Photo Gallery Britain's Forgotten Sound Mirrors
An example of the experimental sound mirrors constructed in the United Kingdom before World War II can be found at Capel-le-Ferne. The photo is courtesy of Rob Riddle.
Built in 1928, this sound mirror at Denge in the UK is an imposing nine meters in diameter. Clearly visible in the middle is the metal bar to which an electrical microphone was attached when the system was operational in the 1930s. The photo is courtesy of Thomas Cogley.
In the concrete area in front of the massive wall, scientist William Sansome Tucker installed 20 microphones which made it easier to pinpoint the direction of incoming aircraft.
In the chamber beneath the nine-meter concave sound mirror at Denge, the information was gathered and then sent to headquarters via telephone.
The 60-meter-long curved steel and concrete wall provided promising results during the British military's acoustic experiments in the 1930s, the early days of aircraft detection.
A series of these giant sound mirrors was planned to stretch down the eastern and southern coasts of England, to protect against enemy air raids.
The Il Widna sound mirror in Malta is the only one of its kind outside of the United Kingdom. "Il Widna" is Maltese for "The Ear". The photo is courtesy of Andrew Grantham.
Of the two monumental hemispheres constructed at a military base west of the town of Hythe, Kent in the 1920s, only one remains standing -- the other fell over in the 1980s. Scientists used the shells to determine the direction of incoming aircraft, and the greater the mirror diameter, the better the engine sounds received.
A large chunk has fallen out of the remaining mirror at Hythe. The gap shows how the bowls were constructed, with a metal skeleton. The photo is courtesy of Ian Davies.
Wind and weather have battered the reinforced concrete for decades. The British government has now placed the relics under protection -- the sound mirrors have been fenced off to help prevent further damage. This image was taken on July 4, 2010.
In fact, the sound mirrors on the southeastern coast of England were set to be destroyed in the late 1930s after it became clear that radar was a much better early warning system. But with the outbreak of World War II, the giant listening devices were forgotten -- and they have survived until the present day.
The very first sound mirrors were constructed in Britain during World War I, carved into limestone cliffs as part of experiments to battle enemy artillery. This example is located on the cliffs between Capel-le-Ferne and Samphire Hoe in Kent.
Once upon a time, these sound mirrors were used an early warning system to detect enemy aircraft approaching Great Britain. Nowadays, they are a tourist attraction. This photo was taken in September 2005.
The acoustic experiments were halted in the mid-1930s after it became clear that Radio Detection and Ranging, more commonly known as radar, was much more effective in tracking approaching aircraft.
While radar is still used the world over, both for military and civilian uses, the sound mirrors are merely a relic of a forgotten technology.
