Sound in air is the transfer of periodic movements between adjacent colliding atoms or molecules. This sonic energy typically expands away from the site of the collisions as a spherical or bubble-shaped emanation, the surface of which is in a state of radial oscillation.
The sonic bubble expands and contracts with the same periodicities as the initiating sound source. The accepted model of sound waves is incomplete because it uses the graphical representation of the mathematical law of sinusoidal energy, typically given as amplitude in the vertical axis versus time in the horizontal. While this is correct in terms of graphical depiction, it is not how the energy actually moves through space.
Sound in air does not travel as longitudinal waves as is commonly described in physics text books. Sound propagates spherically in air due to diffraction, the reactive result of atomic collisions. Reciprocal effects in air occur in the jostling of molecules initiated by a sound event, causing components of the sonic energy to move in all directions almost simultaneously. The distribution of energy within the sonic bubble is always concentrated on axis with the direction of primary propagation from the sound source.cymascope.com