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DIY 1x15 (yes another) - advice appreciated


d-basser
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19 minutes ago, Chienmortbb said:

Much of the work has to be empirical, trial and error.

Being an engineer (and a bit of a masochist) the trial and error is part of what I enjoy, otherwise I would do the sensible thing and build one of Bill's designs or save up for another of Alex's wonderful cabs.

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On 03/03/2019 at 09:25, Phil Starr said:

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. 

Would there be any merit in doing a bit of a hybrid cross brace / spline to spread the contact point with the panel. Something like this:

 

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Hi I was just about to message you. Just to make it clear I was absolutely not saying BFM's preferred method of bracing was wrong, just that it is not categorically the only method of bracing or even necessarily the best method in every case. I don't like sweeping statements unsupported by evidence.  I don't want to get into a slanging match any more than he does but I'll leave you to decide whether reading technical journals and books is a bad thing :)

OK, I think your original bracing would have made a decent contribution to damping cabinet resonances and stiffening the cabinet, I'd have suggested adding a couple if braces across the cab, top to bottom, side to side. You could have fixed them between your  splines in that design fairly easily.

Your BFM inspired version would be as least as good, probably very similar in performance as your first design with the additional cross braces. That's a guess though, you'd have to try them both to be certain. 

Your second version is very similar to the bracing I used in the Mk1 Basschat design. I added splines to the end of each cross brace , just a single length of ply offcut, going up to roughly 10cm of the corner of the panel, as Bill says the edges are stiffened by the panel they are glued to at the edges. Each cross brace then was like a wide letter H if that makes it clearer to picture. That's kind of what you are doing in your drawing above but I used much cruder woodwork :) Having the splayed leg you've drawn or the longer spline I used will damp the panel over a greater area and give you a larger and stronger glue area too.

I can't say my approach was particularly 'scientific' I just used the offcuts I had to hand and a bit of experience and background reading. (I have been building cabs for 50 years, including commercially for a couple of years) It was a rush job as I wanted something to take to a bass bash. I don't think you are far away in your thinking and any of your designs would make nice cabs with more bracing than most commercial cabs. The bracing in the second design based upon Stevie's design might be my favourite on the basis that you know some testing has been done albeit on  a different sized cab. 

I think you really have two options, go ahead with one of your designs and try them, and be prepared to modify them if you aren't happy but essentially to take the empirical route, or be prepared to test for resonances with test tones and deal with them one at a time as Stevie did in the MK2.

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I’ve been renovating my garage and clearing out the previous house owners junk found the remains of a carbon fiber fishing rod - boy is that stuff stiff and light. 

I started thinking that one could use carbon fiber box sections as a framework to stiffen cab in a lightweight way... but by the time you’ve done that you might as well make the whole cab out of fibreglass composite panels and having enough stiffness that you wouldn’t need much bracing. 

 

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Cheers @Phil Starr, that is a very useful summary of options. Think I'll play around with options and see what seems to work. I can promise you now my woodworking won't be as pretty as the drawings!

Now to find somewhere around Glasgow that does suitable plywood. Am I right in saying void free birch ply is the weapon of choice?

Edited by d-basser
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Choice of materials is interesting. I believe that Barefaced use a composite with poplar inner and birch outer. The poplar is light but the birch resists damage better. That would be hard to find though. We used 15mm poplar for the basschat design. We got it from Timbmet cut to size and they have a branch in Glasgow. http://www.timbmet.com/uk/contact-us/find-a-depot/glasgow/

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Chienmortbb has it right, birch for toughness poplar is lighter. Beware though birch ply is widely specified for all sorts of things as a premium product, often as 'Baltic Birch'. My experience is that it is very variable quality with a lot of Russian produced timber being highly questionable. I've gone back to Wickes who sell a generic hardwood exterior ply which I've been quite happy with. Not the lightest but good to work with and consistent quality. Poplar ply is harder to source and often comes from the better suppliers who do a bit of quality control themselves. It will be more expensive than most other plies.

 How are you going to cut the panels? I have a table saw which makes it easy but if you don't I'd say go for a supplier who will cut the panels for you. Accurate cutting makes the whole build process much easier.

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  • 2 years later...

Little bit of a necro thread but I'm bringing this plan back to life. Sat on the back burner for a while with work being crazy (who'd have thought starting a tech company then hitting a global pandemic would be tricky eh) but with joining a new and loud band recently I'm going to need some extra oomf in the old amp department.

 

Nothing exciting to show just yet but I've ordered most of the bits needed. Working with a local company who can CNC the ply for me so this should be a neat little solution. Opted for the design that was similar to the basschat cab in terms of bracing but I've modified it with recessed joints in the corresponding panels (dado joints?) so this should go together nicely.

 

Pics and progress to follow

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I must have missed this thread first time round, but am surprised to read that someone thinks there's only one way of bracing a box. It's not true, of course, and the bracing you choose depends to a large extent on the cabinet you're working with. Side-to-side bracing works well with tall, narrow cabinets like hi-fi cabinets, for example.

 

For a typical bass guitar cabinet (as well as others), my approach is to start with a figure-8 brace near the centre of the cab. That braces both side panels as well as the front and back panels and ties them all into each other. Not only does it brace the largest panels precisely where they need it most - near the centre and just above the driver cutout - but it also substantially strengthens the overall structure of the box. 

 

The second area I look at is the baffle. This is usually ignored, but it is the weakest panel because of the cutouts and because the bass driver is clamped directly to it. I notice it's been included in the Barefaced drawing, which is interesting.

 

After that, the improvements from additional bracing are not as great, but still useful. The key is to strike the right balance between an undamped cabinet that sounds dreadful and a Matrix arrangement that you can't carry.

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Thanks for the input @stevie. I think what I have gone for is similar to what you are suggesting, a 'window frame' brace below the speaker and one cut around the back of the cone, both of which connect to the baffle (as much as possible) as well as the other sides. I have also tried to brace the baffle at the bottom between the ports. All off with the CNC company now so can't change it if it is wrong 😂

 

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Edited by d-basser
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Good to see you making progress. I have planned projects two years in the gestation, lot's of them!

 

I always liked the philosophy of the Gen1 Compact; take the best driver you can find and put it in a nice lightweight box with a bit of thought gone into stiffening. I like the midrange peak in the Kappalite 3015 and at the time it had few rivals, it is still a nice driver. That's pretty much what you are building and it is going to sound great.

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