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

Hi Haralanov.

My "friend" said that he made an experiment where he heated a permanent magnet up and thereby made it sound more like a field coil magnet, both with the same front.

If we can take this claim as true, it is evidence that the acoustical-mechanical vibrational properties of a transducer depends on the temperature, this is not counter intuitve to me, especially with the mechanical interfaces causing damping and the temperature dependent softening of glues and insolation of speech coil etc.
I dont think this would be the only explanation, obviously the magneto-hystersis properties of the hard and soft iron parts could in adition be as, or more important.

Regards
be

rullit wrote:

Good field coil speakers mean an entirely different dimension in music reproduction. If I compared ferrit to tap water, AlNiCo would have more or less the range of a middle or maybe, depending on the material of the magnetic wire, high class mineral water, while field coil, manufactured properly and correctly would be the equivalent to mountain water you get directly from the source.

Haralanov,

I would not make any assumption about be’s friend who proposed that the heating up magnet describes the major difference between perm and electromagnet. In fact what he proposed I find very stimulating and to a degree might be very plausible.

I think to confirm it would be necessary to measure an electromagnet driver as soon it went off and then an hour later after it heat up. Why where do you see the people who use electromagnet are trying to talk about facts? They, at least that hat I have seen, mostly stress the “much deeper emotional involvement with music”. Ironically the each time I visited the people with electromagnet inhalation I witnessed that they listed predominately garbage and have musical demand of very limited complexity.  Haralanov, I do not mock you, I juts report the facts of my past experiences.

What I have seen was that electromagnet do have own different sound but I would not describe it as “denser harmonic content” or something that would make the “musical phrases more meaningful”. In fact I personally feel that to a large degree all those comments about advances of electromagnet harmonics come from the facts that the electromagnets are more rolled off at the competitive flux force. Look for instance you, Haralanov, report:

“…typical "screamyness" is still there as if the sound comes from a very little zone, stuffed and compressed in the middle of the speaker with tizzing top octave response …. as it shoots with laser gun right in your eyes. “

They are fear accusation if it is what it is but it is not my expense with my Alnico drivers. In fact my experience with them is that they are lush and very elegant. The harmonic density is to a large degree is the subject of the output tube loading. If your tube runs too idle then you might have the sound you have described. Take your driver with “tizzing top octave response” and short if with a few watt resistors – this will load the tube harder and will take the edge off your divers (as a temp solution). Alternatively run a shit of toilet paper over your driver and see how the transients got eaten. Ironically right alone with subduing of unreasonable transients we got the “denser harmonic content” but pay attention that we do not change magnet yet.

What I am trying to say is that in my view methodologically you all guys do a mistake by comparing badly performing perm magnet drivers with badly performing electromagnet. What you need to do instead is to get the identically good sound from perm magnets and electromagnet and then to observe what one topology can do and another can’t. To comment that one driver sounds screamy and tizzy but another sound “better” is in my view not serious and disrespectful not only to the subject of conversation but also to own time we spend to educate ourselves about the things.

Romy the Cat wrote:

Haralanov, I do not mock you, I juts report the facts of my past experiences.

Romy the Cat wrote:

In fact I personally feel that to a large degree all those comments about advances of electromagnet harmonics come from the facts that the electromagnets are more rolled off at the competitive flux force. Look for instance you, Haralanov, report: “…typical "screamyness" is still there as if the sound comes from a very little zone, stuffed and compressed in the middle of the speaker with tizzing top octave response …. as it shoots with laser gun right in your eyes. “

Romy the Cat wrote:

Take your driver with “tizzing top octave response” and…

Romy the Cat wrote:

What I am trying to say is that in my view methodologically you all guys do a mistake by comparing badly performing perm magnet drivers with badly performing electromagnet.

be wrote:

The diference you observed between high and low impedance fieldcoils, where they in the same unit and did you use the same kind of power supply?

haralanov wrote:

My driver has not even a single trace of  tizzing top end. Tizzines is intrinsic feature of ribbon drivers (including RAAL), not of well designed paper drivers. Actually, the heart of my acoustic system is ultra high performing midrange – high midrange driver with central alnico magnet, wooden spider and leather surround. You could see it here:   http://bgaudio.org/forums/viewtopic.php?f=1&t=17682 Now I’m listening to even better drivers (field coil) powered with 10 x 12V accumulators. You can see a close shot of the paper it uses…

