In Annex III of the “International regulations for preventing collisions at sea, 1972” (COLREG) technical details of sound appliances have been specified. The relation of the fundamental frequencies and intensity of the sound signals to the length of the vessel have been determined and are given in paragraph 1b and 1c of this regulation.

Inportant for all Zet-Horns
1.according to IMO 1972 Annex III
2.with standard electromotor heating
3.low installation cost: no pipe, similar electr. cable as for air whistles

ZET-Horns, Makrofons and Zetfons comply with the requirements governed by “Preventing collision at sea” . ZET-Horns were the first AC 3-phase driven piston-diaphragm sound signal appliances ever produced. Standard appliances are available for 230volt up to 440 volt, 50/60Hz AC three phases power supplies. Other special designs (Arctic) are available on request.
The ZET-horns essentially consists of a piston inside a cylinder with joining horn. The piston is driven by means of a connecting rod, a crankshaft, and two wear-resistant toothwheels of high grade steel (not plastic!) by an AC 3-phase motor. The piston oscillating at the resonance frequency of the horn produces resonant vibrations of air inside the horn. ZET-Horns produces rich sounding signals with a wide range of audibility; higher amplitudes of the harmonics especially make a penetration of the normal background noise level on board possible.

Recommendation for vessels in north- or south atlantic or pacific: Horns only aluminium with electr.trumpet-heating!