Apparently, no. A least according to some info on another forum. I'll post here if I learn more.
The flux is proportional to ampere turns. Fine guage would mean more turns but higher resistance or less amps. Heavy guage would mean fewer turns but more amps. I assume it is like analysis of woofer voice coils shows: in the end nothing matters but the weight of copper you can squeeze into the gap, as long as your power supply is okay with the resultant impedance.
Olson's book has a couple of pages on field coil design.
David S.
Olson's book has a couple of pages on field coil design.
David S.
To me the field coil looks like a big choke. Forget for the moment what else is going on... so it seems intuitively (often wrong it is) that HF response is a non-issue. It don't have none.
So, what happens when you retrofit a FC on a speaker that already has a shorting ring on the pole piece??
As far as practical considerations, I think the inductance of the FC may play a role in the whole thing, especially WRT what is needed for the PS. There may or may not be a resonant freq to be concerned about if one uses a standard cap input filter, or cap before the FC as opposed to a regulated supply... beyond that it seems to me that you want to make sure the things is mechanically stable inside the 'pot'...
Me, I'd just start with whatever I could put in the hole and see what it does, learn, go from there. Doubt you can make something definitive on the first pass right out of the box, unless ur copying a published or reverse engineered design.
So, what happens when you retrofit a FC on a speaker that already has a shorting ring on the pole piece??
As far as practical considerations, I think the inductance of the FC may play a role in the whole thing, especially WRT what is needed for the PS. There may or may not be a resonant freq to be concerned about if one uses a standard cap input filter, or cap before the FC as opposed to a regulated supply... beyond that it seems to me that you want to make sure the things is mechanically stable inside the 'pot'...
Me, I'd just start with whatever I could put in the hole and see what it does, learn, go from there. Doubt you can make something definitive on the first pass right out of the box, unless ur copying a published or reverse engineered design.
Heres the voltage of the current source at a .1 amp DC bias. The current in the coil is pretty constant (+/- 1%) and that depends on the source impedance, the 100k r. The voltage swing varies a lot with the DC bias, inductance ratio, mutual imductance, and will go negative sometimes, depending on a few factors and the DC bias voltage. Some sims the voltage swing was 200 volts! I could see this as being a problem with some designs. Any one have any idea what kinda mutual inductance these will have?
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Field coil resistance.
Dave,
Field coil with stiff PSU is a big block of copper, effectively much better than an aluminum ring. Its DC resistance does not matter.
With stiff PSU , FC coil ends are shorted, and this is equivalent to a single turn ring, no matter how many turns there is, or the total dc resistance.
Do some math, and You 'll see that what matters is just combined total crosssection of the conductors, other factors in the equation cancel each other.
Multiturn coils will simply induce higher AC voltage, which will be equally efficiently dissipated through higher FC resistance and (zero) resistance of the PSU.
The really measurable difference in Fc drivers will be comparison constant current vs. constant voltage supplies. I expect that latter will win, maybe even against the PM with the same B.
Off topic, I think "regulation" of the BL factor is nothing so desirable. Higher BL is always better.
Makes VC intrinsic damping factor higher, and cone/dia mass breakpoint frequency and overall efficiency higher.
I never wish to have lower field in any of my speakers. Taking it to the extreme, 10 Tesla 2445/2360 would go to 20 khz with no CD compensation.
In other opinions, I am in the "scientific" camp with You. If there is a difference in anything, it is measurable.
Dave,
Field coil with stiff PSU is a big block of copper, effectively much better than an aluminum ring. Its DC resistance does not matter.
With stiff PSU , FC coil ends are shorted, and this is equivalent to a single turn ring, no matter how many turns there is, or the total dc resistance.
Do some math, and You 'll see that what matters is just combined total crosssection of the conductors, other factors in the equation cancel each other.
Multiturn coils will simply induce higher AC voltage, which will be equally efficiently dissipated through higher FC resistance and (zero) resistance of the PSU.
The really measurable difference in Fc drivers will be comparison constant current vs. constant voltage supplies. I expect that latter will win, maybe even against the PM with the same B.
Off topic, I think "regulation" of the BL factor is nothing so desirable. Higher BL is always better.
Makes VC intrinsic damping factor higher, and cone/dia mass breakpoint frequency and overall efficiency higher.
I never wish to have lower field in any of my speakers. Taking it to the extreme, 10 Tesla 2445/2360 would go to 20 khz with no CD compensation.
In other opinions, I am in the "scientific" camp with You. If there is a difference in anything, it is measurable.
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This will be fun.... I hate ketchup but love barbecue sauce. My son is just the opposite so that provides us with a difference to measure.
the ultimate question is.... how do you measure taste?
dave
I think that is what I mentioned in a second post with regard to ampere turns, as also seen in voice coils: volume of copper is key and how you slice it is immaterial.
Still, I think that is for the DC part of this only and relates to BL. What I'm not so sure of is the AC part. (and the model of this is frankly beyond my knowledge). In conventional magnets the big difference between magnet materials comes back to the hysteresis induced distrotion and you either use the right material or add shorted turn type rings. The question remains as to where a field coil fits into this and it is the AC stiffness of the field, not the DC stiffness that we are talking about.
Much like woofer damping, saying you have a stiff voltage source driving it isn't the total story. Even a woofer with zero source impedance has finite damping because the coild DCR is always in series with it.
With regard to regulation, this is only significant in terms of long term drift of sensitivity. Any practical field coil will be run at a fairly high level set by how hot you want the beast to run at. If you choose, say, 80 degrees C as reasonable then you well set a current and in a half an hour or so the structure will get up to that point (thermal time constant). Over that time period the resistance of the coil will naturally drift up with temperature as there is a resisitivity coefficient of copper tied to temperature.
You can either live with that or compensate for it. Running a constant current supply provides automatic compensation.
Regards,
David
That is if we choose to leave well enough alone air cooled. Now if we reduce this with fluid cooling, vapor phase change or with thermal diodes etc can be reduced significantly. Now where did I put that super conductor formula...
That is if we choose to leave well enough alone air cooled. Now if we reduce this with fluid cooling, vapor phase change or with thermal diodes etc can be reduced significantly. Now where did I put that super conductor formula...
I know you are kidding (mostly) but some cooling wouldn't be a bad idea, especially since we would typically build the unit and put it in a nicely insulated box (dipole folks aside). A reasonable goal is to get the steel parts well into saturation. That not only gets you as far as you will be able to go in sensitivity, it also gives you the AC linearity we were talking about. Even with ferrite magnets (bad for hysteresis distortion) distortion drops when you get into saturation. The operating point can't move around when it is pushed up against the ceiling.
David S.
I'm not going to argue about religious issues.
You are right, taste can't be measured.
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