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DIY 1x15 (yes another) - advice appreciated


d-basser
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I managed to pick up a Kappalite 3015 (not LF) stupidly cheap on ebay and I am wanting to build a cab to house it. I was going to build a BFM Simplexx 15 but the overall dimensions are a little big for what I want so those plans will be kept for some future project or other. Instead I am wanting to build something loosely based on the Greenboy Bassic 15 and the Gen 1 Barefaced Compact. These are both designed for the 3015 so should be a good starting point. Also I have a Gen 1 BF Midget so something akin to a Compact may compliment it well if I choose to combine them.

I haven't built anything like this before and I am yet to get my head around WinISD but I do know my way around a CAD program so I have mocked up the following:

1274567880_cabmock1.thumb.PNG.1e096c13d31c4538d18e3112a5de6ee2.PNG

Designed with 12mm ply, this would give me a total internal volume (prior to subtracting bracing etc) of 2.856 cu.ft, this is pretty damn close to the the 2.825 cu.ft Eminence recommend for a medium vented cab in the driver docs. Ports would be 2 x 4" dia. 6.86" length, again from the documentation eminence provide. Bracing is based on the Fearful designs from the Greenboy site. 

I would appreciate input from those more knowledgeable in these things, are there any glaring mistakes or oversights in design so far? Are there any modifications you would recommend?

 

Cheers!

 

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If you compare the S15 construction, especially how the braces are configured and how the ports also work as braces, to what you've drawn you'll see no resemblance between the two. That's because spline braces are barely better than no braces. I stopped using them 15 years ago, other than in those instances where there's no other option.

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Thanks @Bill Fitzmaurice, don't know why but I am not a big fan of the corner ports aesthetically. I can completely see why they are great for doubling as braces but if I could avoid using them I would like to. Form over function, terrible I know.

One other option I was thinking of was to go for a slightly more elaborate bracing design similar to the one used on the mkII basschat 1x12 design, I have drawn up the rough idea below. Would this be better than my initial design or do I need to completely rethink bracing?

 

1442255312_cabmock2.thumb.PNG.65285af31199ed18c0d8c331f7860297.PNG

Edited by d-basser
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1 hour ago, Bill Fitzmaurice said:

If that's what Fearful bracing looks like I'm not impressed.

I think there seems to be a few different approaches I've seen to how bracing is used. 

Approach 1 is like Fearful cabs, where they use 12mm ply and then use the splines to stiffen individual panels. Which are then joined. Logic I think being that the panels themselves are braced and you're making up for the lost 3mm of thickness vs 15mm. It makes me think of an acoustic guitar top but less scallops... 
Approach 2 is like I think I've seen you recommend in the past where braces run from opposing panel to opposing panel. I've seen dowels used in that kinda thing before. Simplex, and Mesa use the corner ports as bracing too. 
Approach 3 is when you go a bit crazy, build some matrix structure, a shelf port too and can use 9mm ply. 
 

This should be an image of someones fearful build (found here: http://www.sumitdas.net/fEARful_build1/
damping1.jpg

This should be a simplex 210 (designed by bill) and found on a random site: 

47%20all%20bracing%20complete.jpg 

Barefaced bracing 
Big-Twin-Bracing-5.gif 

 

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3 hours ago, LukeFRC said:

Approach 1 is like Fearful cabs, where they use 12mm ply and then use the splines to stiffen individual panels. Which are then joined. Logic I think being that the panels themselves are braced and you're making up for the lost 3mm of thickness vs 15mm.

That's the theory, but in effect you're settling for the equivalent of 15mm when a single brace connecting the middles of two 12mm panels is the equivalent of using 24mm. I brace my cabs to the stiffness equivalent of at least 30mm plywood, while using less material to do it than other schemes. At least 2/3 of the bracing in that rotating model isn't adding anything to the structure other than dead weight.

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5 hours ago, Bill Fitzmaurice said:

That's the theory, but in effect you're settling for the equivalent of 15mm when a single brace connecting the middles of two 12mm panels is the equivalent of using 24mm. I brace my cabs to the stiffness equivalent of at least 30mm plywood, while using less material to do it than other schemes. At least 2/3 of the bracing in that rotating model isn't adding anything to the structure other than dead weight.

