摘要:

A simplified apparatus for the measurement of the flow resistance of porous acoustical materials is described. The method used is absolute, not comparative. An improved technique for the preparation of the samples is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1916323

出版商:Acoustical Society of America    

年代:1946

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1916324

出版商:Acoustical Society of America    

年代:1946

数据来源: AIP

摘要:

The acoustic wave equation is derived for a moving fluid medium in which all changes follow an adiabatic law, and it is shown that it may be written in a form which is very similar to the usual wave equation. Following this, the transmission and reflection coefficients for a fluid lamina in uniform motion are derived, and it is shown that it is only the component of motion in the direction of incidence which affects these coefficients. Finally, measurements are reported on the transmission coefficients of a non‐turbulent thermal lamina whose motion has no component in the plane of incidence. The acoustic frequencies range from 2 kc to 14 kc and the angle of incidence from 0° to 89°. These measurements are compared with those calculated for a theoretically approximated lamina. The results are in reasonable agreement. It is shown that there is considerable transmission for angles greater than the critical angles and that for very thin lamina the transmission coefficient is a uniformly decreasing function of frequency.

ISSN:0001-4966    

DOI:10.1121/1.1916325

出版商:Acoustical Society of America    

年代:1946

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1916326

出版商:Acoustical Society of America    

年代:1946

数据来源: AIP

摘要:

The effect of a plane discontinuity on a plane wave propagated in a cylindrical tube of arbitrary cross section is calculated by considering the higher order modes excited at the discontinuity. In carrying out the calculations, a transmission line analogy is used and the effect of the discontinuity at a distance is represented by a capacitance placed at the discontinuity. In Part I, the equations of motion for the propagation of a small disturbance in a cylindrical tube are assumed at the outset and are shown to yield the two‐dimensional wave equation, the solutions to this equation constituting an infinite set of modes, in addition to the plane wave usually treated in the literature. Following a discussion of these solutions, the analogy between propagation of sound and an electrical transmission line is established, and it is shown that each mode requires a separate transmission line. The effect of the higher modes excited by a plane discontinuity may be represented by a lumped capacitance, and this capacitance is given by a variational expression which gives a systematic method of calculation yielding an upper bound to the true answer. For the case of a window, a variational principle is produced which gives a lower bound to the true answer. In Part II, this method will be applied to a window in a rectangular tube, to a change of cross section in a rectangular tube, to windows and changes of cross section in circular tubes and to the calculation of resonance in certain types of cavities. The ordinary reflection and transmission coefficients will also be correlated with the theory of Part I. To the author's knowledge this is the first rigorous treatment of the above problems with the exception of an earlier paper calculating the reflection due to a change of cross section in a circular tube (reference 1).

ISSN:0001-4966    

DOI:10.1121/1.1916327

出版商:Acoustical Society of America    

年代:1946

数据来源: AIP

摘要:

The theory of plane discontinuities developed in Part I is applied to a “window” and change of cross section in tubes of both circular and rectangular cross section. In the case of the rectangular tube conformal mapping is introduced as an alternative approach to the problem. Reflection and transmission coefficients are determined from the equivalent circuit of Part I, and the theory is also applied to the analysis of certain types of cavity resonators. Finally, the experimental determination of equivalent circuit impedances is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1916328

出版商:Acoustical Society of America    

年代:1946

数据来源: AIP

摘要:

With the present generators, it has been possible for the ultrasonics to reach up to the wave‐length of visible light but there is a wide divergence between the order of their frequencies. The improvement of ultrasonic wave generators is suggested to reach still higher frequencies which might exhibit some of the dormant properties of the ultrasonics. The investigation of interaction of such high energy ultrasonics with matter is interesting, and it may decide whether the sound wave has also got a dual aspect.

ISSN:0001-4966    

DOI:10.1121/1.1916329

出版商:Acoustical Society of America    

年代:1946

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1916330

出版商:Acoustical Society of America    

年代:1946

数据来源: AIP