EMA and OMA techniques for vibroacustically coupled systems: the example of a helicopter cabin

Noise and vibration levels in vibro-acoustical systems are strictly related, meaning that a good knowledge of the structural dynamics is a useful tool for their reduction. Through an intensive testing campaign on a EC-135 helicopter cabin, a few guidelines are given in order to properly capture the coupled vibro-acoustical behaviour of systems. In particular, four experimental modal analyses have been performed on the cabin, a pure acoustical modal analysis of the enclosure, an experimental modal analysis of the internal and external surface and an operational modal analysis of the external surface. The results presented highlight that a direct acoustical excitation is preferred also for the external part in controlled laboratory conditions and an acoustical reference would be more efficient for operational modal analyses.