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stevie

12" Cab Diary Continued

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The drawings are now with my CNC flat pack supplier. Fingers crossed.

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No, there should be two - remember that cutlist is for 2 cabs.

It was the order of the cuts - what I currently have labelled as Cut 11 needs to be done AFTER cuts 12-15, as you need to have removed the 417mm long parts before you can trim the remainder off to 387 to form the K and L braces. 

Altered on my master now anyway, so I don't forget.

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Yup. It's the cutout from the port. It doubles the thickness of the cabinet at its weakest point, which is at the centre. I have that arrangement in my own cab and it works really well. It's also very easy to do.

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That is a beautiful handle. I had thought a handle like that, and the cut outs etc, was going to be standard. 

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The drawing assumes the use of the original handle I used in my cab, which is a Marshall-type strap handle, but builders can of course choose whatever handle they prefer. The flat packs will have the round handle because it offers a number of advantages that I think owners will appreciate.

For those rolling their own who wish to use the round handle – bracing for the top panel is a ring of plywood 35mm wide with a centre hole the same diameter as the hole for the handle. This arrangement not only stiffens the top panel but it also means that the handle bolts are fixed to 30mmm of plywood. The ring can be cut from the circular piece of wood left over from cutting the hole for the main driver.

 

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Q: your prototype had braces running vertically mid way across the side panels. (As well as curvy braces) were they felt to be not needed? 

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Exactly right, Luke. The idea behind building the prototype cab was to discover what bracing was needed - so it was a bit belt and braces. Surprisingly, the spruce ply in that cab tended to ring more than the poplar ply we're using now. This is an ongoing project for me, which means I may revisit the bracing configuration at some future time, but I think what we have now is a good balance between bracing performance and complexity.

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Hi All,

This thread is awesome! Well done for all the efforts put in so far. What an excellent resource. I built 2 BFM Jack 12's about 9 years ago but the thread/pics have all gone since BC website was updated. I had rehearsals recently after a short (ahem) period of musical inactivity and remembered that I never got on 100% with my cabs or amp (Ashdown Little Giant 1000, with half the power section dead, and the outputs bridged to keep it going...). The Jacks are very very loud, but they're too much for the odd pub gig in Cornwall and take up too much room in my house. They also need EQ to calm some mids and I'd need to add an HF section to get clarity at band volume. I've been looking at the fEARful/fEARless cabs but was really chuffed to then spot that BC has this in-house cab design thread that makes use of newer drivers. Lots of sensible-looking aspects to this design. The compact size, frequency response/range, and potential SPL seem ideal for my needs. I'm very much hoping to build one (or two?) as soon as possible.

Thanks, and fingers crossed for some decent new cabs!

Rich

 

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Thanks for your kind words, rc. The cabinet design is finished - so you can start cutting as soon as you like from the plans in the thread. The crossover is still being tweaked, however. Once I've finished the crossover to my satisfaction, I'll post a list of parts and components you'll need to complete your cab.

I'm struggling to find a company that will supply small quantities of badges for the front grille at a reasonable cost - say a fiver or less. Can anyone help?

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15mm poplar supplier in Cornwall anyone?

First challenge is 15mm poplar ply. I'm struggling to find a supplier based in Cornwall (I'm in Falmouth). Are there any in Cornwall or Devon stocking 15mm poplar sheets? If not, are there places further afield that could cut and deliver? I'd rather not drive a 6 hour round trip to Bristol if it can be avoided.

Cheers,

R

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You could try Duchy Timber: <http://www.duchytimber.co.uk/our-products/sustainable-sheet-material/>

They're part of the Premier Forest Group: <http://www.premierforest.co.uk/premier_forest_products_products.htm> who definitely sell poplar plywood. So if Duchy haven't got it in stock, they should be able to order you a sheet. Try to get Italian or Spanish rather than Chinese.

Your local wood merchant should be able to order you a sheet too. A lot of wood merchants will cut the sheet up for you for a small fee. Not only will that save you a lot of time and effort, it'll make the wood easier to transport home. Just give them the cutting list in the PDF with the drawings.

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3 hours ago, stevie said:

Just give them the cutting list in the PDF with the drawings.

Isn’t the cut order waiting on a wee update? 

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Loving the look of these and will have to give it a go at some point. Out of interest, would it be possible to put in some kind of switchable or adjustable crossover like the Barefaced Big Baby? Like the idea of something that could dial in a more 'old school' sound if I needed.

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1 hour ago, LukeFRC said:

Isn’t the cut order waiting on a wee update? 

Err, yes, you're right, although I don't think that would bother most saw operators.

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1 hour ago, d-basser said:

Loving the look of these and will have to give it a go at some point. Out of interest, would it be possible to put in some kind of switchable or adjustable crossover like the Barefaced Big Baby? Like the idea of something that could dial in a more 'old school' sound if I needed.

