Air acoustics (1927-1940; 1970+)
From the first world war until the thirties of the last century, air acoustics played an important role in air defence. The location of armoured aircraft such as aeroplanes and airships from the ground could not be carried out at night or with overcast. Because radar had yet to be invented, the vision had to be supplemented with hearing using the sound of the engines.
From 1927 to 1940, Ir. J.L. van Soest and his co-workers on the Plain of Waalsdorp in The Netherlands carried out research for this type of aircraft search because existing factory equipment did not meet the expectations of the Royal Netherlands Army. The research in this area has been recorded by Van Soest in an extensive archive and in a collection of many components and remains of equipment that has been preserved.
Inquiries by members of the museum team with former employees who partially witnessed the studies did not provide enough information to describe the investigations. In 1993, the museum team started to study the archives of Van Soest. Reporting by Van Soest is very extensive, even daily activities are in small reports recorded, the so-called Measurement building reports. Components retained by Van Soest, the purpose of which was no longer known, have therefore gained significance again.
There is a lot to be found in the Van Soest archives at the museum, but not everything. The listening device developed to his model has undergone further development by the Dutch industry, with Van Soest playing an important role as an advisor. There is also little in the archive about the experiences of the listening devices in practice. Further research by the museum team has shed some light to history. The following historical developments are supplemented with experiences by military personnel and references to foreign developments:
- Early listening equipment (1915-1930)
- First assignment for the Measurement Building (1928)
- Theoretical and practical research (1928 – 1936)
- Listening device “Van Soest” and the listening cage (1929 – )
- Acoustic correction (1928)
- Transport of angle values to viewer and searchlights (1928 – )
- Small-size, personal listening devices (1930-1935)
- Three-axle listening devices models Van Soest and “Colonies” (1932-1940)
- Listening device Waalsdorp (1937-1940)
- Testimonials: use of listening devices and searchlights (1939-1940)
After WW II, new air acoustics research occurred at TNO:
- Speech Transmission Index (STI) (1970 – 2005+)
- Acoustic sniper localisation (1996 – 1998)