when these noises appear in either signal or nonsignal trials. Except for bias effects, detection on signal trials with the same noise in both intervals was similar to that on trials with different noises. Implications for theories of signal detection are discussed.
Auditory Sensitization and the Method of Interpolated Trials
Authors: Watson Charles S. , Clopton Ben M.
Published: September 2005

Recent neurophysiological evidence suggests that the sensitivity of receptors may be varied through efferent control. A psychophysical method, a “method of interpolated trials,” has been devised for the study of such changes in sensitivity. The method is intended to measure short-term changes (in the order of seconds, rather than minutes or hours) in a listener's ability to detects signals in a noisy background, where the heightened sensitivity is elicited on demand by the experimenter. Observed effects, which are consistent with the hypothesis of efferent control, are found to be generally small, less than might be caused by a 2- or 3-dB increment in the level of a tonal signal. [Work supported by USN Bureau of Ships contract NObsr-72627 and under a grant from the National Aeronautics and Space Administration R-129 through ONR contract 3579 (04).]
Effects of Low-Intensity Noise on Monitoring Performance
Authors: Kirk Roger E.
Published: September 2005

The relative effects of three environmental noise conditions on the performance of a simple vigilance task was investigated. The vigilance task consisted of a cathode-ray-tube display that was monitored by 40 subjects for 4 h. Three environmental conditions were randomly introduced while subjects monitored the display. The condititions were a constant noise of 64.5 dB, a variable noise having an average SPL of 64.5 dB, and a quiet condition of 61 dB. The results indicate that the probability of signal detection is higher for the variable-noise condition than for the constant-noise and quiet conditions. No difference in probability of detection was found between the latter two conditions. It is concluded that auditory stimulation has an alerting and general arousal effect on the performance of a monitoring task performed under conditions of mild sensory deprivation. The data are interpreted as supporting an arousal hypothesis.
Response Characteristics of Polarized Cathode Solion Linear Acoustic Transducers
Authors: Larkam C. W. , English G. Earle
Published: September 2005

A polarized cathode solion (SOLution-ION) linear acoustic transducer contains two matched sets of electrodes, normally biased between 0.2 and 0.8 V. The current passed by each cathode is substantially independent of bias voltage and is a nonlinear function of the velocity of electrolyte flow across it. The transducer output is the algebraic difference of the currents from the two individual flow sensors, which are mounted back to back between flexible diaphragms of compliance C, and which offer flow resistance R. Several transducers having different known values of the pertinent physical characteristics have been built and tested in the frequency range from 0.001 to 100 cps and the pressure range from 0.01 to 10 000 μbar. In accordance with a previously presented theoretical analysis, the pressure and frequency-response pattern can be specified in terms of the RC-controlled lower cutoff frequency fl, the diffusion-controlled upper small-signal cutoff frequency fh, the small-signal sensitivity S0, the equivalent background pressure P0, at which output equals the quiescent current from each cathode, and the steady-flow cathode saturation pressure Pm. Typical values for these response parameters are fl = 0.002 cps, fh = 0.2 cps, S0 = 10 μA/μbar, P0 = 50 μbar, and Pm = 1500 μbar. [Work sponsored by the U. S. Office of Naval Research.]
Relative Effects of Normal-Mode Structure of Loudspeakers and Rooms on Reproduction of Sound
Authors: Bose Amar G.
Published: September 2005

Recorded speech or music signals experience considerable degradation when reproduced by a loudspeaker in a room. This work aims to differentiate between the effects of the normal-mode structure of the room and the loudspeaker. We have produced a tape of speech and music samples as they would be recorded in a room if reproduced through an ideal pulsating sphere. We have developed a spherical speaker with the property that speech and music samples reproduced through it in a room are subjectively indistinguishable from those that would be reproduced through the ideal pulsating sphere. The latter samples are generated by a digital convolution involving the Green's function of the room, which is obtained by a linear operation on signals generated by a spark discharge. This research indicates that a transducer can be designed that is subjectively equivalent to the ideal pulsating sphere; for this trandsucer, the normal-mode structure of the room—not that of the transducer—is the limiting factor in reproduction of speech and music signals. [Work supported ill part by the U. S. Army, U. S. Navy, and U. S. Air Force under contract DA06-039-AMC-03200(E); National Science Foundation (grant GP2495); National Institutes of Health, U. S. Department of Health, Education, and Welfare (grant MH-04737-04); and National Aeronautics and Space Administration (grant Xs(;-496).]
Impedance-Tube Technique for Determining the Fatigue Properties of Compliant Tubes
Authors: Moskal B. J. , Frederick J. P.
Published: September 2005

