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How do I adjust port length when rounding ends? (1 Viewer)

Joe Ku

Stunt Coordinator
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Apr 1, 2003
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69
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.
 

Joe Ku

Stunt Coordinator
Joined
Apr 1, 2003
Messages
69
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.
 

Joe Ku

Stunt Coordinator
Joined
Apr 1, 2003
Messages
69
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.
 

Chris Carswell

Supporting Actor
Joined
Mar 5, 2002
Messages
598
Hey Joe,
Thanks for running the #'s :emoji_thumbsup: .

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

Joe Ku

Stunt Coordinator
Joined
Apr 1, 2003
Messages
69
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?
 

JoelTW

Stunt Coordinator
Joined
Apr 1, 2003
Messages
110
I have the precision port 4", I think I "shortened" the inner section by about 5-6" due to the large radius flare
 

Dennis XYZ

Stunt Coordinator
Joined
Jun 1, 2002
Messages
115
I've always, as a rule of thumb, counted half the flared part in the total length. Example, the sim calls for a 12" port and I'm using flares on both ends with a flare radius of 1". Make the total length after the thing is assembled 13". Of course, in practice, I usually start with them extra long and trim them until I get the tuning I want.

Adire seems to confirm my rule of thumb with their port kits. I think they have about a 1" flare radius.

1. Trim center tube to 5" shorter than the calculated vent length.
2. The vent should be 1" longer than the calculated vent length when assembled.
 

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