Hi,
viewing ESLs from a current side may be more helpful than taking the voltage side.
To create SPL a charging current is required in a loop between two electrodes.
We must differentiate now between basically four ranges of resistivity of the electrodes:
- conductive range, from 0R to ~1k
- resistive range, from ~1k to ~10M
- dissipative range, from ~10M to ~10e12R
- insulative range, above ~10e12R
Both electrodes conductive means full current, hence maximum SPL and no influence on amplitude response within the audio range.
If at least one electrode is within the resistive range current is reduced, hence there is an effect on amplitude response within the audio range.
If at least one electrode is within the dissipative or insulative range current becomes negligible. Hence SPL will become 0.
The difference between both states though is, that the dissipative electrode slowly may take up charge on which a external electrical field can exhibit a force (*).
If we take a look at the classic SingleEnded 2-electrode ESL with one fixed stator electrode and one moveable diaphragm electrode, it is obvious that both need to be conductive to allow for unhindered current flow. A special case occurs in that the electrodes may be partially resistive to realize a segmented ESL to influence on amplitude response over their area.
The electrodes still need to be contacted at the conductive part of the electrode area.
If an electrode were dissipative or insulative the Panel wouldn't work at all as no (sufficiently high) charging current could flow.
One can use the same view to analyze the symmetrical 3-electrode ESL, of which two are fixed and a moveable diaphragm electrode centered in between.
If all three electrodes are conductive the device equals two series connected capacitors, or two in series connected SingleEnded ESL panels, connected with different polarities.
Either the two fixed or the flexible electrode may be made partially resistive as to allow for frequency dependant (and area dependant) current flow --> Segmentation.
The setup may also be changed to two flexible electrodes and one fixed electrode sandwiched in between.
All the above are descriptions relating to the constant voltage principle
The constant charge principle requires a 3-electrode setup, where a dissipative or insulative electrode is centered between two electrodes which may be conductive or partially resistive.
(*) Here the current flow is only between the two fixed electrodes, generating a electrical field, that in turn can exhibit a force on a charge, that is brought onto the middle electrode, which may be positioned anywhere in the space between the two electrodes.
The charge is brought onto the flexible electrode either by a bias voltage supply feeding a coating of the electrode, or it is fixed by a special manufacturing process into a insulative material electrode, called electret.
You may interchange between two-fixed-outer-one-flexible-middle electrodes and two-flexible outer-one-fixed-middle electrode as they behave electrically the same.
The difference is only mechanical.
In short:
- A symmetrical constant voltage ESL is electrically always a 3-terminal device consisting of two (independant) capacitors sharing the middle terminal and middle electrode. The middle terminal is required as a node where current is flowing into and out of.
- A constant charge ESL is electrically a 2-Terminal single capacitor device.
A third middle Terminal functions only as a potential reference point for the moveable charge (membrane).
It has no direct influence on the electrical circuit but influences on the mechanical working (force acting upon the charge)
Out of these differences in functioning differences in the resistivity ranges of the electrodes occur. Just evaluate where currents needs to flow and which values the currents may take up.
jauu
Calvin
viewing ESLs from a current side may be more helpful than taking the voltage side.
To create SPL a charging current is required in a loop between two electrodes.
We must differentiate now between basically four ranges of resistivity of the electrodes:
- conductive range, from 0R to ~1k
- resistive range, from ~1k to ~10M
- dissipative range, from ~10M to ~10e12R
- insulative range, above ~10e12R
Both electrodes conductive means full current, hence maximum SPL and no influence on amplitude response within the audio range.
If at least one electrode is within the resistive range current is reduced, hence there is an effect on amplitude response within the audio range.
If at least one electrode is within the dissipative or insulative range current becomes negligible. Hence SPL will become 0.
The difference between both states though is, that the dissipative electrode slowly may take up charge on which a external electrical field can exhibit a force (*).
If we take a look at the classic SingleEnded 2-electrode ESL with one fixed stator electrode and one moveable diaphragm electrode, it is obvious that both need to be conductive to allow for unhindered current flow. A special case occurs in that the electrodes may be partially resistive to realize a segmented ESL to influence on amplitude response over their area.
The electrodes still need to be contacted at the conductive part of the electrode area.
If an electrode were dissipative or insulative the Panel wouldn't work at all as no (sufficiently high) charging current could flow.
One can use the same view to analyze the symmetrical 3-electrode ESL, of which two are fixed and a moveable diaphragm electrode centered in between.
If all three electrodes are conductive the device equals two series connected capacitors, or two in series connected SingleEnded ESL panels, connected with different polarities.
Either the two fixed or the flexible electrode may be made partially resistive as to allow for frequency dependant (and area dependant) current flow --> Segmentation.
The setup may also be changed to two flexible electrodes and one fixed electrode sandwiched in between.