A laboratory technique has been developed that permits the investigation of the structural integrity of compliant tubes. This technique involves an electrodynamic shaker and an impedance tube filled with water. Standard test procedures to check the dynamic response and fatigue life use sections of specimens and/or full-scale tubes excited by a shaker system in air. In the new technique, the test article is submerged in water and the hydrostatic pressure differential and dynamic pressures applied. This approach assures a more reliable simulation of the operational environment and provides a more accurate method of predicting the life of compliant tubes. The simulation of dynamic pressure is accomplished by driving a 12-in.-diam diaphragm with a 7800-lb shaker. Hydrostatic-pressure differential is simulated by pressurizing the compliant tube with some gaseous media. A description of the test apparatus and test results on several compliant elements are discussed.
Rotor-Stator Interaction Noise Studies of a Single-Stage Axial-Flow Research Compressor
Authors: Copeland W. L. , Crigler J. L.
Published: September 2005

This paper gives some experimental results of a noise study of a single-stage axial-flow research compressor. The objectives of the study were to investigate the noise due to rotor-stator interactions and the propagation of this noise from the inlet duct. The data are presented in the form of radiation patterns and compare favorably with results calculated by the method of Tyler and Sofrin. These data show how the radiation patterns are affected by the relative number of rotor blades and stator vanes. Information is also included to show the effect of perturbation in air-stream velocity in the wake of the stator vane and how the noise is affected by these pertubations. Several tests were run to obtain the optimum spacing between the rotor and stator vanes for best results. A reduction in sound-pressure level of up to 10 dB was observed for the fundamental blade-passage frequency, and the characteristic radiation-lobe amplitudes have been markedly reduced because of increased rotor-stator spacing.
Sound Radiation from Turbulent Flow near Flexible Surfaces
Authors: Ffowcs-Williams John E.
Published: September 2005

It is known that large rigid surfaces reflect the sound generated by turbulent flow, but the reflection is distorted by viscous and nonlinear effects. Surface response to the turbulent flow can alter this conclusion. The paper deals with the particular situation of unsteady flow near a homogeneous plane surface responding to turbulent pressures. It is shown how, if the surface becomes sufficiently limp, the presence of the surface has precisely the opposite effect of a rigid surface, so that it again acts as a passive reflector but the image is of opposite sense. More generally, the sound radiated to large distances from the flow is not increased by surface response, a result that seems contrary to intuition. [Work supported by the David Taylor Model Basin under the USN Bureau of Ships Fundamental Hydromechanics Research Program.]
Preliminary Studies of the Sound Radiated by Orifices in Pipelines
Authors: Contractor D. N.
Published: September 2005

The sound radiated by orifices in pipelines is studied analytically and experimentally. At Mach numbers less than about 0.1, the sound is generated as from a simple source by mass flow fluctuations that are caused by the shedding of vortices from the orifice edge. The spectrum of sound energy has peaks in it, indicating a tonal quality of the noise. At higher Mach numbers, the sound is of a dipole nature, has a wide frequency base, and can be evaluated by considering the fluctuating force exerted by the orifice plate on the jet. Sound generation by multiple orifices in a single-orifice plate is also studied. Two cases are dealt with. First, the number of orifices of a constant diameter is increased and, second, the number of orifices is increased, maintaining a constant total area. Preliminary experiments verify the theoretical relationships for single and multiple orifices. The results are presented in the form of dimensionless spectral-density distributions versus the Strouhal number. [Work sponsored by the U. S. Department of the Navy, Bureau of Ships, contract No. NObs-88200.]
Sound-Power Studies of Model Silencers
Authors: Barnett Norman E.
Published: September 2005

An experimental study, exploring the silencing of jet aircraft during ground-runup operation, was conducted with small model jets. Objects and configurations of objects were placed in and around the jet exhaust to ascertain the effects on the sound-power spectrum. Among the configurations were several that resembled current runup-muffler designs. The acoustical results indicate that certain features of such model mufflers increase the radiated power. One model muffler shell scarcely altered the broad-band power, diminished the high-frequency power slightly, but increased the power over the entire low-frequency range, as much as 26 dB. Augmentation of low-frequency radiation seems to depend upon the extent of solid surface included in the muffler and is practically independent of whether the surface is flexible or rigid. Apparently, extended solid surfaces should be used sparingly, if at all, in muffler designs. Another model configuration, not fully investigated or optimized, has yielded n broad-band power-level reduction of 39 dB and significant reduction at all frequencies. [This paper drawn from research sponsored by the Systems Engineering Group, U. S. Air Force.]
Internal Sound in a Cylindrical Shell, due to an External Random Pressure Field
Authors: Khabbaz Ghassan R.
Published: September 2005

