Speaker Materials 101: Voice Coils [Video]

If you’ve ever taken the grille or cover off of a speaker while it’s playing you’ve seen the diaphragm moving up and down producing the sound you hear. But to see what’s causing that motion you have to dig a little deeper–to the very heart of the speaker–the voice coil. In this video, MISCO’s own Dan Digre explains how the voice coil works, what it’s made of, and how that can impact the tonal quality of the speaker you purchase.

How the Voice Coil Works

When you look at a voice coil, you’ll see a thin strand of wire wrapped around a tube or the former. When electricity is sent through the coil wire, it turns into an electromagnet. How that electromagnet interacts with the permanent magnet attached to the speaker is what causes the speaker to create sound. 

This is a feature of alternating current electricity (a/c). The a/c going into the voice coil changes the polarity of the electromagnet which interacts with the magnetic field of the permanent magnets causing electrical energy to convert into mechanical energy.  That mechanical energy (or motion) pushes the cone making the sound. 

What Materials The Voice Coil is Made Of

A voice coil can be made out of a lot of different materials, although it's typically a copper wire that's wrapped on some type of form material like aluminum, Kapton, or even fiberglass. Which materials you choose is important because it helps the voice coil dissipate heat. 

The voice coil in a loudspeaker only uses about three to five percent of the energy put into it to make sound. The rest of the energy turns into heat.  Said another way: if you put a hundred watts of power into a loudspeaker, you'll get out approximately three to five acoustical watts. The rest of that energy is turned into heat, which means the voice coil is going to get very hot during normal operation.

Other Material Options

While copper wire is the most common type of wire used in voice coils, other types of wires can be considered. One common reason to consider a different type of wire is weight. For instance, copper-clad aluminum wire is lighter and will add less mass if sound pressure sensitivity is a consideration within your application. 

The material technology of the form, the wire, and the adhesives that bind it all together, are all critical elements in making a voice coil that is durable and allows the speaker to perform the way you want it to.