The evaluation of discomfort produced by multiple frequency whole-body vibration

The discomfort produced by multiple frequency whole-body vertical vibration has been studied in three experiments. Subjects were required to adjust the level of a 10 Hz sinusoidal vibration such that it produced a degree of discomfort equivalent to that caused by a variety of multiple frequency stimuli including motions containing predominant beats and up to four sinusoidal components. The levels of the 10 Hz vibration equivalent to the complex motions were always well predicted by the root mean square of the levels of 10 Hz equivalent to the individual sinusoidal components in the complex motion. The equivalent discomfort of the multiple frequency motions could therefore be determined by weighting the vibration spectrum with an electronic network having a frequency response given by the manner in which discomfort due to vibration varies with vibration frequency. The possibility of inhibition occurring in the response to multiple frequency motions was investigated and it was concluded that the complexity inherent in methods based on models of inhibition was unnecessary. The present findings have been compared with the procedures for assessing multiple frequency motions given in the current International Standard on the evaluation of human exposure to whole-body vibration.