The air we breathe is actually an elastic medium that will yield to certain changes and then return to a state of equilibrium. Because of this physical property, sound is created when air molecules are disturbed and set in motion. This disturbance occurs when an object, called a sound source, vibrates. The air molecules around that object are forced into other molecules, resulting in areas of denser and less dense air that radiate away from the source as waves of acoustic energy.
Finally, our ears perceive the fluctuations in air pressure and transmit these sensations to our brain, which interprets them as sound.
Example 1-1: The vibrating sound source causes changes in air pressure that create waves of acoustical energy that we perceive as sound.
In short, sound transmission has three components:
1. the vibrating sound source, such as the string on a violin.
2. the medium through which these vibrations travel. Usually we think of air as the medium, but other things, such as water, will conduct sound.
3. the receiver of sound which senses the resultant fluctuations in air pressure being transmitted through the medium.