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An ongoing trend among automotive exhaust suppliers is the application of loudspeakers in their systems to tailor the exhaust sound to the customers’ needs. In addition to it, undesirable engine order noise can be cancelled by a closed loop control system. Due to the high sound pressure from the engine, the loudspeaker is often required to run at its power maximum. A higher input power eventually causes a nonlinear behavior, resulting in undesirable sound pressure level or harmonic distortion. Thus, the understanding of nonlinear behavior of loudspeakers and the recognition of dominant effects are required. This paper presents the main nonlinearities of loudspeakers and the comparison of theories on linear and non-linear loudspeaker models. For validation of the model, one loudspeaker enclosure and one typical exhaust system with a loudspeaker have been calculated.

Fibrous material is widely used in automotive silencers in order to dissipate high frequency noise components and attenuate the high-level pressure wave propagating from the cylinders. Its accurate acoustic model is in demand with a highly increased reliance on acoustic simulation of automotive exhaust systems. In this investigation, several empirical formulae and fibrous models in one-dimensional CFD codes are reviewed and their acoustic characteristics, e.g. propagation constants and characteristic impedance, are compared. Also, they are applied to some typical automotive silencers in order to check the validity of each model. It was found that some default fibrous models in commercial one-dimensional CFD codes were not satisfying. For the improvement of those results, DOE (Design of Experiment) and a commercial optimization tool were applied to find the optimal input values in their fibrous model.