The layman's version
The purpose of SMC is to reduce sound coloration to a level where the music comes alive inside your living room - as if the artist was present. The ultimate goal is to make the sound reproduction so free of distortion that you are not able to tell the difference between a live or recorded performance.
The technical 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 performance standards, and to take the magnet system design further than ever before, with the launch of the EPICON series.
The goal was to reduce colouration 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 which occur when current runs through the voice coil windings, thus generating "competing" flux in the magnet gap.
Furthermore, it eliminates the frequency dependency of the electrical and magnetic properties of iron parts. In fact, SMC offers exactly the right physical properties; very high magnetic conductivity and very low electrical conductivity (approximately 1/10,000 of that of iron), yielding a dramatic reduction in distortion caused by mechanical loss in the magnet system – 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, since 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.
The magnetization and demagnetization, which happens due to the shifting current directions, does not happen at the same time, since the demagnetization process is slower than the magnetization process.
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 occur in most speaker designs. The movement of the voice coil creates small localized magnetic fields alongside the pole piece, which apply an oppositely directed force onto the moving voice coil.
This is a useful effect in things like magnetic brakes used in busses and trains, and for generating heat in induction hot-plates. But neither braking nor heating are welcome in a speaker magnet motor system, since they both cause distortion in the audio signal being reproduced
SMC in DALI loudspeakers
SMC is used to varying degrees in the following DALI speaker series: EPICON, RUBICON and RUBICON C, OPTICON MK2. CALLISTO C, OBERON and OBERON C.
SMC is used in the pole piece as well as in the ring around the crown/cylinder head – in fact, it is incorporated everywhere it will have an audible effect.
The pole piece 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.
The entire pole piece, which is surrounded by a large ferrite magnet, is constructed from SMC. In this way, the material is used in the most important parts of the driver.
SMC is used in the woofer pole-piece (but how much?).
The iron pole piece of the woofer magnet is crowned by an SMC disk - minimizing the negative effects of the iron.