MASKING EFFECTS UNDER DUAL AXIS WHOLE BODY VIBRATION

Abstract

The existence of masking effects for fore and aft vibration under two axial Whole-Body Vibration (WBV) broadband random vibrations of seated subjects was investigated. Subjects were exposed to two axis excitation in simulated driving condition. Initially, level of excitation was the same in the both direction. Subjects did not have the same sensation in both directions and they had to adjust equal level of stimulus sensation. In laboratory investigation of subjects sensitivity was conducted under varied parameters: level of excitation (0.55 ms-2 r.m.s., 1.75 ms-2 r.m.s. and 2.25 ms-2 r.m.s.) and seat backrest position (position K inclined 14° with respect to vertical axis and position S in vertical position without inclination). Masked Threshold (MT) for vibration in fore and aft direction was determined for r.m.s. head acceleration. Both parameters sitting position as well as level of excitation had impact on MT. Relationship between MT and level of excitation can be represented by linear regression model.