bluuebunny/crossref_metadata_2025 huggingface dataset:
Schlieren Visualization of Acoustic Fields
Authors: Neubauer Werner G.
Published: May 2012

The schlieren method has been used for visualization of the interaction of acoustic fields and solid surfaces. The reradiated waves caused by an incident pulse are observed at different positions by strobe schlieren systems. Individual cycles can be displayed in an acoustic wave, and thus phase information is available in a visualizationsystem that utilizes a very short optical illumination by means of a strobed high-power laser. Color schlieren pictures permit visualization of small-amplitude effects in the presence of larger-amplitude (brighter) fields. A movie is shown demonstrating the usefulness of observing wave motion and changing effects with changing experimental conditions. Applications of schlieren visualization to basic studies of wave phenomena, nondestructive testing, and radiation pressures are shown.
Flexural and Extensional Vibrations of Simply Supported Laminated Rectangular Plates
Authors: Thomas Charles R.
Published: May 2012

The author has previously derived an effective-stiffness velocity-corrected theory of laminated composite plates based upon a microstructure plate theory developed by C. T. Sun. The velocity-corrected effectivestiffness plate theory is now used to study the flexural and extensional vibrations of simply supported rectangular plates; comparisons are made to similar results obtained from a reduced effective modulus or transversely isotropic plate theory. In each instance, free vibrations are assumed and a corresponding set of dimensionless differential equations and boundary conditions is found. Frequency equations for simply supported edges are developed by passing solutions harmonic in both length and width through the differential equations while at the same time automatically-satisfying the boundary conditions for simple supports. The variation of dimensionless frequency for such dimensionless variables as number of layer pairs, width-to-thickness ratio, elastic ratio, width-to-length ratio, thickness ratio, and density ratio is presented graphically and discussed in detail. Also, comparisons of the effective stiffness and effective modulus frequencies are made for each of the varied dimensionless parameters.
Automatic Verification of Hypothesized Phonemic Strings in Continuous Speech
Authors: Gillmann R.
Published: May 2012

A procedure is described for mapping a phonemic string onto a computer representation of an interval of continuous speech. The procedure has as its inputs a hypothesized phonemic string and a matrix of labels and probabilities obtained by computer analysis of a complete utterance. These two inputs are mapped by an iterative technique which (1) searches for individual phonemes in an appropriate order, not necessarily left to right; (2) continuously adjusts for phoneme duration variations; and (3) can deal with intraword coarticulation effects. The mapping procedure yields estimated time boundaries and a goodness-of-match score for the hypothesized phoneme string. A computer program has been written using this algorithm which performs automatic recognition of words and phrases within an operating continuous speech understanding system. Examples and current results from this system are presented.
Syllable Detection in Continuous Speech
Authors: Sargent D. C. , Li K. P. , Fu K. S.
Published: May 2012

A computer program for syllable detection was developed for possible application in future speaker independent speech recognition systems. Usage of both peak-to-peak (P-P) amplitude and rms intensity measurements was considered, but it was observed that P-P amplitude measurements alone provided good results, and that almost none of the resulting syllable detection errors could be eliminated through the additional consideration of rms intensity information. Syllable detection was based upon the recognition of the variations in amplitude which frequently accompany the onset and offset of both syllable nuclei and associated nonvowel sonorants. Changes in P-P amplitude and the maximum amplitude occurring within each change were therefore the primary measurements considered in the recognition process. Thus far, an averaged syllable detection accuracy of 86% has been obtained for nine talkers speaking a total of 3.5 min of continuous speech, with individual syllable detection results ranging from 74% to 96%. Misclassification of nonvowel sonorants comprised about 80% of the syllable detection errors, and it is consequently in this area of the program's performance that improvements are currently being considered.
Second-Generation Theoretical Study of Sound Emission from Turbomacbinery Ducts
Authors: Hogge H. Dwight , Ritzi Emil W.
Published: May 2012

Development of advanced gas-turbine power-plant systems requires the capability to predict accurately turbomachinery noise levels in the farfield. The purpose of the research described herein was to extend the understanding of the propagation of sound through realistically contoured inlet and exhaust ducts and to produce a methodology which relaxes the simplifications inherent in previous analyses of the propagation of sound in hard- and soft-walled ducts. Real inlet and exhaust ducts were simulated by matching an appropriate series of cylindrical and conical elements, terminating in a plane baffle, with specified acoustic wall impedance and mean airflow for each element. At the juncture between each finite element, appropriate solutions to the linear wave equation were coupled to describe the propagation of particular acoustic modes. Some initial results of the theoretical studies were that (a) acoustic power can propagate along a finite duct at frequencies below cutoff; (b) cutoff frequency is increased by constricting duct cross section; (c) specific acoustic modes may be ideally cancelled due to the effect of subsonic axial flow; (d) duct length may be selected to minimize the modal power radiated at a given frequency; and (e) wave reflections at the duct end are strongly enhanced for certain wall impedances.
Nonlinear Acoustic Phenomena in the Presence of Absorptive Liners in Circular Ducts
Authors: McDaniel Oliver , Reethof Gerhard
Published: May 2012

