Like in science lessons at school, if a magnet is brought near a coil of wire, it will cause an electric current. Using this electromagnetic principle, dynamic microphones rely on coils of wire and magnets to generate electrical energy which can later be converted into audio signals.
Of course, you still remember the law of conservation of energy, energy cannot be created and destroyed but can only be changed from one energy to another. So, the energy of the sound waves from our mouths or musical instruments is not lost but is transferred to the membrane or diaphragm in the mic capsule.
When this diaphragm vibrates because it responds to incoming sound waves, the coils on the diaphragm will move away and get closer to the magnet quickly, in other words vibrating. It follows the sound waves it receives. This event certainly creates an electric current in the coil and is later transferred to the microphone cable.
In general, the configuration is as in the image below:
Of course, the electricity generated by dynamic microphones is very small, only a few millivolts, known as the mic level signal. This signal needs to be amplified in order to reach a line level signal (0.5 – 2 volts), usually found on pre-amp mixers, audio interfaces, DVD players (if there is a mic input), etc.
After undergoing the pre-amplification process (pre-amp) and becoming a line-level signal, the audio signal is then amplified using a power amplifier to loudspeakers (PA speakers, home speakers, etc.)
As mentioned earlier, loudspeakers have the opposite function of microphones, namely converting electrical energy into sound waves.
The performance of this loudspeaker can be described as the opposite of a dynamic microphone. If you look at the cross-sectional image of the speaker, it is clear that there is a resemblance to the picture above.
The speaker can be used as a microphone and vice versa, the microphone can be used as a speaker, BUT of course the sound will be very bad because its use is not in accordance with the design.
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