12" Cab Diary Continued

[Passinwind]

[quote name='Chienmortbb' timestamp='1488967960' post='3253270']
I think this is the real point. The 3012LF would have been the speaker of it were 40/50% cheaper over here it would be a good basis for a 1x 12 plus midrange design. It would not work as well as the Beyma in a single 12 configuration like the BC Mk1.
[/quote]

Absolutely, it's all about tradeoffs as always. At this point I have less than zero interest in any bass cab that only uses a single driver though, personally. Many people do prefer that format, of course.

Edited March 8, 2017 by Passinwind

[Chienmortbb]

[quote name='Passinwind' timestamp='1488991489' post='3253564']
Absolutely, it's all about tradeoffs as always. At this point I have less than zero interest in any bass cab that only uses a single driver though, personally. Many people do prefer that format, of course.
[/quote]Once I heard a good two way at Stevie's I came to the same conclusion.

[Passinwind]

[quote name='Chienmortbb' timestamp='1488998493' post='3253634']
Once I heard a good two way at Stevie's I came to the same conclusion.
[/quote]

For things like electric upright it's just mandatory in my world these days. But I really like the option forks you guys are developing, well done.

BTW, how's your amp build coming along?

[3below]

[quote name='Passinwind' timestamp='1488991489' post='3253564']
Absolutely, it's all about tradeoffs as always. At this point I have less than zero interest in any bass cab that only uses a single driver though, personally. Many people do prefer that format, of course.
[/quote]

Having the luxury of both types of cab I find it depends on the bass I am using. Both cabs are 3015LF based in the low department.

[Chienmortbb]

[quote name='Passinwind' timestamp='1489011964' post='3253805']


For things like electric upright it's just mandatory in my world these days. But I really like the option forks you guys are developing, well done.

BTW, how's your amp build coming along?
[/quote] Working on the front panel hope to finish it in time for Basss Bash/GTG on April 2nd.

[Ghost_Bass]

[quote name='Beer of the Bass' timestamp='1488541755' post='3249793']
That's a pleasingly clear set of drawings, and it looks like you should be able to get a pair of them out of a standard sized sheet of ply too. Is there a typo in the side panel size though? It looks like it says 510mm while the baffle and back are 540mm, or is it a combination of the image resolution and me not having my glasses on?
[/quote]

Good eye! After Stevie's double-check and my triple-check to the drawings that missed us. I've sent a new file to Stevie with the correction. If any of you spot any other mistake please tell me or Stevie about it. A PM would be great as i get a e-mail notification instantly.

Hope you're saving up for this build, this cab looks lovely in the specs, i allready have a clear idea of how i'm going to build mine, i'm just waiting for the rain season to stop

Cheers

Edited March 9, 2017 by Ghost_Bass

[Beer of the Bass]

[quote name='Ghost_Bass' timestamp='1489060466' post='3254014']
Good eye! After Stevie's double-check and my triple-check to the drawings that missed us. I've sent a new file to Stevie with the correction. If any of you spot any other mistake please tell me or Stevie about it. A PM would be great as i get a e-mail notification instantly.

Hope you're saving up for this build, this cab looks lovely in the specs, i allready have a clear idea of how i'm going to build mine, i'm just waiting for the rain season to stop

Cheers
[/quote]

Alas, I don't have an excuse to be building more bass cabs any time soon, since the pair of 1x12" cabs I put together last year are doing a fine job, and I'm already keeping myself busy with a guitar combo project! I'm mostly following the thread out of curiosity, and was checking out the drawings to see how the proportions of the box compared to mine. This new design is looking well thought-out, and it's interesting seeing how the choices around the two-way design are made.

[stevie]

I've now attached Marco's excellent CAD drawings to Post #1. Crossover layout and cutting list to follow soon.

Edited March 9, 2017 by stevie

[Chienmortbb]

[quote name='Beer of the Bass' timestamp='1489069385' post='3254140']
Alas, I don't have an excuse to be building more bass cabs any time soon, since the pair of 1x12" cabs I put together last year are doing a fine job, and I'm already keeping myself busy with a guitar combo project! I'm mostly following the thread out of curiosity, and was checking out the drawings to see how the proportions of the box compared to mine. This new design is looking well thought-out, and it's interesting seeing how the choices around the two-way design are made.
[/quote]We have all learned a lot from this and many of the original ideas have changed.We (or rather Stevie) went through several iterations of the port design before settling on the large single port. Also the Compression driver and Horn combination worked so well with Stevie's crossover design that I think he is almost convinced that he does not need a three way.

It is hard to explain but the two way design seems to make the bass sound better but the important thing is that as it is crossed over lower the just about any commercial cab, the "tweeter" really adds sound rather than fizz and zing. It will be really interesting to compare it to other offerings at the South West Bash in April (oops that means I had better start building).

Edited March 10, 2017 by Chienmortbb

[stevie]

[This is a completely modified post.]

I originally laid out the crossover the old fashioned way with pencil and paper, but to make the circuits clearer, I have now drawn everything out in Paint. It works, but it's not great for making corrections.

