摘要:

An overview of the effects of noise on people as can be determined from the scientific literature is presented. Only audible noise is considered and no attempt is made to describe the extent of the noise problem in terms of the number of people affected or in terms of social and economic costs. Rather, emphasis is placed on describing and classifying the adverse effects and relating them in a general way to the intensive and temporal properties of audible noise. For simplicity, the intensive dimension of the noise is usually given as theA‐weighted sound level and detailed descriptions and evaluations of various acoustical measurements are for the most part avoided. The effects of noise are classified as auditory, general psychological, and sociological, or as general physiological. A summary is included.

ISSN:0001-4966    

DOI:10.1121/1.1903322

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Weak plane discontinuities carrying disturbances in orientation can propagate in liquid crystals of nematic type. It is shown that these waves decay exponentially in time, and the rate of decay is determined. It is found that this rate of decay depends on the angle between the direction of propagation and the orientation of the material, and that in most liquid crystals the waves will decay rapidly.

ISSN:0001-4966    

DOI:10.1121/1.1903323

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The method of multiple scales is used to analyze the wave propagation in two‐dimensional hard‐walled ducts with sinusoidal walls. For traveling waves, resonance occurs whenever the wall wavenumber is equal to the difference of the wavenumbers of any two duct acoustic modes. The results show that neither of these resonating modes could occur without strongly generating the other.

ISSN:0001-4966    

DOI:10.1121/1.1903324

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The transition matrix formulation of acoustic scattering given previously by Waterman [J. Acoust. Soc. Am.45, 1417 (1969)] is extended to the case of an arbitrary number of scatterers. The resulting total transition matrix is expressed in terms of the individual transition matrices and in terms of functions which describe a translation of the origin for the spherical (and cylindrical) wave solutions of Helmholtz equation. Explicit formulas are given for the case of two and three scatterers and the (finite) iteration scheme for the general case is described. Some numerical calculations concerning some aspects of the scattering from two spheres are also reported.

ISSN:0001-4966    

DOI:10.1121/1.1903325

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The infrasonic (0.15–30 Hz) responses of several nitrogen‐saturated porous models are measured experimentally. Within the frequency range covered, the results verify a theory proposed earlier by Smith and Greenkorn [J. Acoust. Soc. Am.52, 247–253 (1972)]. Results of a similar response study of water‐filled porous media show the effect of dynamic coupling between the solid and fluid phases, the excitation of which precludes agreement with a rigid frame theory. However, the results significantly indicate an approach to a condition of zero coupling at very low frequencies and/or low permeabilities.

ISSN:0001-4966    

DOI:10.1121/1.1903326

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

A theory is developed to describe the transient pressure response of rigid, isotropic, and uniform porous media, including the higher‐order effects of viscous dissipation and thermal conduction. A transfer function which is transcendental in the Laplace time‐image variable is obtained for the system. For the case of sinusoidal excitation, the results reduce to those given earlier by Smith and Greenkorn [J. Acoust. Soc. Am.52, 247–253 (1972)]. Rational approximations are developed for the regime limiting cases of viscosity (long transient times or low frequencies) and inertia (short transient times or high frequencies), and are used to derive the system step and impulse responses.

ISSN:0001-4966    

DOI:10.1121/1.1903327

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

An integral equation technique is employed to obtain eigenvalues and eigenmodes of the homogeneous Holmholtz equation for a two‐ or three‐dimensional closed region of arbitrary shape with arbitrary first‐order homogeneous boundary conditions. The method is described for general (i.e., nonseparable) geometries, with a discussion of the simplification introduced by having a separable geometry given in an Appendix. A numerical example is given for a nonseparable geometry, i.e., a two‐dimensional right triangle of arbitrary enclosed angle with Neumann boundary conditions. Results for the special case of an isosceles right triangle agree very well with a known analytical solution.

ISSN:0001-4966    

DOI:10.1121/1.1903328

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

A study of the influence of fluid motion on the emission of higher‐order acoustic modes from a stationary source in a duct is presented. In particular, the ratio between the upstream and downstream higher‐order mode amplitudes is calculated. This ratio has been measured for the (1,0) mode in a rectangular duct at flow velocities from zero to 0.25 times the sound speed. The frequency dependence has also been measured at a fixed flow Mach number of 0.1.

ISSN:0001-4966    

DOI:10.1121/1.1903329

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The effects of sound‐speed variations, produced by an assumed Rossby wave, on ray geometry, travel time, and spreading loss are investigated for an ocean region such as the Sargasso Sea. A horizontally discretized sound‐speed model is used, and a bottomed source and receiver are assumed. The phase of the total acoustic field is examined, and it is found that the major effects of the Rossby wave arise through travel‐time variations. The period of the phase is that of the Rossby wave, and a formula for maximum phase variation is presented. In an example, the Eleuthera‐Bermuda area is modeled approximately, and the total‐field phase variation is examined as a function of Rossby wave propagation direction. The phase variation and period are highly sensitive to this direction, to the choice of parameter values, and to source and receiver depth.

ISSN:0001-4966    

DOI:10.1121/1.1903330

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The dependency of the magnitude of acoustic variability in the open ocean on parameters characterizing the medium and the acoustic system itself is examined on the basis ofin‐situmeasurements of transmission loss and concurrent environmental and meteorological conditions. The spectrum of conditions considered consists of frequencies of 2.2 kHz, 8 kHz, 16 kHz, and 25 kHz; transmission ranges up to 24 000 yds; source and receiver depths up to 500 ft; and the environmental conditions experiences in the North Atlantic Ocean. Acoustic variability is observed to depend upon frequency in a nonmonotonic manner; to increase with time between transmissions for values of Δtup to approximately 40 min; to be a maximum at a range of approximately 4000 yds; to decrease significantly at sea state 4 and above; to depend upon the path that the energy travels; and to be higher when encountering the thermocline than when transmission is entirely in the mixed layer.

ISSN:0001-4966    

DOI:10.1121/1.1903331

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP