I do not know how my S2 driver will sound but I defiantly know that it will have the problem with temperature. Looking prematurely at the driver’s sound it looks like it produce the necessary magnetic force at 2A-2.3A, that heats a lot of this driver.

This brings an interesting dilemma about a conceptual design of HF field coil drivers. With the LF driver it is easy and with the lower current a LF driver works very nice. However, to get HF and transits from the HF driver it looks like it is necessary to drive a driver harder with the poles locate as close to gap as possible. However, the drivers witch work “inside”, and particularly if we want to reduce the inner driver tape rate have, no space to locate a sufficient amount of core. So, a solution would be to put coils in the back path but since we do not want to locate coils too far from the gap we still face the temperature dilemma. Is water cooling, low take rate, “inside firing” drive would be too crazy to consider?

So, how to make the “inside firing” drivers shorter, dump inside a sufficient amount of electromagnetic core at high current and still do not heat it up? At this point I do not know. Probably the “outside firing” diaphragm is the only solution for a high current, low temperature filed coil driver but it would not be the Vitavox’s cones and plug anymore, and only God knows how it might sound.

Well, at this point, without known if an electromagnet is worth to pursue, I would not worry about it but purple conceptually I feel that there is no solution for  “inside firing”, HF, low tape rate, filed-coil compression driver, unless you pump a liquid helium through the driver…

PS: Taking about the Cogent drivers with “soft” fifer cones… it woiuld be fun to listen it at triple of qudruple current driving that coil (if they have enoght core matera in there)....

Hi Romy,
Splendid work - much appreciated research this!

I know this is totally premature, but if you do find that you prefer the S2 as the flux is increased and hit a current limit for the coil, then you *might* get a flux benefit by using a lower carbon alloy than 12L14, for example, 1005. But the choice of alloy may not be the bottleneck.

Also admire your restraint in not immediately proclaiming this the best thing ever :-) If you're previous investigations into the S2 are anything to go by, it's going to take a while to get to the bottom of this one, especially as you can now play with the current...

[just edited - I didn't see your above post relating to temperature, believe it or not]
To increase the flux, may want to revisit the part magnet/part field coil idea. Trouble is, Nd doesn't like getting hot. Maybe ferrofluid could be used. Or build your own outer magnetic circuit as you are saying, retaining the S2 diaphragm, phase plug, pole pieces and throat.... OK, maybe Rich will have more useful suggestions....

Great stuff,
cv

cv wrote:

Or build your own outer magnetic circuit as you are saying, retaining the S2 diaphragm, phase plug, pole pieces and throat....

If you read the thread form beginning then you will see that it was my original ultimate intention: to but own magnetic system with S2 diaphragm, phase plug, pole pieces but shortening the S2 driver, making his inner rate 450Hz-500Hz instead of 180Hz. The electromagnet is not really my primary objective but juts the way to generate flux more easily. I would probably do not go there if I have in my disposal available custom-shaped alnico or Neodymium magnets. However, it is much harder, not to mention complicated in the R&D stage to deal with permanent magnets. So, I figure that if I have a change to learn about the field-foil and their constitution to sound then why shouldn’t I. The electromagnetic drivers is kind of “Terra Incognito” in audio and very few people who do it, or who done it in past do it, from my point of view, not at the interpretable level of demands. I had two encouragements last year to try the electromagnetics. The Cogent boys and Shindo. The Cogent boys show that it is very simple to make a filed-coil drives, particularly if a very good quality diaphragm, phase plug and pole pieces have exist. The Shindo drivers encouraged me by pissing me off. There is a guy in NY who sells/import Shindo own electromagnetic and Shindo electromagnetic-modified compression drivers. I have very moderate interest in Shindo Company as I am familiar with their murky electronics, entire their cloudy strategic vision of their sound and also I have a few very credible (from my point of view) people who are very much familiar with the unfortunate (form their point of view) results the Shindo electromagnetic driver achieve. I do not have my own Shindo drivers and never personally heard them in context of interpretable installation. Last year I discover a local guy, here in Boston, with Shindo electromagnetic and I thought to families myself with the results. The guy was very reasonable and welcoming but here is what the mentality of an audio industry whore took over. The US Shindo distributor, somehow leant about my interest to hear the Shindo-using installation and demanded that I should almost sight a written affidavit that would incapable me to tell about my experience with the Shindo sound. The very same distributor proclaimed that I am knowledge, honest and no-nonsense listener.  Can you believe! A person who represents a Shindo company is so firmly stay behind the sound that the Shindo accomplish and so comfortable with the installations of his customers that we wiling to silence the no-nonsense listeners after they heard the actual results? It sounded to pathetic to me to continue be interested in whatever Shindo does. I sent the Shindo with their intimidated results to hell and said to myself that they have no worth to indicative about the advantages or disadvantages of the file coil applications… That all kind of make me pissed and I figured out that I might need to get my own results…

