The tech savvy version
The drivers in a DALI loudspeaker are developed in-house. And for years, designing magnet systems has been a DALI specialty. So it was natural for us to challenge the highest market standards and to take the magnet system design further than ever before with the launch of the EPICON series.
The goal was to reduce coloration of the reproduced sound. The result was the Advanced Soft Magnetic Compound magnet, also known as SMC – a coated magnet granule that can be shaped into any form needed. SMC is a material with many advantages. It eliminates the modulations of the flux in the magnet gap when current, which is running through the voice coil windings, generates new “competing” flux in the magnet gap.
Furthermore, it eliminates the frequency dependency of the electrical and magnetic properties of irons parts. Actually, SMC offers exactly the right physical properties; very high magnetic conductivity and very low electrical conductivity (approximately 1/10,000’s iron), which gives a dramatic reduction in the unwanted distortion caused by mechanical loss in the magnet system – a reduction dramatic enough that it is clearly measurable and indeed audible.
When using an iron based magnet in loudspeakers, it is not unusual to experience a phenomenon called hysteresis, which is a well-known problem in almost all speaker magnet systems. The magnetization and demagnetization, which happens by the shifting current directions, does not happen at the same time as the demagnetization process is slower than the magnetization process. It occurs because iron is not only magnetically conductive but also very electrically conductive.
The problem with hysteresis is that it introduces an unintended resistance to the voice coil, meaning unwanted distortion. This is dramatically minimized when using the very highly magnetically conductive SMC.
In a traditional iron magnet system, the current in the voice coil will modulate a flux in the magnet gap. This flux modulation is a course of distortion, and creates a far from ideal working environment for the voice coil. This modulation of the magnetic flux happens because the iron is electrically conductive.
By introducing SMC into the area close to the magnet gap, this modulation is significantly less influenced by the current in the voice coil. As a result we are able to reduce the distortion from current generated flux variations greatly.
Eddy currents are an issue that occurs in most speaker designs. The movement of the voice coil creates small localized magnetic fields alongside the pole piece. And the nature of these local magnetic fields is that they apply an opposite directed force onto the moving voice coil.
Eddy current is for example used in induction hot plates as it is a very quick and energy efficient way to generate heat. In trains and busses they are very effective breaks. Breaking as well as heat are elements, which are not welcome in a speaker magnet motor system. They both cause distortion in the audio signal that is being reproduced, which of course is unwanted in a speaker magnet motor system.
By using SMC for the pole piece, eddy currents are greatly minimized and removed a very important distortion factor in the magnet motor system. What happens is that the non-electrical conductivity of the Soft Magnetic Compound ensures that only a few local eddy currents build on the surface of the pole piece. This minimizes the heat and resistance in the woofers, which is normally caused by these fields.
SMC in DALI loudspeakers
In the OPTICON series, the entire pole piece, which is surrounded by a large ferrite magnet, is constructed by the Soft Magnetic Compound. That way the SMC material is used in the most important parts of the driver.
The RUBICON speakers, on the other hand, have a pole piece, which is constructed entirely from SMC, and which is surrounded by a copper cap and enclosed within a large ferrite magnet. This maximizes the effect of the SMC, while keeping the design of the magnet motor system fairly simple.
In the loudspeakers of the EPICON series, the Soft Magnetic Compound is used in the pole piece as well as in the ring around the crown/cylinder head – actually it is incorporated in all the parts where it will have an effect.