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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
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
2,740 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.
macrojack
1,303 posts
 
Thanks, duke. So what I get from your answer is that there is lag (sag) at play in the permanent motor whereas the field coil can change direction more precisely.
How does that relate to my other question about diaphragm mass? And what about Metralla's question about cost? There is a enormous difference, it seems, between the price on conventional drivers and FCs.
audiokinesis
2,740 posts
 
Macrojack, to the best of my knowledge there is no direct link between moving mass and flux modulation (though there is a link between voice coil inductance and flux modulation). Now it well may be that higher moving mass makes the effects of flux modulation more audible, but I simply don't know whether or not that's the case.

Duke
atmasphere's avatar
atmasphere
11,841 posts
 
Field coil speakers have always been more expensive to make. When permanent magnet speakers became available, the industry moved to them quite quickly due to the fact that they were cheaper.

Like a lot of things in audio (tubes to transistors, LP to digital), the move from field coil to permanent magnets was fueled more by cost motivation than performance. Field coils are a rising star these days in loudspeaker technology. Although more expensive, they are otherwise an easy way to get the speaker to sound more transparent.
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