Evaluation of the rattle noise of a vehicle seat using the coherence analysis technique

Abstract

The complicated transfer path relationship between the vibrations of a seat and the noise at the locations of the driver's ears was estimated from the residual spectrum. For accurate quantitative estimation of the rattle noise at the locations of the driver's ears, in particular the partial coherence function of the pure inputs to the output was modelled by considering the correlation between the inputs and the input-output. Whenever a coherence analysis was performed with the noise sources in close proximity selected as the inputs and the noise at the locations of the driver's ears modelled as the output, the partially coherent output spectrum as a quantitative contribution of the inputs to the output was determined. In this study, we applied a coherence analysis technique to identify the sources of the rattle noise of a seat by visualizing the noise sources with an acoustic camera while excitation of the seat was carried out using a hydraulic exciter. We were able to generate the rattle noise from the headrest stay, the recliner and the front part of the slide while excitation of the seat was obtained using a hydraulic exciter with white noise. We observed that the noise was generated by utilizing a hydraulic six-axis exciter positioned at the driver's seat of a middle-sized manual transmission vehicle. We determined that the noise measured at the locations of the driver's ears had a frequency of 58Hz using acoustic visualization and a coherence technique. It was selected in particular as the target frequency since the 58Hz resonant frequency caused by the twisting mode of the seat back was identical with the frequency of the rattle noise. Finally, it was verified through a modal test that the rattle noise at 58Hz was generated by the vibration characteristics of the seat, which depended on gaps between the headrest stay and the guide.