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In the Forum: Horn-Loaded Speakers
In the Thread: Vitavox S2 with Electromagnets
Post Subject: Few remarks on FC PS, back-modulation and FC + perm. combo (unintentionally long)Posted by N-set on: 1/12/2006

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Zdravstvui Roman, hi Chris,

I know almost nothing about the relation between sonical effect and physics, so I will only try to speak about the latter. Take it as you wish, I can  as well delete the post if it just increases the entropy.

Chris, I think your point 3) is contradictory with the assumption of low impedance - think of it, why we do it in the audio coils...exactly to have broadband high impedance, but that's why I'd support it :-)At the level of a crude approximation I see it this way: signal current flowing in the voice coil produces magnetic field (B), caught (to some extent) by the FC (now I neglect the effect of the VC field on the pole-piece). This field generates voltage in the coil. Since FC would rather have a lot of turns and a relatively big diameter, I susspect, just like you, that this coupling is not negligeble. Then, if the PS has low impedance for the given frequencies, the induced voltage would cause a high current flow in the FC, producing in turn stronger signal-related addition to the constant magnetizing field. That's why I think that high impedance PS is better, as it blocks the signal "intrusion" into the FC supply. I would even try adding some additional gapped choke in the PS, to present even higher imp. to the signal-induced voltage (Chris, you can try it with your FC's)....unless I got it all wrong

I do not quite get Romyƛ analogies on the "stiffness" of electromagnets. As we once agreed with Chris (unless he has changed his mind :-), deeeep saturation, at least  on the paper looks just wonderful, for the reasons we all know. Roman, your earlier observations with underfed FC are very interesting. A question would be - were the pole-pieces of the drivers you have tested really deep saturated?To judge that, one would have to know the exact material and the B field in the motor. It *might* have been that the operating point of the pole-piece was idiotically chosen by the designer/manufacturer right on the knee of the magnetic curve, where the non-linearity is the biggest, but one gets high Teslas without wasting too much currebt for the FC...this scenario is just a speculation, as I have never calculated that for the existing drivers... Then, lowering DC moves the op. point lower, to more linear region and hence it might be more benefical than the higher sensitivity reached at the price of magnetic linearity....as said, just a though...probably stupid.

Your new observations on rising the voltage, which I just appeared when I was writting this post are even more interesting :-/ I think to try to establish the link between physics and sonics in this case, we must have more concrete data: what is the magnetic material used, at which point it operates, what is the strongest signal we can expect in the VC. Then we can try to judge if the motor stays really saturated under ALL real circumstances, or is it just saturated at no- or low-signal, lab conditions?

As for the perm. + FC combo, I would be very, very careful, especially with simply winding the coil around the existing Alnico magnet. I dont remember the histeresis loops of Alnico (Chris, you lucky dog, you have Bozorth - maybe he has those curves), but permanent magnets are usually much less linear than soft magnets and on top have wide loops. Both facts matter a lot if you dont want to saturate the motor. Leaving linearity aside, wider loop=bigger losses, so the signal, remagnetising the magnet via the VC, gets attenuated. Permendure is usually used to get big Teslas, but I wonder about it's linearity at the saturation region- it seems to have a sharp knee (at least at those curves I have seen). It would have to be driven either at the most linear, unsaturated part (like in AN cartriges???) but then we loose quite some Teslas, or very deeply saturated, so that even very strong VC signal doesnt bring it back close to the knee.  I once tried to get the attention of the AA crowd to the magnetic linearity problem and suggested to perhaps sacrifice some dB/W/m for more linear magnets, but the satanic crowd shouted in their orgy Permendure!Permendure!Teslas!Teslas!

Cheers,
N-set


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