The Effect of Backrest Angles on Discomfort Caused by Fore-and-Aft Back Vibration

The effect on discomfort of the frequency and the backrest angle of x-axis (fore-and-aft) vibration of backrest have been studied. The method of adjustment was employed to obtain contours of equivalent comfort for three types of rigid backrests, whose surface were vertical, inclined 20 degrees and 40 degrees from vertical. Eighteen subjects were required to adjust test vibration over the frequency range 2-80Hz to produce discomfort equivalent to that caused by 10Hz 0.25m/s2 r.m.s. sinusoidal reference vibration for each backrest. The direction of vibration was perpendicular to backrest surface. Results shows that the sensitivity at 20 and 40Hz on inclined backrests is significantly about 1.4 to 1.5 times greater than that on a vertical backrest (p