Brief description

A device that converts sound waves into electrical signals. It is the essential entry point for recording, broadcasting, and telecommunications.

Use / Function

• Primary use: Converting acoustic energy into electrical energy for transmission or recording.
• Secondary uses: Noise measurement, sound-activated triggers.
• Scale: Domestic / Industrial.

Operating principle

Most microphones work by converting the mechanical vibration of a diaphragm into electrical variations.

1. Acoustic input: Sound waves (pressure variations in the air) strike a thin diaphragm.
2. Mechanical vibration: The diaphragm vibrates in sympathy with the sound waves.
3. Transduction:
   • Carbon Microphone: Vibrations compress Charcoal granules, changing their electrical resistance.
   • Dynamic Microphone: The diaphragm moves a coil of Wire within a magnetic field produced by a Magnet, inducing a current (Electromagnetic Induction).
4. Electrical output: The resulting varying current represents the original sound wave.

How to create it

Minimum functional version (Carbon Microphone)

1. Housing: A small non-conductive container.
2. Electrodes: Two Metal plates at opposite ends of the container.
3. Active material: Finely crushed Charcoal (carbon granules) filled between the plates.
4. Diaphragm: A thin, flexible sheet (tightly stretched Paper or thin metal) that presses against one electrode.
5. Circuit: Connect in series with a Battery and a receiver (like an earphone).

Technical level

Intermediate. Requires careful assembly to ensure the granules are packed correctly but still able to move.

Materials needed

• Essential materials:
  • Diaphragm: Thin Metal foil or treated Paper.
  • Conductor: Copper Wire.
  • Magnetic field: Magnet (for dynamic types).
  • Resistive material: Charcoal (for carbon types).
• Tools:
  • Pliers, soldering tools (or secure mechanical connections).

Variants and improvements

• Carbon Microphone: Robust and high output, used in early Telephones, but lower audio quality.
• Dynamic Microphone: Durable and requires no external power; works on the same principle as a Loudspeaker in reverse.
• Condenser Microphone: Uses changes in capacitance; requires a power source but offers very high fidelity.

Limits and risks

• Signal level: The electrical output is very weak and usually requires amplification.
• Fragility: The diaphragm is very thin and can be easily damaged by physical impact or moisture.
• Feedback: If placed near a speaker playing its own output, it can cause a loud, piercing squeal.