Field coil driver for OB design advice sought!

That's exactly what I felt with Voxativ, they do good marketing, but the sound always left me cold.
Can you give an example of a fullrange that gives you the complete opposite reaction?
I am curious to see how many calendars do I have to throw to the side to get to the one corresponding to the year of manufacturing of that driver... I always find it funny the fact that current technology does not seem to match what came out of basically stone age technology in the world of electronics.. when it comes to fullrange speakers.
 
I am starting to read and learn about Field Coil. Rather spending $$$ i was hoping i could make my own using japense washi paper. I am preety sure there are other things as well. Anyone made /recommend any place i can buy these field coil or suggest. I plan to have Open baffle Field coil with some ribbon tweeter or Bass unit

When it comes to making ones own field coil drivers there are precedents on the forum - Project Ryu - DIY Field Coil Loudspeaker - there are I think 3 different units, one was made by Hentai (actually several), one by Frank40 and at the end you have the one made by Gomper. All three of them had commercial aspirations due to their work in diy-ing fieldcoils. If you don't have a time limit, feel free to try it out, cutting corners such as using existing baskets and cone/voicecoil assembly will get you there much quicker. There are many aspects that need to be adjusted to be in the right place for performance.
Another ideea is to make a fieldcoil conversion of an existing driver. Maybe you have a model you really like how it sounds... you can start from there.
 
I am starting to read and learn about Field Coil. Rather spending $$$ i was hoping i could make my own using japense washi paper. I am preety sure there are other things as well. Anyone made /recommend any place i can buy these field coil or suggest. I plan to have Open baffle Field coil with some ribbon tweeter or Bass unit

We can do whatever we want, that is part of the fun of DIY audio. I have developed many different types of audio gear, including interconnect and power cables which kick the patootie of most everything expensive, and I have built my own speakers. I can state from experience whenever you try to roll your own, you will not be saving any money; it costs many times more than just buying something that is very good. But it can be much more satisfying also if you get good results.

The beauty of Field Coil Speakers is the sound from the speaker itself, if done correctly. But if a loudspeaker combines a Field Coil speaker with a regular speaker with a ribbon tweeter, I would think you would lose a lot of the magic. Kind of like gorgeous voices within a choir but the tonalities of the voices are not really matched with each other. What I have found is that “what I think” can cost me a lot of money and can give disappointing results. The reason why is that we have been brainwashed to think in a certain way by “experts“, and the real breakthroughs are by the innovators who walk a different path and maybe come up with something great.

Once I find a design that really works, results can be surprisingly good.

For example, rice paper used in speaker cones could be great. I’ve heard of bamboo and hemp but I haven’t heard of rice paper used for speaker cones before. But I would think unless you are a professional speaker builder, or someone with lots of experience with that, it may turn out not very successful.

There’s a reason why my coil winder intended for making field coils has not been used yet.
 
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thisisvv

Member
2012-04-19 3:03 am
We can do whatever we want, that is part of the fun of DIY audio. I have developed many different types of audio gear, including interconnect and power cables which kick the patootie of most everything expensive, and I have built my own speakers. I can state from experience whenever you try to roll your own, you will not be saving any money; it costs many times more than just buying something that is very good. But it can be much more satisfying also if you get good results.

The beauty of Field Coil Speakers is the sound from the speaker itself, if done correctly. But if a loudspeaker combines a Field Coil speaker with a regular speaker with a ribbon tweeter, I would think you would lose a lot of the magic. Kind of like gorgeous voices within a choir but the tonalities of the voices are not really matched with each other. What I have found is that “what I think” can cost me a lot of money and can give disappointing results. The reason why is that we have been brainwashed to think in a certain way by “experts“, and the real breakthroughs are by the innovators who walk a different path and maybe come up with something great.

Once I find a design that really works, results can be surprisingly good.

For example, rice paper used in speaker cones could be great. I’ve heard of bamboo and hemp but I haven’t heard of rice paper used for speaker cones before. But I would think unless you are a professional speaker builder, or someone with lots of experience with that, it may turn out not very successful.

There’s a reason why my coil winder intended for making field coils has not been used yet.

True...been there...started with plywood and putting the woofer and lowther...went to get accuton to six channel speaker to the i dont know what...hence asking what would be the route to take....So learning and thinking how to reach this journey slowly and efficently while enjoying it.



I am just reading reviews of voxativ and made me think i should try field coil....again my thoughts..



