I think you're right, but every time we have played with field
coils, it seems that the current setting always ends up on high.
While I do have a few nice machine tools, this is still very much a DIY thing .
here. The manufacturing processes. you describe are indeed fairly commonplace in industry and it would indeed be an interesting direction to explore if one had those resources and the inclination. Alas if it became a commercial product I wouldn't be able to afford it.
However a laminated steel pole piece might be do-able hmm.
This has been a great exchange of theory here,hope to be able to cut some metal and wind some copper here soon.
Iam am considering doing a quadrifilar wind as I would prefer to do a low voltage higher current coil.
Thanks for all the info!
here. The manufacturing processes. you describe are indeed fairly commonplace in industry and it would indeed be an interesting direction to explore if one had those resources and the inclination. Alas if it became a commercial product I wouldn't be able to afford it.
However a laminated steel pole piece might be do-able hmm.
This has been a great exchange of theory here,hope to be able to cut some metal and wind some copper here soon.
Iam am considering doing a quadrifilar wind as I would prefer to do a low voltage higher current coil.
Thanks for all the info!
Very interesting guys!
When I vary the voltage on my bass driver, it seems to vary the tone more than the sensitivity - less voltage = deeper tone, more voltage = warmer/brighter tone but with less deep bass.
The full Range Supravox, mounted in an open baffle, seems to vary in sensitivity more than any strong perceived tonal change.
I don't hear any large changes in distortion in either driver with changes in the FC voltage.
If I was just running the FR alone in a large open baffle, I would just find the best sounding voltage. Because I am using mine with a supporting bass and a helper tweeter, I find that the ability to adjust the sensitivity of the FR to match the helper tweeter and Bass a real boon. It means that I don't need to pad the FR down with a resistor to match the lower sensitivity bass and treble.
The fine tuneability of these things is amazing! Another thing I am going to have to investigate is the effect of playing with the quality of the PSU.
Cheer
David
When I vary the voltage on my bass driver, it seems to vary the tone more than the sensitivity - less voltage = deeper tone, more voltage = warmer/brighter tone but with less deep bass.
The full Range Supravox, mounted in an open baffle, seems to vary in sensitivity more than any strong perceived tonal change.
I don't hear any large changes in distortion in either driver with changes in the FC voltage.
If I was just running the FR alone in a large open baffle, I would just find the best sounding voltage. Because I am using mine with a supporting bass and a helper tweeter, I find that the ability to adjust the sensitivity of the FR to match the helper tweeter and Bass a real boon. It means that I don't need to pad the FR down with a resistor to match the lower sensitivity bass and treble.
The fine tuneability of these things is amazing! Another thing I am going to have to investigate is the effect of playing with the quality of the PSU.
Cheer
David
i don't quite understand what the advantage to using Metglas in a speaker field coil would be. Mild steel has a saturation induction of over 21000 gausses and purified iron has slightly more, although with a much higher permeability it will saturate with smaller field strengths (fewer Gilberts).
Using cast iron would be a complete waste of time.
John
Using cast iron would be a complete waste of time.
John
Likely that much of the change is simply the Q. You can vary
that also by placing some resistance in series with the driver.
Member
Joined 2006
A friend of mine of mine has a pair of Voigt Domestic Corner Horns. He had PM6As in them. They sounded (and measured) extremely well. Then he helped a friend build a pair of the Voigts. For payment he got a pair of the original field coil Voigt drivers! (From the 1930s!). These are run at incredible voltages (400?). They trounce the PMs (they are almost the same driver in other respects)
Interestingly the drivers were originally all field coil drivers, and the PM (permanent magnet) replaced them. But on what I have heard, the replacement was not for sound quality reasons. I believe that all the older Lowther PM drivers were Alnico. Most people find the later ceramic drivers inferior to those.
Interestingly the drivers were originally all field coil drivers, and the PM (permanent magnet) replaced them. But on what I have heard, the replacement was not for sound quality reasons. I believe that all the older Lowther PM drivers were Alnico. Most people find the later ceramic drivers inferior to those.
Up to a point it can be done. But to do it properly, i.e. not just ripping one thing off and sticking something else on at random, it needs to be designed, as noted above. That generally means the entire motor design, inc. voice coil needs changing, which also often requires different suspension.
Permanent magnets are cheaper and more convenient; they lack the user-adjustability of field coils of course. As multidriver systems proliferated, they became less useful / common since adjusting it would impact the transfer functions.
Lowther also have neodymium magnet types as well as ferrite and AlNiCo. The ferrite models are supposed to be their entry level units, so not-unnaturally, the pricier units tend to be superior (not that I personally like the Lowther type of presentation in general). AlNiCo can have some benefits over ferrite (likewise the neo) types, but it isn't as simple as that either since they are all available in varying grades. A high grade ferrite may beat out a low grade AlNiCo or rare-earth type in terms of technical behaviour. Depends on the driver design.
Permanent magnets are cheaper and more convenient; they lack the user-adjustability of field coils of course. As multidriver systems proliferated, they became less useful / common since adjusting it would impact the transfer functions.
Lowther also have neodymium magnet types as well as ferrite and AlNiCo. The ferrite models are supposed to be their entry level units, so not-unnaturally, the pricier units tend to be superior (not that I personally like the Lowther type of presentation in general). AlNiCo can have some benefits over ferrite (likewise the neo) types, but it isn't as simple as that either since they are all available in varying grades. A high grade ferrite may beat out a low grade AlNiCo or rare-earth type in terms of technical behaviour. Depends on the driver design.
I am designing and building my own full-range units, and I use field coils.
