Peter; Depends on the tear. If it's a clean line and on the cone and easy to get to then I use tissue paper and white glue. Had pretty good luck fixing those like that.
If it's on the surround (edge) and due to fatigue, then best recone it.
Speakers suffer from fatigue like any other moving item. You can only bend/flex that paper so many times before it doesn't want to flex anylonger. Same with the spider material that holds the voice coil in the magnet.
FYI, if you recone a speaker with the original materials that the factory used then it's as good as a brand new one. There use to be this myth that a recone was an inferior speaker. Not so!! You are replacing all of the moving componets and reconditioning it to new.