Mirror on the coastline / Please talk free...

June 4, 2017 9:14 AM

Before the advent of radar, acoustic mirror stations, like this one in Denge Marsh, were built on the southern and northeastern coastline of England between 1915 and 1935. Intended to provide early warning of incoming enemy aircraft, these structures were the result of research conducted by William Sansome Tucker. In 1935, an acoustic mirror station known as "Il Widna" ("The Ear") was built in Malta.

More on acoustic mirrors:

Andrew Grantham's Sound Mirrors blog, and his Sound Mirror FAQ. His Twitter feed devoted to acoustic mirrors is @concreteear.

Spiegel Online: Listening for the Enemy: Giant Ears on the British Coast

Before Radar, they used these giant concrete “Sound Mirrors” to detect incoming enemy aircraft.

See How Innovative Sound Mirrors Helped Detect Enemy Aircraft.

Jan Crowther talking about the Kilnsea sound mirror on Look North, 2008.

Where to find them:

Details of the sound mirrors, and how to visit the ones which survive.

The acoustic mirrors at Romney Marsh in Kent and East Sussex will be open to the public in July 2017.

Sound mirror locations via listings on Historic England.

Smaller-scale, modern versions of acoustic mirrors exist in various locations. If you're in Houston, Texas, you can try out these stone listening vessels.

posted by mandolin conspiracy (13 comments total)

They had a set of these in the Museum of Science and Industry when I was a kid, set far apart and facing each other, so that you could whisper and be heard many yards away by someone standing at the other focus, and vice versa.
posted by Halloween Jack at 9:25 AM on June 4, 2017

I'm positive the Ontario Science Centre has or had a set too, because I have a distinct memory of doing that as a kid.
posted by mandolin conspiracy at 9:28 AM on June 4, 2017 [2 favorites]

Here are some other devices designed for the same purpose.

They were sometimes called war tubas, not to be confused with the Horns of Jerico.

I have no idea what miltary purpose this horn served.
posted by StickyCarpet at 9:31 AM on June 4, 2017 [2 favorites]

I'm positive the Ontario Science Centre has or had a set too, because I have a distinct memory of doing that as a kid.

I remember them as well - they were set up in a pair and if you coordinated with a friend you could talk to each other across the hall.
posted by sudasana at 9:38 AM on June 4, 2017

They were sometimes called war tubas, not to be confused with the Horns of Jerico.

I was really hoping the "Horns of Jerico" link was to an actual thing I'd never heard of, in the manner of Prince Rupert's Drops. Ah well.

But, war tubas more than makes up for the disappointment.

Also, building a war-tuba symphony, with historical war tubas modified to be used as actual brass instruments sounds pretty fantastic. Perhaps not worth the time to make it happen, but certainly worth the cost of tickets.
posted by eotvos at 9:58 AM on June 4, 2017

St. Louis Science Center had (has?) them too.

I'm sure that one of the many fine links will say this, but when we visited one of the sound mirrors near Dover, the guide claimed that in good conditions a skilled operator could hear cars driving along the French coast... and identify their make!
posted by tss at 9:59 AM on June 4, 2017

The Reuben H. Fleet Science Center in Sam Diego has a pair, elevated above the crowd at the end of two short flights of stairs.

(I spent a summer volunteering there, helping a schoolteacher of mine with some classes. Met Bill Walton when he came to get his kid if you need a date frame of reference).
posted by Samizdata at 10:24 AM on June 4, 2017

Ah. A few others, from the Wikipedia entry on acoustic mirrors:

Parabolic acoustic mirrors called "whisper dishes" are used as participatory exhibits in science museums to demonstrate focusing of sound. Examples are located at Bristol's @Bristol Science Museum At-Bristol UK, Ontario Science Centre, Baltimore's Maryland Science Center, Oklahoma City's Science Museum Oklahoma, San Francisco's Exploratorium,[3] the Science Museum of Minnesota, the Museum of Science and Industry in Chicago, and Parkes Observatory in Australia.
posted by mandolin conspiracy at 10:33 AM on June 4, 2017

Also found at Science World in Vancouver. My impression is that every science museum has a pair of whisper mirrors, seeing as they're cheap, popular and genuinely educational.
posted by justsomebodythatyouusedtoknow at 10:46 AM on June 4, 2017 [3 favorites]

I have no idea what miltary purpose this horn served.

That's a cannon. For to shoot big bullets at tanks.

The Ju 87 had a siren for psychological-warfare purposes -- that's the classic "dive bomber" sound -- but it looked like a little propeller mounted to the landing gear strut.

I was really hoping the "Horns of Jerico" link was to an actual thing I'd never heard of

ISTR that the Ju 87 sirens were sometimes called Horns of Jericho?
posted by ROU_Xenophobe at 10:54 AM on June 4, 2017 [1 favorite]

Great reference to The English Beat in your post title!
posted by Napoleonic Terrier at 8:58 PM on June 4, 2017 [1 favorite]

Heh. That song has been an intermittent earworm for me over the last couple of weeks. I'm pleased it found an outlet somewhere...
posted by mandolin conspiracy at 9:03 AM on June 5, 2017

Can I take you to a capitol with glass whispers? The National Statuary Hall is an inadvertent mirror. Apparently that line they used to sell about Adams using it to his advantage is bullshit, though.
posted by Ogre Lawless at 7:31 PM on June 5, 2017 [1 favorite]