Hi all, a year ago I bought some beautiful pioneer pax 20a concentric speakers. These have paper cones with treated surrounds that almost without fail get brittle and crack. I ended up replacing with new foam surrounds. Anyhow I just bought an earlier pax8l, with the surround in uncracked condition, though with very little flex and definitely hardened.
Can anyone suggest a chemical treatment to restore the suppleness? Some acetone? Pva?
Thanks
Enzo
Can anyone suggest a chemical treatment to restore the suppleness? Some acetone? Pva?
Thanks
Enzo
Acetone is too aggressive. Mineral oil (brake fluid) works on some not on others. Search the topic here and on AK
Something like rubber-renue might be worth a try...
xylene (mixture) 60–70%
ethylbenzene 20–30%
methyl salicylate 15–30%
regards
james
xylene (mixture) 60–70%
ethylbenzene 20–30%
methyl salicylate 15–30%
regards
james
Rubber oxidizes and chemically cracks , irreversible reaction, foam in ~10 years, rubber in 20 or so, only replacement will do.
If it's a cloth or paper surround, impregnated in some "plasticizer" , usually called "doping", the water based one which is whitish on application and dries transparent (you see it as shiny black which is actually the paper/cloth colour) and never really dries, should stay sticky forever, then it can harden somewhat.
Any strong solvent will do, but as mentioned can be overly aggressive.
Acetone does work, but evaporates way too fast so you should brush it 3 or 4 times, separated by 5 or 10 minutes, you want the solvent to soak in .
That said, acetone evaporates too fast, is very flammable and destroys lungs and nerve cells, so be careful, work with adequate ventilation.
I use "slower" solvents, Ethyl Acetate which is the main component of nail polish remover (hint hint) or the slowest of them all: Butyl Glycol, which is added to paint to keep it fluid for a longer time, so brush painting is easier.
If you have an Industrial Chemist shop nearby you may ask them, it's almost impossible to have such solvents mailed.
The idea is to soften the doping and move the cone back and forth, by hand or applying some music, so it becomes flexible again.
Mind you, just playing some loud bass heavy music will also mechanically soften it somewhat.
EDIT: just saw the above post:
yes, any product meant to "renew" rubber, often available for printer paper rollers and such, should do.
As of oil based products, avoid them, rubber in any kind and oil are deadly enemies, plus oil will migrate everywhere (cone included) by capillarity.
If it's a cloth or paper surround, impregnated in some "plasticizer" , usually called "doping", the water based one which is whitish on application and dries transparent (you see it as shiny black which is actually the paper/cloth colour) and never really dries, should stay sticky forever, then it can harden somewhat.
Any strong solvent will do, but as mentioned can be overly aggressive.
Acetone does work, but evaporates way too fast so you should brush it 3 or 4 times, separated by 5 or 10 minutes, you want the solvent to soak in .
That said, acetone evaporates too fast, is very flammable and destroys lungs and nerve cells, so be careful, work with adequate ventilation.
I use "slower" solvents, Ethyl Acetate which is the main component of nail polish remover (hint hint) or the slowest of them all: Butyl Glycol, which is added to paint to keep it fluid for a longer time, so brush painting is easier.
If you have an Industrial Chemist shop nearby you may ask them, it's almost impossible to have such solvents mailed.
The idea is to soften the doping and move the cone back and forth, by hand or applying some music, so it becomes flexible again.
Mind you, just playing some loud bass heavy music will also mechanically soften it somewhat.
EDIT: just saw the above post:
yes, any product meant to "renew" rubber, often available for printer paper rollers and such, should do.
As of oil based products, avoid them, rubber in any kind and oil are deadly enemies, plus oil will migrate everywhere (cone included) by capillarity.