Rgs,
Romy the Cat

Well, I screw-in today the S2 with filed-coil into my horn. I decided to drive it with 2.4A.  I used a regulated DC PS and did not employ my prepared for this tusk 4.2 Farad capacitor: the voltage is too high for my cap. The current gave me a nice window of ~60 minutes it listing and testing before I need to shot it down due to temperature. I spent a few minuts to actulay listen musuc. I can run it slightly longer as the heat is not what I would consider be critical yet but I juts have no need to stress it for now.  Before the listing I made two sweeps if juts MF canal with a microphone at the listening position in the same horn. (I have juts one S2 with field-coil and I was playing only with my left channel. The change of the field-coil polarity did change the phase of the driver signal. Both drivers were heard at the same polarity of course relative to the rest of the channels. Here is the result of the sweeps.

The listening result is quite complicated. Contrary to my expectation I did detected quite large difference in the sound of Electromagnet and the Alnico. I would not say that all of the differences are positive or might be clearly interpreted as positive. I would say that at this point there are more puzzling differences then the understood differences. Also I did not really was listening for the differences but rather juts connected the field-coiled driver and was observing if I would recognize anything new.

I am writing this post and I do not feel comfortable to say anything defiantly. The delta is large and the S2 with electromagnet does sound very different then the driver with Alnico. A few notes about the S2 electromagnet sound that I wrote gown in my log while I was listening. I will not interpret or comment on them, juts a few notes:

1) It sounds “less”. Despite of the same measurable acoustic pressure I need to add !2dB to the MF channel to make Sound accentually neutral
2) It has way less granularity and abrasiveness. It takes some times to get accustomed to it. However, something is not right in here as the harmonic context of the speakers and the amount of upper bass that “penetrations” the MF should be calibrated specifically for this type of none-granular sound. It still need to be learned if the granularly is the granularly but not something else as it appeals a lot but sound too alien, at list in context of my “optimized for different sound” spacers.
3) I do want to drive it at 3A though… I tried. Better, the increase current dose not affect the sound badly.
4) It has some strange softeners (in a very good way), very lush and liquid. But it is soundly not properly integrated with the rest of the bass channels and the bass channels now are too strong. (the same dB output from the MF)
5) The MF channel has heavy honk. Congratulations!
6) I do not feel that a proper assessment of the Vitavox S2 field-coil is possible in Macondo without re-playing with the entire speaker system and re-setting the driver integrations
7) The upper MF is very “clean” and more interesting then with Alnico but they are “disconnected”. It might be the integrations problems.
8) The large string groups and voices sound very different. It reminds a lot the way how the direct-coupled amps sound. Still I do not know if I can say if I appreciate it. Subjectively it is with fewer artifacts but is the luck of the artifacts is the artifact of the field-coil? So far I detect the same “luck of the artifacts” in each voice. I need to leave with this to figure the things out….

