The Physics of Waves

    Sound waves are pressure oscillations in the air or another medium.  The wave moves as the particles in the medium interact with the particles next to them. Thomas Henderson notes, "as one air particle is displaced from its equilibrium position, it exerts a push or pull on its nearest neighbors, causing them to be displaced from their equilibrium position" (Henderson). The speed of sound in air at sea level is approximately 340 meters/second. 
        wave properties

Properties of a Wave

    The crests are the points of maximum height above the equilibrium and the troughs are the lowest points below the equilibrium.  The equilibrium is represented by the horizontal line in the middle of the wave.  One period is the time it takes to  go for one cycle, which means to get from one crest to crest, trough to trough, or to and from corresponding equilibrium points (both equilibrium points same direction).  The units for period are measured in seconds per cycle.  The frequency of the wave is the inverse of the wave length.  The unit is Hertz, and it measures cycles per second.  The frequency is 1/period and period is 1/frequency. The wavelength is often denoted with the Greek letter lambda, and represents the length of the cycle.  The angular frequency is 2pi (frequency), and that is in radians/second and often denoted with the Greek letter omega.

             amplitude pic
The amplitude of the waves corresponds to volume.

        The amplitude of the wave is the height above the equilibrium point.  In sound waves this corresponds to air pressure and volume.  This becomes important for active noise cancellation because opposing waves can interfere with each other and cancel out the amplitude.