Abstract
This paper describes the fundamental aspects of an electrical analog method for the theoretical analysis of acoustic filters and its experimental verification carried out by means of an electric simulator. First, the differential equations of one-dimensional acoustical system are transformed into a finite difference equation with respect to a sound pressure ρ or a volume velocity U, which gives the T or π elementary network of a direct analog type equivalent circuit. It is noticed that each of the two representations has a different physical meaning. Since truncation errors would result under such approximation, the applicability of these analog models are discussed by designating the usable frequency range and the tolerable error. Next, the three-dimensional delay networks and the compound T elementary networks corresponding to the one-dimensional T are derived for the rectangular and cylindrical coordinates. The reduction of dimension is also studied. Finally, the details of the simulator composed of 18 (8 variable, 10 fixed) sets of L, C and R are explained and the comparison between the data obtained by the numerical calculation, acoustical experiment and simulator operation on the various types of filter elements reveals the practical usefulness of this analog method for the parameter change study of acoustic filters.
