Field Coils for Audio Systems

[microstrip]

None of it is rocket science.

It comes from all over! First, the acceptability of the various distortion harmonics is documented in the Radiotron Designer's Handbook, 3rd edition. Fairly early on in the tome IIRC.

It should be common knowledge at this point that lowered harmonics can mask higher orders. This has been known in loudspeaker design for some time. What's less well known is that the 3rd is treated much like the 2nd harmonic in that its innocuous to the human ear (as long as its not too high). We know this from tape recorders, which make a 3rd harmonic as its dominant distortion component if functioning correctly.

The typical distortions of current amplifiers are one, two or three orders of magnitude lower than the levels referred in Radiotron Designer's Handbook and also of other text books of the 50s and 60s.

Do you know of any more recent studies of the masking theory at these very low levels?

 

[Atmasphere]

The typical distortions of current amplifiers are one, two or three orders of magnitude lower than the levels referred in Radiotron Designer's Handbook and also of other text books of the 50s and 60s.

Do you know of any more recent studies of the masking theory at these very low levels?

mp3s rely on masking to save space. I think its safe to assume that masking is going on at any level.

The prevalent theory most of the numbers people trot out is that once you get below about -70-80 dB, the music will mask the distortion, but that implies that somehow the distortion is a separate entity from the music itself! Distortion is imbued into the signal- so it affects how instruments sound, usually by making them brighter. And harsher. I'm of the opinion that distortion must be lower than that; and distortion must not rise with frequency. When it rises with frequency, you get more distortion than the 0.005% or whatever might indicate!

So even at very low distortion levels the masking thing still happens.

 

[MarcelNL]

MP3s rely on masking to hide leaving out data the number crunchers think we can not hear anyway, not distortion. Distortion IME a.o. (depending on where it happens) messes up time information, something us humans are pretty sensitive for.
I started reading up and found this;

https://www.researchgate.net/publication/323914860_THE_EFFECTS_OF_DISTORTION_ON_THE_PERCEPTION_OF_LOUDNESS_IN_LIVE_SOUND

 

[cal3713]

Saw this ad for some nice field coil tungar power supplies on usaudiomart and thought someone here might be interested... https://www.usaudiomart.com/details...dspeakers-dual-output-tungar-dc-power-supply/

 

[adrianywu]

Saw this ad for some nice field coil tungar power supplies on usaudiomart and thought someone here might be interested... https://www.usaudiomart.com/details...dspeakers-dual-output-tungar-dc-power-supply/

Yes, I have had two on order since last autumn, and they should be ready to ship. They are bigger than I expected though.

 

[adrianywu]

The field coil supplies arrived when I was at the Munich High End show. After returning home, I listened to a variety of music with my original regulated lab supplies, and then installed the new Tungar Bulb supplies and relistened. To reiterate, I am using the 4" compression midrange and the 15" bass driver from Classic Audio. The tweeters are Acapella plasma units. The most obvious change on initial listening is the increase in dynamic contrast. Instruments and voice sound more real and 3-dimensional. Plucked bass has more of the elastic quality, and transient attacks seem (even) faster. On more intent listening, there seems to be more detail. I could hear the very subtle sounds such as the different resonance of the strings when up and down bowing. The melodic line seems to be easier to follow, and it seems that the musicians are making an extra effort with their musical expression. The performance becomes more intimate, giving more of the feeling that he/she is playing for me. It is very difficult to explain in audio jargon, but the performance seems more musical. This could be a placebo effect, but I try to be as objective as possible. Whereas I had the midrange and bass at the same voltage before, because the lab supply only has one output, I increased the bass supply by 3V with the new supply according to the recommendation of John Wolff. I doubt this would make such a difference. The circuit looks pretty simple, with a power transformer, the two bulbs, and then a choke and filter capacitors. I don't understand the physics behind the difference that I can hear.

 

[Zeotrope]

Thanks for sharing your thoughts, great to hear! I had a similar experience when I upgraded my lab grade supplies to WVL PSUs. The difference was major.
It can be explained by realizing that the magnetic field is part of the signal - it creates the signal, after all. A permanent magnet or how the electromagnet is formed is going to have a big impact on SQ. If the DC voltage has noise or remnants of AC, it will affect the magnetic field.

