Sound Mirrors:Lydd: Romney Marsh: Kent: England UK 🇬🇧

The Sound Mirrors, also known as Acoustic Mirrors, Concrete Dishes, or Listening Ears, are large concrete structures designed as an early warning system for Britain to detect enemy aircraft.

These worked by focusing the sound from the plane’s engine so it could be heard before it was visible.
There were three designs of mirrors, 20ft, 30ft, and 200ft, and all three can be seen in Greatstone, located at Greatstone Lakes.

The three concrete " listening ears" at Greatstone range in size from 20 to 200 feet in size. Built between 1928-30, the sound mirrors were part of Britain's national defence strategy. They were designed to pick up the sound of approaching enemy aircraft. Sound waves were caught in the belly of the mirror and relayed back through microphones and a stethoscope to an operator who raised the alarm. Anti-aircraft defences were then deployed. The mirrors effectively gave Britain a fifteen-minute warning of an impending attack.

The 20 feet(diameter) mirror was the first to be built in 1928. It was precast as one huge slab of curved concrete. Lessons were quickly learnt and a 30 feet(diameter) mirror, set at a different angle and providing greater accuracy, was built in early 1930 alongside the 20 foot mirror.

The 30ft mirror gave no advantage as to range but it was able to track an aircraft a lot more accurately than the 2oft mirro, which was only able to give estiamtions.

The third mirror is 200 feet in length and 26 feet high, and was built in 1930 alongside the other two smaller sound mirrors. Microphones were attached to the curved surfaces and in favourable conditions could pick up the sounds of aircraft up to 24 miles away.

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