Lesson 5: Loudspeakers/ Headphones

Question 1

How do moving coil loudspeakers/ headphones actually work?

Answer 1

1.) As current passes through the coil (wrapped around the cone, the coil generates a magnetic field. )
2.) Magnetic field from coil interacts with magnetic field from magnet.
3.) This interraction produces a resultant force (causing the cone/ coil to move)
4.) When direction of current reverses, the direction of the force on the cone/ coil reverses.
5.) The cone is moved in and out: generating sound waves.

Question 2

What is the set up of a moving coil loudspeaker/ heaphones?

Answer 2

• Cone with coil of wire wrapped around one end.
• The coil of wire is connected to AC (alternating current) supply.
• Permanent magnet goes inside cone that coil of wire is wrapped around.

Question 3

If the AC supply (in a headphone/ loudspeaker) has a frequency of 15Hz, what frequency will the cone vibrate at?

Answer 3

• The cone will vibrate at 15Hz.
• High frequency (of cone’s vibrations / sound waves) = a higher pitch sound
• Low frequency (of cone’s vibrations / sound waves) = a lower pitch sound.

Question 4

What happens if we increase the size of the current on the coil of wire in loudspeaker/ heaphone?

Answer 4

• Increased amplitude of vibration (of the cone/ air particles)
• This increases the volume of the sound.

Question 5

What do loudspeakers/ headphones do?

Answer 5

• Use the motor effect to convert variations in current in electrical circuits to the pressure variations in sound waves.