porous and hardened Seas rubber surrounds

I posted this in the proper surround/cone thread, but that thread has taken off to discuss once again the merits of various cone materials.

Contrary to popular opinion, even quality rubber surrounds can be ruined in relatively short time:


I have just bought some Seas 17 cm drivers on ebay (the variety with the semi-clear PP membrane and soft dust cap) which have a rubber surround (SR 138/1, most likely made by Kurt Müller). The seller said the drivers were about 11 years old and the surrounds were a bit porous.

Well, they top side was riddled with small cracks and had turned brownish locally. The down side looked ok but was also harder than usual. The stiffness of the whole surround (when pressing down the cone) was about 3x more than usual.

I have asked the seller whether these were exposed to direct sunlight, but he hasn't answered yet. The soft polymer dustcap and the clear cone did not show the least bit of yellowing/aging/hardening.
 
Hi Capslock,

Just so happens that most of my better speaker systems have drivers with rubber surrounds. 2 different 10" drivers in commercial systems seem to have become very stiff, one system is over 15 years old the other over 10, both bought used. I measured Fs of one driver and it was close to 50 Hz, 49 IIRC which indicates that the suspension is more than 3 times stiffer than it should be.

I'm told by a rubber/polymer expert that rubber will absorb oil, much like a sponge but I'm not sure what the best material is to use. Lionel posts above that liquid silicone is good to use, any suggestions on a specific product to look for?

It's intersting that both drivers seem to use the same surround and I was able to purchase a replacement surround that is the same part number. Have not yet tried replacing the old one.

There is a liquid rubber rejuvinator used for rubber parts in the printing industry, but there are some powerful chemicals in the mixture - don't know if this might help or make things worse.

Anyone have experience with this?

Pete B.
 
I think Wd 40 has petrolium distillates in it for the lubricant in addition to or instead of silicones. That would be bad for rubber I'd think.

Then again, a few years a go silicone was the pancea for all protection problems. Now it seems to be the devil himself. Every few weeks I hear of something that you should NOT put it on.
 
Variac said:
I think Wd 40 has petrolium distillates in it for the lubricant in addition to or instead of silicones. That would be bad for rubber I'd think.

I think it might help to resaturate the rubber of the solvents that have gassed off over the years. The addition of silicone it what makes it work after the distilates have evaporated.

Every few weeks I hear of something that you should NOT put it on. [/B]


Ya, like anything you might want to paint in the next twenty years :D
 
A big no no is to put it on inflatable rafts. The are made of sheets of sythetic rubber or plasticy stuff like haphalon with fabric reinforcement, glued together in the handy raft shape. Turns out the silicone slowly works its way into the seams and unglues them- ruining the raft.

I dunno , glued seams hmmmm.... I really dunno so keep that in mind.
 
Thanks for all the suggestions. I read that silicone oil is also used in the scuba world to preserve the rubber products that are used. Here's silicone oil suggested for the seals on underwater cameras:
http://www.bhphotovideo.com/bnh/con...446&is=REG&addedTroughType=categoryNavigation

A product that could be found at the hardware store would be better.

I believe that the formula for WD-40 is a trade secret, or has it been analyzed?

Pete B.
 
2 prodcuts to consider are: Intraclean S711. Used to clean tape paths and quite effective on rubber pinch rollers. I use it to rejuvenate hardened wiper blades (when I am feeling especially cheap!). Also, teac used to make a pinch roller rejuvenator, so you might try someplace that still repairs VCRs.