Investigation of the effects of vibration on dial reading performance with a NASA prototype Apollo helmet Final report, Dec. 1965 - Mar. 1966

Vibration effects on dial reading performance with prototype Apollo helme

Subjective ratings of whole-body vibration for single- and multi-axis motion

Real-world whole-body vibration exposures comprise motion in fore-aft, lateral and vertical directions simultaneously. There can also be components of roll, pitch and yaw. If evaluating vibration with respect to human response, most investigators will use methods defined in ISO 2631-1. This uses frequency weightings that were originally derived from laboratory studies of the subjective responses to vibration in one direction at a time. This paper describes experiments carried out using a 6 degree-of-freedom vibration simulator to validate the applicability of ISO 2631-1 in multi-axis environments. 15 subjects were exposed to 87 stimuli comprising single-axis, dual-axis and tri-axial random vibration, to which they were required to produce subjective ratings. It is shown that in this study the root-sum-of-squares method of summation of subjective ratings in individual axes was an adequate technique for prediction of subjective rating of multiaxis vibration. Better agreement between objective and subjective measures of vibration was obtained for unweighted vibration than for frequency weighted signals. The best agreement for this study was achieved when axis multiplying factors were set at 2.2 and 2.4 for x- and y-axis vibration respectively. Different values could be appropriate for other postures, seats, and vibration conditions and should be determined in future studies

Equivalent comfort contours for vertical seat vibration: effect of vibration magnitude and backrest inclination

This study determined how backrest inclination and the frequency and magnitude of vertical seat vibration influence vibration discomfort. Subjects experienced vertical seat vibration at frequencies in the range 2.5 to 25 Hz at vibration magnitudes in the range 0.016 to 2.0 ms^-2 r.m.s. Equivalent comfort contours were determined with five backrest conditions: no backrest, and with a stationary backrest inclined at 0 degree (upright), 30, 60 and 90 degree. Within all conditions, the frequency of greatest sensitivity to acceleration decreased with increasing vibration magnitude. Compared to an upright backrest, around the main resonance of the body, the vibration magnitudes required to cause similar discomfort were 100% greater with 60-degree and 90-degree backrest inclinations and 50% greater with a 30-degree backrest inclination. It is concluded that no single frequency weighting provides an accurate prediction of the discomfort caused by vertical seat vibration at all magnitudes and with all backrest conditions.Practitioner Summary: Vertical seat vibration is a main cause of vibration discomfort for drivers and passengers of road vehicles. A frequency weighting has been standardised for the evaluation of vertical seat vibration when sitting upright but it was not known whether this weighting is suitable for the reclined sitting postures often adopted during travel

The effects of sound level and vibration magnitude on the relative discomfort of noise and vibration

The relative discomfort caused by noise and vibration, how this depends on the level of noise and the magnitude of vibration, and whether the noise and vibration are presented simultaneously or sequentially has been investigated in a laboratory study with 20 subjects. Noise and vertical vibration were reproduced with all 49 combinations of 7 levels of noise and 7 magnitudes of vibration to allow the discomfort caused by one of the stimuli to be judged relative to the other stimulus using magnitude estimation. In four sessions, subjects judged noise relative to vibration and vibration relative to noise, with both simultaneous and sequential presentations of the stimuli. The equivalence of noise and vibration was not greatly dependent on whether the stimuli were simultaneous or sequential, but highly dependent on whether noise was judged relative to vibration or vibration was judged relative to noise. When judging noise, higher magnitude vibrations appeared to mask the discomfort caused by low levels of noise. When judging vibration, higher level noises appeared to mask the discomfort caused by low magnitudes of vibration. The judgment of vibration discomfort was more influenced by noise than the judgment of noise discomfort was influenced by vibration