Haralanov, your diver might be a very good MF diver but it does not go to region where the “tizzing” live. It just has too large and to heavy diaphragms for it. You can take driver from 30 and 40s (Telefunken, Klangfilm, Tesla and few others) and accommodate them for MF. They have similar to your diver paper structure and generally they sound fine. However, you can’t not make the claims that those drivers does not do “tizzing” as they are juts MF diver and perform more or less comfortable in sub 7kHz area. What you saying is similar to somebody saying that a compression driver tweeter does not have the “boomy baas”.  I also disagree with ribbons. Tizzines is not an intrinsic feature ribbons, it might be if ribbons are not properly used. But anything if not properly used sound like shit…

The better field coil driver powered with 10 x 12V accumulators? Hm, you claim that you were not able to make a PS that would power your driver to a sufficient level of sound? Are you sure about it? At 12V you can use 5F-6F car capacitors that shall cancel any PS influence… I do not know, the buttery-powered electromagnets is too unpractical in my view.  I do like your diver, the suspensions is very cool but still it is very difficult to evaluate how effective all of it and how it sound in reality unless one heard the thing.

Romy the Cat wrote:

your diver might be a very good MF diver but it does not go to region where the “tizzing” live.

Romy the Cat wrote:

It just has too large and to heavy diaphragms for it

Romy the Cat wrote:

(Telefunken, Klangfilm, Tesla and few others) ... However, you can’t not make the claims that those drivers does not do “tizzing” as they are juts MF diver and perform more or less comfortable in sub 7kHz area.

Romy the Cat wrote:

you claim that you were not able to make a PS that would power your driver to a sufficient level of sound? Are you sure about it? At 12V you can use 5F-6F car capacitors that shall cancel any PS influence

Romy the Cat wrote:

it is very difficult to evaluate how effective all of it and how it sound in reality unless one heard the thing.

haralanov wrote:

You may not believe me, but the driver start to  roll off (very smoothly) after 14kHz and at 20kHz is at -6dB. I intentionally do not use it so high, because I have ultra light weight alnico paper tweeter: http://www.bgaudio.org/forums/viewtopic.php?p=9833971#p9833971  So my eliptical driver is able to reproduce almost all of the high frequency information, and as I already said - without any trace of harshness.

Of course it has no “trace of harshness” – it has too heavy cone to operate in the zone where harshness might take place. Yes, the diaphragm does not work as a piston as the properly implemented break-up might do very good job. I also have no doubts that your driver goes to 14kHz and has -6dB at 20kHz.  However, the question is not how far it goes but what kind HF it reproduce, if it possible to get the same 14kHz from another dedicated HF driver and if those “dedicated” HF might be better in quality. My experience shows that use of light cone MF drivers and to push them into HF does not produce the stimulating enough HF. Even if you got some kind of very unique cone, and 4.4g (with suspension) shall be very good, then how low you driver this 4.4g cone? Thins about the Doppler and intermodulation distortion for this type of the driver… Anyhow, it is not my philosophy to try pushing a driver to work in widest bandwidth – I truly see no reason to do it. You can put on cello the short strings and try to play soprano or mezzo violin, the question would be why one need it to play a quarter? The whole point to have 4 individual instruments in a quarter is because when they play together then the combination of them gives birth of new interesting possibility, particularly in the moments of complex polyphony. Anyhow, your accomplishment with this MF driver might be very good for what you are looking for but it is not a direction that I personally find perspective. All my experiences with similar topology that you advocate lead me to confirmed it.

haralanov wrote:

My field coils are powered ot 120V, not at 12V, and the batteries are wired in series

THAT is VERY interesting in context of this thread. I did not pick it up while you were talking above with “be” about impedance that your driver use 120V magnetizing coil. Do you see advantages in it? A am not sure that I do. OK, less current but who cares? From different perspective you shall have much more isolation on coil to handle high voltage. I do not think it is a problem as well. So, what the advantage? When you were talking about high voltage motors I did not realized that it is 120V!!!! To do it you shall have a coil with high amount of DCR and it would tale a LOT of copper to wind. More turns would make more layer and more layer would make the external layers be less affective from perspective of flux/temperature ration.  I do not know how it all works, I would need to consult with my coil people but I do not immediately see any advantage to go for high voltage in electromagnet. Care to educate me on the subject?

Romy the Cat wrote:

Take (hypothetically only!) your Cat or if you are less lucky your dog. Dump her in bathtub, wash he with soup. Then dry your pet with towel. Then put your pet on a middle of carpet and looks at her fur. It is wet and it is not stick out as it should. Now begin to dry your pet with hair blower for instance. The dryer the pet’s fur will be the more distinctive and the more spatial each individual practical of hair will be. The very same is with upper MF and SET amplifiers.

haralanov wrote:

And the very same is with electromagnets. With those so widely used 12V power supplies (Fertin, Feastrex for instance) the sound is always softer than it should be in reality with severally restricted dynamics and transient response. But the people seems to like it...