Putting my WVL PSU on a @Seismion active isolation base made another significant leap forward. I would recommend this for your power supply - especially since it’s tube rectified.

 

[cal3713]

The field coil supplies arrived when I was at the Munich High End show. After returning home, I listened to a variety of music with my original regulated lab supplies, and then installed the new Tungar Bulb supplies and relistenedView attachment 110671. To reiterate, I am using the 4" compression midrange and the 15" bass driver from Classic Audio. The tweeters are Acapella plasma units. The most obvious change on initial listening is the increase in dynamic contrast. Instruments and voice sound more real and 3-dimensional. Plucked bass has more of the elastic quality, and transient attacks seem (even) faster. On more intent listening, there seems to be more detail. I could hear the very subtle sounds such as the different resonance of the strings when up and down bowing. The melodic line seems to be easier to follow, and it seems that the musicians are making an extra effort with their musical expression. The performance becomes more intimate, giving more of the feeling that he/she is playing for me. It is very difficult to explain in audio jargon, but the performance seems more musical. This could be a placebo effect, but I try to be as objective as possible. Whereas I had the midrange and bass at the same voltage before, because the lab supply only has one output, I increased the bass supply by 3V with the new supply according to the recommendation of John Wolff. I doubt this would make such a difference. The circuit looks pretty simple, with a power transformer, the two bulbs, and then a choke and filter capacitors. I don't understand the physics behind the difference that I can hear.

Seems to be a consistent belief among users of the Tungar PSs, even if it is placebo. That said, if you're changing the voltage, you will be changing how the driver performs. I don't remember the formulas, but I remember "Audiophile Bill" discussing that he could use differing PS voltages to change sensitivity (I think) and Q.

 

[Zeotrope]

Seems to be a consistent belief among users of the Tungar PSs, even if it is placebo. That said, if you're changing the voltage, you will be changing how the driver performs. I don't remember the formulas, but I remember "Audiophile Bill" discussing that he could use differing PS voltages to change sensitivity (I think) and Q.

Definitely not a placebo and not even talking about changing voltage. Filtering the DC and reducing vibration will provide a major sonic benefit.
I can switch off the Seismion and clarity and soundstage collapse.

 

[dcathro]

The field coil supplies arrived when I was at the Munich High End show. After returning home, I listened to a variety of music with my original regulated lab supplies, and then installed the new Tungar Bulb supplies and relistenedView attachment 110671. To reiterate, I am using the 4" compression midrange and the 15" bass driver from Classic Audio. The tweeters are Acapella plasma units. The most obvious change on initial listening is the increase in dynamic contrast. Instruments and voice sound more real and 3-dimensional. Plucked bass has more of the elastic quality, and transient attacks seem (even) faster. On more intent listening, there seems to be more detail. I could hear the very subtle sounds such as the different resonance of the strings when up and down bowing. The melodic line seems to be easier to follow, and it seems that the musicians are making an extra effort with their musical expression. The performance becomes more intimate, giving more of the feeling that he/she is playing for me. It is very difficult to explain in audio jargon, but the performance seems more musical. This could be a placebo effect, but I try to be as objective as possible. Whereas I had the midrange and bass at the same voltage before, because the lab supply only has one output, I increased the bass supply by 3V with the new supply according to the recommendation of John Wolff. I doubt this would make such a difference. The circuit looks pretty simple, with a power transformer, the two bulbs, and then a choke and filter capacitors. I don't understand the physics behind the difference that I can hear.

A 3 volt increase in the supply to the bass driver will have a big impact!

It will increase the efficiency of the driver in the midbass and midrange significantly and alter the bass alignment.

If you want to determine any subjective difference in the supplies you need to compare with the same voltages/current.

 

[tima]

Varying the electrical charge to a field-coil driver can dynamically alter its t/s parameters and thus change how the speaker sounds.

When I had the Wolf von Langa SONs in-house I played around with the amount of current the PS delivered to the speakers. The available range was 0.0 to 3.0 amps; the ammeter gauge showed 3 increments of 10 marks each. It was straightforward to hear a single increment (1/10th amp) adjustment.

I found more current brought transient quickness and a wee bit less bass weight. Lower current yielded better tonal balance, harmonics and texture. The trick of course was to find the right balance to cause what I heard to sound more like real music.

