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Aug 1977

Volume 62, Issue 2, pp. 245-479

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Sound propagation in reacting systems

Robert J. Ellis and Robert G. Gilbert

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 245-249 (1977); (5 pages)

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Numerical solutions are given for the set of coupled differential equations describing the dynamic interaction of sound with an arbitrary number of gas phase reactions, for several systems, both near and far from equilibrium. Acoustic response is assumed linear and adiabatic. Absorption by relaxation is included. Results for simple combustion systems indicate that transient effects can result in appreciable amplification of low sound frequencies.
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43.20.Bi Mathematical theory of wave propagation
43.35.Fj Ultrasonic relaxation processes in gases, liquids, and solids

Acoustic diffraction of a plane wave by a semicircular infinite soft strip

Bansi Lal and D. L. Jain

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 250-254 (1977); (5 pages)

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The subject of this paper is the problem of diffraction of a time‐harmonic obliquely incident plane acoustic wave by a semicircular infinite soft strip. An integral‐equation technique is presented to solve this two‐dimensional boundary‐value problem by the standard perturbation method when the wavelength of the incident wave is much larger than the radius of the semicircular strip. Approximate expressions are obtained for the farfield amplitude and scattering cross section.
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43.20.Fn Scattering of acoustic waves

Geometric properties for reflected fields from a general surface using finite differences

Alfred G. R. VanLennep

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 255-261 (1977); (7 pages)

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It is well known that geometrical acoustics (GA) approximations to reflected fields depend on the surface shape incident to the field in a neighborhood. However, because of the general complexity of these solutions certain canonical problems pertaining to regular shapes, such as cones and spheres, have been solved, but little attention has been given to the problem of approximating the essential geometric properties for a general surface in a neighborhood. Approximations to the reflected field (ka≫1) usually assume (although this is not a limitation of GA as pointed out by Fock [Electro Magnetic Diffraction and Propagation Problem (Perganom, New York, 1965), 1st ed. ] that the surface is a well known geometric shape, i.e., ellipse, cone, etc. This is done to make calculations of curvature and other geometric properties straightforward. This paper will discuss the problem of obtaining the needed geometric properties for more general geometric shapes. It will consider only a small neighborhood of the surface. Using differential geometry and finite differences, it will then show that all geometric properties in a neighborhood may be approximated by a small number of points from that neighborhood. This technique can with a few practical limitations geometrically describe any neighborhood on a surface. These neighborhoods form ’’areas’’ called patches. When the entire surface meets certain conditions, these patches when ’’tied’’ together actually describe the entire surface and all its geometric properties.
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43.20.Fn Scattering of acoustic waves
43.20.Dk Ray acoustics

Dynamics of a cylindrical shell system coupled by viscous fluid

T. T. Yeh and S. S. Chen

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 262-270 (1977); (9 pages)

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This study was motivated by the need to design the thermal shield in reactor internals and other system components to avoid detrimental flow‐induced vibrations. The system component is modeled as two coaxial shells separated by a viscous fluid. In the analysis, Flügge’s shell equations of motion and linearized Navier–Stokes equation for viscous fluid are employed. First, a traveling‐wave‐type solution is taken for shells and fluid. Then, from the interface conditions between the shells and fluid, the solution for the fluid medium is expressed in terms of shell displacements. Finally, using the shell equations of motion gives the frequency equation, from which the natural frequency, mode shape, and modal damping ratio of coupled modes can be calculated. The analytical results show a fairly good qualitative agreement with the published experimental data. With the presented analysis and results, the frequency and damping characteristics can be analyzed and design parameters can be related to frequency and damping.
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43.20.Tb Interaction of vibrating structures with surrounding medium
43.40.Ey Vibrations of shells

Reflection of finite‐amplitude waves in a parametric array

T. G. Muir, L. L. Mellenbruch, and J. C. Lockwood)

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 271-276 (1977); (6 pages) | Cited 4 times

