Explainer: Locating a gun with sound waves

In WWI, scientists used sound waves to find big guns

Scientists used microphones to locate and destroy killing machines like this, the remains of a German gun.

Great War Primary Document Archive: Photos of the Great War - www.gwpda.org/photos

Suppose that the boom of a gun is recorded by three microphones: Let’s call them A, B and C. Assume that the three microphones are spaced 386 meters (1,266 feet) apart. That is the distance sound travels through air in one second. The boom reaches microphone A first. One second later it reaches microphone B. One second after that it reaches C. Draw a circle with a radius equal to 386 meters centered on B and a circle with radius twice that distance centered on C. Now draw a circle that goes through the position of microphone A and that also touches the two other circles. The center of this circle is the position of the gun that fired.

Adapted by B. Brookshire from “The World of Sound”, Sir William Bragg, Dover, 1968, with images from WWW.GWPDA.ORG/PHOTOS and Evan-Amos, Wikimedia Commons
In this diagram, the sound of the gun reaches point A first, followed by B and C. Using geometry, sound rangers could use the differences in how fast that sound reaches each point to determine the location of the gun.


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