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The recently updated pass-by noise measurement procedure prescribes a mix of acceleration tests and constant speed tests. This has led to an increased relevance of tire noise relative to the past, when the procedure prescribed only acceleration tests. In addition, the next phase of the roadmap for pass-by noise limits for passenger vehicles is 70 dB(A) by 2020, later followed by 68 dB(A). In this context, exterior tire noise has drawn increasing attention. OEMs, suppliers of passive acoustic treatments, road manufacturers and tire manufacturers are, at the moment, devoting strong efforts to the definition of solutions for the control of exterior noise. This paper is concerned with the potential of existing passive exterior treatments to reduce the exterior noise generated by the tires. Different countermeasures are analyzed, namely wheelhouse liners, under-engine shields, under-body panels and under-trunk panels.

The assessment of the Transmission Loss (TL) of vehicle components at Low-Mid Frequencies generally raises difficulties associated to the physical mechanisms of the noise transmission through the automotive panel. As far as testing is concerned, it is common in the automotive industry to perform double room TL measurements of component baffled cut-outs, while numerical methods are rather applied when prototype or hardware variants are not available. Indeed, in the context of recent efforts for reduction of vehicle prototypes, the use of simulation is constantly challenged to deliver reliable means of decision during virtual design phase. While the Transfer matrix method is commonly and conveniently used at Mid-High frequencies for the calculation of a trimmed panel, the simulation of energy transfer at low frequencies must take into account modal interactions between the vehicle component and the acoustic environment.