[bigshot]

I have Christmas lights strung above my stereo system. It gives me the "warm glow" of tubes with solid state fidelity.

 

[analogsurviver]

Wow! There's a whole magazine for amateurs!

If you have missed it, you SHOULD check it out - and its offsprings, Speaker Builder and later Glass Audio, whose names say it all.

Because in those magazines, MANY by now premier manufacturers/designs were first making a public appearence. And in a honest, no holds barred fashion, not in a commercially limited aimed only at profit way. Many were THE true labours of love . And many things you can buy today can be directly traced to TAA, SB and GA articles. One of the most recognizable designs that will be around long after we on this thread will long be gone, is D'Appolito loudspeaker arrangement. If you are not blind, you must have seen it applied in countless commercially available designs following its first appearence in a Speaker Builder article.

Here the video presentation by the man himself - and what a pity the video about one of the best sounding loudspeaker arrangement/array simulating a point source with non coincident drivers itself has a very poor sound quality. Blacksmith's mare syndrom strikes again ... :

 

[analogsurviver]

Just to be transparent ...i have owned(and loved) some truly beastly tube amps(sonic frontiers power2 to name 1)they would drive antthing.....but i don't believe for a second that they couldn't be equaled in ability to drive speakers or headphones by solid state devices(sonics might be debatable...maybe)We are talking about volts/ohms/amperage here ....solid state is king here my friend.Unless of course you are fllying an older MIG fighter jet where tubes where used for there immunity to EMP.

I am NOTORIOUS for picking on tube/valve lovers - for all the reasons you may have in mind in the above . I have even invented a rather mocking name for tubes/valves :

HSD ( Hollow State Device , as opposed to the SSD = Solid State Device )

But, if there is any application for HSDs where they are NATURALLY superiour/more adapted to the task than SSD can ever hope for, it IS the output stage in high voltage amps.

The BIG amp for the electrostatic loudspeakers is completely built with HSDs. No SSD in signal path in sight, only few in rectifiers for power supplies. The reason WHY can be very quickly deduced from its power supply requirements:

input stage ; + - 275 VDC
driver stage: + - 650 VDC
output B+ : + 6.5 KVDC

Following the EU regulation for safety, this schematics has been, naturally, removed from the internet. And, as always, THE MOST INTERESTING is NOT available online - never was or will be.

 

[bigshot]

Huh?

 

[analogsurviver]

Now you're trying to say that designing an amp that is flat is harder to do than one with rolled-off high end??? Nonsense! And then you say headphones exceed the requriemenst of speakers for drive in the HF range? Again, nonsense. Electrically, that cannot be. The impedance of an electrostatic speaker drops to below 2 ohms at high frequencies. The impedance of electrostatic headphones is nowhere near 2 ohms....it's more like 20K or higher! With a tiny capacitive reactance or 150pf? Why, on earth, is that hard to drive? You're theories defy physics.
You should re-read the above. You just said the electrostatic headphone amp needs to be the size of the Sanders amp, but only not the size of the Sanders amp. You're counteracting yourself. Which is it? I can't be both. And again, where's all that power going????
Hogwash. I have the right probes in my junk box. Several copies.
Please state the model number. Standard Tek 10X probes would be just fine.
Sorry, this is also nonsense. You should work with RF for a while, and get used to working around 100mHz or so...then get real. It's all measurable.

Why do you think a capacitor doesn't dissipate heat? Unused power is converted to heat. Always. Make the load capacitive and it changes how you calculate it, but it doesn't get converted to acoustic energy, and it doesn't just vanish. Remember, conservation of energy? It all can be accounted for. It has to be. Sorry, that's physics.

However, the reality is, you're not dumping 70W or so into the drivers, they are far too high impedance for that. They're handling likely about 2W, possible 5W tops. Look at the impedance of the drivers your working with. And most of that power is lost to heat because you're not shoving 5W at your ears at close range without permanent damage.

