A hierarchical approach to the assessment of the variability of interior noise levels measured in passenger cars

A hierarchical approach is first presented to analyse the variability of structure-borne interior noise levels. A new terminology is proposed to clearly distinguish between intra variability, inter variability and measurement uncertainty. The hierarchical approach has been applied to experimentally determine the intra variability of booming noise on the same vehicle due to variations of the environmental conditions. The booming noise at several locations inside the vehicle was measured as well as the vibrations of the engine, the dynamic stiffness of the engine mounts and a structural acoustic transfer function of the body. Interior noise level at the driver’s ear shows measured intra variability level between 2 and 20 dB depending on the engine speed. The inter variability of booming noise was also measured: it turns out that its level is lower than the intra variability one.