From Longman Dictionary of Contemporary Englishstage whisperˌstage ˈwhisper noun [countable] 1 APTa loud whisper used by an actor in a play, which the other actors on the stage seem not to hear2 SAYa loud whisper that is intended to be heard by everyone
Examples from the Corpus
stage whisper• He dropped to a conspiratorial stage whisper with Margaret: Where is she anyway? 