High acoustic intensities are often encountered in acoustically lined ducts, such as in jet aircraft intake ducts and with gas turbine power-generating installations. Many acoustically absorptive materials have characteristics at high intensity which differ from those in the low-amplitude linear region. There are two basic nonlinear phenomena which are encountered with lined ducts at high intensities. First, the absorption properties of the material become nonlinear and, second, the propagation of the acoustic wave in the duct can no longer be described by linear acoustic theory. This is, of course, true even for a hard-walled duct where there is no liner present. A hard-walled circular duct has been employed which is driven by a horn-coupled high-intensity sound source and is anechoically terminated. Sound pressure measurements, waveform photographs, and spectra were obtained at a number of locations in the duct for the unlined case and for several absorptive liners. A previously reported high-order harmonic ringing effect has been further studied at various intensities and for different linear lengths. Possible theoretical explanations for the effect will be presented along with the experimental data and the additional complications caused when higher-order duct modes are present will also be discussed. [This work is supported under NSF Grant No. GK-32584.]
Self-Generated Noise of Duct Treatment
Authors: Hehmann H. W.
Published: May 2012

Self-generated noise due to flow over acoustic treatment diminishes its effectiveness. A formulation of noise generated by flow over the treatment and its effect on linear performance based in part on J. E. Ffwocs-Williams's analysis [“The Acoustics of Turbulence Near Sound Absorbent Liners,” J. Fluid Mech. 51, Part 4 (Feb. 1972)] are presented and compared with measurements.
Static and Dynamic Impedance of the Chinchilla Middle Ear
Authors: Woodford C. , Henderson D. , Hamernik R. P.
Published: May 2012

Two electroacoustic bridges were used to obtain static acoustic impedance measures on 41 chinchilla. These measures were obtained awake and under varying doses of sodium pentobarbital. The mean impedance of the awake chinchilla is 880 acoustic ohms. The effect of sedation is twofold: (1) a negative pressure is developed in the middle ear; (2) the static impedance is decreased. Since a negative pressure is normally associated with an increase in impedance, a possible explanation of the seemingly contradictory results is represented. The acoustic reflex threshold was measured on 27 ears using stimuli of 0.5, 2, 4, and 8 kHz and signal durations of 10, 20, 50, 100, 200, and 500 msec. The acoustic reflex of the chinchilla is approxmately 20 dB more sensitive than man's after the stimulus is corrected for the transmission characteristics of the chinchilla external meatus. The reduction in stimulus duriaton from 500 to 10 msec elevated the reflex threshold by approximately 25 dB.
The Effect of Seamounts on Sound Channel Propagation
Authors: Bannister R. W. , Browning D. G. , Denham R. N.
Published: May 2012

Recent measurements of low-frequency propagation across seamounts extending into the deep ocean sound channel are described. With the receiving hydrophone located in the farfield, sound signals were detonated at the sound channel axis by a ship crossing a seamount to determine the relative signal enhancement and shadow regions. Newly discovered peaks in the Louisville Ridge located to the east of New Zealand were used for two separate experiments. In the first experiment the seamount extended above the depth of the sound channel axis; in the second, a seamount was chosen that was slightly below the axis. The results are compared with mode cutoff and simple scattering theory and also with previous propagation experiments conducted across the Louisville Ridge.
SOFAR Sound Speeds and Axis Depths in the North and South Atlantic Ocean
Authors: Northrop J.
Published: May 2012

SOFAR channel sound speeds in the Atlantic were calculated from NODC hydrographic data using Wilson's equations. Minimum sound speeds selected from each profile were tabulated, machine plotted in 1° squares, and contoured. The deep sound channel axis sound speeds range from 1441 m/sec near 70°N and 70°S to 1503 m/sec at 3S°N, 10°W. The depth of the sound channel axis varies from near surface at high (>65°) latitudes to a maximum of 2000 m at 40°N, 10°W in the North Atlantic and 1300 m at 40°S, 15°E in the South Atlantic. There is a double, or split, sound channel extending throughout the North East Atlantic basin, from the Canary Islands to the Faroe Islands, caused by outflow of warm saline water from the Mediterranean Sea. A split sound channel also exists in the Norwegian Sea in summer, due to surface heating. The upper sound channel disappears in winter due to seasonal cooling, storms, and vertical mixing. These data were obtained for a SOFAR computer program for the Atlantic Ocean. Sound speeds used in the program are the harmonic mean of axis sound speeds averaged over great circle paths between fixed receivers and specific areas of interest in the North and South Atlantic. [Work supported by Naval Ship Systems Command.]
Effects of Sea Ice Ridge Characteristics on Under-Ice Reflection Loss
Authors: Diachok O. I.
Published: May 2012

