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Vent too long for enclosure

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ssbb1fire View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ssbb1fire Quote  Post ReplyReply Direct Link To This Post Topic: Vent too long for enclosure
    Posted: 28 March 2021 at 10:46pm
Hello guys !
I'm designing a 3 way enclosure and I'm having a reurent problem within my enclosure designs overall : my vent, for my vented enclosure is wayyyyyyyyyy too long !

Let's give an example :
The 3-way enclosure was designed in WinISD, its volume is 31,44L and its tuning frequency 30,5 Hz.
In order to minimise the air velocity in the rear port for when the woofer is given its maximum power, I design the vent diameter to be 14 cm wide.
It's just an example, but it could fit nicely.
The lenght asked by WinISD is of 147,23 cm, wich by no means can fit in a 31,44L box, whatever the proportions I choose.

Is there any way to go from a vented design to a transmission line design?
To me (I might be wrong), a transmission line design look like a bented vented design. How can I translate my vented design to a transmission line design ?
Is there any information on this ? I've searched a lot on the internet and find nowhere information on solutions about how to deal with a vent too long.

Thanks in advance.
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JonB67 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JonB67 Quote  Post ReplyReply Direct Link To This Post Posted: 28 March 2021 at 11:12pm
You do realise that the volume of the vent isnt subtracted from the volume of the cab?

So volume taken by the vent, plus cab volume, plus driver volume plus handle volume gives you the total internal volume of the box you need to make.  Dont forget this is internal and you need to add the thicknesses of the ply to give outside dimensions. 

It's not always easy to package with small cabs. 

30hz in 30litres? what driver and for what use?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 29 March 2021 at 2:38pm
what size driver are you using?
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ssbb1fire View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ssbb1fire Quote  Post ReplyReply Direct Link To This Post Posted: 29 March 2021 at 4:02pm
Hey guys !
The goal of this vented 3-way enclosure is to challenge the Neumann KH-310(lol).
The woofer used is the Dayton Audio RS270-4
(http://www.loudspeakerdatabase.com/fr/Dayton/RS270#4%CE%A9).
In WinISD, I get a very good simulation with a vented enclosure of 31,44L and a box tuning of 30,50 Hz : the frequency drops at 50 Hz and group delay is very good.
In order to minimise air velocity in the port, I'm simulating the driver at the maximum power (100W, right before the xmax of the driver) and I try to keep the air velocity as low as possible.
So I make the vent bigger , wich also makes it longer(to keep the tuning).
My problem, as said before, is the lenght of the vent, wich a lot of the time (because of the low tuning of my enclosures) is wayyyyy too long.

Is there a way to cheat to put it inside of the box, with a vent that bents on itself, kind of like a transmission line design ?
Ain't it the point of this design ?
Am I mistaken ?
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Conanski View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 29 March 2021 at 4:41pm
It seems to me the Neumann uses a sealed enclosure so you are fighting a challenge they didn't.

If you are determined to make this a vented design you will have to compromise somewhere. 
What port velocity are you targeting? I know 17m/s is recommended but you can relax that some as the average port velocity will be lower anyway.
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Elliot Thompson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 29 March 2021 at 6:51pm
Bear in mind the Neumann KH-310 is a powered speaker and, more than likely have a lot of processing going on in the box. WinISD does not take processing into factor so, trying to replicate the Neumann KH-310 in WinISD will bring forth more cons than pros.

Best Regards,
Elliot Thompson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Contour Quote  Post ReplyReply Direct Link To This Post Posted: 29 March 2021 at 7:30pm
Instead of very long reflex port use a passive membrane. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 29 March 2021 at 8:26pm
10" driver with 6mm xmax - you can probably get away with a 3" vent which will make the vent a quarter of the length. going down to 2" will halve it again. stick a flare on both ends of the port if your are worried about chuffing. or use a passive radiator as suggested.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ssbb1fire Quote  Post ReplyReply Direct Link To This Post Posted: 29 March 2021 at 8:40pm
Yeah Neumann uses a sealed enclosure, and they still have an outstanding frequency response and group delay.
I'm guessing their self-made loudspeakers are just incredibly well tought to allow that.
I don't have the same woofers but I can try to match their data (or even try to do better, who knows ?).

I'm targeting the lowest air velocity possible of course.
But I think a limit to target is 15 m/s because there will also be pressure from others drivers and that will increase air velocity (I think ?).
15 m/s is of course when the driver is exited with its maximum power (here 100 Watts).
I have put the dimensions for wich the air velocity is 15 m/s as an attachement, can you see it ? [IMG]uploads/24032/air_velocity.png[/IMG]

Ps : I have a problem, why does WinISD keeps setting the end correction of the vent as 0.732 ??? Changing it doesn't affect anything.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote infrasound Quote  Post ReplyReply Direct Link To This Post Posted: 29 March 2021 at 10:19pm
You can head up to 30m/s if you have well rounded edges on a round port, in my experience.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 30 March 2021 at 3:38am
Originally posted by ssbb1fire ssbb1fire wrote:

Yeah Neumann uses a sealed enclosure, and they still have an outstanding frequency response and group delay. I'm guessing their self-made loudspeakers are just incredibly well tought to allow that.
It's not rocket science they are just using bass boost to bring the lowend up.


Originally posted by ssbb1fire ssbb1fire wrote:

I'm targeting the lowest air velocity possible of course.
But I think a limit to target is 15 m/s because there will also be pressure from others drivers and that will increase air velocity (I think ?).
No, the mid and high freq drivers do not contribute to port air velocity, in fact they must be acoustically isolated from the woofer either within their own sub enclosure or by having a sealed frame.



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ssbb1fire View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ssbb1fire Quote  Post ReplyReply Direct Link To This Post Posted: 30 March 2021 at 9:52am
Why does the medium and tweeted must be acoustically isolated from the woofer ? That's the first time I've heard someone tell me that.
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