Not too long ago, something happened that was really quite remarkable and it sort of crept into our lives without most of us taking much notice. The magnets in our lives became 10 times stronger than what we had been used to before.
Although they are called Neodymium magnets, Neodymium (Ne) is only one element of the alloy used in magnets. The other parts are Iron, and Boron, together forming a tetragonal structure. In 1983, two teams, one headed by Dr. Masato Sagawa of Sumitomo Special Metals, and the other by Dr. John Croat of General Motors, invented NdFeB rare earth permanent magnets independently.
I only first took note of this attractive revolution about four years ago. I saw a video on YouTube about little highly magnetic balls that were sold as toys and would let the user assemble them into crystal-like structures such as cubes, triangles, and pyramids but could also be formed into more intricate shapes like dodecahedra, soccer balls formed from hexagons, and pentagons.
I knew immediately that I wanted some and bought nearly a thousand of these fantastic balls for fewer than 100 dollars. My kids have been mesmerized ever since, as have been I.
What I saw was the advent of what are known as Neodymium rare earth magnets, but what I didn´t know was that they were soon to enter my professional life as a loudspeaker manufacturer.
As shown by the good people of MagnetGuys, these magnets are incredibly useful to make stuff break:
But they do also find far more constructive uses: Now Neodymium magnets are all around us: In hospital MRI machines, headphones, in highly efficient electric motors, in toys, and surprisingly, in highly efficient air-conditioner units. These magnets, you see, are so strong that they will reduce the temperature in any magnetic material that is first exposed and then removed from their magnetic field by reducing the oscillations of molecules temporarily. By creating a rotating contraption that approaches and then moves away from a magnetic material from a Neodymium magnet, a cooling effect is created, apparently due to several laws of thermodynamics. And of course these magnets have found their way into professional and high-end loudspeakers.
Neodymium magnets are the strongest magnetic material known to man. How strong? Well dangerously so. Two magnets the size of an apple placed 2 feet away will chase towards each other and impact enough to have sparks fly. Put your hand in between and your orthopedic surgeon will explain that that’s what caused you to not have one anymore.
The following video shows this very graphically and I applaud Mr. Magnet Expert for his commitment to our learning. Do not watch if you are even mildly queasy:
The reason for this eerily strong magnetism lies in the molecular layer of the material. Neodymium, Iron, and Boron form a complex tetragonal crystal that has some rather lovely high value of… Hold your breath… uniaxial magneto crystalline anisotropy. For those of us who are new to this speech impediment provoking concept, what this means is that while normal permanent magnets align the electron spin of an electron in any direction that they are magnetized in, NdFeB magnets only have one direction that the electrons can be aligned in. They do that rather willingly however, leading to a very high percentage of electrons being permanently aligned versus only a few in ferrite magnets.
When it comes to loudspeaker manufacturing Neodymium magnets have a clear advantage. Just before the turn of this century, speaker manufacturers started seriously evaluating the potential benefits of using Neodymium magnets in loudspeakers. Although Neodymium magnets are expensive, the advantages are very tangible. They can do 10 times more for the weight. The immediate benefit is in portable devices like headphones or all-in-one speakers. That advantage for us high-end loudspeaker manufacturer is rather small. A harmonious relationship with our local UPS delivery guy, perhaps might be all. We actually intentionally add weight to our speakers by using a heavyset cast iron base to provide a low center of gravity and additional stability against tipping over. Weight in a speaker also helps with reducing vibrations and keeping it solidly coupled to the ground. With that being said, we are obviously not in it for the lightweight quality of the driver's magnet.
Some loudspeaker manufacturers sometimes claim that the use of the exotic material reduces the moving mass of the driver and thus leads to better dynamics, clearer high notes, and less distortion. In a conventional driver, however, the moving part is the voice coil not the magnet. Good voice coils are always designed with extreme attention to low weight and they don’t usually have a magnet.
So, if the reduction of moving mass is not accomplished with the introduction of this valuable material, what other purpose would it serve? The answer here lies in the fact that the extremely high magnetic flux level in the driver's magnetic gap increases efficiency to where even a small full range driver can reproduce music at a rather high SPL level. The material also vastly helps with reducing distortion and since the magnet stores a lot more energy, the dynamics are vastly improved.
While these attributes are not as vital for drivers that are designed to operate in a narrow frequency band, Neodymium is outright heaven sent for those of us who believe that the sound of a full range speaker is a unique experience. By eliminating all acoustic lobing, comb pattern filtering, crossover issues and membrane colorations they simply provide a very unique and astonishing listening experience. Add the punchy bass from a high-powered magnet in a quarter wave design and one can build a pretty great sounding sound system without much money. We at KVART & BØLGE would not know how to do what to without NdFeB.
Arved Deecke is founder of the Danish / Mexican Loudspeaker company KVART & BØLGE that makes audiophile quarter wave loudspeakers and sound systems at a price anyone can afford. In his free time he blogs about all things related to sound, music and audio.
