Echoes From The Sky

April 7, 2005 11:52 PM

First built in the 1920's, and predating the use of Radar in World War II, early warning "sound mirrors" were used to provide some means of detecting incoming enemy aircraft. First used in World War I to listen for Zeppelins, their vestigial remnants dot the English coastline. The bizarre legacy of the sound collectors lives on through some decidedly nerdy enterprises.
posted by basicchannel (26 comments total)

Militaries today need passive detection systems. Radars can be isolated and destroyed pretty easily. ALARM and HARM missiles are designed for this, traveling at extremely high speeds towards the source radiation. I'm surprised third world countries don't employ some form of the portable systems. It wouldn't work against aircraft, but it seems effective against low flying cruise missiles that could be stopped with a wall of AA fire if this stuff is really accurate to within two degrees.

Fascinating stuff, basicchannel.
posted by trinarian at 12:11 AM on April 8, 2005

Awesome post.
posted by kickingtheground at 12:12 AM on April 8, 2005

Thanks, I'm enchanted.

This one in particular has peaked my interest. I want to see a pic from inside the house.
posted by sourbrew at 12:25 AM on April 8, 2005

outstanding post basicchannel.

interesting, obscure find, well reseached, and nicely presented.

i'm surprised these things are not still in use - patched, repaired, and kept in service long past reason - like everything else on this island.
posted by three blind mice at 12:52 AM on April 8, 2005

It wouldn't work against aircraft, but it seems effective against low flying cruise missiles that could be stopped with a wall of AA fire if this stuff is really accurate to within two degrees.

How would a sound mirror work as a defense against any object travelling faster than the speed of sound?
posted by Rothko at 3:06 AM on April 8, 2005

I wonder what a zeppelin sounded like through one of those.
posted by TwelveTwo at 3:31 AM on April 8, 2005

You might want to have a look at :
soundMirrors.org

A bit of a self-link but that's allowed as long as it's not a FPP isn't it ?
posted by silence at 4:18 AM on April 8, 2005

How would a sound mirror work as a defense against any object travelling faster than the speed of sound?

You could hide behind it. They look pretty solid.
posted by Jimbob at 4:58 AM on April 8, 2005

More pictures and details: Listening Ears, Greatstone, and Lade Mirrors.

silence: good site, and I also like the Black Shoals, but really, the Internal Communication Amplifier confirms my worst prejudices about contemporary art.
posted by raygirvan at 5:04 AM on April 8, 2005

raygirvan: you're allowed to laugh, you know.
posted by silence at 5:54 AM on April 8, 2005

wonderful post - five stars, basicchannel!
posted by madamjujujive at 6:28 AM on April 8, 2005

This is great.
posted by Busithoth at 6:37 AM on April 8, 2005

Pardon my ignorance, but how do you reconcile "First built in the 1920s" with "First used in WWI", which ended in 1918?

Great find, regardless.
posted by GhostintheMachine at 6:54 AM on April 8, 2005

raygirvan: you're allowed to laugh, you know.

Oh, I did. Out of interest, how's the project for the new mirrors going? The physics of it looked a bit borderline to me.
posted by raygirvan at 7:09 AM on April 8, 2005

If this interests you be sure to visit The Museum of Retrotechnology (which I'm sure has been mentioned here before).
posted by glider at 7:24 AM on April 8, 2005

excellent post. I had no idea . . .
posted by petebest at 7:39 AM on April 8, 2005

GhostintheMachine: Good catch. WWI is actually correct, however, the linked site delivers up that nugget of disinformation(!!!zomgilluminati!!!). Yes, I blame internets.
posted by basicchannel at 8:44 AM on April 8, 2005

Wow, fascinating stuff I never knew about before today.
posted by brownpau at 9:04 AM on April 8, 2005

Great post, and excellent tag: cleverhumans.
posted by safetyfork at 10:14 AM on April 8, 2005

Wow, that's great. When I was a kid, my brother and I built something along these lines (from a book of scouting projects) so we could listen to our neighbors fuck.
posted by breezeway at 1:56 PM on April 8, 2005

Cool. When we were stationed in England I always wondered what those were.

So, if your mate was a sound mirror operator, you can guess what the popular practical jokes of the day were.
posted by tkchrist at 1:56 PM on April 8, 2005

A bit like whispering galleries.
posted by pracowity at 2:41 PM on April 8, 2005

great post
posted by Substrata at 2:44 PM on April 8, 2005

Pardon my snarkiness - there's no doubt that this is historically fascinating - but does anyone have any thoughts on the practicality of the new mirrors by Autogena et al that supposedly will allow cross-Channel communication over 25 miles? Looks to me like one of those artistically interesting but physically unfeasible projects.
posted by raygirvan at 5:31 PM on April 8, 2005

raygirvan : I'm not directly involved with the new mirrors project (the project is mostly the work of Lise Autogena, who I often work with), but as far as I can tell it's moving on slowly, despite some fairly gruelling bureaucracy. There should be a new website and booklet coming out about it soon, I think. The audio transmission for the new mirrors isn't done acoustically - as you point out that's pretty difficult. Though, we did actually work out a way that it might have been done acoustically at one point, but it would have been very, very technical and probably a bit of an environmental hazard (it involved transmitting the sound underwater, rather than through the air, and I don't think the fish would have enjoyed it).
posted by silence at 10:45 AM on April 9, 2005

Thanks for the details. It'd be neat to do it over a shorter distance somewhere high-profile - maybe over the Thames, where it could work acoustically (like the one over the Royal Military Canal at Hythe).
posted by raygirvan at 3:50 PM on April 9, 2005