bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation of Subharmonics of Order One-Half by Bubbles in a Sound Field
Authors: Eller Anthony , Flynn H. G.
Published: September 2005

Under proper conditions, bubbles driven by a sound field will pulsate periodically with a frequency equal to one-half the frequency of the sound field. This frequency component is the subharmonic of order 12 and is generated when the acoustic pressure amplitude exceeds a threshold value. The threshold for subharmonic generation is calculated by means of a theory that relates the presence of the subharmonic to properties of Mathieu's equation. It is found that, for a given bubble, the threshold is a function of the driving frequency and is a minimum when the driving frequency is close to twice the resonance frequency of the bubble. In addition, solutions of a nonlinear equation of motion for the bubble wall, obtained on a computer, illustrate the growth of subharmonics and are used to determine the steady-state amplitude of the subharmonic for a sequence of values of various parameters. [Work supported by Acoustics Programs, Office of Naval Research.]
Motion of Bubbles in a Moderate Sound Field
Authors: Crum L. A. , Eller Anthony
Published: September 2005

A standing acoustic wave in a liquid exerts on a bubble a net translational force that, under proper conditions, propels the bubble through the liquid. Measurements are presented of the velocity at which bubbles, driven below resonance, are drawn toward an acoustic pressure antinode of a standing wave in a cylindrical container. Bubble velocities, ranging to 25 cm/sec, were measured by photographing the bubble under stroboscopic illumination as it moved in the sound field. Bubble radii ranged from 20 to 80 μ, and pressure amplitudes from 0.0 to 0.9 bar. It is found that, if the acoustic pressure and its gradient are known accurately as a function of position, then the observed bubble motion agrees with the motion predicted analytically. Experimental results also indicate a threshold for an instability in the rectilinear motion of the bubble. This threshold appears to be identical with the threshold for the observed onset of dancing motion of stationary bubbles trapped in a sound field. Theory indicates that this instability threshold is caused by the onset of nonspherical oscillations of the bubble. [Work supported by the Office of Naval Research.]
Parametric Amplification of Subharmonics in an Acoustical Cavity
Authors: Cook Bill D.
Published: September 2005

It has been reported previously [J. Acoust. Soc. Am. 41, 1584(A) (1967)] that several subharmonic frequencies can be produced in an acoustical Fabry-Perot cavity. Although it can be shown from the nonlinear wave equations that one progressive acoustic wave cannot parametrically amplify another progressive wave except in one special case, a frequency-dependent phase shift at the reflector of the cavity may permit amplification to occur for many frequencies. The frequencies whose phase shifts are important are the amplified or signal frequency, and the sum and difference frequencies of the signal and pump waves. [This research was supported by the Office of Naval Research.]
New Model of Binaural Hearing
Authors: Colburn H. S.
Published: September 2005

Preliminary results are presented on a model of binaural hearing in which the firing patterns on the auditory nerve are regarded as inputs to a central processor. The model is a continuation of work by W. M. Siebert on monaural phenomena, and the random-process description of the firing patterns is based on data from the cat. Initially, it is assumed that the processes for the two ears are statistically independent and the central processor is ideal. Predictions are derived for jnd's in interaural time and amplitude for tone bursts as a function of the amplitudes in the two ears, the interaural time delay, and the frequency and duration of the tone burst. These results define the limitations on performance imposed by the peripheral transformation. A more realistic model is achieved by placing restrictions on the central processor. The theoretical results are compared with available data. [Work supported principally by a grant from the National Institutes of Health and in part by the Joint Services Electronics Program.]
Monaural Detection with Contralateral Cue (MDCC): Signal Bandwidth and Frequency
Authors: Taylor M. M. , Clarke D. P. J.
Published: September 2005

In an MDCC experiment, a signal masked by noise is presented as a detection task to one ear, while a cue is simultaneously presented to the other ear. In the two experiments reported here, the cue either was absent or was a replica of the unmasked signal. In the first experiment, the signal was a burst of low-pass filtered noise. With no cue, the two observers performed like 25%–40% efficient energy detectors. With the cue, performance for nominal signal bandwidths below about 1600 Hz approximated that of 25%–40% efficient correlation detectors, an improvement of 10–15 dB. Increasing signal bandwidth to 3200 Hz dropped absolute performance level by 3 dB, and efficiency by a factor of 4. In the second experiment, soft-gated sinusoids were used as signals. For signals below a frequency typically about 1150 Hz, performance of the five observers with the cue averaged about 30% efficient and was about 7 dB better than without the cue. Signals of higher frequencies, typically above 1350 Hz, gave about 12 dB worse performance. At the higher frequencies, the cue acts as a masker rather than as an information source.
Maximum-Likelihood Sequential Procedure for Estimation of Psychometric Functions
Authors: Hall J. L.
Published: September 2005