What’s the mechanics behind it and being able to quantify it? I’ve read so many cab build design threads and never seen people discuss calculating it. 

Like the 2/3 of ‘dead weight’ plywood on the spinning Barefaced model I’ve always took as how they have engineered in using 9mm panels

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I'm a little surprised that Bill is so categoric that Alex Claber of Barefaced doesn't understand bracing and that 2/3 of his bracing designs are adding unnecessary 'dead weight' to his cabs. Perhaps he is just grumpy because someone rejected building one of hi Simplexx cabs earlier in the thread.

Actually bracing is moderately complex and to date there is no single mathematical model of what goes on inside a speaker cab. Most designs are a combination of the experience of the builder, trial and error, a bit of testing and only rarely extensive measurements of the cabs, and that tends to be in hi-fi speakers rarely musical instrument speakers. Even then practical considerations dominate, there isn't a lot of space in a cab and there are almost more places you can't fit a brace than ones where you can.

Cross bracing which Bill clearly prefers is a perfectly good way of bracing cabs, I assume he gets his 24mm figure by simply adding the thickness of his two 12mm panels. I wonder how he derives his 30mm figure? The big advantage of cross bracing is that it is easy to do and it uses very little material so adds little to the weight. The disadvantage is that it stiffens the panel at one point crating an antinode but allowing the panel to vibrate elsewhere. The worst places to fix your braces are centrally, effectively the same as trying to kill a bass string by touching it above the 12th fret, you create harmonics an octave above the original problem frequency. A couple of Bill's braces are central but he does add more. I'm not really criticising, if you have a 2x10 then you have nowhere else to put your brace other than the line between the two speakers and I'd go for that spot myself probably.

Spline braces are a perfectly valid way of bracing a cab. they effectively create a 'T' beam along the line where they are fixed. They also spread the damping effect over a greater area of panel. They take a little more effort to fix but as they are only around the edges of the cab there is more freedom to place them where you want. Most splines are made of the same material as the cab itself so they are effectively made from scrap left over from cutting the panels. Weight for weight you'll get more rigidity from cross bracing but Barefaced have designed their cabs from very thin material where simple cross bracing wouldn't work well. If you look at the rotating model you can see two of the braces are annular, running right round the cab, another accepted technique. This effectively couples all the panels to the two adjacent panels, as they will resonate at different frequencies they will damp each others resonances, the central brace has two members that run from front to back so an element of cross bracing is also included. There's nothing really new in this, you could probably see this sort of bracing in theatre speaker designs from the 1920's and 30's but it's a lovely neat solution for lightweight bass speakers. I don't honestly believe 2/3 of the material is wasted.

Have a look at Stevie's 12" design, it's probably as far as you can go for a home builder. His technique was to build the cab then test it by passing low frequency tones from a signal generator (You can get apps on your phone or access these online) That enabled him to identify the points where his panels vibrated most. He then braced those points.

Finally don't discount mass, the movement of the panels under pressure will be proportional to the mass. One way of reducing the sound coming from the cab is to use thicker or more dense panels.

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Looks like I've got some reading and thinking to do this morning, feel I may have started a bit of a bracing battle. 

Thanks to everyone for the input and info, great stuff. Hope Bill isn't grumpy about me not opting for the Simplexx, designs look great and I'll almost certainly build an S12 or two in the future. 

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3 hours ago, d-basser said:

Looks like I've got some reading and thinking to do this morning, feel I may have started a bit of a bracing battle. 

Thanks to everyone for the input and info, great stuff. Hope Bill isn't grumpy about me not opting for the Simplexx, designs look great and I'll almost certainly build an S12 or two in the future. 

How much off is the simplexx size wise for what you need to do? The beauty in using a design someone’s already done is that you can build it and never need to think about port end correction, or baffle step or anything like that...

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9 minutes ago, LukeFRC said:

How much off is the simplexx size wise for what you need to do? The beauty in using a design someone’s already done is that you can build it and never need to think about port end correction, or baffle step or anything like that...

