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Discussion Starter #1 (Edited)
trilithon
[trahy-lith-on, trahy-luh-thon]
noun
a prehistoric structure consisting of two upright stones supporting a horizontal stone.


Firstly I would like to thank @LTD02 for designing this subwoofer along w/ helping me through the entire process including answering all questions that I had. Also thank you @Erich H for answering some questions I had about the bracing.

This is a subwoofer based on the designs of @Erich H ‘Stonehenge’ at DIYSG modified by @LTD02

I have always loved the aesthetics of the Stonehenge subwoofer but, slot ports have always been a turn off of mine which is where this journey began.

Designs

Here is the designs for both a single & double baffle using 3/4” MDF.

Single baffle


Double baffle


The dimensions above (double baffle) are 30” x 30” x 19.25” which equals 10.026^3 external volume. Internal volume is approx 8.9 - ~9^3


Ports

(2) flared four inch precision ports w/ a 17” length equals ~19-20Hz port tune.

https://www.parts-express.com/precision-port-4-flared-speaker-cabinet-port-tube-kit--268-352




Cut sheet

Here is my cut sheet — (2) 3/4” MDF 4’ x 8’

depending upon your assembly process you may want to add or subtract from the following as I know everyone’s process is different.




Bracing

Bracing will be exactly the same as the Stonehenge pictured below except instead of the slot wall on the left side there will be (2) 2” x 19.25” braces supporting the back wall & left side as shown w/ the right & top plates.





Below you can see how I have marked each brace on the back wall.





Top & side bracing — (6) 2” x 19.25”

Marked 2” inwards each side & top plate will be marked at 8-10” & 20-22” shown below



The “Stonehenge” driver bracing — (8) 2” x 19.25”

Drawing an X as shown below will give you direct center of the back wall



Next you will find the bolt circle diameter of your preferred driver, mine was 17.5” so we’ll use that as an example.
I divided my BCD by 1/2 which equals 8.75. I started directly center & measured 8.75” out from center marking a 2” line at all (8) lines throughout my {T} & {X} drawn above. Therefore giving the structure bracing while also giving extra MDF for the driver screws to bite into.





I hope to see some other AVS members build the Trilithon, if you have any questions please feel free to post below or PM me directly.

Throughout the next week or two I will be posting updates in this thread documenting my build & hopefully inspiring others.
 

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trilithon

[trahy-lith-on, trahy-luh-thon]

noun

a prehistoric structure consisting of two upright stones supporting a horizontal stone.





Firstly I would like to thank @LTD02 for designing this subwoofer along w/ helping me through the entire process including answering all questions that I had. Also thank you @Erich H for answering some questions I had about the bracing.



This is a subwoofer based on the designs of @Erich H ‘Stonehenge’ at DIYSG modified by @LTD02



I have always loved the aesthetics of the Stonehenge subwoofer but, slot ports have always been a turn off of mine which is where this journey began.



Designs



Here is the designs for both a single & double baffle using 3/4” MDF.



Single baffle





Double baffle





The dimensions above (double baffle) are 30” x 30” x 19.25” which equals 10.026^3 external volume. Internal volume is approx 8.9 - ~9^3





Ports



(2) flared four inch precision ports w/ a 17” length equals ~19-20Hz port tune.



https://www.parts-express.com/precision-port-4-flared-speaker-cabinet-port-tube-kit--268-352









Cut sheet



Here is my cut sheet — (2) 3/4” MDF 4’ x 8’



depending upon your assembly process you may want to add or subtract from the following as I know everyone’s process is different.









Bracing



Bracing will be exactly the same as the Stonehenge pictured below except instead of the slot wall on the left side there will be (2) 2” x 19.25” braces supporting the back wall & left side as shown w/ the right & top plates.











Below you can see how I have marked each brace on the back wall.











Top & side bracing — (6) 2” x 19.25”



Marked 2” inwards each side & top plate will be marked at 8-10” & 20-22” shown below







The “Stonehenge” driver bracing — (8) 2” x 19.25”



Drawing an X as shown below will give you direct center of the back wall







Next you will find the bolt circle diameter of your preferred driver, mine was 17.5” so we’ll use that as an example.

I divided my BCD by 1/2 which equals 8.75. I started directly center & measured 8.75” out from center marking a 2” line at all (8) lines throughout my {T} & {X} drawn above. Therefore giving the structure bracing while also giving extra MDF for the driver screws to bite into.











I hope to see some other AVS members build the Trilithon, if you have any questions please feel free to post below or PM me directly.



Throughout the next week or two I will be posting updates in this thread documenting my build & hopefully inspiring others.

What driver you pairing with this one eyed two nostril beast?
 
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Discussion Starter #3
What driver you pairing with this one eyed two nostril beast?
“One eyed two nostril beast” :D

I knew I was forgetting something. It is an 18” Dayton Pro woofer. I’ll have to report back w/ the exact model #.

I sourced it locally for relatively nothing compared to it’s MSRP. My plan is in the somewhat near future upgrade to an 18” Ultimax or the 18” FI driver they made per AVS members request.

I’ve already checked & the Pro woofer that I have has a smaller baffle cutout than both of them so after a few hundred dollars & a little sanding I’ll be in ULF bliss.
 

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Discussion Starter #5 (Edited)
Port velocity will be very high with an Ultimax.
Ah probably so. The port was designed w/ the Pro woofer in mind so I hadn’t considered the negatives of when I upgrade.

What would be the fix when I’m ready? Albeit it’ll be ~6mo away I’d still like to plan for this.

Thanks for bringing that to my attention

Edit: this is my first build so the physics/intricacies surpasses my knowledge
 

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Discussion Starter #6
Let the build begin.

Here is all my cuts beforehand, I used 2 4’ x 8’ sheets of 3/4” MDF w/ lots of excess.






