摘要:

In this paper two new algorithms for computing annth‐order Hankel transform are proposed. The algorithms are based on characterizing a circularly symmetric function and its two‐dimensional Fourier transform by a radial section and interpreting the Hankel transform as the relationship between the radial section in the two domains. By utilizing the property that the projection of a two‐dimensional function in one domain transforms to a radial section in the two‐dimensional Fourier transform or inverse Fourier transform domain, several efficient procedures for computing the Hankel transform exploiting the one‐dimensional FFT algorithm are suggested.

ISSN:0001-4966    

DOI:10.1121/1.384765

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A technique for predicting the expected number of shipping‐produced lines in an observed underwater acoustic ambient noise spectrum is described. The method is based on a mathematical model which includes the sonar equation, available information on the acoustic signatures of individual ships, and data concerning the oceanic distribution of shipping. The average number of detectable spectral lines in a given frequency band (line density) is shown to depend on the location of the sensor, sea state, and frequency. The line density also depends on the parameters of the sensor system. The results of calculations based on the model imply, for example, that the spectra observed with more directive receivers will contain more spectral lines. The results and methods described have application to passive sonar systems engineering.

ISSN:0001-4966    

DOI:10.1121/1.384766

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

For 80 male subjects (age 60–90) and 30 female subjects (age 71–89) the monaural Speech–Reception Threshold (SRT) for sentences was investigated under five reverberation conditions at a constant noise level. The reverberation times used were between 0 and 2.3 s. The noise, with the long‐term average speech spectrum, had a level of 52.5 dBA. Each subject was assigned to one of several subgroups formed on the basis of the maximum reverberation time at which the subject was still able to understand the sentences correctly. The mean SRTs and the standard deviations are given, per subgroup, as a function of reverberation time. It is shown that, for each subgroup, the SRT in different reverberant sound fields can be expressed as a single number, namely the required Speech Transmission Index (STI) as introduced in room acoustics by Houtgast and Steeneken [Acustica 28, 66–73 (1973)]. Furthermore, it is shown that a model of SRT as a function of noise level, developed by Plomp [J. Acoust. Soc. Am. 63, 533–549 (1978)], can be combined with the STI model and can thus include the effect of reverberation.

ISSN:0001-4966    

DOI:10.1121/1.384767

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The theory of higher order modes in circular ducts is reviewed and applied to expansion chambers. Numerous schemes have been proposed for use in labeling the various higher order modes in a circular duct. This has led to confusion and, in at least one case, to erroneous descriptions of the higher order modes. In an attempt to solve this problem, a specific approach, analogous to that used in rectangular ducts, is recommended that has geometric clarity and elegance. The cutoff frequencies for these various modes are discussed with respect to propagation in an expansion chamber. Incomplete and misleading statements in the literature concerning the calculation of cutoff frequencies are reviewed. Higher order mode propagation through an expansion chamber is analyzed for various inlet and outlet locations, and experimental results presented. The interaction between plane wave and higher order mode effects is discussed.

ISSN:0001-4966    

DOI:10.1121/1.384768

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

An extensive sample of North Carolina industrial audiometric test data has been compiled. The sample includes data from several different types of industrial environments, with the size of the industries represented ranging from less than fifty to over eight thousand employees. The total population considered is in excess of 14 000 employees. The data are examined using analytical techniques developed over the past six years while investigating the effectiveness of industrial hearing conservation programs. One of the findings is significant differences in the initial hearing threshold levels by race and sex. A second observation is differences by race and sex in the change in hearing levels with time. It is concluded that the hearing levels of industrial employees differ significantly by race and sex. The differences are of such magnitude that meaningful evaluations of industrial audiometric data bases are not possible unless the race and sex compositions of the population are considered.

ISSN:0001-4966    

DOI:10.1121/1.384769

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A technique for obtaining a uniformly valid solution to the problem of nonlinear propagation of surface acoustic waves excited by a monochromatic line source is presented. The method of solution is an extension of the method of strained coordinates wherein both the dependent and independent variables are expanded in perturbation series. A special transformation is proposed for the independent variables so as to make the expansions uniformly valid and also to satisfy all the boundary conditions. This perturbation procedure, carried out to the second order, yields a solution containing a second harmonic surface wave whose amplitude and phase exhibit an oscillatory variation along the direction of propagation. In addition, the solution also contains a second harmonic bulk wave of constant amplitude but varying phase propagating into the medium.

