This AES paper may be of interest to you:
Low Impedance Voice Coils for Improved Loudspeaker Efficiency
Iversen, Niels Elkjær; Knott, Arnold; Andersen, Michael A. E.
Published in:
Proceedings of 139th International Audio Engineering Society (AES) Convention
The conclusion comparing voice coils with double wound round wire (Re of 5.2 and 4.1 Ohms) to a rectangular wire with an Re of .5 Ohms was:
"Moreover the sensitivity increases and the difference between the use of round wire, with low fill factor, and rectangular wire, with high fill factor, is approximately 1 dB, corresponding to approximately 30% efficiency improvement.
That said, the sensitivity increase was above 90 Hz, below it lost 1dB...
One problem with low impedance drivers is damping factor is reduced by roughly half for each halving of impedance. To have a damping factor of above 20 (generally considered less than the minimum for "hi-fi") with a driver of less than 1/2 ohm would pretty much require the amplifier be built in to the enclosure, or use huge speaker cables- any copper saved in the voice coil would result in a lot more used to connect it.
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If you want to experiment with current drive, the speaker impedance does not have to be low and you can take an off the shelf speaker. Take a regular voltage amplifier, measure the voltage across a shunt resistor that's in series with the speaker, feed this back to a controller, use the controller to drive the voltage amplifier. You can design the controller using control / feedback theory.
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Damping factor is irrelevant with current drive though.
I don't like this method of current amp design. I prefer other methods.
Also your suggestion goes against my entire reasonings for doing such an experiment which I listed earlier.
Off the shelf drivers are no suitable for current drive anyway, the FR will be all wonky.
Anyway, with a ribbon coil I can get the inductance down to arbitrarily low levels with parallel coils. What roll does inductance play in the response of the driver?
I'm trying to understand what parameters would be ideal.
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I suggest (again) that you try reading one of the many textbooks that cover driver design. These provide substantial grounding in the functions and effects of the constituent components. Since you state you have many unique ideas for driver technology, it seems rather peculiar that you don't appear to know a great deal about the basics.
What you appear to be saying, to my chronically sleep-deprived mind, is that by replacing the VC of a moving coil drive unit with an alternative very low impedance coil, it is no longer an MC / dynamic drive unit, but in fact becomes something completely different.
If that is what you are saying, you are wrong. It is not 'other driver tech'. It is exactly the same. The impedance of the VC does not determine whether a drive unit is a moving coil driver or not.
Quaere
1/ Is there a voice coil?
2/ If so, is it attached to cone and where applicable suspension?
3/ Does said coil move within a magnetic gap when an alternating current is applied?
if the answer is 'yes' to the above, and you have given no indication of any other changes, then it is a dynamic (moving coil) drive unit. It doesn't make a monkey's nuts worth of difference to whether it's an MC driver whether the VC impedance is 0.1ohm or 1000ohms.
If that is what you are saying, you are wrong. It is not 'other driver tech'. It is exactly the same. The impedance of the VC does not determine whether a drive unit is a moving coil driver or not.
Quaere
1/ Is there a voice coil?
2/ If so, is it attached to cone and where applicable suspension?
3/ Does said coil move within a magnetic gap when an alternating current is applied?
if the answer is 'yes' to the above, and you have given no indication of any other changes, then it is a dynamic (moving coil) drive unit. It doesn't make a monkey's nuts worth of difference to whether it's an MC driver whether the VC impedance is 0.1ohm or 1000ohms.
That is not what I am saying.
When I say other driver tech I am talking about unusual or advanced implementations of thermoacoustic drivers, ribbons, ect.
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.
I want to try replacing the voice coil of an existing driver with a thick and wide copper foil in order to make it near 0 ohms so it becomes an ideal driver for current drive.
This method of voice coil also reduces the inductance and capacitance to almost non existent levels.
This method would still require thick interconnects due to the RL filter caused by the low resistance in order to keep the drive voltage down to the milivolts where it is intended but since the overall reactance of the driver will be almost nothing I am wondering if there is an advantage to FR or other performance characteristics using this method or if there are other factors I am not taking into account.
I don't know how VC parasitics interact with overall driver response because dynamic driver tech has never interested me so I know little about it. Which is why I am here asking for opinions about the proposition and how I might source the required components for the test.
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Except for the minor point that while it's uncommon / unusual, it isn't any more or less 'advanced' than any other implementation happens to be.
-I don't need to read your posts carefully to know there are advantages (and disadvantages -a point that should not be overlooked) to current drive over voltage drive. That is self evident to anyone who has even a moderate understanding of drive unit and system design. A driver does not necessarily need to have a zero Ohm impedance to 'use these advantages' (or suffer the disadvantages for that matter). We are dealing with engineering realities that are merely a matter of degree.