Rgs,
Romy the Cat

My first impressions a about the “differences” of field-coiled derived form the time when I ran the Telefunkens war time drivers but at that time I had no reference how the same driver would act with permanent magnet. Also, the Telefunkens are the regular MF 8” drivers - the compression driver is totally different story. The only more or less illustrative indication about the compression field-coil driver I got from listening the Klangfilm Bionor with permanent manger vs. the set of it’s own electromagnet drivers. Still, since I do not like the results I heard from any of Bionors it was hard to say anything defiantly then.

This morning I spent another few hors this morning with field-coiled S2.  The entire speaker sounds horrible and the S2 field-coil sounds “strange” and “different”. I did have a chance to reconcile a little my feeling about it.

I have a constant sensation that the field-coiled S2’s sound remarkably reminds me the sound or OTL amplifiers. It has the same ability to super precise to follow the very minute dynamic fluctuation of signal and superb transient but those phenomenal qualities are not connected with anything else, primary it has no correct harmonic backup for the sonic events.  The instantaneous feeling of those “absentminded sounds” is very impressive and many people ignorantly fall for it  ythe long run or generally correct sound.

I sense that the field-coil, at least the one that I made, has a lot of common with OTL sound. It is very clean, it is electrostatic-like free from grain, it is very softly and very naturally enters the sonic stresses but it always, I mean always, always, always too thin, meaning it has no acoustic-like harmonic stricture. As the result it sound remarkably sonically imprecise and insultingly musically hollow and worthless.

I do like SOME deferential effects of the field-coil has but the biggest revelation I got this morning when I un-screw the S2 field-coil and put back the S2 with it’s default permanent magnet. 

Well #1:  the perfectly tonally and harmonically balanced sound went back to its normal state and the horrible honk that I got using the electromagnet completely despairs.

Well #2: to my big surprise the softness that very much impressed me with field-coil did not become an anti- softness with permanent magnet. The regular S2 did hold it’s own. It did not demonstrate “hardness”. Instead the S2 demonstrate it’s ability to be “stressed” to deeper level of impassiveness then the S2 field-coil. I find that S2 field-coil can not be aggressive or bold if the music calls for aggressiveness and the S2 field-coil mellows down the stress of impressionism aka act like electrostatics. Why the Mravinsky orchestra’s strings sound like Vienna Philharmonic and why Mravinsky orchestra woodwinds sound like Prague Philharmonic? Since then Russian brass sounds elastic and fertile but not nasal and bruttal?

Well #3: Harmonics, harmonics, harmonics … here is where all music lives. The very first note from the S2 permanent magnet immediately set the things straight.  Using adjectives I would characterize is as “rich” vs. “thin”. The S2 permanent magnet has large tone with beautifully-connected notes.   Each note is not juts a note itself but has a referenced via harmonics to what was before and after, It has sot of harmonic ambiance noise that dose slightly masks the appearance of the fundamental pitchers but without that harmonic noise the pitchers sound too contrived and artificial.  The S2 field-coil is less loaded with ambiance and the core note are more naked. Also, the tone is less grained and more hygienic.  It is very positive for sake of observation and dissection but it is slightly destructive as it makes listening less fluent but more intellectual.

Are the harmonics or distortions? I do not know. Is it possible to make the S2 field-coil to sound harmonically correct by injecting a long tail of upper bass channel. Possible.  Is it possible that using larger magnet the harmonics pattern of the field-coiled driver might be changed? Possible.

I do not know where I go from here, as well that I do not know how final my observations are. So, far I see a LOT of problems with field-coil and what I learned make me do not take seriously the experience of other folks who try to make the field-coils. For instance they are some Japanese, German and French speaker makers who try to make two channels field-coil speakers. Now I know that it is foolishness. The field-coils can not work well across a wide range and should operare only within a limited amount of octaves. The higher frequency is the more flux the driver want and the less frequency is the medium or low flux sound much more useful.

