摘要:

A very small condenser microphone has been developed which exploits materials and methods of construction only recently made available by the post‐war developments in plastics. These techniques have made possible a microphone with extremely regular voltage amplitude and phase responses as functions of frequency and with a reasonably high sensitivity. An analysis is given for the resonance frequencies of a circular membrane stretched over a closed cavity with its center fixed over a small area.

ISSN:0001-4966    

DOI:10.1121/1.1908320

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

A systematic determination of the electromechanical coupling coefficientkhas been made for Fe‐Al alloys containing aluminum percentages between 12 and 14 by weight and annealed at temperatures between 600°C and 1100°C. For annealing temperatures in the neighborhood of 1000°C,k2is about equal to 0.05 and is nearly independent of composition, a result in agreement with earlier measurements of Masumoto. For lower annealing temperatures,k2becomes sensitive to composition, the highest value measured being equal to 0.12 for an alloy containing 12.3% Al and annealed at 650°C. In all cases eddy current losses are lower for Fe‐Al than for soft annealed “A” nickel.

ISSN:0001-4966    

DOI:10.1121/1.1908322

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

A complete set of the elastic, piezoelectric, and dielectric constants of polarized barium titanate ceramics is presented. The various electromechanical coupling factors, as derived from the piezoelectric equations, and their numerical values are also given. The determination of the elastic and piezoelectric constants using the resonant method applied to small bars, square plates, and disks is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1908324

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The theory for a plane wave method of measurement of acoustic impedance in a tube is worked out. The effect on the measurement of irregularities in the surface of the sample has also been investigated. It is shown that the measured impedance differs from that of the average impedance evaluated at the surface of the specimen. A number of recommendations for the method of preparation of a sample have also been given.

ISSN:0001-4966    

DOI:10.1121/1.1908326

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The use of a high impedance acoustical load for the type B diaphone is capable of raising the efficiency of the fog horn system to values of 10 to 16% for normal operating pressures. The high impedance is provided by a resonant exponential or catenoidal horn. To provide the high degree of frequency stability required by highQresonant loads the mechanical impedance of the diaphone is reduced to permit it to lock in with the horn frequency. The reduction of the mechanical impedance is achieved by reducing the mass of the piston through the use of aluminum and reducing and stabilizing the frictional forces by using a central shaft for supporting the piston instead of allowing it to float in the liner. The resulting frequency stability is such that the efficiency under field conditions equals that obtained in the laboratory. An incidental benefit arises from the fact that the horns are smaller and made of aluminum reducing the weight by a factor of six.

ISSN:0001-4966    

DOI:10.1121/1.1908328

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The Fourier series solution for the radiation field of a circular pressure ring is applied to the synthesis of a sound field expressed in the form of a Tchebyscheff polynomial. This leads to an exact solution in closed form for the amplitude and phase of excitation of point source elements on a circle when the main lobe width of the radiation pattern, the side lobe suppression, and the array circle diameter are specified. Calculations are carried out for two sample beam patterns to show the effects of different choices of array circle diameter and number of point source elements.

ISSN:0001-4966    

DOI:10.1121/1.1908330

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Calculations and measurements are reported of the summation and difference frequency components which are scattered from the interaction region of two sound beams in air intersecting each other at right angles.

ISSN:0001-4966    

DOI:10.1121/1.1908332

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

A method is presented which can be used for the calculation of the distribution of energy reflected from irregular surfaces. The formulation is useful for the first boundary value problem and can be used in either two‐ or three‐dimensional problems with any given incident field. The solution is reduced to quadrature with negligible error when the average square of the slope of the reflecting surface is small and when the wavelength of the incident radiation is not small compared with the displacement of the surface from its average value. A numerical example is worked, the sinusoidal surface, and is compared with experiment and with a method due to Rayleigh. It is found that the Fourier transform method is preferable to previous methods, notably those which can be classified physical optics (such as Rayleigh's), since the error in the transform method is of second order in the surface slope whereas the error in previous methods is of first order in the same quantity.

ISSN:0001-4966    

DOI:10.1121/1.1908334

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The pressure fluctuations exerted on a flat plate by a turbulent boundary layer flow are investigated. The approximate dependence of the mean‐square intensity, spatial scale, and frequency scale on Mach number and distance from transition point are estimated through the use of similarity arguments. The wave number spectrum of the pressure fluctuation distribution over the surface of the plate is expressed in terms of transforms of two‐point velocity correlations and expressions are derived for the driving force exerted on a rectangular piston set in the surface of the plate. It is found that the integral over the boundary surface of the two‐point quadratic correlation function of the pressure fluctuation should vanish, with the result that the mean‐square force per unit area exerted on a large area of the surface should tend to zero as the area increases indefinitely. An idealized model of turbulent boundary layer flow is constructed and used to relate the spectrum and correlation function of the surface pressure distribution to the corresponding functions for a homogeneous turbulent flow. Application of the theory to Laufer's data on turbulent channel flow indicates that the dominant contribution to the pressure fluctuations should depend only on the mean velocity profile and the two‐point quadratic correlation of the fluctuating velocity component perpendicular to the boundary surface. On the basis of the seriously incomplete data available the rms pressure fluctuation from this source is tentatively estimated. The treatment of the present paper is based on the assumptions of (1) adiabatic conditions, (2) small compressibility, and (3) slow rate of growth of the boundary layer.

ISSN:0001-4966    

DOI:10.1121/1.1908336

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

A formulism for predicting the motion of continuous systems excited by random noise fields is applied to the special case of a one‐dimensional string. Several examples are attacked: (1) Brownian motion of finite strings, (2) response to a spatially stepped‐temporally delayed noise field, (3) response of finite ribbon to moving, random pressure fluctuations, (4) response of an infinite ribbon to moving, random pressure fluctuations. Cases (2) and (3) are investigated experimentally, the latter by using flowing turbulence.In case (2) appears the interesting phenomenon of the capability of the string “remembering” or “forgetting” a signal which it received in the past. The larger the damping of the string, the sooner it will forget a previous signal. In cases (3) and (4) a coincidence effect appears between the flow velocity of the forcing field and the velocity of waves on the ribbon. Here again, the phenomenon of forgetting appears and sharply determines the magnitude of any coincidence effect which may appear.

ISSN:0001-4966    

DOI:10.1121/1.1908338

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP