A web forum with discussion of RAF sound reflectors and the use of sound in early warning systems.
Sound mirrors
Early electronic warfare
There is an interesting article about Electronic Warfare in WW1 on the Landships website, in which Robert Robinson describes a somewhat obscure aspect of the Great War.
There is a common misconception that electronic warfare began with the Second World War but, even if it was not so labelled, it played a significant part in the First World War at both a strategic and a tactical level.
Fans of sound mirrors might be interested in the tale of how the Eiffel Tower was used to confuse Zeppelins.
The forgotten sound mirrors
“Deputy Dog” writes about The forgotten sound mirrors
, with some pictures.
Sound mirror on Bass Communion album
A correspondent e-mails to say that he first discovered the sound mirrors when he saw pictures on the CD booklet/cover art of a Bass Communion album. They are great images, done by Carl Glover of Aleph Studios
, showing a view up the 200 foot mirror at Denge.
Bass Communion is a project by Steven Wilson, leader of the band Porcupine Tree. According to the Bass Communion website, it specialises in recordings in an ambient and/or electronic vein, sometimes in collaboration with other artists. Most of the pieces are experiments in texture made from processing recordings of real instruments and field recordings.
The March 2003 album Bass Communion (remixed) contains Reconstructions and recycling of Bass Communion music by artists from the experimental, electronic and ambient music scenes
.
2008 guided walks to the Denge sound mirrors
The Romney Marsh Countryside Project is running three guided walks to the Denge sound mirrors in the gravel pit near Lydd-on-Sea over the summer.
This year’s walks are planned for Sunday 13 July, Sunday 17 August and Sunday 14 September 2008.
They will be led by Dr Richard Scarth, author of the book “Echoes From The Sky”, and are your only chance to see the three mirrors close up.
ECHOES FROM THE SKY
A rare opportunity to visit the Sounds Mirrors of Lade Pit. The walk will be led by Dr Scarth, the world’s expert on sound mirrors, who will tell the fascinating story behind them. Meeting point is at 2pm in Lade car park on Coast Drive (approximately half way between the Pilot Pub and Romney Sands) (TR 085 208). It is free of charge but donations are appreciated. No booking is required.
Obviously you should check the details with RMCP before travelling, but it is well worth the effort of getting down there.
Acoustic mirrors for finding bats
David’s Bat Blog has a details of a bat detector (that’s “bats” as in “belfries”), partially inspired by sound mirror design.
The prototype is only 60cm by 20cm, so I wasn’t expecting miracles, but tests at varying ultrasound levels showed that, using the reflector a Duet bat detector could pick up the artificial bat between 30% and 70% further away than it could on its own. Positioning of the detector microphone is critical, as it needs to be at the precise focal point of the reflector for best results.
More at Bats, bombers and acoustic mirrors.
Wat Tyler’s sonic marshmallows
A pair of sound reflectors were installed at the Wat Tyler country park in Essex during February 2007, as of a regeneration program launched by Basildon Council.
The permanent installation is one of a series of sculptures commissioned for the park. The brief was to create something playful and challenging for the children there. The sculptures allow their users to whisper to each other while 60m apart.
The Sonic Marshmallow create a stunning acoustic experience: their shape focuses sound and allows people standing in front to hear each other’s whispers 60 metres over the pond that separate them. They work like reflectors to create a precise beam of sound.
The cylinders are also concave on their other sides, allowing the users to respectively spy on the people in the nearby car park, and the animal in the woodland, thanks to those 2.5m ears.
Designers Troika say Basildon being so close to the coast, we were also inspired by the early sound mirrors built between the two wars as early attempts of detecting incoming enemy planes approaching. Famous remaining examples lye off the Kent coast, near Dungeness.
Acoustic engineering consultancy was provided by Sandy Brown Associates, and fabrication by London Engineering.
Seaham site sussed?
David Angus of the Seaham online community history project www.east-durham.co.uk has tracked down the probable location of the Seaham sound mirror, though cautions “it is at least 55 years since I saw it and then only once.”
He’s found two men who agree on the location shown below. Apparently the mirror may have been used for shooting practice by the local Home Guard during World War II.
Sadly it would appear it is no longer in existence; when it did exist it looked something like the surviving Sunderland mirror.
Selsey listening post sold
Various e-mails have arrived this week telling me that the sound mirror in East Beach Road at Selsey in Sussex which was up for sale has been bought. Known locally as the Listening Post, this acoustic mirror is unique as the only one to have been converted into a house! The garden was in a bit of state – it “looked like a jungle” says one local – but apparently it is now being cleared.
The Selsey Community Website records
The Listening Post was in April 1999 [12 March 1999 according to Images of England] recognised as a Grade 2 Listed building. During the 1st World War a listening post was built in Selsey at East Beach to provide early warning of approaching Zepplins. The structure took the form of an “acoustic mirror” which was built of concrete and shaped like a modern satellite dish. The structure survived and is currently the subject of great interest due to its rarity.
Roger Whitehead has a couple of photos of it on Flickr.
The relevant Images of England page says:
SZ 5289 SE SELSEY EAST BEACH ROAD (North side) 23/10031 Number 2, The Listening Post II Sound mirror, now incorporated within house. 1916, converted into house by late 1930s. Sound mirror built of reinforced concrete, the shuttered lifts to the exterior clearly visible. House has slate-clad stud walls and corrugated asbestos roof, with 2-window front and window inserted into left-side wall; extensions to rear and right. INTERIOR: curved profile to mirror wall. HISTORY: This house incorporates a complete example of a sound mirror, built in 1916 (recorded as under construction in March of that year) and one of a series of listening posts built for the Admiralty along the south-east and north-east coasts. The attacks by the German Fleet on east coast ports in December 1914 had alerted the Admiralty to the need to provide early warning of future raids, soon underlined by the threat posed by Zeppellins to British ports and urban areas. The sound signal was reflected by the dish, via a duty observer armed with a stethoscope, to a microphone which enabled the course of the intruder to be plotted. These signal stations thus formed a precursor to the development of radar from 1936. Due to the obsolescence of the technology from the late 1930s, and later coastal clearance work and urbanisation, very few examples (such as Fulwell in Sunderland and the Hythe/Dungeness group in Kent) have survived. It also bears a very direct relationship, through its form and design, to its intended use and thus its technological and historical context. Source: (Chichester Observer, March 1916).
Sound mirror at Seaham?
Vernon Prior writes:
I left Seaham in 1947 and have rarely been back. I do remember as a child, however, playing around an acoustic mirror (complete with metal rod for supporting the microphone) situated on the high ground (Kinley or Kilney Hill) to the south west of Dawdon, Seaham Harbour. Having looked at the photographs, I can report that it was similar to the Sunderland example in terms of shape and size. I have no idea what state it might be in now, or even if it still exists.
Anyone got any ideas? Let me know! Looking at a map, it would make sense for there to be a mirror in the area, as it would be in the “gap” along the coast between the mirror at Sunderland and the now demolished mirror said to have existed at Clavering, Hartlepool.
UPDATE 15 March 2008: I’ve just rediscovered a previous post about Seaham. It looks like there is agreement on its existence – now we just need to find it!