Sound Mirror Parabola
Sound Mirrors
Dungeness Sound Mirror
There are two of these intriguing structures left standing in the world. This one is on the south coast of England, near Dungeness, Kent.
A forerunner of radar, the sound mirrors were intended to provide early warning of enemy aeroplanes (or airships) approaching.
Il Widna Sound Mirror
Il Widna, the ear, is a sound mirror based on the island of Malta.
Finding Sound Mirrors
The illustrations above were taken by finding them in either Google Earth or Flash Earth.
Google Earth is an application that, once installed, has the advantage of 3D views, and a close relationship with its sister program Google Sketchup.
Flash Earth runs directly online, so is immediately available - designed by a very creative young Englishman Paul Neave - it is well worth looking at some of his other material too: such as his Planetarium and his Fractal pages.
Find out more about Sound Mirrors
Andrew Grantham has a website devoted to the history and detail of sound mirrors around the world.
- What were they for?
- When were they built?
- What direction do they face, and why?
- What shape are they, and why?
- How effective were they?
- Why were they not adopted widely?
Analysing Sound Mirrors - the mathematics
Is a sound mirror parabolic?
Douglas Butler illustrates how to create an Autograph file to test the parabolicality of a sound mirror.
Play with this Autograph file here...
Click the image to load the online Autograph file.
If you have Internet Explorer, Firefox or Safari browsers, you will be able to download the Autograph Player plug-in to explore this file for yourself. Unfortunately this facility is not yet available to MAC users.
Of you have Autograph installed, you can click here for an Autograph fileApplying the Same Ideas Today
Radio Astronomy uses parabolic reflectors, with the receiving device clearly at the focus.
Domestic satellite television receivers are also parabolic, but their receptors are offset from the focus, at least the one on my house is! I wonder why this is?
Douglas Butler
Jing is a free on-screen recorder that uploads to the web or saves as a Flash file