ISSN:0001-4966    

DOI:10.1121/1.384663

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Based on a fully Galilean electrodynamics of dielectric deformable bodies, a completely deductive derivation of the coupled, dynamical, electromagnetic, electroacoustic, and energetic equations and constitutive equations for elastic, pyroelectric, ferroelectric dielectrics accommodating viscosity and dielectric‐relaxation phenomena is presented. Of necessity the theory is first constructed in a fully nonlinear framework even though applications to signal processing are envisaged. Then a linearization is performed by Lagrangian variation about an initial ferroelectric state in which there exist no strains, but there are present both stresses and local electric field as well as an initial electric polarization. The latter provokes a breaking of the ideal symmetry of the material, so that finally linearized coupled electroacoustic and heat‐propagation equations are deduced on which can be based the study of coupled acoustic‐soft optic modes in ferroelectrics of the BaTiO3‐type. No thermodynamical restriction other than the fulfillment of the second principle of thermodynamics is considered, so that dissipative processes such as viscosity and dielectric relaxation appear naturally on an equal footing with elasticity, piezoelectricity, thermoelasticity, and pyroelectricity.

ISSN:0001-4966    

DOI:10.1121/1.384770

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Based on a fully Galilean electrodynamics of ferroelectric dielectric deformable bodies and the equations for weak fields linearized about an initial rigid‐body ferroelectric state with hexagonal symmetry deduced in a previous paper (in which a symmetry breaking was exhibited), a rather complete study of coupled, dispersive, and attenuated bulk wave‐propagation modes is presented. Apart from usual optic modes, resonance couplings and repulsion of branches for acoustic modes and polaritons are exhibited for various directions of propagation (longitudinal, orthogonal, and arbitrary settings of the bias polarization field). A birefringence effect for polaritons and an acoustical activity are placed in evidence. In addition to the analytical study which leans on the use of small coupling parameters in order to allow for a manageable discussion of the dispersion behavior for both nondissipative and dissipative processes, and to illustrate these theoretical results, numerical estimates and plots of the most interesting coupling effects are given for a test material such as ferroelectric barium titanate.

ISSN:0001-4966    

DOI:10.1121/1.384771

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A new technique for the measurement of the plane‐wave reflection coefficient of a horizontally stratified ocean bottom is described. It is based on the exact Hankel transform relationship between the reflection coefficient and the bottom reflected field due to a point source. The method employs a new algorithm for the numerical evaluation of the Hankel transform which is based on the ’’projection‐slice’’ theorem for the two‐dimensional Fourier transform. The details of the algorithm are described in the companion paper. Although the algorithm is applied to the case of an isovelocity ocean, the general theory for measuring the plane‐wave reflection coefficient in a refracting ocean is developed. The technique provides information about the reflection coefficient, not only for real incident angles, but also for complex angles, thus potentially providing substantial additional structural information about the bottom. The method is shown to yield excellent results with synthetically generated data for the cases of a hard bottom and slow isovelocity bottom.

ISSN:0001-4966    

DOI:10.1121/1.384772

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The effects of receiver and source motion are examined for a cw signal transmitted through a deep ocean at ranges of tens to hundreds of km. Ray theory is used to develop results for multipath signals consisting of a wide variety of combinations of SRBR and RSR ray arrivals. A bilinear sound‐speed profile is assumed for which bottom and surface sound speeds need not be equal, and receiver and source are chosen to move on the surface. Numerical results are presented using time‐dependent total‐field expressions, valid for suitably limited time intervals. Analytical expressions are developed which closely approximate numerical results and which provide general conclusions regarding acoustical effects of receiver–source motion at different ranges. When only SRBR rays can occur, total fields are shown to have significantly different characteristics depending on range, in contrast to the virtually range‐independent total fields which contain RSR rays. When total‐field phase is interpreted in terms of an approximate Doppler shift, the frequency change shows relatively wide variations with both range and total‐field composition. Thus, a given frequency shift at the receiver may be the result of considerably different receiver–source directions and speeds.

ISSN:0001-4966    

DOI:10.1121/1.384719

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP