Application of Acoustic Modeling Methods for Vehicle Boom Analysis

This paper describes a system modeling technique for predicting passenger compartment “boom” for a specific car design prior to the building of a prototype vehicle. Since “boom” — defined here as auditory response in the 20 Hz to 80 Hz frequency range — is dependent on body panel vibrations as well as air acoustic properties, three-dimensional finite element models of both body and air are constructed. These models are incorporated in existing vehicle models which include powertrain and chassis representations of the type previously used for performing shake and harshness analyses. To avoid non-symmetric mass and stiffness matrices, a modal method using auxilliary variables is utilized to couple the acoustic and body models. Included in the paper are discussions of modeling issues unique to structural acoustic simulation as well as several examples of studies in which sound pressure level response to realistic inputs is predicted and reduced by simulated design modifications. Test results are presented for comparison. Finally, graphical presentation of panel acoustic contributions is shown to be a useful tool in selecting possible body structure design changes for “boom” improvement.