Although I seem to have good voice projection and people can hear me, I find that longer sentences help focus everyone's attention. I walk to the middle of the room (open space), raise my hand above my head, and say:
Good afternoon, ladies and gentlemen, the time is 2 o'clock. If I can have everyone's attention, please?
By the time I'm done talking, they've stopped, and I only have to pause for a few seconds while everyone turns to look. Then I can hand it over to the director, conductor, call places for the scene, etc.
Also, for those who couldn't hear what I was actually saying, they get the idea with me in the middle of the room and my hand up. It's a good visual clue.