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The effect of a pressure‐release reflector on the parametric interaction process is examined theoretically and experimentally. It is shown that the 180° phase change upon reflection instigates a reversal of the finite‐amplitude distortion process in the primary radiation. Although energy then passes from the harmonics to the fundamental components of the primaries, the difference frequency component suffers a phase interference effect that leads to its partial annihilation.
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43.25.Lj Parametric arrays, interaction of sound with sound, virtual sources
43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves
43.30.Dr Hybrid and asymptotic propagation theories, related experiments

Layer model for assessing acoustic refraction effects in echo sounding

P. D. Phillips, H. Richner, and W. Nater

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 277-285 (1977); (9 pages) | Cited 2 times

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Acoustic refraction effects in the atmosphere by wind‐speed and temperature gradients are investigated using a simple multilayer model for plotting the ray path of a signal transmitted by an acoustic echo sounder (AES) and scattered back at various heights to be received monostatically. It is found that while nonperfect backscattering has negligible effect on the scattering cross section for acoustic waves in a turbulent medium, the effect on the ’’angle of arrival’’ and the Doppler shift is important. A purely horizontal wind can produce a Doppler shift in a vertically pointing monostatic AES which for a wind of 20 m/sec at 1 km can simulate vertical wind speeds of 50 cm/sec. For nonvertical sounding, this effect is of little importance. The generally accepted first‐order approximation for the angle of arrival of the scattered signal appears, as a result of this more detailed analysis, to be incorrect. The problems of the height resolution of a horizontal scatter layer using a nonvertical AES are briefly considered in terms of the antenna characteristics as well as the length of the transmitted pulse.
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43.28.Fp Outdoor sound propagation through a stationary atmosphere, meteorological factors
43.20.Dk Ray acoustics
43.20.Fn Scattering of acoustic waves
43.28.Tc Sound-in-air measurements, methods and instrumentation for location, navigation, altimetry, and sound ranging

Frequency coherence and time coherence in random multipath channels

S. L. Adams and J. W. Doubek

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 286-294 (1977); (9 pages) | Cited 1 time

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The underwater acoustic propagation channel is dispersive in time, frequency, and space. This paper investigates frequency coherence and time coherence for simple multipath channel models with an emphasis on situations where there are a few paths. The propagation channel is postulated to consist of a finite set of paths with random amplitudes and lengths. The fluctuation characteristics of the frequency selective fading in a random time spread channel are investigated in terms of the statistics of the channel transfer function. The effects of the fluctuations in path length are clearly separated from the effects of nominal multipath structure in the channel statistics. The conditions under which coherence bandwidth and coherence time provide reasonable characterizations for the multipath channel are examined. All of the results obtained for the random time spread channel can be applied to the mathematically dual problem of a random frequency spread channel.
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43.30.Bp Normal mode propagation of sound in water
43.20.Dk Ray acoustics

Relation between the solutions of the Helmhotz and parabolic equations for sound propagation

John A. DeSanto

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 295-297 (1977); (3 pages) | Cited 5 times

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In this paper we establish an integral transform relation between the solutions of the Helmholtz and parabolic equations for sound propagation in an arbitrary two‐dimensional waveguide. The sound speed is a function of both depth and range. For range‐independent sound speeds, the integral transform is proved to be exact by using a normal‐mode expansion. For range‐dependent sound speeds the stationary phase approximation of the transform is, in lowest order, equivalent to the usual parabolic approximation. Corrections to the parabolic approximation are also calculated using the stationary phase method.
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43.30.Bp Normal mode propagation of sound in water
43.20.Bi Mathematical theory of wave propagation
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.20.Ks Standing waves, resonance, normal modes

One‐dimensional model for acoustic absorption in a viscoelastic medium containing short cylindrical cavities

G. Gaunaurd

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 298-307 (1977); (10 pages) | Cited 4 times

