Project Ryu - DIY Field Coil Loudspeaker

Thank you for your words.
My impressions, hmm i stayed away from that as i tried to keep it things objective as ofc i cannot show how it sounds on a forum but since you asked...
The best thing this speaker does is dynamics and is something i always crave for in sound.

Wow, what an incredible thread. And so much of it is over my head, but I keep on reading, mesmerized.

This is my favorite post. I know you want objective, but I have been craving for pages to get to this. A few years ago I had the pleasure of hearing a Field Coil system at a trade show. By far and away the best speaker I have heard. And the dynamics were what stood out for me.

About page 8 or 9 someone asked you why Field Coil. It is my impression that Field Coil has a much more stable flux density than magnets. That the tesla factor does not vary as the power band changes. (and that to a certain extent alnico magnets are more like this than other magnets, and that is why they sound better.)

I think the best comparison is microphones, and that condensor mics compare to field coil speakers, with better dynamics than their magnet counterparts.

Now back to more reading for me.
 
Hello Frank, you will need to machine a form with grooves corresponding to your rolls ofc you will need positive and negative.
For cloth surround tho you can find good options off the shelf and treat it to reach the mechanical properties that you need in order to terminate the cone properly.
However it will contribute less mass than a foam one.


Hello Jack, thank you so much for reading and confirming the search for improved dynamics.
Yes Flux density is more stable, but there are also some interesting interactions within the system that i am studying. Keep on reading as soon i will return with a informative update.
 
Hello,

***First i want to say I'm not sure if i should post this under Fullrange or Multiway. Since at this point, there is a high posibility of the need for a supertweeter i chose Multiway forums. I won't mind tho if moderators think it's more suited for Fullrange forums.

About 6 months ago, i started thinking about a DIY fieldcoil speaker. I know opinions vary quite a lot on this matter and so i will do my best to offer as much data as possible for things to be judged objectively. Since that time I have been talking with some fellow countrymen and audio enthusiasts about this project and these conversations helped me in making some of the design decisions. The work is still in progress and i hope your opinions and comments can help tune it to higher performance.

To begin, here are the basic aspects about this project:

- field coil underhung motor structure
- 12" diameter
- Wide range (up to 10kHz), hopefully fullrange (up to 20kHz)
- high efficiency
- to be used in BLH

My personal taste in sound is that i like it when it comes out of large radiating surfaces. Large SD, large horn mouths etc. I think it's a necesity when one tries to reach real, live music levels and at the same time keep a good response to instruments' attack, sustain and decay. This is the reason i chose 12 inch diameter. I would've liked 15" better but it would've been too difficult to make it wide range. Perphaps a future project.

Field Coil Motor Structure:

I have spent a lot of time looking for other field coil projects, for any information on FC design or about available products and i have to say there isn't

much out there. From the pictures of opened FC units i could see a basic shape of the pole pieces. I have to say this is amongst the first design issues i encountered, there isn't much freedom to design these pole pieces, not like the case with permanent magnets anyway.
The next thing one can notice is that the new FCs are low impedance type and this is easily understandable. I have decided that my field coil will also work with 12-15V supply.
Underhung design means thick top plate. Of course this will cause a drop in flux density in the gap. The compromise here i found to be between flux density value and voice coil excursion. Since this speaker will mostly be used horn loaded i sacrificied Xmax to make a thinner top plate. I use standard 1010 steel with a maximum of 0.13% carbon, the best i could get my hands on.
I ran simmulations in FEMM for different values of top plate thickness, FC's number of turns, dimension, wire diameter etc. Here are the results i stopped at:

- magnetic gap height: 12mm
- magnetic gap width: 1-1.5mm
- 5.3 ohm FC 1400 turns of 1.25mm copper wire

Below you can find a rather crude sketch of motor structure:

FC_Structure01.jpg


Here are some results from FEMM analysis:

I ran simmulations with 1010 steel as well as 416 steel (has slightly more carbon typical 0.15%) to see the differences.

