Author: Andrew Grantham

Would the sound mirrors have been much use?

Posted on by Andrew Grantham

Denge sound mirror

Probably not, concludes Brett Holman in a posting on his Airminded blog entitled The widening margin. It is an interesting analysis by someone doing a PhD at the University of Melbourne, examining the impact of airpower propaganda on the British people between 1908 and 1939. The whole site looks worth a poke around.

Lastly, here’s a counterfactual which I’ve long wondered about. Between 1933 and 1935, the Air Ministry put a fair amount of effort into researching the feasibility of using acoustic mirrors as a comprehensive early warning system. The acoustic mirrors were, mostly, concrete hemispheric dishes for focusing sound, which had been used as early as 1916. The biggest ones, at Dungeness in Kent and Maghtab in Malta, were 200 feet long curved walls. Land was actually purchased along the Thames Estuary for the beginnings of a national acoustic mirror system, but work never started because radar came along. But if it hadn’t, then in 1940 Fighter Command might have relied upon a network of these acoustic mirrors all along the coast. How useful would they have been?

The experimental mirrors had a maximum detection range of 22 miles (on very windy days it was a lot less). I’ll be generous and call it 25 miles, which is then added to the 50 miles from the coast to London for a total distance of 75 miles. The Thames Estuary acoustic mirrors probably would have come online in 1936, and so again I’ll be generous, and assume that London at least would have a working early warning system from that year.

Taking all this into account, the results can be seen above [article has a graphic]. And sadly the acoustic mirrors wouldn’t have made much difference — a margin of only about 10 minutes, not much improved on the 5 minutes with no warning system. Of course, even a few minutes’ extra warning was worth having, but the Air Ministry was right to terminate development of the acoustic mirror network in order to concentrate on the far more promising radar.

Read Holman’s full article (and some warnings about the assumptions made).

Early electronic warfare

Posted on by Andrew Grantham

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.

Sound mirror on Bass Communion album

Posted on by Andrew Grantham

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 album cover
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

Posted on by Andrew Grantham

Guided walk to the 30 foot sound mirror at Dungeness

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

Posted on by Andrew Grantham

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

Posted on by Andrew Grantham

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.

Sonic marshmallows at Wat Tyler country park in Essex. Photo: Troika

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.

Pillboxes of Britain and Ireland book

Posted on by Andrew Grantham

Cover of Pillboxes in Britain & Ireland I’ve acquired a copy of the newly-published book Pillboxes of Britain & Ireland, by Mike Osbourne.

While it doesn’t cover sound mirrors, it is an excellent and comprehensive book on pillbox design and development, with typologies, plans, photographs and details of the theory and use of pillboxen. It is well worth any connoisseur of concrete defensive structures getting hold of a copy.

While we’re at it, I’ll also mention another good recent read, the new Osprey book on Armored Trains. I would review it, but this review says it all pretty well.

Unfortunately the book doesn’t mention the armoured train in Sarajevo.

Seaham site sussed?

Posted on by Andrew Grantham

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.

Sunderland sound mirror

Sadly it would appear it is no longer in existence; when it did exist it looked something like the surviving Sunderland mirror.

Probable location of Seaham sound mirror

Probable location of Seaham sound mirror.