The style of staged documentary sometimes called Interview Theater puts real people’s stories on stage. Taking that approach one step further, Eliza Jane Schneider recreates their voices and mannerisms. For years she traveled the country in an old ambulance, recording conversations with the people she met. She reproduces some of these encounters in her one-woman show, Freedom of Speech. It’s playing this weekend at City Stage in Springfield, Massachusetts, and critic Chris Rohmann has a preview.