The Museum Waalsdorp near Den Haag
reflects the history of TNO Defense, Security and Safety at location Waalsdorp (and its predecessors) since 1927.
At the Waalsdorp site, Dutch scientist JL van Soest investigated the use of listening equipment for aircraft observation by the army, developing his own equipment.
The Van Soest apparatus was a great success and has led to industrial production for the Army.
The museum’s website has an interesting short history of Dutch sound location.
From the first world war until the 30′s air acoustics played an important role in the air defence. Air vehicles carrying a weapon could not be located from the ground e.g. at night time or under cloudy conditions. As radar was still to be discovered, vision had to be supplemented by hearing using the sound of the engines.