“Cause you are a magnet, and I am steel.” – Walter Egan
Magnets play a vital role in hundreds of thousands of devices, ranging from small toys and disk drives, to washing machines, industrial motors, and of course, loudspeakers (and microphones). And chief among magnetic material is the rare-earth composite called neodymium.
It’s more properly known as Nd–Fe-B, for indeed, what we casually call “neo” is really a processed alloy of three elements: neodymium, ferrite, and boron. Neo is highly coveted because it is light, small, and yet can hold higher energy than any other magnetic material known at this time.
We like our loudspeakers to be light – and sometimes we like them to be small – but we also want to pay as little as possible. The progress of neo, from an exotic material adopted by only a handful of loudspeaker driver manufacturers – to a staple that the pro audio industry has come to rely upon, is an interesting story.
The current geo-political challenges of obtaining neo for a reasonable cost, and in the quantities that our industry needs, are what this story is about.
What’s It Really Do?
Magnets are needed in drivers to provide an opposing force for the voice coil to work against. (In this article, the term “driver” applies to both cone- and compression-type devices.) When AC current passes through the voice coil, it produces a magnetic field that’s proportional to the frequency, time constants, and magnitude of the current. If there were no opposing force for the voice coil to work against, it would produce only heat – no sound.
Several types of magnetics have been utilized for acoustic drivers, and also for rotary motors. An acoustic driver is essentially a reciprocal linear motor, as opposed to the familiar rotary one that runs your disk drive, your Leslie speaker, and your Skillsaw.
In the early days, almost all loudspeakers used an electromagnetic field coil instead of a permanent magnet, requiring a high-current DC power supply to energize the coil. Later, permanent magnets made their debut, with ceramic materials being the best that the industry could offer in terms of size, weight and power.
Several grams of pure neodymium. (click to enlarge)
Then came alnico, which quickly moved to the forefront of loudspeaker technology because it could hold a higher magnetic charge, and thus produce greater sound pressure levels. The term alnico is another “amalgamated” word that describes an alloy of aluminum, nickel and cobalt.
Those first two are pretty common, but cobalt is a rare earth element that’s found only in certain geographic locations, mainly the Republic of Congo and Zambia. It’s used in radiology and nuclear weapons, which limits its availability for mundane uses such as loudspeakers.
Moreover, the cobalt mines in Africa became the subject of geo-political issues in the late 1960s – much like neo is today – with the result being an almost complete discontinuation of alnico in loudspeaker products.