Modifying driver impedance?
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JMFahey
diyAudio Member

Join Date: Mar 2009
Location: Buenos Aires - Argentina
A few points I think relevant but Forum didnīt let me add to my earlier post, so here they are.
Hope they add some extra clarity:
Quote:
 Still, a wide strand of copper ribbon should have much less inductance than a typical voice coil. Especially if it's only a few turns.
Even a single turn will have inductance. FWIW even a straight wire has inductance.
Yes, single turn coil will have 10000 times less inductance than a 100 turn one ... it will also have 10000 times less resistance (do the Math) .... inductance to resistance ratio will stay the same, go figure.
Thatīs why I said: "everything scales down" ... but keeping the proportions/ratio the same, it will also behave the same, same curves, everything.
Quote:
 Could even run parallel layers of ribbon to reduce the inductance further.
No.
If all ribbons are single turn and wound around the same core, and obviously connected in parallel and in phase, they are all "a single turn coil" meaning inductance will be the same.
Quote:
 Damping factor is irrelevant with current drive though.
Agree, since source impedance is infinite, by definition.
Quote:
 Anyway, with a ribbon coil I can get the inductance down to arbitrarily low levels with parallel coils.
No, see above paralleling in this case means nothing, what you will lower is DCR ... but there is a problem, there is VERY limited space inside the gap, so I already did my calculations assuming you fit maximum available amount of copper wire/ribbon there.
No physical space for "more coils".
Quote:
 What roll does inductance play in the response of the driver?
I already explained it, it increases impedance, typically above 400 to 1000Hz, and again typically doubling it around 8 or 10 kHz.
Just look at a few published impedance curves.
On voltage driven speakers, it reduces power reaching it, itīs a "crossover" series coil after all, but speakers have a rising measured response on axis, so both factors partially compensate and speakers end up having a roughly flat response up to 4 or 5 kHz (higher in small light ones) .
IF you current drive same speakers, they will show increased output at higher frequencies (also near resonance) which is used to advantage in Guitar speakers to provide desirable treble and bass boost.
Quote:
 If you read carefully, what I said was that there are advantages to current driver over voltage drive. To use these advantages a driver needs to be ideally 0 ohms or close to it.
No, you can current drive any impedance speaker, as long as:
a) your amplifier has enough current capability
b) your amplifier has enough voltage capability to push said current through that voice coil, which will always have some resistance and some impedance.
"Low" does not mean "zero" by any means.
Quote:
 This method of voice coil also reduces the inductance and capacitance to almost non existent levels.
"Almost non existent" is a label, not a number.
10000 times less resistance and 10000 times less inductance means the inductance to resistance ratio remains exactly the same.
Quote:
 I don't know how VC parasitics interact with overall driver response because dynamic driver tech has never interested me
Quote:
 so I know little about it.
Not a sin, unless left uncorrected, thatīs why I warmly encourage you about reading about speaker principles theory.
Iīd go as far as suggesting 2 classics:
Acoustical engineering: Harry Ferdinand Olson: 9780193007048: Amazon.com: Books

Acoustics: Leo L. Beranek: 9780883184943: Amazon.com: Books

the first one is very rare and so expensive if you have to buy it, but both are readable in most University Libraries.
FWIW both were the core of what *I* studied at the Buenos Aires University Engineering Faculty in the early 70īs, go figure, and they are still valid.
Every single time I browse them, I find a new pearl of wisdom, a new exciting idea, howīs that?
So now you know where Iīm coming from
skip the red clothes and the reindeer, but the white beard (and the paunch) fully apply

You can add: Sound System Engineering, Third Edition: Don Davis, Eugene Patronis: 9780240808307: Amazon.com: Books

not exactly focused on the raw loudspeaker itself but on how speaker systems behave in the Real World environment, outside the anechoic chamber, and so very useful.

This is the basic "old school" trio; there are many excellent and more modern books available, but all somehow rest on these giants shoulders, one way or another.