You really SHOULD sit back and reconsider ALL of the above - because you've just raised the bar for Barking Up The Wrong Tree; and not by a small margin. Frankly, it is amazing for someone who otherwise is very knowledgeable to COMPLETELY fail at task that is VERY different from everything else you are accustomed to work with.

Just in case you plan to continue with this lunacy, please DO check https://ifi-audio.com/portfolio-view/pro-iesl/

Just how do you expect normal 10x probes rated at 400 V to survive 640 VRMS ( it CAN exceed this value, it is only spec'd at it ... ) ? You do know what VRMS means ?

Only 1:100 probes are really suitable in the case of electrostatic amps ( the BIG one produces over 10 kVpp output ... ) - and here they are : https://www.tek.com/high-voltage-probe-single-ended

 

[pinnahertz]

Just in case you plan to continue with this lunacy, please DO check https://ifi-audio.com/portfolio-view/pro-iesl/

I might suggest you do the same. Please note the power consumption of the above device then come back and tell me how it delivers 70W to the headphones. And why you'd want to in the first place.

Just how do you expect normal 10x probes rated at 400 V to survive 640 VRMS ( it CAN exceed this value, it is only spec'd at it ... ) ?

Ever heard of resistors? They're great for getting voltages down.

You do know what VRMS means ?

Knock it off.

Only 1:100 probes are really suitable in the case of electrostatic amps ( the BIG one produces over 10 kVpp output ... ) - and here they are : https://www.tek.com/high-voltage-probe-single-ended

Did you check the pricing? The P5122, which would be just fine in this application, is completely affordable. But also, unnecessary. I own two HV probes, 15KV, 100mHz, and I think I got them used for $20.

Now look. I've raised numerous objections to your nonsense. You chosen to ignore the key ones and focus on what? A high voltage probe? And somehow are trying to use that argument as some sort of excuse for what? Why some amps aren't tested? OR we can't build an adequate ABX switcher?

Well, let me remind you. You claimed that an ABX switcher that added to the already tiny capacitance of the system would be inadequate for the job and could not be built. I countered that, both with that it could easily be built and questioned that adding a bit more C would even cause an issue. You responded with, "The only thing you are probably correct in this post is tha ABX switching device could be conceived without too adverse effects."

So, we're done. We agree about the core issue. All the rest of this is more nonsense that clouds the core issue. So if you have any other pertinent points to make, other than insulting me, then make them. Or move on.

 

[analogsurviver]

I might suggest you do the same. Please note the power consumption of the above device then come back and tell me how it delivers 70W to the headphones. And why you'd want to in the first place.

Ever heard of resistors? They're great for getting voltages down.
Knock it off.

Did you check the pricing? The P5122, which would be just fine in this application, is completely affordable. But also, unnecessary. I own two HV probes, 15KV, 100mHz, and I think I got them used for $20.

Now look. I've raised numerous objections to your nonsense. You chosen to ignore the key ones and focus on what? A high voltage probe? And somehow are trying to use that argument as some sort of excuse for what? Why some amps aren't tested? OR we can't build an adequate ABX switcher?

Well, let me remind you. You claimed that an ABX switcher that added to the already tiny capacitance of the system would be inadequate for the job and could not be built. I countered that, both with that it could easily be built and questioned that adding a bit more C would even cause an issue. You responded with, "The only thing you are probably correct in this post is tha ABX switching device could be conceived without too adverse effects."

So, we're done. We agree about the core issue. All the rest of this is more nonsense that clouds the core issue. So if you have any other pertinent points to make, other than insulting me, then make them. Or move on.

Now, this is NOT meant to insult.

You have failed - miserably so - at understanding the CORE problem of DRIVING the electrostatic transducer.

It is ( if we neglect some extremely small resistive and inductive components ) more than 99% PURE CAPACITANCE. Furthermore, more of 80% of this capacitance is air ( the rest are spacers, made from some high quality dialectric material ) - so, whatever electrical losses/dissiapation can occur, they are VERY small. For all practical purposes, it does not dissiapate heat - and even if it does get to dissiapate a watt or so of heat, what are ES loudspeaker sizes again ? 1W across a > 1 square meter surface - will anybody be able to perceive that ? The same ratio goes for headphones, they MIGHT dissiapate 0.1W or less heat - again, negligible .

