WW2 AIR RAID&FIRE SIREN in ACTION - special WW2 siren double

This is a sound-experiment how sound two different air raid sirens running at same time: Both kinds are heavy electro-mechanical sirens constructed in middle of the 30ies. Each motor of one siren has the power of 4000 W. One siren is a high-tone unit (called "Elektror L1" as 9 port version) with a frequency of approx. 420 Hz. The other one, a low-tone unit (called "Elektror F2" as 3 port version) has a deep&scary frequency of approx. 145 Hz. They were in use especially for fires (low-tone) or air raids (high-tone) in times of WWII. So the population could make easier a difference between fire or air raids. I also have other videos of both siren-units which are seperate in action, too. Look for them. :-)