Determination of acoustic contributions of car components to the far field using transfer functions

The exterior noise of a vehicle is an increasingly important criterion for the homologation of road vehicles. According to DIN ISO 362-1, it is measured by a standardized procedure, where numerous perturbations exist. Therefore, the aim of the current research is the transfer of this procedure into acoustic chambers with roller test benches, the so called simulated pass-by. In this contribution, a new method for the determination of the exterior noise of vehicles in an early stage of the development process is presented. For that matter, a virtual acoustic vehicle model, based on measurements on a roller test bench in an acoustic chamber is to be developed. By the use of a modular structure, it allows conlcusions about the influences of modifications of single components of the vehicle. Therefore, the airborne transfer functions from dominant sound sources of the vehicle to the microphone positions in the far field are determined reciprocally, using a dodecahedral speaker and a vehicle on the roller test bench at IPEK – Institute of Product Engineering. The vehicle measurements and the airborne transfer functions are used to establish a virtual acoustic vehicle model in the time domain using digital filters. The playback of this model is carried out in the flexible audio-visual stereo projection system at the competence center virtual reality at TU Ilmenau.