Field Coils for Audio Systems
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Field-coil drivers, pros and cons. Relics of the past, or still relevant?
I've been thinking about so called Field-Coil speaker drivers lately. Or "electromagnet drivers" as some seem to label them. Do they have any technical benefits that make them worth the extra expense and trouble? Nearly all info I can find online is vague mentionings of their superior "sound"...
www.audiosciencereview.com
Lots of opinions with very little experience - even anecdotal! - to back it up. Unfortunate.Field-coil drivers, pros and cons. Relics of the past, or still relevant?
I've been thinking about so called Field-Coil speaker drivers lately. Or "electromagnet drivers" as some seem to label them. Do they have any technical benefits that make them worth the extra expense and trouble? Nearly all info I can find online is vague mentionings of their superior "sound"...
songeraudio
Manufacturer Handmade Field Coil Speakers
Yes @Atmasphere, I believe you're correct. There is a relationship in magnetic materials that generally expresses high hysteresis in materials with low permeability and low hysteresis in materials with high permeability. Neodymium for all of it's good qualities has very low permeability, even though it is capable of producing a very strong field. In a field coil, the permeability is limited by saturation of the material in question, which is comparatively a very high value in a low carbon steel and even higher in (for example) permendur, or iron.
Bear in mind, these comments are coming from an artist, and not a physicist. I find myself exploring topics like this in an effort to fill out my understanding, after the fact, about why our driver sounds the way it does. I can subjectively attest that all things in a driver being equal, a field coil retrieves finer detail and offers a more lifelike, natural presentation of music. However... while electromagnetism offers the greatest potential for sound reproduction, it's just one of many equally important factors in the development of a driver. I have made some field coil drivers that sounded utterly sublime. I've also made a few that have not sounded great at all.
Bear in mind, these comments are coming from an artist, and not a physicist. I find myself exploring topics like this in an effort to fill out my understanding, after the fact, about why our driver sounds the way it does. I can subjectively attest that all things in a driver being equal, a field coil retrieves finer detail and offers a more lifelike, natural presentation of music. However... while electromagnetism offers the greatest potential for sound reproduction, it's just one of many equally important factors in the development of a driver. I have made some field coil drivers that sounded utterly sublime. I've also made a few that have not sounded great at all.
I have the original book by Barkhausen, if I only knew where...
en.wikipedia.org
Barkhausen effect - Wikipedia
Yes, my understanding is that the temporary magnet is better focused in the VC gap and may sag less. My question re sagging is how much does this impact the sound. Neodymium has greatest flux field intensity, so sagging may be less influential than with other magnet types. I will not say a field-coil driver is inherently yields better sound. It has its virtues, yes. We can compare numbers for various parameters, but how do those cash out in terms of what we hear.
Sure, no problem - I was just wary of a description of one magnet type as having better sound as factual. I agree the world of speaker magnets is ripe for more investigation and reporting. WvL appears to be one of a handful who is active in those investigations and does much work in-house Building his own power supplies is a differentiator.
It is an interesting question. Apart from a few larger manufacturers it is still one-offs and hobbyists. I suppose there is not wide spread agreement on there being clear reasons to adopt the technology or introduce a different level of complexity. The topic of power quality for the magnet introduces that issue to speakers, likely the power cable to the speaker become a topic. Some might see more complexity and more expense when the overall technology is not recognized as somehow inherently better or preferred in terms of sonic results. Neither has it gone away.
If the magnetic field sags when current is applied to the voice coil, its a pretty safe assumption that the coil will not move as quickly.
A powered static field is exactly why ESLs seem so 'fast and detailed'. Field coils allow cone drivers to have similar 'speed'- the cone world's answer to ESLs.
Because of the sag that would otherwise occur in the generated magnetic field, it is important that the field coil have a regulated power supply for best performance.
So as long as the driver is properly designed (because so much depends on design and execution of anything for it to show off its stuff) it will be faster, therefore more dynamic, more efficient and likely also lower distortion. This is both measurable and audible. One minor advantage of field coils is you can vary the field current to affect the Theil Small parameters a bit.
Ugh. Audio “Science” Review is the worst forum - pure garbage (although there are a few valuable members). There’s no “science”, it’s just Amir trying to demonstrate -- with false logic and irrelevant charts — why high-end audio is a waste of money.Field-coil drivers, pros and cons. Relics of the past, or still relevant?
I've been thinking about so called Field-Coil speaker drivers lately. Or "electromagnet drivers" as some seem to label them. Do they have any technical benefits that make them worth the extra expense and trouble? Nearly all info I can find online is vague mentionings of their superior "sound"...