A set of coincident measurements of low-frequency under-ice transmission loss and sea-ice ridge characteristics were made in the Arctic Ocean using airborne acoustic and environmental remote sensing techniques. The resulting measured transmission loss data were compared to theoretical computations of long-range transmission loss which include a parametric surface reflection loss factor to account for absorption/scattering losses at the ice-water interface. Preliminary analysis of data and theory indicates that under-ice reflection losses at frequencies below 500 Hz may be quantitively related to the ridge frequency (number per kilometer) and the rms ridge depth. Using the results of this analysis and a recently compiled atlas of the temporal and spatial variability of sea-ice ridge frequency in the Arctic Ocean, estimates of low-frequency reflection loss were computed over the measurable range of ridge frequencies. Comparisons of predicted reflection loss with measurements by previous investigators show good agreement, thereby demonstrating the feasibility of making meaningful predictions of reflection loss from ice roughness data anywhere in the Arctic Ocean.
Measurements in an Insonified Ocean and Comparison with Room Acoustics
Authors: Arase E. M. , Arase T.
Published: May 2012

In comparison to the problems of room acoustics in measuring the diffuseness of reverberant sound, the problem in underwater sound is in determining the directionality and spatial distribution of the sound field. The ocean is a large stratified medium bounded by a free surface and a hard bottom with relatively low attenuation, so that the sound propagates very well for long distances and by several different paths. Background sound is generated at the free surface as a result of wind-wave interaction and by ships, in the medium by whales and other marine life, and in the bottom by seismic sources. In this paper, the theory, advantages, and limitations of the techniques used—such as linear arrays, digital correlators, and theoretical models—are discussed.
Needed: A New Definition of Diffusion
Authors: Lyon Richard H.
Published: May 2012

The conventional definition of diffusion of sound in resonating systems has important major deficiencies. Firstly, it is oriented toward acoustical spaces and, therefore, is difficult to apply directly to the vibrations of structural systems, for example. Secondly, as a result of its conceptual heritage in kinetic theory, it is impossible to reach the state of perfect diffusion in any finite space. Furthermore, any reasonable metric of diffusion predicts finite system diffusion as very far from the ideal. Thirdly, the definition applies only to systems of irregular geometry. A new definition of diffusion is proposed that would provide a continuous metric for finite systems. acoustical or otherwise. The new definition approaches the current definition for very large irregular systems.
Theoretical Prediction of Sound Attenuation in Acoustically Lined Annular Ducts in the Presence of Uniform Flow and Shear Flow
Authors: Ko Sung-Hwan
Published: May 2012

An investigation is made of the sound attenuation in a lined annular duct in the presence of fluid flow. The eigenvalue equation in the presence of uniform flow is derived by matching the radial component of the particle displacement and acoustic pressure across a vortex sheet located an infinitesimally small distance from the facing sheet of an acoustic lining. The eigenvalue equation in the presence of shear flow is developed by matching the acoustic pressure and the radial component of the particle displacement at the interface between the regions of uniform flow and shear flow. Theoretical prediction of the sound attenuation spectrum is based on an acoustic energy flow in which the effect of the mean flow is taken into account. The results presented in this paper are limited to those which are typical to the geometry of an annular duct. Effects of mean flow Mach number, boundary layer refraction, and acoustic impedance on the sound attenuation for a given duct configuration are found to be similar to those in rectangular and circular duct problems.
Latency Changes in Human Brainstem Evoked Potentials as a Function of Signal Intensity and Age of the Subject
Authors: Hecox K. , Galambos R.
Published: May 2012

This report extends observations presented by Galambos el al. at the 1972 Miami meeting of this society. The human brainstem evoked response consists of a series of six waves that reflect successive activation of the auditory nerve and brainstem nuclei. The major and most reliable component of this evoked response is wave V. We report here on the latency changes of this wave. Three adults were tested repeatedly over a period of eight months, providing a quantitative estimate of the variability of these responses within sessions, between sessions, and between subjects. The measurements made at intensities ranging from 10 to 60 dB SL (clicks) demonstrate a systematic and highly stable relationship between the strength of the signal and both the latency and variability of the response. Similar measurements, when made on normal infants as young as three weeks of age, show the same inverse relationship to hold. Within this infant group, as the age of the subject increases, the latency of wave V decreases until 12 to 18 months of age, when it attains adult values.
Use of Multivariate Statistical Methods with Audiological Data
Authors: Yonovitz A.
Published: May 2012

An audiogram can be viewed as a multivariate vector that is assumed distributed in multivariate normal form. The practical effect of treating audiological data in this manner is to allow variables (frequencies) to be studied simultaneously. When this is done the principles and techniques of experimental design, linear estimation, and tests of hypotheses may be generalized to the multivariate case. Three techniques will be described as paradigms for use with audiological data: (1) the multivariate analysis of variance, (2) profile analysis, and (3) discriminant analysis. Data from Martin and Wofford [J. Aud. Res. 10 (1970)] comparing audiometry of brief tones in normal and cochlear-impaired ears were analyzed by multivariate techniques. Each observation consisted of the difference between 10- and 500-msec pulses tracked at threshold for six audio-metric frequencies. Mean difference audiograms were established for both cochlear-impaired and normal ears. Multivariate analysis of variance procedures and profile analysis indicated that the mean difference audiograms were parallel and furthermore that they were at different levels. Additionally, linear discriminant analysis was used to classify an individual into one of two groups. The variates used in the classification were audiometric frequencies. Additional subjects, both cochlear-impaired and normals, were classified in the correct diagnostic group. Further implications for multivariate analysis of audiological data are discussed.
Theoretical Calculations of the Penetration of Narrow Acoustic Beams into a Sand Sediment
Authors: Horton C. W. , Thompson Lewis, A
Published: May 2012