I agree that each and single electromagnets driver that I head was dull and with restricted transients, something that the unfortunate filedcoil devotee mistakably call “harmonically rich”.

So, you feel that high voltage filedcoil do excite the electromagnets driver somehow? If some then I think if would be worth to try to experiment with high voltage electromagnet.

I will make a few inquires with my cold people and will see if they would propose any rational for it. In any case it might be a good idea to wind a high impedance coil around my S2 driver and to see what it will be able to show off. What voltage you feel is appropriate? Was your selection of 120 was some kind of arbitrarily?  If 120V is better then 12V then why not the 380V for instance? You went to the troubles to use DC battery to drive your 120V coils, why DC battery? How in your view the advantage of DC battery supply relates to the advantage of the high voltage supply? If we accept my above association with a wet Cat as accurate then can your extend that association to the use of DC battery power?

Romy the Cat wrote:

So, you feel that high voltage filedcoil do excite the electromagnets driver somehow?

Romy the Cat wrote:

What voltage you feel is appropriate?

Romy the Cat wrote:

If 120V is better then 12V then why not the 380V for instance?

Romy the Cat wrote:

You went to the troubles to use DC battery to drive your 120V coils, why DC battery?

cv wrote:

But I wonder if, Haralanov, you have experimented with current sourcing the coils - I would imagine that this would vastly reduce the differences you are hearing

cv wrote:

Dave Slagle is in the process of making some low impedance coils for what was a high impedance driver, so he may have the answers, both theoretical, and soon, practical: http://www.hifiheroin.blogspot.com/ (see the Wireman post)

Wireman wrote:

and decided to take them from high voltage to low voltage for safety reasons.

cv wrote:

Yet, I don't think the "safety" aspect may be neglected; I suspect he feels more comfortable with coils running at low voltage than (what I guess was) 200-400V or so.

cv wrote:

Whilst I will take risks with crazy voltages etc for myself, I will not subject others to them, no matter what potential sonic benefits.

cv wrote:

Obviously, targeted experimentation is preferable, but let's not pretend that progress never came from the occasional stab in the dark. So if something interesting comes out of a change that is motivated by making things safer, than why not?

cv wrote:

In any case, *very* interested to hear more about your devices, particularly the long fibre paper cones and leather suspension - are you willing to divulge more?

Romy the Cat wrote:

haralanov wrote: And the very same is with electromagnets. With those so widely used 12V power supplies (Fertin, Feastrex for instance) the sound is always softer than it should be in reality with severally restricted dynamics and transient response. But the people seems to like it... I agree that each and single electromagnets driver that I head was dull and with restricted transients, something that the unfortunate filedcoil devotee mistakably call “harmonically rich”. So, you feel that high voltage filedcoil do excite the electromagnets driver somehow? If some then I think if would be worth to try to experiment with high voltage electromagnet. I will make a few inquires with my cold people and will see if they would propose any rational for it. In any case it might be a good idea to wind a high impedance coil around my S2 driver and to see what it will be able to show off. What voltage you feel is appropriate? Was your selection of 120 was some kind of arbitrarily?  If 120V is better then 12V then why not the 380V for instance? You went to the troubles to use DC battery to drive your 120V coils, why DC battery? How in your view the advantage of DC battery supply relates to the advantage of the high voltage supply? If we accept my above association with a wet Cat as accurate then can your extend that association to the use of DC battery power? Rgs, Romy the Cat

haralanov wrote:

I will not call this excitement, let say it dynamic stability.

Hm, the “dynamic stability”. This is a new objective…

cv wrote:

I suspect [David]he feels more comfortable with coils running at low voltage than (what I guess was) 200-400V or so.

David had commented on this in private email. He looks like has no attitude about it and will be experimenting with it.

cv wrote:

In any case, *very* interested to hear more about your devices, particularly the long fibre paper cones and leather suspension - are you willing to divulge more?

Yes, the driver is very good and it is long know that a properly made leather suspension is the most interesting for MF drivers. The problem is that those cones is VERY difficult to get nowadays, I guess Haralanov use some kind very old diaphragms that he took from old driver. Those cones are not being made like this nowadays.

haralanovwrote:

Don't you think some of the old dirvers use high voltages (some of them 250V) for their electromagnets because of a very rational reason?

