Field-coil drivers, pros and cons. Relics of the past, or still relevant?

[arivel]

if what is said around is true, it would be interesting to make a measurement to compare the level of distortion between one of the best permanent magnet loudspeakers and a field coil loudspeaker

 

[egellings]

What difference would it make if the source of MMF is a coil or a PM? The pole piece & iron around the gap should be saturated, and once that's achieved, it would make no difference how it got that way.

 

[atmasphere]

What difference would it make if the source of MMF is a coil or a PM? The pole piece & iron around the gap should be saturated, and once that's achieved, it would make no difference how it got that way.

That is true. We do know though that the magnetic field sags when current is put through the voice coil. So is the gap still saturated?

 

[egellings]

That is true. We do know though that the magnetic field sags when current is put through the voice coil. So is the gap still saturated?

If you hit the gap with a strong enough field so that the voice coil field generated during loud playback cannot pull the gap metal out of saturation, then yes. With inadequate MMF in the gap metal parts, then it would be possible for loss of saturation to occur due to large voice coil excitation currents. So, it's design-dependent.

 

[atmasphere]

If you hit the gap with a strong enough field so that the voice coil field generated during loud playback cannot pull the gap metal out of saturation, then yes. With inadequate MMF in the gap metal parts, then it would be possible for loss of saturation to occur due to large voice coil excitation currents. So, it's design-dependent.

Exactly.

 

[Newman]

I think most people assume that magnets don't react to current in the VC which isn't the case.

Are we still discussing advantages of field coils? I would have thought that the mutual induction of a field coil loudspeaker's two electromagnetic coils means that it will also "react to current in the VC".

 

[Newman]

Based on my subjective evaluation of dozens of speakers/setups at a recent major audio show with hundreds of exhibitors, I have to say that the Songer field-coil speakers were in the top three. The clarity and full-range coverage of the demo setup incl. model S1 speakers were unbelievable and rivaled those of a setup spec'ed at almost $900k+. A result of 6+ years of R&D, the rep said. And it shows. Have started saving money now to get to the ~$37k MSRP (with the requisite PS).

Personally I think there is a real risk of the Class A Amplifier Effect taking hold. Namely, just because someone can describe a technical advantage (for Class A, no switching of the output devices and no crossover distortion), then suddenly in demo rooms around the world we start 'hearing' them as superior.

I advise caution. Especially with a $37,000 speaker that would have a pretty bad spinorama. The love affair might come crashing down when the poor attributes of the sound waves themselves start to soak through the romantic glow of the story behind the tech.

cheers

 

[Killingbeans]

I would have thought that the mutual induction of a field coil loudspeaker's two electromagnetic coils means that it will also "react to current in the VC".

Absolutely. After all, some servo subwoofer use an additional coil as their sensor.

A well designed field coil driver should include at least one feedback loop of some sort. Most (if not all?) of the modern field coil implementations I've seen seem to use a simple "dumb" DC power supply as the driver, and that's just, well... dumb.

 

[atmasphere]

Are we still discussing advantages of field coils? I would have thought that the mutual induction of a field coil loudspeaker's two electromagnetic coils means that it will also "react to current in the VC".

Apparently we are. A regulated supply solves the 'react to current in the VC' thing. I think a constant current supply is better, but the point is its regulated.

Absolutely. After all, some servo subwoofer use an additional coil as their sensor.

A well designed field coil driver should include at least one feedback loop of some sort. Most (if not all?) of the modern field coil implementations I've seen seem to use a simple "dumb" DC power supply as the driver, and that's just, well... dumb.

Field coils tend to be a pretty constant load for their power supplies- only changing as the coil slowly heats up. Regardless of program material, I've not seen the current change with it.

 

[computer-audiophile]

The switch from AlNiCo to ceramic for magnets was driven by the Cold War and the use of cobalt in other technologies (not so hifi-friendly ones) and supply constraints that also had geopolitical underpinnings.

The ability to make more or less arbitrarily powerful electromagnets is at least possibly a "plus".
Your high field FFT NMR instruments, e.g., use superconducting electromagnets. Could audiophile drivers be too far behind?


From ASR's perspective, field coil (electrodynamic) drivers probably make no sense.
Not everyone shares the canonical ASR perspective, though.