All the above are descriptions relating to the constant voltage principle
The constant charge principle requires a 3-electrode setup, where a dissipative or insulative electrode is centered between two electrodes which may be conductive or partially resistive.
(*) Here the current flow is only between the two fixed electrodes, generating a electrical field, that in turn can exhibit a force on a charge, that is brought onto the middle electrode, which may be positioned anywhere in the space between the two electrodes.
The charge is brought onto the flexible electrode either by a bias voltage supply feeding a coating of the electrode, or it is fixed by a special manufacturing process into a insulative material electrode, called electret.
You may interchange between two-fixed-outer-one-flexible-middle electrodes and two-flexible outer-one-fixed-middle electrode as they behave electrically the same.
The difference is only mechanical.
In short:
- A symmetrical constant voltage ESL is electrically always a 3-terminal device consisting of two (independant) capacitors sharing the middle terminal and middle electrode. The middle terminal is required as a node where current is flowing into and out of.
- A constant charge ESL is electrically a 2-Terminal single capacitor device.
A third middle Terminal functions only as a potential reference point for the moveable charge (membrane).
It has no direct influence on the electrical circuit but influences on the mechanical working (force acting upon the charge)
Out of these differences in functioning differences in the resistivity ranges of the electrodes occur. Just evaluate where currents needs to flow and which values the currents may take up.
jauu
Calvin
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The “inverted” ESL configuration is shown in Figure (2A). Equal and opposite charge potentials are placed on the stators by charging the two stator-to-diaphragm capacitances. Note the two large capacitors “Cbig” in the circuit. These are required to complete the low impedance AC circuit so that audio currents i1 and i2 can flow thru their respective stator-to-diaphragm capacitance and change the voltage potential between diaphragm and stators at audio rates. Without them you would have the proverbial case of one hand clapping. See Calvin’s post from some years ago:
http://www.diyaudio.com/forums/planars-exotics/164745-inverted-esl-2.html#post2147612
Note that these large capacitors not only form a low impedance path for the audio signal from the transformer, they are also charged up to the same potential as the HV bias supplies. Since they will need to have capacitance > 10x the ESL panel capacitance to minimize loss of audio signal they act like a low impedance source of bias voltage as well. So, if you choose to use the inverted configuration, you are stuck with the constant voltage mode of operation. As Calvin mentioned in the last post, this results in two current loops driving the two separate stator-to-diaphragm capacitive impedances Zc1 & Zc2.
By now, it should be clear that placing resistance anywhere in these current loops(Figures (2B/C/D)) will cause a roll off in the HF response and if resistances are made very high, will reduce sensitivity. The arrangement shown in (2B) was used by Final to low-pass the response of their bass and midrange panels.
The main advantage of the inverted configuration is that the step-up transformer needs only half the step-up ratio to produce the same output as that from the standard configuration. For the same operating bandwidth, this tends to make the transformer cheaper and easier to design. But this comes at the cost of the inability to operate in the low distortion constant charge mode.
More info here:
http://www.diyaudio.com/forums/plan...d-ask-why-bias-voltage-esl-2.html#post3592875
http://www.diyaudio.com/forums/planars-exotics/164745-inverted-esl-2.html#post2147612
Note that these large capacitors not only form a low impedance path for the audio signal from the transformer, they are also charged up to the same potential as the HV bias supplies. Since they will need to have capacitance > 10x the ESL panel capacitance to minimize loss of audio signal they act like a low impedance source of bias voltage as well. So, if you choose to use the inverted configuration, you are stuck with the constant voltage mode of operation. As Calvin mentioned in the last post, this results in two current loops driving the two separate stator-to-diaphragm capacitive impedances Zc1 & Zc2.
By now, it should be clear that placing resistance anywhere in these current loops(Figures (2B/C/D)) will cause a roll off in the HF response and if resistances are made very high, will reduce sensitivity. The arrangement shown in (2B) was used by Final to low-pass the response of their bass and midrange panels.
The main advantage of the inverted configuration is that the step-up transformer needs only half the step-up ratio to produce the same output as that from the standard configuration. For the same operating bandwidth, this tends to make the transformer cheaper and easier to design. But this comes at the cost of the inability to operate in the low distortion constant charge mode.
More info here:
http://www.diyaudio.com/forums/plan...d-ask-why-bias-voltage-esl-2.html#post3592875
A double diaphragm/triple stator arrangement is electrically nothing more than two standard ESLs operating in parallel. As such you will still need to have relatively low circuit impedances for driving the two capacitances (center stator-to-front stator) and (center stator-to-rear stator) at audio frequencies.
Attachments
but that's not what I propose - drive the 2 low resistance membranes with the audio diff V creating the audio varying E field between them
the single central stator is biased and has high R to give the stationary charges that the E field reacts against
the single central stator is biased and has high R to give the stationary charges that the E field reacts against
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Aaah...I follow now.
