Decreasing tuning frequency: slot port wall

[WalledSonic]

I designed a ported enclosure for my (4) 15's.  12.5 cu ft (pic below says 13, its actually 12.5), dimensions shown below, tuned to 33Hz with TermPro.  Port is 5"W x 21.5"L x 28.25"H. I want to drop my tuning down a bit.  TermPro says if I add ~2.5" of port, I can decrease the tuning a couple hertz.

 

Question: is it worthwhile to add a triangle or kerfed 'splitter' at the back of the box?  If I am careful with my measurements and am able to maintain an appropriate cross section, can this help drop my tuning down a bit?  Pic of what I mean shown below as an overly simplified darkened triangle:

Any input is appreciated.

 

[Jessica]

adding 45°'s  is hit or miss with enclosures. but i think adding a triangle at the port split would help some. are you chasing numbers or just looking to make it sound better"?

[audiofanaticz]

If your port is 5 inches wide, then where the port turns against the back wall should be 2.5 inches wide, not 4.

Where your port turns, that extended length of it is doing nothing at all as far as tuning goes.

[ShadeTreeMechanic]

Maybe building up the back wall behind the port will make use of the end of the port that goes to the right and to the left?

[WalledSonic]

10 hours ago, audiofanaticz said:

If your port is 5 inches wide, then where the port turns against the back wall should be 2.5 inches wide, not 4.

Where your port turns, that extended length of it is doing nothing at all as far as tuning goes.

AF, 4" in the back is just how my box is designed now.  I shouldve spent more time on the sketchup. I would indeed make the rear two 'ports' 2.5" width.  

I'm not sure how trustworthy the TL calculations are to real world since I've only made one box with the calcs from TL.

I'll assume from the 3 replies above that the answer is 'it'll work if you make your rear ports correctly'.

One issue is that I'll be using up some volume to add this rear kerfed splitter.  About 0.5 cu ft lost.  Unfortunately, once I go from 12.5 cu ft to 12 cu ft, that bumps my tuning up a bit, so I dont know if the whole exercise will be moot at the end of it.

Duck, I was hoping to have better low end response without rebuilding my box.  Its currently tuned to 33-34Hz.

[ShadeTreeMechanic]

It is hard to get the port to fit in the box sometimes. Is there any way to bump the back wall out or even a section of it?

[audiofanaticz]

The TermLab design software is pretty good. Its what I use the majority of the time, but there are some things I dislike about it and still have to adjust for some things manually.
Going off your port height measurements, adding that 45 in the middle of the port if you make each 45degree panel 5 inches wide will only displace .204 cubic feet.
Adding the the 45 in the middle will not increase your port length, and it will take up space making it raise the tuning opposite of your desires.
Unless that is if you do away with the 90 degree port walls and angle them 45 degrees to match the middle triangle and have 2.5 inches of spacing on each side.
But before doing it, you should crunch the numbers to see if the additional 45 triangle and port extensions would give you a lower tuning even though your taking up more displacement.

It could only maybe drop you down 1hz after its all said or done, or for that matter raise it.

Like so:

[ShadeTreeMechanic]

Is there a way to extend the port straight back to get the needed distance from the back wall? Or maybe make another port?

[DLHgn]

If it's possible with your enclosure you may want to think about extending the port outside the enclosure. This way would let you play with a couple different sizes to see what you like the best. 

[WalledSonic]

Thanks for all the input guys. The port is VERY non-removable, lol.  I also have a nice stain on the face of the box, so the back-wall-area is all I can change.  The tuning isnt bad, but if I had a bit more control on the low-lows, then this effort may be worth a shot. 

I'm thinking of doing a curved/kerfed 'splitter' at the back and just screw it in without glue to see how it does.  That way I can remove it and refinish the back wall if it doesnt go as planned. Here's the idea, I sketched it up real quick in CAD.  Its an optimum version of AF's advice from above:

With this piece added, I expect to lose ~0.5 cu ft of box volume to "extended port volume and splitter volume".