How do I calculate slot port (sharing enclosure wall) displacement?

[Based]

I'm trying to design a box and I know I want to have it 4 cubic feet internal airspace tuned to 27hz.

I don't quite understand how I'm supposed to calculate for port displacement. I've read the stickies and I don't get it. And is it different if my port shares the walls of the enclosure? I want it to be a standard slot port at the bottom of the box so it would share the bottom wall and the two side walls.

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[Based]

Can someone please shed some light on this for me? Am I trying to calculate the displacement for the wood inside the box? Or the section of the box the port will take up? Or both?

 

[nismotwin 10+ year member]

The number of walls the slot port shares with the walls of the box is referred to as "common walls". Slot ports are typically 0,1 or 3 common walls. Are you using a box building program for what you're doing?

 

[Jeffdachef 5,000+ posts]

I'm trying to design a box and I know I want to have it 4 cubic feet internal airspace tuned to 27hz.
I don't quite understand how I'm supposed to calculate for port displacement. I've read the stickies and I don't get it. And is it different if my port shares the walls of the enclosure? I want it to be a standard slot port at the bottom of the box so it would share the bottom wall and the two side walls.

Use torres box calc. it does it for you.

 

[Based]

Use torres box calc. it does it for you.

I want to understand how to do it myself.

 

[nismotwin 10+ year member]

Good luck with that. I don't think you understand the math involved. It's not as simple as configuring all the parts and putting them together.

 

[Umbra]

Anything solid inside the box takes up volume and needs to be subtracted from your gross volume (i.e. bracing, subs, port walls). Also treat the space the port takes up in this same way. No, it's not solid, but the volume inside the port does not belong to the box as far as net volume is concerned. Treat the entire port as if it were filled with cement; subtract it from the gross volume.

+1 for Torres calc. There's so many calculations to be done, if there's already a program that does this on the fly it's silly not to use it

 

[Based]

Anything solid inside the box takes up volume and needs to be subtracted from your gross volume (i.e. bracing, subs, port walls). Also treat the space the port takes up in this same way. No, it's not solid, but the volume inside the port does not belong to the box as far as net volume is concerned. Treat the entire port as if it were filled with cement; subtract it from the gross volume.
+1 for Torres calc. There's so many calculations to be done, if there's already a program that does this on the fly it's silly not to use it

Alright I will try Torres. Thanks. I think I'm gonna just build a sealed box for the sub I have anyway. It's EBP is only 40 so it will do better in a sealed. I want to buy a sub with an EBP high enough to warrant a ported box. Even my kicker cvr 12's EBP is only 49.