 

[morricab]

Varying the electrical charge to a field-coil driver can dynamically alter its t/s parameters and thus change how the speaker sounds.

When I had the Wolf von Langa SONs in-house I played around with the amount of current the PS delivered to the speakers. The available range was 0.0 to 3.0 amps; the ammeter gauge showed 3 increments of 10 marks each. It was straightforward to hear a single increment (1/10th amp) adjustment.

I found more current brought transient quickness and a wee bit less bass weight. Lower current yielded better tonal balance, harmonics and texture. The trick of course was to find the right balance to cause what I heard to sound more like real music.

Yeah the higher current meant high magnetic field strength and probably significantly lower the Qts of the driver. This will make it fast but lean in a standard cabinet. Low Qts likes HUGE reflex or horn loading.

 

[morricab]

Varying the electrical charge to a field-coil driver can dynamically alter its t/s parameters and thus change how the speaker sounds.

When I had the Wolf von Langa SONs in-house I played around with the amount of current the PS delivered to the speakers. The available range was 0.0 to 3.0 amps; the ammeter gauge showed 3 increments of 10 marks each. It was straightforward to hear a single increment (1/10th amp) adjustment.

I found more current brought transient quickness and a wee bit less bass weight. Lower current yielded better tonal balance, harmonics and texture. The trick of course was to find the right balance to cause what I heard to sound more like real music.

What did you think of the SON? I know some people who rave about this speaker but honestly I haven't heard it where it impressed me...it always sounds thin and insubstantial to me. Same for the bigger Chicago model. Maybe they have the current turned up for fast impulse but I am always wondering where the body is.

 

[arivel]

Just learned about hysteresis in audio and the fact that electromagnets exhibit far less hysteresis than permanent magnets. Since hysteresis is essentially distortion, this could validate why field coil drivers sound better than permanent magnet drivers (all things equal).

Hysteresis distortion - This kind of distortion occurs in audio products based on magnetic principles: loudspeaker drivers, crossover inductors, or all those magnetic components in a Class D amplifier. Once the passage of a varying audio signal magnetizes a piece of magnetic material in one direction, it retains that state. When our constantly changing audio signal then reverses direction, the magnet's historic memory adds or subtracts from the audio signal causing distortion.

Hysteresis

Hysteresis describes how something appears or responds based on its history. What we see in the present is that way only because of what happened in the past. Stretch a rubber band and upon its release, the band does not return to its original shape. That's hysteresis. Understanding hysteresis...

www.psaudio.com

Which type of magnet produce less hysteresis loss?
Soft magnets (low coercivity) are used as cores in transformers and electromagnets. The response of the magnetic moment to a magnetic field boosts the response of the coil wrapped around it. Low coercivity reduces that energy loss associated with hysteresis.

hysteresis does not exist in either a field coil or a permanent magnet because their magnetic field is static.

 

[tima]

What did you think of the SON? I know some people who rave about this speaker but honestly I haven't heard it where it impressed me...it always sounds thin and insubstantial to me. Same for the bigger Chicago model. Maybe they have the current turned up for fast impulse but I am always wondering where the body is.

Here is a thread for my review at Positive Feedback; I oriented the review to people unfamiliar with field-coils:

Field-Coil Speaker Review: the Wolf von Langa SON

https://positive-feedback.com/reviews/hardware-reviews/wolf-von-langa-wvl-12639-son-loudspeaker/

www.whatsbestforum.com

A 10" field coil mid-woofer coupled with an AMT tweeter in a smallish in box. I used it with both SET and the Lamm hybrids. I liked the SET more. You can note where my emphases are and are not.

I understand your speculation on higher current. Snappy transients can draw the ear but at the cost of richness. To use the distributor's words, too high current can lead it to sounding hard and bleached.

I have not heard his other models.

There is another review on TAS -- they gave it an award.

 

[Zeotrope]

hysteresis does not exist in either a field coil or a permanent magnet because their magnetic field is static.

??
Magnetic hysteresis occurs when an external magnetic field is applied to a ferromagnet such as iron and the atomic dipoles align themselves with it. Even when the field is removed, part of the alignment will be retained: the material has become magnetized. Once magnetized, the magnet will stay magnetized indefinitely.

