The Makrofon is a compressed air powered diaphragm sound transmitter. It is most commonly installed on board of all types of vessels, as well as on rail vehicles. Makrofons are reliable whistles distinguished by their low air consumption, strong sound intensity and wide range of audibility. Due to the simple and solid design, Makrofons are practically maintenance-free. The diaphragm housings are made of reliable materials, seawater resistant plastic is used for the protective cover only. For vessels the sound frequencies of Makrofons range between 90 Hz and 370 Hz and go up to 660 Hz for rail vehicles and may exceed 1000 Hz for alarm purposes.