Acoustic Variables

• When analyzing acoustic systems, the primary variables of interest are pressure and velocity.

• Acoustic pressure is defined as force per unit area. It can also be interpreted as energy density.

• In acoustic systems, velocity can be expressed either in terms of particle velocity ($v$) or volume velocity ($u$).

• In enclosed air ducts, it is more typical to consider volume velocity or particle velocity times the cross-section area $A$ of the duct ($u = A v$).