# How do I adjust port length when rounding ends?

Discussion in 'Home Theater Projects' started by Joe Ku, May 12, 2003.

1. ### Joe Ku Stunt Coordinator

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I am currently building the Audax Center channel. The plans call for two 5"long 2"id ports with streight cut ends. I want to use a 1/2" roundover on the exit and a 1/4" on the entrance. Do I keep the total length 5" including the rounded sections? Or do I use 5" plus the roundovers (total of 5.75")? Or something in between?

Thanks for any input you can give me, I am hoping to glue it up tonight or tomorrow, I will post pics when I am finished of course.

2. ### Joe Ku Stunt Coordinator

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Got the answer, thanks guys, if anyone is curious here it is

2"id port
1/2" roundover is equal to .62 inches on streight port
1/4" roundover is equal to .28 inches of streight port

so the short answer would be it doesn't matter much at all.

3. ### Chris Carswell Supporting Actor

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What is 3/4" & 1" roundover is equal to?

4. ### Joe Ku Stunt Coordinator

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Here are the numbers I have, I would like to know if anyone disagrees,

2"dia port
1/4" radius = .28" of streight pipe
1/2" radius = .62" of streight pipe
3/4" radius = 1.03" of streight pipe
1" radius = 1.52" of streight pipe

3"dia port
1/2" radius = .58" of streight pipe
3/4" radius = .93" of streight pipe
1" radius = 1.33" of streight pipe

4" dia port
1/2" radius = .56" of streight pipe
3/4" radius = .88" of streight pipe
1" radius = 1.24" of streight pipe

What these numbers indicate is that if you use a 2"port with a 1 inch roundover on one end you would shorten the port length by .52" to account for the port rounding.

5. ### Chris Carswell Supporting Actor

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Hey Joe,
Thanks for running the #'s .

Are you sure about the shortening part? IIRC, you add length to a rounded port.

6. ### Joe Ku Stunt Coordinator

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I'm never sure of anything... with that said, The numbers I listed are based on equivelent volumes, the example I gave will maintain the same volume of air in the port. However I think you may be right about lengthening instead of shortening because of the inverse relationship between port length and diameter.

Could someone who has used a precision port clairify this?

7. ### JoelTW Stunt Coordinator

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I have the precision port 4", I think I "shortened" the inner section by about 5-6" due to the large radius flare

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