2x Jack 12 Lite build

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fender3x
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2x Jack 12 Lite build

#1 Post by fender3x »

It has been a while...but I am about to embark on a J12L build. If history is a model, it may take me a while to finish... My first build was an Omni 10, a discontinued cab. Second was a T-39, back when they were top loaded. Third was a DR250 which I started before the melded array had been invented.

Lately I have been on a kick to get my bass and rig to be as light and flexible as possible. While I was not building speakers, I was building basses. A Precision that I got down to around 6 lbs, and two ES335 style basses that I got to around 6.5 lbs. Got a class D bass head...now for the cabs. The DR250 is not at all bad for weight, but I wanted to see if I could do better...and potentially have a set of PA cabs for light use (no pun intended).

I purchased almost everything I needed several years ago. Recently remade my table saw jig, and built a melded array jig. Also built a test jig for the tweeters, and found 49 good ones out of 50. The build officially began this week when I cut 32 tweeters on them. So far, that's it, but more to come!
One man's magic is another man's engineering. --Heinlein

1 x DR250
1 x T39
1 x Omni 10

9830Lark
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Re: 2x Jack 12 Lite build

#2 Post by 9830Lark »

6 lb P-bass sounds wonderful, especially if it doesn't neck dive. Both of mine are around 8, which is fairly comfortable.

Did a J10 Lite a few months ago, loving it. Didn't use tweets and it seems fine, but I'm no expert. Of course, if you want to use them for PA also, you'll need the highs.

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fender3x
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Re: 2x Jack 12 Lite build

#3 Post by fender3x »

I have a fairly light mid-70's bass that is around 8.5 lbs. I wanted a bass that sounds like it, but that was lighter and had more of a jazz neck profile. The '70's bass actually has more neck-dive than the light one. There's hardly any neck dive with it. I was prepared to live with worse to get the weight off my back ;-) It helped quite a bit, I think to use a fairly heavy bridge and a Hipshot ultralight tuners. I usually keep the tweeters off on my DR250. Guessing I'll do the same with the Jack. Glad you're enjoying yours!
One man's magic is another man's engineering. --Heinlein

1 x DR250
1 x T39
1 x Omni 10

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fender3x
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Re: 2x Jack 12 Lite build

#4 Post by fender3x »

I have officially glued up my first melded array!

Tested all the elements with an LCR meter, and for sound and polarity with a found-object test jig. The only innovation in the jig are the chopsticks to hold the test tweeter in place on the screw-contacts. It was quick to build, quick to use, but low on visual appeal.
tweetTestJig.jpg
tweeter_array_1.png
The # on the blue tape is the capacitance, and the "dot" means it passed sound and polarity tests. In the Dyslexia land everything must be labeled.

Interestingly, I only had one tweeter failure. It was fine for polarity and capacitance, but had a weak sound. Turned out to be a messed up paper cone.

I used acetone with some cutoff tweeter bits mixed in. About 50 ml of Acetone and 10g of ABS. That amount was about exactly right for one 16 element array. I experimented with it a bit before starting because I was not sure it would have enough setup time, but it turned out to be about optimal. There is enough time to paint the sides and then it sets very quickly. there is enough viscosity to fill small gaps. One interesting thing is that it started thinner than it finished. The glue was considerably thicker on tweeter-pair 8 than an tweeter-pair 1. The good part about this is that I could go back and fill gaps with glue that had become more slurry-like.

Will go back and give a coat of thicker slurry to the back when I finish the 2nd array. I am considering reinforcing with the "strips of abs that I cut off the sides of the tweeters...but maybe that's overkill? It seems like a simple enough thing to do, but I haven't seen others doing it.
One man's magic is another man's engineering. --Heinlein

1 x DR250
1 x T39
1 x Omni 10

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Seth
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Re: 2x Jack 12 Lite build

#5 Post by Seth »

Grant pointed this option out to me once and I really like it. I don't recall if these are pics of his or someone else's. The array is assembled the way you did it, alternating housing direction, but each module is rotated in it's housing so that the lugs align better for a more direct wiring scheme.
MeldedArray01.png
MeldedArray02.png

In any case, looking good :thumbsup:

I appreciate the research into the solvents and cements. I did the same thing. You must be a genius too. LOL
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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fender3x
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Re: 2x Jack 12 Lite build

#6 Post by fender3x »

Grant seems to also mark the positive terminal with a red dot. If you look close at the pic there's a some red nail polish to mark the positive side of mine as well.

