Direct and indirect vibro-acoustic measurements for road noise NVH predictions

ABSTRACT This paper describes vibro-acoustic direct and indirect measure-ments for road noise NVH predictions from a complete car. Attention is devoted to the dynamic response of the structure and interior pressure field toward tire patch displacement inputs. The direct measurements exploited the Team Corporation CUBE™ high frequency 6 degree-of-freedom (DOF) shaker recently installed at the KULeuven Vehicle Technologies Labo-ratory; the input was provided directly at the tire contact patch, while the responses were measured as accelerations and pres-sures on the structure. In the indirect measurements a low-mid frequency volume velocity source (LMFVVS) was used to acoustically excite the structure in the reverse path direction from the inside of the interior car cavity, while accelerations on the car and forces/torques where acquired by a 6-DOF dyna-mometer at the tire patch. From both types of excitations Fre-quency Response Functions (FRF) were calculated in the fre-quency range [0-500 Hz]. The non-linearity of the full car system was investigated with different direct and indirect measurement tests, in order to assess the feasibility of the reciprocity principle in such a com-plex structure. Measurement set-ups, results and comparisons are de-scribed and discussed in detail.