Before Radar WW1 style

[Cobaltblue]

These sound mirrors were completely unknown to me.

Now I want to know more.

https://www.bbc.co.uk/news/in-pictures-46348917

Amplification would have been in its infancy during WW1

Cheers

Mike T

[barrymagrec]

There was a TV programme about them some years ago - I seem to remember they put an ordinary modern microphone at the appropriate point in front of the large mirror at Dungeness and the result was astonishing.

[crackle]

https://en.wikipedia.org/wiki/Acoustic_mirror

[Nymrod121]

Also referred in a previous post by McMurdo:

https://www.vintage-radio.net/forum/...29&postcount=7

[G4YVM David]

Youll need to google.it but at least once a year you can have a guided tour of the area.

[The Philpott]

Some of them are still there, as i recall. Only marginally effective due to the bombers coming in at relatively high speed.

Dave

[Cobaltblue]

Yes I have done some further googling originally designed in the days of the Zeppelins they soon became outmoded.

I just don't know how such thing could have passed me by till now.

Doesn't help none in my part of the country I guess

I will make an effort to have a look next time we go to visit the sister in law

Cheers

Mike T

[turretslug]

I'd heard it said that this was the motive behind de-synchronising bomber engines on raids, in order that locating a maximum would become more ambiguous and time-consuming (when time was very much of the essence). Not sure how much true this was, or whether it was (yet another!) cover story as part of the general muddying of intelligence, the "fake news" and maskirovka of modern times. There's also the very pertinent question of increased bomber crew fatigue when de-synchronised with the mind-numbing vibration and noise periodicity.

[Brigham]

I live near the East Coast mirrors, and I always had the impression that the listener used a stethoscope-type receiver, rather than a telephone type.

[G3VKM_Roger]

Originally Posted by Cobaltblue

These sound mirrors were completely unknown to me.

Now I want to know more.

https://www.bbc.co.uk/news/in-pictures-46348917

Amplification would have been in its infancy during WW1

Cheers

Mike T

Mike,

There is a book "Echoes from the Skies" by Richard M Scarth. I bought my copy after seeing the Hythe mirrors whilst working in the Dover area. The book is very detailed and I believe has recently been updated and reissued.

Quite a lot of info on YouTube as well.

Cheers

Roger

[The Philpott]

I recently walked past the yard in Sheringham where the first bomb fell on the mainland during WWI. I looked to see comparative ages of the buildings but there were no huge clues so i suspect it was a small hand-held bomb. (Terror bombing) I withdraw my previous comment regarding speed as regard to Zepps!

Dave

[barrymagrec]

Originally Posted by G3VKM_Roger

There is a book "Echoes from the Skies" by Richard M Scarth. I bought my copy after seeing the Hythe mirrors whilst working in the Dover area. The book is very detailed and I believe has recently been updated and reissued.

Just ordered, thank you.

Barry

[Cobaltblue]

Originally Posted by G3VKM_Roger

There is a book "Echoes from the Skies" by Richard M Scarth. I bought my copy after seeing the Hythe mirrors whilst working in the Dover area. The book is very detailed and I believe has recently been updated and reissued.

Thanks Roger I will search that out

Cheers

Mike T

[G6Tanuki]

"Sound mirrors" and acoustic location might have made some sense in the era of biplanes flying at low altitudes and 80MPH but when planes flew faster-and-higher they were obviously redundant, given the speed-of-sound is only 650-ish MPH and a plane flying at 30,000 feet doing 300MPH will be miles away from the sound-mirror-identified point by the time the sound arrives at ground-level.

Google "Japanese War-Tubas" for some amusing 1930s examples of sound-locators. Whether these were for-real or as a cloaking-device for RADAR developments is always a matter of conjecture.

[Electronpusher0]

Thanks, I have ordered the book.
Echoes from the Sky (not Skies)
ISBN 9781872836171

Peter

[m0cemdave]

A later development, on a rather smaller scale, was the trailer mounted transportable sound locator. They were used in WW2 for aiming searchlights.

The locator contained four horns, 2 spaced vertically and 2 horizontally, on a frame that could be moved in each plane. They were used in stereo pairs and each operator had stethoscope tubes (carefully matched for length) to his pair of horns.

Both operators turned the locator until the sound appeared from the centre of the soundstage (ie directly ahead) and the azimuth and elevation angles were read off by a third operator and given to the searchlight operator to provide an initial aiming point.

I remember inspecting a British-made one, in well preserved condition, at a small military museum on a visit to Portugal about 30 years ago.

The best engineered locator of this type, unsurprisingly, was the German Horchgerat which had the horns built neatly into a circular frame. Contemporary pictures from a searchlight unit equipped with them are here:
http://www.la6nca.net/bilder/mik/index.htm

One thing to be aware of is that sound waves don't travel in straight lines, especially in the vertical plane. They are refracted by the atmosphere depending on how the air temperature varies with height, so at low elevation angles there can be quite large errors. But most of the searchlights would be working at fairly high elevation where the errors are less, and these systems seem to have worked well for their intended purpose.

[McMurdo]

I think it was Tom Flowers or part of his department who was asked to design an electromechanical computer for the later microphone-equipped sound mirrors. He was already working on some sort of automatic plotting system for Chain Home but secrecy meant he was unable to tell them their system was about to be made redundant.

ISTR I read it in Alfred Price's 'Instruments of darkness' or even RV Jones' 'most secret war' both of which are essential reading for the fan of WW2 technology.

Instruments of Darkness ISBN 978-1473895645

Most Secret War ISBN 978-0141042824

PS An edition of BBC2's 'Coast' did experiments with the mirrors, microphones and some sort of audio spectrum analyser.

[crackle]

They have a couple of demonstration sound mirrors in Wat Tyler park Pitsea, Essex.
I went there today for a stroll and we filmed the mirrors.
Here are a couple of photos,

The mirrors are about 100m apart and some thick scrub bushes have grown up between them, masking them so they are difficult to see from each other.

But they do work, if you stand in front of each mirror and talk in a normal voice you can clearly hear one another over the distance of about 100m.
It is quite critical where you listen from, if you move your head forward or backward by more than 6 inches then the sound fades away.
Here is a short demonstration, the video is confusing because Gill could not make out where I was to point the camera. But the audio comes out clearly.
https://www.youtube.com/watch?v=D2tTDYGkiJ8

Mike

[Nymrod121]

Originally Posted by McMurdo

(snipped)
ISTR I read it in Alfred Price's 'Instruments of darkness' or even RV Jones' 'most secret war' both of which are essential reading for the fan of WW2 technology.

Instruments of Darkness ISBN 978-1473895645

Most Secret War ISBN 978-0141042824
(snipped)

I agree 100%

[Gridiron]

According to the section on sound ranging in the Haynes "Battle of Britain" book, Visual Indicating Equipment (VIE) was used with the mobile sound ranging units, which used a CRT to give a visual display which apparently greatly improved the accuracy of location. Does anyone have any information on this equipment?