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History: Sound Mirrors

The Sound Mirrors on Greatstone Lakes, looking NE
The Sound Mirrors on Greatstone Lakes, looking north east [ack 13.]

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.

There were three designs of mirrors and all three can be seen in Greatstone, located in  the north east side of the Dungeness Nature Reserve. These three concrete " listening ears" 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 third mirror was 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.

The 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 the  microphone would have been located. (note the microphone in the pictures of the 30 foot mirror). 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 1935.

The sound mirrors are now a scheduled ancient monument (Number 462809). Please see National Monuments Record for more information.

How to See the Mirrors

The mirrors are situated  on an island in  Greatstone Lakes  in the nature reserve.  They are  private and only accessible close up  on poen days and guided walks. However they can be seen  quite  clearly  from the east side of the south lake.

To  see  the  mirrors, take one of the roads running west off Leonard Road eg Coleville Crescent,  Hull  Road and walk almost due west across the shingle and cross the style onto the footpath  (what  used  to  be  the  railway  track) (see  the Greatstone Map). From here, walking north will take you past the larger lake where you can see the mirrors.
Alternatively, you can park in the car park in The Parade just past Hull Road, walk westwards down Taylor Road and then follow the signs for The Mirrors. 

To see them close up, however, you need to go on one of the guided walks organised by The Romney Marsh Countryside Project and Dr Richard Scarth during the summer months.

For details of the open days and guided walks, please contact Owen Leyshon, Romney Marsh Countryside Project   01797 367934 or   mail@rmcp.co.uk.




Sound Mirrors at Greatstone Lakes
Sound Mirrors at Greatstone Lakes

200ft Sound Mirror at Greatstone
The 200 foot mirror is a near vertical, curved wall

30ft and 20ft Sound Mirrors at Greatstone
  The 30 and 20 foot mirrors are circular dishes

How Does it Work?

There is a working model of a Sound Mirror by the Hythe Military Canal, just south of Hythe [walk south from Hythe RH&DR station down either side of the canal until you came to the footbridge, where you will see the Sound Mirror model on the west bank. Here you can, with the help of a friend, try it out for yourself. see here

  Video icon  Video of the Sound Mirrors

Aeriel  View  of  the  Sound  Mirrors                    View Larger Map  Get Directions

To learn more about Sound Mirrors please read:
Mirrors by the Sea: Account of the Hythe Sound Mirror System Based on Contemporary Letters and Reports

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