Sound mirrors

Photo: Mark Dyson, March 2003.

The acoustic mirror at Kilnsea in East Yorkshire was one of a number built on the northeast coast around the time of the First World War. A forerunner of radar, they were intended to provide early warning of incoming enemy aeroplanes and airships about to attack east coast towns.

Other sound mirrors were built at Boulby, Redcar, Hartlepool, Seaham and Sunderland. Further examples existed on the south coast.

These pictures were taken in December 2001. Click on a picture to see a bigger version.

The mirror stands behind a nature reserve in a field just north of Kilnsea at the landward end of Spurn Head. It is set back from the current coastline (which is eroding nearer every year), possibly to prevent the noise from waves breaking on the shore interfering with the mirror.

The mirror worked by focusing the noise of aircraft engines onto a microphone, which amplified the sound. In this way the relatively slow aircraft of the time could be heard and located before they came into view.

The microphone would have been fitted to the metal post set in a concrete block in front of the mirror. An operator would use headphones to listen for an approaching enemy.
With the development of faster aircraft the sound mirrors became less useful, as an aircraft would be within sight by the time it had been located.

The mirror is made of concrete, with a dish about 15 feet in diameter in the side facing the sea.

Location

The mirror is roughly between Kilnsea Grange and the sea. Map.

More

News and updates about the Kilnsea sound mirror.