Building a sound amplifier
The aim of these experiments is to use parabolic reflectors to concentrate sound coming from a particular direction. The principle is exactly the same one as satellite dishes which you can see on many roof tops.
You will need:
For the volcano shape:
- An old plastic umbrella, old satellite dish, wok or shallow mixing bowl. The wider these are, the better. A plastic umbrella has some advantages and some disadvantages which we will use to describe below. Really large parabolic surfaces (7 feet + diameter) can be used to talk in whispers across a room.
- Some tape
- A large plastic funnel
- 2 feet of rubber tubing
And last but not least ... a helping hand from an adult.
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Method
If you are using an umbrella, to make the simplest sound telescope, be aware that you will have to destroy it – so only use old unwanted ones.
Simple method
Attach the rubber tubing to the thin end of the funnel.
Point the wide end of the funnel towards the wok or reflector (if it is an umbrella, you will have to remove the central pole up to a certain point – see below)
Point the centre of the wok towards the quiet source of sound – such as a wind up clock across the room or a radio with the volume turned down.
Put the rubber tubing in your ear.
You should be able to hear the clock or other source of sound from 20 feet away or so.
More complicated method
For a better result you can add on the amplifying system of a microphone.
Temporarily stick a small hand mirror on the curved surface of the plastic umbrella and point it at the sun. The reflected light will hit the central pole of the umbrella at the point where the parabolic reflector will best focus sound.
Now you could:
1 - tape a small microphone (ex. web cam microphone or head set microphone) to this point. This would be ideal since you could plug it into your computer or portable stereo and really get a good parabolic microphone set. It is important to make sure that the microphone is pointing towards the inside of the umbrella. Test it and see if you can pick up your friends whispering across the room/street.
or
2 - remove the umbrella's central pole at this point and use the same funnel system as above with the central hole of the inside of the funnel positioned at this same point where you would have put the microphone.