Acoustic mirror

"Sound mirrors" redirects here. For the album by Coldcut, see Sound Mirrors.
4.5-metre-high (14 ft 9 in) WW1 concrete acoustic mirror near Kilnsea Grange, East Yorkshire, UK. The pipe which held the "collector head" (microphone) can be seen in front of the structure.

An acoustic mirror is a passive device used to reflect and focus (concentrate) sound waves. Parabolic acoustic mirrors are widely used in parabolic microphones to pick up sound from great distances, employed in surveillance and reporting of outdoor sporting events. Pairs of large parabolic acoustic mirrors which function as "whisper galleries" are displayed in science museums to demonstrate sound focusing.

Between the World Wars, before the invention of radar, parabolic sound mirrors were used experimentally as early-warning devices by military air defence forces to detect incoming enemy aircraft by listening for the sound of their engines.

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 cancelled owing to the development of the Chain Home radar system. Some of these mirrors are still standing today.[1]

  1. ^ The concrete blocks that once protected Britain BBC News website 7 January 2019