This paper describes a computer-oriented sequential procedure for the estimation of parameters of a psychometric function. In common with other sequential procedures (BUDTIF, PEST, UDTR), the goal is to concentrate observations in the region of interest. The experimenter assumes a parametric form of the psychometric function (cumulative normal from 0 to 1, for example, but any other desired form could be used). After each response, values of the parameters are computed that maximize the probability of the set of responses that have been obtained, given the set of stimuli that have been presented. These values are then used to determine the placement of the next stimulus. A compromise between fidelity of tracking a time-varying threshold and accuracy can be effected by appropriate choice of the weighting function for previous observations. The procedure has been simulated on a GE-645 computer and applied in the laboratory with a DDP-516 computer.
Random Response of a Multibay Panel System Using Finite Elements
Authors: Olson Mervyn D. , Lindberg Garry M.
Published: September 2005

A finite-element approach to the dynamic analysis of continuous skin-stringer panels in presented. The method is illustrated in the calculation of vibration modes and random response of a five-bay stringer-stiffened panel with all outer edges clamped. The panel skin is represented by finite plate elements; and the stringers, which are assumed infinitely stiff in bending, are represented by beam torsional elements. Results are presented for the first 35 panel vibration modes. These modes occur in distinct groups with five similar modes in each, the number 5 corresponding to the number of panel bays. The response of the panel to plane-wave propagation of acoustic noise (propagating normal to the stringers) is also calculated by a generalized harmonic method. The resulting response spectra were found to be fundamentally different from those associated with single span-panels. These power spectra did not have widely separated peaks; but rather, the peaks tended to be squeezed into groups corresponding to the groupings of natural frequencies for the panels. Hence, it is no longer correct to think of the response as the summation of independent modal responses.
Vibrations of Rib-Stiffened Circular and Elliptical Plates
Authors: Desiderati F. W. , Laura P. A.
Published: September 2005

This investigation deals with the determination of the fundamental frequency of vibration of simply supported and clamped rib-stiffened plates of elliptical boundary. It is assumed that the stiffeners are closely spaced and their height is moderate when compared with the thickness of the plate. Variational techniques are used to determine the fundamental frequencies. The values compare reasonably well with other results available in the literature. This same straightforward approach can be used for other boundary shapes; experimental determination of the coefficients of the orthotropic biharmonic operator is not required.
Reverberation-Room Testing of Space-Vehicle Structures
Authors: Kennedy David R. , Saint Lester D.
Published: September 2005

Recent reverberation-room acoustical tests on large space-vehicle structures have revealed an interesting effect. The vibration levels measured on some structures exposed to a given sound-pressure level in a reverberation room have been higher than the vibration levels predicted or measured during flight. This seemingly excessive vibroacoustic response may be the result of an unrealistic in-plane static load. This paper presents the results of an experiment conducted in a 100 000-ft3 reverberation room on a SATURN IVB Forward Skirt/I.U./S.L.A. specimen. The structure was subjected to three levels of acoustic excitation at three static-load conditions. Simple vibroacoustic transfer functions obtained illustrate the importance of loading the test specimens during acoustical-qualification tests. Comparison of test data with flight data indicates the effect of the reverberation room on the vibration response of the specimen. [This work was performed for the Marshall Space Flight Center under contract.]
Noise Reduction and Response of Two Concentric Cylinders
Authors: Wong D. M.
Published: September 2005

The equations for the noise reduction and response of two concentric cylinders subjected to a reverberant acoustic field were derived based on the statistical-energy approach. Using the derived equations, the noise reduction and response of two concentric cylinders were calculated and compared with experimental data. To verify the analytical results, two cylinders with the physical properties described above were placed inside an acoustic reverberant room. The ends of the cylinders were sealed with plywood. Microphones were placed outside, between, and inside the cylinders. Accelerometers were placed at random on both the cylinders. The resulting study can be applied to the prediction of the acoustic and vibration enironoments of a typical space vehicle enclosed within a shroud.
Transient Response of a Sandwich Ring to Radial Impact
Authors: Sagartz M. J. , Keer L. M. , Herrmann G.
Published: September 2005

The transient response of sandwich rings to concentrated radial impulsive loads is studied on the basis of a Timoshenko-type theory. Solutions are obtained by integral transform techniques and also by representation in a series of normal modes. Numerical and experimental results show that the ring's response is predominantly flexural and is highly dependent on the ratio of the extensional stiffness to the shear stiffness. It is also found that, as the core stiffness decreases relative to the facing-sheet stiffnesses, the influence of the thickness-to-radius ratio becomes more important.
Sound Systems for Electronic Organs
Authors: Martin Daniel W.
Published: September 2005