This is my point off view on field coils..... Any magnetics system can bee converted to a electrical circuit, and when doing that you will see the magnet as a power supply with a output impedance. I believe that the output impedance is off interest here (should bee as low as possible), this will decrees magnetic modulation of the field due to magnetic changes in the voice coil. The impedance of magnets is not that good compeered to the surrounding steel, that is why field coils are better, if they are designed properly.
A nice feature is that you can change the Qe by changing the current in the coil, but it has a price...Due to the power consumption of the field coil it gets hot, mine is about 40-45°C...This results in a lower power handling.
About selecting the steel, well it depens on what you are looking for. If your flux is very high you will have a hard time making your Qe to a decent level, high flux thend to make very low Qe units. To increse Qe you can use CCAW for voice coil, this will increse the resitens in the voice coil.
This is my point off view on field coils..... Any magnetics system can bee converted to a electrical circuit, and when doing that you will see the magnet as a power supply with a output impedance. I believe that the output impedance is off interest here (should bee as low as possible), this will decrees magnetic modulation of the field due to magnetic changes in the voice coil. The impedance of magnets is not that good compeered to the surrounding steel, that is why field coils are better, if they are designed properly.
A nice feature is that you can change the Qe by changing the current in the coil, but it has a price...Due to the power consumption of the field coil it gets hot, mine is about 40-45°C...This results in a lower power handling.
About selecting the steel, well it depens on what you are looking for. If your flux is very high you will have a hard time making your Qe to a decent level, high flux thend to make very low Qe units. To increse Qe you can use CCAW for voice coil, this will increse the resitens in the voice coil.
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field coil vs alnico
As a designer who has worked with every type magnet including field coils I must say the real point get overlooked by people who have not heard for themselves the difference and just speculate. I have had the opportunity to hear the Lowther cones with several magnets and it is fascinating that everything is audible. The silver vs copper coils the ferrite vs alnico vs ticonal vs neodymium vs field coils. The good news is I was able to use the same Lowther cones. The magnetic flux does vary a bit from magnet to magnet. What became absolutely clear is the superiority of field coils on good to great recordings. The size of the sound stage the width height and depth and low level detail are incredible. There is a scientific reason for this. The magnetic deflection is least with field coils followed by Alnico then neo and lastly ferrite. Imagine standing on a trampoline and shaking a 30lbs weight up and down, then imagine the same 30lbs weight standing on the ground. The ground is the field coil, it barely moves when the AC voice coil field pushes against it. Again power supply design is critical and you can not use a lab grade supply or DC battery for best results. GAS audio designed a dedicated supply for us at Surreal Sound. Weather a field coil is better all comes down to money. If not using the best upstream electronics and source components a permanent magnet is the better choice. The field coil will simply reveal every flaw of your system
As a designer who has worked with every type magnet including field coils I must say the real point get overlooked by people who have not heard for themselves the difference and just speculate. I have had the opportunity to hear the Lowther cones with several magnets and it is fascinating that everything is audible. The silver vs copper coils the ferrite vs alnico vs ticonal vs neodymium vs field coils. The good news is I was able to use the same Lowther cones. The magnetic flux does vary a bit from magnet to magnet. What became absolutely clear is the superiority of field coils on good to great recordings. The size of the sound stage the width height and depth and low level detail are incredible. There is a scientific reason for this. The magnetic deflection is least with field coils followed by Alnico then neo and lastly ferrite. Imagine standing on a trampoline and shaking a 30lbs weight up and down, then imagine the same 30lbs weight standing on the ground. The ground is the field coil, it barely moves when the AC voice coil field pushes against it. Again power supply design is critical and you can not use a lab grade supply or DC battery for best results. GAS audio designed a dedicated supply for us at Surreal Sound. Weather a field coil is better all comes down to money. If not using the best upstream electronics and source components a permanent magnet is the better choice. The field coil will simply reveal every flaw of your system
Dear all,
this seems to be an old thread, but I might as first post (despite being reader for some time) add my experience with PM versus FC motors.
I was able to listen to the Fertinacoustics 20M8 both with permanent magnet and with fieldcoil motor in the same enclosure, same source and amp, same room, same music.
I preferred the latter - although I´m in trouble describing musical events with words, I found the fieldcoil unit to have better detail, better microdynamics and a more realistic illusion.
Depending on the motor, the TSP of the units are not the same, but are comparable, both being quite strong.
I can´t offer any scientific reasons for the fieldcoil´s superiority, nor did I do any measurements on that occasion in the south of France, but hearing the difference persuaded me to buy the fieldcoil variant, despite much higher price.
It has been said before that fieldcoil drivers are very revealing and will show any upstream problem easily. I found that to be true of the drivers, but I´m not sure if this is only due to the fieldcoil motor; I think that every other aspect of the driver counts as well here. A fieldcoil motor alone won´t be a guarantee for good sound, it´s the sum of all parts that counts.
Best regards
Mattes
this seems to be an old thread, but I might as first post (despite being reader for some time) add my experience with PM versus FC motors.
I was able to listen to the Fertinacoustics 20M8 both with permanent magnet and with fieldcoil motor in the same enclosure, same source and amp, same room, same music.
I preferred the latter - although I´m in trouble describing musical events with words, I found the fieldcoil unit to have better detail, better microdynamics and a more realistic illusion.
Depending on the motor, the TSP of the units are not the same, but are comparable, both being quite strong.
I can´t offer any scientific reasons for the fieldcoil´s superiority, nor did I do any measurements on that occasion in the south of France, but hearing the difference persuaded me to buy the fieldcoil variant, despite much higher price.
It has been said before that fieldcoil drivers are very revealing and will show any upstream problem easily. I found that to be true of the drivers, but I´m not sure if this is only due to the fieldcoil motor; I think that every other aspect of the driver counts as well here. A fieldcoil motor alone won´t be a guarantee for good sound, it´s the sum of all parts that counts.
Best regards
Mattes
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