Had the same lack of manners at the AmDram theatre group I was with.
While members were on stage rehearsing the rest of the attendees would sit around talking loudly, playing music on phones, creating litter, arsing about and preventing the director, and the actors on stage, from being heard. No amount of telling would get them to keep quiet for more then a few minutes before it was back up to full volume.
If I was directing I would have them all standing outside the hall, regardless of weather, if they couldn't keep quiet.