The Kirchhoff theory of refraction is used to calculate the acoustic field in a sand sediment when the incident beam in the overlying water is highly directional. The attenuation in the sediment and the finite size of the insonified area conspire to localize the acoustic field in the bottom. Thus, when the incident angle of the acoustic beam in the water is equal to or greater than the critical angle, the refracted ray of plane wave theory does not provide an adequate description of the pressure field in the sediment. Theoretical curves are shown and compared with the experimental results of the preceding paper.
Traversing Microphone Spectroscopy as a Means for Assessing Diffusion
Authors: Lubman David
Published: May 2012

Traversing microphone (TM) spectroscopy provides a rapid and sensitive means for assessing sound diffusion in rooms. TM spectra are power spectra obtained at the terminals of a small microphone during its traverse through a room at constant speed. The TM spectral shape is a sensitive indicator of the degree of directional diffusion. If the field is perfectly diffuse, the TM spectrum is precisely rectangular. Observed deviations from the ideal rectangular TM spectra are at once symptoms of imperfect diffusion and clues to their causes. The TM spectrum provides a measure of diffusion averaged over the path of traverse rather than at point locations. The present technique is limited to discrete frequencies. The frequencies must be moderate to high, since the path of traverse must be large in wavelength in order to obtain statistically stable results. Quantitative as well as qualitative assessments of diffusion may be possible with this promising new technique. [Work supported by ONR, Code 468.]
Paraholography—A New Method for Measurement of the Directional Distribution of Sound Waves in a Reverberation Chamber
Authors: Cook Richard K.
Published: May 2012

We describe a method for experimental determination of the various plane waves composing the sound field in a reverberation chamber. The physical quantities needed are (1) the directions of propagation, (2) the time mean of the squared sound pressure, and (3) its phase. These quantities are usually needed, for sound having a narrow band of frequencies, as running functions of time. The basic holographic principle is comparison of the actual sound field with a reference plane wave having precisely known direction of propagation, sound pressure, and phase. The reference wave is not a “real” wave but is created electronically, on the electrical side of microphones sensing the actual sound field, so as to be “parallel” to a real wave. The comparison of the paraholographic wave with the actual sound field so as to measure the latter is achieved with a least-squares principle, in which the product of the two sound pressures is time-integrated. Simultaneous integrals for several paraholographic waves may be carried out. We present the results of the analysis and some preliminary data for a standing-wave (impedance tube) for which only two paraholographic waves are needed.
Transmission of Radial Shear Forces to Cochlear Hair Cells
Authors: Billone M. C. , Raynor S.
Published: May 2012

The radial shear forces transmitted to the cuticular plates of cochlear sensory cells are investigated by means of a mathematical model. The model is based on the fine anatomy of the hair cells and their supporting structures. It predicts that the inner hair cells are stimulated by a viscous force which is linearly proportional to, and in phase with, basilar membrane velocity. The outer hair cells are stimulated by a shear force which is linearly proportional to, and in phase with, basilar membrane displacement at low frequencies (e.g., less than 700 Hz for a mid-basal turn cell). At higher frequencies, the shear force transmitted to the outer hair cells is a function of both displacement and velocity. This outer hair cell shear force is at least an order of magnitude greater than the corresponding inner hair cell force for the frequencies and cochlear positions studied. These results compare favorably to recent cochlear microphonic data from normal and kanamycin-treated guinea pigs for frequencies less than 4000 Hz. Shear force amplitude envelopes are presented for 800-Hz and 1600-Hz pure tones. The results suggest that the “velocity-sensitive” inner hair cells are candidates for “place mechanism” receptors while the outer hair cells are candidates for “frequency mechanism” receptors. The model predicts no mechanical fine tuning in the force transmission.
Functional Modeling of Auditory Analysis of Transient Signals
Authors: Rozsypal Anton J.
Published: May 2012

It appears that the time evolution of critical bands as response to an incoming auditory stimulus is the crucial process in perception of transient sounds. The mechanical system represented by the basilar membrane of the inner ear can not account for the frequency resolution of hearing Some other mechanism, possibly lateral inhibition located in the auditory neural network, is needed to achieve the frequency selectivity obtained in experiments investigating the dynamic properties of hearing. A functional model of a lateral inhibition neuron network is suggested which simulates the organization of critical bands in time. In this network, short-term adaptation is modeled by differentiators in the direct neural paths with a time constant of 24 msec. Integrators in the lateral inhibition branches with a time constant of 188 msec enhance the frequency selectivity by gradual superimposition on the neural excitation function of its negative second spatial derivative. Steady state is reached about 300 msec after the onset of a stepwise stimulus. Such a system simultaneously enhances contrast both in the frequency and time domains.
Structural Information Theory Based on Electronic Configurations
Authors: Barrett T. W.
Published: May 2012

