Predicting the acoustics of rattle

Buzz, Squeak and Rattle (BSR) are acoustically perceived quality attributes that consistently rank among the top "things gone wrong" in initial quality surveys for many new products. BSR issues discovered late in the design cycle of a product can lead to significant manufacturing costs for OEMs and significant warranty costs for suppliers. There is therefore a need to be able to predict BSR upfront in the design cycle. Predicting the acoustics of BSR is complicated by the requirement to model the vibro-acoustic response of large complex structures across a broad frequency range. The complexity of the analysis can be reduced by making use of standard methods for mid and high frequency vibro-acoustics. In particular, this paper discusses a computationally efficient method for assessing the propensity for rattle in large complex structures. A finite element model is used to predict the probability that impacts will occur when a product is exposed to a particular low frequency random vibro-acoustic environment. The expected contact forces arising from each impact are then estimated by making use of expressions involving the drive point impedances of infinite structures. Finally, the vibration and acoustic radiation associated with the various impacts are predicted and ranked using SEA models. The method is discussed and particular attention is given to the validation of the contact force arising from a localized impact between two elastic bodies that support wave propagation.