A study of exhaust noise in a motor vehicle using statistical energy analysis

Abstract

This work uses statistical energy analysis (SEA) to study noise transmission through a commercial motor vehicle and in order to do this various sound and vibration power inputs associated with flanking transmission via the exhaust and engine noise are calculated. A modern commercial motor vehicle that has an exhaust noise sensitivity problem is studied in this work. The aim of this work is to demonstrate the application of SEA and to study the effects on noise transmission when the exhaust is incorrectly fitted (misaligned). Airborne and structural paths for sound and vibration transmission to a vehicle saloon are considered. Also, the SEA framework is used to identify the relative importance of each structural and airborne power input in relation to the sound power that is transmitted to the vehicle saloon. It is shown that the importance of each sound power input varies with frequency. At low frequencies, sound transmission through the vehicle structure is most important. At high frequencies, airborne flanking noise transmission to the floor is important. In this case, exhaust vibration transmission is most important at frequencies between 250 Hz and 1 kHz when the engine is running at 5700 r/min, and the SEA model predicts the change in performance associated with exhaust misalignment.