The method recommended in current standards for evaluating vibration-induced discomfort in cabin environments was determined separately for excitation at the seat pan, backrest, and floor. However, passengers typically sit with a backrest and experience vibrations at multiple human-seat interfaces simultaneously. In this study, 18 seated subjects with a backrest support were exposed to single-axis fore-aft, lateral, vertical, and pitch vibration between 0.5 and 20 Hz at six magnitudes in a controlled environment chamber, and evaluated discomfort using the magnitude estimation method. Equivalent comfort contours were identified, revealing the effect of vibration frequency and direction. A new index reflecting the equivalence of vibrations in different directions was then defined, based on the equivalent comfort contours. Results showed that the current standard overestimates the sensitivity of fore-aft vibration relative to vertical vibration for 0.5–2.5 Hz and underestimates the sensitivity of lateral vibration relative to vertical vibration for 1.25–20 Hz and the sensitivity of pitch vibration relative to vertical vibration for 0.5–4.0 Hz.
Kuang et al. (Fri,) studied this question.