Principle:
Resistance varies with change in pressure sensed by diaphragm of a microphone.
Construction:
Consist of a thin diaphragm which is connected to a capsule having flexible bellow.
A capsule containing carbon granules.
Electrical circuit to for signal conditioning and indication of output.
These elements are joined together as shown in figure.
Working:
Sound waves strikes on thin diaphragm
Diaphragm displaces the bellows. ( expansion or compression)
Diaphragm compresses the carbon granules in flexible capsule.
Compression of flexible capsule causes change in resistance and current.
The output voltage change is calibrated in terms of sound pressure.
Advantages:
High output signal
Simple in construction and rugged in design
Simple working principle
Cheap in cost
Simple to manufacture
Tolerates extremely high sound pressure levels
Disadvantages:
High background noise
Poor frequency response
Requires battery or other supply for its operation
Carbon granules get damaged and sometimes fused together
Requires amplifier to amplify the signal to be reproduced at the speaker end
Bandwidth is extremely limited
Applications:
Carbon microphones were initially used in telephones and radio broadcasting.
They are still used in some applications today, such as sound reinforcement systems and public address systems.
