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PA 21" laminar port sub bracking

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Augusts View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Augusts Quote  Post ReplyReply Direct Link To This Post Topic: PA 21" laminar port sub bracking
    Posted: 27 October 2021 at 11:58am
I have finally redesigned everything, done test measurements with impedance sweep in a test box, tuned to 34Hz

The last thing on the list is bracing? I understand this is a compromise, because using psychopatic bracing on a PA sub would be very heavy, but still some bracing is needed. I am thinking of using a 15mm ply, I hope you can understand the bracing pattern from the cut sheet. the braces are going to be 65mm plus here and there I would join the opposite corners. As this has a laminar port, the bracing does not go that simmetrically as for a straight ported sub. I am thinking maybe add a central brace horizontally that would join the opposite walls of  the sub. Any thoughts welcome! I have never built such a big box.
Thanks
August



This is the first prototype made from 18mm ply, tuned to 29Hz, too low.
Here I used only corner bracing plus a large wall to wall in the center





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smitske96 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote smitske96 Quote  Post ReplyReply Direct Link To This Post Posted: 29 October 2021 at 3:49pm
Looking really cool! Any measurements you would like to share?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sypa Quote  Post ReplyReply Direct Link To This Post Posted: 29 October 2021 at 6:56pm
Can't help with the. bracing but also interested in some measurements. 
Why was the 29 tuning too low?

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Augusts View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Augusts Quote  Post ReplyReply Direct Link To This Post Posted: 29 October 2021 at 7:05pm
Because 34Fb got us 3,5 db more and a -3db of 30Hz
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Augusts Quote  Post ReplyReply Direct Link To This Post Posted: 29 October 2021 at 7:07pm
Because of that being an allround PA sub that seemed like a lot of wasted energy.  I have only a few unweighted freq measurements indoors that wont give you much satisfaction
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AndyWave Quote  Post ReplyReply Direct Link To This Post Posted: 22 February 2022 at 9:03am
Hello Augusts

I have drawn something similar to be used with 18sound 18LW2600.
(210L net, fb=31Hz, Ap 600...1200cm2)

Did You measure the port output ie. mic inside port, and were there any resonances because of the port length?

Asks Andy

edit:spelling


Edited by AndyWave - 22 February 2022 at 9:04am
torturing electrons since ......
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Post Options Post Options   Thanks (0) Thanks(0)   Quote smitske96 Quote  Post ReplyReply Direct Link To This Post Posted: 22 February 2022 at 10:32am
@AndyWave

There will always be resonances due to the port, only question is where Wink
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AndyWave Quote  Post ReplyReply Direct Link To This Post Posted: 24 February 2022 at 6:54pm
Yes, preferably outside the intended frecuency range...But I have not measured any modern reflex enclosure with venturi port in practise, only on paper and in computer LOL

In my intended design there will be possibility to suck out reflex port resonances in small chamber. Maybe You remember apaxial horns with side chamber opening near horn mouth, I'm going to use same principle to tame lenghtwise port resonance if needed.
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