BTW long time back my system YouTube
 
Last edited:

thisisvv

Member
2012-04-19 3:03 am
When it comes to making ones own field coil drivers there are precedents on the forum - Project Ryu - DIY Field Coil Loudspeaker - there are I think 3 different units, one was made by Hentai (actually several), one by Frank40 and at the end you have the one made by Gomper. All three of them had commercial aspirations due to their work in diy-ing fieldcoils. If you don't have a time limit, feel free to try it out, cutting corners such as using existing baskets and cone/voicecoil assembly will get you there much quicker. There are many aspects that need to be adjusted to be in the right place for performance.
Another ideea is to make a fieldcoil conversion of an existing driver. Maybe you have a model you really like how it sounds... you can start from there.


I dont ahve any model...but open to suggesstion and i am in orange county...anyone can suggest something that would be helpful if i can demo it as well...
 
Can you give an example of a fullrange that gives you the complete opposite reaction?
I am curious to see how many calendars do I have to throw to the side to get to the one corresponding to the year of manufacturing of that driver... I always find it funny the fact that current technology does not seem to match what came out of basically stone age technology in the world of electronics.. when it comes to fullrange speakers.

Telefunken 1939, Klangfilm, Philips 9710, Rullit, Musical Affairs
 
That was allot of calendars to move to get back to the 30-60's... the Musical Affairs cabinets have PHY HPs which are old fashioned units (alnico magnet + paper cones), EMS drivers, not 100% old fashioned but they are field coils with paper cones, and the most "smartphone" like speaker they use is Davis Acoustics 20DE8 which has alnico magnet and paper cone... but does have an evil aluminium dustcap resembling an alien ship from the future and the future is not something good, the past is good...
There was a thread here - What's the best 8" fullrange that you've heard? - and just making a statistic from what names came up you realize that all drivers had paper cones and many of them had alnico magnets - interesting... what about alnico vs fieldcoil? The head of Voxativ said somewhere (I don't remember where) that alnico does not have any sonic advantages but the fieldcoil does and that's the reason for which the top of the line model is a field coil; he did not have an explanation for why this is "it was a mystery".
 
Cagomat you seem to be very familiar with the Musical Affairs cabinets - from what I know (from internet) the modified EMS units where never made in large numbers, perhaps just e few pairs - for example: DHTRob - A Mini open baffle with customized EMS units - I am very curious how were the modifications chosen? like spider geometry? leather thickness? was there a year of experimenting behind before achieving these results you say are better than what the industry provides? Or as a I presumed there was no year of experimentation it was more of taking a recipe and using it (wooden spider, goat leather etc). I presume you must know these people because these are the "limited edition" Musical Affairs line.
As far as Philips 9710 for me it's a legend, there is something mystical about the whole thing, there was even an article somewhere in which Hans Kortenbach says that it was a pivotal point when he got to (re)listen to a 9710 and after that he abandoned the industry prescribed solution (the large power/low sensitivity speakers)... among many references; I measured my units and like with a Stradivarius there are too many geometric coincidences to say they are just that, somebody drawed this cone/wizzer and than build it, maybe changing a few small things... so why does it work then? It's the paper! Besides being very very light and people don't know how light that cone is but acording to some published data from a german magazine this is sub tweeter level (Mms/Sd value), literally an average 1 inch dome tweeter is heavier in moving mass to surface than the 8 incher cone of Philips 9710. There are other factors that I know off that make 9710 what it it (something to do with internal damping). The other more fancy hypothesis is that the geometric coicidences of the cone resulted from experimentation... which means that there are "golden" (that work best) ratios in sizing a cone. Other than that the cone/wizzer seems to conserve energy in the higher frequency, this is what I believe is the key point when it comes to why are these drivers still relevant today. I don't know about the magnet type contributing, maybe listening to the ferrite version in direct comparison is the simple way to answer that question.
 