Make it yer own Tungar Supply

Went to the "Secret Land of Walter" last weekend to have some fun with some friends. On the agenda for the weekend were some Tungar Supplie...

hifiheroin.blogspot.com

Low voltage, high current power supplies for field coil drivers using Tungar tubes.

View attachment 259979

Oops, I just discovered this thread. Is the photo from you? Have you been there?

Some of old audio friends I know use such Tungar PSU for their Western Electric Horn speaker systems, obviously it must be so to sound right. I may still have photos I took of it. I must have a look in my photo archives.

 

[computer-audiophile]

Some examples of my own photos: These vintage WE original devices still work without any problems as I could see and hear.
It is better not to look at it for too long, because of UV radiation. This can harm the eyes.

 

[Spocko]

Absolutely. After all, some servo subwoofer use an additional coil as their sensor.

A well designed field coil driver should include at least one feedback loop of some sort. Most (if not all?) of the modern field coil implementations I've seen seem to use a simple "dumb" DC power supply as the driver, and that's just, well... dumb.

This appears to be the audiophile Rolls-Royce of field coil drivers from Voxativ https://voxativ.berlin/products/acx hopefully not "dumb"!

 

[atmasphere]

That driver uses a simple field coil like the rest of them. Its not a bad driver but it certainly doesn't do 20Hz!

 

[KSTR]

A well designed field coil driver should include at least one feedback loop of some sort. Most (if not all?) of the modern field coil implementations I've seen seem to use a simple "dumb" DC power supply as the driver, and that's just, well... dumb.

I also always wondered why nobody AFAIK has implemented a modulated field coil drive, modulating the DC current with a scaled copy of the momentary VC current. When dialed in properly, this could reduce significantly force factor modulation BL(i).

Some PA midwoofers from18sound have a secondary stator coil which could be used in a likewise fashion. 18sound suggest using the stator coil simply in parallel to the VC but I tend to think that even better results could be obtained when truly driven with a copy of the VC current, not voltage, in an active speaker design.

 

[egellings]

That driver uses a simple field coil like the rest of them. Its not a bad driver but it certainly doesn't do 20Hz!

Only 14 grand? Get a couple for the kids!

 

[computer-audiophile]

Only 14 grand? Get a couple for the kids!

LOL (You are right!)

 

[mhardy6647]

Oops, I just discovered this thread. Is the photo from you? Have you been there?

Some of old audio friends I know use such Tungar PSU for their Western Electric Horn speaker systems, obviously it must be so to sound right. I may still have photos I took of it. I must have a look in my photo archives.

Yes, my photo.
A system which is one of my favorite hifi experiences in terms of scope, scale, and emotion.
Not quite practical for most folks (myself included), though.
I don't think that there's much UV from Tungars -- pretty much just a thoriated tungsten filament like an incandescent light bulb.
Now, I certainly wouldn't recommend staring at a mercury vapor rectifier like an 866jr, though!
My eyeglasses should attenuate most incident UV (most plastics are not very UV transparent) -- but, yeah, vision (eyesight) isn't something to gamble with.

^^^ Here, e.g., are a couple of 866jr tubes from the power supply of Gary Kaufman's 211 amplifier.

 

[computer-audiophile]

@mhardy6647

Sorry, it's a little off topic here, but one of the speakers I like best are the Klangfilm Bionor. I could listen to such ones several times, even once with excellent master tapes and an old Telefunken tape machine as source. Dreamlike!

BTW: The Photo from a typical Bionor Setup is from the Web. I do not want to show private photos in this case.

 

[computer-audiophile]

Wolf von Langa (Germany) is among those I know of that build modern field coil speakers. It's all very elaborate what he does. He is an absolute perfectionist and in my opinion has very good taste.

Picture from his Website:

 

[computer-audiophile]

My eyeglasses should attenuate most incident UV (most plastics are not very UV transparent) -- but, yeah, vision (eyesight) isn't something to gamble with.

^^^ Here, e.g., are a couple of 866jr tubes from the power supply of Gary Kaufman's 211 amplifier.

HaHa, they shine beautifully blue.
In the past, when the blue LED was not yet invented, blue light was rarely seen.

I remember power supply setups by Thomas Mayer (aka VinylSavor) with such rectifiers, which would be better described as 'lighthouse'. I don't like them that way, as they make a lot of RF noise.