Last edited:
Cleaning and reconditioning rubber speaker surrounds
I've heard the best way is to clean rubber surrounds gently, dry, then "condition" with a small amount of Gylcerine/Glycerol. I just did my Kef B139 SP1044 units which I just removed from the cabinet for the second time since I bought them new in around 1972. 45 years old and the rubber surrounds still seem supple to me, and the rest of the units fine!. Very dirty though, so we did this :
(These units have racetrack shaped rubber surrounds that are concave looking at the front)
Put 1 drop of Fairy Liquid (detergent/dish soap for hand dishwashing) into about 2 pints / half a liter of warm water. Soaked a new microfibre cloth in it and wrang it out really well. Form the cloth round your index finger so it is a nice fit in the concave surround, and just rub lightly back and forth doing about an inch or two at a time. Then move on to a clean part of the cloth and carry on round the surround. All the time, one person supported the polysyrene cone with finger and thumb at each end. Then we washed the cloth, wrang it out and went round the rubber surround again with the clean damp microfibre cloth. We repeated the operation on the flat driver front face. The amount of 1980's nicotine that came off them was truly scary.
Got a bottle of pure pharmaceutical grade Glycerol (Glycerine) from eBay. Used another new dry MF cloth. Wrapped round finger again, tipped the bottle against it in the normal manner, let it soak into the cloth for a few minutes. Then proceeded similar to the clean up, but with a very small amount of Glycerol and longer lighter strokes, and stopping and wiping it with another clean dry cloth after every few inches. Left it to dry for a couple of hours and it looks great and feels more supple than at the start.
That's where I'm at right now. I'm considering a second application. The inside of the surround and whole speaker looks pristine so I think I will leave it well alone. The rubber would be very difficult to clean on the inside and a higher risk of damaging things. I don't know if there is any practical reason to, but I may put a light amount of silicone oil on the flat driver face. It would at least look good when the grille is next removed (if I'm still here 🙂
Before I refit them I will probably measure fs and maybe some other TS parameters to see how far they've drifted from the datasheet. I'll try to remember to report it back here. I have heard some accounts of B139's getting as high as fs=45Hz when old and dropping to fs=25Hz after reconditioning. I'll know soon...
I've heard the best way is to clean rubber surrounds gently, dry, then "condition" with a small amount of Gylcerine/Glycerol. I just did my Kef B139 SP1044 units which I just removed from the cabinet for the second time since I bought them new in around 1972. 45 years old and the rubber surrounds still seem supple to me, and the rest of the units fine!. Very dirty though, so we did this :
(These units have racetrack shaped rubber surrounds that are concave looking at the front)
Put 1 drop of Fairy Liquid (detergent/dish soap for hand dishwashing) into about 2 pints / half a liter of warm water. Soaked a new microfibre cloth in it and wrang it out really well. Form the cloth round your index finger so it is a nice fit in the concave surround, and just rub lightly back and forth doing about an inch or two at a time. Then move on to a clean part of the cloth and carry on round the surround. All the time, one person supported the polysyrene cone with finger and thumb at each end. Then we washed the cloth, wrang it out and went round the rubber surround again with the clean damp microfibre cloth. We repeated the operation on the flat driver front face. The amount of 1980's nicotine that came off them was truly scary.
Got a bottle of pure pharmaceutical grade Glycerol (Glycerine) from eBay. Used another new dry MF cloth. Wrapped round finger again, tipped the bottle against it in the normal manner, let it soak into the cloth for a few minutes. Then proceeded similar to the clean up, but with a very small amount of Glycerol and longer lighter strokes, and stopping and wiping it with another clean dry cloth after every few inches. Left it to dry for a couple of hours and it looks great and feels more supple than at the start.
That's where I'm at right now. I'm considering a second application. The inside of the surround and whole speaker looks pristine so I think I will leave it well alone. The rubber would be very difficult to clean on the inside and a higher risk of damaging things. I don't know if there is any practical reason to, but I may put a light amount of silicone oil on the flat driver face. It would at least look good when the grille is next removed (if I'm still here 🙂
Before I refit them I will probably measure fs and maybe some other TS parameters to see how far they've drifted from the datasheet. I'll try to remember to report it back here. I have heard some accounts of B139's getting as high as fs=45Hz when old and dropping to fs=25Hz after reconditioning. I'll know soon...
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