This was the Field Coil vs Alnico quote - ""While I personally hear no advantages with Alnico, field coils are different. I simply cannot explain why. Our AC-X is my top driver and a field coil for a reason. Its sonic performance is superior to the AC-3X without altering any other parameters like the voice coil, diaphragm or suspension. " from 6moons audio reviews: Voxativ by Schimmel Pianos Ampeggio
 
Hans told me that he and Cees Pel had conducted countless series of tests over a very long period of time, which were also supported by the EMS company. The same applies to the cabinets, each strut was glued on the outside for testing. You can imagine that it takes a long time to choose different woods, material thicknesses and geometries if you are a perfectionist. Even the speaker feet have been optimized in geometry and material selection. I had a pair of Crecendo from Hans with the Davies chassis at home for a year. The cabinet is for me one of the best ever built. For chamber music and small ensembles, a dream
 
I'm having the impression these statements are just presumptions since I recently remade the electromagnet coil of a vintage field coil driver and I had similar thought in my head... they all ended when I turned the unit on with a 12 volt power supply, the dirt cheap kind, and there was no humming, in fact my reaction was - knowing that the magnetic field has inertia, so it does not die off immediately even if you cut the power off - that it was highly unlikely... so I don't know what king of variation of current/voltage induces a hum in field coil drivers; my unit had a humbucking coil but this was serving some kind of problems of a different nature with radios from the 30s I think it was. I simply told the humbucking coil "happy retirement" after all these years, and that was the end of the thing.
By the way - forget about power supplies - just use battery for the DC you need.

I believe we are talking about DC high-voltage power supplies. Not 12 V power supplies.

And a 12 V battery can be very good for Audio. I currently have my Tortuga LDR preamp, a high-grade tripath amplifier for rear speakers, and a volume control for are all on 12 V DC from a large BatCap battery.

But even so, did you know the batteries can put noise into 12 V DC? The chemical reactions within a battery can actually create noise and a DC purifier can be helpful for that.

Can you tell us:
how did you rewind the coil?
What gauge of magnet wire did you use?
How many turns, or how much length of wire did you use?
Did you use a soft iron core for the core of coil?
how many ohms resistance is that coil?
how many gauss of magnetic field strength does that coil produce at 12 V DC?
And how many amps is required by each coil at 12V DC?

Inquiring minds want to know…
 
Ok let me ask some questions here - first thing I am no expert, but in order to do what I had to/wanted to I needed some research, basic understanding of electromagnets and electromagnetic force, field coil in speakers etc, the ProjectRyu thread had a central position in understanding these things.
The purpose was to make usable an existing field coil driver from an old radio I got last year in order to answer some questions - how does Qts or should I say Bl affect the way highs sound (above 1000 hz, far away from the downslope generated by a low Qts) ? - this is due to the fact that I am making my own fullrange units, the magnet of choice is alnico. I discovered at some point that in order to get maximum bass you need to stay away from low Qts and since Fs would be kept low I needed to lower Bl - so what is the effect on the sound (excluding bass) ? I haven't answered this one yet.
I needed to remake the coil of the electromagnet because it was 1470 ohms, as opposed to only about 7-9 ohms that Hentai has chosen and modern field coils generally have less than 20 ohms resistance - this explains why they use a 12-25 volt power supply. I made some calculations based on the original coil how much electromagnetic force was it generation (estimation based on external size and wire thickness) and calculated how much wire would get me to the same sort of force (=current x windings) on a 12 volt PS. I ended up using an existing coil of 15.1 ohms at 0.65 mm thick wire, I just rewinded the wire on the correct inner diameter using improvised things from the house (like a drill, no special tool for winding). I have no ideea how long was the wire; I haven't changed any of the components I just repaired the cone, I eliminated the humbucking coil (small thing hooked in series with voicecoil); 15.1 ohms is the resistance of the coil... when cool... and there is a problem - by the time you get to 20 minutes of use it's just too hot and you have to turn it off, so I'm going to have to remake it with thicker wire (which I don't have right now). What I did is an improvisation done with research and common sense to the point it worked but the second time I am going to do it (same coil needs to be redone) it's going to do it better - Qts was too high at 0.9 and the minimum I am interested in is 0.2 and for that I am going to need (much) more magnetic force.
 
The line between too damped and too resonant in cabinet design is very narrow

I totally agree. The body of a cello is firm, but if dampened too much it wouldn’t sound like anything. My quasi-open baffles for my Rullit lab8 field coil speakers are resonant, but dampened to some degree. Hans with musical affairs took quite a while to get his quasi-open baffle speaker cabinets resonating just right. There is a YouTube video where Hans talks about this.
 
