I've always designed the box with the port on the side, but now I need it in the middle (using 2 subs). I do know that when the port splits off the port width gets halved, but is the whole length of the port mean that each side is the port length?

 

Let's say I have a box that is 6" wide and 30" long. When it splits off each side will have a width of 3", but does each side equal 30" long? Someone also told me that you add half of the width of the port to each side of the port length. So each length would actually be 33" long. I don't know why that would work though.

 

When I design boxes I use torres and there's a box that says "# of common port walls". I put 2 in there, but does that mean that I don't have to add half of the port width since it knows the port is in the middle?

Yes each side will equal the 30" length.  I've also found that adding the width of the split to the length helps to ensure tuning is where it's supposed to be.  So with your example you would add 3" to the 30" length making a total length of 33" to keep the tuning on par.

 

On Torres calculate it like you would for a standard slot port that's on the side.

 

 

EDIT:  I think I get the dilemma in your question now.  The calculation is still for the 30" total length.  I'll find one that I drew up and toss it up for an example.

No need to add length to the port depending on the formula used. The most common equations have something along the lines of...

)+r^.5

At the end if the formula. This is the "extra" length people refer to. It's already calculated in the formula.

And yes. Each port must be whatever length the port must be for tuning.

Okk thanks guys. Just wanted to make sure!!