When calculating a port, I know it is common practice to have 12-16in^2 of port area per cubic foot of air space.

Now is this for all ports or just slot ports?

 

Port area has virtually zero to do with box volume. Port area is governed mostly by cone displacement and then way down in second place, tuning frequency.

But to answer your question - treat round ports and rectangular vents the same way.

 

Thanks Dukk.

 

x2, big time!

 

but its still common practice/common sense not to go lower than 12 sq in of port per cubic foot unless you enjoy port noise

 

^ Absolutely not. How can you relate port area to box volume?

Port area is related to cone displacement.

 

I thought that port noise was caused by the port itself. The faster the air is moving through it and the smaller the port equals noise. It makes sense that it has virtually nothing to do with the box attached to it.

 

^ Exactly. And to expand on that, what is making the noise? The velocity of the air.

what affects the velocity? The volume of air forcing it's way through the opening.

what dictates the volume of air? The displacement over time of the driver.

Where does the box volume come in? nowhere.

I understand where this 'rule of thumb' came from but the theory behind it is bad - I suspect someone tried to really dumb box theory down for people and in doing so can cause more harm than good.