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Old 02-18-2012, 03:19 PM
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Default Project Differential-Drive Recone

So here is what I had, a practically immaculate JBL W12GTi subwoofer that I got from a member here for $150 shipped:





Problem: there was some metallic (ferrous) debris that had made its way into the magnetic structure, as I could hear a slight buzzing/rubbing sound at low-volumes, and ONLY when the speaker was held horizontally and ONLY in a particular orientation (probably because the tiny amount of voice coil rocking that is inevitable in any coil-type loudspeaker). This is probably why the seller didn't notice it; I'm guessing it was tested 'standing up', where the noise was not noticeable. Anyways, that is neither here nor there; I bought a used subwoofer at a steal of a price, so I was going to deal with it.

I cut open the dustcap, and played some 20Hz tones at low volume, and then this little sucker jumped up from the edge of the pole piece:






How it made it's way in there, God only knows, lol. Luckily it didn't scratch the former on the inside. But that's not all; there was still something else where in there, and I had a feeling it was going to be in the lower gap of the DDD magnetic structure. So now the question was, if I take it apart to clean it, how will I get the parts to put it back together?

Normally this is not a problem, PSI sells adequate cones, and has a variety of spiders. The issue was that this speaker uses a not-so-common 8.5" spider. So PSI said he could whip up a spider from one of the larger ones and modify it to bring it down to 8.5" on the OD. I agreed, and ordered a few other things while I was at it (CA glue, tinsel, etc).




Here is the original spider still attached to the cone/coil assembly:




It was quite soft, so I had PSI customize my spider using a medium stiffness one; I purposely wanted to bring the Fs up to bring the sensitivity up a tiny but, since I don't tune all that low with the music I listen to (rock/metal). Any missing low-end can always be tailored with the appropriate enclosure type/alignment.

Here is the original assembly, minus the spider:




As you can see, it has those square tabs where the tinsel lead is soldered onto, so I didn't order any sewn-in leads because I wasn't sure if it would have been compatible with this type of coil setup.

I decided to keep the cone and just replace the surround, as this cone is extremely extremely stiff. Here is the assembly with the CA glue ground off the former:




Soldering the leads (oem size: about 0.060" diameter) was a pain because of those square tabs. I had to use masking tape to hold it and conform to the curvature of the former while I slathered on solder:




Here, with the camera at about 10 elevated from the horizontal and using the spider to set the coil "height" in the gap, you can see about a mm or two above the top plate; this is done on purpose as the whole thing will sink just a tad after the spider settles/breaks in.




Here, the spider is partially dry-fitted, with just a few drops of some clear CA to hold it:




In this next pic, the spider is already sitting on a small bead of black CA glue, and the coil is properly centered using LONG plastic shims. Remember, this thing has two longitudinally separated coils--each in it's own gap. Shimming the top coil does not mean the lower coil is properly centered. You have to use long shims that go all the way down into the lower magnetic gap to center the extremely long former.




Here you can see the spider is already CA'd to the former, and to the spider landing as well.




Since the custom spider doesn't have a very wide flat part on the outside, I decided to double up on the edge of the spider with some more CA:




Here you can see the surround I used. It's an old 1-pc thick rubber surround that I got from some old speakers I had forgotten I had. It was almost identical to the original one on this sub. The only difference is that the angle-attach part was a little shorter (ID was a hair larger than the orig.):




It's important to keep the shims in place while the standard rubber adhesive dries on the surround/cone because the surround is what stabilizes the opposite end, the end of the former. It is even more critical here because of the sheer length of the former in the DDD design:




Tinsel leads soldered in place:




Original dustcap glued back, almost imperceptible difference from when it was unmolested:





...and there you have it. The first documented recone (that I know of anyways) of a JBL mobile audio DDD subwoofer. We don't have the luxury that the Pro-audio sector has with their readily available recone kits, so we do what we have to do. If PSI would whip up some mean coils, and spider setups, I'm sure he could corner the market for reconing these subs. Special thanks to PSI for great customer service on this unique project!


Now I'm thinking that maybe I should do this to my two other W10GTi's. The stock spiders are nice, but just too soft for my tastes. I really don't need Fs to be in the 20s for any of my subs......I'd rather have a bit more sensitivity at the expense of sub-30Hz bass.....Hmmmmm

Last edited by guitar maestro; 02-18-2012 at 03:24 PM.
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Old 02-18-2012, 05:25 PM
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Good Job!...
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Old 02-18-2012, 06:45 PM
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Nice, very nice!
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