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Acetone frees up surround...until it dries

JRhoBurton

JRhoBurton

All roads lead to music
The 10" woofers in recently acquired Optimus 4's are very stiff. The finger-thumb test, with moderate force, moved them perhaps a mm. Fs measures 95 hz. I took one outside to avoid house fumes and applied acetone to outside and inside surround surfaces, using a 1" soft bristle paint brush. After that, it showed a huge improvement, probably a half inch peak to peak. Once the acetone evaporated, it was back to stiff. I tried again, scrubbing moderately with a new toothbrush, same result. There did not appear to be any doping material etc coming out.

Am I doing this wrong? At least the spiders don't seem to have a problem.

I removed the "hair net" before I started.

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My (limited) experience is that you'll have to apply a butyl rubber/solvent solution after softening the old sealant with acetone. The product I used on a few of these type of speaker surrounds (Fisher Presidents, Sansui XP2500) was "AR sealant" bought off the auction site.
 
mikehd said:
My (limited) experience is that you'll have to apply a butyl rubber/solvent solution after softening the old sealant with acetone. The product I used on a few of these type of speaker surrounds (Fisher Presidents, Sansui XP2500) was "AR sealant" bought off the auction site.
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Thanks. I have seen that stuff before. Will it make the surrounds black? I'd like to avoid that.
 
Good question. The sealant is an amber color, my surrounds were black. Only difference I noticed was they looked shiny afterwards. And they were more flexible.
 
In the past both the clear and black were sold, but I'm not sure what's available now since I've not had to purchase any recently.
 
I finally had a chance to apply some of the nasty Rubber Soft. I did it outdoors for maximum ventilation. It did nothing. The surrounds stayed stiff during and after a good soaking. I let them dry out for a few days.

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I moved on to the last resort, brake fluid. Bingo! Full flexibility has returned, again even after several days.

(Cloudflare sure makes it hard to post pics.)

I searched for a tweeter surround fix, and have something coming from Simply Speakers. I also stumbled upon a video showing a woofer surround fix using different methods but it was too late.

(Edit to insert vid link:
)

The tweeters (Foster 8F3) are built like small full range. The surround mesh is intact but coatings have vanished. You can see or shine a light thru them. Or blow through them with a straw. I will work on these after vacation.


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In retreating my klh 5s, the small mids (which are similar to yours) benefited just as much from treatment as the woofer did.
 
BmWr75 said:
Acetone is a solvent that dissolves organic compounds. But, if what is dissolved is not wiped away, the dissolved material probably rehardens as the acetone evaporates.
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I tried wiping, but the material seemed unaffected except for becoming briefly elastic.
 
loudnoises said:
In retreating my klh 5s, the small mids (which are similar to yours) benefited just as much from treatment as the woofer did.
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They both need treatment, but the problems are different. The woofer surrounds had "frozen up" and become very stiff, but all the material appears to be present. On the mids, the elastic stuff is pretty much gone, leaving only the mesh. I plan to recoat.
 
JRhoBurton said:
I tried wiping, but the material seemed unaffected except for becoming briefly elastic.
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I had some KLH 6 once and treated the cloth surrounds with rubber cement. Don't know if that was really a good idea or not but didn't notice it hurting anything.
 
I think I am on the right track with the woofers. I tested one pre-treatment with DATS, and just tested both again.

Fs: dropped from 95 hz to 24.
Qts: dropped from 2.3 to 0.61
Vas: increased from 1.45 ft3 to 10.6
Sensitivity about 90 db @ 2.83v

These would work fine in a huge box at low sound levels. Probably won't do that. After I fix the tweeters I will probably end this thread and start a "Optimus 4 refurb" thread, if mods permit.
 
I just picked up a pair of Sansui SP-2000s for $75 (cheap for a reason). The original woofers are long gone, replaced with after market somethings (haven't pulled them yet). I knew this going in, expecting to either keep the woofers or buy original replacements on Ebay. But now that they are mine, I've noticed that the mid-range speaker surrounds are stiff. Now that these speakers have a long history, what is the consensus on softening up the surrounds? Acetone, Lacquer thinner, transmission fluid, or just replace them. I mainly bought them because I love the vintage cabinets.
 
I have no idea how it compares to what you're using, but I've found this product to be amazing for restoring pliability to rubber surrounds:

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Hi, thanks for the reply!
I haven't tried anything yet, just reading posts by others. Have you tried this stuff of speakers?
 
Your Foster 8F3 drivers look alot like the 4 1/2" KLH Mid/Tweets found in Model 5, 14, 24, etc. These benefit greatly from the "RoyC Butyl Sealant" (sometimes referred to as "AR Sealant") treatment after 50 years of drying out and disappearing. RoyC's stuff is relatively thin and remains pliable and sticky whereas Rubber Cement is denser, adding more mass to the skiver and will eventually stiffen up.
 
Well, now we are getting into the details! Thank you. If I were to use the RoyC Butyl Sealant, would I attempted to remove any existing coating first, or just apply it to the surround as is? I was probably about to follow some poor advice and try dot brake fluid before purchasing new replacement mid range speakers. I do want these to sound good, but with after market woofers, I'm not expecting too much.
 
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