The topic of this paper is how different forms of acoustical information may be measured. The specific problem addressed is how information is transferred from a three-dimensional source of longitudinal waves to a one-dimensional vibrating membrane. In previous papers [Barrett, TIT J. Life Sciences 1, 129–135 (1971); Acustica (1973), in press], the author has demonstrated through the derivation of different forms of informational “quanta” that the modulating envelopes for the wave packets representing these quanta are functional solutions to the Weber equation (the Helmholtz equation in parabolic cylinder coordinates). The geometrical structure described by the Weber equation suggests a resonance effect existing between an “angular momentum” involving an “azimuthal quantum number” and one involving a “magnetic quantum number” in analogy with structural chemistry formulations [Barrett, Acustica (1973), in press]. In the present paper the geometrical formulation is carried further. A sound source is commonly spherical; therefore, solutions are found for the wave equation in spherical coordinates, giving a precise meaning to the “azimuthal” and “magnetic quantum number” analogy. These informational wave packets must then be translated into a one-dimensional representation because of the nature of the receiver (the tympanic membrane). The difference between descriptions of electromagnetic and acoustical forms of energy is presented as consisting in the number of variables remaining constant in the acoustical formulation (as compared with the electromagnetic) but not in the basic geometrical formulations, which are primary.
A Possible Sex Difference in Degree of Lateralization of Dichotic Stimuli?
Authors: Remington Roger , Krashen Steve , Harshman Richard
Published: May 2012

In an experiment using a standard set of dichotically presented monosyllables /pa,ta,ka,ba,da,ga/ it was unexpectedly observed that only the males showed a statistically significant right ear advantage. To test the reliability of this result, the same stimuli were administered to a new set of subjects. Again only the males showed a significant right-left ear difference, although the females showed a trend in the expected direction which might become significant with a larger N (males' left ear percentage of errors was 54%; females' was 51%). This result is consistent with the findings of Kimura of a greater male lateralization of depth perception, and forthcoming results by Krashen showing a greater male lateralization of environmental sounds. In light of this, data from several previous dichotic studies at the UCLA Phonetics Laboratory were reanalyzed considering males and females separately, and the same trend was noted.
Forward Velocity Effects on Jet Noise with Dominant Internal Noise Source
Authors: Von Glahn U. , Goodykoontz J.
Published: May 2012

Flow-related internal noise generated by a control valve in an air jet-noise rig or, by analogy, combustors in an engine can become the dominant noise source at low jet velocities or provide a floor for jet noise suppressors. Acoustic data, with and without forward velocity, were obtained with a convergent circular nozzle using a quiet flow system and one dominated by a low-frequency internal noise source. Forward velocity effects were obtained by installing the test nozzle in a free jet. Farfield noise data, obtained at jet pressure ratios from 1.3 to 1.7 and forward velocities up to 260 ft/sec, are presented in terms of SPL and PWL spectra, directivity, and total power. With a quiet flow system, jet noise is reduced by forward velocity as a function of the product of the sixth power of the relative velocity and the second power of the jet velocity. However, with a dominant low-frequency core noise source, the portion of the noise spectra dominated by this source was not appreciably affected by forward velocity. The high-frequency spectral portion of the jet noise was reduced by forward velocity independently of the flow systems used.
Noise Tests of a High-Aspect-Ratio Slot Nozzle with Various V-Gutter Target Thrust Reversers
Authors: Stone J. R. , Gutierrez O. A.
Published: May 2012

This paper presents the results of experiments on the noise generated by a 1.33X91.4-cm rectangular slot nozzle (69 to 1 aspect ratio) with and without various V-gutter target thrust reversers. Some aerodynamic data on flow, thrust, and exhaust-jet velocity fields are also presented. In addition, preliminary ground-reflection results are included. These experiments were conducted with near-ambient total temperature jets at nozzle pressure ratios of 1.25 to 3.0, yielding isentropic jet velocities of about 190 to 400 m/sec. At nozzle pressure ratios of 2.0 or less, the reversers, in addition to being noisier than the slot nozzle alone, also had a more uniform directional distribution and more high frequency noise. The maximum overall sound pressure level and the effective sound power level both varied with the sixth power of the isentropic nozzle jet velocity over the range tested. The experimental data are scaled up to sizes suitable for reversing the wing flow of a 45 400-kg augmentor-wing-type STOL airplane. These calculations indicate perceived noise levels well above the 95-PNdB design goal on the 152-m sideline.
Lateral Line Organs and Amphibian Hearing Organs
Authors: Flock Åke
Published: May 2012

