[Arran]

I think that you may be thinking of the fish paper that they used as an insulator, I don't know exactly what it is made from but it isn't asbestos. Whenever I have seen asbestos used in a speaker it's wrapped around the field coil, most often on speakers from the late 30s and into the 1940s but not on something like a Philco 20 speaker. I haven't seen any asbestos insulated wire in an old radio at all, I think that they reserved that sort of thing for appliances like clothes irons and space heaters that draw a lot of current.
Regards
Arran