Well-known acoustical advantages of electronic organs over pipe organs include (a) the small number of acoustical sources required, (b) the relatively small amount of building space needed for an acoustically powerful instrument, (c) the ease of providing alternate or supplementary sound sources in additional locations, and (d) the independence of tuning from the rather temperature-dependent velocity of sound. Other potential acoustical advantages include (e) the control of direct-to-reflected sound ratio, (f) supplemental reverberation, (g) more effective expression control, and (h) spatial modulation and vibrato. There have also been inventions in electronic-organ sound systems intended to overcome inherent acoustical advantages of pipe organs such as (1) spatial spread and (2) acoustical mixing; and to eliminate any inherent disadvantage of electroacoustical versus direct acoustical radiation. The patent literature is quoted extensively.
Current Practices for Amplifying or Modifying Tones of Individual Musical Instruments
Authors: Kent Earle L.
Published: September 2005

There is a resurgence of interest in attaching electrical transducers to musical instruments in order to amplify the tones produced by the instrument or modify the tones in other ways. The current trend began with guitars and has now spread to wind instruments, as well as other stringed instruments. Tone modification includes the production of “brighter” or “darker” tones than those normally produced by the instrument, “fuzztone,” “electronic tremolo,” “electronic echo or reverberation,” octavely related tones above and/or below the tone normally produced, and other novel effects. This paper reports the major commercial means for accomplishing these effects. The methods, circuitry, and taped examples are given. Some of the potential problems and musical possibilities related to these devices are also discussed.
Rôle of Electronics in Rock-and-Roll, or Popular, Music Will Never be the Same Again
Authors: Moog Robert A.
Published: September 2005

Like all popular music directions, rock-and-roll reflects the day-to-day experiences of its audiences. An important feature of current rock-and-roll is its total dependence on electronics. It began with the electrically amplified guitar and now is characterized by sound levels at the threshold of pain. Brass, woodwind, and some percussion instruments have succumbed to amplification, and a raft of new musical instruments designed especially for use with electronic equipment is now in wide use. But mere amplification is not the only significant current use of electronics in rock-and-roll. Signal-modifying procedures, both linear and nonlinear, are being explored and exploited to create new timbres. The next logical step, which has already been explored by the avant garde, is the use of “performance systems” of musicians and electronic equipment, wherein the equipment is programmed to interact with the musicians to introduce a “game” element into the musical product.
Spectrum Analysis of Stationary Noise Signals
Authors: Kundert Warren R. , Peterson Arnold P. G.
Published: September 2005

The wide variety of analyzers now available enables the user to choose an instrument closely suited to his particular problem. The choice includes analyzers with constant-hertz bandwidths from 1000 to 1 Hz and the more generally preferred constant-percentage-bandwidth type, with bandwidths from 1 oct to 1%. It is generally recognized that the analyzer bandwidth, the time spent on the analysis, and the nature of the signal affect the accuracy, the statistical confidence, and the resolution. Less obvious but also important factors are: the spectrum shape, the total analysis range required, the effective filter cutoff points, the ultimate rejection outside the passband, and the dynamic range. Their effects on the analysis of various signals are discussed. Other questions related to analysis are reviewed. For example: When is a “quick look” needed? Is the interest in a 1-Hz bandwidth based on numerology or science? How seriously can accessory instruments affect the results of an analysis? Only through an appreciation of these many factors can one obtain the full benefit of modern analyzer characteristics.
Acoustic Techniques for Machinery Diagnostics
Authors: Tatge R. Bruce
Published: September 2005

Reliability of machinery is improved by maintenance procedures that detect malfunctions at an early date so that corrective action can be taken before failure occurs. When deterioration is recognized, spare parts can be ordered as needed and repairs scheduled for a noncritical time. Use of sound or vibration as the carrier of diagnostic information has several advantages over other techniques. First, many malfunctions are first evidenced by changes in the sound or vibration signal. Second, sensor attachment can be accomplished with minimum modification of the machine. Third, such diagnosis does not require disassembly of the device under study. Evaluations of this kind by skilled mechanics have been used for years, but the full potential can only be realized by application of modern techniques of problem definition and acoustic signature evaluation. Understanding of the processes by which signals are generated and transmitted permits the investigator to develop an analytical model by which normal and abnormal signatures can be established. Once the discriminants are known, it is possible to choose and locate sensors and decide on a data-analysis technique for extracting the desired information from the raw signal. In some instances, this may be found most easily by spectrum analysis, while on others the waveform contains more meaningful information. New tools, which have been useful for signal analysis, are transient averaging, high-speed spectrum analysis, and recognition of signal patterns by digital techniques.
Experimental Study of Spectral Fluctuations in Nonstationary Acoustical Noise
Authors: Taylor William A. , Maling George C.
Published: September 2005

