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View Full Version : JBL 12'' Needs Repair



vifa32144
03-08-2005, 04:02 AM
My JBL 12'' woofers used in the 4311 or 4312 Studio Monitors needs some kind of repair and I'm hoping I will not need to recone them.
It seems the surround, spider, and cones are pushed down towards the magnet which unbalances the alignment to the point of effecting the sound. Is there any work I can try without having to recone them?

Robh3606
03-08-2005, 04:33 AM
Gravity can be your friend. Try turning them upside down for a couple of days to see if they will start to come back the other way. If they were stored to long that way they may not come back.

Rob:)

GordonW
03-08-2005, 09:51 PM
If gravity alone won't do it, here's a last-ditch effort. Cut out the dustcaps, and shim the voice coils, so that the coil is perfectly straight in the gap. Pull the cone assembly FORWARD so that the driver cone/voice coil is JUST FORWARD (cone just to the OUTSIDE of its "normal" rest position, away from the magnet), like 1mm forward. Take a hair dryer, and HEAT the spider and the backside of the surround (away from the sticky stuff). Let the spider and surround cool to room temp, and try removing the shim. Should "re-set" the spider and surround to a better rest position. If it's not enough, try the procedure again, but pull outwards before heating, about another 1mm (total of 2mm outward, away from normal rest position). Once it's good, get another 3.2" paper dustcap (available from most any reconing center), and glue it back in.

I've actually managed to do this WITHOUT cutting the dustcap and shimming the voice coil, but you're on your own here, as far as keeping things aligned so that you don't warp the spider and such. If you don't shim and the heat causes your voice coil to rub afterwards due to spider warp, don't say I didn't warn you...

Worst case, it is possible to remove the cone assembly from the driver, and replace BOTH the spider AND the fabric surround, reinstalling the original cone/voice coil assembly into the driver. I've done this before for a couple people... PM me if you'd like me to do that for you. Not terribly expensive...

Regards,
Gordon.

transducergeek
03-10-2005, 07:21 PM
Hello, I just recently "invented" a rubber band method of "training" the cone to stay farther out like it should be. I had gotten an EV woofer that I think was stored for many years on it's "back" and slumped the cone in the suspention to the rear. I took a series of interlinked rubber bands and made a "ring collar" around the cone above the tinsel or lead in wires, and had two more rubber bands pulling up on the "ring collar" at 180 degrees apart. These two bands were attatched with tape just under the mounting flange on the "arms" of the cast basket. This pulled just enough to line up the cone to the "normal" position. And allowed a good sounding "burn in" test tone to run.. Thanks, hope this might help.. Rolf Erickson.

hector.murray
03-10-2005, 08:33 PM
Worst case, it is possible to remove the cone assembly from the driver, and replace BOTH the spider AND the fabric surround, reinstalling the original cone/voice coil assembly into the driver.

Hey, from where I stand, it would be worth a shot , since this is where he is at anyway, so nothing to lose.
I still haven't had the spider on my LE10H-1 done yet, and this may help me out too, as I'm suffering from a weak spider on that unit.