Macrophone
A macro microphone (from the Greek μακρός large , φωνή sound ) is a device on vehicles that can be used to generate a loud warning tone with a fixed frequency . It is used in emergency vehicles , rail vehicles and ships.
functionality
With the macro microphone, an acoustic oscillation ( tone ) is generated that is within a good (lowest hearing threshold around 1 kHz) and wide ( fog horn ) audible range (around 100 Hz to 2 kHz).
It is compressed air passed over an occluding through an opening metal plate, which periodically closes due to the flow increase the opening and will open again after the interruption of the flow and thus generates the sound. The sound is amplified and emitted by a bell of a specific length. The funnel or the pipe length, together with the natural frequency of the metal plate, determine the frequency and adapt the acoustic impedance to the free space. This type of sound generation corresponds to that in the clarinet , the saxophone , the Martin's trumpet or shawm or also the accordion and the harmonica and is particularly rich in overtones.
use
Rail vehicles
In today's rail vehicles, the macro microphone is used to warn people and other road users, for example on platforms or of non-technically secured level crossings , of the approaching train , and also to give a train crew signal or a shunting signal . The microphone replaces the whistle that was used in older rail vehicles. It is comparable to the horn of a motor vehicle , but significantly louder. In addition, two macrophones with different frequencies are usually used, which can be controlled at the same time. This results in a consciously disharmonious and penetrating warning tone, which one hopes will have a special signal effect. Often, however, the two macrophones can also be controlled individually.
According to UIC 644, the A-weighted sound pressure level at a distance of 5 m in the axis of the acoustic signaling device must be between 120 dB and 125 dB . The frequency of the low tone is 370 ± 10 Hz , the frequency of the high tone is 660 ± 15 Hz.
Examples:
Motor vehicles
In emergency vehicles, two macrophones of different frequencies are also used. These are not used at the same time, but alternately. See following tone horn (Martinshorn).
Mobile warning device
Signal horns are operated on compressed air cylinders during blasting and track work.