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The equations of motion of linear viscoelasticity (Kelvin–Voigt Model) in cylindrical coordinates are reduced to an axisymmetric plane‐stress situation valid for short hollow cylinders. The analysis models the deformations and oscillations occurring in the annular region conceptually constructed around one of the holes in a multiperforated rubber sheet to be used as an underwater acoustic absorber. The eigenvalue problem for the ring’s natural frequencies is solved in two cases: first, when both rims of the ring are subjected to a stress boundary condition; second, when the inner rim (r=a) is stress free and the outer one (r=b) is fixed. For incompressible materials with Poisson’s ratio very close to 0.5, the first few eigen‐wave‐numbers are numerically computed and plotted in nondimensional form versus the b/a ratio, in both cases, and the resulting sets of curves are shown to be interlaced, the ones from the first case being below those of the second. The transient vibration problem for the displacement ur is solved by the Laplace‐transform method in the first case only. The finding that the frequencies at which absorption is maxima are the resonant frequencies of the cavity, is verified. We show a simple technique to estimate the amount of absorption present at these eigenfrequencies, and the estimates reasonably check with experimental meaurements within the limitations of this model (i.e., below critical damping).
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43.30.Dr Hybrid and asymptotic propagation theories, related experiments
43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance
43.35.Mr Acoustics of viscoelastic materials

Effects of temperature microstructure on low‐frequency propagation in the South Tasman Sea

A. C. Kibblewhite, T. G. Shirtcliffe, and B. R. Stanton

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 308-319 (1977); (12 pages)

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The attenuation of underwater sound at very low frequencies exceeds the values expected on the basis of the variation observed at higher frequencies, and this excess attenuation exhibits a regional dependence. Two theoretical models have been proposed to account for the effect observed. Temperature soundings made along a Tasmania‐Antartica section have revealed variations of fine structure which an be correlated with variations in acoustical transmission properties and provide a test for the two theoretical models.
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43.30.Bp Normal mode propagation of sound in water
43.30.Cq Ray propagation of sound in water

Mode conversion in shallow‐water sound propagation

Suzanne T. McDaniel

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 320-325 (1977); (6 pages)

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Coupled equations for modal power transfer are applied to calculate the energy transferred between normal modes as a result of scattering from the ocean floor. Numerical estimates are presented for mode conversion in a typical shallow‐water environment. The results show that mode coupling can have a significant effect on propagation loss. Mode‐coupling predictions obtained for farfield transmission loss are found to display both frequency‐ and range‐dependent features in qualitative agreement with observed shallow‐water transmission loss. Excellent agreement is obtained between mode‐coupling predictions and experimentally measured mode attenuation.
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43.30.Bp Normal mode propagation of sound in water
43.30.Dr Hybrid and asymptotic propagation theories, related experiments
43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance
43.20.Ks Standing waves, resonance, normal modes

Experimental agreement of stochastic ray‐theory relations

Jerome A. Neubert

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 326-334 (1977); (9 pages)

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The ray‐theory intensity relation has been modified to allow consideration of the effects of medium randomness. This study compares the theoretical model with actual sea data. It also investigates the theoretical relations for the standard deviation and the coefficient of intensity fluctuation in a variable and random ocean. In all cases, good agreement is found within the sampling limitations imposed by the sea data. In addition, the higher‐order statistical quantities are remarkably well behaved even beyond the predictions of the model.
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43.30.Bp Normal mode propagation of sound in water
43.20.Dk Ray acoustics

Rotated Y‐cut quartz crystal with two different electrodes treated as a one‐dimensional acoustic composite resonator

F. Boersma and E. C. van Ballegooyen

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 335-340 (1977); (6 pages) | Cited 2 times

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In this paper a quartz crystal coated with electrodes of different materials is considered as a one‐dimensional composite acoustic resonator. The piezoelectric properties of quartz are incorporated in the model. The model leads to a transcendental equation from which the resonant frequencies can be calculated. It will be shown that earlier develolped models can be derived from this more general model by making the proper approximations. The difference between the theoretical resonant frequencies, as calculated from the various models, is discussed. To express this difference a systematic error is defined which proved to be negligable for small mass loading, corresponding to a relative frequency shift <1%, and in the case independent of the electrode material. In case there is a larger mass loading, the discrepancy between the previous models and the model presented in this paper can be of the order of 5%–10%, depending on the properties of the electrode material, i.e., the acoustic impedance and on the ratio of the thicknesses of the electrodes.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.40.Sk Inverse problems in structural acoustics and vibration
43.40.Dx Vibrations of membranes and plates
43.38.Fx Piezoelectric and ferroelectric transducers

