Box Volume in real part application

Background: Building my own 3way speaker cabinet, trying to do as small possible with response aas effective as possible with my speakers I have. I tried to use this app to define correct Volume parameters , define frequencies for Bass reflexes, and I am trying to rework it in my CAD, because this app generator cannot build complete speaker cabinet, only the simple Subwoofer part....

Question: https://ibb.co/tKQKfnz  From this app I defined Woofer Box 40liters of Volume. But in real part, I need to have the box as Stiff as possible with aditional stiffeners, and also put there a closed volume for Midrange and tweeter...... Do this area counts as a net volume (of course in CAD I can calculate air space correctly) ? Or those grills and its cavity shape counts as some kind of Port or some kind of transmission? I am confused in that.

Thank you for help, dont wanna start with it untill I will be sure about that.

VB on this tab shows a useful volume. It doesn't include any displacements such as drivers, braces, and so on. If I correctly understand the question.

that means, all those internals, like stiffeners and this "L" shape cavity, will not affect calculation?

What you told me is exactly how I understood it, but I dont know if the Volume must be strictly "Cubic" , or it should have such a complex designs like I shared on the picture?

I'm sorry for the delay. All internals take space from the box and you should be sure that you added their displacements to the total box volume if you mean volumes. If you mean the transfer function and others, they also have an influence on the total plots but it is not taken into account by the program, I don't think that they are too large. Also, the geometry is the same thing.