Spectra of impulsive noise bursts are less stable than predicted by conventional formulas based on filter bandwidth and integration time. The Fast Fourier Transform (FFT) was used in this study to compare spectra of segments of different time functions in an attempt to find reasons for the unexpectedly large fluctuations in impulsive noise spectra. Spectral slope was not responsible for the anomalous fluctuations. Comparison among spectra of short noise segments showed that all portions of a white noise signal contribute about equally to over-all power level, but that only a fraction of each impulse contributes significantly. This fraction can be estimated by examining a series of impulses with an oscilloscope. Since spectral stability is directly proportional to the length of the time signal analyzed, the fractional contribution gives an estimate of spectral fluctuations that is valid for nonstationary noise.
Finite-Amplitude Traveling Waves in Ducts
Authors: Coppens Alan B.
Published: September 2005

A nonlinear, dissipative, acoustic wave equation generalized from the linear, dissipative wave equation valid for one-dimensional motion in a duct (where the dominant absorptive mechanism is the energy loss in the boundary layer) has been obtained. The equation admits straightforward solution for traveling waves by a perturbation expansion in Mach number. Prominent features of the results include a first-order contribution in absorption to phase velocity. This effect generates spatially dependent phase angles among the different harmonics. Preliminary results suggest that the solution can profitably be applied to all distances when the Mach number is small enough to preclude shock. Differences in the properties of standing-wave and traveling-wave solutions may be discussed.
Improved Capacitive Microphone for Measuring the Temperature Dependence of Nonlinear Effects in Solids
Authors: Peters R. D. , Breazeale M. A.
Published: September 2005

Finite amplitude distortion of 30-MHz longitudinal ultrasonic waves in solids is observable when the ultrasonic displacement amplitude is as large as 1 Å. Measurement of the absolute values of the fundamental and second harmonic amplitudes allows one to calculate nonlinearity parameters, which are combinations of third-order elastic constants. The capacitive detector that has been used for these measurements was found to be sensitive to temperature changes when attempts were made to use it at liquid nitrogen temperatures. An improved detector in which the gap spacing can be adjusted pneumatically between 3 and 10 μ to compensate for thermal expansion is discussed. This detector now makes it possible to determine the thermal variation of the nonlinearity parameters of solids. [Research sponsored by the U. S. Atomic Energy Commission under contract with Union Carbide Corporation.]
Acoustic Radiation from a Finite Line Source with N-Wave Excitation
Authors: Wright Wayne M.
Published: September 2005

A shock wave with an N-shaped pressure profile is propagated in the equatorial plane of a weak spark in air. In the present work, the directional dependence of the acoustic waveform is examined for 0.5- and 1.0-cm sparks having discharge energies between 0.01 and 0.1 J. The transient signals are detected with a wide-band capacitor microphone that has a rise time of less than 1 μsec. As the spark axis is approached, an interval with no acoustic disturbance appears near the center of the waveform. The angular dependence of both the shock amplitude and the length of this central interval is found to be in qualitative agreement with the results of a linear analysis in which it is assumed that each point along the spark acts as a source of N waves. [Research supported in part by the U. S. Office of Naval Research and by the National Science Foundation.]
Spikes on Sonic-Boom Pressure Waveforms
Authors: Pierce Allan D.
Published: September 2005

The cause of the spikes or peaks frequently observed on sonic-boom pressure waveforms is generally attributed to small-scale atmospheric variations representing deviations of the atmosphere from a stratified medium. A detailed mechanism consistent with this theory is proposed that interprets the spikes as due to the simultaneous focusing and diffraction of a nearly planar N wave by an inhomogeneous layer in the atmosphere. Spikes appear on the waveform in regions where a ray analysis indicates a magnification due to focusing. That the mechanism does lead to spiked waveforms is exemplified quantitatively by analysis of a simple model. Examination of a limited amount of data showing very pronounced spikes at one site and showing gradually vanishing spikes at adjacent sites during a given experiment suggests that the scale of the atmospheric irregularities should be of the order of 200 m, which is compatible with turbulence correlation coefficients derived by Panofsky for unstable air. The width of the spikes is related somewhat simply to the travel delay time of waves diffracted around the “edges” of irregularities.
Psychological and Distinctive-Feature Relations of English Consonants
Authors: Singh Sadanand
Published: September 2005

The interconsonantal relations may be described by presence/absence of distinctive features, which may be transferred into units. Such transfer simplifies descriptions: /b///d/=V1-OICING+C1-ONSONANTAL+G1-RAVITY+D1-IFFUSENESS/V1-OICING+C1-ONSONANTAL+D1IFFUSENESS=G1-RAVITY. The model was tested using results of ABX. The interconsonantal relationships of some features, e.g., continuant, was found more real than others, e.g., vocalicness. The relations were more real when difference between consonants was of one unit than of two, etc. In the present experiment tested was the above model using results of paired comparison on a one-to-seven-point scale. The 23 consonants of English were recorded in 506 pairs in conjunction with post-consonantal /a/ and presented to 50 native listeners in undistorted condition and to 50 when tape was played back backwards. Significant correlations were found between inter-consonantal relationships of distinctive-feature measures and the measures obtained by subject's rating in both modes of presentations. The reality of relation against the reality of distinction was confirmed when comparing the relative importance of features and places of articulation. Bilabial and palatal places, independently, showed more real relation and alveolar and velar places more real distinction.
Voice Timing: Cross-Language Experiments in Identification and Discrimination
Authors: Abramson Arthur S. , Lisker Leigh I.
Published: September 2005

