Reactive Muffler IL

The effect of source impedance on IL of an automobile muffler was investigated theoretically in 1970 by Young [45]. Some results are shown in Figures 10.70 and 10.71. In Figure 10.70 it is seen that there is a large difference between the IL curves for the muffler for the three different source impedances investigated: Z_e = 0, ρc/S, and ∞, when the prediction is made for discrete frequencies. However, Figure 10.71 shows that if the IL is averaged on an energy basis (with a theoretical 25 Hz filter) that the differences in IL predictions are much less. Note that the vertical scales in Figures 10.70 and 10.71 are different and that a different engine firing frequency is chosen. Also, of considerable interest is the fact that in both figures the TL curve passes through the middle of the IL curves. In Figure 10.70, the hills and valleys in the IL curves are thought to be caused by standing waves in the lengths of straight (exhaust and tail) pipes in the muffler systems.