Its the non-linear impedance of the coil as it moves thru mag field which is a source of distortion corrected by the sense resistor method or current FB..
Some mental notes for app of the sense resistor is that it would work better over-all in high OLG amp.... Where you can throw away some gain and still have low thd from amp. The amp used was not high OLG design so the sense resistor value was lower than it could be in other amps. But, 0.1 -0.2 is a good starting value. IMO.
There is a practical limit to this approach, besides the volt drop across the Rs. The limit in practice seems to be between 10 and 20 dB improvement at low freq. I found it best use was in 2 and 3 way separate amp systems where the Rs can be used for the bass only... as the Z non-linearity is greatest at large cone/coil excursions. Especially in the region of resonance.
Fortunately, audiopower amps all fall in a narrow range for CLG requirements and so the Rs chosen for one amp is close to being the same value for the others... generally. That is "optimising" wont gain you much difference.
Then there is the choice of the Rs itself..... sense resistor. You want a low TCR type. Making Sense of Current Sensing| Mouser etc
Enjoy.
THx- RNMarsh
Some mental notes for app of the sense resistor is that it would work better over-all in high OLG amp.... Where you can throw away some gain and still have low thd from amp. The amp used was not high OLG design so the sense resistor value was lower than it could be in other amps. But, 0.1 -0.2 is a good starting value. IMO.
There is a practical limit to this approach, besides the volt drop across the Rs. The limit in practice seems to be between 10 and 20 dB improvement at low freq. I found it best use was in 2 and 3 way separate amp systems where the Rs can be used for the bass only... as the Z non-linearity is greatest at large cone/coil excursions. Especially in the region of resonance.
Fortunately, audiopower amps all fall in a narrow range for CLG requirements and so the Rs chosen for one amp is close to being the same value for the others... generally. That is "optimising" wont gain you much difference.
Then there is the choice of the Rs itself..... sense resistor. You want a low TCR type. Making Sense of Current Sensing| Mouser etc
Enjoy.
THx- RNMarsh
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Ah, I know...I'll get one of those inductors from my old test, make a copper ring, and repeat the sweep. duh..
Not sure what the inductance is though, that coil has been sitting on my desk for years now, and the label has fallen off.
I also have some 5 mil copper foil, I could make a shorting ring with that.
I also got a ups notice, my visaton 20-8driver is on the front porch as of noon today, so after I figure out how to disassemble it I can sweep the inductance measurement with and without a shorting ring at the vc. jn
Found it, it was on my other computer...go figure...
From IEEE -1050-2004, page 31, 4.3.2,3, Cable shielding:
The action of an ideal shield conductor can best be illustrated if it is assumed that any magnetic flux, which links the signal conductor, also links the cable shield. The shielding effect is the result of eddy currents set up in the shield by the external magnetic field. These eddy currents set up magnetic fields opposing and counteracting the disturbing magnetic field and will exist regardless of whether or not the shield is connected to ground, but only for cables longer than one wavelength at the interfering frequency.
They show how the shield loop makes magnetic field that opposes the disturbing field.
In a shorting ring, it too sets up magnetic fields opposing and counteracting the disturbing magnetic field. In our discussion, the disturbing magnetic field is the field of the voice coil, both it's current variation and it's position variation.
That opposition field reduces the total field in the space, so the net energy stored within the magnetic field is reduced.
Because E = 1/2 L I^2....
L = E*2/I^2.
So, L is directly proportional to the total energy stored, assuming the terminal current is the same.
The only disagreement we are having here is essentially in terminology. You guys speak in electronics terms, I am talking about field and energy relations. But we are absolutely in the same boat.. jn
Interesting. Mills and Hawksford show lower inductance as the vc moves towards magnet (fig 1), yet Klippel has the opposite, higher inductance towards the magnet..
From Klippel, top of page 9:
Klippel is correct.
ps...not every typo is caught in the proofreading..
jn
Not sure what the inductance is though, that coil has been sitting on my desk for years now, and the label has fallen off.
I also have some 5 mil copper foil, I could make a shorting ring with that.
I also got a ups notice, my visaton 20-8driver is on the front porch as of noon today, so after I figure out how to disassemble it I can sweep the inductance measurement with and without a shorting ring at the vc. jn
Found it, it was on my other computer...go figure...
From IEEE -1050-2004, page 31, 4.3.2,3, Cable shielding:
The action of an ideal shield conductor can best be illustrated if it is assumed that any magnetic flux, which links the signal conductor, also links the cable shield. The shielding effect is the result of eddy currents set up in the shield by the external magnetic field. These eddy currents set up magnetic fields opposing and counteracting the disturbing magnetic field and will exist regardless of whether or not the shield is connected to ground, but only for cables longer than one wavelength at the interfering frequency.
They show how the shield loop makes magnetic field that opposes the disturbing field.
