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JBL 4312 Crack in woofer cone

J

jonpk

New Member
I have the above speaker with a crack in the woofer cone from the dust cover dome to the suspension ring. Is this repairable? If it is how can I do this. I've had the speakers since the early 80's and they've been in storage for the last 20 or so. I have to buy a new receiver. The one I have has a blown left pre amp so the output is very low. It will no doubt be cheaper, and I could probably buy a better receiver as well rather than get this one repaired. Thanks for the help.
 
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Yes; you can glue a piece of coffee filter paper, sized to cover the crack, to the back of the cone using Aleene's Tack Glue. Should be fine. (Attaching it to the front would work too, but look awful.)

I might also be tempted to lightly spray-paint the cone white to hide the crack, and paint the other cone to match. (Empirical testing by other enthusiasts seems to show that the mass of the paint has a negligible effect on the sound of the woofer.
 
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I repaired a 4312 woofer a few years ago with the coffee filter method from the back side and it turned out great.
I could hardly see the crack afterwords and could hear any difference from the other undamaged speaker.
Go for it :thmbsp:
 
I've done it tha same way except with a piece of paper towel.

I like the repainted idea Eric!

Glenn
 
I never had a tear on my L100s but I got them with brown stains. I used acrylic paint from JoAnn. Started with base white and added tiny drops of brown (very tiny, on the end of a toothpick) to match the ivory shade of my cones. Watered down the paint and wiped it on very lightly. Used multiple thin coats and went all the way around to eliminate color differences. They came out PERFECT. Try it on your repair job.
 
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Thanks all for the info. So all I need do is remove the four screws, pull the driver out of the cabinet and then perform the suggested repair. Re assemble when the glue dries. I do have a small bottle of Aleene's Fabric Fusion that I was going to use to re glue the fabric to the speaker cover. Will this work or is there a different formula product? Thanks
 
jonpk said:
Thanks all for the info. So all I need do is remove the four screws, pull the driver out of the cabinet and then perform the suggested repair. Re assemble when the glue dries. I do have a small bottle of Aleene's Fabric Fusion that I was going to use to re glue the fabric to the speaker cover. Will this work or is there a different formula product? Thanks
Click to expand...

Pretty much yes. The woofer is heavy. When I repaired one, I used a wide blade screw driver to get under the woofer basket edge, and a metal putty knife against the baffle edge for protection.

Not sure about that specific Aileens vs. the Tacky glue. I actually used a very thin epoxy for the repair. These cones are pretty rigid.
 
Is the driver rim "sealed" to the front of the cabinet with a sealant compound or does it just rest in the opening? Will I need to reseal the driver once the repair is made? One thing with these speakers, they sat for a long time, 20 or so years and there was a glue type material that looks to have seeped down from the bottom of the woofer (in both cabinets) and collected in a small pool. The material got onto the fabric cover in that area because of it. I tried goo gone, mineral spirits and plain soap and water but that is some resistant stuff. The fabric was glued to the frame that covers the actual drivers. One frame had gotten broken over the years so I made some new frames, painted them black and then re applied the fabric using a staple gun.
 
I don't think the drivers are sealed but it's been a while since I did mine .
Like GD 70 said the drivers are very heavy so be careful when pulling them out of the cabinet not to drop them and cause more damage !

The Aleens fast grab seemed to be a good match for the project and held up well
My driver had a little bit of the dripping black goo but not enough to worry about so no help there
Good luck
 
The woofers aren't sealed in, but getting them loose can be tricky since they adhere to the paint a little bit. It may help to warm them up with a hair dryer. Some people will thump the back of the cabinet to get them to pop out (be careful). I use the tip of a mounting screw or screwdriver in a mounting hole to pry them out.
 
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That glue that seeped from the woofers is the surround dope or goop or whatever you want to call it. Look at enough 4311/4312/L100 photos and you will see you are not alone. One solution is to rotate the woofers periodically. You may want to turn yours 180 degrees when you reinstall them so you can make the remaining goop run the other direction....and fight 20 years of gravity trying to make the woofer sag in one direction.

By now you have probably figured out that those really were worth keeping for 20 years. Next up...how does the veneer look and do you have a bottle of Howard's Feed N Wax?
 
I did the same repair on mine. I watered down the Alene's glue and paint brushed it on the paper while it was laid over the back of the damaged area . I mixed acrylic paint to match the off-white color of the front of the cone. You can not see the repair or hear it and I push these babies at times. The damage on mine was like someone punched the woofer, it was big.
 
I'm a little late to this thread, but I've had great success with the following product:

22072.jpg


This is Permatex Ultra Black. It's a gasket maker. The "Ultra Black" product can be laid on ultra thin to make a permanent bond between the torn driver cone parts. It works on paper and synthetic driver cones. If you do a very neat job, take your time, and lay it on fairly thin front and back, you will make a permanent repair that looks decent, especially if you have a black cone to begin with.

You don't need anything else. No coffee filters, nothing. The gasket maker becomes part of the damaged cone. I have used Q-Tips and small paint brushes to put it on as professionally as possible. I've also repaired torn surrounds with it. Not "rotted" surrounds, but good surrounds that somehow got a tear or hole in them.

BTW, you can get it at most auto parts stores. I know Autozone carries it. Amazon also carries it.
 
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Lots of great info guys. Thanks. I'm going to remove the woofer today to take a peek on the back side. The crack is of a nature where one edge is pushed back behind the other edge and I will need to realign the edges so they are flat and even. As for the cabinets, they are probably 99.5% in great condition. The only areas that may be of some concern are the bottoms as they were not protected when moved around over the past 20 years or so and the grills. I recall buying the speakers shortly after getting married so that would place the purchase right around 1980-81. I used some Old English wood restorer on the cabinets and it seems to have helped the finish as well as hiding the very few surface scratches that were present. I'll try to improve the bottoms as well. I'm in the hunt to find a decent and reasonably priced old Pioneer SX-939. That is what I had in the early 70's with a pair of L100's. They sounded great together and I hope to do the same with these.
 
A little update. I got the woofer out and used a strip of coffee filter for the patch. The glue I used, I happened to have and it is the canopy glue mentioned earlier. I used a little more of the glue on the front of the cone applied with a toothpick into the surface crack. The stuff dries clear. I do have some model paints so I'll try to match color on the come to further disguise the repair. Thanks everyone for the great info and help.
 
One last thing re: my 4312's. My wife and I are former smokers. The woofers have turned an aged slight yellowish cream color. Is there a solution I can use to possibly clean them up a bit? They work fine but the yellow is a little strong. We haven't smoked in years but 20 or so years of exposure does make a difference.

The midrange in one cabinet and both tweeters have a very small minor dent in the dust covers. Is there a way to pull them out?
 
Slight yellowing in those woofers is typical, smokers or not. I'd consider lightly dusting them with matte white spray paint, but I'm anal that way.

Aren't the midrange dust caps concave on those? If they're truly convex, and dented, some people have had success with a vacuum cleaner hose applied carefully to suck out the dents. Maybe damped them first. Or maybe try sticky tape.

The tweeter "domes" may be fixable. You can try getting them slightly damp with a sponge and sucking them out with a vacuum or using a pin to prick a tiny hole and pry them out, then apply a drop of glue to the pinhole.
 
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The midranges and tweeters are convex. I believe on the 4312b' or c's they are concave. JBL changed both the tweeter and midrange units on the later versions. I'll just leave the woofers alone. Your other suggestions sound doable. Thanks again.
 
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