Motors

The voice coil is a tiny copper or aluminum cylinder buried inside your speaker, and almost every aspect of how a driver sounds traces back to choices made about it.

Most of us, when we talk about a speaker, talk about the cone. The cone is what we see. We argue about cone material — paper, polypropylene, aluminum, beryllium, ceramic — and assume it's where the action lives. The cone matters, but it's a passenger. The thing actually doing the work, the thing that converts electrical signal into mechanical motion—the motor—is a small cylinder of wire wound around a former and suspended in the gap of a magnet at the back of the driver. That's the voice coil. Everything else in the speaker is a consequence of what the coil decides to do.

The decisions a designer makes about the voice coil ripple through every aspect of how the speaker sounds. Wire material matters — copper has high conductivity but is dense, aluminum is lighter but less conductive, and some designers use combinations to balance the two. The length of the coil relative to the magnet gap determines how linearly the driver moves at high excursion, which is what you hear as bass control or the lack of it. The mass of the coil shapes the speaker's transient response. The thermal capacity dictates how much power the driver can handle before the wire literally heats up enough to change resistance, which makes the speaker sound progressively duller as it warms up.

There's another thing the voice coil does that most explanations skip. As it moves through the magnet's field, its inductance changes — sometimes by a factor of two or more between rest and full excursion. That changing inductance is a moving load the amplifier sees. Some amplifier designs handle that gracefully and some don't—and we refer to this as damping factor in an amplifier.

We listen to cones.

The coils are what we're really hearing.