ResonanceCalc is the app which can do a vent design more in detail.
It calculate the resonance frequency from the box volume and vent size.

The box volume corresponds from three sizes or volume(Liter).
There is setting by which the volume of the vent is subtract from the box volume.
It's possible to estimate filling of a fibrous material.
The open end correction of a vent is included.
An air column resonant frequency of a vent is displayed.
An effective vent length by open end correction is displayed.
A Q of vent value is displayed.
Capture of a window screen.