Chapter 32. Noise Measurement
32.1. Sound and Sound Fields
32.1.1. The Nature of Sound
If any elastic medium, whether it be gaseous, liquid, or solid, is disturbed, then this disturbance will travel away from the point of origin and be propagated through the medium. The way in which the disturbance is propagated and its speed will depend upon the nature and extent of the medium, its elasticity, and density.
In the case of air, these disturbances are characterized by very small fluctuations in the density (and hence atmospheric pressure) of the air and by movements of the air molecules. Provided these fluctuations in pressure take place at a rate (frequency) between about 20 Hz and 16 kHz, then they can give rise to the sensation of audible ...