When I first started working as an engineer in the loudspeaker industry, the term “speaker motor” really confused me. It is a term often used by speaker designers, but what does it mean and is there actually motors in speakers?
Speaker engineers or those working within the audio industry will refer to the large magnet and metal assembly attached to the back of the speaker as “the motor” since the operation of this part of the speaker is the same as a regular electric motor.
An electric motor comprises two key parts – an electromagnetic coil (or voice coil) and a permanent magnet. Since speakers use these components to create motion, they form the basis of a motor system.
“Speaker Motor” is a term used to describe the metalwork of a speaker within which a voice coil oscillates in a magnetic field. Since these parts of the speaker operate just like an electric motor, they are called the speaker motor.
In this article, I will clarify what parts of the speaker make up the speaker motor and how it operates, covering:
- Does a speaker have a motor?
- How does a speaker motor work?
Does A Speaker Have A Motor?
You might be familiar with electric motors, such as those used to power golf caddies, caravan movers or pneumatic cleaners.
These electric motors work by converting electrical energy into mechanical motion.
A permanent magnet is used to create a magnetic field, which interacts with a current-carrying copper coil mounted in the centre of the motor.
When an alternating current flows through the copper coil, the electromagnetic field generated opposes or enhances the magnetic field created by the magnet. This causes a force to be applied on the coil, resulting in a rotation motion. This motion can then be transferred to a drive shaft to create a circular motion.
A speaker operates on the same principle. However, instead of the motion being circular (like in a motor used to drive a golf caddy), the motion is linear, which causes the cone to move up and down in the speaker.
As the components of a speaker operate just like an electric motor, it makes sense that we refer to the speakers to as “speaker motors”.
How Does A Speaker Motor Work?
When audio engineers mention speaker motors, they are referring to the components contained within the metalwork of the speaker, as shown in the following image. The components that make up the speaker motor are:
- The front plate
- The back plate
- The magnet
- The voice coil.
Like a regular electric motor, a speaker motor converts an electric signal into mechanical energy.
Inside the speaker, there is a coil of copper wire called a voice coil. When an electric current passes through this coil (your AC input signal), the current in the coil interacts with the permanent magnet to create a force that pushes or pulls the voice coil back and forth.
The voice coil will move up and down within the speaker’s magnetic field, as the AC current flows through the coil.
This moving voice coil is attached to the speaker cone. Therefore, as the voice coil moves up and down in the magnetic gap of the speaker, the cone also moves.
The motion of the cone causes the surrounding air molecules to move, which produces sound waves which then reach our ears which we can hear.
Final Thoughts
In conclusion, speaker motors are an important part of speaker design. They comprise a voice coil attached to the cone, which is located in the magnetic gap between two steel plates.
When an alternating current passes through this coil, it interacts with a permanent magnet of the speaker, causing the cone to move up and down, producing sound waves.
Speaker motors are part of the speaker that creates motion, allowing us to recreate audio as they convert electrical energy into mechanical motion for us to hear sounds more clearly and loudly.