Audio components convert sound wave into current and current into sounds. device that convert sound wave to electrical current are normally know as microphone and device that convert current to sound speakers. Let look at getting sound to current first.
Sound wave have an effect of surfaces. place a glass of water next to a speaker and turn up the volume and you can see this in action. There are many ways this movement can change a current but these are the most common:
- Carbon - A diaphragm capture the sound vibrations and passes it onto a a carbon capsule. When the vibration hits the carbon it applies different pressures and changes the conductivity of the carbon. When a current is passed through the carbon the different resistance result in different output currents. These output are recorded and stored to represent the incoming wave of sound.
- Condenser - A diaphragm captures the incoming sound waves. A metal plate is fixed to the center of the diaphragm and a fixed point away. When the wave hit the diagram the distance between the plate alters and the capacitance of the plate change. The change is measured and recorded.
- Crystal - some materials actually form a voltage when the are bent or pressure is applied. So, once again, sound is captured and on of these piezoelectric substances are placed behind it so that when sound move the diaphragm, the diaphragm move the crystal, which generates a current, which is measured and recorded.
- Dynamic - A Small magnet is attached to the back of a diaphragm. When sound moves the diaphragm, the diaphragm moves the magnet in and out of a coil of wire. This generates a current in the wire which is measured and recorded.
A speaker does the reverse process. It converts variations in current into vibrations in a diaphragm, which produces sound. Most speaker are magnet based, where the current runs through a coil changing it's position over a magnet. The coil is then attached to a paper cone. So when a variable current is passed through the coil it bounces up and down the magnet bouncing the paper cone as well, creating sound vibrations.
On some small circuits, crystal speaker are also used. A current bends the piezo crystal which is attached to a diaphragm creating sound.