How can I mount a speaker on the ceiling?
Shelf is dead easy. Your basic shelf with a lip on the front edge so the speaker does not slide off, as beautiful as you like or as ugly as you don't is really up to you. Perhaps some felt to protect the speaker.

4 threaded rods or chains, 8 hooks (if using chains) 16 nuts and 8 washers if using threaded rod. Best option with threaded rod is to place a board in the attic above the framing and run the rods through the ceiling and through it (now you'll tell me you don't have an attic...) but lag screws with a machine screw threaded part are available, and can be screwed into the framing and have a barrel nut added to join to threaded rod.

The angle is achieved by making the back chains or rods shorter than the front ones. If you are willing to screw into the speaker, put 3-4 hooks on it and hang it with chains directly. Hooks for chains should go into framing.