The Use of in Vehicle STL Testing to Correlate Subsystem Level SEA Models

Abstract

For the assessment of vehicle acoustics in the early design stages of a vehicle program, the use of full vehicle SEA models is becoming the standard analysis method in the US automotive industry. One benefit is that OEM'sand Tier 1 suppliers are able to cascade lower level acoustic performance targets for NVH systems and components. Detailed SEA system level models can be used to assess the performance of systems such as dash panels, floors and doors, however, the results will be questionable until test data Is available. Correlation can be accomplished with buck testing, which is a common practice in the automotive industry for assessing the STL (sound transmission loss) of vehicle level components. The opportunity to conduct buck testing can be limited by the availability of representative bodies to be cut into bucks and the availability of a transmission loss suite with a suitably large opening. In addition, the temporary fixture used to mount the test structure does not typically provide representative boundary conditions. Boundary conditions are particularly important when the in-vehicle performance is dependent on point connections at hinges / locking mechanisms and flexible seals at the perimeter of the system such as found in doors or lift-gate. In this paper the use of in-vehicle testing on prototype vehicles to assess the STL for the vehicle systems and the SEA models are discussed. Results are presented for a dash panel, floor system and door systems. The measurements are compared with predictions from system level SEA (Statistical Energy Analysis) models of the test systems. It is concluded that subsystem level SEA models can be used to assess the design and correlate well with STL measurements from in-vehicle tests.