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.
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.