Exhibit: Bucket Radio
The radio has most of the loudspeaker missing, so you can’t hear it unless you put a plastic bucket where the loudspeaker should be.
A loudspeaker has a magnet and a coil of wire, just like any other electric motor. The vibrations of the coil are normally converted into sound waves by a large cone which is fixed to the coil – as the cone vibrates, it compresses and expands the air in front of it. These compressions and expansions travel through the air and are heard as sound by our ears.
If the cone is removed, only the tiny coil is left to compress and expand the air, so hardly any sound is produced. If a plastic bucket is placed touching the coil, the bucket is made to vibrate and passes it’s vibrations through the air, so the sound is a great deal louder.