A generalized methodology for a compensation of test-bench specific influences of a simulated pass-by compared to real outdoor measurements

Due to new regulations regarding exterior noise of vehicles, requiring a more complex measurement procedure, and the increasing number of models and vehicle derivatives, the demand of pass-by measurements is increasing. Under these intensified conditions and while keeping organizational efforts low, the simulated pass-by has been widely accepted as an alternative for measurements on real test tracks. Although the ISO 362-3 exactly depicts the setup of the indoor-testing of pass-by noise, some differences between outdoor and indoor measurements can be observed. These are usually caused by the semi-anechoic room itself and the dyno, which doesn't necessarily represent the real tire-road contact. While the entire development process can be efficiently conducted in the indoor test-bench, type approval has to be performed outdoors. Even small deviations in the indoor measurement results may cause the developed vehicle to fail the type approval. Hence, we suggest a new method for a prognosis of the exterior noise on real test tracks based on indoor measurements. Therefore we have tested a wide range of current vehicles both indoors and outdoors in order to define a transfer function between both test methodologies either for individual vehicles or as a generalized model for test-benches.