摘要:

Most steady‐state methods for measuring the noise power of equipment and the sound absorption in a room depend on knowing the sound‐power output of a standard source. But the output of any sound source depends in principle on the radiation impedance presented to it, and this impedance is likely to change with the location of the source, as well as with changes in the amount and distribution of absorptive material in the room. Moreover, no generally accepted method has been available for measuring the sound‐power output directly. For these reasons, the validity of steady‐state methods has been under suspicion for some time. This paper comments on recent progress in making steady‐state methods respectable and calls attention to some remaining problems.

ISSN:0001-4966    

DOI:10.1121/1.1914355

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

In the past we have known, from first principles, that estimates of the sound power radiated from large machines, based on measurements of only the pressure near the source, are likely to be wrong. There has been substantial progress, during the last few years, in our understanding of how serious the errors may be and also how to minimize the error by suitable choice of measurement technique. This paper summarizes these conclusions briefly and suggests possibilities for further study.

ISSN:0001-4966    

DOI:10.1121/1.1914356

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

An extensive noise measurement survey was made in Medford, Massachusetts, suburb of Boston, during March, April, and May 1971, to assess the importance of transportation noise in a typical urban community, and to obtain validation data for a mathematical model developed to simulate such noise levels. Noise measurements were made at 49 locations distributed uniformly across the community, with continuous 24‐h measurements at five of the locations. The median noise level over the entire community was 54 dBAduring the morning rush hour, and 51 dBAduring the midday period. Noise levels were influenced primarily by highway traffic, with a major highway arterial corridor producing the highest noise levels in the community.

ISSN:0001-4966    

DOI:10.1121/1.1914357

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Sound‐absorption spectra of three chemical systems (I:CO2/H2O, II:Mg++/CO2/H2O, III:Mg++/SO4=/CO2/H2O) are simulated on a computer using available, and estimated kinetic and thermodynamic data. System III is used as a simplified model for seawater and is described by a nine‐state mechanism. Using the chemical‐relaxation theory described, six nonzero relaxation times are obtained for III. The relaxation frequency and absorption amplitude of two of the times agree reasonably well with oceanic data, which indicate excess sound absorption in the 1–5‐ and 150‐kHz frequency regions.

ISSN:0001-4966    

DOI:10.1121/1.1914358

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A method is presented for determining the elastic constants of general anisotropic solids. The methods utilizes a numerical parameter estimation technique to determine the values of the elastic constants such that the phase velocitites (as a function of wavenumber) calculated from theory fit (in a least‐square sense) those obtained experimentally.

ISSN:0001-4966    

DOI:10.1121/1.1914310

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A technique is presented for transforming certain acoustical boundary value problems in subsonic moving medium to a problem involving a stationary medium. The method is described by discussing the Sommerfeld problem of diffraction of a plane wave by a half plane immersed in a subsonically moving medium. It is shown that additional sources are induced by the flow at a leading edge impinged by a plane wave, while a trailing edge only gives rise to the usual diffracted wave. The flow also convects the geometrical acoustics part of the field. A transformation applied to the supersonic diffraction problems yields a unique reference problem, which is solved by Fourier transform methods. The pressure field is decomposed in a sum of a geometric acoustics field and a supersonic diffracted wave showing some remarkable similarities with the subsonic solution.

ISSN:0001-4966    

DOI:10.1121/1.1914311

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The nonlinear differential equations and boundary conditions in small‐field variables, for small fields superposed on large static biasing states, are obtained from general rotationally invariant nonlinear electroelastic equations derived previously. The small‐field equations are directly applicable in the consistent description of parametric effects in high‐coupling piezoelectric materials in terms of the fundamental material parameters. The application of the equations to homogeneously polarized ferroelectrics reveals that in the linear limit the electroelastic equations are identical with the equations of linear piezoelectricity for the symmetry of the polarized state. The influence of a thickness directed homogeneous biasing electric field on the thickness vibrations of a piezoelectric plate, to second order in the biasing field, has been determined. To first order in the biasing field the results indicate that the effective fifth‐rank tensor assumed in earlier quasilinear work on the subject did not have correct symmetry properties because the influence of the homogeneous static deformation under the biasing field was ignored.

ISSN:0001-4966    

DOI:10.1121/1.1914312

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The response of beams and plates to fluctuating loads with high mean values is considered. The static deformation is obtained separately; the vibration of the statically deformed structure is then discussed in terms of the induced static in‐plane membrane stresses. It is shown that the response of a deformed plate can be predicted by defining an effective uniform tension. Simple expressions are obtained for the loss factor in terms of the impedance of the supports of the beam or plate. Expressions are given for the changes of modal resonance frequencies and loss factors due to the tension, with the assumption of constant boundary impedance. The predicted changes in loss factors agree quite well with some previously published experimental data for very thin plates. The changes for most cases of practical interest, however, are small.

ISSN:0001-4966    

DOI:10.1121/1.1914313

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Pressures are determined in a layer of fluid bounded by two parallel elastic plates, one of which is harmonically excited at a point. The response of the coupled plate‐fluid system is obtained for infinitesimal displacements in both the plate and the fluid. The pressures are obtained through a numerical integration of the inverse Hankel transform along an approximation to the steepest descent path. Some numerical results obtained for frequencies both above and below the coincidence frequency are given. These show a complex spatial variation in pressure in addition to that on the scale of the wavelength in the fluid.

ISSN:0001-4966    

DOI:10.1121/1.1914314

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The distortion of longitudinal pulses in slightly curved elastic rods is discussed in terms of an elementary theory in which the effects of rotary inertia and radial shear are neglected. Moreover, when the wavelength of the pulse is long enough, practically all the bending effects can be justifiably neglected. The experimentally observed strain—time curve produced at one end of a curved brass‐alloy rod by the impact of a pellet shot from an air gun is compared with that obtained theoretically using Fourier synthesis. Good agreement is found between theory and experiment. The main shape of the pulse travelling down the rod is retained even after the rod has turned 90° with respect to the initial direction.

ISSN:0001-4966    

DOI:10.1121/1.1914315

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP