A measurement system for the assessment of the effectiveness of sound-insulating multilayers against structure-borne excitation: design, prototyping and validation

Abstract

This paper proposes a measurement system to assess the effectiveness of sound-insulating multilayers against structure-borne excitation, meant to complement the well-known and established systems used in the automotive field for airborne excitation. 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. This layout intends to mimic the noise radiation from an automotive body panel. The development of such a system, in spite of its simplicity, presents non-trivial aspects, such as the design of a frame sufficiently rigid not to have modes in the frequency range of interest and the definition of a metric to evaluate the effectiveness of an acoustic multilayer in a robust way based only on SPL measurements. The paper describes how these challenges were overcome, using topological optimization to design a frame made with magnesium suitable for tests up to about 1kHz and FE simulations to define a robust assessment metric by placing the receiving microphones at a fixed distance from the plate and at positions corresponding to integration Gauss points. Besides the design, the paper describes also how the system was prototyped and eventually validated.