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Converting ports
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Young Croc
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Joined: 23 December 2018
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    Posted: 28 November 2023 at 9:40pm
I have a BR design with a slot port without flare, but i need to convert it to a flared oval shaped port.

Slot port is 50x470mm and 185mm long. Should give 4,3475 Liters.
Am i on the right track if i make a port with the same crosssectional area and length as the slot port?

What does the flares do for the total length of the port?
The goal is to ad a 25mm radius flare at both ends.
What would the total length of the 185mm long port with 2x radius 25mm flares be?

From what i understand i have to take the effective length (185mm) and add half of the flare radius (12,5mm) to the effective length of the port.
In this case that would be 185mm + 12,5mm + 12,5mm = 210mm.
That will end up being a 235mm long port including the 2x radius 25mm flares.

Is this total bull?

And finally, what would these changes do to the sound and performance?
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smitske96 View Drop Down
Young Croc
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Points: 1217 		Post Options Post Options   Thanks (0) Thanks(0)   Quote smitske96 Quote  Post ReplyReply Direct Link To This Post Posted: 29 November 2023 at 7:01pm
If the slotport is adjecent to some cabinet walls, tuning will be lowered because of it.
Also I would not put such a radius on the ends. You will need a much larger curved vent with those sizes.
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Elliot Thompson View Drop Down
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Points: 5365 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 29 November 2023 at 7:06pm







Originally posted by FOO FOO wrote:

And finally, what would these changes do to the sound and performance?




There should be no difference. You should just scale the box and let the software simulator predict the performance.

Best Regards,  


Edited by Elliot Thompson - 29 November 2023 at 7:59pm
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smitske96 View Drop Down
Young Croc
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Points: 1217 		Post Options Post Options   Thanks (0) Thanks(0)   Quote smitske96 Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2023 at 10:51am
@Elliot

As said before, port placement does matter. As far as i am aware the above program does not take in account any boundaries just like hornresp, winisd etc.
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Young Croc
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The port sides are up against the side wall. Like on the Gsub.
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Elliot Thompson View Drop Down
Old Croc
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Points: 5365 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2023 at 7:07pm
Originally posted by smitske96 smitske96 wrote:

@Elliot

As said before, port placement does matter. As far as i am aware the above program does not take in account any boundaries just like hornresp, winisd etc.


Yes. Port placement matters based upon frequency tuning and/or the overall dimension of the box. Since FOO never offered anything other than the port size, it is up in the air what is the dimension of the enclosure. So from a port standpoint, there should be no difference from a rectangular to circular port, all things considered equal.

There are old spreadsheets (pre Windows XP days) that will show the influence of the port output. However, such spreadsheets half long faded away due to operating systems moving forward with technology.

Best Regards,  
Elliot Thompson
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Young Croc
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Points: 953 		Post Options Post Options   Thanks (0) Thanks(0)   Quote FOO Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2023 at 7:19pm
Sorry, but plans only exist on paper for now.
But it's a box measuring 950x1000x500mm (DxHxW).

Tuning should be 35hz. That's what I have been told.
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Elliot Thompson View Drop Down
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Points: 5365 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2023 at 7:43pm
Without adding the driver in the equation and, using 18 mm wood, the tuning is 25.29 Hz. So the port only comes into play when frequencies approach 25 Hz and below. Bear in mind that is without any loudspeaker(s) taking up internal space. So the tuning could be higher than that. Possibly, it may be best to build your own box based on your driver's specifications. 

Best Regards, 




Edited by Elliot Thompson - 01 December 2023 at 7:53pm
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Young Croc
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Points: 953 		Post Options Post Options   Thanks (0) Thanks(0)   Quote FOO Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2023 at 8:42pm
Aaarh sorry you want the internal volume of the chamber? That's 190L.
The chamber with the driver is part of a larger enclosure. Just like a Turbosound TMS4. But not hornloaded Smile
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Points: 263 		Post Options Post Options   Thanks (0) Thanks(0)   Quote fudge22 Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2023 at 8:52pm

If you don’t know the basics of flared port design, how did you determine that the radius of the flare needed to be 25mm?

There are quite a few academic papers on this topic. A good one to start with is:

 Maximizing Performance from Loudspeaker Ports by Salvatti, Button and Devantier

It used to be downloadable from jbl’s web site, but I don’t know if their tech library is still available. A quick internet search, using your favourite search engine should locate a copy though. This paper references plenty of other works on the topic, which are worth looking at.

Unfortunately, to determine the exact difference between the cabinet with the flared and unflared ports, you would have to build a couple and listen to them.

If you are just building someone else’s design, it might be best just to stick with the original port.
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Elliot Thompson View Drop Down
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Points: 5365 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2023 at 8:52pm
FOO. No need for the internal chamber. You are approaching the method backwards (reverse engineering). Just build a box based on your loudspeakers TS Parameters. You will have more control on getting what you want than, trying to make a box work based on it's limitations. 

Best Regards, 


Edited by Elliot Thompson - 01 December 2023 at 8:54pm
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Young Croc
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Points: 953 		Post Options Post Options   Thanks (0) Thanks(0)   Quote FOO Quote  Post ReplyReply Direct Link To This Post Posted: 01 December 2023 at 9:14pm
The flare radius are purely for good looks. I have milling bits from Radius 25mm and smaller, so I just had the idea going with the biggest possible. 

The box is designed around the driver (18sound 18lw1400).
The idea to make a round port with flare instead of a slot is purely for good looks.
But sounds like I have to stick with the slot then.

This is not a box for the road. It's for my man cave Embarrassed
Raw plywood layered together and coated with a clear varnish
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