Lateral line organs are the simplest vibration receptors in vertebrates. They serve to detect water displacement by means of receptor cells and synapses similar to those in hearing organs and may be used as convenient models of function at a cellular level. Epidermal lateral line organs are present in fishes and aquatic amphibia. Each organ contains 10–30 hair cells coupled to the surrounding water via a cupula. During evolution, some lateral line organs in fishes have become enclosed in canals on the head and along the body. Canal organs contain several hundred hair cells which receive a more extensive efferent innervation than those of epidermal organs. The ion content of canal lymph can differ considerably from outside water. Adaptation from aquatic to terrestrial life requires impedance matching at the interface between air and inner ear fluids. In frogs this is achieved by a single middle ear ossicle. Frogs have two hearing organs, the amphibian and the basilar papillae. They differ in their frequency sensitivities and are also different in that hair cells in the basilar papilla have only afferent synapess, while efferent synapses are missing. Basilar papilla primary units still show sharp tuning curves.
Fluctuations of Signals and Noise in Phase-Random Multipath Propagation
Authors: Dyer Ira
Published: May 2012

Sound fluctuations in the ocean have many origins. One of the more important mechanisms is multipath propagation, for example, in channel propagation or in high-frequency reflection from a rough surface. Fluctuations in multipath propagation are intrinsically associated with motion, for example, with range-rate in channel propagation or with sea surface waves in surface reflection. For either signals or noise with about 10 or more multipaths, a suitable and useful statistical ensemble yields strikingly simple results. The intensity probability densities are chi-square or simple extensions thereof. The logarithmic probability densities are simple transformations of the intensity ones, with a standard deviation of S.6 dB for a narrow-band signal and with smaller standard deviations for ambient noise modeled by multitones. A range of practical computational methods have evolved to cover conditions apt to be met in the ocean, and are presented and discussed. The autocorrelation of intensity (or its logarithmic transformation) is an equally useful measure of fluctuations. Unlike the probability density, it involves motion parameters explicity. Progress to date on understanding autocorrelation in multipath propagation is outlined and discussed.
An Application of the Theory of Partial Coherence to Describe the Fluctuation of Acoustic Signals in the Ocean
Authors: Parkins B. E.
Published: May 2012

The statistical description of acoustic propagation is often formulated to second order using the space-time covariance of the pressure fluctuations. However, in many cases a greater insight is obtained if the second-order statistics are given in the form of the mutual coherence function and its normalized version, the complex degree of coherence. The principal advantage in this approach is that it allows the second-order statistics to be separated into amplitude and phase components. This separation enables a useful characterization of the statistical properties of a multisensor system to be made and, in particular, it leads to a direct relationship between the performance of that system and the coherence properties of the medium. In this paper these concepts are discussed and are illus-strated with the results from a long-range propagation experiment.
The Cobb Seamount Acoustic Transmission Experiment
Authors: Ewart T. E.
Published: May 2012

We have measured phase and amplitude fluctuations in pulses sent from a fixed transmitter to a fixed receiver at the same depth 17.2 km away. The receiver tower was located at a depth of 1000 m on the flank of Cobb Seamount (located 275 miles west of Grays Harbor, Washington) and the transmitter tower on a subsidiary peak to the southwest. Eight- and 16-cycle pulses of 4.166 and 8.333 kHz were sent alternately every 15.729 sec and received at three receivers located at 0, 5, and 15 m along a rigid self-leveling arm oriented perpendicular to the transmission path. From the 144.5-hour time series we have computed spectra and probability distributions for phase and amplitude at a single receiver and phase difference between two receivers. The phase spectra show distinct tidal peaks and a sharp falloff above 0.1 cph; the amplitude spectra exhibit tidal peaks to a lesser extent and show a sharp falloff above about 1 cph. The amplitude spectra at 4.166 and 8.333 kHz are acoustic frequency dependent above 1–2 cph, which is close to the local Brunt Väisälä frequency. They exhibit more energy in the higher frequencies at 8.333 than at 4.166 kHz. The phase differences show extremely small variance corresponding to a plane wave arrival angle of 1 to 2 minutes of arc. The amplitude and phase spectra exhibit distinct bands characterized by different power law scaling.
Fluctuations in Sonar: A Short Survey
Authors: Urick R. J.
Published: May 2012

Sonar fluctuations received intensive study during the hectic days of World War II, when the causes of fluctuation were identified and some quantitative data were obtained at the frequencies and ranges of current interest. Since then, in the search for mean values of the sonar parameters, fluctuations have tended to be neglected as a subject of serious study. They are the result of the mobile, varying nature of the medium and the objects within it. For example, echoes fluctuate because of the constantly changing heading of a submarine underway; the ambient background fluctuates because of changing ship traffic, wind speed, and biological activity; CW signals fluctuate because of a changing multipath structure of the medium. Examples of these effects, as observed in NOL field work, are presented. Their effect on detection is to improve detection at low mean S/N ratios and to cause lost contacts at high S/N ratios. Quantitatively, this behavior can be expressed by means of ROC curves modified to include fluctuations. However, much more work needs to be done on the second-order statistics of underwater sound before their magnitude can be predicted and their effects understood.
Internal Wave Induced Fluctuations of Low-Frequency Long-Range Acoustic Propagation
Authors: Porter Robert P. , Spindel R. C. , Jaffee R. J.
Published: May 2012

