摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.4734346

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Abstract not available.

ISSN:0001-4966    

DOI:10.1121/1.417254

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.417316

出版商:Acoustical Society of America    

年代:1996

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:10.1121/1.417317

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The perception of pitch forms the basis of musical melody and harmony. It is also among the most precise of all our human senses, and with imagination, this precision can be used experimentally to investigate the functioning of the auditory system. This tutorial presents auditory demonstrations from the zoo of pitch effects: pitch shifts, noise pitch, virtual pitch, dichotic pitch, and the pitches of things that are not there at all. It introduces models of auditory processing, derived from contemporary psychoacoustics and auditory physiology, and tests these models against the experimental effects. It concludes by describing the critical role played by pitch in the important human ability to disentangle overlapping sources of sound.

ISSN:0001-4966    

DOI:10.1121/1.417248

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The relation between the wavefront speed and the group velocity concept is studied in this work. The relationship between the more well‐known velocity concept named as the phase velocity and the speed of propagation of a front of an acoustic pulse is discussed. This is of interest since it concerns transient wave propagation and is, in general, not well known. The form and properties of a pulse can be obtained by means of a Fourier integral and estimates based on quantities derived for monochromatic waves, such as the phase velocity, can be severely misleading and confusing. The wavefront velocity is defined as the high‐frequency limit of the phase velocity. This quantity can be far less than the value of the phase velocity for finite frequencies which for example is the case for bubbly fluids. Then the group velocity concept is discussed, which was introduced in order to characterize the propagation of water waves of essentially the same wavelength. However, more confusion occurs in that it is sometimes believed that a wavefront is propagating with the group velocity (a limit process not mentioned) since it can be related to the propagation of energy. This interpretation of energy propagation is based on sinusoidal waves and involves time as well as space averages and is not applicable for pulses. However, by means of the expression for the group velocity given by Stokes it is shown that the speed of a wavefront can be found from the group velocity at a limiting high frequency. This result can be understood geometrically from the definition of the group velocity given by Lamb which is conservation of wavelength. A wavefront is a discontinuity and limiting short wavelengths will be found there.

ISSN:0001-4966    

DOI:10.1121/1.417249

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

For acoustic applications in which there is a ‘‘preferred direction of propagation’’ (the axial direction) it is useful to arrange the two‐way and one‐way wave equations into the same matrix‐vector formalism. In this formalism, axial variations of the wave vector are expressed in terms of lateral variations of the same wave vector. The two‐way wave vector contains the field quantities pressure and velocity (axial component only), whereas the one‐way wave vector contains waves propagating in the positive and negative axial direction. By exploiting the equivalent form of the two‐way and one‐way matrix‐vector equations, it appears to be possible to derive two‐way and one‐way reciprocity theorems that have an equivalent form but a different interpretation. The main differences appear in the boundary integrals for unbounded media, in the contrast terms, and (for the correlation‐type theorems) in the handling of evanescent waves.

ISSN:0001-4966    

DOI:10.1121/1.417250

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

In theory, when an incident plane wave strikes a perfectly reflecting periodic surface, the resulting scattered field is comprised of a discrete spectrum of plane waves. Upon applying Dirichlet boundary conditions to the surface, one can construct what is referred to as a spectral‐coordinate (SC) formalism for the scattered amplitudes. A Fredholm integral equation of the first kind is involved, and the integration is performed over a single surface period. Since the Rayleigh approximation is not utilized in the construction of this formalism, one may use this method to determine the exact scattered field above the highest surface excursion. The problem will be approached numerically by directly discretizing the mixed SC representation, then solving the system using a pseudoinverse SVD technique. It is very important to note that the scattered amplitudes are obtained without constraining the value of normalized energy. This particular approach is unique. It differs from others in which the discretizations are implemented entirely in coordinate space or entirely in spectral (i.e. Bragg) space. It is thus an additional computational tool designed for cases when a mixed representation is appropriate. Although this numerical scheme has been developed for arbitrary periodic surfaces, the results presented in this paper are restricted to sinusoidal surfaces. Particularly interesting features of this approach are the high level of accuracy attained for near‐grazing incident fields and the maintenance of stability even for badly conditioned systems of equations.

ISSN:0001-4966    

DOI:10.1121/1.417326

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

The elastic wave field and the excitation mechanism of the surface waves in multilayered elastic solid media are studied in this paper. On the basis of Abo‐zena [Geophys. J. R. Astron. Soc.58, 91–105 (1979)] and Menke [Geophys. J. R. Astron. Soc.59, 315–323 (1979)], the elastic wave field is further investigated in theB,P,Ccoordinate system. The so‐called new type of propagator matrix introduced by Menke to avoid loss of the precision problem is improved. It presented an important result and some new properties. The dispersion characteristics and excitation mechanisms of the surface waves (Rayleigh and Love waves) are also investigated via numerical simulation. The excitation intensities of the surface waves strongly depend on the frequency range of the source. The source frequency should be controlled in a proper range to effectively excite the surface waves. Two quantities, β1(the ratio ofBtoPcomponents of displacement) and β2(the ratio ofBtoPcomponents of stress), are defined for the Rayleigh wave. It is found that β1and β2are sensitive to the material property of the medium and the layered geometry, and they are two important physical quantities for exploring the structures of the interfaces and the velocity distributions of layers under the free surface. The relative error in estimating the thickness of each medium by β1and β2is less than 10%. The effects of the thickness of each layer of media and other factors on the dispersion characteristics of Rayleigh and Love waves and the values of β1and β2are also analyzed.

ISSN:0001-4966    

DOI:10.1121/1.417329

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP

摘要:

Previous applications of lumped parameter models to acoustic radiation problems assume that the characteristic dimension of the vibrating structure is small in comparison to the acoustic wavelength. In this paper, the frequency range of the lumped parameter model is extended by dividing the surface of the structure into elements and characterizing the amplitude of the radiation from each element by its volume velocity. The model is derived by truncating all but the lowest‐order (monopole) terms of a multipole expansion for the acoustic power output. The multipole expansion differs from those derived previously because it is based on elemental quantities rather than global quantities. By comparing the full multipole expansion for the power output to the lumped parameter model, the error in the lumped parameter model as a function of the acoustic and structural wavelengths (kandK) and the size of the largest surface element (L) is determined. This approach is general and provides a means of determining bounds on the accuracy of any lumped parameter model based on elemental quantities. For example, the analysis predicts that when the overall volume velocity of a vibrating structure is nonzero, the maximum possible error in the lumped parameter model is equal toC(kL)(KL), whereCis a constant. Likewise, when the overall volume velocity of a vibrating structure is zero, the model predicts that the maximum possible error in the lumped parameter model is equal toC′(KL)(L/R12), whereC′ is another constant, andR12is the largest distance between any two points on the structure. The results of the analysis show that it is desirable to formulate acoustic models in terms of elemental volume velocities, because the power output predicted by any such model converges absolutely to the correct solution as the element mesh is refined.

ISSN:0001-4966    

DOI:10.1121/1.417330

出版商:Acoustical Society of America    

年代:1996

数据来源: AIP