3.18 Loudspeakers & Microphones

Question 1

What does a loudspeaker contain?

Answer 1

A loudspeaker consists of a coil of wire which is wrapped around one pole of a permanent magnet and connected to a cone. The coil of wire is permanently attached to the cone, but the coil and cone can slide back and fourth along the magnet.

Question 2

How do loudspeakers work? (6)

Answer 2

• An alternating current flows through the wire and creates a magnetic field (electromagnetism) in the coil.
• The magnetic field of the coil interacts with the magnetic field of the permanent magnet.
• The interacting magnetic fields will exert a force on the coil (motor effect), causing it to move back or forth along the permanent magnet.
• This causes the cone to change shape.
• As the current is alternating, its magnetic field and the force it experiences will also alternate. This means that the coil of wire and cone rapidly move back and forth, meaning they vibrate.
• These vibrations are so fast that the cone vibrations cause pressure variations in the air - which are sound waves

Question 3

How do microphones work? (5)

Answer 3

• Microphones are basically loudspeakers in reverse.
• Sound waves hit a flexible diaphragm that’s attached to a coil of wire, wrapped around one pole of a magnet.
• This causes the diaphragm and coil of wire to move.
• As the wire is moving within the magnetic field of the permanent magnet, it will generate a current (electromagnetic induction / generator effect).
• The frequency and amplitude of the sound waves will determine how much the diaphragm vibrates, and therefore determine the frequency and amplitude of the current.

Question 4

What is the function of a loudspeaker?

Answer 4

Loudspeakers take electrical signals and use the motor effect to convert them into vibrations, which then generate sound waves.

Question 5

What is the function of a microphone?

Answer 5

Microphones detect vibrations caused by sound waves and use the generator effect to convert them into electrical signals.

Question 6

For both microphones and loudspeakers, what type of current are the electrical signals?

Answer 6

Alternating currents/Alternating voltage.

Question 7

Do loudspeakers rely on the generator effect (electromagnetic induction), or the motor effect?

Answer 7

Motor effect