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Old 18th February 2005, 07:41 PM   #1
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Default Ports/Vents

I'm sorta confused with how and what to do with a port. I want to make a slot port for my brahma 15 for HT. Not sure how to make that. How do I figure out the specs for the port? I think I want it tuned to 26hz because that's what the FS is. I thought that is what people are supposed to do... tune it to the FS of the driver. Is that right?
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Old 18th February 2005, 07:49 PM   #2
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There is only one alignment where you tune to Fs and that is the BB4.

To design a slot vent simply work out the cross-sectional area of the slot and then calculate what round vent has the same CSA and work out the length with any of the popular programs. If the slot is extreme in aspect then you will find that the tuning is a little lower than the equivalent round vent.
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Old 18th February 2005, 08:53 PM   #3
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this seems like a useless thread to me, seeing you already had one going about a brahma box for HT
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Old 22nd February 2005, 12:26 AM   #4
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Yeah, I know I had a thread earlier, but I did this one because I am concerned about the port. I have a slot port straight back. I was curious if I need to add an "L" shape on the end of it. I heard that that helps. Whats the advantage to that... or did I just hear some BS ?
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Old 22nd February 2005, 12:47 AM   #5
simon5 is offline simon5  Canada
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You mean some kind of flare? It's good but a bit hard to do on a slot port...
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Old 22nd February 2005, 01:21 AM   #6
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Yeah, I mean a flare. Is that needed? You said it helps... how does it help?
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Old 22nd February 2005, 02:14 AM   #7
simon5 is offline simon5  Canada
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It reduces the vent noise at high volume near the box tuning.

It's not needed but if you can do it, it's a good idea.

If your slot port is quite big, only some sanding to make each opening round could be enough.
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Old 22nd February 2005, 05:24 PM   #8
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The idea of a rectangular vent is that you can wrap it around the walls of the box, where it's big. With a tube you would need a lot of bends and it can get awkward. However, a rectangular port is more difficult to flare, hence you need a greater cross sectional area compared to a circular vent, since you will probably have a bigger flare on your circular vent. If you don't need a flare on your rectangular vent, then I would say it's bigger than it needs to be, hence it's taking up more box volume.

I prefer circular vents if you can make them practical. Start with a 4" circular vent with a flare as big as you can make practical on both ends. If that's not enough then consider a bigger diameter, or a number of them. Aim for a max vent velocity of 34m/s when you either reach the power limit of your amp, or driver max excursion, whichever is lower. A rumble filter also helps reduce turbulence.

It sounds like you need to do some more work on what you want with your sub as a whole. 26 Hz tuning doesn't sound right. You will get higher vent air velocity, turbulence is more likely. 20 Hz tuning is more like it, although you really need to model. With a driver like this with so much excursion, it will take a lot of power to use that excursion, an EBS might be worth considering.
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Old 22nd February 2005, 06:04 PM   #9
andytv is offline andytv  United States
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I think your box should be fine without the flare, however if its not you can then try sanding the edges as previously stated. Fazorcat is an interesting username, what does it mean if you don't mind me asking?
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