Yes, that is certainly possible. There will probably be a fixed-value L-pad on the crossover (2 resistors connected to the HF unit). You could replace those with an 8-ohm L-pad attenuator. If you wish, I can provide more precise instructions once the finished crossover is ready.

However, I don't like L-pads on speakers. And I'll tell you why.

- First, it's one more thing to go wrong - and L-pads aren't nearly as reliable as wirewound resistors.

- When you rely on an L-pad for attentuation, you have no idea what is flat. The 12 o'clock setting means absolutely nothing. If the frequency response is not flat, the phase of the crossover will be out. That means dips (and peaks) in the response, especially off-axis.

- This particular design measures as flat as a very expensive studio monitor. Why would you want to compromise that when you can roll the top off with the tone controls on your amp or bass? When was the last time you saw an L-pad attenuator on a studio monitor, or a hi-fi speaker? About 50 years ago.

- Finally, from what I can gather, most people attenuate the HF unit on their cabs because it doesn't sound very good. I can understand that, but that's certainly not the case with this cab. The HF is not strident, edgy or honky. Your P-Bass with flats will sound like a P-Bass with flats, and if you want a more old-school sound turn the treble down on your amp or use the tone control knob on your bass.

You are entitled to disagree with all of this, and if you'd really like to fit an HF attenuator, I'm happy to provide the details. It's not a difficult job.

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Oh, and another (even more important) reason why an adjustable attenuator is not a good idea is that our crossover rolls the bass unit off fairly steeply at 2kHz. On almost every other bass cab (with very few exceptions), the bass unit is not connected to the crossover; it just carries on happily as high as it can. If there is a tweeter, it is added at a relatively high frequency - usually about 5kHz, which is too high to be much use - and protected by  a cap and a coil. So when you attenuate the tweeter, you get the sound of the bass/mid driver on its own.

 

 

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Thanks for the informative response, interesting points. Certainly sounds like adjustments on the amp rather than the cab are the way to go.

Edited by d-basser
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Having used the Mk2 design with the Beyma driver for well over a year. I can tell you that it is not like a normal cab with a tweeter. The horn is wide angled and on the new design arranged v erticall , you can hear yourself more clearly but there is no nasty excessive top end ( yes i had my hearing checked on Tuesday, all OK). I play a P/J but almost always have the J pickup off, simulating a P.

The reason for the tweeter is that above about 1KHz, all the sound goes into your knees and the audience with a 12" speaker. It is even worse with a 15".  I don't know if anyone has done any research on the subject but I think the main reason people have stacked cabinets is so they can hear themselves. The top cabinet will be raised to the point where you can here the mids, and that is where the clarity is. However that is also where the 12" drivers start to have a very strange response. That is why the Basschat design crosses over at 2Khz.

Most low cost cabs with tweeters ( i am not calling any manufacturers out here) traditionally use a piezo tweeter with just  a resistor instead of a crossover. Some add an attenuator but this does not work well for the reasons stated above by Stevie.

Just a word about piezos. They are not as good as a really good tweeter or compression driver BUT they do get a bad press mainly because the are misused. They have to be properly crossed over and that means that some of their benefits (ie low cost)  are lost. However the really good professional Motorola ones of old cost a lot more than the cheapos put in many bass and PA cabs.  A really good horn/compression driver is not much expensive..

Edited by Chienmortbb
stupidity
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Cheers for the further info, interesting stuff. 

Another query - would a pair of these be a mental idea? Ultimately I am looking for something I can run with an oldschool / doom metal band (think sabbath etc), want to have a nice thumpy sound and compete with loud drums and guitar without having a massive amount to move or carry (live in a 3rd floor flat 😫). 

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Stevie will be the best person to answer this but as far as I know, two identical cabinets would not be ideal. We had discussed this and this current full range cabinets would be best on top with an Identical cabinets below but with it's frequency response restricted so that only frequencies below 800 Hz reach the lower 12 inch driver. This would ensure maximum benefit and minimise interactions between the drivers in the two cabinets.    So the lower cabinet would have no tweeter/horn and have a low-pass filter restricting its bandwidth.

I must stress that we have not tried yet.

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6 hours ago, Chienmortbb said:

Stevie will be the best person to answer this but as far as I know, two identical cabinets would not be ideal. We had discussed this and this current full range cabinets would be best on top with an Identical cabinets below but with it's frequency response restricted so that only frequencies below 800 Hz reach the lower 12 inch driver. This would ensure maximum benefit and minimise interactions between the drivers in the two cabinets.    So the lower cabinet would have no tweeter/horn and have a low-pass filter restricting its bandwidth.

I must stress that we have not tried yet.

that's interesting, different approach than I've seen taken by other folk

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The latest version of the PDF drawing is now up on page 18 of this thread along with the revised cutting list. Thanks Richard!

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