Calvin already covered this configuration, and yes it will operate in constant charge mode.
"...You may interchange between two-fixed-outer-one-flexible-middle electrodes and two-flexible outer-one-fixed-middle electrode as they behave electrically the same. The difference is only mechanical..."
The earliest mention I have seen of this configuration was in a 1956 WW article by Leak(attached).
Many years ago I experimented with this configuration for its immunity to dust and contaminates in the airgap.
There were a few drawbacks though, that caused me not to pursue it further.
1) In the zero signal state, the diaphragms do not have equal forces pulling on them from both sides as in the standard stator-diaphragm-stator arrangement. So I could only use about half the HV bias level before the diaphragms collapsed to the central stator. This dropped sensitivity by 6dB or more.
2) The top octave response suffered because of the phase difference between the two spaced diapahrams.
3) It was difficult to construct reliably as the central stator needed to be stiff, flat, and thin with no ability to add external bracing as is common with the standard configuration.
as long as we're waiting for lage enough graphene sheets why not speculate about Diamond Materials - Diamond Disks and Wafers stator?
doped for volume resistivity? - or just coated both sides
doped for volume resistivity? - or just coated both sides
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Hi,
and 4) even though its doubled its membrane area will the output be the same as the classic single-membrane-two-stator ESL as the same amount of force acts upon two membranes, so the force/area factor is halved for each membrane.
jauu
Calvin
and 4) even though its doubled its membrane area will the output be the same as the classic single-membrane-two-stator ESL as the same amount of force acts upon two membranes, so the force/area factor is halved for each membrane.
jauu
Calvin
Good point.
Graphene is basically flat sheets with the same basic structure as buckytubes. A lot of work has been done with doping buckytubes to change its electrical properties (the report I read was aimed at producing high temperature superconductors). Doping to produce resistors should be possible. As graphene is in its early development is is reasonable to assume that by the time the technology to produce large sheets is developed the technology to dope will have also developed. So graphene with probably be available with ideal diaphragm properties for ELS.
Here's hoping.
Niffy
Graphene is here. I unwrapped my new "EarFun Free" ear pods (like just us$50) and they claim to have graphene diaphragms. Some Rice-Kellogg drivers also use the term in their promotion too.
Isn't that amazing. Seven and a half years ago, we were dreaming of seeing graphene (thought be well beyond practical reach at the time) in speakers and now it is here. Great.
I guess quantum amps are next.
B.
Isn't that amazing. Seven and a half years ago, we were dreaming of seeing graphene (thought be well beyond practical reach at the time) in speakers and now it is here. Great.
I guess quantum amps are next.
B.
50$ graphene membranes.... smells like ******** 🙂
Graphene has become a red flag for everything that is not what they say it is.
just put graphene in the most stupid tech, and its innovating.. or just marketing 🙂
halve of the products have just graphite in them, nothing more. a new technique to produce pure graphene using the flash technique, for instance is not really a MASS MASS production method. all other methods are well not pure graphene. highly contaminated with graphite 🙂
Graphene has become a red flag for everything that is not what they say it is.
just put graphene in the most stupid tech, and its innovating.. or just marketing 🙂
halve of the products have just graphite in them, nothing more. a new technique to produce pure graphene using the flash technique, for instance is not really a MASS MASS production method. all other methods are well not pure graphene. highly contaminated with graphite 🙂
LOL, totally agree. The same as with nanotechnology.
They wont tell you how much graphene is in the product. As grahene is highly flexible, it is likely to be dispersed in kind of a resin to get some solid material
Article from September 2019 discussing the current state of graphene in speakers. Discusses the various ways it can be used and is being used currently.
The Current State of Graphene in Commercial Loudspeaker Products - Speaker Related Companies - Products & Services Feature Article By LIS STAFF
The Current State of Graphene in Commercial Loudspeaker Products - Speaker Related Companies - Products & Services Feature Article By LIS STAFF
I worked briefly as a consultant for a company purporting to be in the Graphene loudspeaker business. Let's say briefly should say it all.
Thanks much. Explains a lot. Seems next few years of R&D may result in great improvements, as suggested by the plot for the new Ora headphones.
I wonder if Mark worked for any of the companies in that report that used a kind of "graphene" compounded by the "chemists" in the Marketing Department?
B.
Let's just say that the company has already been named.
Production cycles to manufacture a diaphragm were glacial. True differences between materials negligible. The merits of any product end up being found in one way or the other.
Ben. Call me if you want to talk.
Production cycles to manufacture a diaphragm were glacial. True differences between materials negligible. The merits of any product end up being found in one way or the other.
Ben. Call me if you want to talk.
Perhaps headphones are a better fit currently, given the smaller diaphragm size needed and the reduced sound level demand.