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Vent too long for enclosure

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Category: General
Forum Name: Newbie Discussion
Forum Description: Newbie Discussion/Questions. Look less stupid here...
URL: https://forum.speakerplans.com/forum_posts.asp?TID=106187
Printed Date: 19 June 2021 at 3:25pm
Software Version: Web Wiz Forums 12.03 - http://www.webwizforums.com


Topic: Vent too long for enclosure
Posted By: ssbb1fire
Subject: Vent too long for enclosure
Date 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.



Replies:
Posted By: JonB67
Date 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?


Posted By: snowflake
Date Posted: 29 March 2021 at 2:38pm
what size driver are you using?


Posted By: ssbb1fire
Date 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" rel="nofollow - 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 ?


Posted By: Conanski
Date 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.


Posted By: Elliot Thompson
Date 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


Posted By: Contour
Date Posted: 29 March 2021 at 7:30pm
Instead of very long reflex port use a passive membrane. 


Posted By: snowflake
Date 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.


Posted By: ssbb1fire
Date 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.


Posted By: infrasound
Date 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.



Posted By: Conanski
Date 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.





Posted By: ssbb1fire
Date 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.


Posted By: smitske96
Date Posted: 30 March 2021 at 10:40am
The LF driver will interfere with the MF driver. 


Posted By: Earplug
Date Posted: 30 March 2021 at 10:54am
Yes - the tweeter should be ok, as they are (usually) isolated already, but the MF driver won't. You can use something as simple as a plant pot! Anything that seals it off from the LF waves within the cabinet.




-------------
Earplugs Are For Wimps!


Posted By: ssbb1fire
Date Posted: 30 March 2021 at 8:28pm
Don't take it personnaly, but as I never heard of such thing, I'd like to know more about it. Can you explain to me why the medium would be influenced by the woofer if they are in the same enclosure ?
Where have you learned that ? A book, youtube, video, forum ? To get some data about it.


Posted By: APW
Date Posted: 30 March 2021 at 9:22pm
The pressure generated by the woofer will cause the mid into high excursion.


Posted By: ssbb1fire
Date Posted: 30 March 2021 at 9:37pm
I've searched a lot this afternoon about that.
You're right, I have to isolate the medium for the woofer.
Now I have to find how to do that in the most efficient way possible. Do you have any advice ?


Posted By: infrasound
Date Posted: 30 March 2021 at 9:57pm
Depends how big it needs to be.. But you can use a pot or pan with epoxy, or use bolts and bracing


Posted By: Earplug
Date Posted: 31 March 2021 at 7:10am
"Now I have to find how to do that in the most efficient way possible. Do you have any advice ?"

It's really quite simple. Something like this:-

https://www.parts-express.com/Eminence-ISO-5-5-Midrange-Midbass-Isolation-Enclosure-290-5506" rel="nofollow - https://www.parts-express.com/Eminence-ISO-5-5-Midrange-Midbass-Isolation-Enclosure-290-5506

Or just use a plant pot!  LOL







-------------
Earplugs Are For Wimps!


Posted By: snowflake
Date Posted: 31 March 2021 at 10:57am
it looks to me like the KH310 uses a sealed-back mid, so it already has its own rear chamber built into the driver

google kh310 disassembly


Posted By: ssbb1fire
Date Posted: 31 March 2021 at 1:48pm
Oh my that's a great solution !
I just have to find it in a store wich delivers to France lol, I might pay up to 100$ in fees from the USA...


Posted By: ssbb1fire
Date Posted: 31 March 2021 at 9:04pm
Thank you for that reminder about volume, I completely forgot.


Posted By: DMorison
Date Posted: 01 April 2021 at 1:45pm
Originally posted by ssbb1fire ssbb1fire wrote:

I've searched a lot this afternoon about that.
You're right, I have to isolate the medium for the woofer.
Now I have to find how to do that in the most efficient way possible. Do you have any advice ?

