Vibro-acoustic modal analysis of automobile body cavity noise

One important aspect in the development of modern passenger vehicles is their noise and vibration characteristics. These properties are governed by a combination of excitations to a vehicle and possible amplifications due to acoustic and structural resonances. To avoid excessive noise and vibration transfer into the passenger cabin, relevant structural and acoustic modes need to be separated from each other. This is the well known concept of modal alignment. Although finite element analysis (FEA) tools have become very powerful, confidence levels for full vehicle predictions are still not high enough to base development decisions solely on them. In these cases, experimental techniques, such as Vibro-Acoustic Modal Analysis, are very useful to gain an understanding of the complex structural-acoustic mode interaction. This article presents the experimental approach and the results obtained from such an analysis. The motivation for the investigation was the presence of a high speed boom in a midsize, prototype stage passenger car.