John Curl's Blowtorch preamplifier part III

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#10,666
TNT said:
....reduced harmonic distortion by more than 6 dB. The proposed feedback and control scheme can be easily implemented using inexpensive analogue components, which can further reduce the cost and complexity of the system.

(PDF) Passive voice coil feedback control of closed-box subwoofer systems

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Thank you for the link.

sigh, mechanical engineers..I woulda preferred real engineers...you know, EE's..😉
Those mechanical guys with their eeequations and stuff..where's the fun in doing them there equations.

The second coil is essentially co-wound I assume. However, I don't know if it was over/under, or front/back. Front/back is a problem to me, as they see different environments during excursions. I would prefer one be inside the former and one outside the former.

Do we have any choice in that?

If they are perfectly co-wound, then the only difference between the two should be the IR drop in the driven conductor. They should both intercept the exact same flux and changing flux, so any non linearities should be cancelled out.

This is the exact scheme I designed for the ITER thermonuclear fusion guys, for almost the exact same reasons. Course, their VC is about 35 feet tall, 14 feet wide, and carries 40 kA. And the secondary currents are about a million amps.😱

Nelson, do you have any graphs showing the improvement? I would love to know. If you sold it all, the specifics might be IP that you cannot divulge, and I would understand..

jn
 
#10,667
Dual coil driver winding, hm..my best guess would be to go to something almost bifilar-like.

If inside or outside of the vc former and in the gap, then you might get magnetic cut-off, of a sort, in the peak delta?

whereas with a bifilar-like winding you might get a maximum interference and integration pattern?

Just my off the cuff guess, without actually sitting down and really thinking about it.

Oh I think you kinda just said that, at least in the winding method. Had to go back and actually read it....

I like guessing, even when the answer is to be presented. Keeps the brain nimble.
 
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#10,668
KBK said:
If inside or outside of the vc former and in the gap, then you might get magnetic cut-off, of a sort, in the peak delta?

whereas with a bifilar-like winding you might get a maximum interference and integration pattern?.
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You'll have to excuse my lack of understanding, my experience only covers thermonuclear fusion superconducting magnets, high energy particle physics accelerator magnets, synchrotron undulator magnets, and antimatter confinement bottles....

What exactly did you just say??

jn
 
#10,669
Jn, I'm not sure, exactly what I said, but I'm workin on it...

ok, two magnets, double gap. Morel driver type gap, and then an innie. Good luck stabilizing the two vc's though.

I've seen the top bottom gap systems, probably makes more sense. At least some of the mechanical makes sense stability wise, and some don't. Spyders damp the distortions but don't kill them.

How can I say such things and then talk earlier about the speaker company? Because this stuff is not important (as one might think) for, er, that stuff ....and can be learned in minutes, so I don't sweat it. Electromagnetic legos!

Remember to speak loudly though, I'm really far away, I can't hear you, and I've got your shoes.
 
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#10,671
If the coils are close they will act as a transformer. Extracting useful errors may be difficult.

You can make a bridge to get the back end pretty easily. Also limited in useful bandwidth.

With a speaker it's the equivalent of controlling a whip from the handle. Once it's moving its too late to change it.
 
#10,680
Joe Rasmussen said:
I put this to an authority that must be respected (no, I am not going to do name dropping as that would be insensitive) and I stand by that statement and it is solidly based.
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As a scientist I don't respect authority, whether named or not.

PMA said:
I am always assuming at least some elementary knowledge of circuit theory and acoustics - electric-acoustical transducers, so I assume people are not confused. Contrary to my optimism, even some people involved in audio design seem not to understand very basics.
Distortion seen in current with a voltage drive only reflects speaker nonlinearity converted to the electrical side. On the acoustical side, we can see both mechanical and electrical issues reflected in distortion.
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Yes. There is good coupling between electrical and mechanical sides of a speaker drive unit only around low bass. Elsewhere the current gives it a push and it then does whatever it does. Meauring current and trying to deduce something acoustic from this merely exhibits ignorance, whoever was the "authority" who approved this.

Before I arrive here a few years ago, I too naively believed that people involved in audio basically understood it, even if they still argued about details at the edges. I now know this is not the case; in fact there could even be a slight negative correlation between understanding and commercial involvement, especially when accompanied by dogged persistence in asserting nonsense.

Joe Rasmussen said:
At least have you guys thinking. The dB-SPL is off course related to all sorts of things, like Jn indicates. But some times you have you use thought logic like "if all things were equal, then..." or else we shall be buried in minutia. So in that conditional sense, the dB-SPL is still directly related to the current (which can be influenced by many things) in the voice coil. I struggled with that a bit too, so even if eddies exist, air load impedances, cone imperfections and resonances, poor cone edge impedance terminations and poor design basket reflections, oh boy, the list is endless... but then it just occurred to me what was obvious, and I played this idea before others, that this simply alters the back-EMF impedance (an impedance is the degree to which current is impeded, not voltage).

What is the back-EMF impedance? The impedance that measures above the Re value of the voice coil. Just pure logic, because they are in series.

The Re is stable, the back-EMF impedance is not. The Re has some thermal dependency, but the back-EMF impedance is highly malleable to all sorts of flaws and conditions. This alters the current of the voltage amplifier, the current is then presented to the driver and the result is that the current changes the dB-SPL. This is what Paul's measurements have demonstrated (and others too, but his example I do like). But now comes the final and most important point, the current being modified becomes a loop, the modified current is further modified and goes back to the amp, which reacts to and further modifies the current, and you got time smear and potentially something that roughly speaking becomes some kind of noise floor. The modified current continues to be modified as if stuck in a loop, a cat constantly chasing its own tail.
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So many words, so much confusion. Anyway, congratulations in getting "time smear" in there: that will impress some audiophiles. Probably the purest nonsense in all that was "an impedance is the degree to which current is impeded, not voltage" - that is the kind of thing which might be said by a philosopher or etymologist, but would never be said by an engineer who actually understands engineering. If you cannot get the basics right, what hope have you for understanding anything a little bit complicated (e.g a speaker).
 
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