Ok let me ask some questions here - first thing I am no expert, but in order to do what I had to/wanted to I needed some research, basic understanding of electromagnets and electromagnetic force, field coil in speakers etc, the ProjectRyu thread had a central position in understanding these things.
The purpose was to make usable an existing field coil driver from an old radio I got last year in order to answer some questions - how does Qts or should I say Bl affect the way highs sound (above 1000 hz, far away from the downslope generated by a low Qts) ? - this is due to the fact that I am making my own fullrange units, the magnet of choice is alnico. I discovered at some point that in order to get maximum bass you need to stay away from low Qts and since Fs would be kept low I needed to lower Bl - so what is the effect on the sound (excluding bass) ? I haven't answered this one yet.
I needed to remake the coil of the electromagnet because it was 1470 ohms, as opposed to only about 7-9 ohms that Hentai has chosen and modern field coils generally have less than 20 ohms resistance - this explains why they use a 12-25 volt power supply. I made some calculations based on the original coil how much electromagnetic force was it generation (estimation based on external size and wire thickness) and calculated how much wire would get me to the same sort of force (=current x windings) on a 12 volt PS. I ended up using an existing coil of 15.1 ohms at 0.65 mm thick wire, I just rewinded the wire on the correct inner diameter using improvised things from the house (like a drill, no special tool for winding). I have no ideea how long was the wire; I haven't changed any of the components I just repaired the cone, I eliminated the humbucking coil (small thing hooked in series with voicecoil); 15.1 ohms is the resistance of the coil... when cool... and there is a problem - by the time you get to 20 minutes of use it's just too hot and you have to turn it off, so I'm going to have to remake it with thicker wire (which I don't have right now). What I did is an improvisation done with research and common sense to the point it worked but the second time I am going to do it (same coil needs to be redone) it's going to do it better - Qts was too high at 0.9 and the minimum I am interested in is 0.2 and for that I am going to need (much) more magnetic force.

Can you measure how many amps that coil is pulling? At least it sounds pretty good, right? It sounds like you’re getting there.
 
I could I guess but since somebody who knew transformers told me I used too thin wire and that's were the problem is (I need to replace it because it gets too hot too quickly) ... I don't have any reason to measure... but we have Ohm's Law you know > 12 volts, 15.1 ohms so about 0.75 amps, but what I am interested in is how much is the Qts, the lower it is the stronger the magnet and at 0.9ish this is very high, so I need more wire or more amp to get more electromagnetic force, the current wire does not take more amps.
By the way the resistance goes to 20 ohms with minor warming... so when it's hot who knows how much is the internal resistance and that drives the amps down.
Are you asking about the sound? well I guess you could call it dynamic, I call it strong, the highs are very absent (no wizzer and too old paper to be good at highs) but I am learning how to solve that as well without replacing the cone (the voice coil is actually a bit special, one layer on the inside, one on the outside of the former, this one will remain there no matter what).
 

techsi

Member
2008-11-24 1:02 am
Italy
Produce hum through the speakers or just from the power supply?

It's the magnetic induction to transfer noise from the Field Coil (coming from the Field Coil's power supply) to the driver's voice coil hence to the sound. The noise mixes to the signal. So I think a Field Coil driver is a double-edged sword and the only way to get rid of the risk of mystification of the original signal is to use a battery power supply for the Field Coil. A regulated battery power supply with a rheostat on the output to fine-tune the voltage, one per speaker, most probably! I strongly believe if you think the sound of a battery-powered Field Coil driver is "dull" you should go searching for the causes in your system or in your audio tastes. You shouldn't make your sound more "thrilling" by adding noise from the Field Coil's power supply, in my humble opinion.

I'm ready to be refuted, of course!
 
Generally, I no longer post here though still get notices of postings.
My personal advice will not be what you seek, and perhaps somewhat unpleasant to hear, but it could be valuable as an antidote to all of the BS encountered here, so here it is:
Get rid of or exchange your field coil driver for a good alnico and don't look back! If there ever been a hype in DIY, it has to do with field-coil (electromagnet-driven dynamic driver), and, of course, OB's. Now, there will be many here who will disagree, either because of the heavy investment in time and moneys that they undertook to finally sort out their field coils enough for them to at least sound similar to a permanent magnet driver. And there will be those who just love eating up their field coil placebo and other horse-deworming meds that cure covid... Well, to those I can only say - continue by all means!
Ultimately, it's like a losing streak at casino - do you have enough balls to stop the bleeding of money and efforts, or are you one of those who keeps at it hoping that the next game must be the winning one, and end up losing it all?
If you really want your "jump" factor (and got the space and money for it), nothing comes close to a properly implemented compression driver, but a field coil drivel with the added bother of supply (and its attendant hum, etc.) will not get you there, sorry...
Cheers!
 
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