FC_Field_h_C_2_2_Amp.jpg

FC_Field_LC_2_2_Amp.jpg


1010 Steel Curve over 20mm and 12mm:

FC_B_LC_2_2_Amp_20mm.jpg

FC_B_LC_2_2_Amp_12mm.jpg


416 Steel Curve over 20mm and 12mm: (actually the curves are smoother had to lower resolution a bit because of my computer)

FC_B_h_C_2_2_Amp_20mm.jpg

FC_B_h_C_2_2_Amp_12mm.jpg


Magnetic gap:

FC_Field_gap_LC_2_2_Amp.jpg


AS it is, at 2.2 Amps we have 25W for the FC. I don't expect to have too much trouble with heat at this power. Test will tell tho, depending on how well the metal does the job of sinking the heat. The value predicted by FEMM lies around 1.6 Tesla. In reality i believe this value will be smaller 1.4-1.5 T. In tests i will drive the FC with 3 amps and see how much it heats up.

In this design the gap width is 1.5mm. Somewhat large, I'm thinking to add a 0.5mm thick copper ring right in the gap (yellow part from picture below). Now
it's true i have never seen a picture with a FC unit having a faraday ring and I'm not sure if it's necesary. I guess the FC itself has a role in that too.

Gap_faraday.jpg


I'm also making a 1mm gap variant (without copper ring) in hopes to get more flux density. The FEMM simmulation shows:

FC_1mm_gap.jpg

FC_1mm_gap_B_high_res.jpg


Here are some parts of the magnetic structure after machining:

DSC02849.jpg

DSC02854.jpg

DSC02857.jpg

DSC02858.jpg

DSC02863.jpg





se me lo consenti vorrei farti alcune domande perchè piacerebbe anche a me imparare ad fare i field coil ma non sò alcune cose.:D

che temperatura raggiunge il solenoide dopo mezz'ora di funzionamento continuo e quanto diminuisce la resistenza e di conseguenza amperaggio e campo magnetico ?
quanto aumenta il voltaggio tra la prima serie di spire e la seconda e tra la seconda e la terza ?
con che formula hai calcolato, dato il diametro del nucleo, larghezza e altezza del solenoide ?
cos'è questa formula ?
An externally hosted image should be here but it was not working when we last tested it.


nei tuoi solenoidi il numero di spire per ogni strato è sempre uguale o cambia?
cos'è un'elettrocalamita a doppio nucleo nudo?
 
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Hi

Here is a update on the full range project. I would like to back up my impression on the unit so I decided to use my Room correction unit, to make some measurements.... And it confirmed what I was hearing.......But I still have some doubt can this relay be true? it's almost to perfect, sense the unit is not in a box I cut it at 300Hz.

Here is a pic one how I measured it and the result.

Take care
 

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Hello audiofilofine,

I'm sorry but i don't understand the language, can you use english please?
I can tell it's about temperature. On page 5 you can find these graph:
Tvs_I_measured.jpg

Revs_T_measured.jpg


Im not sure what formula you are referring to, all i see is a calculation.

If you would allow me some questions why'd I learn to do the field coil but I do not know a few things.:D
that temperature reaches the solenoid after half an hour of continuous operation and how much resistance decreases and consequently amperage and magnetic field?
as the voltage increases between the first set of loops and second and between the second and third?
with that formula you calculated, given the core diameter, width and height of the solenoid?
What is this formula?




in your solenoids the number of turns for each layer is always the same or change?
What is a dual core electromagnet naked?
 
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Hello audiofilofine,

Temperature of the whole system depends on a few factors. Fieldcoil power disipation being perhaps the most important one. The amount of steel and geometry plays a role also.

The drop in current with increased field coil resistance due to rising temp i found to be around 0.1-0.3A depending on the driving current with the same number of turns on each layer.

About formulas, there is no general formula for what you are asking. Giving inside and outside dimensions all you need to calculate is a coil that will a specific DC resistance in order to meet your power requirements.

In my design proccess i started from the voice coil actually, chose diameter, underhung topology, voice coil height, plate thickness and then moving down to fieldcoil. Core diameter is in close relationship to voicecoil diameter about 150-200% so that you dont saturate plates too soon.
So designing the field coil i did knowing what i want to get in the gap and the structure around the gap.

