摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.421266

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.421255

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The purpose of these acoustical patent reviews is to provide enough information for a Journal reader to decide whether to seek more information from the patent itself. Any opinions expressed here are those of the reviewers as individuals and are not legal opinions. Printed copies of United States Patents may be ordered at $3.00 each from the Commissioner of Patents and Trademarks, Washington, DC 20231. Patents are available via the Internet athttp://www.uspto.gov.

ISSN:0001-4966    

DOI:10.1121/1.421256

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

This paper describes the theory of sound propagation in a toroidal waveguide with driven walls. This configuration has the advantage of simulating a tube of infinite length. The general solution for the velocity potential is derived in terms of an arbitrary function which represents the angular dependence of the disturbance of the driving wall. Two different cases are considered. The first is a toroid with the wall driven at a single angular position. The second case is a toroid with walls driven such that a traveling wave is generated in the wall with a controllable wave number and frequency. A traveling wave is produced inside the toroid when the circumference of the toroid is a whole number of wavelengths for the wave in the wall. The amplitude of the traveling wave is a function of the intrinsic speed of sound in the medium inside the toroid. A device we call anacoustitronwas constructed to verify the results of the latter case. Experimental results agree well with those predicted by theory.

ISSN:0001-4966    

DOI:10.1121/1.423231

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

A model of pitch perception is presented involving an array of delay lines and inhibitory gating neurons. In response to a periodic sound, aminimumappears in the pattern of outputs of the inhibitory neurons at a lag equal to the period of the sound. The position of this minimum is the cue to pitch. The model is similar to the autocorrelation model of pitch, multiplication being replaced by an operation similar to subtraction, and maxima by minima. The two models account for a wide class of pitch phenomena in very much the same way. The principal goal of this paper is to demonstrate this fact. Several features of the cancellation model may be to its advantage: it is closely related to the operation of harmonic cancellation that can account for segregation of concurrent harmonic stimuli, it can be generalized to explain the perception of multiple pitches, and it shows a greater degree of sensitivity to phase than autocorrelation, which may allow it to explain certain phenomena that autocorrelation cannot account for.

ISSN:0001-4966    

DOI:10.1121/1.423232

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The scattering by a pair of spatially disjoint local regions of complex (multiscale) stiffness heterogeneity in an unbounded thin linearly elastic plate is investigated. Issues of the mutual interaction of the spatially disjoint scatterers and its manifestation within a homogenized, or effective, formulation governing large scale response fields are the focus. It is shown analytically and numerically that while one must incorporate scatterer/scatterer coupling for estimating the large scale response field, one can neglect this coupling in estimating the effective measures for describing the scatterers.

ISSN:0001-4966    

DOI:10.1121/1.421267

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The conventional formulation of geometric acoustics in the presence of inhomogeneous (spatially varying) absorption is examined. This formulation is found to fail under conditions of multipath propagation, because interference between ray paths is not taken into account when the absorptive losses are calculated. The example of high-frequency attenuation due to a surface bubble layer is studied, and Weston’s correction term is discussed.

ISSN:0001-4966    

DOI:10.1121/1.421268

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

A method is proposed for solving the wave diffraction problem by employing a system ofNspace-localized inhomogeneities in a longitudinally homogeneous waveguide. The method combines integral equations and eigenfunction methods. As an illustration of this method, acoustic diffraction is calculated from a system ofN,different, parallel cylinders arbitrarily placed in a liquid layer. The problem is reduced to a system of2Nintegral-functional equations relative to fields excited in elastic bodies and sources of scattered waves on the surface of the cylinders. Standard methods may be used for solving the systems of equations. Numerical solutions are found for various versions of the system of elastic cylinders(N=1,2)in a liquid layer with perfectly “soft” and “hard” walls. The method allows: (1) the calculation of the scattering matrix for reflected and transmitted waves with any given accuracy; (2) the construction of the amplitude-frequency and the phase-frequency characteristics for the matrix elements; and (3) the calculation of the distribution of field sources on the surface of each cylinder and the scattered wave field both in the near and far zones.

ISSN:0001-4966    

DOI:10.1121/1.421269

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The acoustic resonances of a submerged fluid-filled cylindrical shell are analyzed as the shell cross section is deformed from circular to elliptical geometry. A schlieren visualization system is used to image standing wave fields within insonified water-filled shells of different eccentricities, and to locate the resonance frequencies of the fluid column. The acoustic behavior of elliptical cavities with infinite and finite surface impedances are modeled and the theory used to predict the resonance frequencies of the fluid column and calculate the pressure distribution in the acoustic field. As the symmetry of the circular shell is broken by deforming it to the more general ellipse the resonance spectrum changes; mode splittings and level crossings are observed as the eccentricity increases. The experimental observations of resonance patterns and frequency variation are in good agreement with the theoretical predictions.

ISSN:0001-4966    

DOI:10.1121/1.421270

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

A method is described for assessing the precision of wavefront direction-of-arrival (DOA) estimates made by acoustic arrays. Arrays operating in turbulent atmospheric boundary layers are considered. The method involves calculating the Cramer–Rao lower bound, which describes the best obtainable DOA precision (performance) for a given array and environment. For simplicity, it is assumed that the source is monochromatic, and multipath effects are not considered. The predicted performance bounds are found to degrade with increasing propagation distance, increasing frequency, and increasing turbulence strength. Performance predictions using several different three-dimensional turbulence models are compared: isotropic and anisotropic Gaussian models, the von Kármán model, and the Kolmogorov model, with the last in both intermittent and nonintermittent forms. When array performance is limited by turbulence (as opposed to background noise), the turbulence model strongly affects the calculated performance bounds. The results also suggest that degradation in DOA estimates results primarily from shear-generated, small-scale fluctuations in the wind velocity. Large, boundary-layer-scale eddies may still play a significant indirect role by driving intermittent episodes of high wind shear.

ISSN:0001-4966    

DOI:10.1121/1.421271

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP