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Free Plan: 21" 30hz Ported Sub

Printed From: Speakerplans.com
Category: Plans
Forum Name: New Projects Forum
Forum Description: Forum for new speakerplans projects, in memory of Tony Wilkes, 1953 - 2014
URL: https://forum.speakerplans.com/forum_posts.asp?TID=101606
Printed Date: 26 March 2026 at 5:36pm
Software Version: Web Wiz Forums 12.08 - https://www.webwizforums.com


Topic: Free Plan: 21" 30hz Ported Sub
Posted By: vertx
Subject: Free Plan: 21" 30hz Ported Sub
Date Posted: 03 April 2018 at 12:03am
I imagine this would do well under a good 15", crossover in the 60hz region.

** Everything below is theoretical and has not been built and measured yet **

Driver: Eighteensound 21LW2500
Enclosure Volume: 267.2 L 
Cabinet Tuning Freq: 31hz

Fusion 360 Public Share Link:

https://a360.co/2Ik9Ffe" rel="nofollow - https://a360.co/2Ik9Ffe

^^ This will let you view in 3D, explode, measure, etc all in a web browser window!


Cabinet Processing: 


SPL @ 2500w:



xmax @ 2500w:



Port Velocity @ 2500w:



Port Area:












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www.instagram.com/translate.sound



Replies:
Posted By: sgarfa
Date Posted: 24 May 2018 at 2:21pm
nice project, but especially on  so performing woofers i I prefer to use to big vent ports..  ... even at cost to tuning bit higher...
there are 1x21 "reflex pro subs with over 700cm2 of mouth (not diy)



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http://www.soundcloud.com/ramirez_amd" rel="nofollow - Ramirez_amd TECHNO


Posted By: PHATpedro
Date Posted: 10 May 2025 at 7:54pm
Do you have any plans available? 

I am desperately looking for a single 21" reflex cabinet i can use with my 21LW1400 driver. But so far without succes I am specifically looking for a reflex. No bandpass or horn.

Kind regards from mexico


Posted By: MarjanM
Date Posted: 10 May 2025 at 10:53pm
Originally posted by PHATpedro PHATpedro wrote:

Do you have any plans available? 

I am desperately looking for a single 21" reflex cabinet i can use with my 21LW1400 driver. But so far without succes I am specifically looking for a reflex. No bandpass or horn.

Kind regards from mexico


That is easy, design your own one.


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Marjan Milosevic
MM-Acoustics
www.mm-acoustics.com
https://www.facebook.com/pages/MM-Acoustics/608901282527713


Posted By: PHATpedro
Date Posted: 11 May 2025 at 9:50pm
I would if I knew what to do and how to calculate and all that stuff.
I am a productdesigner who does carpentry now on a small scale, so tools I might have.
Knowledge not so much.
Great wood - nope. 
Waterproof Marina Plywood or MDF is my best bet here.

Also I know this exists, but i do not know how to upscale it for a 21" driver.
https://eighteen.it/media/W1siZiIsIjIwMjMvMDcvMTcvMTRfMDVfNTlfMzA3XzE4U3ViX3YxXzEucGRmIl1d - https://eighteensound.it/media/W1siZiIsIjIwMjMvMDcvMTcvMTRfMDVfNTlfMzA3XzE4U3ViX3YxXzEucGRmIl1d

Driver: 18Sound 21LW1400

Freq Range: 24-2000hz
Res Freq: 28Hz
VCdiam: 4"
Xmax: 9,5mm
Rec Tuning: 30Hz
Rec Volume: 300L

Alternatively i could get this driver here:
RCF LF21X451

The only two 21" drivers available for me here. The RCF is more expensive. 
The 18sound will cost me roughly 650Usd per driver.



Posted By: MarjanM
Date Posted: 11 May 2025 at 10:32pm
The RCF is much much better driver.



-------------
Marjan Milosevic
MM-Acoustics
www.mm-acoustics.com
https://www.facebook.com/pages/MM-Acoustics/608901282527713


Posted By: PHATpedro
Date Posted: 15 May 2025 at 11:17pm
Thank you. It will be the RCF then.
Trial and error and hopefully not lose all the money I hardly have.

I made a design but I somehow cannot figure out how to put the pictures in here.
roughly 340l
triangular ports 2x base/height 25cm 45degree, 488m long (28hz)
one u shaped brace in the middle horizontally (or is it better vertically?)

Can anybody help me to move forward?
I would love to have it built before rainseason arrives and you can watch every sheet material warp live.



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