Speaker Voice Coils - Kapton vs. Nomex Formers

Written by: Kenny Prochazka

In a world full of guitar speakers, there are a vast amount of different specifications and preferences that give each model a voice of its own. One can spend years combing through what each difference does to your sound, and multiple companies have been born through this exact process. Rather than overly confusing things, we will start by focusing on specific parts of speakers, how they work and how they were developed, beginning with voice coil formers.

What is a voice coil former?

A speaker is a cone of stiff, lightweight material, held by a frame and backed by a (typically) hollowed-out magnet. In that hollow rests the voice coil, which is an actual coil of wire wrapped around a stiff but lightweight tube (or former). That former is attached to the cone, which amplifies the vibrations of the voice coil as it moves, to create the sound that we ultimately hear.

What are voice coil formers made of?

Original voice coil formers were made of stiff paper, which was favored for its acoustic qualities, but there was one major drawback. You see, paper is known for burning relatively easily, and the voice coil in a single guitar speaker can be driven to vibrate from about 70 to 60,000 times per second. You really could burn out your speakers if you rocked too hard!

In the 1960's, DuPont invented the polyimide Kapton, which is a much better material for tolerating heat and stress, and speaker companies had found their solution to burning voice coils. The main drawback presented by some listeners was that Kapton is a bit heavier than paper, which leads to a perceived stiffness and darkness in the tone. However, Kapton's stability quickly made it the go-to for voice-coils into our modern day.

Developed around the same time as Kapton, and often used in combination, DuPont also introduced an aramid fiber called Nomex. Nomex is a flame-resistant fiber very similar in weight and stiffness to paper, and can bond more easily with the cones of speakers than Kapton, so it can reproduce some vintage brightness and openness that tends to elude the more plastic material.

What are Mojotone voice coil formers made of?

Because much of our focus is on vintage reproductions of amps and pickups from an era when paper voice coils were the only game in town, many of our speakers have followed suit. Our Anthem series and most of our British Vintage series of speakers are built with Nomex voice coils to help replicate those vintage tones that we found largely missing from the options available to us. This is one of many reasons that both series' have quickly become favorites of players around the world.

On the other hand, our British Vintage BV-30V and Greyhound speakers are rated for higher wattage, so we have employed Kapton formers in those for its increased power handling. Once you are pushing 60-70 watts through the speaker, a few grams of weight become less of an issue, and Kapton is the more durable option.

Which one should I choose?

The answer to this question is very personal, and depends on your amp, your playing style, and your desired tone. For higher wattage applications, Kapton is a more stable, if stiffer option. For vintage openness and a bit more touch-sensitivity, Nomex usually offers more than enough durability.

In any case, hopefully you now understand more about the differences between Kapton and Nomex, and how each material affects a speaker. Now it is up to you to find your voice and love your sound.