So, what will I end up using? Hm… I do not know yet.  The S2 field-coil “as is” is not correct direction and to get the most out of the concept the entire magnetic structure of the driver should be rebuilt to take care bout the heat dissipation. So far the conversions cost me ~$700. I have an idea how the S2 driver might be changed to run off the field coil. I would estimate that I would cost around $2500K. Then I need to change the entire Macondo configuration trying to make the field coil to sound harmonically correct.  I doubt that I would go for it, as I frankly speaking have no needs. I would like to inject into the regular S2 some softness but I am not wiling to change anything else in the sound of this driver. So far, at the level in whish I did it, a field-coil magnet does not sound to me like a useable solution to me. I will give more time to the field-coiled over the next few weeks but so far you have heard my preliminary observations…

cv wrote:

I presume this is with the new production diaphragms? Just wondering if the old ones might restore some of the youthfullness which was diminshed by the field coil?

I gave another run to Vitavox S2 with electromagnet and while I was listening I come across to an interesting observation. I screw the S3 in 330Hz horn and was trying to run it with 500Hz crossover point. It is pretty standard configuration, the way in which Altec, JBL, Vitavox and many others. This setting never produces good results (due to multiple reasons) but I did not search for result but was interested how the S2 with electromagnet would act.

It was kind of predicable. At 3 amperes (at full blow) the electromagnet did OK above 3kHz region and at 1.2A it sounded Ok around 500-700Hz. (Remind you that the electromagnet produces at 2.4A the same flux in the gap as the default Alnico magnet does). However, what was the most fascinating to observe is HOW the S2 with electromagnet sounded at it lower knee.

When I heard the bass of the S2 with electromagnet I suddenly realized that I heard something that remotely resemble the Lowther driver. Let me to explain. Let forget that people out there are using the Lowthers with stupid back-loaded horns and to lets to abstract out the sad contribution of the back-loaded concept (particularly for this driver). So, if disregard the back-horn sound and to pay attention at the lowers Lowther region (200-500) then it is very annoying that Lowther upper bass never free, never has that “fog sound” and always insultingly dry. I always attributed it to always too low crossover point that usually used with Lowther but now, after the play with electromagnet, I have another opinion.

I feel that Lowther is juts have too strong magnetic field for proper bass reproduction. The Lowther people scream that this driver have huge magnet, huge amount of BL, huge flux, super small gap, low excursion and so on…. This is all fine and it does allows to make a very effective magnetic saturation in the gap but it …. horribly affects the lower knee performance of this driver. The Lowther just has too strong and too stiff magnet system that does not allow the driver to play soft…. Apparently it DOES exist a reasonable balance of the flux density projected to the rest qualities of the driver (cone, suspension and so on…) The Lowther is obviously is on the HF side and should not used for any bass. Whatever it does below 800 is very inappropriate… Who knows… If the Lowther would have somewhere around 1.6T in the gap then it might have some lower midrange and perhaps it’s upper mid would not be so barbarianly-resolute.

Rgs,
Romy the caT

cv wrote:

But the real reason for my post is to ask: I was thinking about the results you reported and am really scratching my head as to why the FC S2 should sound honky, given that its acoustic geometry is completely unchanged. Any ideas as to why??

Yes, Chris, this is the question that I also ask myself and I have no explanation. The acoustic geometry was not changed, the crossover and response was not changed. What was the problem? I would in a way understand it if the S2 with electromagnet would give up more harmonics (primary second) then it might “overwhelm the crossover point”. (Now it is one octave from the horn rate but with “fatter” driver it might need to go further). However, the electromagnet gave up opposite result and I would characterize its sound as harmonically “thinner”. I really have no explanation of this phenomenon. Also, it would be worth to mention that honk generally more inclined to show up in mono horn installations then properly phase-alighted stereo installations. I do not know why but stereo does minimized honk. When I play with the field-coil I did run juts one channel. From another prospective my single channel with permanent magnet has no honk qualities and the same channel with permanent magnet has no honk as well. Go figure!

cv wrote:

I don't suppose the 330 horn was any different in this respect? It's the 4 sector vitavox right?

Yes, it was.

