抄録
Acoustic cavity has been studied by numerous investigators from different points of view. As is well known, a cavity behaves as a typical lumped capacitance element, provided that the wavelength of sound is sufficiently large compared with the dimension of the cavity and that viscosity loss can be neglected. This simple characteristic of cavity is widely used to the design of acoustic devices based on circuit theory. On the other hand, detailed investigations based on wave theory show us the complex behavior of cavity depending on wavelength of sound as well as shape and dimension of the cavity. In this paper wave theory is applied to a cylindrical cavity which is obtained by rigid or another suitable termination of an acoustic transformer element with a simple plane discontinuity of circular cross section (See Figs. 1 and 6), and the sound field and input impedance of the cavity are determined. Based on the exact theory, a systematic approach to plane-piston approximation and plane-wave approximation is made in order to clarify the differences as well as the limitation of each of the approximate methods. Comparison of input impedances obtained from these approximate methods and exact theory is given in Figs. 2 and 7. Next, the pressure distribution along the axis of the cavity is measured by using the standing wave method, of which several examples are shown in Figs. 8 and 9. In addition to the measured values, the calculated values are also plotted in the above figures and they are in good agreement with each other. Moreover, the equivalent circuit representation of the cylindrical cavity is compared with one corresponding to the acoustic transformer and the relationship between them is discussed.
