What is Herons Trumpet?For the use in temples, Herons Trumpet Signal created a sound when a temple door was opened. The sound of a trumpet was triggered by the opening of the temple doors. Heron proposes following construction in his 'Pneumatic': A rope is mounted on the door of the temple, which pulls a lever. This lever pushes a hemisphere into a water jar. The water presses air into the hemisphere. This air will now float through a trumpet, which is mounted on the hemisphere. A tone is created by pressure. If the door is closed, the lever falls back to its first position. The hemisphere lifts and air will float into it.
The animation below shows what the process would look like in action.