How Does Voice Coil Diameter Affect Speaker Sound?

loudspeaker diaphragm assemblies with voice coils

In order to produce sound, loudspeakers use a voice coil. This coiled wire is attached to the cone or diaphragm of the speaker, and when an electric current passes through it, the coil moves back and forth.

The size of the voice coil’s diameter affects how much power a speaker can handle. A larger voice coil can handle more power. In loudspeakers, more power results in more volume.

In this blog post, we will discuss how voice coil diameter affects speaker sound, covering the basics of voice coils, including:

  • What is a voice coil in a speaker?
  • How does a voice coil of a speaker produce different sounds?
  • What is the voice coil diameter?
  • How to measure voice coil size?
  • Is a larger voice coil better?
Copper Wire For Voice Coil Windings

What Is A Voice Coil In A Speaker?

The voice coil in a speaker is a coil of copper wire that is wrapped around a lightweight material such as paper, thin aluminium or kapton.

The lightweight material that is wrapped around is known as the “former” in the loudspeaker industry. Together they are known as the voice coil.

This voice coil component is then attached to the speaker cone or diaphragm.

The voice coil is then positioned into a magnet assembly. When a current is passed through the voice coil (by attaching your external signal), it will move up and down in the magnet assembly.

As the moving voice coil is attached to the speaker cone or diaphragm, it will vibrate, which produces sound.

In essence, the voice coil is the beating heart of a loudspeaker and the fundamental component in the motion, which produces sound.

Here is a great cross-section image, from Simply Speakers, showing the internal construction of a loudspeaker and where the voice coil is positioned.

Photo via Simply Speakers

How Does A Voice Coil Of A Speaker Produce Different Sounds?

To understand how a voice coil of a speaker produces different sounds, it is important to understand how it works.

The voice coil of the speaker does not produce the sound. It is the motion of the voice coil, which is attached to a cone, which produces the sound. As the cone moves, it will move the air in contact with it, which produces the actual sound.

The voice coil is placed into the magnet assembly of the speaker.

When a current is passed through the voice coil (in simple terms, the input signal), the voice coil will vibrate at the same frequency as your input signal.

As this voice coil is attached to the cone, the cone will also vibrate at the frequency of your input signal.

As a result, the cone will vibrate the surrounding air at the frequency of your input signal. This produces the sound you hear.

What Is The Voice Coil Diameter?

Voice coils come in many different sizes.

In guitar speakers for examples, there are some standard sizes for example, 1″, 1.25″, 1.5″, 1.75″ or 2″.

Generally, the voice coil diameter refers to the internal diameter of the coil. In the professional studio industry, this is usually the internal diameter of the former, which is the lightweight material around which the coil is wound.

How To Measure Voice Coil Size?

If the voice coil is not attached to a cone or diaphragm, it is very easy to measure the internal diameter. Simply use a Vernier’s or ruler to measure the internal diameter of the coil.

If the voice coil is in an assembly, this is harder to do and less accurate.

To do this, get a string, and wrap it around the base of the cone, where the voice coil is attached to the cone.

Measure the length of the string needed to wrap around the voice coil. Next, divide this length by 3.14 to calculate the diameter of the voice coil.

Given that other components will be in your way, such as the cone or suspension (also known as the spider), this will not be a perfect measurement, so you will need to account for some discrepancy due to the interference of these components.

As voice coils tend to be of a standard size, you can get an idea of what the voice coil’s internal diameter should be and round to the nearest size.

To double check, look at the specifications from the manufacturer to see if your measured voice coil matches any of their standard voice coil sizes.

Is A Larger Voice Coil Better?

A larger voice coil will result in better power handling, which will result in a louder speaker.

The downside of a larger voice coil, however, is that it will get much hotter. This can be an enormous challenge for loudspeaker manufacturers as if it becomes too hot, it will fail power tests.

As a general rule, large speakers for low frequencies, such as sub-woofers, will have larger coils. For example, a voice coil diameter of 5 inches / 125mm.

These speakers need to be vented and allow lots of air cooling as they will overheat and fail with components degrading and overheating.

In summary, a larger voice coil does not mean a better speaker. It depends on the application of the speaker. Many small voice coil speakers produce great loudness and sound.

A loudspeaker with a moderately sized voice coil that is not too big for your application is the most efficient design.

Final Thoughts

A voice coil is a fundamental component of speaker operation.

The size of the voice coil does not have a great impact on sound quality but affects how loud a speaker will be.

Typically, the larger the voice coil, the louder the speaker as the speaker can handle more power.

The best-sized voice coil is one that suits your application. If you want a loud speaker, then a sub-woofer with a larger voice is a good choice, however if you are interested in audio quality, then comparing speakers on the diameter of their voice coil is not useful.

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