22 Acoustic Cavity Modal Analysis for NVH Development of Road Machinery Cabins 225 Fig. 22.5 (continued) column. It is also noted that the modal response increases with the addition of the seat and steering column. Regarding the relative strength of modes, the vertical mode #4 is the most dominant one for both cases. In practice, this vertical mode may induce high sound pressure levels if it is coincident with excitation frequencies such as the engine firing orders. Such a mode should be precisely identified from the FEA model prior to the physical prototype to facilitate the cab NVH development. The corresponding mode shapes are compared in Fig. 22.8. Note that when the seat and steering column are added, the vertical mode #4 somehow tends to start coupling with a lateral mode in y-axis. For the longitudinal mode #6, the region where the maximum pressure response concentrates migrates from the front top left corner to the front bottom right corner.
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