I agree, yet SOMETIMES there is actual information in between the bashing, typically from folks trying to argue against it.
songeraudio
Manufacturer Handmade Field Coil Speakers
That's the body of the motor, @Zeotrope . I'm going to be documenting the entire experience of having developed my own drivers and loudspeakers over the past decade or so, in a new expert's forum that was just announced in the newsletter last night. That's here:
Modern Field Coil Loudspeakers- by Ken Songer.
Welcome to the Songer Audio Industry Expert Forum. Songer Audio is the product of the lifelong passion of Ken Songer, Founder and CEO of Songer Audio. It is the sum of thousands of hours of design and redesign, of refinement and production, and of an obsessive drive to perfect the joyful...
www.whatsbestforum.com
I'll be starting out with my design design goals and the development of the field coil motor, in the next post.
Interesting, thanks, looking forward to reading it!That's the body of the motor, @Zeotrope . I'm going to be documenting the entire experience of having developed my own drivers and loudspeakers over the past decade or so, in a new expert's forum that was just announced in the newsletter last night. That's here:
Modern Field Coil Loudspeakers- by Ken Songer.
Welcome to the Songer Audio Industry Expert Forum. Songer Audio is the product of the lifelong passion of Ken Songer, Founder and CEO of Songer Audio. It is the sum of thousands of hours of design and redesign, of refinement and production, and of an obsessive drive to perfect the joyful...
I'll be starting out with my design design goals and the development of the field coil motor, in the next post.
This would explain why the body of the RCA 1428/1443 midrange is made of cast iron (and very heavy)!
Don't ask me how I got these in as checked baggage on a flight
The failure over there isn't the measurements so much as a failure to understand how measurements show what we also hear. As a result the right measurements are not always made.
One spectacular failure was a review of a PSAudio regenerator, measured with no load as opposed to a simple power cord. To really see what the regenerator could do, a variac (which was on hand), could have been used to demonstrate its ability to regulate the line voltage while under load, and then graph the distortion of the resulting AC sine wave when distortion was introduced to the AC line.
Yes, totally agree.
The other related failure is that they start with the desired outcome (i.e., to prove that high end audio components are a waste of money) and then work backwards from that result to "validate" the conclusion. This is absolutely the wrong approach in any scientific, or business, experiment or decision.
When they measured the Wilson TuneTot speakers, Amir misplaced the mic and did not between the two drivers (i.e., not where Wilson specifically states to place it - i.e., where the acoustic center is). Was this on purpose or a result of carelessness?
The other problem is that so much of what we hear cannot be measured. They simply go by signal to noise and distortion data. Everything is just "bits", etc...
If you cannot afford, or do not want to pay, for more expensive gear, why can't you just be happy with what you have without trying to prove that expensive gear is worthless?
That site really bothers me !
Regarding that, I think we can measure what we hear, but so often people simply don't understand the implications of the measurement including the people that make them.
Distortion is a good example; there's a failure to understand how sensitive the ear really is to higher ordered harmonics. That's why THD and SINAD are not enough; you have to also show the distortion spectra (at 50Hz and also at 1 and 3KHz) and distortion vs frequency
songeraudio
Manufacturer Handmade Field Coil Speakers
I'd love to read about that, @Atmasphere , if you have some resources to share that may be helpful. Always looking to learn more, especially regarding the accurate interpretation of measurements.
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.
So the masking principle is an important part of understanding how this works.
This is only a personal theory at this point, but as far as I can make out when distortion increases with frequency (and with 99% of amps made with feedback since its inception this is the case), it contributes to harshness and brightness since lower ordered notes can make higher ordered harmonics that are a lot louder than you might expect. If they fall inside the Fletcher-Munson bump then the ear will be more able to pick them up.
I also hope we all understand that harmonics give instruments their tone color! What isn't well understood but is super easy to demonstrate with simple test equipment is that the ear uses higher ordered harmonics to sense sound pressure. This is probably the case because pure sines don't exist in nature.
On this account, the ear is keenly sensitive to higher ordered harmonics since it has over 120dB range. Add to that the ear assigns tonality to all forms of distortion (just as it does to musical instruments) and you can see that knowing the distortion spectra, seeing if the lower ordered harmonics can mask higher orders and so on will tell you a lot about how a bit of electronia will 'sound'.
You can see that there's nothing all that complex here.
I think Daniel von Recklinghausen of HH Scott understood a lot of this when he said
I seem to recall Bruno Putzeys coming to a similar conclusion....
songeraudio
Manufacturer Handmade Field Coil Speakers
Thank you, @Atmasphere - I had no idea that the ear uses higher ordered harmonics to sense sound pressure! Honestly, I didn't know that lower ordered harmonics mask higher ones, either. My loudspeaker work is pretty straightforward - I look to see if I'm over 1% THD above 50Hz, 2nd-9th harmonics, taking measurements nearfield < 500Hz, and 1M on axis > 500Hz. If not, I'm happy!
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