Excessive vibrations can manifest themselves in terms of internal organ malfunctions and skeletal disabilities. Damage may be rapid when noise is either extremely intense or prolonged. More often, it is insidious in onset and results from continual exposure at lesser intensities. All aviation personnel need to recognize that the damage may become permanent. Sound and vibration energy have measurable characteristics.
Frequency is the physical characteristic that gives a sound the quality of pitch.
Frequency of periodic motion is the number of times per second that the air pressure oscillates. The number of oscillations, or cycles per second, is measured in hertz. Human Hearing and Speech Range 7-7. The human ear is very sensitive and can detect frequencies from 20 to 20,000 hertz. Speech involves frequencies from 200 to 6,800 hertz, the range in which the ear is most sensitive.