An acoustic mirror is a passive device that reflects and focuses sound waves, often used in early aircraft detection before radar and today in parabolic microphones and science museum exhibits. Large concrete acoustic mirrors were built along the British coast between about 1916 and the 1930s to detect incoming enemy aircraft by engine noise (Wikipedia contributors, 2026).
Background
Acoustic mirrors, which are regarded as precursors to radar technology, were constructed along the southern and northeastern coasts of England from approximately 1916 until the 1930s (Grantham, n.d.). These structures were designed to detect the sounds of approaching enemy aircraft and airships, thereby providing early warning of potential attacks on coastal settlements. However, the increasing speed of aircraft reduced their effectiveness, since aircraft could often be visually detected by the time they were located acoustically. The subsequent development of radar ultimately made acoustic mirrors obsolete.
Although the acoustic mirrors at Denge in Kent are widely known, fewer people are aware that numerous other examples were constructed according to a variety of designs. The associated webpages document surviving mirrors through photographs and provide information about their locations for those interested in visiting them.
During the First World War, acoustic mirrors were constructed along the northeastern coast at Kilnsea in East Yorkshire, Boulby in North Yorkshire, Redcar, Hartlepool, Seaham, and Sunderland. The mirrors at Hartlepool and Seaham have since been demolished.
Additional mirrors were constructed at various locations along the southern coast, including Abbot’s Cliff east of Folkestone, Denge at Dungeness, Fan Bay east of Dover, Hythe, Joss Gap, Selsey in West Sussex, and Warden Point on the Isle of Sheppey.
An acoustic mirror was also constructed overseas at Maghtab in Malta. In addition, an alternative aircraft-detection system, consisting of a horizontal disc, was tested at Snave on Romney Marsh.
Sources
Grantham, A. (n.d.). Early Warning Sound Mirrors. Sound Mirrors. Retrieved 01 September. 2026, from https://andrewgrantham.co.uk/soundmirrors/.
Helfer, Martin. (2000). 1 Localization of Sound Sources.
Wikipedia contributors. (2026, February 4). Acoustic mirror. In Wikipedia, The Free Encyclopedia. Retrieved 09:07, September 1, 2026, from https://en.wikipedia.org/w/index.php?title=Acoustic_mirror&oldid=1336595025