Depends what it's made of. If it's a foam material and a small hole, you can use a liquid nails type of compound. Or another compound as long as it's safe to use with styrafoam (spell?). I fixed a couple JL subs (foam surround) with I think it was liquid nails and they were fine for years. If it's rubber, you'll be fine repairing it with silicone. As for the cone many times I've seen superglue or epoxy used and work fine.