Super‐resolution ultrasonic imaging by combined spectral and aperture synthesis

Takuso Sato and Osamu Ikeda

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 341-345 (1977); (5 pages)

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In conventional sonar systems, high azimuth resolution is achieved by synthesis of the aperture, and range resolution by utilization of pulsed waves. When the aperture synthesis is done over a fairly large area, however, the duration of the pulse should be reduced to less than a few wavelengths in order to keep the range resolution within the azimuth resolution. The use of such short pulses makes difficult the precise detection of the amplitude and phase of the waves reflected from the object, mainly because of the sensitivity to noise caused by the short averaging time in the heterodyne detection process. In this paper a new method is proposed which realizes the impulselike range resolutions through the synthesis of detected signals for several frequencies of continuous waves. The fundamental idea is to synthesize the Fourier transform of a very short pulse by using several frequencies of ultrasonic waves. This method gives the synthesis in range, while the conventional synthesis gives the azimuth direction. The principle of the method is presented together with an analysis of the resolution, a noise analysis, and a discussion which includes a numerical example.
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43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography

Tube method of sound‐absorption measurement extended to frequencies far above cutoff

F. Douglas Shields, H. E. Bass, and L. N. Bolen

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 346-353 (1977); (8 pages) | Cited 2 times

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Equipment had been constructed for measuring sound absorption in the frequency range from 4 to 100 kHz in a large tube 25.4 cm in diameter and 4.8‐m long. The technique employs a large, moveable, solid‐dielectric capacitance transducer that completely fills the tube cross section and generates pulses of plane waves. An identical transducer terminates the other end of the tube and serves as a microphone to detect and reflect the sound pulses. Measurements in argon, nitrogen, and air indicate that the attenuation of the sound pulses differs by less than 1% from values calculated for the zero‐order mode for frequencies up to 44 times the cutoff frequency for the first ’’nonplane’’ mode. Above that frequency, the measured values are less than those predicted by theory by an amount that is approximately proportional to the wavelength to the −3.1 power. In a smaller tube (5.72‐cm inside diameter) of similar construction, the high‐frequency deviation from theory is absent. The equipment has been used to measure absorption in moist air at relative humidities from 0% to 100%, and at temperatures from 0° to 100° F. The results of these measurements will be reported in a later paper.
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43.35.Ae Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in gases
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.35.Yb Ultrasonic instrumentation and measurement techniques

Ultrasonic studies of relaxation in dichloromethane and dibromomethane with high‐resolution Bragg reflection method

Kenshiro Takagi, Pak‐Kon Choi, and Katsuo Negishi

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 354-360 (1977); (7 pages) | Cited 2 times

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A method of high‐resolution Bragg reflection was utilized to measure ultrasonic velocity and absorption in liquid dichloromethane and dibromomethane near the room temperature, over the frequency range from 60 to 700 MHz. In both liquids, considerable velocity dispersion and decrease in α/f2 were observed and described with single relaxation frequencies, 192 MHz for dichloromethane and 393 MHz for dibromoethane at 20° C. The observed relaxation strengths were roughly consistent with the theoretical values calculated from the hypothesis of the vibrational relaxation associated with all but the lowest mode. The hypersonic velocities were measured in dichloromethane with the technique of Brillouin scattering. No dispersion was observed between 700‐MHz and gigahertz region. The second relaxation involved with the lowest mode was expected to be in the range higher than 10 GHz, and the volume viscosity was estimated to be ηv?3ηs, the shear viscosity.
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43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
43.35.Fj Ultrasonic relaxation processes in gases, liquids, and solids