Permanent magnets do absolutely nothing better than field coils, other than reduce cost. Read the “A visit to Audiophile Bill...” thread here. Forgetting about the adjustability, FC magnetic fields have lower distortion than permanent magnets. This was explained in this forum.

 

[audioquest4life]

The field coil supplies arrived when I was at the Munich High End show. After returning home, I listened to a variety of music with my original regulated lab supplies, and then installed the new Tungar Bulb supplies and relistenedView attachment 110671. To reiterate, I am using the 4" compression midrange and the 15" bass driver from Classic Audio. The tweeters are Acapella plasma units. The most obvious change on initial listening is the increase in dynamic contrast. Instruments and voice sound more real and 3-dimensional. Plucked bass has more of the elastic quality, and transient attacks seem (even) faster. On more intent listening, there seems to be more detail. I could hear the very subtle sounds such as the different resonance of the strings when up and down bowing. The melodic line seems to be easier to follow, and it seems that the musicians are making an extra effort with their musical expression. The performance becomes more intimate, giving more of the feeling that he/she is playing for me. It is very difficult to explain in audio jargon, but the performance seems more musical. This could be a placebo effect, but I try to be as objective as possible. Whereas I had the midrange and bass at the same voltage before, because the lab supply only has one output, I increased the bass supply by 3V with the new supply according to the recommendation of John Wolff. I doubt this would make such a difference. The circuit looks pretty simple, with a power transformer, the two bulbs, and then a choke and filter capacitors. I don't understand the physics behind the difference that I can hear.

Thanks for posting your feedback. I will be getting the Tungar power supplies once our home is ready for us to move in and I get my house hold goods delivered. I too have the Classic Audio Loudspekers, the T1.5 Reference which has a 15” forward mid bass driver and an 18” downward firing deep bass driver. Your impressions really provide insight on the benefits of a tube power supply.

 

[DasguteOhr]

Varying the electrical charge to a field-coil driver can dynamically alter its t/s parameters and thus change how the speaker sounds.

When I had the Wolf von Langa SONs in-house I played around with the amount of current the PS delivered to the speakers. The available range was 0.0 to 3.0 amps; the ammeter gauge showed 3 increments of 10 marks each. It was straightforward to hear a single increment (1/10th amp) adjustment.

I found more current brought transient quickness and a wee bit less bass weight. Lower current yielded better tonal balance, harmonics and texture. The trick of course was to find the right balance to cause what I heard to sound more like real music.

the current determines the qts of the speaker. you can use it to simulate the best for each speaker housing.exsample qts horn 0.2 or bassreflex 0.5 -0.7 and openbaffle 0.8 -1.0. listen immediately in the bass range. avantage you can use in every sort of speaker diy fans love it. The problem is if you choose a very high current, distortions increase rapidly. the field coil heats up the voice coil, the achievable volume with low distortion decreases. can sound very good at low levels but horrible at high levels.
P.S
there is always an achilles heel, no matter how beautiful it is

 

[gestalt]

What did you think of the SON? I know some people who rave about this speaker but honestly I haven't heard it where it impressed me...it always sounds thin and insubstantial to me. Same for the bigger Chicago model. Maybe they have the current turned up for fast impulse but I am always wondering where the body is.

I think you and I are on a similar audio preference spectrum, which gives me confidence to say that it's probably just not the right amplifier pairing. WVL lets you hear your system. Put them with something like e.g. NAF and they're rich with tons of body. (I brought this exact pairing to AXPONA this year and it was lovely.)

 

[arivel]

??
Magnetic hysteresis occurs when an external magnetic field is applied to a ferromagnet such as iron and the atomic dipoles align themselves with it. Even when the field is removed, part of the alignment will be retained: the material has become magnetized. Once magnetized, the magnet will stay magnetized indefinitely.

Permanent magnets do absolutely nothing better than field coils, other than reduce cost. Read the “A visit to Audiophile Bill...” thread here. Forgetting about the adjustability, FC magnetic fields have lower distortion than permanent magnets. This was explained in this forum.

the hysteresis appears only if the magnetic field is variable over time. but this is not the case with permanent magnets or field coils.
what you are talking about is the remainder (Br) which is something else.