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Cogent horns

Count me among those who have to say that the Cogent field-coil horn system is the single most realistic (and satisfying) speaker system I have heard. The system at RMAF 2006, powered by Welborne 45 (top) and 300B (bass) SETs, was *literally* jaw-dropping (for me).

(For whatever reason - I was not impressed to the same level the next year, in the very large conference room. Perhaps there is something about near(er) field listening these things. By all rights the Welborne room was *way* too small, but they sounded fabulous to me and many others.)

They are far beyond my price range.

How do the Classic Audio speakers with field coil drivers compare? And how come I see no mention at all of field coil options on Classic's site, including no pricing info? (I'm sure they're beyond me as well but just curious.)
paulfolbrecht
atmasphere's avatar
atmasphere
11,936 posts
 
Paulfolbrecht, the Classic Audio Loudspeakers model T-1 with the field coil drivers is about $52,000 for the pair. The T-3 set up the same way is about $36,000 for the pair.

The reason field coils sound better is that they are like ESLs in the way that the field reacts to the energy in the voice coil. That is to say, it does not react (or sag) whereas permanent magnets of all types do (Alnico sags the least and so has the reputation for the best sound). The difference is quite audible.
audiokinesis
2,749 posts
 
Thanks for that insight, Ralph. I hadn't made the connection between the static field of an ESL and the electromagnet in a field coil, but it makes sense. And in my experience both types excel at low-level detail and nuance and liveliness, though of course the high-efficiency field coil drivers do macrodynamics better.

In permanant magnets, as you said alnico sags the least (has the least flux modulation under dynamic conditions), followed by neodymium and then ferrite - but shorting rings (Faraday rings) can help ferrite and neo motors more closely approach alnico.

Duke
metralla
945 posts
 
Why do field coil drivers cost so much? Are they particularly hard to make? Or is the answer just the inverse effect of the economy of scale?

Regards,
macrojack
1,303 posts
 
Ralph,

By "sag" I guess you mean a delay in response to signal. Is that correct? If so, I can see that as an issue with a driver that has some mass but I wonder how significant it can be on the wispy little diaphragm of a compression driver.
audiokinesis
2,749 posts
 
Macrojack, thanks for asking, as that's a very good question.

The "sag" mentioned by Ralph (Atma-Sphere) is a short-term reduction in magnetic field strength. As the magnetic field induced by the voice coil interacts with the permananet magnetic field, it modulates that field, so the permanent field strength is actually constantly varying a little bit whenever the speaker is playing. Because an electromagnet's magnetic field is instantaneously restored by the power supply, modulation of the field strength is negligible. One implication of this is that the quality of the power supply is a factor with a field coil motor, but fortunately high quality regulated power supplies are not terribly expensive.
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