If you can't get a dedicated enclosure like Earplug suggested, just build a box within the main speaker box. Loads of examples in DIY projects all over the web, here's a good one to show what I mean:  http://www.troelsgravesen.dk/Discovery-3WC-mkII.htm" rel="nofollow - http://www.troelsgravesen.dk/Discovery-3WC-mkII.htm


Posted By: ssbb1fire
Date Posted: 01 April 2021 at 2:19pm
I found this but it's for 5" and my driver is 4" so I d'ont know if that's the best choice.
https://www.toutlehautparleur.com/charge-close-0-8l-pour-haut-parleur-13-cm.html" rel="nofollow - https://www.toutlehautparleur.com/charge-close-0-8l-pour-haut-parleur-13-cm.html


Posted By: BJtheDJ
Date Posted: 01 April 2021 at 6:50pm
Originally posted by ssbb1fire ssbb1fire wrote:

I found this but it's for 5" and my driver is 4" so I d'ont know if that's the best choice.
https://www.toutlehautparleur.com/charge-close-0-8l-pour-haut-parleur-13-cm.html" rel="nofollow - https://www.toutlehautparleur.com/charge-close-0-8l-pour-haut-parleur-13-cm.html


It will do the job for you and is most likely only slightly larger than that for a 4".

It will take up slightly more volume, but will do exactly the same job.




-------------
If your vaccinations were mandatory and
nobody in your class had measles, then
you know that you're not a Millenial kid.


Posted By: smitske96
Date Posted: 01 April 2021 at 7:57pm
You could also fill up the remaining space with some material. However, I would test first before doing that permanently.


Posted By: ssbb1fire
Date Posted: 01 April 2021 at 8:14pm
Thank you guys.
I have no problem with it being too big, I just thought that with a 5" driver it would line up perfectly, and a 4" driver wouldn't line up.
If I can just go with it, so I will.
I just need to figure out how to set it efficiently now.


Posted By: ssbb1fire
Date Posted: 09 April 2021 at 10:05pm
Excuse me, but working on loudspeaker has raised some question and when I was talking about the frequency response and group delay you said :
Originally posted by Conanski Conanski wrote:

It's not rocket science they are just using bass boost to bring the lowend up.

I'm wondering, is there a way to lower the group delay of a loudspeaker or loudspeaker system ? There's information here and there, but I can't fin an acceptable group delay reference (like 20 hz => 30 ms is ok, 30 Hz => x ms, etc...) and I don't know if there's something I can do about group delay after the loudspeaker is build, by some signal processing...
(tell me if I'm not clear)
In short :
group delay too big
filter goes beep beep boop boop
less group delay
tl,dr : happy


Posted By: DMorison
Date Posted: 10 April 2021 at 2:07pm
I have seen a rule of thumb that GD(ms) > 400/f is likely to be audible, but I don't know if that is based on solid science or not, sorry.

Things that you can do to improve it: 
If a ported system, reduce the tuning frequency.
If using a high pass filter, reduce its frequency and order.
If using EQ to shape the low frequency corner of the system's response, make sure you don't try to make that corner too sharp. 

Note that several of these have other consequences you may not want.

HTH,
David.


Posted By: ssbb1fire
Date Posted: 11 April 2021 at 12:01am
I agree with everything you said.
I'm looking for explanation on this : https://circuitcellar.com/research-design-hub/group-delay-basics-more-filter-fun/" rel="nofollow - https://circuitcellar.com/research-design-hub/group-delay-basics-more-filter-fun/
It's a very complete document, where negative group delay though filters is mentioned. I don't know if that can help me or anyone can explain it in simpler words, because I d'ont understand everything, and that could be very interesting !


Posted By: DMorison
Date Posted: 11 April 2021 at 2:16pm
The method used in that example to create -ve GD would not work for a subwoofer as it relies on a notch filter, which would have to be positioned at the frequency of maximum GD. 
This of course would result in you notching out content that you want to keep, right around the low frequency corner of your system.

FWIW,
David.


Posted By: studio45
Date Posted: 12 April 2021 at 2:34pm
Group delay is one of the things that defines the "feel" of a subwoofer or bass driver's output. In general, a sub with lower group delay will be reviewed using terms like "tighter", "dryer", "accurate" and so on, whereas one with higher group delay will elicit responses like "warm", "full", or "rounded". HOWEVER these are obviously very subjective terms and in fact the room the subwoofer is placed in, and its position within that room, can have a MUCH larger effect on its perceived sound. And, GD has nothing in particular to do with the actual output achievable. A very high or very low GD box could be just as loud.
The only mistake to avoid is to have a *large* narrow spike in group delay, such as might be caused by a port tuned for excessive gain in a small box, or application of too much bass boost EQ. I like to tune boxes to have the flattest GD curve I can get, while retaining as much low end extension as possible. Not necessarily the lowest possible GD figures, but the *least change* across the frequencies below 250Hz. 


-------------
Studio45 - Box Builder Commotion Soundsystem -Mobile PA



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