Question

On which principle does a moving coil microphone work?

Hint:

Dynamic microphones are highly favored for live stage performances because they are exceptionally rugged, require no external power (phantom power), and can handle very high sound pressure levels (SPL) without distorting.

Answer 1

Step 1: Identifying the Core Principle:
A moving coil microphone (commonly called a dynamic microphone) operates on the principle of Electromagnetic Induction, as described by Faraday's Law.

Step 2: Working Mechanism:

• Acoustic Coupling: Incoming sound waves hit a lightweight, flexible diaphragm, causing it to vibrate back and forth in response to the sound pressure.
• Voice Coil Movement: A small, light coil of copper wire (the voice coil) is glued to the rear of the diaphragm and suspended within a concentrated magnetic field created by a permanent magnet.
• Induction of EMF: As the diaphragm vibrates, it moves the voice coil back and forth through the magnetic field lines. This changes the magnetic flux linkage, inducing an electromotive force (emf) across the coil terminals: $$e = -N \frac{d\Phi}{dt}$$

This induced voltage is a precise electrical copy of the acoustic sound wave.