After the weekend we will start building the bass reflex cabinet design by 18sound: http://www.eighteensound.com/Portals/0/EnclosuresKits/18sound_18_dual_subwoofer_kit.pdf

It will be my (our) first speaker build. We will go as per their recommendation and use the 18TLW3000.

Here is the CAD modeled version that I made. In addition to the original picture, I added the 45* braces to the corners and a double strength baffle, as well as grooves for the baffle, "X" structure and 45* braces to sit in. Still need to decide on places for the handles. It will be built from 18mm baltic birch ply. Do you think it will be plenty strong?

The only other thread where I've seen this cabinet built is here: 

https://soundforums.net/community/threads/18-sound-design.205627/

He's done a crazy good looking job on the bracing, but seems a bit too complex for me, and I hope ours will be enough.

Will add more photos as soon as the build starts.

That's what I was afraid to hear. Thanks for the photo. 

I don't really know how I will achieve this. Maybe something like this...?

Marjan is absolutely right. You need more bracing. You probably need more than your modified diagram too.

I built a low tuned reflex a few years ago with no bracing on the back panel or side panels and they resonated like crazy. Before modification it was totally unacceptable at levels 10x less than you'll be feeding that box.

The design looks pretty cool. Looking forward to seeing the build.

Hmm okay. I think I will then try to copy the bracing as is shown in the other forum topic I linked; I think I will make the bracing exactly same, but just from 2pieces that meet in the middle with half lap joint,  so that I can cut them with my 600 x 900 CNC. 

snowflake wrote: don't put braces exactly in the middle of panels. it will stop the lowest frequency panel vibration but do absolutely nothing to stop the next highest one. optimum positions are either 45% across the panel, or two braces at 35% and 65% across the panel.

This is very interesting information, thanks for this. However, I think making the bracing somewhere else than the middle will be difficult if I want to join the bracing with the ”X” -shape, since the flat piece of it is dead center... I don’t think panel vibration should be an issue with above mentioned bracing, at least the builder of that cabinet has not mentioned anything about vibration/resonance. 

If it was that easy, everyone would be making those free plans and not investing in "branded" products.

Contrary to the belief, most often you dont pay only for the badge.

If they provide enclosure plans for their drivers, they are meant to boost the sales of their drivers. This means they SHOULD want the cabs sounding as good as possible, so I definitely expect them to give uber professional design that makes their drivers sound as good as possible, otherwise it is just shit marketing from them to provide plans for a bad sounding, vibrating cab. 

DIY market makes aproximalety 5% of the total sale. They would not like to endanger the sale of the companies that buys thousands of those drivers. They would be shoting them self in the leg.

That’s a fair point and I get that. Agree to disagree. However, not really relevant with this topic anymore.

The 45deg panels in the corners will probably do little to reduce resonances.  You'd be better off with bracing going down the end panels then attaching to the ear.

You don't always need a lot of bracing, just in the right places.  The aim is to push all the resonances out of the range the cab will be used in.  In this case ~150Hz would be a good figure to aim for.

You might have to do what everyone else who design cabs does, which is to build one, find out where the resonances are, add bracing in that area and keep going til they're all high enough.

One good way of doing it is to lie the box down, put a thin layer of dry sand (or similar) on the panel then run a sine wave sweep.  The anti-nodes (points of highest movement) will show up by the sand moving away from those areas.  Alternatively my own method is just to tap the cab with a screwdriver handle etc and listen to the frequency of the resonances....

18Sound and other manufacturers provide this type of plans as an example of how the drivers can be used and are intended as a starting point, not a finished design.

The really modern tech version would be to buy a small acellerometer of the sort used in your phone, attach to box in various places under load and turn the data gathered into a a graph of frequency vs displacement. Then use it as a sort of stethoscope to identify the worst areas that need work. This is how modern enclosures will be tested, using multiple sensors all over the cabinet.

I like the sand idea too though, that's neat and simple. Need to open and close the box which is a pita but then you would always need to when adding any extra bracing required I guess.

Hi

Slight OT at first - Violin/cello makers map the resonances with rice grains. They put violin body pieces above a speaker cone, some 5cm away, and watch the grains making a pattern. I once made a 10-100 Hz 10" closed box and suitable analogue oscillator to a violin luthier as tuning tool. Of course the maximum spl is not the point here.

Back to the point;

I've done resonance mapping just like Ceharden says, on unbraced empty cabinet prototype but with rice grain or just feeling un-braced cabinet sides with my fingers and marking resonance nodes with a pencil. Almost every time node points form a pattern, just draw straight lines with ruler through these points and there are your required bracing lines visible. Therefore its handy to have one side of the prototype cabinet attached by screws and sealed with window weather stripping.

Usually I use 10-500Hz continuous sweep signal at first, naturally at sensible SPL level. Watch out the driver excursion! After bracing cabinet, apply recommended or calculated processing and repeat approaching nominal RMS power.

looks much better now.. maybe join the back to the baffle by extending the middle braces aswell and you should get as nice solid cab..!