Electrostatic transducer is 100% efficient over most of its operating range, but most notably the midrange - EVERYTHING gets converted into sound, that's why they are considered the best , particularly for midrange. At lower frequencies, limitations due to speaker diaphragm tension come into play - and at higher frequencies, the mass of the driver. The mass of the ES driver is the diaphragm itself, air in both side gaps, air in both side perforations of stators - AND air on both side gaps and mass of the "dustcover" diaphragms IF used in the design. For ESLs that use gas other than air in their drivers, it has to be recalculated for the gas in question ( most usually hellium ). In ANY case, the mass of the diaphragm itself is FAR lower than the the mass of the gas portion of the driver, meaning the diaphragm is inherently well damped.

Above was for ACOUSTIC efficiency of transduction. Electrical efficiency is an entirely different matter - as driving the electrostatic driver does not only mean swinging the volts required, but it requires CHARGING that capacitance first in order to be able to swing that voltage... Yes, you need ever higher output/current capability of the amp with ever increasing frequency - and HERE lies the core problem. Before you know it, Volts multiplied by miliAmperes required mean - BIG amplifier. And that's WHY loudspeaker amps with their mandatory EQ for speakers with falling response in the treble ARE easier to make than the flat linear characteristics required by headphones. If anywhere in audio slew rate limiting is a real and very tangible AND extremely audible problem, it is in high voltage amps for electrostatics - either speakers or headphones. Basically, NEVER enough power - as capacitor is ultimately dead short, requiring infinite power to drive.
Only the biggest/best/most expensive escape being caught out audibly ...

The funny aspect of this is the fact that some of the world's best subwoofers are - electrostatic ! They can be made to operate at near 100 % efficiency ( normal dynamic driver loudspeaker howers around 1% efficiency - 100 W electrical input produces 1 W acoustic power output ) - and imagine WHAT can be achieved with two 10 W ( more appropriately : 10 VA ) ES amps driving those nearly 100% efficient electrostatic subwoofers. For anything required by the subwoofer in frequency, the impedance of the driver remains so high that hardly any current is required from the amp - FYI, the acoustic power output of a symphony orchestra is "around" 5 watts IIRC ...

These ES subwoofers have to be one of the most closely guarded secrets in audio - but possible versions are two:

- an ES "ceiling" built in situ
- a series of diaphragms driven in acoustical series and placed in the corner ( looks much like the Klipshorn at first glance ); this has even been - VERY briefly - offered as plans in Speaker Builder in 80s . Unfortunately, decided to pull the trigger too late...

Now, PLEASE look at the figures - voltages, impedances, etc. It is ultra clear you have no experience with electrostatics - NONE whatsoever. You simply CAN NOT make a voltage divider ( aka probe ) with resistors alone; for the thing to have anything even remotely approaching the linear frequency response, it HAS to be compensated by capacitor(s).

http://how-to.wikia.com/wiki/How_to_make_a_100X_oscilloscope_probe

You have to design with voltage swings in mind - it also has to withstand the power required. And, in the Sanders amp article you can find WHY the above described probe is not fully adequate for measuring distortion of ( really good ) high voltage amps ( or transformers driven by the conventional low voltage amps for dynamic speakers ).

And, if you still have not figured it out where the power goes - it is dissiapated in the amplifier ; either direct drive high voltage or conventional low voltage driving step up transformer. That's why any of these amps will never be minuscule affairs.