Quote:
 I was talking about other driver tech. Not dynamic drivers. Read carefully.
Quote:
 A flat strip of copper that is wide, thick, and short enough to be 100 miliohms or less over a few turns is naturally going to have vanishingly low reactance.
Niot at all. Relative to speaker impedance it will be VERY significant.
And again: "vanishing" does not mean zero.

Quote:
 I'm asking if the FR or performance characteristics would be superior to the typically used solutions.
performance will be the same as before, except for a scaled down impedance, resistance, reactance.
But resonance, curves, etc. will be the same.
Quote:
 the voltage axis of device transfer curves almost do not come into play.
Oh yes they will.
350A RMS through your coil will definitely drop significant voltage across it.
And again: "almost" is not a number and definitely is not Zero, please do the Math using numbers, not labels.
__________________
Design/make/service musical stuff in Buenos Aires, Argentina, since 1969.

hellokitty123
diyAudio Member

Join Date: Dec 2017
Location: Connecticut
Quote:
 Originally Posted by JMFahey A few points I think relevant but Forum didnīt let me add to my earlier post, so here they are. Hope they add some extra clarity: Even a single turn will have inductance. FWIW even a straight wire has inductance. Yes, single turn coil will have 10000 times less inductance than a 100 turn one ... it will also have 10000 times less resistance (do the Math) .... inductance to resistance ratio will stay the same, go figure. Thatīs why I said: "everything scales down" ... but keeping the proportions/ratio the same, it will also behave the same, same curves, everything.
Yeah, I was wondering about that. That's why I asked what the relationship between VC parasitics and driver performance was. Wasn't sure if it was that simple.
Quote:
 Originally Posted by JMFahey No. If all ribbons are single turn and wound around the same core, and obviously connected in parallel and in phase, they are all "a single turn coil" meaning inductance will be the same.
Hmmm, not sure I understand that one. If I split a 4 turn coil into 4 single turns in parallel wouldn't that reduce the inductance 4 fold while maintaining the effective turns ratio?

Quote:
 Originally Posted by JMFahey No, you can current drive any impedance speaker, as long as: a) your amplifier has enough current capability b) your amplifier has enough voltage capability to push said current through that voice coil, which will always have some resistance and some impedance. "Low" does not mean "zero" by any means.
I was referring to my statement that if you drive a near zero ohm load, the electrical system will become more linear in certain aspects due to the lack of voltage swing required.
IMO a near zero ohm load using current drive removes a number of problems with minimal tradeoff. Assuming the load is suitable to current drive.

Quote:
 Originally Posted by JMFahey Iīd go as far as suggesting 2 classics: Acoustical engineering: Harry Ferdinand Olson: 9780193007048: Amazon.com: Books Acoustics: Leo L. Beranek: 9780883184943: Amazon.com: Books the first one is very rare and so expensive if you have to buy it, but both are readable in most University Libraries. FWIW both were the core of what *I* studied at the Buenos Aires University Engineering Faculty in the early 70īs, go figure, and they are still valid. Every single time I browse them, I find a new pearl of wisdom, a new exciting idea, howīs that? So now you know where Iīm coming from skip the red clothes and the reindeer, but the white beard (and the paunch) fully apply You can add: Sound System Engineering, Third Edition: Don Davis, Eugene Patronis: 9780240808307: Amazon.com: Books not exactly focused on the raw loudspeaker itself but on how speaker systems behave in the Real World environment, outside the anechoic chamber, and so very useful. This is the basic "old school" trio; there are many excellent and more modern books available, but all somehow rest on these giants shoulders, one way or another.
I'll check those out. Thanks

Quote:
 Originally Posted by JMFahey 350A RMS through your coil will definitely drop significant voltage across it. And again: "almost" is not a number and definitely is not Zero, please do the Math using numbers, not labels.
Yeah well, I certainly won't be building an amplifier capable of putting out 350A so that kills the idea anyway.
The entire idea hinged on the current requirement being not too far off from the typical driver requirement.
You've cleared that up for me.
I'll stick to other driver technologies that are more conducive to lower currents.

Last edited by hellokitty123; 16th September 2018 at 03:48 AM.

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