What is SMC driver magnet material?

Debuting in 2012 with our acclaimed EPICON series, SMC (Soft Magnetic Composite) is a coated, magnetic, granular material that offers a highly unusual combination of very high magnetic permeability and very low electrical conductivity. 

Being a granular composite, SMC can be formed into almost any shape, including components used in the driver magnet system of many of our speakers.

SMC removes a lot of the common braking effects that iron introduces to the free movement of the voice-coil – effects such as hysteresis, eddy currents, and frequency nonlinearity, which result in unwanted distortion and colouration of the sound you hear. 

The ultimate goal of SMC technology is to make the reproduction of sound so free of distortion that you aren't able to tell the difference between a live or recorded performance. 

Hysteresis

Hysteresis is a characteristic of many materials that result in different behaviour when it reverses the direction of an action. A spring, for example, may be stiffer in compression than in extension. In a speaker driver magnet system, a magnet may take longer to de-magnetise than magnetise, which leads to significant distortion.

With an iron driver magnet system, the problem is that the behaviour changes as the frequency changes – it's this nonlinearity that causes uneven harmonic distortion. If iron behaved the same, regardless of the frequency, there would be much less of a problem. 

Eddy currents

Eddy currents form in the nearby electrically conductive materials surrounding the magnet gap and magnetic fields created by the voice-coil.

With an iron pole piece (the part that sits closest to the voice-coil), eddy currents (or opposing magnetic fields) are generated in the iron, causing a braking effect on the voice-coil.

The eddy currents 'steal' the energy from the voice-coil's magnetic field, which would otherwise have been used to move the voice-coil.

The impressive thing about SMC material is that it doesn't suffer from hysteresis or generate eddy currents, since it's non-electrically conductive and also completely linear – no matter the frequency or volume level.

Frequency and Inductance Linearity

In practice, the magnetically conductive material inside, or close to, the voice-coil will influence its self-inductance. Although this happens irrespective of whether iron or SMC is used, the transparency to the flux lines is very different between the two materials. Unlike iron, SMC behaves uniformly, regardless of frequency, which greatly lowers distortion in the magnet system.

In a loudspeaker where the same current is running through the voice-coil and filter components, SMC's properties mean the voice-coil's self-inductance is unchanged with frequency. This helps the crossover to operate freely across the entire frequency range.

The illustration below shows how flux density remains unchanged with frequency, which greatly reduces unwanted odd-order harmonics in the driver.

SMC's combination of very high magnetic conductivity and very low electrical conductivity (approximately 1/10,000th of iron) results in a dramatic reduction in measurable and audible distortion caused by mechanical loss in the magnet system.

Other uses for SMC Gen-2

Because of its magnetic yet non-conducting properties, we also incorporate SMC Gen-2 material into one of our high-end crossover components.

Called the SMC-KORE inductor, this advanced component improves over standard air-core inductors (especially at high inductances) by lowering DC resistance, shortening signal path, and reducing vulnerability to crosstalk between inductors.

It also reduces crossover distortion significantly, compared to standard iron-core inductors. 

DALI speakers with SMC

What was once reserved for our high-end EPICON series, today SMC and SMC Gen-2 technology is incorporated into many of our loudspeaker series, from OBERON and OPTICON MK 2 to EPIKORE 11 and our flagship DALI KORE speaker. We've even integrated SMC technology into our luxury DALI IO-12 headphones. 

To find out more about SMC and some of our other advanced technologies, download the white paper from the DALI KORE product page.