Description
We now consider an open ended duct.
The boundary conditions imply approximately that
(zero pressure at the output as shown on the left) and more precisely that
(see figure on the right), where,
is the radiation impedance defined in section 3.1.
Physically, and at low frequencies, this corresponds to the displacement of a volume of air in the length of tube. The volume velocity is therefore homogeneous in the tube and there is a pressure drop between the input and output due to the inertial effects.
Complément :
The radiation impedance expresses the reaction of the surrounding medium to the volume velocity source at the output of the tube, creating pressure at the output
