Microphone & loudspeaker

• Transducer


  A device that changes one energy type into another
• Microphone


  Transfers sound energy into electricity
• Loudspeaker


  Transfers electricity into sound
• Loudspeaker

  • Annular permanent magnet
  • Cardboard cone diaphragm
  • Tube with wire coil wound around it (solenoid)
  • Coil fits snugly into circular cavity of magnet
• How a loudspeaker works

  1. Motor effect: Current flows in solenoid, magnetic field interacts with permanent magnet, solenoid and diaphragm pushed out or pulled in, creates compression wave that spreads out as longitudinal sound wave

  2. Output frequency matches input AC signal

  3. Loudness depends on magnitude of voltage signal
• How a microphone works

  1. Incoming sound wave causes membrane to move, solenoid moves to and fro over magnet, generates small electrical current in wire coil by electromagnetic induction (generator effect)

  2. Output frequency matches incoming sound signal

  3. Output signal is usually very weak and needs amplifying