Yes, but you didn't say that and the copper alone would have done nothing unless the gap gets larger.
And I still don't get what you FEA plot is supposed to show. I know that piece of software and I'm guessing that it is the magnetic field of a sheet of current between two permanent magnets.
I was thinking at first that it was just a cg=hange in materials, but it now seems like the entire shape changed and that makes the whole test invalid. Except the inductance going down with a steel core - that's completely wrong.
Yes, this is precisely why we have shorting rings, to prevent the coils magnetic field from modifying the static field - "armature reaction".
Here is the right simulations
(and sorry for the sauron eye look simulation... i've found it fun on the moment)
With the coil
Without the coil
But IMHO if the gap gets larger, the coil and the gap height get longer, or the Q get higher.
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Experience would say that this is probably not the case or shorting rings would not be very effective - there already is a dominate shorting ring, the iron core.
Exactly, virtually no change at all. Correctly done the shorting ring is not in the gap (for a woofer. Tweeters are different because we want to lower the inductance.)
Ok to make it simple, the piece of copper is transparent to the magnetic flux but resistive to the electromagnetic flux.
So, the elecromagnetic flux of the coil is not absobred at all because the elecromagnetic resistance of the shorting ring is too low, but this low resistance is enough to absorb a significant part of the parasitic electromagnetic flux that flow into the pole parts ?
The coil makes a magnetic field that produces a voltage (emf) in the copper cylinder. Since a current can flow around the copper cylinder, it does flow in response to the voltage. When current flows in the copper cylinder that creates it's own magnetic field that then produces a voltage (counter-emf) in the coil. If current can flow in the coil in response to that voltage, then it does flow. Whether or not such current can flow in the coil depends on how it is being driven (from a power amp). If driven from a voltage source, current can flow into that since by superposition a voltage source is a short, and the coil produced flux is then decreased. Eventually, some equilibrium is reached, which is why we use calculus and/or numerical modeling to see where it ends up. If the coil were driven from a current source, according to superposition the source is an open circuit, so nowhere for the current to flow so no change of flux from the coil. That would be my basic understanding. Anyone feel free to correct me if I got it wrong somewhere, its not my specialty area.
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With regard to steel cores, transformer and most electric motor cores are laminated to reduce resistive loses and heating from eddy currents.
As frequency goes up, the permeability of iron makes skin depth increasingly shallow, although at audio frequencies it isn't as predicted by the usual formulas for RF, since those formulas are approximations based on a wave normally incident to the conductor, (which is not a close approximation at audio frequencies). Bessel function models or numerical modeling can come closer.
Again, my understanding. Feel free to correct anything that's is wrong. I look forward to learning something new.
As frequency goes up, the permeability of iron makes skin depth increasingly shallow, although at audio frequencies it isn't as predicted by the usual formulas for RF, since those formulas are approximations based on a wave normally incident to the conductor, (which is not a close approximation at audio frequencies). Bessel function models or numerical modeling can come closer.
Again, my understanding. Feel free to correct anything that's is wrong. I look forward to learning something new.
Maybe my view is the same thing that you are saying, but my terminology will be different.
The copper is invisible to a static flux, but not to a changing one. If the flux changes across the sheet then a current is generated in the sheet. Or likewise if the flux through a loop changes then a current is generated in the loop opposing the flux change. If the loop were a super-conductor then the flux change would be completely nulled. If there is resistance then the null is incomplete.
If there is no flux change then no current flows and the copper is invisible to the flux.
A magnetic field don't tranfers any energy (it is just atraction or repulsion), a pulsated magnetic (electromagnetic) field transfers energy (it atract and repulse alternatively ferromagnetic materials in our exemple, it is a mecanical energy transfer).
If you put a induction saucepan on a DC coil, the energy flow into the resistive saucepan material (shaking electromagnetic flux in a non ferromagnetic material) and the heat appear.
If you put your saucepan on a permanent magnet or a CC coil, it will not heat, but eventually jump at your face (if there is some ferromagnetic material in it like in some bad quality stainlesss steels) making a « dong » noise on your skull bones.
The copper ring act as a shorted coil.
Terminology is very tricky, through the rise of frequency an electromagnetic wave is becoming heat radiation and higher it is becoming the visible light.
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If they are that good, why doesn't Harman provide data? Might be they are too busy firing the people who can measure those things.
can anyone illustrate how a motor and a loudspeaker share the same problem that a shorting is supposed to solve?
vacuphile
vacuphile
good question, contact them and ask, maybe if they get continuously badgered they might change their mind and provide the info!(how is asking that question here going to get you an answer?)
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Yes I understand that. I was referring to the parallel between the induced current in the shorting ring in a loudspeaker, and the similar phenom on the shorted "bars" in the AC motors rotor.
Both I assume have a counter emf due to current flow and counter flux acting on flux from coil. I originally thought this may have some damping effect at large coil movements such as at cone resonance but I believe some here are saying that it will be very small.
I thought I read once about making these "shorted turns" with varying cross sections or even partial slits to make the effect variable at different excursions. My memory is foggy here but that would seem to imply variable damping of motion at larger excursions. I dont see why a varied cross section would be useful in lowering inductance at higher freq.
Hey vac.
They are damn good. Ever heard them? The Al series in the Everest’s are even better.
What is it that you would like to see that you cannot find about the M2 drivers?
Barry.
Hi Barry,
What I would like to see about the M2 drivers are the distortion figures at let's say 100dB/m, which should be a breeze for drivers this size. I may have mislooked, but I can't find these figures in the documentation. Have you perhaps made some measurements? Thanks ahead if you can share some.
This is not to say that I don't think they will be brilliant performers, but I would like to know how brilliantly they perform exactly.
Vac
What I would like to see about the M2 drivers are the distortion figures at let's say 100dB/m, which should be a breeze for drivers this size. I may have mislooked, but I can't find these figures in the documentation. Have you perhaps made some measurements? Thanks ahead if you can share some.
This is not to say that I don't think they will be brilliant performers, but I would like to know how brilliantly they perform exactly.
Vac
As I have said before, like me, JBL does not believe in those numbers, so why show them?