MEASUREMENTS OF VIBRATION FIELD CORRELATION ON A CAR BODY SHELL

In mid-frequency range of internal noise problems in cars the vibrational modal density of the shell is fairly high while the acoustic modal density of the passenger compartment is low. Therefore, one proposal for modelling the coupling is a hybrid approach in which the structure is probabilistically described and a deterministic model is adopted for the air space inside the car. A widely used probabilistic model of wave fields is the diffuse field. The diffuseness of a car body shell is assessed using correlation coefficients of acceleration measured on a fully trimmed car. Some evidence of diffuse wave field behaviour in the 100-300 Hz frequency range is found on the roof vibrational field. However, in view of other results, it is not possible to regard the entire car body structural wave field as diffuse in this frequency range. Reasons for this deviation are given, based upon the number of excited modes, local perturbations, edge effects and type of excitation used.