Duct modes
# Duct modes

The acoustic pressure in a cylindrical duct can be expressed as the superposition of duct modes:

    $p=\sum \alpha _{i}\phi _{i}$

where $\alpha _{i}$ is the participation factor or modal amplitude and $\phi _{i}$ is the mode shape. The duct mode shape are analytically determined from the solution of the Helmholtz equation.

