Reflex PA Sub - Volume and Port Design?

[Xoc1]

I Own 2 Fane XB 15" 600W drivers and my brother has aquired another 4 Fane 15" 15B 400W Drivers.
They are quite similar in construction, and are both usable in the same type of enclosure without any modification.
We have decided that it would be a good idea to design a new cabinet suitable for both speakers. The drivers would be in separate enclosures for portability. This would allow us to combine our systems for larger venues.
I still have my original bass cabinets that I built in 1999 but their major shortcoming is that the port size is to small. We have tried various tuning frequencies, and are confident that approx 46hz works for what we want.
Volume is 120 litres.
New enclosure design is to be a simple rectangular box with a full width shelf port. Port size will be approx 10 x 46 cm and the depth of the port would be 36.5 cm according to winISD.
Construction will be in 18mm birch ply, with bracing.
Crossover is a tweeked Behringer DCX2496, and I can keep within Xmax at the drivers rated power with 4 order butterworth hi pass at 38Hz.
Low pass is about 190Hz.
So having decided on what we want to build, and simmed it up in winISD, I need to draw up a prototype.
Questions I have include:-
I have never built a cabinet with such a large port. When calculating the internal volume do I subtract the volume of the port?
How close to the rear of the cabinet can the shelf forming the port be before performance is affected, if the port is 10cm wide what would be a minimum safe distance?
(If need be I will reduce the port size to reduce the depth.)

[Xoc1]

First draft of cabinet
Looks like distance between the port and the rear panel will not be an issue
Panel sizes will hopefully work well with 8 x 4 feet stock timber sheets.
Any comments welcome.

[jwmbro]

Originally Posted by Xoc1

When calculating the internal volume do I subtract the volume of the port?

Yes

Originally Posted by Xoc1

How close to the rear of the cabinet can the shelf forming the port be before performance is affected, if the port is 10cm wide what would be a minimum safe distance?

Well, if you have exactly 10cm, you can basically consider the port to be longer, like this (measurement between the red lines):


If you want to measure only to the orange line, I'd suggest using at least double the width, so in your case 20cm.

[Xoc1]

Thanks
Distance to rear panel from the shelf is 231mm. So that should be OK.