Getting the first side glued to the bottom plate


 

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Discussion Starter #7
First side dried & cured. Now to start the second side. I ended up w/ a much nicer glue line/fit w/ this side.






 

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What would be the fix when I’m ready? Albeit it’ll be ~6mo away I’d still like to plan for this.

Sadly there won't be an easy fix for that issue. Basically you'd have to redesign your ports entirely. Bigger diameter or more ports.


I think those issues only arise at very high output levels, so if you won't be pushing it too often you might find that it's not a problem. I would say just swap in the new driver whenever you're ready and try it out. You'll notice port noise at high enough levels most likely and you can decide if it's bearable or not.
 

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Discussion Starter #9
Sadly there won't be an easy fix for that issue. Basically you'd have to redesign your ports entirely. Bigger diameter or more ports.


I think those issues only arise at very high output levels, so if you won't be pushing it too often you might find that it's not a problem. I would say just swap in the new driver whenever you're ready and try it out. You'll notice port noise at high enough levels most likely and you can decide if it's bearable or not.
Which dependent upon how well this pro woofer does on the low end is whether I’ll actually add an Ultimax or FI.

My room is only 1200^3 so I’m hoping to get some considerable room gain. I’m assuming output should be sufficient.

But yes I guess if I do upgrade I’ll just test the waters & go from there. Thanks for the input regardless.

Do you like the design?
 

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Discussion Starter #10
After having both sides dry & cure for 24hrs we move to the back plate.





 

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Discussion Starter #11
Extra pic of the woofer next to my 85lb Bulloxer :)


 

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Which dependent upon how well this pro woofer does on the low end is whether I’ll actually add an Ultimax or FI.
That seems like a good plan.



My room is only 1200^3 so I’m hoping to get some considerable room gain. I’m assuming output should be sufficient.
1200 cubic feet? So, 12x12x10 or so, small office you said right?
Just remember with the iNuke3k you'll only get about 500 watts rms actual into one channel at 4 ohms for the UM18 which would only be half if what it's rated, so you'll only get half the UMs potential output. Again that would be ok in a small room if you're not trying to max it out, but you will be leaving some output on the table.
Of course with that power you're less likely to have issues if you put a UM18 in that box. Port velocity should stay quite a bit lower. You could model it I guess :)



Do you like the design?

Yea! I love it. Looks like a really good box. I think the dual round ports look sweet - impressive and menacing. Good job.


Which driver is it again? PA460 or PA465? Or something else?
 

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Discussion Starter #13
That seems like a good plan.


1200 cubic feet? So, 12x12x10 or so, small office you said right?
Just remember with the iNuke3k you'll only get about 500 watts rms actual into one channel at 4 ohms for the UM18 which would only be half if what it's rated, so you'll only get half the UMs potential output. Again that would be ok in a small room if you're not trying to max it out, but you will be leaving some output on the table.
Of course with that power you're less likely to have issues if you put a UM18 in that box. Port velocity should stay quite a bit lower. You could model it I guess :)


Yea! I love it. Looks like a really good box. I think the dual round ports look sweet - impressive and menacing. Good job.


Which driver is it again? PA460 or PA465? Or something else?
9x15x8. Spare bedroom.

I’m still yet undecided on an amplifier. I’ve been looking at the Chane 3600

https://www.chanemusiccinema.com/3600

& Behringer KM1700

https://www.amazon.com/Behringer-KM1700-BEHRINGER/dp/B01MAY7S7W

Realistically I’d like to stay under 300. Unfortunately the woofer is 8ohm so finding an adequate amp is presenting more of a challenge than first thought.

Thanks for the compliments.

Also the driver is Dayton NEO Pro PN470 18”. Not my first choice but, I sourced it locally for $40 so compared to its $349 MSRP I’m happy regardless. That’s actually what started this entire process, I found it so cheap that I couldn’t pass it up, then I needed a box.
 

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Yea those amps look good though I'm not familiar with Chane. Any of the 3 you've mentioned should be fine for your purposes as long as you've got DSP. Or at least aHPF you can set.
 

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That PN470 looks like a great driver BTW. nice score!
 
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Discussion Starter #16
I’ve been busy the past few days so I’ve had to take a break in my build.

After letting the back plate dry & cure we start on the bracing.














 

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Discussion Starter #17 (Edited)
Time to start on the front baffle. I’m doing a double recessed baffle of 3/4” MDF.

Edit: Recessed baffle.

I oiled my jigsaw before using it & found out the hard way I used too much. Left plenty of sanding to be done.





















 

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Time to start on the front baffle. I’m doing double baffle; not entirely sure of the terminology regarding my design but the top piece will be cut around the driver leaving it mounted flush. Infinite baffle?

No, you are creating what is commonly referred to as a recessed baffle. Infinite baffle is explained here http://www.ibsubwoofers.com/, completely different things.

Build is looking good!
 

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Discussion Starter #19
No, you are creating what is commonly referred to as a recessed baffle. Infinite baffle is explained here http://www.ibsubwoofers.com/, completely different things.

Build is looking good!
Makes total sense after seeing the name hence one part being recessed. I’ll edit my post.

Thanks for the compliment! It’s been more work than I had originally thought but, I’ve learned quite a bit invaluable information. I cannot wait to start on my next build already. I’m thinking either an LCR of HTM 12’s or a MartyCube. As long as this driver has sufficient extension it’ll probably be the HTM’s.
 

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I cannot wait to start on my next build already. I’m thinking either an LCR of HTM 12’s or a MartyCube. As long as this driver has sufficient extension it’ll probably be the HTM’s.

You should absolutely do both! :D


I finished a VBSS variant a few months ago, now working on a L/R HTM-10 build. Can't wait to hear them.
 
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