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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.

The continuous pursuit for lighter, more affordable and more silent cars, has pushed OEMs into optimizing the design of car components. The different panels surrounding the car interior cavity such as firewall, door or floor panels are of key importance to the NV performance. The design of the sound packages for high-frequency airborne input is well established. However, the design for the mid-frequency range is more difficult, because of the complex inputs involved, the lack of representative performance metrics and its high computational cost. In order to make early decisions for package design, performance maps based on the different design parameters are desired for mid-frequencies. This paper presents a framework to retrieve the response surface, from a numerical design space of finite-element frequency sweeps. This response surface describes the performance of a sound package against the different design variables.

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.