diaphone

The diaphone is a type of fog signal that produces a loud sound. It is similar to a siren but emits a two-toned blast. The diaphone works by using a slotted piston that reciprocates within a cylinder with matching ports, causing a vibration that creates the sound. These signals were developed around the beginning of the 20th century and could be heard up to eight nautical miles away under favorable conditions. The diaphone required a significant amount of compressed air to operate, necessitating a powerful compressing plant and air-storage tanks. A related device, the diaphragm horn, produces a loud signal through the vibration of a disk diaphragm.123