Sitting Room Build: Jack 12 Lite

[HugoMack]

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Moving on! Waiting for plastic hats from Blue Arran and some nice speaker cable.

[Jools4001]

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The box feels like there's nothing in it, but I'm sure I put a couple of balls in there. The woman at the post office asked me whether I'd sent any batteries with it, I haven't, so if you need battery powered phase plugs you'll have to fit them yourself.

[HugoMack]

Excellent Jools. Very many thanks! Reminds me of my electric toothbrush starting up in my luggage at Helsinki airport and having to be searched.... I think passive phase plugs sound more natural so I won't be going the battery route.

[DJPhatman]

I think passive phase plugs sound more natural so I won't be going the battery route.

Phase plug pre-amp!!! Gives it that "moar excitement" range!!

[HugoMack]

I am EQ'ing them though.

Thanks Jools!!

[HugoMack]

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More delay through injured shoulder, but almost there!

[Jools4001]

Looks pretty good from here, although I found that getting cab number one from that stage to the finish seemed to take forever; crossovers, melded arrays, installing speakons and so on... the second seemed to go much more quickly.

I found the Jacks to be well worth it though and it's getting better with every gig - although sods law dictates that no sooner do I finish the Jacks than we land an outdoor gig in a big marquee where we'll probably need T39s...

[HugoMack]

Thanks Jools. I've now got your magnificent balls in place too!

I've had a few little glitches - which is why these threads are useful....

- like for example assembling the 'framework' for the backs before gluing in place. I think this is the right way to do it, but got caught up in lining up where to fire the staples and didn't notice that the 'frame' had slipped sideways in the glue. But with the speaker in place it does fit on so that's OK.

I urge everyone to draw carefully on the firing side. I have quite a few misfires sticking out here and there. Also, a proper air gun is the way to go - lots of power. That and the saw were great investments. Using screws would have taken for ever, and messed up my shoulder even more.

I would also have used my disc saw more than the jig saw - drop it in to every straight line, then use the jig for the ends and curves. My straight lines aren't always straight, and I've had to use a squeeze or two of glue to fill the odd gap...

One of the backs has somehow ended up a tad small - about 1/8th along one edge. Is there any beading that might help the seal - speaker tape or something? Or should I not worry?

I haven't worked out how to get the router to cut smaller circles (it was great for the main horn curves) or things like the speakon plates. Still the latter will cover up my jigsaw efforts - but it would be good to do them smoothly.

Finally... I'm guessing that being airtight is more important than utterly smooth, perpendicular surfaces or straight edges...? The stand hat is in a pretty 'disruptive' place for example. I will go over the ports and main flare with a craft knife to remove glue lumps....

I'll be like you with the T39's. But I assume that when you crossover the bottom end away from the Jack 12's, they can deliver with even more? So I'm not going to have to build another set - or DR250s (although they look great).

[Jools4001]

My cheapo Stanley electric staple gun got as far as the back brace frame before it died, so I had nothing to fire staples with when making the backs. I just drew out where the bracing should go then used another method that Bill recommended somewhere, of using a bead of PL as normal, but just using a few blobs of hot glue to tack the brace in place while the PL cured....that worked well and avoided the dreaded PL squirm.

I just put a blob of PL anywhere that a staple poked through, and then only in places where there was going to be some sort of pressure difference, if it was inside the cab I didn't bother.

One of my backs ended up a bit small by about 1/8" as well, but you can just slide it to one side to make a 1/16 gap on either side can't you? Or am I missing something? In any case the back flanges are 1" wide on either side, so there should be enough wriggle room. I used 20mm wide gasket foam to seal the backs on mine so there was still at least 15mm of compressed gasket on each flange when the back was screwed down.

I know that Jacks give me enough low end, for now, in the typical UK bar gigs we do where my bass backline does all the low end, and the bass drum is loud enough with just a smidge in the mains. I know that they'll be even happier high passed at 100-125hz..

[HugoMack]

Thanks Jools. I'll use some gasket foam. The Duratex will make it all look rather splendid!!

Wish I'd used hot glue on the backs. I'm using it on the small braces as recommended.

[Jools4001]

Any updates?

[HugoMack]

Hi Jools,

Thanks for the call! I haven't yet been able to re-start; being sensible and allowing my shoulder tendons to settle. I was almost there so this is frustration. I'm back playing guitar again which is a relief.

I need to reduce the bracing strips, which requires slicing 20 little triangles, trim the horn flares and glue in the little horizontal horn flares. I also need to router out 3mm on part of the back bracing to make the back cover sit flush - as I'm worried about getting a good seal. This requires a bit of tool hefting, so I'm leaving it - but next week is looking good.

But everything else is ready; melded array, all the bits, speakers etc. So I hope hope once I've finished building and have tidied it all up, installing the hardware won't take too long.

[HugoMack]

Up Date: I've now got the construction done. Next step is installing the hardware.

The main suggestion I've got - apart from trying to buy as small a air-powered nail/staple gun as possible (to get into the horn spaces at the right angles), regards the flares.

I managed to secure mine initially (at the speaker baffle) using a combination of hot glue blobs and normal glue plus nail gun nails into the underlying supports and speaker baffle. Left this overnight to cure, then was able to bend both sets of flares into masses of glue using clamps, again tightened up with air-nails into the underlying supports. Nails rather than staples to ensure they go into the supports.

I have to say that I've made liberal use of glue!

[Jools4001]

It'll be worth it. I've used mine on about three gigs since I completed them and even though I haven't done enough with them to really dial in the EQ completely they are seriously impressive. Full, rich and as loud as f.

The good thing is that I think there is more to come. I'll try and get some gig video and a review together, but our next gig is not until late August. We've had to cut our gig schedule drastically because our drummer's wife is seriously ill and we don't want to give him a crappier time than he's already having by using a dep and giving him cause to doubt his place in the band.

Anyway, enough about me...lots of glue is good, it's a bugger to clean up but at least it should ensure airtightness.

[HugoMack]

Thanks Jools.

I'm wondering about both running-in the speakers and doing the air-tight testing. What shape wave does the tone need to be? And how does the voltage Bill suggests in the instructions relate to amp output - or how do I measure it? And is the volume difference when establishing polarities for the woofer and melded array obvious? I guess if it isn't - as Bill says - it doesn't matter, but I want to get that right, especially as the next step is building a set of T39's, so that in that rig, the Jack 12's are going to be putting out a lot more HF.