Microphones

Any device that converts one form of energy into another is called a transducer.  A microphone is a transducer and so does a loud speaker.

According to the theory of electro-magnetic induction, a metal suspended in a flux field of magnet will produce a current of certain direction and magnitude within the metal.

The most commonly microphone used is dynamic microphone.  They are extremelyt durable and less expensive.  They are commonly used in live performance and concerts.  The mic is constructed based on a diaphragm connected to a coil of metal floating in the flux planes of a magnet.  When the diaphargm vibrates to the sound pressure, the coil moves and sending an electrical current through the coil connected to an output line.

Dynamic mic contains rather heavy magnets which makes it durable.  However, weight of component also limits its frequency response.  High frequencies require a diaphragm to move very quickly but the response of the heavy component is slower, thus antenuattimng higher frequencies.

Condenser mic, on the other hand, is not based on magnetic but can generate a voltage.  The voltage however has no power behind it.  The design is based on the movement of electrons and the open-air capacitor.  Behind the diaphragm, there is a conductive back plane separated by a small pocket of air.  This forms a capacitor.  A current is sending through the plane.  When the diaphragm vibrate, closing up and opening up the gap between the diaphragm and the plane, it varies the amount of current through, thus generating a signal.  Condensor mic requires an external power source, known as phantom power (48 volts).  The power can be supplied by battery.  Condenser mic is delicate and can be damaged when falls.

Ribbon mic are least used but in radio broadcast.  It uses same principle as the dynamic mic, wherein a thin ribbon of corrugated aluminium is located between 2 strong magnets.  It generate a current but typically not strong enough.  Instead of using phantom power, ribbon mic contains a built-in transformer to boost the level up.  It is like a mic with a signla booster (pre-amp) built in.  Ribbon mic are famous to have a warm sound, which lends well with voice.  The microphone is fragile and heavy.  They are also very expensive.