The advantage of the step up transformer is the fact that it does not step up only voltage, but also the SLEW RATE of the amp driving it - but until the advent of the iFi unit, other undesirable characteristics of the transformers ( core saturation, distortion, hysteresis, too much deviations from linear response, etc ) have been bad enough for almost everybody to prefer a high voltage amp - even of lower quality than say Stax SRM1MK2. Now, only the very best > most expensive high voltage designs for driving headphones can claim being equal or slightly better than iFi unit driven by a decent speaker amp. The iFi unit can output 70w+ into the headphones themselves - if the amplifier driving it has enough power and is stable into this reactive load . It is, basically, achieving the same thing as my super amp - with far lower cost and above all, much better safety - those few shortcomings it does have compared to the non plus ultra amp be damned.

BTW - the power consumption of the iFi unit covers ONLY polarizing voltage and pilot light requirement - it is dead cold in operation ...

I hope this explains the matter well enough.

 

[KeithEmo]

There's some truth on both sides here.

It is in fact true that some "electrostatic amplifiers" do interact significantly to small differences in capacitance.
For example, many headphone/amp combinations actually have a significantly different rated frequency response depending on whether you use a six foot extension cable or not (yes, really).
More significantly, some transformer-type energizers react in more interesting ways (they may have a resonance that has a significant effect on their frequency response, and altering the capacitance will change it).
Many "garden variety" relays, and even many switches, don't handle high voltages very well, and some have significant capacitance between the electrodes, but all this means is that you have to pick a relay or switch that's appropriate to the job.
(If you wanted to match things precisely, you would shorten the cable by the precise amount necessary to compensate for the capacitance of the relay or switch.)

An ideal capacitor, by definition, consumes NO power.
A pure capacitor is purely reactive; you may put voltage across it, and current may pass through it, but they are out of phase - so the actual power consumed is absolutely zero.
Capacitors only "burn" power to the degree that they are not ideal capacitors (that would be that "ESR" number - which stands for "equivalent series resistance" in a capacitor).
As it so happens, because of the way they're constructed, most electrostatic headphones and speakers are very near ideal capacitors.

Any power that is consumed driving electrostatic headphones or speakers is consumed as a side effect of how the circuitry driving them operates (and it may be unavoidable given that context).
For example, a Class A/B amplifier is about 70% efficient, at full output, into a resistive load.
However, assuming it is stable into a purely capacitive load, it will still consume power proportional to the voltage and current it is delivering.
So, a typical class A/B amplifier, delivering 20 watts into a resistive load, may consume 8 watts as heat.
And that same amplifier, assuming it's stable into a capacitive load, and is delivering 20 VOLT-AMPS to a capacitive load, will consume a similar amount of wasted power as heat.
However, the purely capacitive load will "consume" that 20 VA of voltage and current, while dissipating no heat and burning no power whatsoever.
(In an electrostatic speaker, the actual energy used to move the air will appear in the equation as a resistive inefficiency in the capacitor... but it's a tiny percentage.)

The short answer is that the power is being consumed by the amplifier and the other electronics involved.
It is true that, depending on the design, it may end up consuming a significant amount of power as a side effect of delivering the required voltage and current.

Yes, ABX/DBT in the case of comparing electrostatic headphone amps/energizers must be done with the same pair of headphones. 5 second switching time is unacceptable. However, anyone who can design such a high voltage amplifier can easily conceive of the correct design for a switching device, and capacitance should not be a problem.
Are you seriously trying to say that the amp, normally driving about a 22K load, can't deal with an additional C of up to 50pf without changing response? Seriously? The capacitive reactance of your 145pf headphones and cable is about 33K at 30kHz! No amp designer worth his salt would attempt to drive that with a matched source Z in the first place, so the 10:1 rule would still apply.

The additional possible C of any switching system would absolutely NOT be a problem. At least on Planet Earth where the laws of physics still apply.
Oh, really? So where's that power going??? If it's not going into acoustic energy (which is absolutely is not), then it's going up in heat...in the drivers....on your head? So, you want a pair of 70W light bulbs strapped to your skull? You plan 2 minute listening sessions with 6 weeks of healing?

The resources you should seriously attempt to acquire is technical knowlege and understanding of electronics and physics.