Since you brought up the temperature subject, i am developing a tool for this kind of analysis. It is almost done and will allow monitoring of fieldcoil resisntace increase and voice coil resistance increase in time. A temp probe can be placed on the center pole piece near the voice coil to calculate a temp coef. This can help in determining large signal parameters and create a more precise model.
The tool is based on PIC18F4550 and connects to the PC via USB for data logging and visualization. It can export data for archiving.
Will show you what it can do once it is completly done but here are some teasers with a test unit, i heated up the temp senzor with a lighter thats why it goes up. Im designing a PCB now hope by next weekend to be done.

DSC03384.jpg

export.jpg

screenshot.png


PS. Not sure what you refer to as dual core electromagnet naked
 

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Hello audiofilofine,

Temperature of the whole system depends on a few factors. Fieldcoil power disipation being perhaps the most important one. The amount of steel and geometry plays a role also.

The drop in current with increased field coil resistance due to rising temp i found to be around 0.1-0.3A depending on the driving current with the same number of turns on each layer.







About formulas, there is no general formula for what you are asking. Giving inside and outside dimensions all you need to calculate is a coil that will a specific DC resistance in order to meet your power requirements.


this is formula
An externally hosted image should be here but it was not working when we last tested it.


In my design proccess i started from the voice coil actually, chose diameter, underhung topology, voice coil height, plate thickness and then moving down to fieldcoil. Core diameter is in close relationship to voicecoil diameter about 150-200% so that you dont saturate plates too soon.
So designing the field coil i did knowing what i want to get in the gap and the structure around the gap.

use hbc ?

Since you brought up the temperature subject, i am developing a tool for this kind of analysis. It is almost done and will allow monitoring of fieldcoil resisntace increase and voice coil resistance increase in time. A temp probe can be placed on the center pole piece near the voice coil to calculate a temp coef. This can help in determining large signal parameters and create a more precise model.
The tool is based on PIC18F4550 and connects to the PC via USB for data logging and visualization. It can export data for archiving.
Will show you what it can do once it is completly done but here are some teasers with a test unit, i heated up the temp senzor with a lighter thats why it goes up. Im designing a PCB now hope by next weekend to be done.

DSC03384.jpg

export.jpg

screenshot.png


PS. Not sure what you refer to as dual core electromagnet naked


example for professional work

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.
 
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example for professional work

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.

Whats your point exactly? I assume we all know Ohm's law. Also if you post material in other languages please provide a translation.
temp related rising of FC resistance is easily addressed if you use CCS as FC PSU

Yes that is true, flux density in gap wont be influenced by change in FC Rdc with temp. Even so, with a normal PSU the differences will be very low. Once you reach saturation region 200mA wont make a difference.

Also i liked the idea of people having the ability to use even a laptop adapter PSU with the proper current rating. For the purist however a CCS would be the best.
 
just a little personal observation related to the topic discussed some posts earlier : ideal stiffening solution.

when i wanted to stiffen the centre-part of a paper cone, i got inspired in violin-making territory. There's a lot alchemy going on in bowed instruments' finishes, but there are known hardness attributes of various resins, from wich the hardest is gum sandarac, (harder than shellac for example). So i chose it since i wanted the best stiffness-to-lightweight ratio (=high dilution in pure alc=not much material added, but stiffening effect to the desired level achieved)

maybe helps. take care

misok
 
Hi there

misok, thanks for the info sound like a good material.

I am working on my new cone, this time I will make it with a positive and a negative from. I bought some two component silicone to make the positive from, this will make it easy to experiment with other cone materials. The new form has a build in surrounding, It is my goal to make cone and surroundings in one part.... But I have to see how it works out.

A note of observation.

I was in a hurry to listen to the driver so I used a standard spider that I had, it has a very high suspension. I have always believed that a spider should be soft, so I was surprised how good it's sound. Any comments regarding the spider, pro or cons on soft spider will be appreciated.

Take care
Frank
 

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Hi Frank,

Good work there.
Regarding spider and Cms value. You need to reach a balance somewhere. I too like softer suspesions because it will enable the loudspeaker to perform well at low volumes and seems to be more revealing in details.
However it must be carefully chosen as there is the danger to have a long impulse response because the recovering force that brings the cone back to its resting position is smaller.
In your case and mine with a low moving mass the inertia will be lower and allows for a softer suspension system. Also a powerful motor will help in controlling its movement.