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stevie

12" Cab Diary Continued

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Although it's been a while since there was any visible activity on the Basschat 12” cabinet diary, we have recently been discussing it again in pm. I have started this new thread because we have decided to take the project in a new direction.

Phil’s original design objectives for the cabinet were these:
Capable of keeping up with an unamplified drum kit (120dB across most of the frequency range)
Compact (60l or less)
Neutral /clean sounding
Easy to handle
Good low frequency power handling
Readily available components, and easy to build
Value for money.

The end result was a 50-litre cab containing a Beyma 12” driver – the SM212, which a few of you have built and which Phil has been gigging for a while now. But we didn’t want to leave it there: this box has a lot more potential that we would like to bring out.

A thread that Luke started a few years ago piqued my interest and got me messing around with bass guitar cabs based on PA/stage monitor design principles. I’ve knocked up a few cabinets since then, using some pretty tasty drive units picked up cheaply from eBay, and am convinced that this is the way forward. It also seems to be the direction that a few of the boutique builders are going in – so that’s a good sign.

I therefore persuaded Phil that a flat-response, PA-type design would be a good avenue to pursue, although I have to say that Phil remains convinced that non-flat cab also have their benefits.

Unfortunately, it has been necessary to alter the size of the baffle from the original design to make room for additional drivers. If I remember rightly, Phil built the original box in response to requests for a cabinet 19” wide. We are now going to jettison that requirement (sorry!) and adhere to the principle of form follows function – not a problem for everyone with a modern compact amp, but anything else will overhang. If that disturbs you, you need read no further.:-)

At about the same time as we were discussing this, John, who is Chienmortbb and lives not far away from me in another less salubrious part of Dorset, offered to build a suitable cab using some spruce ply panels he had in his garage. As the plan was to try for a lightweight, poplar ply cabinet this time round, it seemed like an excellent opportunity to develop a prototype.

The cab is here and I’ve marked it up for cutting. Game on!

33lnvo9.jpg&key=016db8b90b736070b3c8ca70c2e9547dbbf72afeed37e1b47a1d6fa93e0e26e4

The parts list is for the latest version of this cab. It will be updated at regular intervals to reflect changes in the market.

 

 

 

 

 

 

 

 

 

basschat-112-v3.pdf

PartsList.docx

Edited by stevie

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What thoughts on the mid range driver? I got quite taken by the Faital Pro M5N8-80 and have a pair awaiting use.

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At the moment, the project is for a two-way cab, 3below. We're going to start with a reasonably priced but high quality tweeter and then move on to a compression driver and horn.

The Faital looks very impressive. I'm not quite sure how they get that kind of efficiency out of a 5" driver. If I were doing a three-way, it would probably be at the top of my list to audition. What are your plans for them?

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I had originally started building a pair of 3 way PA cabs: 9mm lightweight ply - 3015 Kappalites, Faital M5N8-80 mid range and 18 sound XD125 compression driver and flare. Initially with a 3 way crossover driver. The Faital M5N8-80 choice came about indirectly from developing a custom 3 way bass cabinet with Shermann Audio. The project has stalled - lack of time, other stuff intervenes as usual (I blame Andyjr and build threads). I built two prototype lightweight cabs at the start of my early retirement (55 lol) however I keep getting work thrown at me that is fun and financially worthwhile. Retirement, what is that?

Would you like the long term loan of a Faital driver and an XD125 with flare? I also have some 'big' inductors and capacitors for a suitable crossover network. From what you have developed before I guess the eventual designs will be 'open source / creative commons' or similar. If this is so PM me.

Edited by 3below

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Hopefully I can reply to your last question. It is our intention to publish the design on here once it has been finalised as with the original 1x12 Cab Design Diary.

Edited by Chienmortbb

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[quote name='Chienmortbb' timestamp='1485813267' post='3226968']
Hopefully I can reply to your last question. It is our intention to publish the design on here once it has been finalised as with the original 1x12 Cab Design Diary.
[/quote]

I saw the drawing of the 1x12 cab. Was there any more detail published about construction anywhere that I missed?

btw, think it's fantastic that some talented and knowledgable people are doing this sort of thing on here. :)
Looking forward to seeing the new design.

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[quote name='fftc' timestamp='1485858758' post='3227186']
I saw the drawing of the 1x12 cab. Was there any more detail published about construction anywhere that I missed?

btw, think it's fantastic that some talented and knowledgable people are doing this sort of thing on here. :)
Looking forward to seeing the new design.
[/quote]

I went through the thread a couple of times already and I found only that one drawing. It actually has all the information needed, although much of it just implied. I think you won't need anything more.

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That design was basically Phil's baby, and I know he has some assembly instructions and photos nearly ready to post. I think life got in the way a bit. I'm sure he'll be along shortly to confirm. It's true, however, that there is enough information contained in that thread to build a working cab.

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The cab is the same internal volume as the one from the first thread ([url="http://basschat.co.uk/topic/227904-1x12-cab-design-diary/"]http://basschat.co.u...b-design-diary/[/url]), but the height has been increased to allow for an HF unit. It has also been sized to accommodate a half-inch picture frame for a cloth (or similar) grille, which should be easier, cheaper and lighter than a punched metal one. We discussed, and decided against the use of a slot port, as it would make the box too tall and ungainly. The porting arrangement has been taken over from the first design, although the ports have been repositioned.

