Neodymium - The Perfect Storm...
Neodymium magnets (also known as NdFeB, NIB, or Neo magnets) are a stupendous alloy of neodymium (Nd), iron (Fe) and boron (B), delivering a huge increase in force over ferrite, samarium cobalt, and the combination of aluminum (Al), nickel (Ni), and cobalt (Co) — more commonly known as Alnico. Neo magnetics have enabled lighter headphones, more compact compression drivers that can more tightly be arrayed, portable DJ speakers that do not cause hernias, and ribbon speakers with an extended and smoother response.
Developed independently but simultaneously by Sumitomo and GM (Magnequench) in the early 1980s, and first appearing in an Electro-Voice compression driver soon after, early neodymium had its issues from corrosion to loss of characteristics when the speaker heated, up to legal issues with non-licensed Chinese vendors. But in the 1990s, performance improved and it seems that as the process was refined, it was the impurities that were one of the main sources of corrosion so mGO (the magnetic strength measured in megaGauss Oersteds) went up along with the long-term stability of the magnets. Neodymium became even more enticing as pricing dropped as many Chinese vendors entered the supply chain.
Alnico vs. Ferrite
Back in the 1950s and the 1960s, magnets made of Alnico were commonly used in loudspeakers. However, a shortage in materials and increased costs for Alnico in the early 1970s precipitated a shift to the widespread use of the ceramic (Ferrite) magnets. Specifically, it was the political and the military conflict at the cobalt mines, which were in the control of the “insurgent forces” in central Africa in the Congo (Zaire during that period) that drove prices up and supply stability down.
I remember a “mercenary surcharge” on Alnico, which was often levied just to get the stuff to the port. By the way, today, cobalt is again nearing supply limits (see Figure 1). While more widely available, the ceramic (Ferrite) magnets were quite a compromise, often deprecatingly called “mud magnets,” requiring huge magnetic structures just to come close to the sound that was more elegantly achieved by Alnico. In the 1990s, most speaker manufacturers started seriously evaluating the potential benefits of using neodymium magnets in loudspeakers.
Although neodymium magnets themselves were more expensive, they allowed loudspeaker motors to be as little as half the weight of comparable ceramic magnet motors, and the cost of the steel magnetic return structure offset some of the bill of materials (BOM) cost.
Sources of Neodymium
Yet, today's transducer designers think long and hard before going with a neodymium design because, back in 2011, price fixing resulted in skyrocketing magnet costs. The dynamics were more complex than just “price fixing,” rather it was some composite of differing forces ranging from a decision by the World Trade Organization against China on neodymium exports, health, and environmental concerns on rare earth mining, and conservation of resources. The bottom line was that the Chinese government decided to limit and control pricing on neodymium magnet exports (while keeping neodymium pricing down for domestic consumption).
This article was originally published in The Audio Voice newsletter of August 23 and 30, 2018. An extended version, also divided in two parts, was later published in Voice Coil magazine in November and December 2018.