Here is the similar approach undertaken with Altec 288C to the one that I took with my Vitavox

http://chaudioroom.com/CH288287.html

Some critiques. A minor mistake in the text is that the author says that “magnetic fields generated will go down to zero when the power to the field coil is removed”. If it not as the core still get some residual magnetism but it is not so important. I would not also agree that it is possible to moderate sensitivity of the driver with change of electromagnet magnetizing force. The biggest question I would have about the heat dissipation design. They look like did a good job to have a magnetizing coil’s filler to propagate the heat from the coil to the outer wall of the driver. I do not know if it is sufficient as the coil’s filler does not touches the wall of the driver – this is VERY big mistake in my view.  I would like to see the temperature of this thing after 2 hours running at 2A. The core mass is also seems a little too small and I would like to see another coil at the outskirt of the coil’s filler, magnetizing the return pass. That would force to turn a new driver’s can though….

So, I generally feel that such a driver might be a good prototype to learn about a character of field-coil (the same as I did with my S2) but it is not a final solution.

The good part is that the author makes a sonic claim that is not as idiotic and the claims of other who play with field-coils (“more flux” etc…). The author says:

“A permanent magnet driver sounds somehow louder due to the high pitch distortions, the field-coil driver will sound slightly lower due to lack of distortions and with the most natural and sweetest sound.”

I would agree that field-coil is in a softer side but I am not convinced that it is due to “lack of distortions”. I do not say that the guy is wrong I just do not feel that what author said exhausts all differences between the field-coil and perm magnet.  There is much more than just that. I might understand how he deals with the fact that field-coil less loud (perceptual) but how he deals with field-coil lost of transient characteristics? The guys do not talk about it at all.

Here is how I see the game: he needs to load the amp that drives the electromagnet driver much idler.  This would give some transients back at lover distortion but it would also eat output. The increase of current in field-coil with attempt to gain more sensitivity would not work as it will screw the bottom knee of the driver’s response, not to mention the alleged heat buildup in the field-coil. So, as I see it we have a need to have a dedicated amp with higher gain to drive electromagnet driver. It might work and it might not as we will essentially send more voltage to the voice coil…

I have no judgment how it all work all together but the simple generalizing statement that the “permanent magnet have high pitch distortions” does not address the whole picture in my view.

Listening the argument of the field-coil’s people I note that they constantly stress the demagnetization subject of the driver’s magnet, advocating that with electromagnet “the field coil will always produce the same strength now and 100 years in the future.” It is true but let to see how important it is. The myth of demagnetization was born from the fact that all compression drivers derive from professional sound application where max sound pressure is the key  and where the channel are driven by powerful, mostly SS, mostly PP direct-coupled amplification. Yes, in those cases the Alnico magnets are vulnerable for demagnetization and you might find a lot of used partially demagnetized compression driver from movie theaters and sound reinforcement fields. However, how “dangers” the demagnetization fear in the really of home use.

First of all the contemporary rare-earth magnets do not care (care much-much less) about demagnetization. Even of the old Alnico-based magnets are use then it is also I feel is not big deal. The home used compression drivers do not exposed to heat or to shaking – something that demagnetizes drivers very aggressively in pro outside use. The home compression driven by low power SET amps with output transformer- so, there is not DC component in there and the voltages are very low. My Melquiades amp outputs to Vitavox under 3V and 110dB sensitive S2 screams at 3V like wounded in ass hippopotamus. The normal operation of my driver is at 0.4-0.9V with this voltage and with no LF submitted to driver is it imposable to demagnetize it. Even if the demagnetization does take place then to recharge a driver costs $20 and you do it just one what you buys the driver (as it might come from unknown source and it might be used by some cretin who drives his playback with 500W Crest amp.

