Denge mirrors at Exploring Kent’s Past

“Acoustic Sound Mirrors at Greatstone-on-Sea, Lydd” at Kent County Council’s Exploring Kent’s Past.

The remains of three large concrete structures, formerly an anti-aircraft Acoustic Detection installation. Microphones were attached to the three reinforced concrete structures in order to pick up the sound of approaching enemy aircraft. The smallest ‘sound mirror’ was found to be fairly ineffective so it was superseded by a larger dish, 12 m in diameter. This in turn was replaced by a 70m long ‘sound wall’. The structures were built by the RAF between 1930-4. They were rendered obsolete by the introduction of radar in 1935, and by advances in aerial technology.
Source: Exploring Kent’s Past

WWII radar in Malta

Radar stations during wartime Malta, by Charles Debono, curator of the National War Museum in Valletta.

… as radar technology was in its infancy, in Malta, the British authorities decided to build an early-warning system, the Parabolic Acoustic Mirror known as Il-Widna (ear), constructed at Ta’ San Pietru, Maghtab.

Il-Widna became outdated when the British government decided to install the first RDF [Radio Directing Finding] in Malta. It is important to say that this was to be the first RDF installed outside the UK.

More at the Times of Malta website

Dutch acoustic research in the 1920s and 30s

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.

Kilnsea sound mirror on the BBC

A huge concrete dish, pointing at the North Sea from an East Yorkshire field, was once a vital part of Britain’s defence system says a BBC video about the Kilnsea acoustic mirror.

The interview with local historian Jan Crowther is part of the BBC Look North programme’s Abandoned series with Matt Richards.

Matt was recently in touch seeking information for a proposed broadcast about Drewton tunnel on the old Hull & Barnsley Railway.