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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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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 Romyś 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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