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Denge acoustic mirrors

    
A cache by : jlik

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Address : Prior Road 22, Greatstone, United Kingdom     Google maps

From Wikipedia (Creative commons license)

Denge is best known for the early experimental acoustic mirrors which remain there. The acoustic mirrors, known colloquially as 'listening ears', at Denge are located between Greatstone-on-Sea and Lydd airfield, on the banks of a now disused gravel pit. The mirrors were built in the late 1920s and early 1930s as an experimental early warning system for incoming aircraft, developed by Dr William Sansome Tucker.

There are three acoustic mirrors in the complex, each consisting of a single concrete hemispherical reflector.
1. The 200 foot mirror is a near vertical, curved wall, 200 feet (60m) long. It is one of only two similar acoustic mirrors in the world, the other being in Magħtab, Malta.

2. The 30 foot mirror is a circular dish, similar to a deeply curved satellite dish, 9 m (30 ft) across, supported on concrete buttresses. This mirror still retains the metal microphone pole at its centre.

3. The 20 foot mirror is similar to the 30 foot mirror, with a smaller, shallower dish 6 m (20 ft) across.

Acoustic mirrors did work, and could effectively be used to detect slow moving enemy aircraft before they came into sight. They worked by concentrating sound waves towards a central point, where a microphone would have been located. However, their use was limited as aircraft became faster. Operators also found it difficult to distinguish between aircraft and seagoing vessels. In any case, they quickly became obsolete due to the invention of radar in 1932.

Access to them is managed by the Romney Marsh Countryside Project and are currently closed for close up access. However they can be seen quite clearly from the east side of the south lake.


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Published :  10/11/2015 (d/m/y) 11:00

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