Predicting the discomfort caused by simultaneous vertical and fore-and-aft whole-body vibration

In two experiments, subjects adjusted combinations of vertical and fore-and-aft whole-body sinusoidal vibration (frequencies in the range 2. 5-10 Hz) so that their discomfort was equivalent to that produced by a reference motion. The aim was to find the best procedure for predicting the discomfort caused by simultaneous vertical and fore-and-aft vibration. The procedure was assumed to be of the form (V**n plus H**n)**1**/**n, where V and H represented the discomfort that would have been caused by each of the vertical and horizontal components if they had occurred separately. The first experiment, where the vibration in each axis was at the same frequency and the ratio of V to H was varied gave an optimum value of 2. 07 for the exponent n. Root-sums-of-squares was generally the best procedure in the second experiment where the vibration in both axes was not at the same frequency, although there was a significant difference between the predicted and actual discomfort for some combinations of frequencies.