In the automotive industry, it is common to use Air-Borne Insertion Loss (ABIL) to assess the performance of an acoustical multilayer, while Structure-Borne IL (SBIL) is rarely used.

This paper first addresses some aspects concerning the definition of SBIL when applied to the automotive field where noise-radiating panels have limited size and are subject mainly to boundary excitation rather than forces applied onto their surface. The physical mechanisms allowing an acoustical multilayer to reduce the sound radiation of an automotive panel subject to this kind of excitations are analyzed by means of FE simulations.

After this, a measurement system suitable for assessing the effectiveness of sound-insulating multilayers against SB excitation is proposed. The system consists of a shaker, a frame connected to it and a plate clamped along its edges to the frame. When the frame is put into vibration by the shaker, the plate radiates noise into a small anechoic cabin where microphones are positioned. The paper briefly addresses some critical aspects related to the development of such a systems (e.g. the design of a frame sufficiently rigid not to have modes in the frequency range of interest thanks to topological optimization), how the system was prototyped and validated.