I like the idea of turning the elements, but I probably won't do it on mine. I opened two tweeters and three of the six screws stripped. Most of the rest are tight, and I have filled a few that were not with a bit of toothpick and acetone slurry. I don't really want to open them if I don't have to on the "ain't broke" theory. That said, I really like the way that patter straightens out the wiring course.

I am hoping that my wiring chart will keep me on course if dyslexia rears it's ugly head ;-)
tweeter_wiring.png
In any case I appreciate being in the company of other geniuses! Ha!
One man's magic is another man's engineering. --Heinlein

1 x DR250
1 x T39
1 x Omni 10

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Seth
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Re: 2x Jack 12 Lite build

#7 Post by Seth »

fender3x wrote: Tue Aug 30, 2022 8:39 pm I appreciate being in the company of other geniuses! Ha!
:loler: I'm quite literally chuckling out loud. Hahaha. Completely enjoying the exchange of (dim)wits. :thumbsup:

The wiring scheme looks solid.
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

Grant Bunter
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Re: 2x Jack 12 Lite build

#8 Post by Grant Bunter »

fender3x wrote: Tue Aug 30, 2022 8:39 pm Grant seems to also mark the positive terminal with a red dot.
In my DR250 thread? No, I think that was Anton posting up a picture of what he does, talking about reversing every other piezo, and adding dots.

I just went standard myself.
I didn't bother marking the positive. It already has a + on it.
If, on testing, I was to find a piezo with reverse polarity, I would put it aside.
Another reason to buy more than you need...

Edit: I wire mine differently.
positive and negative to appropriate terminal on piezo 1 bank one, wire through to last piezo in that bank then cross pos and neg (think a large X, to bank 2 and continue on. Why? So you can run the wire back to the filter down 1 leg only. Not have to split it and run it up 2 legs...
Built:
DR 250: x 2 melded array, 2x CD horn, March 2012 plans.
T39's: 4 x 20" KL3010LF , 2 x 28" 3012LF.
WH8: x 6 with melded array wired series/parallel.
Bunter's Audio and Lighting "like"s would be most appreciated...

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AntonZ
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Re: 2x Jack 12 Lite build

#9 Post by AntonZ »

Grant Bunter wrote: Wed Aug 31, 2022 12:37 amI think that was Anton posting up a picture of what he does, talking about reversing every other piezo, and adding dots.
The pictures posted by Seth look suspiciously familiar so: yep, that could have been me :cowboy:

The colored dots were already on my piezo's if I recall correctly. I found them helpful when soldering. Big red dots are harder to miss than a plus sign that requires my constant attention. I did check all piezo's for polarity. In fact I added a phase reverse switch in my pizzer test jig specifically for this purpose. Don't recall if I found any out of phase, it has been a long while. It was reassuring anyway to know for sure that not only all sounded similar, but also none were off in polarity.

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fender3x
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Re: 2x Jack 12 Lite build

#10 Post by fender3x »

I only found one reference to someone who found piezos with reversed polarity. Never from someone who used Goldwood. I tested, but I am not sure it's necessary. Same with capacitance. I read about one person who had wildly different capacitance. In my case all were between .120 and .167. The only one that wasn't good, had good capacitance, but was quiet due to a damaged cone. So in my checking of 50, a simple sound check would have caught me only defective one.
One man's magic is another man's engineering. --Heinlein

1 x DR250
1 x T39
1 x Omni 10

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fender3x
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Re: 2x Jack 12 Lite build

#11 Post by fender3x »

Not doing this build in exact order. I decided to pieces that required a router and that used half inch plywood. Did the rings and circles first.
senso-rings.png
My 1/2" ply varies in age, which is the reason for the color difference in this pic. Using up the old stock. The big circle was easy using a milescraft circle jig and a full-sized router. Unfortunately I don't have the Milescraft small circle jig, so I improvised using something cobbled together with a $20 Harbor Freight trim router. It worked, but took a few tries to get it right. Don't think I would recommend this tool to anyone.