There is another subject why I personally do not feel threaten by demagnetization and do not feel that is it a serious argument. There are two types of compression drivers: high flux and medium flux. Some drivers run 2.2T-2.4T in gap and have cone’s suspension to operate the in the environment where the diaphragm is over damped by flux force.  I do not use those drivers and I prefer the moderately flux drivers (1.5T-1.8 T in gap) as I feel that they have higher compliance of diaphragm and the diaphragm more hams by suspension instead of the intrinsic stiffness of the flux. So, those moderately flux drivers get demagnetizes much slower (of the same magnet was used). In fact it is very difficult to fully magnetize the 2.4T driver as when the magnetizing machine of off then the driver is losing right the way around 20% of charge. With 1.7T in gap (Vitavox, Altec, JBL etc…) there is a room to step back in flux density…

Anyhow, I do not feel that demagnetization is a factor that needs to be considered. In fact I do not see any utilization advantages of the field-coil beside that the driver become much simpler and easy to assemble. If electromagnets have any sensible advantage then it should be in the realm of sonic results. However, so far I do not see anybody (beside me?) trying to talk about the actual SOUND of the electromagnets.

be wrote:

I just spoke with a guy who have made both permanent magnets and electro magnets for loudspeakers. He said that the reason that electro magnetic speakers have a smoother and more grain free sound, is due to the temperature rise in the mechanical parts of the magnet, this sligtly changes the mechanical resonance characteristics of the magnet. He even experimented with heating up a permanent magnet of a loudspeaker to the working temperature of the fieldcoil version and was thereby able to emulate the benefits of the latter. So gentlemen, put a lit candle under your compression drivers.

 Eventually the people not just blobbing the imaginary idiocy about electromagnets but taking business and demonstrate sane thinking. Vey very good! If we presume that he is right (and it is very much might be so) then the following thoughts might derive from it:

1)    Is it the “slightly changes the mechanical resonance characteristics of the magnet” or rather it is softening the suspension of the cone?

2)    It would be interesting to measure the primary resonance of the cold electromagnet driver and “hot” one.

3)    The “heating up a permanent magnet of a loudspeaker” does simulate the working temperature of the field coil but it also demagnetizes permanent magnet. The different magnets react differently but still: was it softening sound due to temperature or due to redaction of flux in perm driver?

4)    How your friend (who is he, can you bring him in?) compensates the softening of sound with warm electromagnets? Less loading?

5)    If your friend is correct then I presume that the different cores of the electromagnet might react differently to temperature change.

6)    If your friend is correct and flux acts differently in different temperature then can we use this effect by putting output transformers into a soft heating chamber and impact sound this way?

Hi.

1)  He was very certain that it was not a result of a softening of the suspension or the speech coil for that matter.
2)  Probably it it is more significant to look at the harmonic structure and decay of the vibrational spectrum of the magnet when excited.
3)  It was definetly not a matter of weakening of the field, the temperatures used where way to low to have any effect on this.
4)  He has not pursued electromagnets since they have sonic ill effects as well and the small advantage of grain freeness over permanent magnets can be elliminated with the said heating anyway.
"He" is Filip Keller / AER
5)  Probably
6)  I am shure of that, you could just mount a power resistor on transformer core and put some current in it.

Regards
be

Somebody at AA asked about the difference between electromagnets and perm magnet. Thankfully the AA idiots who pick the pieces of brain at my site and already learned that the idiotic blabbering about “the electromagnets have more flux” is completely out of picture. Now they come up with more refines explanations. Still, I feel that it is off the mark.

Somebody Al Sekela posted a reply that I found worth to comment upon:

http://www.audioasylum.com/forums/hug/messages/14/143034.html

 I composed a reply, that of was deleted from AA, but I did not truly intend to post it in the AA sewers to rather to advanced the concept at my site. Her is the deleted post:

***************************************

I am glad that after the years of foolish drooling and proclaiming faulty idiotic statements the AA people gained some more or less common sense and look at the electromagnets more rational then just brainless glorification. Still, there is a lot of wrong in what people sell to themselves about electromagnets. In what Al Sekela said I see some inconsistencies that I would like to comment upon. I am glad that you do not sound as a Moronic industry whore, (there are some voices in this thread that do), so I would extend to you some credibility and integrity.