In a shorting ring, it too sets up magnetic fields opposing and counteracting the disturbing magnetic field. In our discussion, the disturbing magnetic field is the field of the voice coil, both it's current variation and it's position variation.
That opposition field reduces the total field in the space, so the net energy stored within the magnetic field is reduced.
Because E = 1/2 L I^2....
L = E*2/I^2.
So, L is directly proportional to the total energy stored, assuming the terminal current is the same.
The only disagreement we are having here is essentially in terminology. You guys speak in electronics terms, I am talking about field and energy relations. But we are absolutely in the same boat.. jn
Interesting. Mills and Hawksford show lower inductance as the vc moves towards magnet (fig 1), yet Klippel has the opposite, higher inductance towards the magnet..
From Klippel, top of page 9:
Klippel is correct.
ps...not every typo is caught in the proofreading..
jn
This is done in the Peavey Rage 158 solid-state (chipamp) guitar amplifier, to raise the output impedance driving the speaker and give it a "tube" sound.
Yes, I covered this in a previous post which people didn't seem to understand.
First done in Marshall Valvestate amps. I posted a link to the schematic.
Same circuit used in most SS reverb driver applications for current drive.
improved Howland current pump - Google Search
More reading
improved Howland current pump - Google Search
improved Howland current pump - Google Search
Indian Journal of Science and Technology, Vol 8(12), DOI: 10.17485/ijst/2015/v8i12/65739, June 2015
ISSN (Print) : 0974-6846
ISSN (Online) : 0974-5645
Design and Analysis of Current Mode Amplifier as Drive Electronics for Linear Voice Coil Motor N. Sriram*, P. Swaminathan and D. Manivannan
School of Computing, SASTRA University, Thanjavur, 613401, India;
improved Howland current pump - Google Search
-RM
More reading
improved Howland current pump - Google Search
improved Howland current pump - Google Search
Indian Journal of Science and Technology, Vol 8(12), DOI: 10.17485/ijst/2015/v8i12/65739, June 2015
ISSN (Print) : 0974-6846
ISSN (Online) : 0974-5645
Design and Analysis of Current Mode Amplifier as Drive Electronics for Linear Voice Coil Motor N. Sriram*, P. Swaminathan and D. Manivannan
School of Computing, SASTRA University, Thanjavur, 613401, India;
improved Howland current pump - Google Search
-RM
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In your experiment, the magfield was perpendicular to the copper on the PC board.
Not the situation of a copper shortening ring on a pole piece, except for magnetic variations caused by flux modulation in the pole piece. The transformer thing as correctly described in the second part of your post. But you need the intermediary of the pole piece to generate these currents.
In your experiment with the PC board, no such intermediary is required, which should lead you to believe correctly that it is something not related to the mechanisme behind a shortening ring that you are finding here.
Now correct up to this point, and the fields are in 90 deg phase shift, but...jneutron said:
VC current -> VC field -> ring EMF -> ring current -> ring field
There is only one 90 degree shift in this cause-effect chain - not two.
Diy-audio.narod.ru/lite/FaradayRingsVoiceCoilimpedance.pdf.
Lenz law.
Search shorting ring operation.
Jn
Google Hyper physics Lenz law.
Jn
Received the 8 inches.
Dissapointed, the whizzer cone was not glued on straight.
I'm not used to playing with such a small driver.
I am putting together a host of tests to perform on the virgin unit prior to disassembly. Inductance sweeps for Ls/Rs free air and face down, thinking how to move cone position for Le(x) sweeps. Some matched angle solid conical piece perhaps. Since the meter is not large signal, I suspect a slight physical offset will require more force than the signal so the readings should be locked coil inductance. But pulling the cone outwards will be interesting.
I am also thinking about making a baffle to mount an 18 incher facing the 8, using an rmx1450 to drive the 18 at 10 Hz up while driving say, 1 kHz into the 8. Measure the current in the 8 to look for changes vs location, amplitude modulation due to Le(x).
Still thinking.. I want to optimize the amount of information I can glean from a co-wound coil before I've added it so I can learn more after. Well, that and do as much as I can in case I trash the driver..
Actually, I can put together a Hotwire cutter and make the matched angle cones out of high density styrofoam. It's no different than the airfoil cutting I did for a middle school stem project on windmills. If I put the foam block on a turntable, I can cut a matched set of concave and convex.
Jn
Quoted by jneutron
The IEEE of all people should know better than to suggest that something magic happens when an ungrounded cable shield exceeds one wavelength. Someone somewhere will quote this to support some misconception they have. Quite apart from the alleged 'one wavelength' magic, the action of a shield depends on how its thickness compares with skin depth, whether it is truly coaxial with the inner core, and whether it also carries the signal return current. The electric field shielding is affected by whether the shield is grounded or not; magnetic field shielding does not care. As an IEEE Member maybe I should ask them who writes this stuff?
Agreed, as a standalone quote it does appear to be as you say.
