In the proceeding paper(this Journal 25(3)1969, p. 122), it was shown that the noise reducing effect of a muffler is deduced by means of the four-terminal constants of the equivalent electrical network of the whole muffler system, and for expansion chamber type mufflers, approximate equations are very simple and the noise reducing curve is easily obtained by a graphical method. In this paper, a similar method is applied to the resonator type mufflers, and equations are shown in Eq. (11), (12), (13) and (16), and a graphical method in Table 1 and Fig. 8. Practically, as shown in Fig. 7(a), the resonator type muffler is efficient only in the region near the first resonant frequency, and furthermore the loss at the mouth of resonator is not negligible. But the calculation of the loss is very difficult, so the loss is estimated as convenient to the graphical process as shown id Fig. 9. By this estimation, the noise reducing curve is very easily obtained by a graphical method, and as shown in Fig. 7(b), the resulted curve is useful for practical purposes. When the connecting points of the cavity of a resonator and the pipe are in two locations or are distributed as Fig. 11, the four-terminal constants are shown in Eq. (28) and (31). In a practical case, when the distance between the two connecting points or the distributing length of connecting points and the total connecting area are very large, the muffler is approximately equivalent to an expansion chamber type muffler as illustrated in Fig. 13.
