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Genghis the Engineer
24th Aug 2002, 18:32
A couple of days ago I was on my way into Lydd for lunch, a first visit (and I recommend the German sausages on the menu).

Under the downwind leg, which was to the South of the runway were two rather strange parabolic concrete structures, sat on an island in the middle of a lake. One was 2-dimensional (constant in the vertical plane), the other was 3-dimensional. Both were pointed out to sea, approximately in the direction of what is now Dungeness power station.

Being a nosey so and so, and also fancying a stroll after my lunch, I asked in the club about them. It turns out that these devices date back to WW1 and were listening stations for Zeppelins - the parabola focussed sound onto one spot, where an observer could hear the distinctive drone of the engines in plenty of time to alert coastal defences.

Sadly, the local geography (and the fact that they're apparently within the airfield perimeter) prevented me walking out to them to take a look more closely. But, they have rather grabbed my imagination, so a couple of questions for the history buffs amongst you...

(1) Are these the only ones, or are there more on the coast somewhere?

(2) If there are any more, can they be visited?

(3) Can anybody point me at any published history on the subject?


Below is a picture I managed to take of the device.

G

http://www.btinternet.com/~guy.gratton/Lydd_s.jpg


Postscript: After a web search, I now know that the devices are called "Sound Mirrors", and there's a write-up about them at http://www.ttforumfriends.com/historysoundmirrors.htm Still fascinating, and anything anybody can add, I'll be interested anyway.

ORAC
24th Aug 2002, 18:57
Sound Mirrors (http://www.castlekas.freeserve.co.uk/sound_mirrors.htm)

Echoes from the Skies (http://website.lineone.net/%7Erhsadmirals/)

Preservation (http://www.guardian.co.uk/Archive/Article/0,4273,4203067,00.html)

Kermit 180
26th Aug 2002, 08:26
I read somewhere many moons ago that they used to employ deaf people with listening tubes situated on top of buildings and tall structures to listen for the Zeppelins, as their hearing was more acute than the average person. The listener would hear the Zeppelin and turn the movable tube in the direction of the noise. The structures you have above appear to be more permanent and definitely more complex than the listening posts I read about.

Lu Zuckerman
26th Aug 2002, 14:49
It is my understanding that the Viet Cong employed a similar system. They would hollow out a mound of earth in the shape of a RADAR dish. A VC would sit at the focal point of the reflected sound and they could hear helicopters and aircraft long before they normally would. Of course for a Bell helicopter the normal hearing range was ten or so miles. The listening device added several miles to that giving them the advantage of knowing that the helicopters or aircraft were coming.

:)

poetpilot
27th Aug 2002, 14:22
Kermie do you mean DEAF people or blind people?

..Mind you, knowing the UK Civil Service as I do, it wouldnt surprise me to find they's employ deaf people as listeners...

Kermit 180
28th Aug 2002, 08:39
I stand corected, I meant to say BLIND people. Doh!:rolleyes:

Kerms:o

spekesoftly
29th Aug 2002, 02:02
Interesting TV programme on BBC2 last night (Invasion - Battle for Britain) - mentioned quite a bit about 'sound mirrors'. Dan Cruickshank was concluding his exploration into the history of Britain's defences. His book 'Invasion' is available from www.bbcshop.com priced 18.99.

Matt Black
31st Aug 2002, 14:08
Hi Genghis,

The programme mentioned is well worth a look if it is repeated. BTW, they said in the prog that the mirrors didn't work too well and by the time they were built and put into operation, the Zeppelin had been overtaken by fixed wing attack. This meant that the sound mirrors would give only around three minutes warning. What did result from the mirrors was a system of communications which would later become the basis of the integrated radar-fighter control system used in WW2. Hope this is some use. BTW, thanks for the heads up on the books a few months back.

MB