The outer skin of a space vehicle is exposed to a random pressure field. This pressure field causes the skin of the vehicle to vibrate and radiate sound to the interior of the vehicle. In the paper, we idealize the space vehicle by a finite cylindrical shell. Relations are derived for the mean-square pressure inside the vehicle. These relations explicitly depend on the spatial and time correlation function of the random pressure acting on the outside of the shell. It is shown that the effect of the internal fluid on the response of the shell is to cause a change in the inertia of the shell. The change in the inertia assumes various magnitudes and could be positive or negative, depending on the particular mode shape. Moreover, it is shown that there are optimum frequencies at which most of the sound is propagated to the inside of the vehicle. A set of curves showing the effect of the various parameters on the root-mean-square level of the internal acoustic pressure is given. Comparisons with field measurements are given where pertinent and available.
Response of a Loaded Sandwich Panel with Mass Attachments
Authors: Weingarten V. I. , Jacobson M. J. , Preston J. L.
Published: September 2005

The flexural motion of a rectangular sandwich panel with mass attachments is investigated both analytically and experimentally. Differential equations are derived that include the effects of rotatory inertia of the panel and masses, transverse-shear deformation of the core, damping, and in-plane loading. The influence of the concentrated masses on the natural frequency is first obtained and compared with experimental values. The dynamic response of a simply supported panel with mass attachments to a point sinusoidal excitation is then calculated and compared with experimental values. The effect of in-plane loading on the natural frequencies and response to a point loading is considered. The variation of the natural frequencies due to the rotatorv inertia of the panel and mass attachments is discussed in detail. The results of a number of special cases are discussed and compared with experimental values.
Electroacoustic Transducer Efficiency of R, L, and C Components
Authors: Nordby Knut S. , Lang William W.
Published: September 2005

It has long been recognized that electrical components under ac excitation behave as electroacoustic transducers (e.g., thermophone, transformer). The development of high-frequency power supplies for microminiaturized electronic packaging revived interest in resistors, inductors, and capacitors as sources of acoustical noise. The sound-power levels of 3 types of resistors, 3 types of inductors, and 4 types of capacitors were measured in a 0.75-m3 a reverberation chamber. Each component was excited by 13-octave bands of noise in the frequency range 1–16 kcps. From the PWL data and the input electrical power, the transducer efficiency and the average mean-square sound pressure at a distance of 1 m in a free field were determined. At 4 kcps, the efficiencies are approximately 10−14, 10−9, and 10−8 for representative R, C, and L components, respectively. For some C and L components, the sound pressures were sufficiently high to require noise-control measures. The effectiveness af various noise-control treatments (e.g., capsulation, potting) was evaluated.
Transient Response of Pipes
Authors: Ingalls Clyde E.
Published: September 2005

The response of pipes to excitation by the sound of a spark was obtained as a function of time. The results are shown by photographs of the responses. The response waveform is affected by direct transmission through the air in the pipe, reflections from the walls of the pipe, diffusion, radiation, absorption, material and shape of the pipe, ratio of cross-section area to length of pipe, and position of the sound source and microphone on the cross section at the ends of the pipe. The relationship of the transient response to the sound produced by a pipe-organ pipe is discussed by use of the convolution integral.
Digital-Computer Phase Techniques for Determining Noise-Source Location
Authors: Schmid Charles
Published: September 2005

The problem of locating submarine self-noise sources is approached from the phase technique rather than the usual method of observing high amplitudes in certain frequency ranges. Individual SONAR hydrophones were simultaneously recorded at sea during various no-target speed events and subsequently digitized in the laboratory. A digital computer was programmed to calculate the phase angle between selected pairs of hydrophones as a function of frequency, using the real and imaginary parts of the crosspower spectral density function. Low ship speeds exhibited broad frequency ranges having linear changes of phase as a function of frequency, indicating the dominance of a coherent source. High ship speeds showed more dispersion in the phase plots, but did display general groupings of points. If a velocity of propagation is assumed, then the slope of this line can be used to determine the bearing of the coherent noise source with respect to the hydrophones.
Performance of Optimum Detection Receivers in Amplitude-Fading Channels
Authors: Gittelman Joseph N.
Published: September 2005