-A 'thick and wide copper foil' rather than an unspecified alternative does not automatically create a VC of 'near zero Ohms impedance', nor does it automatically reduce L & C 'to almost non-existent levels' sans any kind of qualification whatsoever.
-Presumably by 'interconnects' you are referring to the fly-leads? How do you define 'thick', and on what basis are you making the universal pronouncement sans qualifications that reactance will automatically be 'almost nothing'?
-How do you define 'an advantage (or disadvantage for that matter) to FR or performance characteristics'? Since you haven't specified any of these or the above, the answer to your question about whether there are other factors you are not taking into account is 'on current evidence apparently yes'.
-You have already recieved advice on how to test; summarising, you will need to obtain a drive unit which has replacement suspension components available, along with data on the appropriate adhesives and quantities used, and, where applicable, the correct jigs. This will ensure only one variable (the coil, which you will wind yourself) is changed.
None of which is intended to discourage (let alone disparage). Current drive is perfectly valid, just as voltage drive is, and has its advantages & disadvantages, same as anything else. It is certainly worth exploring.
-I don't need to read your posts carefully to know there are advantages (and disadvantages -a point that should not be overlooked) to current drive over voltage drive. That is self evident to anyone who has even a moderate understanding of drive unit and system design. A driver does not necessarily need to have a zero Ohm impedance to 'use these advantages' (or suffer the disadvantages for that matter). We are dealing with engineering realities that are merely a matter of degree.
-A 'thick and wide copper foil' rather than an unspecified alternative does not automatically create a VC of 'near zero Ohms impedance', nor does it automatically reduce L & C 'to almost non-existent levels' sans any kind of qualification whatsoever.
-Presumably by 'interconnects' you are referring to the fly-leads? How do you define 'thick', and on what basis are you making the universal pronouncement sans qualifications that reactance will automatically be 'almost nothing'?
-How do you define 'an advantage (or disadvantage for that matter) to FR or performance characteristics'? Since you haven't specified any of these or the above, the answer to your question about whether there are other factors you are not taking into account is 'on current evidence apparently yes'.
-You have already recieved advice on how to test; summarising, you will need to obtain a drive unit which has replacement suspension components available, along with data on the appropriate adhesives and quantities used, and, where applicable, the correct jigs. This will ensure only one variable (the coil, which you will wind yourself) is changed.
None of which is intended to discourage (let alone disparage). Current drive is perfectly valid, just as voltage drive is, and has its advantages & disadvantages, same as anything else. It is certainly worth exploring.
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I think you need to get some sleep brother. I was talking about other driver tech. Not dynamic drivers. Read carefully.
Clearly you do need to read carefully because you are misunderstanding my plain english and talking passed my points. Read my previous posts again.
The advantages I spoke of inherently require as close to zero impedance as possible.
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.
By interconnects I mean the connection between the amplifier and the driver.
ad·van·tage
noun
A condition or circumstance that puts one in a favorable or superior position.
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And these claimed advantages are, with your proof of them? Not your assumptions: your proof. Quotations from the Oxford English dictionary of a word familiar to most people who speak the language at primary school level do not in themselves confer this.
Beyond that, no: I don't think I will obey your commands, nor is your 'plain English' very 'plain' given your lack of precision when referring to components, leaving people to guess what you are talking about. As such, I fear you are not in a good position to present yourself as an authority, which itself is a slightly peculiar stance given that you claim you were asking for 'basic information' but do not appear to have studied any texts on moving coil driver design.
Good luck.
Beyond that, no: I don't think I will obey your commands, nor is your 'plain English' very 'plain' given your lack of precision when referring to components, leaving people to guess what you are talking about. As such, I fear you are not in a good position to present yourself as an authority, which itself is a slightly peculiar stance given that you claim you were asking for 'basic information' but do not appear to have studied any texts on moving coil driver design.
Good luck.
You are even having misunderstandings about your misunderstandings.
The word advantage in my context implies that I'm asking if the FR or performance characteristics would be superior to the typically used solutions.
A logical conclusion from the definition of the word advantage.
My english could not be more clear.
Also if you read my words you would know my "claimed" advantages are a physical fact of the parameters I said would be operating under.
Almost no V-swings means capacitance is almost irrelevant and the voltage axis of device transfer curves almost do not come into play.
This is obvious.
I also don't know what you mean by "obey your commands" I didn't command anything of you. So on top of poor reading comprehension you are also taking my obviously rhetorical suggestions as "commands". Nice.
I also very clearly laid myself out to be a non-authority in the matter. So I'm not sure where you got the idea that I think that I am one.
