What Is A Loudspeaker Voice Coil? (And how it works)

a speaker voice coil from a compression driver

Speaker voice coils are an integral part of any loudspeaker system, allowing them to produce sound accurately and efficiently. It is important to understand how loudspeaker voice coils work in order to design great loudspeakers.

The basic principle behind a speaker voice coil is that it converts electrical energy into mechanical energy, which then causes the speaker cone (to which it is attached) to vibrate and create sound waves.

The voice coil is wrapped in a cylindrical shape (called a former) and is usually made of aluminium or copper wire.

When electrical energy passes through the wire, it generates an electromagnetic field which interacts with the permanent magnetic field of the speaker magnets. This creates a magnetic force which causes the voice coil to move back and forth.

Since the voice coil is attached to the speaker cone, the speaker cone also moves back and forth, which generates the sound waves which we hear.

In this article, I will explain what a loudspeaker voice coil is and how it works in greater detail, answering the following questions:

  • What is the function of a voice coil?
  • Where is the voice coil situated in a loudspeaker?
  • How does a loudspeaker voice coil work?
  • Do all speakers have voice coils?
  • Does a bigger voice coil mean louder?
  • How do you know if a voice coil is blown?
  • Can a voice coil be replaced?
  • How do you make a voice coil?

What Is The Function Of A Voice Coil?

The function of a voice coil is to convert electrical signals into vibrations which move the speaker cone, creating sound.

When you connect a signal to your loudspeaker, this signal flows through the speaker voice coil, which is attached to the loudspeaker cone, and is suspended in the magnetic field of the loudspeaker magnet system.

The voice coil is simply many windings of thin copper wire, wound around a cylindrical former made from a lightweight material which is connected to the speaker cone.

When an alternating current (AC) signal travels through the copper wire, (this is your input audio signal) it creates a varying magnetic field that interacts with the permanent magnet in the loudspeaker’s motor structure, resulting in vibrations that move the cone and as a result, creates the sound waves we hear.

Where Is The Voice Coil Situated In A Loudspeaker?

The following image shows a cross section view of a typical loudspeaker. The voice coil is generally situated at the centre of the loudspeaker, attached to the speaker cone or diaphragm.

The loudspeaker voice coil must sit in the magnetic field of the loudspeaker permanent magnetic system.

The following image is a closer image of the voice coil as it sits close to the magnets in the loudspeaker.

There is a tiny gap in the magnetic structure of the permanent magnets of a loudspeaker, where magnetic flux is greatest. We call this the “magnet gap” in the speaker design industry, and generally, there is very limited space in this region.

Often, clearances between the loudspeaker voice coil and the surround permanent magnets can be as small as 0.3mm.

It is essential that the voice coil remains centred in this magnetic gap, as otherwise, it will interfere and scrap on the surrounding metalwork. In this instance, you will get a “rub and buzz” sound.

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How Does A Loudspeaker Voice Coil Work?

A loudspeaker voice coil is an essential component of a speaker system that helps to convert electrical signals into sound. It comprises a length of wire, wound in a circular pattern around a cylinder called the former.

Here is an image of what an actual loudspeaker voice coil looks like. This one is used and has had the cone removed, hence it looks dark and worn.

When an electrical current passes through this coil, it creates a magnetic field that interacts with the permanent magnets or motor system of the loudspeaker. This causes the voice coil to move up and down.

As this voice coil is attached to the loudspeaker cone (or diaphragm), as the voice coil moves in the magnetic gap, so does the cone.

This movement of the cone produces sound waves that the listener can hear.

Here is a step-by-step overview of how an input signal moves through a loudspeaker and how the voice coil works to assist in sound production.

  1. Connect your input audio signal (which is an AC signal) to the terminals of the loudspeaker.
  2. The speaker terminals are connected to the speaker voice coil. Your input audio signal flows through the speaker voice coil.
  3. The speaker voice coil is suspended in the magnetic field of the permanent magnet of the loudspeaker motor. When an AC signal flows through the voice coil, it will oscillate up and down at the frequency of the input signal.
  4. The speaker voice coil is glued to the cone of the loudspeaker. As the voice coil moves up and down to the frequency of the input signal, the cone will also move up and down.
  5. The cone moves the surrounding air, which produces sound waves which we hear as sound.

