Transmission Loss Analysis of an Exhaust System of Combustion Engines. Part I: Measurements

Aiming to solve pass by noise issues, where the exhaust system is the main source, a bench test was built. It was based on an impedance tube method to measure the transmission loss of exhaust systems of vehicle combustion engines. The test bench reduces time on investigation of acoustic performance of exhausts systems and does not depend on weather conditions. The results were used to compare several proposals under investigation before assembling on the vehicle and also to give a comparable metric for validating numerical simulation modeling and analysis procedure. This paper describes the problems involved in the construction of the evaluation system. Three types of noise source were evaluated, considering pink and white noise. Four methods for calculating the transmission loss were compared against easiness of implementation and robustness of results: the decomposition method, a modification of the decomposition method proposed by Chung, the two-sources method and the two-loads method. A single expansion chamber was used to validate the bench test and also to start the CAE correlation procedure. A deeper view on the problems regarding the implementation of CAE procedure and correlation with bench test will be discussed on part II of this work.