Experiments have shown that listeners' ability to detect differences along some physical continuum of variation appropriate to stop consonants is closely bound up with their assignment of stimuli to linguistic categories. A dimension that we have shown to be used in similar but not identical ways across a large variety of languages for the differentiation of word-initial stops is voice-onset time (VOT), the temporal relation between the onset of glottal pulsing and acoustic features that mark supraglottal articulation. We focus our attention here on English, a language with two stop categories along the VOT dimension, and Thai, a language with three categories. Prevocalic labial, apical, and velar synthetic stops with VOT varying in small steps were produced on the Haskins formant synthesizer. The labeling responses show a good fit between production and perception. Discrimination responses by speakers of the two languages suggest that discriminability is essentially determined by specific language experience rather than by general phonetic categories.
Timing of Glottal Movements in Plosive Production
Authors: Rothenberg Martin
Published: September 2005

A model is presented for the primary parameter distinguishing plosive phonemes having the same place of articulation. This parameter is expressed in terms of the timing between the period of articulatory closure and a maximally fast change in glottal adjustment. For intervocalic plosives, the change in glottal adjustment is “cyclic,” either voiced-breathy-voiced, or voiced-open-voiced, and requires at least 100 to 150 msec. In the prevocalic position (after an open glottal adjustment), the change is unidirectional, from open to voiced, except for certain phonoaspirated plosives in which the change is approximately open-voiced-breathy-voiced. The model is unusual in that (1) it is based on the adjustment of the glottis, and not on the actual occurrence of voicing, and (2) it takes into consideration the dynamic constraints inherent in changes of glottal adjustment. The adjustment of the glottis can be monitored by bypassing the articulatory closure with a low-resistance air path and recording the resulting air flow. Four intervocalic and four prevocalic categories of timing pattern are described that have the potential of supporting a phonemic distinction.
Experiments on Speech Rhythm
Authors: Allen George D.
Published: September 2005

In many studies involving the rhythm of English speech, the onset of the nuclear vowel of a stressed syllable has been in some way identified with the rhythmic beat of that syllable. In our experiments, however, we have found that the relation between vowel onset (VO) and syllable beat depends upon the consonants that immediately precede the stressed syllable, upon the nuclear vowel itself, upon the number of syllables between successive stressed syllables, and upon tempo. In one experiment subjects repeated the sentence “This is the beat in—,” in such a way that the stressed syllables in “This,” “beat,” and the word in the blank coincided with three successive, equally spaced clicks that they heard through headphones. For each subject, the VO of the syllables with initial /p/, /t/, or /k/ were later (relative to the click) than the VO of those with initial /b/, /d/, or /g/; onsets of the nuclear vowel /i/ were later than those of /a/; and syllables preceded by an extra unstressed syllable were later than those that were not. Large changes in tempo altered these relationships significantly.
Rôle of Physical Phonetics in a Theory of Universal Phonetics
Authors: Fromkin Victoria A.
Published: September 2005

Recent formulations of linguistic theory depend considerably on accurate specification of phonetic events. Implicit in all approaches is the recognition of the fact that despite the semicontinuous nature of the speech signal, quantization into discrete units is possible and necessary; furthermore, a finite set of such units can be used to describe the sounds of all languages. It has been pointed out that without reference to the “intrinsic” content of phonetic units, incorrect generalizations and predictions will result. This paper presents arguments that the nature of the universal phonetic units and the universal laws pertaining to the segmental and sequential constraints of these units must therefore be based on the data of physical phonetics obtained by instrumental and experimental techniques. Illustrations will be provided demonstrating that without reference to physiological, acoustic, and perceptual data, claims about the intrinsic content (“naturalness”) of phonological representations are without substance. [This research was partially supported by the National Institutes of Health, U. S. Department of Health, Education, and Welfare, the Office of Naval Research, and the National Science Foundation.]
Comparison of Three Schemes for Filtering Signals That Have Propagated through a Random Multipath Medium
Authors: Mangano D. T.
Published: September 2005

