Since the ear is not equally sensitive to all frequencies, two noises having the same sound pressure levels may or may not sound equally loud, depending on their frequency composition. Furthermore the pattern of sensitivity to different frequencies changes with age, with sensitivity to high frequencies dropping off disproportionately more with age. Reduce noise at its source. Interrupt or absorb noise along its path of transmission. Provide personal hearing protection.
Vibration is the alternating motion of a surface or body with respect to a reference point.
Vibrating objects may cause the whole body, or only parts of it, to vibrate Vibration may be transmitted to operators by direct mechanical paths or through several flanking paths. Example of head-seat transmissibility of a sitting subject, either leaning against a backrest or without using the backrest Figure 5.9 from K.Kroemer 1994 Human Responses to Vibration Chain saws pneumatic compactors, and electric hand tools, transmit vibrations to the hands and arms and are often responsible for cumulative trauma disorders. Vibrations from tools can be absorbed by cushioned seats, foot restraints, handholds, and mountings. Vibration may affect performance either by modifying perception, blurring visual images of dials and indicators, or affecting control movements. Table 5.9 shows some effect of vibration.