I had a large speaker that was a victim of archery practice. I got some black construction paper, wetted it with some flowable silicone, applied some around the hole and patched it, taking away the excess. It made a nice repair.

I remember now. Years ago I repaired a speaker whereas it was the "surround" that I fixed and I used a flexible, never drying-out silicon sealer. That seemed logical to me at the time.
I just found lots of info with a Google search on "Speaker Cone Repair" and "Speaker Parts".

cook#yum

Contact cement works very well. It drys quickly and is very flexible. For tears, I spread a thin layer along the tear. for holes, I use one ply of paper towel and the contact cement. Use the minimum necessary to cover the hole and make sure the paper is saturated in the glue. feather the glue out from the hole with a small brush. I've had excellent results using this method.

I recall in college, where rolling papers seemed to abound (ya know Zig-Zag and the like—ah, those were the days), repairing the tweeter from a beloved set of Harmon Kardon HK40's with several layers of "papers" and rubber cement. I kinda had to use what I had on hand. Worked great. I wish I still had those old HK's...