Several filtering techniques that can be employed in the recovery of a signal after it has propagated through a nonrandom, distortionless, multipath channel have been studied. The generalization of these studies to the random-medium situation is the purpose of this paper. A fixed, omnidirectional, source emits a signal that propagates through a multipath medium and is detected by an array of point-receiving elements located at some arbitrary distance from the source. The medium is characterized by a set of attenuation and delay random variables associated with each of the multiple paths. The detected signals are then processed by either delay filtering, matched filtering, or frequency-inverse filtering. The criterion for comparison of these three filtering schemes is the ratio of the standard deviation of the filtering scheme's output time-average power to the expected value of this power. It is found that, under certain constraints, this ratio is approximately independent of the delay statistics of the medium, and the duration and frequency of the input for the three filtering schemes. In addition, this ratio is approximately equal for delay and matched filtering and is √ times greater for frequency inverse filtering.
Transformation of Signals in Nonlinear Media
Authors: Childress John W.
Published: September 2005

This paper describes a generalized approach to the analysis of non-Gaussian signals after passage through nonlinear media. It is shown that an arbitrary signal may be expanded in an orthogonal series of elementary functions with Gaussianlike properties. These orthogonal functions are linear combinations of Gaussianly weighted sinusoids, and consequently, possess many of the statistical properties normally associated with Gaussian processes. (Although my elementary functions can not be used individually as density functions for random variables, an arbitrary density function can always be specified in terms of them.) Further, any function that has finite mean, which includes functions of integrable square as a subclass, can be treated in this manner. Thus, the convergence (or practicality) questions which are often raised in connection with the use of the Gram-Charlier (or Edgeworth, or Bruns') series do not arise. The treatment of the input as the sum of elementary functions sometimes makes the characteristic function method suitable since the Fourier transforms of a linear sum is equal to the sum of the Fourier transforms of the individual terms. (This is contingent on knowledge of the joint characteristic function when random inputs are considered.) The most important utilization of elementary functions appears to be in series approximations of the resultants of nonlinear transformations of non-Gaussian random processes.
Nonlinear Detection of Noise Modulating Signals
Authors: Hariharan P. R.
Published: September 2005

The low-frequency output, signal and noise, is determined following nonlinear detection of a sinusoidally modulated noise carrier. The noise carrier as well as the noise added are considered to be spectrally wide as compared to modulation. Results are obtained for both full-wave as well as half-wave νth-law detection. The important cases of linear (ν = 1) and quadratic (ν = 2) detection become special cases of the general theory considered. Expressions for the output signal-to-noise ratio (SNR)0 are obtained for (i) low values of the input S/N ratio (SNR)in and (ii) high value of the input S/N ratio. The results obtained are for a single modulating frequency, and these could be easily extended to multiple signal cases. Plots are given for (SNR)0 as a function of (SNR)in.
Ocean Thermal Fronts and Sonar Range Prediction
Authors: Carr Jerome Brian
Published: September 2005

The question of horizontal variability of the ocean's thermal structure has long plagued sonar range prediction. The thermal structure of the surface duct is discussed with its variations in space and time. Study of the thermal structure in four dimensions reveals presence of minor thermal fronts in the ocean, which delineate homogeneous water masses. These water masses and their thermal fronts are seen to migrate on a day-to-day basis within the major current systems, and their behavior is analogous to high- and low-pressure systems in the atmosphere. The minor thermal fronts, which cover about 30% of the ocean's surface, are shown to produce either partial or complete destruction of the surface duct. The presence of these fronts in the ocean means that the present antisubmarine-warfare environmental-prediction system must incorporate the frontal concept for valid sonar-range predictions to be made. Furthermore, the viability of bistatic ship operations will depend on knowledge of these thermal fronts and their attendent surface-duct destruction.
Detection-Performance Prediction for Passive Sonar Systems
Authors: Kits van Heyningen Arent H. , Ehrlich Stanley L.
Published: September 2005

Horton has derived the “direct-listening equation” as one of a set applicable to specific classes of sonar systems. From this equation, he determines the maximum allowable one-way propagation loss for a passive sonar system to detect a noise source that radiates a known energy spectral density. This paper reviews and extends Horton's results to provide an engineering estimate of passive sonar detection capability, assuming that all the terms in a more detailed “direct-listening” equation are effectively separable. Of particular interest is the attempt to model a “real” system by accounting for anisotropic noise, deviation losses, quantizing and sampling losses, separate electronic and display processing gains, and a malfunction loss allowance in a simple manner. Postdetection and other nonlinear parameters are translated to their effective values in a linear system. Sample calculations and their significance in signal excess versus range will be shown based on a set of reference conditions.
Predicting Total Sonar System Performance
Authors: Hahs Orrie A.
Published: September 2005

Present prediction techniques for sonar performance take into account acoustic-propagation conditions and signal-processing characteristics of the sonar system under consideration. These predictions are useful for technical comparisons of different systems, but they have not provided a useful prediction of performance for the user of a given system. A more useful prediction technique has been developed, which includes man-machine interactions relating to operator proficiency and tactical constraints that affect allowed times for detection, classification, track, and attack. Taking these factors into account in predicting over-all system performance provides answers much nearer to those realized in the fleet.
Prediction and Evaluation of Active Sonar-System Detection Preformance
Authors: Clearwaters Walter L.
Published: September 2005

