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 in the north east side of the Dungeness Nature Reserve.

How the Sound Mirrors Work

The Sound Mirrors worked by using their curved surface to concentrate sound waves by capturing the noise of incoming enemy aircraft approaching from the European mainland and focus it onto a microphone or a human listener equipped with then state-of-the-art stethoscopes. Once the receivers were adjusted for best reception, the results would be compared with those from one of the other ‘ears’ and used to calculate an aircraft’s height, speed and flight path. They worked best at a range of between eight and 24 miles.

An operator using a stethoscope would be stationed near the sound mirror, and would need specialist training in identifying different sounds. Distinguishing the complexity of sound was so difficult that the operators could only listen for around 40 minutes.