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Very interesting… Earl Geddes just posted his thoughts for the Morons at the AA. I do not know is he was inspired by my post of by the completely foolish nose that the AA’s idiots razed around the Cogent’s Steve and Rich experiments but still – it was a good timing…

Earl Geddes wrote:

"Could someone explain to me the theory behind the use of field coils in loudspeakers. And please, don't just say that "they simply sound better". Please leave that kind of comment to for wires.

The only reasonable comment that I heard was that they reduce flux modulation, but that doesn't hold water.

They will reduce flux modulation over a ceramic magnet, and perhaps even an ALNICO magnet, BUT NOT over a well designed flux modulation ring. The internal impedance of the field coil is much higher than the ring and thats if it is terminated by a very low source impedance power supply.

And the cleaness of the power supply! Don't get me started on that. Can you say Lots-O-Dollars?

Since most compression drivers have saturated magnet structures its not possible to get more flux in the gap no matter how high the currect through the coil.

So I'm at a loss to see an advantage. When all one can say is "Hey they sound great" this usually turns out to be a myth when the smoke clears.

There were very good reasons that they went away many years ago and I don't see how things have changed.

There ARE very good reasons to use ALNICO over ceramic or Neo, and Samarium Cobolt would be even better - I discussed these aspects in my book. But I fail to see any advantage to a field coil. And I'm also not convinced that the difference in magnets is all that audbile either. We did a test of a ceramic magnet compression driver and a massive ALNICO one in otherwise identical systems. The differences were small enough to be statistically insignificant, but the trend was for the ceramic one (and of course this test was blind).

So any thoughts on the theory?"

I think that Earl in correct in his observations. If  (big if) the advantages of electromagnets do exist then we do not know what they are and how it relates (if they do) to the flux modulation. The extra flux is fine nit it make the flux “too stiff”. I have heard a few drivers with 2.4T in gap and all of them sound like crap. Evan with electromagnet when you raise voltage and generate more flux the driver begins to sound very-very bad. Actually the stories of the more powerful flux are kind of bogus generally and good enough only for “AA-level of intelligence”. The Cogent’s Steve and Rich drive their MF compression driver at 108dB. Well, with 100% of efficiency 1W applied to a perfectly saturated gap should give up 111dB sensitively, so, where they lost the 3dB? Perhaps in the under-magnetizing the gap? If convert my S2 driver into the field coil I would do the very much the same to drive the magnet very soft….

Theoretically, yes, when we juts shut down the magnetizing machines we do loose the large amount of magnetic power right there, so what? Get bigger magnet!

I do not know any advantages because the fact that the sound softer. I personally believe that the electromagnets have HIGHER MOMENTUM FLUX MODULATION and that make them to “sit” slightly…  or exactly what I would like to get out of the Vitavox S2 drivers that is very colorful and very contrasty and might be benefited slightly from a very mild “gentleisarion”…

Rgs,
Romy

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