The mid-frequency range acoustic response between 400-1000 Hz has gained particular interest in the automotive industry recently. Simulation of this region is challenging due to the non-negligible statistical effects, especially when acoustic trim is applied. In order to be able to investigate the effect of these materials in the presence of an air cavity, this paper describes the design methodology behind the design and manufacturing of two test apparatuses that include an air cavity. The apparatuses were designed to serve as a validation tool for Finite Element Method (FEM) and Statistical Energy Analysis (SEA) simulations, which meant that an optimal size had to be found based on the number of fluid modes in the cavity. Two types of plate-cavity apparatuses have been designed: one with “rigid walls” and one with “soft walls”. In the “rigid wall” cavity, the walls are made out of concrete since these boundary conditions can be perfectly represented in simulations. In the “soft wall” cavity, the walls are made of steel plates and this allows validation of coupling loss simulations between multiple structural subsystems as well as an air cavity. Details of the joining methods, geometries, material selections are elaborated to fully describe the theoretical and practical implications of the designs.

The constantly evolving customer demands in the automotive industry necessitates vehicle manufacturers to perform ever more accurate acoustic simulations. Acoustic simulations especially in the mid-frequency range (400 Hz - 1000 Hz) pose particular challenges: statistical methods lack the necessary modal density for accuracy, while Finite Element Methods (FEM) have difficulty accounting for statistical effects. In order to resolve the conflict that FEM solvers face, an academic case is investigated. A flat plate of 650x 750 mm in free-free condition is examined as a low-complexity platform to investigate the sensitivity of FEM simulation results to parameters, such as the value of structural damping, the frequency dependency of structural damping as well as the variations in the plate thickness due to manufacturing tolerances. FEM simulations were performed using ESI VPS and compared to measurements. Results show that slight variations in plate thickness and Young`s modulus can have significant impact on the frequency response. Results have shown that a 0.5% variation in the thickness already has a pronounced effect on frequency response peak locations, especially between 600 and 1000 Hz. Beside this, the paper provides novel results on evaluating the effects of frequency dependency of structural damping on the results.