Al Sekela wrote:

Permanent magnets are not ideal. When used for speaker motors, their magnetic fields may respond to the fields created by the signal currents in the voice coils. This response may have some granularity, depending on the magnetic domain properties of the motor. The result is a subtle distortion that increases in fraction of the signal as the signal decreases in level. This kind of distortion gives a mechanical character to the sound, especially in well-recorded natural music, where the decay into silence has musical significance. This kind of distortion limits the resolving ability of the speaker.

To the problems flux modulations the permanent magnets driver and electromagnets are exposed equally, In fact if you look more carefully then you might observe that electromagnets sink flux faster then permanent magnets of the same magnetic density.  So, if you explain the less granular decay by electromagnet driver (and I partially agree with you) then it might not be explained by “fields created by the signal currents in the voice coils”.  It shall be something else. Also, let have some perspective about it. If we deal with Cogent-like MF drivers that are 500Hz and up and if it has 110dB sensitively then to develop let say 90dB it needed 50mV. If the driver runs at 1.8T then the 50mV in the voice coil generate the field that is absolutely negligible it relation to 18.000 Ga. So, the explanation of the flux modulations and contra-modulations I feel are very inappropriate. It is not bass driver but FM.  BTW, if you did experiments with use of  bass drivers and electromagnets then you might know that  electromagnets have very questionable advantage in lower frequency.

Al Sekela wrote:

Two other areas in audio have similar problems. Push-pull output stages suffer from what is called "crossover distortion." The tube or transistor amplifier characteristics change as the signal approaches zero. A band-aid is to increase the bias, so most power amplifiers are called "Class A-B," with both sides of the push-pull topology conducting current at zero signal. A true Class B amplifier would allow each side to go into cutoff (no current) exactly at zero signal. A true Class A amplifier never cuts the output devices off, and is very inefficient. However, many audiophiles prefer this type because it avoids crossover distortion. Single-Ended Triode (SET) amplifiers avoid the problem completely because the output device does not get close to zero except at maximum signal.

And how the electromagnet driver deal with crossover distortions better then permanent magnets? It is not to mention that people who run MF with PP amps are a bit … wrong, unless it is a ceramic magnet with hard suspension (that would be totally different subject)

Al Sekela wrote:

Tube amplifier output transformers also have grain that depends on the core material. Different choices for core material give different tradeoffs in distortion verses ability to handle large bass levels, efficiency, and cost. The tradeoffs are so severe that some folks use so-called Output Transformer-Less (OTL) tube power amps, such as the Atma-Sphere amps. These amps are entirely free of the transformer grain problem and are capable of superb resolution.

Sorry, it is absolutely wrong and you might to educate youssef a bit deeper about the harmonic problems of OTL amps. BTW, do not use AtmaSphere as it is a very bad example of OTL amps. Also, there is no conflict in SET between “grain” and ability to handle large bass levels – you looks like confided about it.  Still, if to accept that what you propose is accurate then what it has to do with the subject of electromagnets drivers and their alleged advantage over perm magnet?

Al Sekela wrote:

Good reproduction requires the audio equipment to work well at the extremes of maximum and minimum signal as well as at average signal levels. Field coil speakers have an advantage over permanent magnet motor speakers at low signal levels. Whether they perform well at high levels depends on other design choices that are common with permanent magnet motor speakers.

Ok, you feel that a permanent magnet motor has an advantage at minimum signal then can you propose an explanation why you feel so and how can one verify it? I am not sure that I agree with it, I do not disagree either. I am not sure that you have a right explanation and I am not sure that it leads to a right concussion. I have mine explanation but I would hold my view until you indicate that we at least talking about the same thing.

Despite my generally-negative experience of driving Vitavox S2 from field-coil I might consider to try in the coming year the same experiment one more time, since I am driving my MF driver now by a different DHT amp. I would like to see how the DHT-neess of amp would work with electromagnet.

Well, it is not that I had too negative experience with electromagnet; I just did not find it advantageous… BTW, what I am considering to do if I move to new home is to build a small and vey rudimental magnet charger devise. It is very simple but I have an idea how to “exit” the re-charge, the idea that I would like experiment with…