Acoustic Locators - A Different Kind Of Acoustic Technology

Being involved with acoustic cleaning, I am always interested to read any material relating to acoustic technology. The truth is that acoustics can be used for all manner of things.

Just the other day in fact I came across the term acoustic location - essentially the science of using sound to pinpoint the direction of something travelling and its distance. Primarily used for military purposes as one might imagine, acoustic location can be conducted in different environmental situations - in the atmosphere, in water and also in solids - and it can be done in two different ways:

Active acoustic location

The principle involved is to use a signal generator and a listening device. Sound is generated to produce an echo and this echo is analyzed and the object's location detected.

Passive acoustic location
The principle is simply to detect the sound or vibration created by a specific object.

Passive acoustic location was used as early as the First World War in fact and continued to be used into the early part of the Second World War in order to detect aircraft engine noise. However, it became outmoded with the invention of radar. I was fascinated to read how, during both World Wars, acoustic location was used in various countries and in different ways.

In Britain acoustic mirrors were placed at strategic points around the coast during WW1 in order to detect any potential aerial attack.

(Photo) In Sweden they used acoustic location as anti-aircraft defence during the early part of WW2. Photograph taken in 1940 copyright Carl Gunnar Rosborn

In Japan, acoustic locators were used in WW2 - they opted for large metal tuba-shaped devices, subsequently referred to as war horns. See Wikipedia's page

Fascinating though it is to read all of this, I still prefer a more 'peaceful' application of acoustics. Give me silo cleaning any day!