Do you mean the braces that are on either side of the baffle that aren’t touching the baffle? I extended them to touch the baffle after posting this, but I’m not sure if the drivers will fit to mount when done this way. Otherwise the back is joined with the baffle via the port divider, which is also sitting in a groove within the baffle.

Right back at ya! 

On another note: Building has begun. I will post some photos maybe later today or tomorrow when all of the panels have been cut!

Here's some photos I've snapped during the process.

Bracing structure cut on the CNC in three pieces and glued together with half-lap joints. And my cut list.

Milling the baffle. The CNC is 600 x 900 mm, so I couldn't mill the whole thing. 

So I decided to cut part of the second opening and make a jig that attaches to the mounting screws so that I can use a router with a flush trim bit (actually, I used a scroll saw to remove most of the material before using the router).

Voilá!

Dry-fitting everything before screws. The bracing sits in a 7mm deep groove all around, and the baffle sits in a 7mm deep groove on every side as well. 

A lot of screws, I know... But I want(ed) everything to sit as flush as possible, so I don't need to fill a lot of potential gaps. 

Here's how it looks now. Everything is screwed in place from outside to inside. Still need to route the holes for handles and Speakon. After that, I will take it apart, sand, and put everything except the top back together with glue and hide the screws with some woodfiller. Then I will use some silicone (or something else?) around the inside seams to make sure there is no leaks. 

Would you recommend to put silicone, glue, or something else in the screw holes with the screws?

No need to glue screws, as the screwhole will pass through the glue layer (which will glue the screw).

In a damp bathroom or dirty kitchen scenario, pehaps not.

Inside dry dark cabinets - not a problem.

Some are marketed specifically as "neutral curing" - these should be ok.

Examples:

https://www.sealantsonline.co.uk/Products/neutral-cure-silicone-mastic-sealants" rel="nofollow - https://www.sealantsonline.co.uk/Products/neutral-cure-silicone-mastic-sealants

https://www.screwfix.com/p/no-nonsense-builders-silicone-clear-310ml/83710" rel="nofollow - https://www.screwfix.com/p/no-nonsense-builders-silicone-clear-310ml/83710

Also, see if you have a shop in town that caters to people who keep tropical fish - they often build aquaria using sealant and would need to have it free of acidic residue after curing to create a liveable environment for the fish.

Thanks for this. He did have some to use in aquariums. Very small tube though = expensive. I'm starting to lean towards the acrylic sealant, since it can be painted on as well. 

This.

I really appreciate the nice words from everyone! I have a need/tendency to make it as good as possible with my skills, but I don't trust the outcome to be seamless even though that's what it looks like to the eye. Why not play it safe?  Also wondering about what to use to seal the driver to the baffle. I need to read up on that soon, will probably find a ton of different possibilities. 

And took the cab apart to fix mistakes.

I screwed everything atleast 40mm from the corners, except 2 screws by mistake. Ofcourse both of these corners were cracked when I opened the box up, even though I pilot drilled them. I tried prying the cracks a bit open with a screw and inserted glue inside the cracks and the screw hole. 

So no gluing the cab together as of yet. My goal is to able to test the sound on Monday!

no updates yet the man has been in Denmark for sometime we were working on a project for next month here in denmark , some guys we knowneed to use a setup like this , will start another post about it .

Yes boss , 

The box is 98% ready. Glued & painted, but still gotta attach the rubber feet and mount the drivers. We will try and do some measurements next week and I will post some photos of the finished box. We will get some Powersoft at a later stage, we don't yet know what we will use for the time being. 

bob4 wrote: Just....... Wow!  Wili, with that level of precision and deep rebates I don't see any reason to be afraid of air leaks. No need for additional sealing. If your cuts are spot on, dont waste time sanding, except if you are certain that there is a problem. Also you could build without screws...... Fantastic work!

Much obliged 

PMd mate

With the kick:

Yes, we used the 18TLW3000. We have made two of these subwoofers, and they sound really, really nice. However, I am starting to build a prototype for a new subwoofer design called the "Skram" by Josh Ricci, just to get a little bit more lower extension. If you are interested, I am thinking about selling both of our double 18's. I could bring them to Denmark as I will be driving there during the fall/winter months. They have barely been "driven in", and have been used for only 4 gigs, all with a Powersoft amp and with all limiters in use, so they haven't been abused in any way. DM me if you are interested. 

The tuning can be dropped by blocking a vent. Also, we'll see the comparison regarding loudness Atleast two will be louder than one 218 box, which will be about the same driver and amp cost. Also it might have nicer dimensions. I don't know what I want yet 

danielpedersen650@gmail.com

Oh yeah you cannot send private messages before having 10 or so messages on the forum. I sent you an e-mail. 

Also would making it into a single 18 be as simple as cutting this box in half, to effectively get two triangular vents similar to he B&C sub18