How to remove hot glue from 136A cone?

[Johnny_Law]

Some genius re-foamed these 136As with crappy mis-sized foam on the outer edge using ... hot glue.

I have proper surrounds from the one and only Rick Cobb waiting to go on.

How do I get the hot glue off the outer front edge of the 136A cone?

• An iron to melt the glue and a paper towel to absorb it?
• Chemicals like acetone?
• Very careful surgery with a blade?
• Something else?

Thanks in advance for any tips ...

 

[mech986]

Hey Johnny, please show us some pics of the mess you may have. I have four 136 or 2231 drivers with similar issue of surrounds glued to the front of the cones. These were done in the late 90’s or early 2000’s and had thick wide roll surrounds glued on, likely because they were generic 15” driver surrounds and the only ones available before widespread availability of the proper fit narrow roll surrounds for these JBL driver cones. The thicker surrounds is noticeably stiffer and I’m sure the low bass extension is limited while the upper mid bass is probably enhanced. Certainly it isn’t anywhere near OEM spec. Not good for the L300 and 4333B cabinets they are in currently.

My friend Bao at Speaker Repair Pros (successor to the late Orange County Speaker Repair) says it’s almost impossible to get properly glued surrounds off the front of the cone without some damage to the cone or top circumferential paper layer and that may leave a visibly poor cosmetic result when you glue the new surround onto the back of the cone edge. He also stresses that using volatile solvents can weaken the paper pulp cone fibers and binders permanently.

My notion is carefully consider how to get under the edge of the surround, lift it up to break the glue bond, and then slowly work your way around the surround - cone interface pulling up the glue and surround, hoping for minimal injury or lifting of chunks of cone. Once done, one may be able to hide any damage with mild sanding or flattening of the damaged areas (or light fill in with very dilute PVA white glue which dries clear?). Then if needed, a light dusting of a very closely matched gray spray paint which should not appreciably add mass. You may need to mask off the center dome and glue line.

Now with your specific case, you may get lucky because IME hot glue doesn’t exactly stick very well to non-porous surfaces and you just might be able to lift and break as above. Maybe even use some freezing spray to get it to shrink and break off?

 

[Johnny_Law]

So I made some progress peeling it off manually by hand, it's coming off in VERY small chunks, but the cone appears to be preserved very well with no discoloration or anything.

Maybe I'll just put on some music and chip away at it.

I thought about freezing it but I'm not sure that's a good idea and I'm nervous about getting the Alnico too cold.

Here's one I haven't touched yet, and the other I'm making progress on ...

 

[4-2-7]

That does not look like hot glue to me, hot glue does not flow out like that.

Is it pretty hard?
Or rubbery?

 

[Johnny_Law]

That does not look like hot glue to me, hot glue does not flow out like that.

Is it pretty hard?
Or rubbery?

It's rubbery. What else could it be? Silicon? I've only seen hot glue flow like that when a ton is applied or when something pushes on it. The close-ups I took, that glue was all under the surround which I cut away carefully with a blade, leaving just the thin layer of glue still there. So it seems like the ring of hot glue (or whatever it is) was applied, and the new surrounds were pressed onto it from the top.

What isn't pictured is the annular piece of original surround behind the cone was still there, and the hot glue caught that too. So the edge of the cone was sandwiched between the original surround and new surround, with the adhesive in the middle.

Maybe if it's something else there's an easier way to take it off without affecting the cone

 

[4-2-7]

It's rubbery. What else could it be? Silicon? I've only seen hot glue flow like that when a ton is applied or when something pushes on it. The close-ups I took, that glue was all under the surround which I cut away carefully with a blade, leaving just the thin layer of glue still there. So it seems like the ring of hot glue (or whatever it is) was applied, and the new surrounds were pressed onto it from the top.

What isn't pictured is the annular piece of original surround behind the cone was still there, and the hot glue caught that too. So the edge of the cone was sandwiched between the original surround and new surround, with the adhesive in the middle.

Maybe if it's something else there's an easier way to take it off without affecting the cone

Do you have a heat gun, thats what I would try first to see if it will soften it. If it does you might be able to gradually peal it up with a X-ACTO knife. If it is a rubbery glue I doubt it has the absorbency factor that saturates into the paper like other glues, it might just lift up.

