Bass-reflex frequency response formula?

[Blight]

I am looking for a bass-reflex enclosure frequency response formula for plotting a curve in a calculator program I am making as a course project. Can anyone give me any leads to where I can find that formula? I tried this :

http://homeswinghome.free.fr/audioreceipes/bassreflex.htm

but it doesn't seem to work. Am I doing something wrong?

 

[gberchin]

I've used this. From Neville Thiele himself.

 

[Blight]

Awesome, thanks! I'll see if this works.