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Help, refoaming JBL L112 woofers (128H)

code46

code46

Active Member
Removing the old foam from under the rim of the cone. Is it safe to use 70% or 91% isopropyl alcohol to wet the old foam and then scrape it off carefully? I've read somewhere of using goof off also. Or better not to use any solvents and mechanically scrape away? I've also read someone using 1200-grit sandpaper, is that a bad idea?

The gasket glued to the basket, is it safe to wet with water or 91% alcohol to help remove the four pieces?

How do you use the 30Hz tone? Does the woofer need to be connected to the speaker as in normal use? Playing the tone through an amp connected to the speaker?? Or somehow only through the woofer?
 
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I bought a pair of "re-foamed" JBL 128H woofers from someone for dirt cheap. He was parting out a pair of 4412A's and figured he could get more for the woofers if he re-foamed them. They sat on craigslist for over a month until I made a low-ball offer.

It was his first time re-foaming and they looked pretty bad.

I plan on re-doing them. Hopefully, he didn't hack up the cones too much. Sad thing is, had he left them alone, he could have sold them faster and probably for more.

As they are now, it will take more work to undo the bad job he did than it otherwise would have.
 
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code46 said:
Removing the old foam from under the rim of the cone. Is it safe to use 70% or 91% isopropyl alcohol to wet the old foam and then scrape it off carefully? I've read somewhere of using goof off also.
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It's fine to use rubbing alcohol. 91% would be preferable since it dries more quickly. Try not to use more than necessary, mainly because it can potentially leave a noticeable stain on the front of the cone after it dries if it soaks in too much.

code46 said:
How do you use the 30Hz tone? Does the woofer need to be connected to the speaker as in normal use? Playing the tone through an amp connected to the speaker?? Or somehow only through the woofer?
Click to expand...

You would have the amp connected directly to the positive and negative input terminals on the woofer, with the woofer completely removed from the cabinet and laying on it's back on a flat surface.

I usually glue the foam to the cone (rear) first. Then after that dries, you can glue the foam to the frame, centering the voice coil mainly by feel. Use the test-tone as often as necessary to verify that there is no voice-coil rubbing while the glue is still wet enough to make adjustments.
 
I had some 99% isopropyl alcohol and with a dropper I placed the ipa around the edges of the gasket, and the four piece gasket pretty much lifted right off the basket.

Does every bit of the old surround need to be removed from the underside of the cone? Or is it okay if a very thin layer is left? This seems to be the most painful part.

Thsnk you, now I know how to use the 30Hz tone method.

Found this old thread which was informative and the OrangeCounty Instructions thankfully via The Internet Archive.

solvents for removing old foam

got cocky after re-foaming some old Cerwin-Vegas with kit from Simply Speakers. i had cleaned the cones of foam/glue residue with rubbing alcohol as per generally mentioned guidelines without any obvious problems. foam/glue off, alcohol evaporated, cone color and sheen uniform. so... tried...
audiokarma.org
 
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As long as the remaining glue layer on the cone is clean and smooth (no significant bumps, holes, ridges or gaps), a thin layer of original glue won't be a problem. I frequently leave "well behaved" thin glue layers, as an alternative to possibly damaging a vintage cone, aggressively trying to remove that last bit of glue. Usually winds up taking paper off with it, in many cases.

Regards,
Gordon.
 
I've refoamed many woofers and the L112s were probably the most difficult due to the foam attaching to the back of the cone. Still not too hard a job though. just more aggravating.
 
The majority of re-surrounding I've done has been JBLs with rear-mounted surrounds. It really doesn't bother me anymore. I prefer to use the scraping method and only use solvents or alcohol for cleaning the basket underneath the surround and not the cone itself. My tool-of-preference is the curved X-acto blade as seen in the photo below. A plastic turntable (lazy susan) has made life much easier, too. Also, getting the correct surrounds from Rick Cobb over several decades now assures the job is well-done.

I've recently completed six 12-inch JBL woofers, four 14-inch JBL woofers, and four 10-inch JBL woofers all with surrounds on the backside, including everything in the photo at the bottom here. The most difficult were the 5-inch drivers in the JBL Pro-III-Plus satellites which just gave very little room to work—and that was after prying their glued cabinets apart to remove the woofers!

1735572256989.jpeg

JBL Basement updated.jpg
 
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code46 said:
Just wanted to say the 30Hz method worked quite well. I would be confident enough to do any future refoams. This was my first time. The most tedious part is removing the old foam.
Click to expand...
congratulations. Can you share some photos with us?
 
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