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Discussion Starter · #1 · (Edited)
Hello all, first of all thanks all the participant in DIYMA i have been reading this for years and learning a lot in this forum.

I am building a ported box that must be as slim as possible and i came with the idea of a labyrinth port, but the internal port opening, is ~ 4 inch close to the driver and was wondering if there can be any issue being too close.


Port area is like 14,6 per cubic foot and tuned to ~33 hz, port dimension is 14,6 H x 1.9 W and my port speed is bellow 16 m/s

Thanks in advance.

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I'm doing something similar and decided against a slot/labyrinth because I wasn't sure how that angle would affect the port and how to properly calculate the length. I'm doing a tube port using pcv pipe instead.

Alternatively could you add one more fold and have the port opening on the back wall?
 

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Discussion Starter · #3 ·
I'm doing something similar and decided against a slot/labyrinth because I wasn't sure how that angle would affect the port and how to properly calculate the length. I'm doing a tube port using pcv pipe instead.

Alternatively could you add one more fold and have the port opening on the back wall?
Port Length is not a doubt to me as the angle is made to balance the length so it should be the same all over the port, i am only concern on the opening being close to the driver at some point. I've seen some design with the opening on the back of the sub but on the front?

I also think on making two 4 inch port but air speed is slightly higher. With this setup i am getting < 16 m/s and with two 4 inch tubes i am getting 19.5 m/s peak at 29 - 31 hz.
 

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Port Length is not a doubt to me as the angle is made to balance the length so it should be the same all over the port, i am only concern on the opening being close to the driver at some point. I've seen some design with the opening on the back of the sub but on the front?

I also think on making two 4 inch port but air speed is slightly higher. With this setup i am getting < 16 m/s and with two 4 inch tubes i am getting 19.5 m/s peak at 29 - 31 hz.
Gotcha. The rule of thumb is one port diameter distance of clearance, for a round port of the same area that would be 4". Here they say 2x the port width for a slot which is also 4"


I think you should be good.
 

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Port Length is not a doubt to me as the angle is made to balance the length so it should be the same all over the port, i am only concern on the opening being close to the driver at some point. I've seen some design with the opening on the back of the sub but on the front?

I also think on making two 4 inch port but air speed is slightly higher. With this setup i am getting < 16 m/s and with two 4 inch tubes i am getting 19.5 m/s peak at 29 - 31 hz.
19.5 m/s peak is nothing to be concerned about.

I've made boxes with 30+ m/s air speed on the port with zero noise during play, I think you should be ok.
 

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Gotcha. The rule of thumb is one port diameter distance of clearance, for a round port of the same area that would be 4". Here they say 2x the port width for a slot which is also 4"


I think you should be good.
That is rule of thumb for port to interior wall clearance but does that also apply to port to sub clearance?
 

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Discussion Starter · #7 ·
Gotcha. The rule of thumb is one port diameter distance of clearance, for a round port of the same area that would be 4". Here they say 2x the port width for a slot which is also 4"


I think you should be good.
Thanks in that case it should be ok, my port width is 1.9 inch and the clearance from the port opening to the sub hole is 4.2 inches and the sub will move to the inside , and it is only on the upper part of the port. I will try and will post later how it goes.
 

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A bit more info from the WinISD help section:


End correction
End correction factor is analytically or empirically determined factor, how much port extends beyond its physical ends. For free end, end correction is 0.30665 times port effective diameter. For flanged end, more analytical expression is available, 4/(3·pi) ~= 0.42441 times port effective diameter. Flanged end is calculated assuming that tube terminates to infinite baffle.
For your slot, the "effective diameter" is 2*sqrt(14.6x1.9/pi) = 5.94 inches. The end correction is essentially how far past the physical port the air is acting as part of the port, or basically how much clearance you need. So for flanged that would be 2.52 in. and for free end that would be 1.82 in. In reality it's probably somewhere in between, since on one side of the port is the front baffle and on the other just the inside of the box. But in either case I think 4" is good and gives you plenty of safety factor. And the rule of thumb for 1 port diameter or 2*port width makes sense too looking at this.
 

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Discussion Starter · #10 ·
A bit more info from the WinISD help section:




For your slot, the "effective diameter" is 2*sqrt(14.6x1.9/pi) = 5.94 inches. The end correction is essentially how far past the physical port the air is acting as part of the port, or basically how much clearance you need. So for flanged that would be 2.52 in. and for free end that would be 1.82 in. In reality it's probably somewhere in between, since on one side of the port is the front baffle and on the other just the inside of the box. But in either case I think 4" is good and gives you plenty of safety factor. And the rule of thumb for 1 port diameter or 2*port width makes sense too looking at this.
This logic applies also for the outside of the box? i mean the port extends 1.82 from the outside of the box
 

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This logic applies also for the outside of the box? i mean the port extends 1.82 from the outside of the box
Yes both sides of the port

Edit:

Actually the end correction would probably be different on the outside because the walls surrounding the port are different. But again I'd expect somewhere in between the flanged and free end values.
 
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