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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.

The final interior noise of a vehicle is due to the contribution of several sub-systems sources and their transmission paths (airborne and structure-borne) to the driver's ear. Ford Motor Company had developed a Windows based software using simple noise path analysis to estimate the final vehicle level acceleration noise. Measurement data of several sub-system components were inputted to software that computed the airborne and structure-borne contributions in 1/3-octave and order spectra to give the final vehicle interior noise level. The predicted noise was compared to the measured one and model was validated. Then, observing the frequency range of the boom phenomenon, it was possible to identify the main contributors. Still using the same tool, a new component target was set.