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Listening the argument of the field-coil’s people I note that they constantly stress the demagnetization subject of the driver’s magnet, advocating that with electromagnet “the field coil will always produce the same strength now and 100 years in the future.” It is true but let to see how important it is. The myth of demagnetization was born from the fact that all compression drivers derive from professional sound application where max sound pressure is the key  and where the channel are driven by powerful, mostly SS, mostly PP direct-coupled amplification. Yes, in those cases the Alnico magnets are vulnerable for demagnetization and you might find a lot of used partially demagnetized compression driver from movie theaters and sound reinforcement fields. However, how “dangers” the demagnetization fear in the really of home use.

First of all the contemporary rare-earth magnets do not care (care much-much less) about demagnetization. Even of the old Alnico-based magnets are use then it is also I feel is not big deal. The home used compression drivers do not exposed to heat or to shaking – something that demagnetizes drivers very aggressively in pro outside use. The home compression driven by low power SET amps with output transformer- so, there is not DC component in there and the voltages are very low. My Melquiades amp outputs to Vitavox under 3V and 110dB sensitive S2 screams at 3V like wounded in ass hippopotamus. The normal operation of my driver is at 0.4-0.9V with this voltage and with no LF submitted to driver is it imposable to demagnetize it. Even if the demagnetization does take place then to recharge a driver costs $20 and you do it just one what you buys the driver (as it might come from unknown source and it might be used by some cretin who drives his playback with 500W Crest amp.

There is another subject why I personally do not feel threaten by demagnetization and do not feel that is it a serious argument. There are two types of compression drivers: high flux and medium flux. Some drivers run 2.2T-2.4T in gap and have cone’s suspension to operate the in the environment where the diaphragm is over damped by flux force.  I do not use those drivers and I prefer the moderately flux drivers (1.5T-1.8 T in gap) as I feel that they have higher compliance of diaphragm and the diaphragm more hams by suspension instead of the intrinsic stiffness of the flux. So, those moderately flux drivers get demagnetizes much slower (of the same magnet was used). In fact it is very difficult to fully magnetize the 2.4T driver as when the magnetizing machine of off then the driver is losing right the way around 20% of charge. With 1.7T in gap (Vitavox, Altec, JBL etc…) there is a room to step back in flux density…

Anyhow, I do not feel that demagnetization is a factor that needs to be considered. In fact I do not see any utilization advantages of the field-coil beside that the driver become much simpler and easy to assemble. If electromagnets have any sensible advantage then it should be in the realm of sonic results. However, so far I do not see anybody (beside me?) trying to talk about the actual SOUND of the electromagnets.

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