Moving Iron Speaker

A moving iron speaker, also known as a moving-coil loudspeaker, is one of the earliest types of speakers. It is an essential part of small size speakers due to their size and low-cost. Its design involves a ferrous-metal diaphragm, a permanent magnet, and an insulated wire.

The Moving Iron Speaker: Mechanics

The coil usually wraps around the permanent magnet, which creates a solenoid. This coil, or voice coil, inhabits inside a uniform magnetic field. For this reason, when an audio current runs through it, there is an interaction between the current and the magnetic field. As a result, a force operating on a moveable coil emerges. This force is directly proportional to the audio current so it generates a vibration in the coil. In turn, this vibration creates movement in the conical paper diaphragm as well as in the air. With these mechanics in progress, sound waves emerge.

Moving Iron Speaker: Types

Moving iron speakers can be classified in old undamped and modern damped . On the one hand, old undamped moving iron speakers have a unique sound—but a terrible sound quality. On the other, modern damped moving iron speakers provide an excellent sound quality. 

In addition to this classification, we can also consider the moving iron coil loudspeaker. This device involves a voice coil twisted around a cardboard or fibre cylinder, which receives an audio current through its terminals. The coil is located within a magnetic field and has a pot-type permanent magnet with a central pole and a peripheral one. Its structure includes a high-grade magnetic material that preserves the magnetism’s perfect conditions. This high-grade magnetic material is commonly alnico, a mixture of aluminium, nickel, cobalt, copper, and iron. Incredibly, this magnet is so precise that it creates a strong magnetic field between both poles within the annular space.

The voice coil, also known as a permanent magnet type speaker, moves constantly through the annular space. The coil is tied to a paper conical diaphragm known simply as a paper cone. It has circular corrugations, as well as a flexible strip made of rubber. This cone also includes spider strings that support the diaphragm and makes it motion resistant. In turn, the spider strings keep the coil centered. When you apply electromagnetic induction, the coil can move steadily within the magnetic field.


As you can see from this entry, the moving iron speaker is not particularly practical in today’s context. For this reason, we invite you to read our entries on digital, electrodynamic, full-range, mid-range, woofer, subwoofer, tweeter, and coaxial speakers. Amongst these options you can find one that’s a perfect fit for you.