Basri, B. and Griffin, M.J.
Discomfort caused by x-axis vibration of the back: effect of backrest inclination.
In, 45th UK Conference on Human Response to Vibration, Gosport, GB,
06 - 08 Sep 2010.
Vibration of the back is a potential source of discomfort for car passengers, with vibration in the x-axis (i.e. fore-and-aft with an upright backrest) often dominant. This study investigated how vibration discomfort depends on both the frequency of x-axis backrest vibration and the inclination of the backrest. Twelve subjects seated with a rigid backrest inclined by 0, 30, 60, or 90 degrees rated the discomfort caused by x-axis backrest vibration at 11 frequencies (between 2.5 and 25 Hz) at 9 levels (from about 3 to 24 dB above the absolute threshold in 3 dB steps) relative to the discomfort caused by 0.15 ms-2 r.m.s. 8-Hz x-axis backrest vibration. The subjects also rated the discomfort caused by 9 levels of 8-Hz x-axis backrest vibration relative to the discomfort caused by 2.0 ms-2 r.m.s. 8-Hz x-axis (i.e. vertical) vibration of the hand. The vibration acceleration of the backrest required to cause discomfort tended to be least at 8 Hz with the upright backrest and at 10 or 12.5 Hz with the backrest inclined by 30, 60, or 90. At frequencies from 4 to 8 Hz, about 30 to 40% less acceleration was required to cause discomfort with the upright backrest than with the inclined backrests. It is concluded that frequency weighting Wc is appropriate for predicting vibration discomfort caused by x-axis vibration of an upright backrest, but that another frequency weighting (e.g. Wb) would be more appropriate for inclined backrests.
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