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For vehicle Original Equipment Manufactures (OEMs), road noise inside the vehicle is an important aspect that contributes to the comfort and the sound quality image of the vehicle. Road noise inside a vehicle is a function of the source (tire design interacting with road surface) and of vehicle sensitivity functions. Road noise targets and tire targets are typically developed by characterizing the tire as a noise and/or vibration source and by characterizing the vehicle as a matrix of acoustic or structural paths (1) . This paper focuses on the development of a simplified procedure for measurement of Noise Reduction (or acoustic vehicle sensitivity function) from tire patch to vehicle interior. Several procedures are available from either literature, vehicle manufacturers or software providers, which exhibit important differences regarding sound production, number and position of source and receiver microphones, or measured parameters (2) . The objective of the investigation described in this paper was to evaluate these different procedures and identify the simplest one that can provide data that can be used to simulate, with a reasonable accuracy, the noise reduction effect of a vehicle. Tests of Noise Reduction were conducted in a hemi-anechoic chamber on a production vehicle with the following methods: point source, reciprocity with volume velocity source, ad-hoc tire-patch speaker (grate box) and off-the-shelf loudspeakers. The averaged Noise Reduction (NR) functions between a binaural head inside the vehicle and each of the four tires were computed using each method. These functions were applied to time data acquired in vehicle, on a chassis dynamometer, to validate the prediction of interior noise by comparison to measured noise. The paper describes the test methods, their comparison and includes the authors’ recommendations for best method. |