Haralanov, Haralanov, let do not mislead ourselves. The old drivers use high voltages for electromagnets not due to the sonic reasons but because economic reasons. They use fieldcoil of electromagnets combined with input choke filter of power supply for the entire unit. I have to note that all of drivers where high ripples just after rectifiers go into fieldcoil of electromagnets sound bad if they used “as is”. I do have quite many of them.

audiofilofine wrote:

are pair of jbl 2420 work with 100-130 volt power supply is with 5u4 tube i use with diy tactrix horn and jensen field coil woofers. crossover at 800 hz 6 db or when use 3 way multiamplification 800-8000 in this case tweeter is old jensen-magnavox.

Audiofilofine, I am sure you have compared the permanent magnet JBL 2420 with 2420 electromagnet. Would you mind to share your observations?

Romy the Cat wrote:

So, I guess you do not measure flux if are getting. You might measure sensitivity and we might presume what when perm magnets has the same sensitivity as electromagnets then the drivers have the same magnetic flux density. Let also presume that when you report that “at 100 volts sounds almost equal” then you have equalized flux and the drivers output. I think you do not see a lot of HF restrain with electromagnet because the JBL 2420 is not so strong HF performer and it rolls off relatively fast, right after 9K-10K. So, you drive your electromagnet with more voltage (in fact with more current) that yields more flux and to “stiffer” sound. Then you wait until the driver warm up and soften sound to the level you like. Here is in my view is the most interesting thing happen. I am in contrary to haralanov do not deny the proposal of the be’s friend that heat might do magnetic benefit (softening). The key question would be in my view if heat induces mechanical benefit of magnetic benefit. If we were are taking about the drivers like Vitavox with new diaphragms or Goto or any other driver what a metal cone surrounded with softer syntactic suspension then I would undeniably felt that the temperature-susceptive plastic suspension doe warmed and change sound. However, the diaphragm in the small JBL 2420 driver is full metal (correct me if I am wrong) and there is absolutely nothing in that driver that might be soften mechanically. So, there is a very high possibility that a hot magnet radiate some kind of different flux that makes some kind of difference. That is the qestuion that I would like to keep as opened question. The Cat

be wrote:

Romy wrote: "However, the diaphragm in the small JBL 2420 driver is full metal (correct me if I am wrong) and there is absolutely nothing in that driver that might be soften mechanically." The speach coil former seems to be made of some kind of fiber and capton, the speach coil wires are fixed by glue and the insulation on them must be a polymer. I think these must be as strongly influenced by temperature as a plastic suspension.

Be,

I thought about it but I do not think that it is the reason. There are two motives:

1)    VC glue is usually epoxy-base and for epoxy 30-40 degree difference is not a difference at all.

2)     If the glue got soften and begin to damp the compliance between the turns of VC and the former then everyone would note that driver would stop to react or became less sensitive to the low level signals. I mean the very minimum currents would be consumed by elasticity of the glue and would not acknowledge by diaphragms. You do not see the field-coil peoples report it. In fact they look like report opposite. I do not have a lot of credibility in their reports as most of what they esteemed sounded very mediocre in my view but I do NOT think that electromagnets do it details.

So, I do not think that the temporary “liquefying of glue” would be the case, but who knows…

Haralanov,

I spoke with a guy who consulted me during my Electo-Vitavox project. He helped me with selection of core material, deliberated the core and calculated the right coil to keep the core mass optimally magnetized. He has over 40 experiences to deal with all of it, so I pretty trust his expertise. He read your posts and I asked him if what you report has any justification. He was supervised with my question as according to him what you report is very self-evident. He insisted that higher voltage will substantially fasten rise time and will make VC to react much faster. I asked him why his did not tell me about it before and he replied: “You did not ask”.

Well, if so then you, Haralanov, have “discovered” a cool way to cure those always inappropriately soft-sounding to my taste electromagnet drivers. Most of the electromagnets that I have seen were under 20V, I think the first RCA versions used 110V and they switch to 12V… and no one Moron had noticed it. So, the high voltage can inhale some transient live into them – that is cool and it has revised my interest in the electromagnets.

I have ordered an experimental coil for my Vitavox. It will be with anti-corona measures (vacuum impregnated and so on) and I asked the coil to be able to be rated for 400V-450V. I think (home) sometime in the end of summer or during the fall I will have my fully functional playback back and will be able to try it. Thanks, Haralanov for the high-voltage tip, I am VERY surprised that no one spoke about it before. I am not sure about your battery experience – I think experimenting with different type of power supplies and filtering would be more fruitful, but the idea to excite and to energy the field with more voltage I think is very much worth to explore.