Not a million miles, Simplexx is 24" x 25.5" x 13.5" (w x h x d), my design is currently 48cm x 64cm x 35cm so around 19" x 25" x 13.75". Realistically it is just a narrower cab however I will be carting the thing up and down to a 3rd floor flat so narrower is much much easier.  

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5 hours ago, Phil Starr said:

Spline braces are a perfectly valid way of bracing a cab. they effectively create a 'T' beam along the line where they are fixed.

That's the reasoning behind them, but for them to be effective the brace wouldn't be the typical one to two inches, they'd be four inches or more. Most of the rest of what you say is also incorrect. Not that you're at fault, you're just repeating what you've seen stated elsewhere. My comments are based on my own experience.

Quote

What’s the mechanics behind it and being able to quantify it?  

It's pretty simple. Any and all of the bracing that's within four inches of the corners isn't doing anything, as that's where the cabinet is inherently the strongest and doesn't need bracing. Most of the spline bracing that's between the cross braces has minimal effect. That material would be better employed if it was used as cross bracing, reducing the spans between the cross braces. For that matter I don't see any bracing connecting the midway point of the sides, nor do I see a connection path from the top to the bottom. It's mainly a spline braced design, with the only significant cross bracing being those that connect the baffle to the back.

Quote

Hope Bill isn't grumpy about me not opting for the Simplexx, designs look great and I'll almost certainly build an S12 or two in the future. 

Not in the least. If you didn't have the driver in hand and asked what to do due to your size constraints I'd have said build a Simplexx 10 or 12. Since you have the driver and the S15 is too large for you then you obviously have to take a different tack.

Like the arguments about mixing cabs, mixing driver sizes and tube versus SS watts discussions on this topic always seem to end up in an endless back and forth with no resolution, so having said what I have to contribute I'll now bow out of the thread.

Edited by Bill Fitzmaurice
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1 hour ago, d-basser said:

 

Not a million miles, Simplexx is 24" x 25.5" x 13.5" (w x h x d), my design is currently 48cm x 64cm x 35cm so around 19" x 25" x 13.75". Realistically it is just a narrower cab however I will be carting the thing up and down to a 3rd floor flat so narrower is much much easier.  

12cm on the width then. My take would depend on How narrow the stairs are. If wide enough I would build the tried, tested and measured simplex design and invest in some good handles. If narrow I wouldn’t. I had a lovely GK combo for a while but it was literally was the width of the staircase and had no room for your hands.

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7 minutes ago, Bill Fitzmaurice said:

Like the arguments about mixing cabs, mixing driver sizes and tube versus SS watts discussions on this topic always seem to end up in an endless back and forth with no resolution, so having said what I have to contribute I'll now bow out of the thread.

Second Luke's sentiment, your expertise is always appreciated. 

S12 or S212 would have ideal but the 3015 was 50quid on ebay! Too good to pass up

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1 hour ago, d-basser said:

Second Luke's sentiment, your expertise is always appreciated. 

S12 or S212 would have ideal but the 3015 was 50quid on ebay! Too good to pass up

How do I never find these ebay auctions! 

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One of the problems with cabinet designs, as Bill rightly says, is that much of the so called information out there is wrong. It is difficult to use maths/physics to design cabinets. The work of Thiele and Small took the guesswork out of much of the work cabinet designers do, i.e. cabinet dimensions and tuning,  but cannot account for the fabrication or material. 

Much of the work has to be empirical, trial and error. All credit to Bill in that  he does publish graphs to show the performance of his designs. However the work Alex Claber and Stevie cannot be discounted. All three have gone beyond what almost all commercial manufacturers have. However when you put your views out there as an expert you have to back it up, and sometimes accept that you don't have the monopoly of knowledge. The problem is that if you put it out there, you must be prepared to justify you opinions.

Whatever design you decide to build, in my opinion, you need to test it to ensure that the cabinet has as few resonances as possible, as described by Phil Starr above.

 

 

Edited by Chienmortbb
added more after re-reading the thread.
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