Conventionally a sound wave is considered as a compression wave whose activity is usually likened to a periodically compressed and stretched coiled spring (Figure 8.3 - Coiled Spring showing Longitudinal Wave) and/or swinging pendulum (Figure 8.9 - Four Fundamental Motions of a Pendulum). This is a mechanical force against force (Newtonian) model. This model is predicated on the idea of an outside sound source compressing a medium (such as air) by molecular bombardment; or as molecules set in motion, striking other molecules repeatively much like billiard balls across a billiard table. After the strike comes an alternate relaxing or expanding of the media to a state of rarefaction - of a less dense or compacted state or condition. This view of course cannot work as presented for two reasons:
1) impact force and motion does not conduct or transfer further than one or two occurences or iterations and
2) there is nothing (such as placement/inertia memory) to continue the back and forth motion (inertia?) of the media particles other than continuous motion of the causitive disturbance (such as a tuning fork).
A simple observation of a vibrating violin string in a concert auditorium reveals there is no conceivable way that that single string can so orderly move that many air molecules with the over simplified impacting molecule theory of wave propagation. Propagating waves are not a Newtonian phenomena though they do manifest as such. Therefore the cause or method of propagation is periodic quantum or Etheric Disturbance of Equilibrium. More on this later. Of course, the destruction of the impacting molecule theory of wave propagation will dismantle vast sweeps of conventional Newtonian physics.

See Also

9.1 - Propagation Function and Rates
9.2 - Wave Velocity Propagation Questions
9.12 - Velocity of Sound and its Propagation Rate are Proportional
9.34 - Wave Propagation
17.04 - Speed of Gravity Propagation
Disturbance of Equilibrium
Propagation