Knowledge needed on Port Clearance question. Gurus explain something to me.

[Chris Hammer]

In another thread..I believe the one about switching to a 10" aero/sonotube JoeX stated that a downside to this would be needing 10" of clearance behind the port.

I never thought about it before and it made sense at the time...

but I have been thinking about it all night...about port area and spacing.....I don't feel you would need 10" of clearance for a 10" port from the back wall of the enclosure. Actually it seems to me you would need much less...but I am probably wrong.

Either way let me tell you my thought process here so someone can point out the flaw. I will do my best to describe what I see in my head, as sometimes its really hard to get your point/ideas across effectively on the internet.

If you have a 10" sonotube/straight tube port...with my though process you would only need to have the back of the port 2.5" off the back wall to be able to flow the same volume of air that the port can handle.

The area of the port if its actually 10" inside diameter would be pi*R^2. So pi*(5*5)=78.5 (for arguments sake using 3.14 for pi)

To figure out how far off the back wall the entrance to the port has to be to flow the same volume...Im looking at that area like a cylinder..and figuring the surface area of the side of the cylinder neede equal the surface area of the port.

So to get the area of a cylinder its circumference x height or 2(pi X R) X Height.

2(3.14 X 5) X Height. Now since we are trying to figure out the height so the equation is equal to 78.5 I will set it up to solve for H or Height.

H = 78.5 / 2(3.14 X 5)

H = 78.5 / 31.4

H = 2.5"

I know its not exact because I didn't use actual PI but this is just an example so I can try and explain my thought process.

SOmeone who is more knowledgable can you explain if I'm on the right track here and if there is an error or problem? Also maybe some explanation. I'm sure air velocity and port noise etc will come it to play and this is just scratching the surface..but basically what I'm trying to get at is do you need 10" of clearance for a 10" port or 4" for a 4" port for it to actually be effective?

EDIT: I know I didn't put inches squared or inch signs for the calculations..but everything is in inches.

[Chris Hammer]

Also another thing I noticed. Some people make sure their ports hav emore then enough clearance on the exit side of the port from parts of their car. Like rear facing port in a suv...but I have seen some that have less then the port size and good results.

[bkolfo4]

When you have less distance like in your SUV example, you are actually changing the effective length of the port by changing the end correction factor. In some designs, they might be a good thing

Sort of like the same reason common walls inside the box change the effective length of the port.

It is all about how the air flows through the port and resonates. Anything you do to change the flow or resistance of that air will change how it resonates and changing the tuning frequency. Choke it enough, and it will act just like the port is too small.

[Chris Hammer]

FINALLY someone answered lol. Thanks for the input.