Some of the fluctuation of acoustic signals at long ranges is due to the passage of acoustic radiation through the internal gravity wave field. A ray theory is presented that predicts the amplitude and phase of the acoustic field perturbed by the internal wave field. A postulated internal wave model [C. Garrett and W. Munk, Geophys. Fluid Dynam. 2, 225–264 (1972)] is used to estimate the perturbation of the sound-velocity field. The acoustic-gravity interaction is assumed concentrated near the top of the main thermocline. It is found that ray cycle lengths comparable to, or a multiple of, an internal wavelength induce large phase fluctuations at internal wave frequencies and high-frequency random amplitude variations. Based on the proposed internal wave spectrum, predictions of phase variations as a function of range, frequency, source, and receiver locations are possible. Comparison between measured and predicted acoustic fluctuations is discussed.
Edward C. Wente, Pioneer in Engineering Acoustics
Authors: Soffel A. R. , Harvey F. K.
Published: May 2012

Wente's impact on engineering acoustics commenced in 1916 with his invention of a practical condenser microphone. This and his following contributions to early motion picture sound recording, high fidelity sound reproduction, stereophony, room acoustics, instruments and facilities for acoustic measurement, plus other items are recalled by the authors. Both were witness to many of the later developments while involved in operation and experiment with associated equipment at Bell Laboratories, beginning in the late twenties and continuing for two decades.
Improved Unidirectional Microphone
Authors: Sessler G. M. , West J. E.
Published: May 2012

The directional characteristics of second-order unidirectional microphones Qsee G. M. Sessler and J. E. West, IEEE Trans. Audio Electroacoust. AU-I9, 19 (1971)] have been considerably improved by alterations in the mechanical design. Relative to the direction of maximum sensitivity at θ = 0° (referred to the rotational axis) the attenuation in the directions of minimum sensitivity at θ = 90°, 180°, 270° now exceeds 20 dB in the midfrequency range.
Electret Tablet for On-Line Encoding of Graphical Data
Authors: Nigam A. K. , French J. C. , Sessler G. M.
Published: May 2012

An electromechanical electret transducer which can be used for point-by-point continuous encoding of pen-drawn graphical data (electret tablet) is described. The tablet consists of a rigid insulating backplate and a thin electret foil separated from the backplate by a shallow air gap. Both foil and backplate are selectively metalized along parallel strips and positioned such that the strips on the foil are perpendicular to the strips on the backplate. Each overlap between foil metal strips and backplate metal strips forms an individual electret transducer [electroacoustic arrays of this kind are described in A. K. Nigam and G. M. Sessler, Appl. Phys. Letters 21, 229 (1972)]. The functional characteristics of the tablet are analyzed both theoretically and experimentally. Full-size tablets having a resolution of 3 lines/mm over a writing surface of about 30X30 cm2 appear feasible. The electret tablet is operable with an ordinary stylus, such as a fine-tip ballpoint pen, is unaffected by hand-pressure on the writing surface, and is capable of extremely fast digitization rates of up to 50 000 coordinate-pairs/sec.
Noise Due to Brownian Motion of the Diaphragm, of Electret Microphones
Authors: Sessler G. M. , French J. C.
Published: May 2012

The electrical noise generated by thermal agitation of the molecules striking the diaphragm of electret microphones has been studied analytically and experimentally. This Brownian-motion noise can be calculated from the equivalent circuit of the microphone-amplifier combination and depends mainly on the resistive part of the air-gap impedance of the microphone. It is superimposed on other kinds of noise, such as Johnson noise, but can be detected under certain conditions with low-noise preamplifiers in the mid-frequency range. Measurements on a circular electret microphone with a radius of 1.8 cm and a sensitivity of 5 mV/µbar yield Brownian-motion noise voltages of about 9 nV/Hz1/2 in the frequency range between 1 and 5 kHz, in good agreement with calculated results. The total noise voltage over this frequency range corresponds to a sound pressure level of −5 dB relative to 0.0002 µbar, or an average diaphragm displacement of 5X10−12 cm.
The NRL-USRD Type J15-3 Low-Frequency Projector
Authors: Ivey L. E.
Published: May 2012