So let’s get cutting! Here is my 70mm hole cutter, which makes a perfect hole for 63mm (internal) drainpipe.






Four holes cut in next to no time. I love hole cutters!




And here are four ports that I cut earlier.




Now installed.


Just grabbing my 80mm hole cutter to cut the hole for the tweeter.


The first HF unit we will be working with is the P. Audio PHT-407, available in the UK from Blue Aran for a very reasonable £13. Don’t be put off by the price; it’s a quality unit.





Install drivers, connect up, and we are ready to carry on.

Edited by stevie

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This is Stevie's thread and I don't want to hijack it but I thought a little background might be useful. I originally contacted Stevie and Phil as I had bought an SM212 and was planning to build the original design. However it was mentioned that the spec for the SM212 had changed and I did not want to build a cabinet that was not optimal.

I took the speaker over to Stevie's Den and we measured its main parameters ( Thiele Small parameters amongst others). It seems that Beyma changed the spec because the units being produced were consistently better than the original spec. Our measurements were almost identical to the ones for Phil's driver, purchased when the older spec was current.

While I was there, I heard the original prototype of the 1x12 and was impressed with it, especially the low end, it had plenty of h***.
Then I heard another cab of similar dimensions, equipped with a 12 plus a tweeter with a proper crossover. That cab had an OEM Eminence as the woofer. It's low end was nowhere near as extended as the BC 1x12 but the extra dispersion from the tweeter/crossover combination was an ear opener. I could hear detail standing directly in ffrot of the cab. At 6ft 2in that is impressive (me not the cabinet). This was how we started out on this leg of the 1x12 design.

The beauty of having both Stevie and Phil contributing is that they come at things with a different perspective. Rather than causing conflict this means each stage is scrutinised and challenged. I am learning an awful lot and hopefully others will too.

Edited by Chienmortbb

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It would be a bit lonely if nobody commented. So all comments and suggestions are, of course, welcome.

One of the problems I've encountered over the years of playing on small stages and in typical pub settings is the inability to hear what you're playing when you're directly in front of your cab. The usual solution is to raise the cab or to use a second one closer to ear height. It should be possible, however, to design a speaker with dispersion characteristics that allow you to hear your bass even when you're right in front of the cab. That is one of the design objectives of this speaker.

Edited by stevie

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[quote name='hrnn1234' timestamp='1485868263' post='3227295']
I went through the thread a couple of times already and I found only that one drawing. It actually has all the information needed, although much of it just implied. I think you won't need anything more.
[/quote]
Sorry about that, life really has thrown the kitchen sink at me in the last few months and is continuing to do so, the cost of elderly parents not to mention that my kids don't still have their moments.

So yes I have the detailed instructions in draft form and some photo's of the construction process but just haven't got round to typing it all out and investigating why my ancient computer doesn't seem to want to upload photo's If anyone want's to build the original version I'm happy to email a word file and a link to photobucket or similar. PM me if you are interested

And all the dimensions are on the original thread so you should be able to build it from that, well people already had.

John you used the h**t word!

Edited by Phil Starr

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[quote name='Chienmortbb' timestamp='1485870960' post='3227339']

The beauty of having both Stevie and Phil contributing is that they come at things with a different perspective. Rather than causing conflict this means each stage is scrutinised and challenged. I am learning an awful lot and hopefully others will too.
[/quote]

Stevie may not remember it but he picked me up on my maths a few years ago. He was right. We've been 'exchanging views' ever since :)

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That can't be right. My maths is rubbish! :)

[Edited for a grocer's apostrophe]

Edited by stevie

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[quote name='Phil Starr' timestamp='1485876760' post='3227423']

Sorry about that, life really has thrown the kitchen sink at me in the last few months and is continuing to do so, the cost of elderly parents not to mention that my kids don't still have their moments.

So yes I have the detailed instructions in draft form and some photo's of the construction process but just haven't got round to typing it all out and investigating why my ancient computer doesn't seem to want to upload photo's If anyone want's to build the original version I'm happy to email a word file and a link to photobucket or similar. PM me if you are interested

And all the dimensions are on the original thread so you should be able to build it from that, well people already had.

John you used the h**t word!
[/quote]Just seeing if anyone would b*te!

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Before we can even think about working with the drivers, we need to take a closer look at the cabinet to make sure it’s fit for purpose. So let’s install and connect the bass unit. I’m going to carry out some tests on the box, which you can easily replicate on your own cabinet at home if you wish.

The standard material for wooden cabinets in the world of sound reinforcement is, and has always been, 18mm birch ply. Because they are stiff, cabinets made from birch need relatively little bracing (I say relatively....). The lighter stuff is different, however: here, bracing is mandatory. The lightweight spruce plywood that our test box is made of is unlikely to be as stiff or well damped as the poplar ply we will ultimately be using, and it is certainly nowhere near as stiff as birch. Bracing is therefore a necessary exercise and we should be able to transfer the lessons learned to the final version.