However, it is within the context of a shielded cable that forms a complete conductive loop among various pieces of equipment. So, it is not penetration depth, but rather Lenz exclusion at work. I also suspect they meant that the cable was not earthed nor bonded, but still forming loops among equipment (to cover flight hardware).
In other sections, they do deal with far field coupling via e/m wave propagation, but this context is entirely nearfield induction coupling.
jn
You misunderstand. Or, I just didn't present properly.
I find that the Georgia university site hyperphysics is excellent in terms of providing explanations which do not require a PhD to understand. I refer to it myself many times both as a sanity check and as a refresher.
At no time did I mean to slight you, which apparently it came across as.
My apologies, no insult was intended..I'm still an engineer with not so good people skills..
jn
ps, I also cannot copy links on my I pad..here is that writeup I found this morning. Although quite long, certainly worth the read.
http://diy-audio.narod.ru/litr/FaradayRingsVoiceCoilImpedance.pdf
I linked to the GSU Hyperphysics doc a few years ago - its a very useful tool for anyone that wants to dip into just about any aspect of physics you care to mention. Part of it came about from you guys throwing physics stuff around here that I'd either long forgotten, or had not really heard about.
Here is the link top the top page (I have my link on my iPad favourites)
HyperPhysics Concepts
NB - there's also GSU Hypermath as well.
Been busy, looks like my microphone design will need someone to build me a few thousand to start.
Max, the guys mixed up my goop test samples, but it was very clear one sample reduced the HF content just placed around a guitar cable at the amplifier end.
DF,
My resistor bit has now made it into two textbooks I have been told, but don't have copies yet. It has been promoted by Audio Precision even though they seem to have missed the reciprocity bit. It has also been adopted by at least three manufacturers of resistors.
JN,
I know you don't like my experiments like the new one with goop. But as it is for my consumption, not really concerned with others' opinions.
So far I have tested resistors, capacitors, transformers, relays, cables and Burblebees.
Resistors... mentioned. Capacitors showed moisture and vibration were under-rated issues. Film type pretty much followed expected data sheet info. Transformers a bit interesting as bandwidth was as expected but flux and noise leakage turned out to be easily handled if allowed for in the physical design. Cable measurements have been demonstrated to visitors, but won't name drop. Reason for differences is perhaps slowly becoming clear, but further work is needed.
Now when I posted the Burblebee data folks chimed in from emotional positions only. A careful examination of the data showed interesting results and it seemed no one actually noticed what it meant!
I believe enough information about all of the tests has been shown to allow others to try the same experiments.
As I use the results in my own work, that is what matters to me.
BTY my microphone design was compared to the other contenders, suffice it to saw mine came out on top. Might even sell at least 10,000 of them over the next few years! I will however need a better source of C13.
Max, the guys mixed up my goop test samples, but it was very clear one sample reduced the HF content just placed around a guitar cable at the amplifier end.
DF,
My resistor bit has now made it into two textbooks I have been told, but don't have copies yet. It has been promoted by Audio Precision even though they seem to have missed the reciprocity bit. It has also been adopted by at least three manufacturers of resistors.
JN,
I know you don't like my experiments like the new one with goop. But as it is for my consumption, not really concerned with others' opinions.
So far I have tested resistors, capacitors, transformers, relays, cables and Burblebees.
Resistors... mentioned. Capacitors showed moisture and vibration were under-rated issues. Film type pretty much followed expected data sheet info. Transformers a bit interesting as bandwidth was as expected but flux and noise leakage turned out to be easily handled if allowed for in the physical design. Cable measurements have been demonstrated to visitors, but won't name drop. Reason for differences is perhaps slowly becoming clear, but further work is needed.
Now when I posted the Burblebee data folks chimed in from emotional positions only. A careful examination of the data showed interesting results and it seemed no one actually noticed what it meant!
I believe enough information about all of the tests has been shown to allow others to try the same experiments.
As I use the results in my own work, that is what matters to me.
BTY my microphone design was compared to the other contenders, suffice it to saw mine came out on top. Might even sell at least 10,000 of them over the next few years! I will however need a better source of C13.
Ed, don't get me wrong, I do not hate your experiments, not at all.
It's you I hate...
Baddaboom..😀
Actually, I haven't been following for a while here...seems that may have been a wise choice..😉
Hope all is well, good luck with the mike business.
And life is easier when you do not worry about the opinion of others.
Jn
Ps.. ESA, if I offended you as well, I also apologize. This was not an easy day.
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Thanks for putting the thought and effort into this Jn,
We'll all get to learn something! ... even if it kills us! 😉
Cheers,
Jeff
I think I still have all the pieces of that Bybee, you are welcome to it. Don't worry the battery should still be good, though I suspect it does not matter. 😉
BTW your use of the term reciprocity is not the one generally used in physics, but let's not bother discussing it. https://asa.scitation.org/doi/10.1121/1.415227
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