slot port fitting problem, help please!

[mestapho]

So I am designing a 38 x 13 x 21.75 box (external including double front baffle) for 2 SA12 dual 4's

net after subs and port is 3.8 cubes tuned to 33.5 (sundown says 35 hz, forums I'm seeing 32 so split the difference) 

4 x 11.5 x 21 center port.  

1200 watts from Pioneer 9601.

Here's the issue,  If I stop the ports to make turns to the sides of the box, half the port width, 2" from the rear wall, the center measurement over 21 inches (22.75") just with the width of the port wall.

Will this tune like a 19" port, or like a 22.75" port?

Is it fine how it is? Should I change it, if so what/how? 

Any advice is much appreciated.

[Joe X]

In your situation port length should be measured as follows:

Port physical length = L1+L2

[mestapho]

5 minutes ago, Joe X said:

In your situation port length should be measured as follows:

Port physical length = L1+L2

 

I was really hoping you'd see this post, Thank You!

 

Ok, so should I make the L1 longer/shorter so the L1 + L2 = 21 even if that means that L2 width is less/more than 1/2 port width?

That's my problem.  Currently L1 + L2 = 22.75, with L2  width at 2" (1/2 port width). If I shorten L1 I can get 21" in middle port measurement but the width of L2 will not be 1/2 port width.

 

I hope that makes sense.

[Joe X]

If doing a shared port L1 needs to stay 1" from the back wall in this case, any extra length will come from L2.

Looking at your port area, it seems you might need more, that would also get your needed center line length off the turn.

[mestapho]

My port is 4" wide so L1 should be 2" from the back, correct?

 

At 1200 watts WinISD is modeling at around 26 m/s, should be fine, I might play with a 5" port but then I'm eating up volume. trying to stay between 3.75 and 4 net cubes.  Thanks for the help I play with it some more tomorrow evening.  Really appreciate your time.

[Joe X]

The width of the side ducts would be 2" each, that will put the center line for them at 1" from the back wall and that puts L1 at 1" from the back wall as well. No rush, you can also change your tuning a little, one or two Hz difference is not going to be noticeable to most people 

[mestapho]

26 minutes ago, Joe X said:

The width of the side ducts would be 2" each, that will put the center line for them at 1" from the back wall and that puts L1 at 1" from the back wall as well. No rush, you can also change your tuning a little, one or two Hz difference is not going to be noticeable to most people 

Ok, I see what your saying.  I was confusing L1 with the port wall.  It’s the center port line.  I see now.  

[mestapho]

Redid the design and got it put together.  

3.5 cubes at 35 Hz

sounds great, just need to sand and round the edges and finish it  with duratex