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In the Forum: Horn-Loaded Speakers
In the Thread: New superlative horn build - ESD acoustic
Post Subject: Field coil with feedbackPosted by martinshorn on: 5/14/2018
It was honestly like "oh a big horn, gotta listen .... nice, who did that, hello, how did you..." .... "lets go outside for a talk". I actually thought to the last moment that they were japenese. Coz majority of eastish industry is, and me as western dump i dont spot the difference 
Now, coming to the field coil, they had nice ideas.
They were not pleased with soft magnets.
But also they dared to take the Goto apart to measure the flux. I guess no one did that before
Including Goto themselves. They found to have only 1.6 of the claimed 2.4. Funny enough...
That actually confirms the theory of a buddy i know who sais according to their material and geometry Goto cannot reach that high tesla.
Doesnt matter, Goto sounds nice, and thats what matters.
But how to get real 2.4 tesla?
So they got Sam on the boat, and just did hugely oversized field coils.
The saturation clips at 2.2 tesla.
Unless you use the hell expensive permadure, then it takes u to 2.4 tesla measured in this reality.
But they had a ugly warm up phase, like western electric.
Also eddy current, and temperature dependent current. Like all field coils have.
The transient attacks soften. Not nice.
What they do, they have one big device that looks like an amp, that has one individual circuit per driver, so 10 in total (2x5), for the field coils.
Its a current-driven dc-amp. That makes the voltage variable, but constant current. By that the warmup is eliminated. The transients are are back to full attack. Theres even an eddy-current flux sensor integrated with a feedback-loop to the dc-amp that compensates the flux-modulation. This really kills even the tiniest motor-distortion possibly left.
The next problem in line then was the temperature in this design. The coils did just melt down.
Also they didnt fit the magnet around the phase-plug, and the throat-tunnel became very long which was coloring sound.
This was solved by 2 steps, one is described later within the phase-plug part.
The other explains why the drivers are so big: theyre wrapped in coolers. That covers for most circumstances.
As an emergency backup, a temperature sensor is connected to the dc-supply with a protection circuit.
Im impressed to see how much care went into each detail.
Josh
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