摘要:

Measurements of underwater sound reflection and transmission properties of several sound‐absorbent materials in the frequency range from 10 to 150 kilocycles per second at hydrostatic pressures up to 350 pounds per square inch are presented, and the method of measurement is described.

ISSN:0001-4966    

DOI:10.1121/1.1917218

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The rate at which Paramecium caudatum is destroyed in a sound field of fixed intensity increases markedly in the neighborhood of 1.2 kc/sec. Similar optimum destructive frequencies have been found for six other species of paramecium and for a blepharisma species. Although the shapes of these animals are too complex to treat on a theoretical basis, reasonable theories can be developed for spheres having radii equal to the average radius of the animal. One theory, based on the existence of a non‐rigid membrane with interfacial tension,T, separating two incompressible liquids, givesT=ca.3 dynes/cm, agreeing in order of magnitude with values found for other cells by very different methods. An alternate theory postulates a rigid envelope surrounding the cell giving coefficients of rigidity about 104dynes/cm2; this is within the range of values of fibrin gels. Either type of vibration would be excited readily by cavitation. The formulas for these modes and their derivation will be discussed.

ISSN:0001-4966    

DOI:10.1121/1.1917227

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The exact theory of the acoustic interferometer will be discussed following the three stages of its development. First will be discussed the original approximation introduced to simplify the solution in the case of moderately dissipative media. Second will be discussed the more rigorous solution necessary in the case of highly dissipative media, including the approximation for low acoustic impedance to simplify the solution in the case of gases at low pressures. Third will be discussed the exact solution necessary in the case of very highly dissipative media now being approached inH2and He. This indicates a departure of the maxima and minima of the real part of the acoustic impedance from the simple hyperbolic functions, necessitating corrections to the absorption and reflection calculations. Also at very high dissipation these maxima are no longer a half‐wave‐length apart, requiring corrections to velocity calculations.

ISSN:0001-4966    

DOI:10.1121/1.1917232

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

A survey has been made of the various mechanisms that have been suggested for the absorption of sound in fluids. These can be classified into two groups,viz., (1) viscosity absorption and (2) relaxation absorption. In the second group are included the effects of heat radiation, heat conduction, thermal relaxation, structural relaxation, and a more general type of relaxation proposed here. This last mechanism includes both thermal and structural relaxation as special cases. For mechanisms of the second group the expression relating the absorption coefficient and the velocity with the frequency can be derived by starting with the first law of thermodynamics and arriving at an acoustical equation of state. This transformation can be made without any special assumption as to the nature of the substance. The equation of state permits one to make a simple comparison of the various approaches to the problem. A study of the velocity and absorption as a function of frequency shows important differences between the two classifications. Thus the assumptions that the additional absorption in water (beyond the classical viscosity contribution) is due to structural relaxation (Hall) or dilatation viscosity (Eckart and Liebermann) are not precisely equivalent.

ISSN:0001-4966    

DOI:10.1121/1.1917235

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The theoretical work of W. J. Jacobi on the propagation of sound waves along liquid cylinders has been extended to the case of sound transmission through a liquid bounded by two concentric cylinder of infinite length. Longitudinal phase velocities and radial distributions of pressure amplitude have been calculated, and the form of the Fourier‐Bessel expansion coefficients has been worked out for rigid, pressure‐release, and elastic wall boundary conditions. Similar calculations for the case of a single liquid filled cylinder have been made for comparison. The case of two concentric cylinders approaches that of a single cylinder as the radius of the inner cylinder approaches zero. Experimental values of phase velocity have been determined for the case of two finite concentric cylinders with elastic walls and are in good agreement with theory over parts of the range from 3 to 200 kc.

ISSN:0001-4966    

DOI:10.1121/1.1917242

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

If a polarized hydrogen or oxygen electrode is irradiated with ultrasonic waves, an alternating component is produced in the electrode potential. This effect is believed to depend primarily on the formation of a gas phase at the surface of the electrode. Indications are that the acoustical sensitivity is a function of the polarizing current and the nature of the electrolytic solution as well as the frequency. Pulse techniques have been used in the investigation of the effect in order to avoid the complications associated with electromagnetic coupling. The response of the polarized hydrogen electrode has been observed to be as large as − 150 db re: one volt per dyne/cm2. Such an effect may find interesting amplications in acoustics, since it can be utilized in the form of virtually a point probe.

ISSN:0001-4966    

DOI:10.1121/1.1917246

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

With modern record reproducing systems, a degree of fidelity of reproduction is attainable in which the wow inherent in commercial records is the limiting factor in the enjoyment of the reproduced music. In the manufacturing steps which lead to the stamper, the mechanical center of the record is lost, and is later re‐introduced. In the re‐centering, errors of 0.005 to 0.01 inch are typical, and occasional records have centering errors as large as 0.02 inch. At the inner grooves, a centering error of 0.01 inch produces a peak‐to‐peak frequency modulation of one percent, whereas 0.3 percent is detectable in a free field, and 0.03 percent is detectable in a room. Three different devices have been constructed whose purpose is to reduce the effect of the centering errors on the reproduction. All three employ the amplitude of the lateral oscillation of the reproducing stylus as the measure of the error to be corrected Two of them introduce a motion of the stylus along the groove which is equal in amplitude to, and in phase quadrature with, the lateral oscillation. The third device involves two servo mechanisms which center the record on the turn‐table during the first few seconds of reproduction. The advantages and limitations of the three devices will be described.

ISSN:0001-4966    

DOI:10.1121/1.1917251

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP