Effect of vibration in combined axes on subjective evaluation of ride quality

Two experiments investigated the effects of simultaneous sinusoidal vibration in the vertical and lateral axes on ratings of discomfort in human Ss in a simulated passenger aircraft. In Exp I, each of 24 undergraduates experienced each of 10 levels of lateral frequency of vibration at 10 levels of vertical frequency and rated the discomfort produced on a 9-point, unipolar scale. Both vertical frequency and lateral frequency, as well as the interaction between the two, significantly affected the subjective ratings. In Exp II, 72 undergraduates experienced 1 of 4 levels of vertical frequency at each of 4 levels of vertical amplitude combined with 16 lateral frequency and amplitude conditions. Not only did the 4 major variables studied significantly affect ratings of discomfort, but the interactions between them had significant effects as well. Results of the 2 studies strongly suggest that there are effects on discomfort that occur when Ss are vibrated in several axes at once that cannot be assessed with research using vibration in only one axis.