How Is Sound Made In A Speaker? (A simple guide)


a speaker will sound waves emanating from the speaker cone

Speakers are really amazing products. Such simple designs can reproduce some of the world’s greatest music and sounds.

But how is the sound made by a speaker? How do speakers work?

Sound is made when a speaker’s cone oscillates. This cone moves the air in front of the speaker, which produces airwaves, which produce sound. This cone is connected to the input signal, through a voice coil which sits in a magnetic field. 

This may sound very technical at first, but when you break this down, it can be easy to see how an input moves through a speaker, which results in sound.

In this article, I am going to break down the fundamental parts of a speaker, explaining what each part does and how each part works together to create sound.

I will cover:

  • What is inside a speaker?
  • How a speaker works with a simple explanation
  • What part of the speaker produces sound?

What Is Inside A Speaker?

When you look at a speaker, you may just see a round component sitting in a box, but if we break this down, we can see that there is a set list of components in every speaker.

Image via Wikimedia

Here are the components common to all speakers and what they do:

1. The Voice Coil

The voice coil is simply windings of copper wire, which are typically wrapped around a lightweight material such as paper.

It is the movement of the voice coil in the magnetic gap that oscillates, and as a result, moves the cone to make a sound.

2. The Top Plate (Also Called A Front Plate)

This is a piece of metal, (usually steel) that sits on top of the magnet and helps to maintain the magnetic field. 

The design of the top plate can impact the strength of the magnetic field.

3. The Yoke (Also Called A Pole Piece)

This is a piece of metal (usually steel) that sits below the magnet. 

Similar to the top plate, the design of the yoke can impact the strength of the magnetic field.

4. The Magnet

Magnets are fundamental to the operation of a speaker. The magnet is sandwiched between the top plate and the yoke.

When a copper wire coil (the voice coil) is placed into a magnetic field with a current running through it (your input signal) it will oscillate.

It is this oscillation of the voice coil in the magnetic gap which causes the voice coil to move. As the voice coil is connected to the cone, the cone will also move.

5. The Spider (Also Called A Suspension)

A component called a spider is usually attached to the voice coil and cone assembly.

The voice coil cannot oscillate in free space; it needs to be attached to something with a spring effect to hold the voice coil in the magnetic gap. 

The spider is usually made from a woven cloth or plastic, which is strong enough to keep the voice coil in position, but with enough spring effect to allow the voice coil to move.

6. The Cone (Also Called A Diaphragm)

The cone is the most easily identified part of the speaker. It is attached to the voice coil.

As the cone moves, it produces sound by moving the air surrounding the cone. 

7. The Surround

Just like the voice coil, the cone cannot oscillate in free space and needs to be attached to something which holds it in position but allows enough movement to allow the cone to move up and down.

One side of the surround is attached to the edge of the cone and allows it to move.

The other side of the surround is attached to the chassis, also known as the frame. 

8. The Chassis (Also Called The Frame)

This is the metal frame within which all speaker components are mounted and held together. 

We usually glue the surround and suspension to the frame. 

In addition, the magnet, top plate and yoke assembly are screwed into the frame.

The frame holds all these components together to form the speaker structure.

9. The Box (Also Called A Cabinet)

Finally, every speaker needs to be mounted into something for a customer to use. This can be an open or closed box, also called a cabinet in the industry.

How A Speaker Works With A Simple Explanation

So how do all these components come together to produce sound from a speaker?

It can be overwhelming when trying to understand how speakers work. All these components may seem easy to understand in isolation, but knowing how they work together to create sound is key to understanding the fundamental operation of a speaker. 

In order to produce a very simple explanation of how a speaker works, I have described how an input signal moves through a speaker until it reaches a cone and is converted into sound in 5 steps.

Step 1. Connect Your Input Signal

When you play music through a speaker, you are sending an audio signal to the speaker. 

Step 2. The Signal Moves Through The Voice Coil

This audio signal (a current) moves through the voice coil. 

A magnetic field is created when a current moves through a copper wire. This magnetic field interacts with the magnetic field of the speaker magnet, which causes the voice coil to move. 

Step 3. The Voice Coil Oscillates At The Same Frequency As The Input Signal

How much force is created by this voice coil and the magnetic field is calculated in the formula: 

F = B xL

Where:

  • F = force
  • B = magnetic flux
  • L = length of the voice coil in the gap

Step 4. The Voice Coil Moves The Cone

The voice coil is attached to the cone. As the voice coil oscillates, the cone oscillates. 

Step 5. The Cone Moves Air To Make Sound

As the cone moves, it is moving the surrounding air. 

It is this movement of air that creates sound waves, which we hear as sound. 

What Part Of The Speaker Produces Sound?

The voice coil, magnetic field and cone work together to produce sound in a speaker. 

When you connect your input signal to your speaker, the input voltage (current) flows through the voice coil.

The voice coil is just a copper wire, wound multiple times around a cylinder card or lightweight material.

As this voice coil is suspended in the magnetic field of the speaker (by the suspension) it will oscillate.

Any copper wire, with a current running through it, placed in a magnetic field, will start to move. This is the principle on which electric motors work, hence why the magnetic assembly of the speaker is sometimes called the speaker motor within the audio industry.

As the voice coil is attached to the cone, the cone will also move at the same frequency as the voice coil.

As the cone moves, the cone is moving the surrounding air. This creates sound waves, which is the sound you hear.

You could over-simplify the operation of a speaker and state that it is the cone that produces sound. However, it is the combination of the cone, voice coil and magnetic field that produces sound in a speaker. 

Final Thoughts

Understanding how a speaker works can be daunting, but by breaking it down into simple steps, it becomes easier to comprehend.

In this article, we have described the basic operation of a speaker in 5 easy steps, which can be summarised as:

  1. The audio signal goes into the speaker.
  2. The signal moves through the voice coil.
  3. As the voice coil is in the magnetic gap, it oscillates.
  4. As the voice coil is attached to the cone, the cone oscillates.
  5. The cone moves the surrounding air, creating the sound waves you hear.

While it is the cone that moves the air and creates the sound waves, it is the voice coil and magnetic field that are responsible for producing sound in a speaker. Thus, all three components work together to create the sound you hear coming from your speakers.

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We love all things audio, from speaker design, acoustics to digital signal processing. If it makes noise, we are passionate about it.

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