The size of the voice coil, along with the number of windings, all affect how much power it can handle, as well as how loud the speaker will be. [source]

A larger voice coil will typically provide greater power. However, a consequence of creating more power is that the voice coil will create more heat.

For example, large sub-woofers who have very large voice coils produce a lot of heat under intense operation. Trying to keep the voice coil cool can be a real challenge for loudspeaker sub-woofer designers.

To learn more about voice size and how it affects loudspeaker performance, check out this article which covers the topic in much greater detail; How Does Voice Coil Diameter Affect Speaker Sound?

Do All Speakers Have Voice Coils?

The vast majority of speakers have voice coils. However, there are some exceptions, such as the electrostatic and planar magnetic speaker design designs.

These types of speakers create sound using other methods, such as an electrical field or an electromagnetic flux field created between two plates.

Does A Bigger Voice Coil Mean Louder?

A bigger voice coil means a louder sound. The larger the voice coil, the more power it can handle and consequently, the louder the sound it will produce. [source]

This is because a larger voice coil has more windings of wire, which can create a stronger magnetic field, resulting in greater movement of the cone and thus louder sound output.

However, be aware that having a larger voice coil will also generate more heat and so this should be taken into account when designing and constructing loudspeakers.

How Do You Know If A Voice Coil Is Blown?

If a voice coil is blown, you will likely hear signs of distortion in the sound coming from the speaker. You may hear crackling or popping sounds, or even static-like noises.

Additionally, if you measure resistance across the voice coils terminals with an ohmmeter, you should find that the resistance is at zero ohms, which indicates there is a break in one of the windings.

In order to repair it, you will need to replace either just the damaged winding or replace the entire voice coil assembly, depending on how severe and widespread the damage is.

Can A Voice Coil Be Replaced?

Yes, a voice coil can be replaced. Replacing the voice coil is often done when it has been damaged due to too much power being sent to the speaker or if the voice coil has become worn by hitting on the surround metalwork.

As a general rule, the voice coil alone cannot be replaced in typical loudspeakers.

Since the voice coil is glued to the cone and suspension system of the speaker, by removing the voice coil, you will easily tear and damage the cone.

Speaker manufactures typically supply cone repair kits, which include a new voice coil.

This will be a sub-assembly of the voice coil, cone and suspension system of the loudspeaker so you can replace all the soft parts of your loudspeaker in one go, including the voice coil, without risking damage to the softer parts such as the paper cone.

How Do You Make A Voice Coil?

Making a voice coil involves winding a specified length of insulated wire around a bobbin. The bobbin can be made from aluminium or paper and is generally called a former.

The length of the wire depends on the size of the speaker, with larger speakers requiring more wire.

The insulated copper wire is then wound onto the bobbin, ensuring the wire is tightly wound with no gaps or overlaps.

Once all the wire has been wrapped, it needs to be soldered at either end to the speaker terminals so that an electrical connection can be made.

After this process is complete, the voice coil is ready for installation in a speaker and can then be connected via its terminals to the amplifier.

Here is a great video showing the voice coil manufacturing process:

Final Thoughts

In conclusion, voice coils are an integral part of most loudspeakers. They help create the sound we hear from our speakers by creating a strong magnetic field to move the cone and produce loud sound output.

It is important to note that bigger voice coils mean louder sounds but also generate more heat, which needs to be accounted for in speaker design and construction.

Furthermore, it is possible to replace a damaged or worn out voice coil with either just the winding itself or via sub-assembly kits supplied by speaker manufacturers.

Voice coil design is a fundamental aspect of speaker design, with the number of coil turns and voice coil size impacting the performance of the speaker.

To read more about voice coils and how they impact the sound of a loudspeaker, check out this article, How Does Voice Coil Diameter Affect Speaker Sound?

Happy listening!

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