Experiments in ultrasonic imaging for weld inspection

William R. Turner

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 361-369 (1977); (9 pages)

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Defects in butt welds were visualized against a dark field by obliquely insonifying the weldment and focusing the scattered ultrasonic energy onto an electronic sensor for conversion into a nonholographic visual display. Also shown are comparative images obtained by radiographic and ultrasonic Delta techniques. The artifacts encountered as a result of source side lobes, cylindrical collimation, multipath distortion, and wave interference are described together with the techniques for analyzing and suppressing them. The system appears adaptable to automatic object movement and computerized interpretation of data at rates approaching 10 000 resolvable image points per second.
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43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography

Variational solution for the reflection and transmission of waves at a material interface between waveguides

A. Bedford and A. L. Sorensen

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 370-374 (1977); (5 pages)

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A variational procedure is presented for the modal superposition solution of the reflection and transmission of steady‐state waves at a material interface between two elastic waveguides. As an example, the solution is applied to the reflection and transmission of waves at an interface between two elastic plates using the Rayleigh–Lamb modes.
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43.40.At Experimental and theoretical studies of vibrating systems
43.20.Mv Waveguides, wave propagation in tubes and ducts

Parametric excitations of linear systems having many degrees of freedom

A. H. Nayfeh and D. T. Mook

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 375-381 (1977); (7 pages) | Cited 3 times

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The method of multiple scales is used to analyze parametrically excited, linear systems having many degrees of freedom and distinct natural frequencies. Explicit second‐order expressions are obtained for the characteristic exponents which yield the transition curves. Various combination resonances are treated. The results are applied to the buckling of free‐clamped columns under the influence of sinusoidally varying axial loads.
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43.40.At Experimental and theoretical studies of vibrating systems
43.40.Cw Vibrations of strings, rods, and beams

Real‐time bispectral analysis of gear noise and its application to contactless diagnosis

Takuso Sato, Kimio Sasaki, and Yoichi Nakamura

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 382-387 (1977); (6 pages)

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Real‐time bispectral analyses of gear noises are carried out, intending to distinguish abnormal states from the normal one without stopping the machine. Firstly, a real‐time bispectral analyzer which consists of bandpass filters, multipliers, and integrators is constructed. Then, the noises of gears are analyzed. The results show that when scorings have been grown on the gear surfaces the moduli of bispectra of the nosies are reduced markedly comparing to those of normal state, while conventional spectral analysis fails to distinguish the difference. And it is shown that this fact can be used to diagnose the conditions of gear surfaces. Finally, a proper stochastic model of gear noises based on physical considerations as well as the spectral and bispectral characteristics obtained by our study, is proposed.
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43.40.Hb Random vibration
43.50.Ed Noise generation
43.55.Ka Computer simulation of acoustics in enclosures, modeling
43.50.Cb Noise spectra, determination of sound power

Rejection of flow noise using a coherence function method

J. Y. Chung

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 388-395 (1977); (8 pages) | Cited 5 times

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A method has been developed for rejecting transducer flow‐noise interference. The method makes use of coherence‐function relations between simultaneous pressure measurements at three transducers in the signal field and extracts from the flow‐noise background the power spectrum of the signal as received at each transducer. The signal in question can be periodic or stationary random. The coherence function relations are derived on the basis of a multivariate, random‐process model. The theory indicates that for a single source or for a group of completely coherent sources, the three transducers can be placed at arbitrary locations in the signal field. For a group of sources that are not completely coherent, the transducers must be located close together relative to the distance from the group. In any case, however, the flow noises at the transducers must be mutually independent. Successful results were obtained in laboratory tests of the method. In these tests a 10–15‐dB reduction in flow‐noise interference was attained. The method can also be used to reduce other types of noise such as instrument electronic noise.
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43.50.Nm Aerodynamic and jet noise
43.20.Rz Steady-state radiation from sources, impedance, radiation patterns, boundary element methods
43.50.Ed Noise generation

Evaluation of C‐weighted Ldn for assessment of impulse noise

Paul D. Schomer

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 396-399 (1977); (4 pages) | Cited 3 times