 

[KeithEmo]

Just to throw in a few facts here.....

1)
The designs for electrostatic speaker amplifiers being discussed here (the ones fro TAA) were published in the 1970's and thereabouts. This was in the early days of the Internet... They did in fact turn up on the Internet after that, and I've seen occasional copies of them. They're difficult to find now simply because they are very old, and so weren't widely distributed - and not on sites that are still around, and nobody looks for them very much any more. At one point, TAA offered all of their back issues in electronic form, on CD. if you do a bit of digging with various search engines you will still find many of them.

2)
I should also point out one of the main reasons why DIY audio equipment was often overbuilt in those days. It's very simple, but not necessarily obvious if you weren't around back then. In the early 1950's through even the 1980's, there was a lot of high quality military equipment, and a lot of mil-spec parts, available as military surplus at absurdly low prices. A part that cost hundreds of dollars on the retail market might cost $1 surplus... and the military had a well-deserved reputation for using ridiculously overspecified and expensive parts. For example, test equipment was often rated to operate at temperatures like -50 degrees (just in case you needed to run it in the Arctic). Therefore, it became common practice among DIYers to use parts like Pyranol capacitors. A 20 uF/600V Pyranol capacitor was about the size of a can of Spam, weighed over a pound, had excellent electrical properties for many applications, and cost a lot... and, yes, they lasted forever and were virtually indestructible. However, you could pick one up at your local military surplus store for $1. Therefore, it became "audiophile chic" to "make equipment that was built like a tank - because it was made with parts from a tank". In some cases, the performance was actually excellent; in others, it was simply an affectation. It was cliche that "military equipment weighed a ton, cost a fortune, and lasted forever". This was certainly not a problem - but it did lead to many situations where a massively overspecified part was used, not because it helped anything, but "just because it was there". (People would, quite literally, acquire a set of big radio tubes, or a set of fancy capacitors, or even a complete power supply module, then look for a project where they could use them. For example, 20 uF/600V Pyranol capacitors were often used because they were a very commonly available value.)

3)
WARNING! Very few modern "standard" oscilloscope probes are rated to tolerate over 600V; and some probes used on modern digital oscilloscopes are only rated for as little as 50V; if you try to use them on the sort of voltages you will find in an electrostatic speaker you WILL burn them out or damage your oscilloscope. You will also find that many super-high-voltage circuits, like electrostatic bias supplies, operate at extremely low current and extremely high impedance. Therefore, even the relatively high impedance of a standard probe will load them impractically.... (A typical x10 scope probe has an impedance of 10 megOhms... the bias output on a typical electrostatic headphone amplifier has a 50 megOhm or higher resistor in series with it.) Real high voltage probes have an absurdly high impedance which won't unduly load down this sort of circuitry. (And they aren't terribly expensive; note that you only need a DC probe for measuring a bias supply.)

4)
The impedance of a capacitor drops with rising frequency.... following the well known formula: Xc = 1 / (2piFC)
Xc is the capacitive reactance (in Ohms)
pi is the constant Pi (3.141592654 ..... )
F is the frequency - in Hz
C is the capacitance - in FARADS (not uF)
(it is never zero... but halves every time you double the frequency or the capacitance)

Single electrostatic panels follow this equation quite precisely.
Once things like crossovers and transformers become involved it becomes rather more complex.
Most normal amplifier designs DO NOT operate well into a purely capacitive load (so slightly different designs are required).

5)
Large flat panel speakers do tend to be directional at very high frequencies - and so some people may choose to EQ them (this is true equally for electrostatics and planars like Magnepans).
However, most large electrostatics solve this problem by using multiple narrow panels in a curved array, or using some sort of curved panels, or using separate narrow panels for high frequencies (there are other solutions).
Electrostatic headphones tend to have a small area, close spacing between the various parts, and a single driver per side.
Most electrostatic headphones operate with between 300V and 650V bias - and most headphone amps deliver several hundred volts RMS of audio signal (many operate differentially, from a supply in the 1000V range).
Most electrostatic SPEAKERS have a much larger area, but also wider spacing (for various reasons).
The wider spacing, and the need to move more air, necessitates higher bias and drive voltages.
Most electrostatic SPEAKERS operate with a bias voltage in the 2000V to 3000V range, and require audio drive voltages in a similar range.

