Comfort contours: Inter-axis equivalence

Inter-axis equivalence for sinusoidal vibrations as stipulated by ISO/DIS 2631 for seated persons was studied by adjusting the acceleration of a horizontal sinusoidal test vibration (x boolean OR y) until it caused equal sensation as a vertical sinusoidal reference motion of the same frequency. The reference vibrations consisted of sine waves ranging from 1.6 to 12.5 Hz and were presented with three weighted accelerations of a(zw) = 0.3, 0.6 and 1.2 ms(-2) r.m.s. (reference contours). 26 subjects (15 men, 11 women, 20-56 yrs, 153-187 cm) participated in the respective experiments. Based on the three reference contours, predicted values for horizontal motions were calculated by using the weighting factors provided in ISO/DIS 2631. The International standard was confirmed insofar as the shape of the contours determined for horizontal motions was independent from vibration magnitudes and as sensitivity to fore-and-aft and to lateral motions was similar. However, the accelerations adjusted for horizontal vibrations were considerably lower than predicted, suggesting that the weighing factors provided in ISO/DIS 2631 need to be corrected. (C) 1997 Academic Press Limited.