The square on the top left for the inputs and outputs is tag strip, which looks like this:



The dots are holes in the board for the components' leads. The straight lines in red between the dots are the connections between the components on the underside of the board. The two 22 ohm resistors connected in parallel result in a value of 11 ohms as shown in the circuit diagram.

Edited March 13, 2017 by stevie

[Gottastopbuyinggear]

I'm relatively experienced building effects on stripboard, have done a bit of PCB etching in the distant past, and have successfully built a couple of the Mk I cabs, but I have to admit I didn't have a clue what material to build a crossover on. I can see from that link that those have been built on ply - is that the easiest or recommended way, or is there a more appropriate alternative?

[stevie]

I usually build my one-off crossovers on 6mm plywood, but stripboard would be perfect for this build. I'm compiling a Word file with a list of parts and suppliers and I'll include information like this. You could also use the plywood offcuts from the wood you make the cab from.

[tauzero]

The LF circuit looks as if A, B, and C are connected together. Surely there should be no connection between A and B as it shorts out L1? HF circuit looks OK.

[stevie]

Yes, you're absolutely right. There should be no connection between A and B on the LF board. I'll correct it and repost.

Done.

Edited March 10, 2017 by stevie

[Chienmortbb]

Stevie I can draw out circuits. It will have to wait though as I am away until Sunday.

[Gottastopbuyinggear]

I think C is wrong in the LF crossover circuit for the feed to the HF crossover? The input to the HF crossover should be the same as for the LF, but C puts it after the inductor?

[stevie]

Yup, you're right. The first change I made was incorrect; I should have moved the output wire from the inductor. I'm now working on this in Microsoft Paint, and will post a revised version.

[Chienmortbb]

Up until now the thread has been a little behind the build and testing of the prototype cab. We are now right up to date, except for some tidying of the drawings, so new information may seem to slow down. The 15mm poplar plywood, cut to size, has been ordered for our cabinets and hopefully the builds can begin next week. I will take some pictures as I build mine and post them on on a separate build diary as I do not want to make this thread any longer than necessary.

Edited March 11, 2017 by Chienmortbb

[stevie]

Actually, John, posting your build on here would not be a bad idea, as it's certainly on topic and it would help anyone considering building this cab. I'm summarising the most important information and placing in Post #1 for easy reference, but the vast majority of the posts in the thread so far contain useful comments.

I've just posted a PDF of your cutting list.

[stevie]

I've now tarted up the first part of the crossover drawings and will do the second one as soon as I can.

[tauzero]

Those revised drawings are a lot clearer, and I can't see any mistakes in the physical layout.

[6v6]

The diagrams do look much clearer, thanks!

One very minor observation - in the LF schematic there's only R1 shown not the parallel R1/R2 shown in the layout and parts list.

I've been having a play spice modelling these in an effort to understand the frequency/phase response better (I'm a novice when it comes to crossover design but once studied the basic principles, many years ago!)

Currently not quite sure the best way to model the electrical characteristics of the drivers (I assume an inductor/resistor but I'm unfamiliar with exactly how to approach specifying this). Modelling the LCR networks is simple enough though so I've started with that.

Happy to share the results for discussion here if such reverse-engineering & analysis is OK by stevie

[stevie]

I take your point about the parallel resistors, 6v6. From a circuit standpoint, 2 parallel resistors are seen as a single component with half the resistance and twice the power handling. But I can see that it could cause confusion.

When I get a minute, I'll change the diagram to show the two components.

[tauzero]

[quote name='6v6' timestamp='1489321278' post='3255970']
I've been having a play spice modelling these in an effort to understand the frequency/phase response better (I'm a novice when it comes to crossover design but once studied the basic principles, many years ago!)

Currently not quite sure the best way to model the electrical characteristics of the drivers (I assume an inductor/resistor but I'm unfamiliar with exactly how to approach specifying this). Modelling the LCR networks is simple enough though so I've started with that.

Happy to share the results for discussion here if such reverse-engineering & analysis is OK by stevie
[/quote]

I don't think it's as simple as an inductor/resistor as there's an impedance peak at the resonant frequency of the speaker.

Just had a look and there's an article on Wikipedia - looks like it's a complex LCR mix.

[url="https://en.wikipedia.org/wiki/Electrical_characteristics_of_dynamic_loudspeakers"]https://en.wikipedia.org/wiki/Electrical_characteristics_of_dynamic_loudspeakers[/url]

[Passinwind]

[quote name='tauzero' timestamp='1489339370' post='3256157']
I don't think it's as simple as an inductor/resistor as there's an impedance peak at the resonant frequency of the speaker.

Just had a look and there's an article on Wikipedia - looks like it's a complex LCR mix.

[url="https://en.wikipedia.org/wiki/Electrical_characteristics_of_dynamic_loudspeakers"]https://en.wikipedia...ic_loudspeakers[/url]
[/quote]

Yep, there are mechanical impedance equations that have to be factored in along with the electrical ones, and one has to measure those things themselves before Spice modeling will work all that well. Spice is very useful for looking at things like power distribution in crossovers though, IME.