The effect of polarity-preserved amplitude fading on the detection of otherwise known signals in additive white Gaussian noise is investigated for several different models of the channel. Both the slow-fading and the fast (independent) fading problems are considered. A simplifying assumption is introduced to establish the general effects of the fading problem. For the slow-fading channel, the polarity preserving property leads to the same receiver design but different performance curves for the different models of amplitude fading. In the fast-fading channel, the various models lead to different receiver designs while their performance curves approach those obtained by the optimum receiver in a “signal known-exactly” detection problem as the fading rate is increased. The receiver-operating-characteristic curves for the several models assumed are presented to illustrate these effects. [Work supported by the U. S. Office of Naval Research, Code 468.]
Air Force Eastern Test-Range Underwater-Sound Systems
Authors: Drake William R.
Published: September 2005

The underwater-sound missile-impact location systems on the Air Force Eastern Test Range are described. A SOFAR system covers the Atlantic Oceans between Florida and Ascension Island to furnish accurate location in calibrated areas of the impact point of missiles carrying a SOFAR bomb. Three target arrays provide accurate impact location in limited areas from the impact signal. Acoustic instrumentation and techniques have been developed that permit these systems to be calibrated with high precision. The Columbia University Geophysical Field Station reported earlier [G. R. Hamilton, M. E. Drake, and C. Hartdegen, J. Acoust. Soc. Am. 35, 1879(A) (1963)] on one stndy (SOFAR velocity stability) made in connection with these systems. The geodetic accuracy of these systems is now limited by the accuracy with which the geodetic position of the calibrating ship can be measured. These systems are now the standard for missile-guidance scoring. Needed improvements are described. The results of work to develop an underwater acoustic telemetry link are described in a separate paper.
Artifacts in Ultrasonography
Authors: Carlin Benson , Brinker Ray A.
Published: September 2005

Ultrasonic mapping techniques in industry are now well-known and for many years the state of the art in ultrasonic theory and practice has been sufficiently advanced to promise application to clinical medicine. Early investigators have reported very promising results in the mapping of various parts of the body, the location and outlining of tumors, etc. Nevertheless, the reports of these workers have not resulted in widespread application, and their duplication on a clinical basis has proved difficult. The reason for this is not only the natural inertia of the field, for ultrasonography has been severely limited by the presence of artifacts, or unwanted signals coming from several sources: the equipment both electronic and mechanical, the technique of the user, and the nature of the ultrasonic wave and the way it travels in the body. The identification and elimination of these signals where possible is the purpose of the present paper. Examples of each type are shown and discussed, together with typical uitrasonographs (B-scans) of sections of the body. Suggestions as to procedures, methods of identification, etc., are given.
Anechoic Surface for Underwater Sound
Authors: Meeks Wilkison
Published: September 2005

A perforated metal plate covered with an adhered thin elastic sheet has been studied as a possible anechoic surface for underwater sound. Assuming that those portions of the sheet covering holes in the plate behave as driven damped circular membranes clamped at their edges, expressions for the acoustic impedance of a single membrane and the specific acoustic impedance of the surface have been derived in terms of the tension in the membrane, the number of holes per unit area, the hole size, and damping constant. The results of calculations showing how the impedance varies as these parameters are changed and the possibility of obtaining an impedance match with water, using available materials, are discussed. [This work supported by the U. S. Office of Naval Research.]
Equipment and Techniques for Noise Measurements
Authors: Goodfriend Lewis S.
Published: September 2005

A wide variety of equipment of commercial manufacture is available for the measurement of noise. The problems that occur in making such measurements for engineering and legal purposes arise from the ability or inability of the user to establish correctly the calibration of the equipment and to understand the process of measurement. The user must ask himself whether his instruments are capable of performing the required measurement in terms of bandwidth, resolution, waveform, meter characteristics, and, in many cases, the statistics of the noise-generating process itself. The application of commercially available equipment including techniques for measuring, recording, and analysis of noise are reviewed and specific examples related to the measurement of machine, airflow, and vehicle noise are presented.
Control of Noise by Legislation
Authors: Pietrasanta A. C.
Published: September 2005

This area of noise control is illustrated by a consideration of the motor-vehicle noise problem. There is a welter of existing legislation in this country and abroad. It is mostly subjective in nature and therefore generally ineffective in controlling motor-vehicle noise. The objective legislation that does exist is expressed in several different measures, such as dBA, dBB, and dBC, and various measurement distances. Suggestions for objective limits have also included loudness in sones and PNdB. These various limits are compared with one another, with existing and proposed standards, and with limits that appear economically and technically feasible as a result of recent studies. The nature and effectiveness of existing legislation and law enforcement practices are also reviewed.