How Do Microphones Work?

Podcast Link

http://techstory.libsyn.com/microphones-and-how-they-work-ep-04

History

  • The mic was invented by multiple inventors working independently.1
  • Thomas Edison found in 1878 that carbon connected to a circuit would change resistance when vibrated by sound waves.1
  • Most notably, Alexander Graham Bell use a magnet and a diaphragm that was sensitive to sound waves and would vibrate.1
    • The magnet created a current in a coil via induction.1
  •  All these innovations were intended for telephone, not amplification.1
  • The inventions of what is called a condenser microphone and the vacuum tube made effective radio broadcasting and the amplification of public performances possible.2
  • In 1929 and 1930 NBC used parabolic dishes with their microphones to create directional recording techniques.2
    • “Paved the way for shotgun mics”2

How it Works

  • Dynamic
    • Dynamic mics use a magnet with a wire coiled around it. When a diaphragm is vibrated with sound waves, it moves the coil along the magnet creating a current in the coil wires as an audio signal.3
    • Described as cold sounding, but very durable and not as sensitive as other mics.
  • Condenser
    • Condenser microphones use two plates. The plate that faces the sound waves acts as a diaphragm.4
    • The system is loaded with 48V of what is called phantom power.4
    • When the diaphragm vibrates the modulation between the plates sends the audio signal in the form of the signal modulation down the wires connecting the plates.4
  • Ribbon
    • Ribbon microphones are highly sensitive mics that use a similar tech as dynamic mics.5
    • In the case of a ribbon mic there is a thin ribbon that both acts as a diaphragm and is also a part of the circuit, such as the coiled wire in a standard dynamic mic. The magnet is in the shape of a U and the ribbon modulates between the U shape to create the audio signal.5
    • They are extremely sensitive (storing on the side, wind, or any kind of voltage spike can break them.5

Uses

  • Most mobile phones and small electronics have traditionally used an electret microphone which is a “condensed” condenser microphone.6 
  • The new kid on the block is the MEMS microphone.
    • MEMS mics use the same principle as the electret condenser mic but on a much smaller scale.7 
    • Used for smaller electronic applications.
  • Company called ReSpeak makes a Raspberry Pi unit with four speakers so that people can mess with voice applications such as the Amazon Echo.7
  • Noise Canceling applications.

Future

  • Internet of Things.
  • Wireless and smaller mics/earbuds.
  • As wearable tech becomes more useful, better mics will become important, as well as the software that can filter the signals and improve voice recognition and clarity.

 

References

History

Types

Uses

Future

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