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

Equal sensation curves for whole-body vibration expressed as a function of driving force

Previous studies have shown that the seated human is most sensitive to wholebody vertical vibration at about 5 Hz. Similarly, the body shows an apparent mass resonance at about 5 Hz. Considering these similarities between the biomechanical and subjective responses, it was hypothesised that, at low frequencies, subjective ratings of whole-body vibration might be directly proportional to the driving force. Twelve male subjects participated in a laboratory experiment where subjects sat on a rigid seat mounted on a shaker. The magnitude of a test stimulus was adjusted such that the subjective intensity could be matched to a reference stimulus, using a modified Bruceton test protocol. The sinusoidal reference stimulus was 8 Hz vibration with a magnitude of 0.5 m/s² r.m.s. (or 0.25 m/s² r.m.s. for the 1 Hz test); the sinusoidal test stimuli had frequencies of 1, 2, 4, 16 and 32 Hz. Equal sensation contours in terms of seat acceleration showed data similar to those in the literature. Equal sensation contours in terms of force showed a nominally linear response at 1, 2 and 4 Hz but an increasing sensitivity at higher frequencies. This is in agreement with a model derived from published subjective and objective fitted data