Acoustic mirrors: how to find planes without radar, by Al Williams at Hackaday (“entertainment for engineers and engineering enthusiasts”):
While today the acoustic mirror is a museum curiosity, before World War II, it was a method of detecting aircraft. The mirror could focus the sound from an aircraft engine allowing early detection. There are several of these stations still on the coast of Britain and one in Malta. A microphone picked up the sound and the construction wasn’t actually parabolic, they were spherical mirrors. The reason is that a parabolic mirror has to move to determine direction, while a spherical mirror could detect direction by moving the microphone.
This year’s annual open day at the Denge sound mirrors is scheduled for 10:00 to 15:00 on Saturday 15 July 2017. Open days are the ONLY WAY to access the Denge listening ears.
There will be a cash-only charge of £4 per adult, £2 per child or £3 per student, with a family discount of one free child per family. Under 5s, carers and RSPB members are also free.
More details on the Romney Marsh website
(Please note that andrewgrantham.co.uk has no connection to the open day, the RSPB or anything else! Please check the details with the RSPB before visiting)
The Guardian article How to amuse yourself in a 14-hour queue at Dover suggests: “The A20 between Folkestone and Dover can be an area of breathtaking beauty, with sea views and endless greenery to distract you from your hellish conditions. Get stranded in the right place and you could go and explore the Abbot’s Cliff sound mirror, or the Samphire Hoe nature reserve.”
The mirrors’ fruitlessness may be forgiven if only because of the uncanny impression one gets that they were built for a future not yet seen or understood. Indeed, its second life as a monument and relic has been more enduring than its first.
Christo Hall visits the sound mirrors on the Kent coast with photographer Stuart Leech and “finds an obscure functionalism melting into majestic land art”, in The Second Life Of Concrete: Brutalism’s Renaissance, published by The Quietus on 10 July 2016.
The RSPB – which now owns the site – is holding an open day at the Denge sound mirrors on Saturday 23 July 2016, from 10:00 to 15:00. Open days are the ONLY WAY to access the Denge listening ears.
Saturday 23 July
Drop in any time between 10am and 3pm
Price: Free. Donations are welcome.
On this day only, RSPB Dungeness will open up the reserve for free! Come and see what this fantastic place has to offer and get up close to our recently acquired, historical Sound Mirrors (or Listening Ears)! Come along for the day where we open them up for everybody to have a wander around the site and talk to our staff and volunteers about what we are doing to give nature a home here. So why not spend the day surrounded in nature and history and afterwards head to the visitor centre for a cup of tea or an ice cream to round the day off nicely.
Please note that I have absolutely no connection with the RSPB or the open days. Make you sure that you confirm the details of the open day with the RSPB before going – do not rely on this Sound Mirrors website.
Huw Morgan is a composer, organist and conductor is “drawn to the power of ancient, haunted landscapes and their lost inhabitants; fascinated by impermanence, space, and time.” This is the first perfomance of his new piece Sound Mirrors for organ and fixed media electronics, inspired by the Denge listening ears: “alien structures haunting the coastal landscape, still listening to the skies…”.
It was given by the composer as part of an Automatronic concert in the JAM-on-the-Marsh 2015 festival. Field recordings were made at St-Mary-on-the-Marsh and elsewhere on Romney Marsh.
BBC interview about the sound mirror in Redcar: “In 1916 it was sitting in open farm land. Since then a modern housing estate has grown up around it. The concrete structure has not always been treated well. When it stopped being used to detect German raids a farmer used it as a spot to store manure. There have been problems with bike enthusiasts using it as a ramp to practice their stunts.” Release date: 22 January 2014.
The £68,000 restoration of the First World War sound mirror at Fulwell in Sunderland was completed with an unveiling ceremony on 9 June 2015.
Fulwell Acoustic Mirror is a 4m high concave concrete dish, constructed on the coast at Fulwell, Sunderland. Completed in 1917, it was designed to act as an acoustic early warning system against air raids, after a bomb dropped by a Zeppelin over the Wheatsheaf area of Sunderland in April 1916 left 22 people dead and more than 100 injured.
After many years of neglect the acoustic mirror’s crumbling condition led to the structure being included on the Historic England (previously known as English Heritage) Heritage at Risk register. This triggered a partnership between Sunderland City Council, Historic England and the Heritage Lottery Fund programme Limestone Landscapes, which has resulted in a glorious restoration, unveiled today, 9 June 2015.
The mirror worked by reflecting sound detected by a microphone in front of the dish to an operator with headphones who could alert the authorities of approaching Zeppelins. Using sound detection methods learnt in the trenches it was designed to give a 15 minute warning of approaching enemy airships.
In 2013 Sunderland City Council secured funding from Historic England. This, together with money allocated to Limestone Landscape Partnership from the Heritage Lottery Fund (HLF), allowed the rescue to go ahead.
Source: Historic England
Sunderland North Young People under the supervision of Groundwork North East and the city council’s area response team cleared the undergrowth. Beaumont Brown Architects led the design work and supervised the repair and landscaping works. The Archaeological Practice Ltd undertook an archaeological assessment of the site alongside a number of other contractors who were involved in the restoration.
The restoration project used specially developed techniques including the use of diluted sheep droppings(!) to tone in the repair work.
The landscaping scheme includes gravel pathways, grassed picnic areas and a wildflower meadow including poppies. There is an interpretation panel with original artwork.
The Acoustic Mirror at Fulwell was part of a chain of important early acoustic detection devices along the coast of Britain and, as one of only four surviving examples in the North East, it is a rare survivor of our 20th century defences and a witness to the conflict of First World War. This has been a very successful partnership to repair and reveal the mirror’s history. It will take a step towards making sure the acoustic mirror will survive for many more years to come and come off our Heritage at Risk register.
Kate Wilson, Principal Adviser for Heritage at Risk for the North East, Historic England
More details at: