From the headline I thought it was going to be about the variously shaped concrete blocks, e.g. Dragon's Teeth [0], used as anti-tank defences, which can still be seen all over the British coastline[1].
Cool! Lots of little radio telescopes, except tuned for audio. I wonder how the triangulation was done: Were the relative sound intensities fed into a computer, to work out the approximate position of the incoming zeppelin?
Not many computers about from 1910s to 1930s! :) (apart from mechanical ones used for e.g. artillery)
My guess is basic lines being drawn on a physical map using observations spaced over time, and then humans trying to spot the pattern. I think these sort of sound mirrors are fairly directional, so with a bunch pointing in various slightly different directions you might be able to find the "sweet spot" and at least get an idea of where the enemy is, even if it is not precise.
From my own personal half-forgotten memories of seeing these as a kid in the 90s, they always seemed to be aligned with the coast, e.g. facing directly out to sea, not at an angle. This I guess would get you a lot of subtlety different directions to take a sounding from.
The mirrors focus sound to a different point depending where it originated from. With a movable microphone, an operator can pinpoint to within a fraction of a degree the direction the sound came from, and if it can be heard on two sound mirrors, that gives an exact location.
The intent was there would be several microphones that could be triangulated. With a hut full of human computers and sets of trig tables presumably.
The chap mentioned here, Tucke, was active in developing sound artillery ranging, which survived well after WW2. Artillery didn't have the speed issues that killed off sound mirrors before they ever really got going.
Watson Watt and his team fortunately gave us workable radar with height and direction finding by war's outbreak. Just.
Nope. No computers with signal processing capability yet. There was usually just a wave guide (or voice tube) leading to a man listening with his ears, or later models had a microphone.
The waveguide was rotatable so that sound direction could be roughly determined. This was done by slowly turning the guide until the sound was at its loudest and then reading off the angle.
I was left very disappointed with the quality of his images. He used a large format camera, so there ought to be a lot of detail and grit in these images, but the framing and the processing leads to pretty dull images...
Too much, and too dull skies, boring central compositions etc...
Traditionally, large format photographers would produce much more interesting work!
Accoustic mirrors could actually be rather effective - a large mirror could perhaps hear a plane in good conditions up to 75 miles away, well over the horizon.
Early radar only had about the same range, but the advantage was it could work in nearly all conditions, rather than just windless sunny days.
They also weren't used by the Germans, so perhaps the accoustic mirrors were as much of a secret as radar.
