1915 __ Acoustic Mirrors
‣ Comment : A forerunner of Radar, acoustic mirrors were built on the south and northeast coasts of England between about 1916 and the 1930s. An acoustic mirror is a passive device used to reflect and perhaps to focus (concentrate) sound waves. Their experimental nature can be discerned by the different shapes of each of the three reflectors: one is a long, curved wall about 5 m high by 70 m long, while the other two are dish-shaped constructions approximately 4–5 m in diameter. Microphones placed at the foci of the reflectors enabled a listener to detect the sound of aircraft several kilometres out in the English Channel. The reflectors are not parabolic as sometimes imagined, but are in fact hemispherical mirrors. The massive concrete acoustic mirrors, or “listening ears,” lining the southeast coast of England were built between the world wars to monitor the skies for the telltale sounds of airborne invasion. (Andrew Grantham) — The Sound Mirrors Project (by Lise Autogena) plans to construct two such acoustic mirrors on opposite sides of the 25-mile-wide English Channel, precisely positioned so as to allow international parabolic communication: Visitors to the new mirrors will be able to climb up to a listening platform in front of the mirror in the manner of the orignal listeners at the historic mirrors. Rather than straining for the sound of distant aeroplane engines, people will be listening to the sounds of the sea, as well as for voices speaking to them from across the Channel. A new advanced acoustic technology will allow transmitted sounds from the other mirror to be audible only at a particular focal point in front of the dish. — focused at the small area around the listener’s head. The person standing at the focus point will hear a complete “holographic” binaural sound image which will appear to becoming from the air all around them. (Lise Autogena)
‣ Source : Ford, James Dillon (1995), "From Vocal Memnon to the Stereophonic Garden : a short history of sound and technology in landscape design", a paper prepared for CELA, Council of Educators in Landscape Architecture Annual 1995.
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