A Theoretical and Experimental Study of the Behaviour of Concentric Perforated Duct Automotive Mufflers

Concentric perforated duct mufflers are broadly used when designing automotive front mufflers because of their acceptable acoustic performance and their low backpressure. In the frame of the design methodologies presently used, suitable theoretical models are needed in order to estimate this performance without the need to build prototypes and perform experimental tests. A lot of work has been performed in this sense; nevertheless, there remains a reasonable doubt that the results obtained with purely linear models are representative of the muffler behaviour under actual engine conditions. In the present paper, a two dimensional finite element model is used in order to compute the transmission loss of several concentric perforated duct mufflers, and the results are compared with experimental measurements performed with a modified version of the impulse method that allows for the use of high amplitude pressure pulses as excitation. The comparison reveals that the linear model gives qualitative guidelines about the muffler behaviour but with important quantitative differences. Moreover, it is demonstrated by means of system identification techniques that the differences observed cannot be attributed to measurement problems.