 

[Johnny_Law]

Do you have a heat gun, thats what I would try first to see if it will soften it. If it does you might be able to gradually peal it up with a X-ACTO knife. If it is a rubbery glue I doubt it has the absorbency factor that saturates into the paper like other glues, it might just lift up.

Yep have a heat gun, will give that a shot!

 

[toddalin]

If it's hot glue, and yes, it can flow out when hot, and heat may just make it worse. I would first very gingerly try to pull back a "glue edge" to see it it can simply be pealed off before I went on to heat.

 

[SaturationPt]

If it's hot glue, and yes, it can flow out when hot, and heat may just make it worse. I would first very gingerly try to pull back a "glue edge" to see it it can simply be pealed off before I went on to heat.

I agree. Be careful with heat, it gets stringy and sticky and could spread.

At first I was thinking hot blade, hot wire, but then see that you're having some success peeling it back. Mech986's suggestion to freeze it is IMO excellent, not sure what the concern is on the Alnico, but chilling the glue locally might make it much easier to remove.

 

[Johnny_Law]

Victory is mine!

What worked best was isopropyl alcohol and vigorous rubbing with my thumb. I needed something with enough traction to peel it off, but nothing that would risk physical damage to the cone. My thumb was the perfect answer - I gripped it between thumb and fingers and rubbed against the edge with my thumb. The isopropyl alcohol both loosened up the adhesion and made it tacky so my thumb got more traction. Bit by bit, it all peeled off. And the best part, the cone is well preserved under the glue! (It's a hair discolored in the pic from the alcohol.)

 

[4-2-7]

Victory is mine!

What worked best was isopropyl alcohol and vigorous rubbing with my thumb. I needed something with enough traction to peel it off, but nothing that would risk physical damage to the cone. My thumb was the perfect answer - I gripped it between thumb and fingers and rubbed against the edge with my thumb. The isopropyl alcohol both loosened up the adhesion and made it tacky so my thumb got more traction. Bit by bit, it all peeled off. And the best part, the cone is well preserved under the glue! (It's a hair discolored in the pic from the alcohol.)

Good job

 

[mech986]

Excellent!!!

 

[toddalin]

Nicely done!

 

[Johnny_Law]

Thanks - after a break because of thumb paralysis, now to tackle the other one ...

 

[Zonker92]

Congrats! Wonderful result.

Seeing that 077 in the background ... are you restoring some L300s?

 

[Johnny_Law]

Seeing that 077 in the background ... are your restoring some L300s?

Sure am. Bringing them back from essentially the same state as the other pair being documented in this forum .... except I paid much, much, much, much, much more for them.

Excited to A/B them against my L200Bs.

 

[Zonker92]

Awesome; have fun and keep posting!

 

[faber12]

 

[mech986]

While you are at it, cover the surround with masking tape and lightly rough file the front exposed frame edge to get back the original bright machined look. Alternatively, you could also fine file, sand and polish the edge for a 4425/5534 studio monitor appearance. Either way, be sure to address the sides of the edges so you don’t catch any sharp burrs that can hurt your fingers, been there, done that.

Also, if the original neoprene front gaskets are in good shape, reuse them for that JBL OEM look. If they need to be replaced, eBay seller doggie.com has them. It’s a nice finishing touch. Alternatively, there are a few foam type gaskets which have a sorta lightly mottled appearance which has the more modern JBL woofer look. Please don’t use any paper or cardboard gaskets commonly seen with redone kits, they make the woofers look generic.

Hope to see both finished woofers soon.

 

[Johnny_Law]

Put them in my L200Bs while I finish sorting out the L300 cabinets.

Observations:

1: These 136A spiders have more sag than my other pair;

2: One of these 136As has weaker output than the other especially in the lowest frequency range (hard to tell unless I play w. balance).

Running test tones on the bench, one didn't seem to displace less than the other (when I'm refoaming two woofers I run inverse signals to each so that the audio wave cancels out and any rubbing / scratching is much easier to detect), so I will need to take some steps to isolate the weakness to the woofer.

I'll start by swapping them left to right to make sure it's not something in the crossover making one side weaker. If I confirm it stays in the speaker, it'll be time to rebuild the N200Bs; if it stays with the driver, I'll need to start diagnosing it, suspecting weak alnico or something wrong with the voice coil; while cognizant of the spider sag, it's even between the woofers. I never noticed un-evenness in my L200Bs before so I'm suspecting it's the woofer, but don't want to pollute my highly scientific process.