The concept of signal excess—that is, the excess of signal received over that required for detection—as commonly used in both prediction and evaluation of active sonar-system detection performance is presented. Some of the results of independent measurements of the nominal value and the variability of the various parameters in the signal excess equation are discussed in terms of the deviation of a prediction from the actual evaluation of over-all system performance. Examples are used to demonstrate that the predicted performance will equal the over-all performance as measured for a total system only after recognition and adjustment for parameter interrelationships are made. Acoustic models that have been developed, validated in system tests, and used for active sonar-system performance prediction are shown. Criteria that have been imposed in the measurement of such parameters as source level, receiving sensitivity, propagation loss, interferring noise, and others, are presented together with illustrations of the effectiveness when used. Uncertainties in predicted system performance resulting from parameters and measurements that cannot be controlled or accurately estimated are cited and discussed.
Project HIAWATHA Long-Range Shallow-Water Sound Propagation in Lake Superior
Authors: Browning David G. , Thorp William H. , Friedel Frederick C. , LaPlante Robert F.
Published: September 2005

Sound-propagation measurements were made along a 100-mile path in Lake Superior during September 1967 in an area in which water depth exceeded 600 ft. One-half-pound TNT charges were detonated at the axis of a sound channel and received on a hydrophone suspended at the same depth. Acoustic reception by totally refracted paths was analyzed in 10 frequency bands between 500 and 8900 Hz. The increase in propagation loss with range was found to be greater below 2 kHz than commonly observed in ocean sound channels and larger throughout the range of frequencies than theory would predict for an isotropic, freshwater medium. It is proposed that the largely unexpected results arise from local changes in the temperature structure within the first 150 ft of water depth which, because of the extreme asymmetry of the sound-velocity profile, scatter sound from the channel.
Judged Noisiness of Modulated and Multiple Tones in Broad-Band Noise
Authors: Pearsons Karl S. , Bishop Dwight E. , Horonjeff Richard D.
Published: September 2005

A series of tests was conducted to investigate noisiness judgments of modulated and multiple tones plus noise. Test stimuli included tones at 500 and 2000 Hz, amplitude and frequency modulated at rates of 5 to 300 Hz. Multiple tone stimuli included two- and five-tone complexes. The frequency spacing of the complexes between the highest and lowest frequency tones was varied from 110 to two full octaves. The results of the judgment tests will be discussed, in particular, with regard to pure-tone correction procedures presently in use. In general, these results indicate that the additional noisiness of the multiple and modulated tones was accounted for when the pure-tone correction procedures developed for single, steady-state tones were utilized. [This work was supported by the National Aeronautics and Space Administration.]
Acoustical Environment Due to Equipment Vibration
Authors: George Ballard W.
Published: September 2005

A rotating or reciprocating equipment acts as a source of vibration and thereby of radiated noise. For noise-control considerations, the sound pressure level (SPL) is needed as a function of the vibration. When the equipment is in an occupied enclosure, the problem can be treated in the framework of the reverberant field, with a constant reverberant SPL that is related directly to source power. Rotation at steady speed produces a pure-tone noise component; a rotating acoustic dipole is created by symmetric rotation of an unbalanced cylindrical unit. This source is omnidirectional in the plane perpendicular to its axis. Treatment of the pure tone as a source of energy in the reverberant field presents some difficulties because of interference patterns, which, however, can be minimized at high frequencies where the room modal density is high. Other factors that facilitate the application of the reverberant field relations include room irregularity and nondirectional character of the source. Relations between source vibration (acceleration and velocity), sound-power output, and reverberant SPL are obtained—sound power being a function of source velocity amplitude, frequency, radius, and length.
Statistical Study of Traffic Noise
Authors: Olson N.
Published: September 2005

To provide the necessary data for noise-abatement programs, a comprehensive study of motor vehicle noise is being conducted. The concept of noise as a form of environmental pollution is accepted as basic, and the noise output of motor vehicles is regarded as a function of the vehicle-driver combination, rather than of the vehicle alone. The noises from more than 2000 vehicles have been recorded on tape and analyzed for over-all dB, dBA, and in octave bands from 31.5 to 8000 Hz. For passenger cars, the peak of the noise-level distribution lies at about 65, 67, 72, and 73 dbA for the speed ranges of 30–39, 40–49, 50–59, and 60–69 mph, respectively, at a measuring distance of 15 m. The values for dump trucks, the noisiest of the heavy trucks, are about 10 dB higher when empty, and 12 or 13 dB higher when loaded. The values for tractor trailers are about 15 dB higher. The scatter for passenger cars is about 10 dB, and somewhat greater for trucks and tractor trailers. Motorcycles may be the noisest of all.
Acoustic Shielding Properties of a Free Standing Wall
Authors: Purcell Jack B. C. , Noppe Roger C.
Published: September 2005

