Brief description

A device that converts electrical signals into sound waves. It is the primary means of audible communication and entertainment in the electronic age.

Use / Function

• Primary use: Reproducing audio for human hearing.
• Secondary uses: Public address systems, alarms, acoustic testing.
• Scale: Domestic / Mass communication.

Operating principle

The most common type (the dynamic loudspeaker) works on the principle of Lorentz force.

1. Electrical input: A varying electric current (representing sound) flows through a coil of Wire.
2. Magnetic interaction: This current creates a varying magnetic field around the coil, which interacts with the fixed magnetic field of a permanent Magnet.
3. Mechanical movement: The interaction causes the coil (the voice coil) to move back and forth rapidly.
4. Acoustic output: The coil is attached to a large diaphragm or cone (usually made of Paper). As the coil moves, it vibrates the cone, pushing the air and creating sound waves.

How to create it

Minimum functional version

1. Magnet: A strong permanent Magnet.
2. Voice Coil: A cylinder of lightweight material with many turns of thin insulated Copper Wire.
3. Cone: A stiff but lightweight cone made of Paper or thin plastic.
4. Suspension: A flexible surround (fabric or soft plastic) that holds the cone in place but allows it to move forward and back.
5. Assembly: The voice coil is glued to the center of the cone and positioned so it surrounds (but does not touch) the magnet. The cone is mounted in a Wood or metal frame.

Technical level

Intermediate. Requires precision in aligning the voice coil within the narrow gap of the magnet.

Materials needed

• Essential materials:
  • Magnet: Powerful permanent magnet.
  • Wire: Enameled Copper wire.
  • Cone: Stiff Paper or cardstock.
  • Adhesive: Strong, lightweight Glue.
• Tools:
  • Scissors, soldering iron, alignment shims.

Variants and improvements

• Electrodynamic speaker: Uses an electromagnet instead of a permanent magnet (common before high-strength magnets were affordable).
• Horn Speaker: Uses a flared acoustic horn to increase efficiency (used in early phonographs and public address systems).
• Piezoelectric speaker: Uses crystals that vibrate when electricity is applied; simple but limited frequency range.

Limits and risks

• Efficiency: Most speakers are inefficient, converting only a small fraction of electrical energy into sound; the rest is lost as heat.
• Distortion: If driven with too much power, the cone can deform or the coil can burn out.
• Enclosure: Without a proper box (baffle), the sound waves from the back of the cone cancel out those from the front, resulting in poor bass response.