In any case you seem to be upset. Don't get so angry, it's the internet.
Hopefully someone else with a straight head can be so kind as to give an opinion to my approach?
Would be appreciated.
The word advantage in my context implies that I'm asking if the FR or performance characteristics would be superior to the typically used solutions.
A logical conclusion from the definition of the word advantage.
My english could not be more clear.
Also if you read my words you would know my "claimed" advantages are a physical fact of the parameters I said would be operating under.
Almost no V-swings means capacitance is almost irrelevant and the voltage axis of device transfer curves almost do not come into play.
This is obvious.
I also don't know what you mean by "obey your commands" I didn't command anything of you. So on top of poor reading comprehension you are also taking my obviously rhetorical suggestions as "commands". Nice.
I also very clearly laid myself out to be a non-authority in the matter. So I'm not sure where you got the idea that I think that I am one.
In any case you seem to be upset. Don't get so angry, it's the internet.
Hopefully someone else with a straight head can be so kind as to give an opinion to my approach?
Would be appreciated.
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I disagree.
When you said:
You had, in 3 pages of posts up to that point, not once mentioned any type of driver technology beyond a standard dynamic driver with a low-impedance flat wound voice coil.
Yet, you say you meant:
If you expect someone to read between the lines, perhaps your lines should be a little closer together.
Scott's head is straight and he is a valuable resource. If you were to read more carefully, you might notice about 3 pages of opinions already- just not the one you want.
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Kitty, you might want to familiarize yourself with Mr Lindgren’s CV - specifically his several years of working very closely with a current designer /manufacturer of full range drivers, and more generally his extensive experience and studies in the fields of electromotive transducers, as well as design of some very effective loudspeaker enclosures- in which an understanding of basic laws of acoustics physics and the operating principles of drivers can be helpful 
.
But enough smug bitchiness on my part - let’s see your proof.
. But enough smug bitchiness on my part - let’s see your proof.
No.
Electromagnetic force is:
BLI meaning:
B= Magnetic Flux Density
L= is wire length
A typical 2" coil has 100 turns inside the magnetic gap (I know, I design and wind them)
Your ribbon coil has 1 turn.
I is current in Amperes.
Hence and for the same magnetic flux you need 100 times as much current as with a conventional speaker.
An 8 ohm speaker driven by 100W is passing 3.5A RMS.
Your speaker, same specs, single turn coil, will need 350A RMS. (so 500A current capacity).
No.
"Ohms" is a secondary parameter, the primary one being voice coil turns inside the gap, or to be more precise, coil wire length inside the gap.
Obviously a single turn coil will be 100 times shorter than a 100 turn one, in the same magnet structure.
.
Here they are.
To which Scottmoose replied
____
I've read the opinions. The discussion is ongoing.
Although I did miss the last post by JMFhaley. I'll reply here.
Most DAC outputs are 2.5V RMS which is much higher voltage than a theoretical 100 miliohm driver would require.
My problem with amplification is the fact that no amplification will ever have 0% distortion.
It is also another stage that takes up physical space and costs money.
This is exactly the kind of answer I was looking for. Sorry for missing your post.
I see, I didn't realize typical drivers had that many coil turns. Thanks for the info. I guess that puts a damper in the idea doesn't it. Not sure of a way around that one. I guess I'll mark dynamic drivers off my list. Thanks.
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Okay, I'll bite one last time before I leave thread since it seems to have concluded unless others have alternative solutions to add.
Quotation marks imply I am mocking the idea. There would be no other reason for quotation marks to exist between the number 0 if I was being literal.
Also amplifiers that can drive a dead short have been known forever. There's been lots of threads about it over the last couple decades on Diyaudio.
Nelson pass sells one. I built one of my own design.
Just design an amp that amplifies current instead of voltage. The ideal load for a current ampifier is 0 ohms and it is dangerous to feed it an infinite ohm load. The opposite of a voltage amplifier.
Quotation marks imply I am mocking the idea. There would be no other reason for quotation marks to exist between the number 0 if I was being literal.
Also amplifiers that can drive a dead short have been known forever. There's been lots of threads about it over the last couple decades on Diyaudio.
Nelson pass sells one. I built one of my own design.
Just design an amp that amplifies current instead of voltage. The ideal load for a current ampifier is 0 ohms and it is dangerous to feed it an infinite ohm load. The opposite of a voltage amplifier.
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Please don’t leave, I’m sure there’s still more entertainment to be had, and perhaps even some enlightenment for us, once we understand when to take your words at face value, and how long to wait for you to digest the suggested resource material to which you’ve apparently yet to avail yourself.
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