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-   -   4"x8" Port = two 4"x4" Ports for MLTL??? More Complex??? (https://www.diyaudio.com/forums/full-range/49719-4-x8-port-4-x4-ports-mltl-complex.html)

OTMOPO3OK 16th January 2005 11:44 PM

4"x8" Port = two 4"x4" Ports for MLTL??? More Complex???
 
Hi, i'm almost done with the sub and the port is the only thing that separates me from it.
It's a Mass Loaded TL and originally i was gonna use 4"IDx8" port with 3/4"flare on both sides but now i only have 2" of space behind the port and back wall of the line. I think it's too little! Yes/no?
What are the rules for breaking port volume in two ports for MLTL.
If only the mass of air inside the port matters then does it mean i can just saw it in half and have 2 4"IDx4" ports side by side?
Or is there a special formula like for regular BR which takes the inside surface area and friction of air into account and the actual volume has to be bigger?
Please advise ASAP, i can't wait to listen to the sub :)
Thank you very much!!!

PS.Yes, I've searched and haven't found an answer.
Edit: i put this into FR forum because more ppl make TLs here and since it's a general question about ports (not sub specific).

Josephjcole 17th January 2005 04:28 PM

The two variables are the effective port cross-section and the length of the port. the narrower the diameter the shorter the port can be. The larger the diameter the longer it has to be. Changing one 4"x8" port into two 4"x4" ports doubles the effective cross-section and halves the length. This would raise the tuning frequency of the box by quite a bit. I would suggest using a 4"x8" port with a 90 degree bend in it.
Joe

OTMOPO3OK 17th January 2005 04:58 PM

Thank you i think i figured it out:)
Regular rules apply, Doh! ((C)Hommer Simpson)
I decided to try 7" port with the extension due to close proximity of the back wall.


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