I used some scrap 1/2" ply...stuff not suitable for a build...to make a template to route the baffles. My inspiration for this was Rickyvt's template:

viewtopic.php?f=30&t=25734

Mine is not as elegant...
template-back.png
That's not really burn on the cut marks. It's residual ABS from cutting tweeters. This was the last use of that saw blade ;-) I glued the pieces together. Since I am using it with a small router table, I also secured the pieces with some scraps of 1/2" plywood that were glued and fastened with brads.

I am pretty happy with the result:
baffles.png
I am doing such a slow build that I may continue doing some cutting before opening the PL. I have a template for routing the horn braces. I may to that next...or cut some panels to size.
One man's magic is another man's engineering. --Heinlein

1 x DR250
1 x T39
1 x Omni 10

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fender3x
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Re: 2x Jack 12 Lite build

#12 Post by fender3x »

...and already a small (I hope) issue...

When I put the rings on the baffle I noticed that the ring covered part of the 1/2" holes.
alighnment1.png
alighnment2.png
Going back to the plans, the holes are in the right place. So I am guessing the ring is the culprit. In the plans, 4 of the straight edges are 5" long, making the other 4 about 5.66" long. Mine are symetric, so they are all about 5.33 in length. I am guessing this is what made the difference?

I cut mine on a chop saw with the blade at 45 degrees. I measured to get the cut line to be 1" from the hole in the narrowest spot on all 8 sides. This produced a symmetrical octagon with the narrow points all exactly the same distance from the circle. I thought I was very clever for doing this...until the holes did not line up.

I can think of three simple ways of fixing this problem. Option #1 is to plug the holes, and re-drill slightly off where they are now. The trick would be to make sure that the new hold does not interfere with the top of the duct sheath braces or the horn sides.

Option #2 is to remove a little material from the ring so that hole in obstructed. This would be pretty easy to do with the table router, and there should still be 1" or more of ring at every point of the circle, so plenty of ring to mount the speaker on.

Option #3 is the simplest, but more radical. I could plug the holes in the baffle and drill a 1/2" hole in the lateral horn sheaths. In other words, to vent the sheath cavity from the side rather than from the baffle.

I am leaning to option #2, but suggestions are, of course, most welcome!
One man's magic is another man's engineering. --Heinlein

1 x DR250
1 x T39
1 x Omni 10

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fender3x
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Re: 2x Jack 12 Lite build

#13 Post by fender3x »

... I am not sure if this would cause any problems, but this would also solve the problem, since it pretty much completely frees up the holes without doing much other than turning the ring.
ring_turned1.png
You can see the clearance a bit better looking at an angle.
ring_turned2.png
Does the orientation of the points make any difference? Or the fact that I'd need to trim 1/4" from the top and bottom points for the duct extensions since I am using a 2012 driver?
One man's magic is another man's engineering. --Heinlein

1 x DR250
1 x T39
1 x Omni 10

9830Lark
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Re: 2x Jack 12 Lite build

#14 Post by 9830Lark »

This is the only picture I have of my J10 Lite spacer. I followed the plans exactly (to the best of my ability) and I didn't have the problem that you're seeing.
spacer installedsm.jpg
I looked in Lightburn (I laser cut most of the parts). The spacer is 11" across, the baffle is 11" across, and the vertical spacing from inside-edge-to-inside-edge of the circles is 10 inches. Now this is a 10" Jack, not the 12".

I could be wrong, but are your holes closer toward the center?
baffle offset (1).jpg

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fender3x
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Re: 2x Jack 12 Lite build

#15 Post by fender3x »

9830Lark wrote: Sun Oct 30, 2022 4:13 pm I could be wrong, but are your holes closer toward the center?
You may be right but the dimensions are a little different for the Jack 12L. The plans put the holes 3 5/8" from the lateral edge and 2.5" from the top/bottom. The holes are pretty darn close to that. The spacer ring is 13" across and the baffle is 14" across.

The holes could certainly go a little closer to the edges or a little up/down for that matter. As far as I know the reason for the holes is to allow air to move in and out of the chamber between the upper/lower horn sheaths and the ducts. If that's right moving the holes a little should not be a problem as long as the chamber stays otherwise airtight. But I am no engineer, so I wanted to at least pose the question ;-)

If I have learned anything here it's that what seem intuitively right to me is often wrong.
One man's magic is another man's engineering. --Heinlein

1 x DR250
1 x T39
1 x Omni 10

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