A friend of mine had a mishap (cab fell off dolly) and discovered a crack and a small piece came out of his jbl 2380 horn near the flange where the driver mounts.
Is there a way to fix this somewhat till his replacement arrives? He's got the piece and it fits tightly. What would you suggest to "glue" it back in place for the time being?
Epoxy or JB Weld may result in a mechanical bond only, which is unreliable. What you're looking for is a chemical bond. When gluing plastic, make sure to use the proper solvent-based glue for the type of plastic being glued. When done properly, the pieces will be essentially "melted" together, and be roughly as strong as the original part.
I don't know what the JBL horns are made of (ABS is likely), but you can probably find out with a little research. It's easy to test a particular glue by putting a small amount on a hidden part, and see if it softens the plastic. If it does, then you're on your way. By the way, Methyl Ethyl Ketone makes a fine glue for ABS plastic. Or just buy the stuff for ABS pipe in the plumbing department of your local hardware store.
Good luck!