Acoustic measurements have been conducted to determine the shielding properties of a free standing wall 10 ft high and 120 ft long situated in an open field of black-top surfacing. The sound source (octave bands of noise) consisted of a high-level high-fidelity loudspeaker positioned at a number of multiples of the wall height on a center line normal to the wall axis. The microphone was in turn placed at “mirrored” distances along the center line on the opposite side of the wall. Measurements were obtained for five source positions and five corresponding microphone positions for a total of 25 sets of measurements. A second series of measurements was performed identical to the first series, but without the wall. Care was taken to maintain an identical source level. The excess attenuation was determined by comparing the data obtained in the two test series. The results indicate that significant deviations can be expected in the acoustic shielding properties of a wall from data previously reported in the literature.
Acoustic Energy Deficit Thickness for Classifying Shock-Boundary Layer Noise
Authors: Luksus E. J.
Published: September 2005

It has been demonstrated that the parameter δ*/M∞ is a good wavelength scale for wall noise under undisturbed, smooth boundary layer flow: indeed, as good as is θ, which has obviously intimate connection to the wall stress that dominates such noise environments [J. Acoust. Soc. Am. 42, 1159(A) (1967)]. This present paper shows how the factor 1/M∞ may be interpreted as approximating the result when an unnormalized relative probability density 1/M(x2) modifies the displacement integrand. It arises, however, that this modification appears anomalous when backflow occurs. Although δ*/M∞ will detect shock, in the present rudimentary state of shock/boundary-layer noise study, it is more satisfying to envisage an acoustic energy-deficit thickness for use as a classifier of one or both, the noise power or the typical noise wavelength, associated with shock/boundary-layer interaction.
Sound Transmission through Aircraft Fuselage Structures
Authors: Cockburn J. A. , Jolly A. C.
Published: September 2005

Theoretical and empirical studies of sound transmission through an aircraft fuselage have been performed and prediction methods developed for determining the interior noise levels due to boundary-layer turbulence and jet-noise excitation. The aircraft fuselage is evaluated by considering three equivalent structural models to represent the entire frequency range of interest. The fuselage reponse at low frequencies is determined from the characteristics of a stiffened cylindrical shell, while the fuselage responses at intermediate and high frequencies are determined from the characteristics of a stiffened panel group and a single panel, respectively. In each case, the equivalent structure and interior acoustic field are treated as a coupled dynamic system whose response is describable in terms of the system normal modes and coupled natural frequencies. Computer programs have been developed for the determination of the applied fluctuating pressures, sound transmission losses, and interior acoustic fields associated with fuselage structures; the geometry of the fuselage, properties of the acoustic treatment and aircraft flight condition are variable input parameters. The program may be used to determine the significant parameters affecting sound transmission and to optimize acoustic treatments within the scope of specific structural design variations.
Mach Bands in Hearing
Authors: Carterette Edward C. , Lovell John D.
Published: September 2005

Everyone believes that there must be laterally inhibitory nerve nets fed by cochlear potentials, for otherwise it is difficult to explain the extraordinary capacity of the ear in discriminating pitch. Mach bands have not been demonstrated in audition as directly and simply as in vision. We have sought to show the existence of Mach bands (“edge effects”) in direct masking. Noise bands having theoretically infinite attenuation rates outside the passband were generated by computer from 56 sinusoids spaced randomly by frequency. Monaural masked audiograms were obtained for each of four subjects at each of two noise bands (480–580 Hz and 960–1160 Hz) and sensation levels of 20, 30, 40, 50, and 60 dB. Edge effects, as measured by contours of threshold shift, were revealed for all subjects, at every loudness, and are similar for both noise bands. Sharpening is greater at the low-frequency end of a band and grows nonlinearly with loudness, as does upward spread of masking. An account of these data can be given in terms of the auditory nerve and central pathways. [Work supported by U. S. Public Health Service grant.]
Low-Frequency Single-Formant Discrimination in Deaf Listeners
Authors: Pickett J. M. , Mártony J.
Published: September 2005

In research on complex sound discrimination in the hearing impaired, we made measurements of frequency discrimination for a simplified speechlike sound, namely, a single resonant peak (or formant) in a harmonic spectrum. The frequency location of the formant was controlled automatically. An adaptive procedure was used to estimate threshold. A reference formant was presented on two of the three sounds heard on each trial; the remaining sound was presented at a higher formant frequency. The listener indicated which of the three sounds was different from the other two; knowledge of the correct answer was given after each response. Reference formant locations were 225, 300, 430, 630, or 870 Hz. The listeners were deaf in degrees ranging from severe to profound. Large learning effects were noted. There was weak positive correlation between hearing loss for pure tones and formant-frequency discrimination threshold which averaged about 3% at 225 Hz and 15% at 870 Hz; normal listeners' discrimination was about 0.5%. [Work supported by a research grant, U. S. Office of Education.]