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Old 04-16-2012, 09:44 AM
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Default Port calculator question

Why when figuring port length for say 30hz if you say the port is 30in tall 8in wide it says it needs to be 28in long, But if you say 8in tall and 30in wide it says it only needs to be 12in long for the same tuning.

This makes no sense to me, so if I took my box and turned it on its side it will not change the tuning?? Can someone explain this to me. This has made designing my next enclosure alittle difficult.

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Old 04-16-2012, 12:28 PM
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how are you calculating your port length?
The port volume isn't changing, it'll be the same length either way.

What can affect port length is if your using one side of your enclosure as a side of the port.
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Old 04-16-2012, 01:04 PM
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Thats what I thought, I am using the wall of the box in both cases.
I always this calculator Car Audio - PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES

But reversing W and H it changes the recommended length. I always have done vertical so I guess I will just use those figures, lol
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Old 04-16-2012, 01:23 PM
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That is odd, what calculator are you using?
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Old 04-17-2012, 12:17 AM
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Quote:
Originally Posted by n8skow View Post
how are you calculating your port length?
The port volume isn't changing, it'll be the same length either way.

What can affect port length is if your using one side of your enclosure as a side of the port.
This is correct. If you are using one of the sides of the enclosure as a port wall, you can subtract half of the width of the port from the length. I'm guessing that the difference here is that you're calculating one port being in the center of the enclosure, while the other (shorter) on is on the side.
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Old 04-17-2012, 01:06 AM
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Quote:
Originally Posted by SPLEclipse View Post
This is correct. If you are using one of the sides of the enclosure as a port wall, you can subtract half of the width of the port from the length. I'm guessing that the difference here is that you're calculating one port being in the center of the enclosure, while the other (shorter) on is on the side.
I understand how to accommodate my port length when using walls etc etc. that has nothing to do with my question.

If you click the link and enter in a slot port h and w and enter in the tuning freq you want and air space it tells you how long to make the port. Now reverse the numbers and it gives a different length. This is the second calculator I have used that does this.
My design is now done but it's strange as to why it does this
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Old 04-17-2012, 01:35 AM
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Quote:
Originally Posted by SPLEclipse View Post
I'm guessing that the difference here is that you're calculating one port being in the center of the enclosure, while the other (shorter) on is on the side.
Quote:
Originally Posted by SWIFT View Post
I understand how to accommodate my port length when using walls etc etc. that has nothing to do with my question.

If you click the link and enter in a slot port h and w and enter in the tuning freq you want and air space it tells you how long to make the port. Now reverse the numbers and it gives a different length. This is the second calculator I have used that does this.
My design is now done but it's strange as to why it does this
It's because when your width is the shorter dimension, It "thinks" the port is not sharing a side wall (think a center slot port in-between two subs).
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Old 04-17-2012, 08:24 AM
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Sorry, I didn't see the link. Explain the difference in using side wall length difference than a center slot port. I'm a little confused on that.
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Old 04-17-2012, 08:36 AM
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Quote:
Originally Posted by SPLEclipse View Post
It's because when your width is the shorter dimension, It "thinks" the port is not sharing a side wall (think a center slot port in-between two subs).
That would make sense if the difference was the port width but it's not. If you actually try it a few ways you will see. 12volt's calculator doesn't do that and equals the vertical example on car stereos. Which is good since I have used carstereo's calculator for the last 6 builds I have done, by entering in all vertical numbers.
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Old 04-17-2012, 08:47 AM
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Quote:
Originally Posted by Kevin K View Post
Sorry, I didn't see the link. Explain the difference in using side wall length difference than a center slot port. I'm a little confused on that.
There is no difference until you get a length that will have a bend in it, at that point you will always measure airflow at the center of the port.

So if it tells you you need 25in length of port but your box is only 25in deep. Well let's say your port is 20 tall and 4 wide. You stop the actual port wall 4 inches from the back wall. The airflow will travel 22.25, then turn go the 2in back to port wall, then .75 wood thickness. 22.25+2+.75 = your 25in length needed. Hard to put in writing
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