The USRD type J15-3 projector is an underwater electro-acoustic transducer for use as a CW source in the frequency range 10–600 Hz. The transducer contains three diaphragm assemblies, each driven by a large moving coil in the field of a permanent magnet. When the diaphragms are connected in series, 750 W can be applied to yield a sound pressure level of 178 dB re 1 µPa. The diaphragms also can be driven in parallel or individually. At frequencies below 100 Hz, the input power is limited by the allowable displacement of each diaphragm. The J15-3 has been used successfully at a depth of 200 m at Lake Pend Oreille, Idaho, and at 300 m in ocean measurements. Pressure compensation is provided by a closed gas system that requires no high-pressure gas bottles; when water enters the compensation chamber, it compresses a butyl rubber bag until the internal air pressure equals the external water pressure.
Illinois Noise Pollution Control Regulations
Authors: Hellweg Robert D. , Moore John S.
Published: May 2012

The recently adopted Illinois Noise Pollution Control Regulations will control noises emitted from “property-line-noise-sources,” e.g., industrial facilities, business, and commercial establishments, etc. The comprehensive regulations contain two parts: the first part contains a “nuisance” provision, and the second part contains octave-band sound pressure level limits for property-line noise sources. For purposes of these regulations, land is classified into three categories according to use, which correspond to industrial, commercial, and residential uses. The numerical limits, which will apply to a given facility, are dependent upon the land usage of both the noise emitter and noise receiver. Impulsive sounds are regulated by A -weighted sound levels, while “prominent discreet tones” are regulated in terms of 1/3-octave-band sound pressure levels. More stringent nighttime limits will apply to new facilities which emit sounds to residential lands. Compliance times for existing noise sources range from one to three years, while new facilities must comply immediately. These regulations are the first step in a program designed to reduce noise pollution in Illinois-future regulations will control noises emitted from transportation sources and construction sources.
Guidelines for the Design of Rotating Difiusers
Authors: Lubman David
Published: May 2012

Successful qualification of a reverberation room for measurement of discrete frequency components under ANSI S1.21-1972 is greatly facilitated by the use of a rotating diffuser (RD). The benefits of the RD in this connection are twofold. First, the RD is the most effective device known for reducing spatial variance of reverberant sound in a room. Second, the RD is known to reduce the variance of power output with source position in a room. In view of its importance, and in lieu of an adequate theory to predict its performance, we offer guidelines for design based largely upon collective experience and judgment. For the modern genera of quiet, high-speed, surface of revolution RDs, the major design parameters are size, shape, percent open area, surface density, number of panels, and panel damping. It is shown and emphasized that RD effectiveness depends not on these parameters alone, but also in a major way on room size and reverberation time. [Work sponsored by ONR Code 468.]
Application of Absorption and Rotating Diffusers on Reduction of Spatial Variance and Qualification of Reverberation Chamber
Authors: Tichy Jiri
Published: May 2012

When determining the precision of the sound measurement in a reverberation chamber, two major effects have to be considered: the spatial averaging of sound pressure squared and the variation of sound power radiated by the source with frequency and source position. The variance of the spatial averaging depends on number of applied microphones or length of the microphone travel path. As discussed in the paper, it can be substantially reduced by a rotating diffuser, which modulates the sound field. The spatial variance reduction is the most important for the sound power measurements at single frequencies. The effect of diffuser size and speed on the modulation parameters and variance reduction is discussed. The wall absorption of the chamber affects the bandwidth of modes and their overlap. In this way the variability of the sound power radiation with frequency is reduced primarily at low frequencies. The qualification procedure as defined by ANSI 1.21-72 and ASHRAE 36-72 Standards to qualify the reverberation chamber for sound power measurements is based on the combined effect of spatial variations of sound pressure and the frequency dependence of radiated power. This paper presents practical data on needed chamber absorption and rotating vane parameters to meet the qualification criteria.
Room Qualification by Averaging over Multiple Source Positions
Authors: Maling G. C.
Published: May 2012

Available data on the effect of averaging over multiple source positions in a reverberation room are summarized. At high frequencies, the source positions tend to be independent, and a reduction in the variance is obtained. At low frequencies, correlation effects are important, and the averaging procedure tends to be less effective. Accuracy requirements for the frequencies used for room qualification are also discussed.
Monaural Heterphonic Auditory Adaptation
Authors: Weiler Ernest M. , Friedman Lynn
Published: May 2012

Recent evidence has been interpreted to suggest that auditory adaptation may not be a peripheral phenomenon. The possibility of an effect on binaural interaction has been inferred. One obvious approach to the peripheral versus central interaction hypotheses is to determine whether it is possible to measure suprathreshold monaural adaptation. If not, one would conclude adaptation is more likely a binaural phenomenon. In the present experiment, two tones of widely separated frequencies, 500 and 10 000 Hz (in the preferred ear), were used, respectively, as the adapting and comparison tones. The 500-Hz tone was presented at 60 dB SPL for 7 min adaptation. Fifteen subjects, aged 20–42, were used. The average amount of monaural adaptation was 22.3 dB (Wilcoxon T = 2, p≤0.01). Individual values ranged from −5.0 to 50.8 dB. Fourteen subjects set the comparison tone at a lower intensity following adaptation. Apparently it is possible to measure sizeable amounts of adaptation monaurally, which can be interpreted in favor of peripheral loudness adaptation. At least all adaptation phenomena cannot be attributed to simple binaural interactions.