6)
Capacitors DO NOT dissipate heat; an ideal capacitor dissipates no heat and consumes no power.
You may put voltage across it, and current will flow through it, but they are always out of phase.
Real world capacitors may get warm - to the degree that they stray from being perfect capacitors (the most common cause is ESR - equivalent series resistance).
However, as it turns out, most electrostatic speaker and headphone drivers are very near perfect capacitors.
Some tiny amount of power is actually consumed moving the air; and some time amount is lost due to ESR and dielectric losses.

The vast majority of the power that is actually consumed as heat is consumed in the amplifier.
(You will find that, if you design a tube amplifier that is capable of delivering several thousand volts, and several hundred milliamps, of audio output, it's probably going to end up big and heavy.)

Now you're trying to say that designing an amp that is flat is harder to do than one with rolled-off high end??? Nonsense! And then you say headphones exceed the requriemenst of speakers for drive in the HF range? Again, nonsense. Electrically, that cannot be. The impedance of an electrostatic speaker drops to below 2 ohms at high frequencies. The impedance of electrostatic headphones is nowhere near 2 ohms....it's more like 20K or higher! With a tiny capacitive reactance or 150pf? Why, on earth, is that hard to drive? You're theories defy physics.
You should re-read the above. You just said the electrostatic headphone amp needs to be the size of the Sanders amp, but only not the size of the Sanders amp. You're counteracting yourself. Which is it? I can't be both. And again, where's all that power going????
Hogwash. I have the right probes in my junk box. Several copies.
Please state the model number. Standard Tek 10X probes would be just fine.
Sorry, this is also nonsense. You should work with RF for a while, and get used to working around 100mHz or so...then get real. It's all measurable.

Why do you think a capacitor doesn't dissipate heat? Unused power is converted to heat. Always. Make the load capacitive and it changes how you calculate it, but it doesn't get converted to acoustic energy, and it doesn't just vanish. Remember, conservation of energy? It all can be accounted for. It has to be. Sorry, that's physics.

However, the reality is, you're not dumping 70W or so into the drivers, they are far too high impedance for that. They're handling likely about 2W, possible 5W tops. Look at the impedance of the drivers your working with. And most of that power is lost to heat because you're not shoving 5W at your ears at close range without permanent damage.

 

[drtechno]

Capacitors don't heat up unless they are used as current limiting applications (like limiting primary transformer currents in "R" core transformers) and phase shift power loading (shaded pole motors) but only if the cap is sized too small for the demand (or deteriorated due to it drying out).

 

[pinnahertz]

Now, this is NOT meant to insult.

You have failed - miserably so - at understanding the CORE problem of DRIVING the electrostatic transducer.

How is the above to be read without insult?

Electrostatic transducer is 100% efficient over most of its operating range, but most notably the midrange - EVERYTHING gets converted into sound, that's why they are considered the best , particularly for midrange.

I just re-read Walker's equation. You know, the one that states that if an ESL is driven with constant current the response is flat, but because it's capacitive, it has a 6dB/octave rising response with constant voltage. The conversion of electrical energy to acoustic energy therefore occurs also on that 6dB/octave slope. And therefore, the ESL cannot be 100% efficient at any frequency. In addition, because of the diaphragm being a dipole, half the acoustic power is emitted from the back, so the forward efficiency must be -6dB below the total. And all of that is without considering the actual efficiency of conversion from electrical energy to acoustic.

Above was for ACOUSTIC efficiency of transduction. Electrical efficiency is an entirely different matter - as driving the electrostatic driver does not only mean swinging the volts required, but it requires CHARGING that capacitance first in order to be able to swing that voltage... Yes, you need ever higher output/current capability of the amp with ever increasing frequency - and HERE lies the core problem. Before you know it, Volts multiplied by miliAmperes required mean - BIG amplifier.

