Jack12 build from the UK: changing parts

The Jack of All Trades pro-sound cabs.
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chyc
Posts: 2
Joined: Sun Nov 10, 2019 3:54 am

Jack12 build from the UK: changing parts

#1 Post by chyc »

Laying out the groundwork for building a new BFM cabinet. Am currently leaning towards the Jack12. Being on the other side of the pond and being weird because of it, I'd like to switch up a few things. Reading the plans a few times I *think* I've got valid swaps, but I thought I'd check here first before I fire up the circular saw:

Woofer
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12PR320 https://www.bluearan.co.uk/index.php?id=FTP12PR320

This looks to be a fairly uncontroversial swap and can save me a few pennies over the similarly spec'd 3012HO. The T/S seems to be within the parameters from the plan. There are other ones available, the 12PR300, 12FH500, 12FH520. The last two have crazy low Fs, but Qts outside the allows params. I do not understand what that means in the real world and do not want to spend more for a speaker that is inappropriate.

Piezo
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Eagle and Altai 1016 https://www.ukdj.co.uk/general-store-c4 ... -rms-p3409

This is more controversial as I can find no information about this brand. The spec recommends monacor, but the price is prohibitive, especially if I'm going to build a meld-array of 16, probably breaking 8 in the process.

Interestingly, searching for "Eagle Altai" in this forum times out and gives an error. I think it's the word Eagle but I do not understand why.

Glue
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Gorilla grab adhesive clear https://uk.gorillaglue.com/gorilla-heav ... tal-clear/

I found Loctite PL Premium at >$200USD a tube, shipping $150! What's drawing me into this adhesive is that it sets clear so will look nicer if I go for a natural finish. It doesn't look to be PU based, but has all the properties.

Wood
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The instructions say to not use thin veneered woods, but it doesn't detail as to why. If it's purely aesthetic then I can live with that. In a way I want this box to look more homegrown.

If Baltic birch is a necessity it looks like Russian Birch is an actually obtainable equivalent here, but sheesh is it pricy at the moment. Any world events that could possibly have caused this? :cussing:

Question: reopening the cabinet
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I cannot find in the instructions anything about what happens if you need access to the woofer. Is it a case of "new cabinet time" or am I misunderstanding how it all fits together?



Many thanks for reading this far! I bought the complete set of plans to read all of them to see which one I would like to start with. I haven't seen the other hot contender, the Simplexx, but I think all these questions would be relevant to that plan also.

chyc
Posts: 2
Joined: Sun Nov 10, 2019 3:54 am

Re: Jack12 build from the UK: changing parts

#2 Post by chyc »

Update on the glue: The Gorilla Clear stuff is non-expanding so would not fill in the imperfections in my cutting. I've found this which is expanding PU, so basically exactly what was asked for

https://www.amazon.co.uk/Gorilla-Filler ... 091HZG52Z/

monekh
Posts: 90
Joined: Mon Mar 31, 2014 5:56 pm
Location: London, UK

Re: Jack12 build from the UK: changing parts

#3 Post by monekh »

greetings from a fellow UK weirdo.

I was recommended this glue by another UK builder on this forum, and have built lots of cabinets with it - https://www.everbuild.co.uk/products/ad ... esive-gel/.
It expands well, and you should be able to find it for about £8 a tube. As long as your panels are cut accurately, the finish shouldn't be an issue, you won't be able to see the glue unless you have big gaps. Any excess that squeezes out of joints you can easily peel off once it's cured.

I don't think the thin veneer cheap Asian 'birch' warning in the plans applies so much in the UK - birch plywood is only really stocked by the smaller timber yards, and I've always found it to be a good and consistent quality. Often hard to find out where it's actually from, but if they say it's Russian it'll be a similar quality to Baltic. I'm not sure where you're based, but I recently bought a couple of sheets from Jennor timber in Enfield (https://www.jennortimber.co.uk/), £82 a sheet, which is madness, but still by far the cheapest I could find at the moment (one place quoted me £160 a sheet!). I also bought some for a very good price years ago from Fall timber in north yorkshire (https://www.falltimber.co.uk/), though I don't know what their prices are like now. I haven't ever tried to build with anything other than birch - it seems from the Jack plans that you can use other types of plywood, but I can't comment on the difference.

The boxes are designed to be reopenable should you ever need to replace the driver / access the inside. You may need to replace the gasket foam before you screw the back back on, just to ensure a good seal again. The plans recommend screwing the back into the flanges, but more recently I've used insert nuts embedded in the flanges, and countersunk head socket screws (https://www.screwfix.com/p/easyfix-coun ... /2398t#_=p), which is a little more costly, but seems to work just as well and means you don't have to worry about screws spinning in old holes if you are taking the back on and off.

I haven't deviated from Eminence drivers and have only ever built the compression driver HF sections, so can't help on those fronts I'm afraid! The guy at lean business is quite helpful though and might be able to recommend similar spec drivers.

Hope that helps.

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Bill Fitzmaurice
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Joined: Tue May 02, 2006 5:59 pm

Re: Jack12 build from the UK: changing parts

#4 Post by Bill Fitzmaurice »

That woofer is OK as far as the specs go, but it doesn't have the rising response in the mids of the 3012HO, so the midrange won't be as good. The tweeters are probably OK. Baltic Birch can be from Finland or Russia. If you need access you take out the screws and remove the back of the cabinet.

keithgrif
Posts: 6
Joined: Sat Nov 10, 2012 10:33 am

Re: Jack12 build from the UK: changing parts

#5 Post by keithgrif »

Another UK maker here.
I made a jack10 with cheap B&Q ply. This ply is absolute rubbish, full of voids and has a thin veneer. Risk is the veneer fails and the box falls apart so I screwed and glued, so far so good.
Second Jack10 I made was with proper Baltic birch ply, so much better, invest in it if you can.

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fender3x
Posts: 647
Joined: Mon May 15, 2006 11:51 am
Location: miami

Re: Jack12 build from the UK: changing parts

#6 Post by fender3x »

I had a build that is an object lesson for why not to use thin veneer woods. I *thought* I was getting good quality plywood, although I knew it was not BB (hard to get in Miami). It wasn't until a joint failed that I realized the veneer was *so* thin and so close to the color of the layer under it that I had not noticed. BFM cabs rely on good glue joints. The screws or other fasteners are mostly just to keep things from moving until the glue sets. If your glue sets to veneer, the veneer will just break off under any sort of tension. Bottom line is that you need a top ply of decent thickness for the glue ups to work properly.
One man's magic is another man's engineering. --Heinlein

1 x DR250
1 x T39
1 x Omni 10

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Bill Fitzmaurice
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Joined: Tue May 02, 2006 5:59 pm

Re: Jack12 build from the UK: changing parts

#7 Post by Bill Fitzmaurice »

Look for Italian poplar. It's hard to come by in the US but I believe it's more common in the UK. It's similar in quality to BB and lighter weight.

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