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Community response to impulsive noise, such as sonic boom, artillery fire, and other military ordinance, and quarry and mining operations, is currently a matter of great public interest. Recently, the EPA has proposed the of the C‐weighted day–night level to estimate community response to large amplitude single‐event impulsive noise. This measurement and its associated exposure criteria have been derived largely on the basis of existing community response to sonic boom data. Recent laboratory measurements of human reaction to artillery‐type noise, reported on herein, strongly support this C‐weighted measure.
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43.50.Ba Noisiness: rating methods and criteria
43.50.Qp Effects of noise on man and society
43.50.Sr Community noise, noise zoning, by-laws, and legislation

Directional characteristics of cylindrical receiving arrays with nonuniform hydrophone response

William C. Queen

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 400-403 (1977); (4 pages) | Cited 1 time

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In a recent paper [W. C. Queen, ’’The Directivity of Sonar Receiving Arrays,’’ J. Acoust. Soc. Am. 47, 711 (1970)] the problem of determining the directional characteristics of abitrary configurations of point‐source hydrophones was considered and the results given for the special case of a cylindrical array. It was assumed that the array was transparent and consisted of onmidirectional, uniformly weighted elements. In this paper, we extend these earlier studies to include both the effects of nonuniform weights as well as nonomnidirectional hydrophone response. The question of optimal weighting with respect to maximum directivity index is considered and closed‐form solutions obtained. These analyses are applied to the special case of an array formed on a cylindrical surface in a ring‐stave configuration and results given in the form of beam patterns and directivity curves. Included are the omnidirectional case as well as the special case where the hydrophones exhibit cardioid response functions.
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43.60.Gk Space-time signal processing, other than matched field processing
43.30.Vh Active sonar systems

Bispectral holography

Takuso Sato and Kimio Sasaki

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 404-408 (1977); (5 pages)

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In conventional holography, information at a hologram plane is obtained by taking the cross correlation between the signals at the points on the plane and a reference signal. In this paper we show that this information can also be obtained by using bispectral analyses of random signals detected at two points on the hologram plane, that is, the signal detected at a fixed point and the signal detected at scanning points on the same plane. The method, which uses this hologram and a conventional reconstrucion process and is named bispectral holography, has two special features: (i) it is completely free from additive Gaussian noises of any power spectra, and (ii) random signals, which have non‐Gaussian properties, can be used as the object illuminating signals. These properties may extend the application of holographic techniques. The theoretical aspects and some discussion of the method are presented.
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43.60.Gk Space-time signal processing, other than matched field processing

Auditory‐filter characteristics derived from direct‐masking data and pulsation‐threshold data with a rippled‐noise masker

T. Houtgast

J. Acoust. Soc. Am. Volume 62, Issue 2, pp. 409-415 (1977); (7 pages) | Cited 16 times

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The masker was ’’rippled noise,’’with a power spectrum (intensity on a linear frequency scale) shaped according to a sinusoidal function. The test signal was a pure tone. The masking effectiveness of the rippled noise depends on the position of its peaks and troughs relative to the test‐tone frequency, but this dependence decreases for high‐ripple densities (thus, for ripples with small peak‐to‐peak distances along the frequency scale). The results of masking experiments as a function of the position and the density of the ripple around the test‐tone frequency allow an estimation of the degree of auditory frequency resolution in terms of a filter characteristic. Several masking paradigms were applied: direct masking, forward masking, and pulsation threshold. It was found that the degree of frequency resolution estimated both from pulsation‐threshold data and from forward‐masking data is substantially higher than that estimated from direct‐masking data. The difference is about a factor of two when expressed in terms of the bandwidth of the auditory filter. This difference is interpreted as reflecting spectral sharpening by lateral suppression which apparently manifests itself only in threshold measurements where masker and test tone are presented nonsimultaneously.
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43.66.Dc Masking
43.66.Ba Models and theories of auditory processes
43.66.Cb Loudness, absolute threshold
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