prevent hardening of speaker surrounds

Armorall--if it works on auto door seals that are exposed to extreme temperatures, pressures, and UV light, it should keep butyl surrounds supple, too. OTOH I've never seen butyl surround degrade. Wouldn't a change in resonance (Fs) be more related to aging/hardening of the voice-coil spider, for which I don't think there's anything you can do....

I feel that one should be VERY careful before applying anything to butyl(or foam) surrounds. The main parameter of a liquid(i.e. a solvent) to consider here is the Kauri Butanol(KB) value. This is a very convenient measure for us audiophiles in this situation, as it is(in layman's terms) a measure of how well a solvent is able to dissolve butyl rubber. While I am not aware of the KB value of Armorall, we should be extremely careful. Damaging the surround, WILL require the poor owner to buy a new driver. And, this type of solvent could also be incredibly damaging to your speaker's finish. All this being true, I am sure there are safe products out there. They should include UV filters, as that is our enemy, along with the drying of the rubber(via evaporation - over the course of time). I would love to run this experiment on a bunch of solvents, but I am no longer working as a chemist(yes, I do miss it). But C++ programming is much more secure/better paying, so here I am. If there are any chemists in our listening audience, I would welcome the opportunity to converse with you on running this type of experiment.

I didn't think Armor All was classified as a solvent. I thought it was classified as a protectant. I have applied it to the rubber surrounds of two of my woofers, with terrific results. Most audiophiles do seem to not like Armor All, and much of that seems based on some bogus "tweak" a few yewars back, where it was tried on CD's (in the first place, that seems idiotic to me, since polycarbonate is not a pourous plastic). Anyway, if I can borrow my brother's digital camera again, I'll photo these woofers and e-mail the photos to you, if you're interested.