The Concrete Acoustic and Sound Mirrors: an early warning system of the past

The Concrete Acoustic and Sound Mirrors ABANDONED SPACES
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.

During World War II on the coast of southern England, a network of large concrete acoustic mirrors was in the process of being built when the project was canceled owing to the development of the Chain Home radar system. Some of these mirrors are still standing today.

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. A forerunner of radar, acoustic mirrors were built on the south and northeast coasts of England between about 1916 and the 1930s.

The Concrete Acoustic and Sound Mirrors
Acoustic Mirror. Photo credit: Paul/Flickr

Dr. William Sansome Tucker developed early warning systems known as ‘acoustic mirrors’ around 1915, and up until 1935, Britain built a series of concrete acoustic mirrors around its coasts. The acoustic mirror was the forerunner of radar, and it was invented to help detect zeppelins and other enemy aircraft by the sound of their engines.

The Concrete Acoustic and Sound Mirrors
Acoustic Mirror. Photo credit: Paul/Flickr

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.

The Concrete Acoustic and Sound Mirrors
Acoustic Mirror. Photo credit: Greg/Flickr

The sound mirrors had a limited effectiveness, and the increasing speed of aircraft in the 1930s meant that they would already be too close to deal with by the time they had been detected. The development of radar put an end to further experimentation with the technique.

Hot-wire microphones designed personally by Dr. William Sansome Tucker that were placed at the focus of each structure made it possible for the listeners to detect the sound of oncoming enemy aircraft and gave a fifteen-minute warning to the English artillery to prepare for the attack. Some of the most sophisticated acoustic mirrors could detect the sounds of oncoming enemy aircraft up to 25 miles away.

As aircraft performance increased, its sound could no longer be heard or located 15 minutes before it reached its target, and that is why acoustic mirrors were no longer useful and were replaced by the newly developed radar technology.

The Concrete Acoustic and Sound Mirrors
The giant Acoustic Mirror. Photo credit: Paul/Flickr
The Concrete Acoustic and Sound Mirrors
Acoustic mirror in Kent, England. Author: Mark Duncan CC BY-SA 2.0
The Concrete Acoustic and Sound Mirrors
Acoustic mirrors at Denge. Author: Paul Russon CC BY-SA 2.0
The Concrete Acoustic and Sound Mirrors
Denge sound mirror from the side. Photo credit: Bodacea/Flickr
The Concrete Acoustic and Sound Mirrors

Acoustic (Sound) mirrors location and coordinates

During World War I sound mirrors were built along the northeast coast, at

Mirrors were also built on the south coast at various times and locations

  • Abbot’s Cliff, east of Folkestone, Kent
  • Denge, Dungeness, Kent
  • Fan Bay, east of Dover, Kent
  • Hythe, Kent
  • Joss Gap, Kent
  • Selsey, West Sussex
  • Warden Point, Isle of Sheppey, Kent.

One mirror was built overseas, at

  • Maghtab, Malta.

A different style of aeroplane detection system was tried on Romney Marsh

  • Snave, horizontal disc

Sources and References:

Andrew Grantham Website
Wikipedia

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