|Definition:|| acoustic energy flow rate per unit area in the direction of propagation
NOTE 1 – Strictly speaking, acoustic intensity is a vector quantity that varies with position. Its component in any direction is the acoustic energy flow rate in that direction per unit area normal to that direction. In most practical cases, however, it is sufficient to consider only one particular component of the intensity vector, namely that in the direction of propagation. This meaning of the term "intensity" is understood in the above definition and in the definitions below, i.e., in 802-01-10, 802-01-14, 802-01-15, 802-01-16, 802-01-17, 802-01-18, 802-01-23, and 802-01-24.
NOTE 2 – In ultrasonics, the term acoustic energy flow rate is more commonly used than sound energy flux.