The test CD I’m going to be using contains test tones at the usual frequencies. Playing them through any cabinet starting at 40Hz quickly reveals resonances and problems, if there are any, with the cabinet’s structure. You could say it’s a bit of a torture test. If you’d like to try your hand at this on your own cab, download some of these MP3s and give it a go: http://www.testsounds.com.

It’s a sad fact that many expensive bass cabinets suffer from cabinet resonances, by which I don’t necessarily mean rattles. It’s often a commercial necessity to build cheaply in order to remain competitive. After all, who checks a bass cabinet for resonances before buying, or even looks inside it to see if it has been properly braced and damped?

The problem is that a vibrating cabinet will colour your sound and detract from its perceived sound quality. Panel vibrations simultaneously add to and subtract from the sound of your bass, continually altering and masking its tonal colour – so it’s important to try to keep them under control. To make matters worse, the bigger the cabinet you have, the more difficult resonances are to control. Fortunately, the DIY builder is not constrained too much by the extra cost of building a well-behaved cabinet.

Test results
Not great. Not unexpectedly, the cabinet as it stands rings like a bell. The worst vibrations were on the baffle – so that will be the first area to deal with. This test is normally carried out using an accelerometer, which is a type of vibration detector. Since I don’t have one, I simply felt the vibrations on each of the panels with my fingertips, rated them subjectively for level, and entered them on a sheet of paper in tabular form.

Rather than reproduce the entire table, which is a bit difficult on here, I can summarise the results as follows:

Baffle
Resonances starting at 40Hz and going through to 400Hz. The worst frequencies were 63 and 80, but 50 and 100 were also excessive.

Sides
Resonances starting at 100Hz through to 250Hz. Then a single resonance at 630Hz.

Top
Resonances at 80 and 100Hz. Then at frequencies between 250 and 400.

Back panel
Resonances from 40 through to 315 Hz, with particularly bad resonances at 80 and 200Hz.

Edited by stevie
To correct site migration issues

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Anny thoughts on using the accelerometer on your smartphone? There are a few free apps around that allow you to make readings from it

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Good call although the vibration sensors in your fingers work pretty well. I suspect we may try a seismometer on the Poplar prototype when we build it.

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Feeling for vibrations with your fingertips works really well. Even with an accelerometer custom designed for this type of work, you have to set up and calibrate your measuring gear, glue the device to various areas of each cabinet panel, and save or print off your results. With your fingers, you can check the different areas of the cab in seconds. The only drawback is that it is subjective, but once you've done it a few times, it's very effective.

I'm now sorting out the bracing for the box, which will take a few days. Has anyone tried the test tone MP3s yet?

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I've built a couple of small bass cabs over the years, and I've found that rebating softwood battens into the cabinet panels not only adds strength but can also damp the panels. It's not a difficult thing to do once you own a router.

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Another thought. I did want to build a 2x12 version of the original 1x12 design but really prefer a slot port design. Without trolling through the whole thread, can someone point me at the relevant posts as to why a slot port wasn't used?

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Yes, we originally planned a slot port and I built one and showed it around to a few people. It did look nicer than the round port version. The problem was twofold, the design was meant to an easy build for someone at home, I found I needed no fewer than eight clamps whilst glueing up which I didn't think most people would have to hand. Without extensive clamping the round ported cab was an easier build. Secondly, and perhaps more importantly putting the slot in meant the speaker was effectively operating into a square space and we got an unfortunate and clearly audible resonance on some notes giving a slightly artificial sound (I quite liked it, but that's just me). We killed that in the end by putting a big slab of wadding on top of the port shelf.

It wouldn't be a problem with a 2x12 as you wouldn't have a short squat cab any more.

If you want me to talk you through a 2x12 version I'm happy to do so at the cost of asking you to post up your progress on BC :)

Edited by Phil Starr

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[quote name='Phil Starr' timestamp='1485949379' post='3227896']
Yes, we originally planned a slot port and I built one and showed it around to a few people. It did look nicer than the round port version. The problem was twofold, the design was meant to an easy build for someone at home, I found I needed no fewer than eight clamps whilst glueing up which I didn't think most people would have to hand. Without extensive clamping the round ported cab was an easier build. Secondly, and perhaps more importantly putting the slot in meant the speaker was effectively operating into a square space and we got an unfortunate and clearly audible resonance on some notes giving a slightly artificial sound (I quite liked it, but that's just me). We killed that in the end by putting a big slab of wadding on top of the port shelf.

It wouldn't be a problem with a 2x12 as you wouldn't have a short squat cab any more.

If you want me to talk you through a 2x12 version I'm happy to do so at the cost of asking you to post up your progress on BC :)
[/quote]

Deal!

I was thinking of a central slot port, with a driver above and below in a sort of homage to the Acoustic designs of old which always looked pretty cool to me, plus the side slot port is pretty much the exclusive territory of Barefaced these days. Having said that, the Berg OBBM is selling at the moment looks pretty cool with those corner ports that remind me of my old Schroeder 21012 (probably the best cabinet I've ever owned for 'tone' and 'projection').

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