But, it's a capacitor, so it has changing impedance with frequency. When you look at the spectral energy distribution of music, it's about 20dB lower at 20kHz than it is below 1kHz. The amp needs to tolerate a low, capacitive, impedance. That's it.

Basically, NEVER enough power - as capacitor is ultimately dead short, requiring infinite power to drive.

This is the kind of statement you make that I have the most trouble with. A capacitor, ANY capacitor, is not a dead short, ever. Capacitive reactance means its impedance drops with rising frequency. It some frequency the impedance becomes very, very low, but it's still capacitive reactance. Depending on the capacitance, the actual load presented to an amplifier can be anything, and for an ESL will drop quite low at high frequencies, but there's very little energy up there, and with rising efficiency of an ELS, less power...much less power...is required to drive that very low Z load. A capacitor is not a dead short, and does not require infinite power to drive when you consider a meaningful value for an audio device. A dead short has an impedance of zero ohms at all frequencies.

The funny aspect of this is the fact that some of the world's best subwoofers are - electrostatic ! They can be made to operate at near 100 % efficiency ( normal dynamic driver loudspeaker howers around 1% efficiency - 100 W electrical input produces 1 W acoustic power output ) - and imagine WHAT can be achieved with two 10 W ( more appropriately : 10 VA ) ES amps driving those nearly 100% efficient electrostatic subwoofers. For anything required by the subwoofer in frequency, the impedance of the driver remains so high that hardly any current is required from the amp - FYI, the acoustic power output of a symphony orchestra is "around" 5 watts IIRC ...

Got an actual reference for all of that?

 

[drtechno]

But, it's a capacitor, so it has changing impedance with frequency. A capacitor, ANY capacitor, is not a dead short, ever. Capacitive reactance means its impedance drops with rising frequency. It some frequency the impedance becomes very, very low, but it's still capacitive reactance.

True, and when the frequency goes greater than the frequency resonance of the circuit (its lowest impedance point), the capacitor starts acting like an inductor, and lags the voltage.

 

[analogsurviver]

True, and when the frequency goes greater than the frequency resonance of the circuit (its lowest impedance point), the capacitor starts acting like an inductor, and lags the voltage.

Yes, true. But amps run out of power/current WAAAAY before this frequency is ever reached in practice. The result is slew rate limiting - which sounds anything but nice.

In real world, it does not matter. I could go and calculate or measure the exact frequency electrostatic speaker or headohone with its cable reaches its resonant frequency and starts behaving like an inductor - but amps, even the mastodont sized and powered accordingly, run out of juice well before that. Not to mention thingies that can run on batteries ...

 

[KeithEmo]

You are describing a resonant circuit - which is comprised of both a capacitor and an inductor.

A pure capacitor does not have any inductance - and does not have a resonant frequency.
Many specific types of capacitors are fabricated by making a sandwich of flat insulators and conductors - and then rolling it up.
Those types tend to have significant inductance, and so may actually be considered to be a resonant circuit, with a resonant frequency.
Likewise, there is often enough capacitance between the windings on a transformer that it ends up acting as a resonant circuit.
(And, yes, at the level of the absurd, a straight one inch piece of wire has some tiny amount of capacitance and inductance.)

However, for most practical calculations, when taken by itself, the driver of an electrostatic speaker is usually a pure capacitor.

True, and when the frequency goes greater than the frequency resonance of the circuit (its lowest impedance point), the capacitor starts acting like an inductor, and lags the voltage.

 

[drtechno]

Yes, true. But amps run out of power/current WAAAAY before this frequency is ever reached in practice. The result is slew rate limiting - which sounds anything but nice.

Yes, that goes hand and hand with the phenomenon that semiconductor amps (both discrete as well as op amps) have that is called "current fold-over" which is the effect of the potential output voltage being lowered due to the loading effect of the load.