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Traditionally, vibration analysis in operating conditions (on the road or on a bench) had to be combined with experimental modal analysis in controlled laboratory conditions in order to understand the modal behaviour of the structure. This requires additional measurements, costs and time. However, in many applications, the real operating conditions may differ significantly from those applied during the modal test and hence the vibration modes from the modal test might not be representative for the active modes in operation conditions. The need for a capability of doing a modal analysis on data from operating conditions is obvious. Over the last years, several modal parameter estimation techniques have been proposed and studied for modal parameter extraction from output-only data. Each method needs to make a number of assumptions and has some limitations.

The development of the different sound packages in vehicles (dash/floor silencer, headliner, door trims…) is often driven mainly by high-frequency, airborne considerations. Nevertheless, those parts can have a considerable impact to acoustic performance at much lower frequencies, and their effect is not limited to airborne phenomena. As such, a proper consideration of their performance is very important when developing typical mid-frequency performances such as engine and road noise. This paper outlines a process that allows development of the vehicle body, and more specifically the sound packages, for mid-frequency acoustic performance. Two main challenges are addressed: first, full-vehicle targets have to be cascaded down towards specific sound package targets. It is shown that an effective cascading process can be set up based on Transfer Path Analysis (TPA) and Panel Contribution Analysis (PCA) techniques.