Field coil driver for OB design advice sought!

[tommydoan84]

Hello my dear audio DIY fellows,

I bet many of you in here already tried out field coil driver for open baffle design ? What is your recommendation for a good field coil driver for OB design that do NOT break the bank? I'm looking for good/ hifi quality sound here.
So far I have tried out so many FR conventional magnet drivers (Ferrite, Alnico, Neodymium) from 6.5 in to 15 in FR with very good result for OB.

Lately, i came across some readings about file coil driver that peaked my interest. Before jumping into the deep, I want to seek your advices for some good FC driver brand, should I go vintage or a good/new brand? What are they ? Some of the Do's and Don'ts that I should watch out for with the Field Coil driver ? One thing I know is you need a really high voltage supply for FC driver, should I go SS or Tube PS for them ? with a high voltage supply, does it affect my preamp/amp output in anyway ?

Any inputs are welcome and thank you in advance!
Warmest regards,
Tom

 

[korpberget]

I tried one from an old Lorenz/Blaupunkt radio console. Stamped 1939 - old!
Sounded insane good! Too bad I only have one.

 

[bvtrinh]

Hello Tommy,

I have Atelier Rullit Lab 8 and although I have not heard any other field coil speakers, they sound pretty good to me. It has a warm midrange and decent bass; however, the highs seemed a little rolled off and missing something. Adding a tweeter really made a difference. I’m not sure what you listen to, but musicals sound fantastic on these. Rap and heavy metal, not so much. These require from 70 to 100v to sound good but there are others that only require 9 to 12v.

Bao

 

[tommydoan84]

hi Bao,
thank you for the feedback. I also read the review from Glow In the dark audio about the Atelier Rullit Lab 8. Is this the one that you bought from ?
Atelier Rullit - Silver LAB 9 AlNiCo FR speakers for SE amps open baffles RESO | eBay

I found it on Ebay. It seems that it comes from the same guy who handmade this in Germany as well but not sure if it's legit.

-Tom

Hello Tommy,

I have Atelier Rullit Lab 8 and although I have not heard any other field coil speakers, they sound pretty good to me. It has a warm midrange and decent bass; however, the highs seemed a little rolled off and missing something. Adding a tweeter really made a difference. I’m not sure what you listen to, but musicals sound fantastic on these. Rap and heavy metal, not so much. These require from 70 to 100v to sound good but there are others that only require 9 to 12v.

Bao

 

[inrank]

Supravox 165EXC, I have the 165-2000 AlNiCo version. Not cheap at around £500/ea....
165 EXC Full range drive unit 35W / 90 at 95dB / 4 Ohms - Supravox
You only need (up to) a 10v supply.

 

[bvtrinh]

Hello Tommy,

That is who I bought my speakers from and those are almost the same speakers except mine are field coil whereas those are Alnico.

Bao

 

[shooter]

The Rullit Aero series are some of the best fullrange drivers out there, they do not have the peaky high end exhibit in most fullrange drivers. The high voltage power supply has no correlation with the amplifier being used, it only powers the field coil. I use selenium rectifiers for my power supply.
There are also some vintage German field coil drivers that sound quite good.

 

[Mattes]

Hi Tom,


I´m not sure how many actual users of "modern" fieldcoil drivers are out there, and here in this forum. Inrank has already participated, Shooter as well, then there´s Hentai and Gomper with their own FC designs, and maybe a few more I don´t remember right now.


If you want to buy a "modern" readily available fieldcoil drivers at "moderate" prices, up to my knowledge you´d have to look to France, there´s Supravox, EMS and Fertinacoustics (I have a 21M8EX myself and am very happy with it, albeight this is an expensive driver). EMS would be my suggestion for a start. The super-expensive Voxativ drivers will be out of range for many, Feastrex seems to be be dead.


Many swear on old drivers, including Oleg Rullit, who rebuilds several. There are a lot of discussions to be found online, and a lot of old fieldcoil speakers are available, choose your poison...


A few personal opinions of mine: do care about the PSU, it´s important. Any fullrange driver, whether FC or PM, will sound better on OB if relieved of bass duties. Don´t expect FC technology to do any wonders. The difference with a well executed PM motor is small, and you´ll pay a lot for it. The law of diminishing returns is already there, as you´ll easily pay several hundreds until a few thousand bucks for a new fieldcoil fullrange driver...


Good luck!


Mattes

 

[JMFahey]

Well, FC speakers still have a point going for them, and it´s that they being active and adjustable they can reach maximum saturation point for any magnetic circuit material, while any "passive" magnet, which by definition is charged by a pulse and then recoils back to a lower level, even if a little.
Just look at classic magnetization curves.

I commercially make speakers, I mean the actual unit, not just the cabinet, own 3 magnetizers an am quite aware of that.

I have also built FC speakers.
Even though very expensive, I was making 30" woofers for Disco use in the 80´s and there was no other magnetic solution.
In a way, each speaker had its own magnetizer built in

Jensen is the oldest speaker manufacturer (Peter Jensen actually invented the moving coil speaker ) and even today the loudest, most efficient Leslie Organ Cabinet driver is F15 LL

this is a modern clone:

 

[Cagomat]

I have both Rullit Super Aero 8 with Fieldcoil and Alnico. The Fielcoil version is much better but only if you build an optimal power supply. The differences between rectifiers and filter chains are blatantly audible. I ended with 4x EY500 and LCLCLC.

 

[YTob]

I am several months late but, in case it is still relevant to you -

1) As you probably know, in this life you get what you pay. A properly good Field Coil driver that makes it worth going field-coil is an investment. Being cheap buys you mediocrity - and there is plenty of choices out there but why bother if when mediocrity is in it is mediocruty also out?

2) A word of caution- I personally never used it, but (I believe his name is Alex) Rullit has a very terrible reputation on ALL the Russian-language and Polish forums, and Poles do care about their audio. He is a Russian expat who lives in and operates from Germany, and, according to forums, is somwhat of a swindler: makes great-looking but not so great-sounding, and certainly not consistent-sounding "eye-candy". If you absolutely must go Field-Coil, then smarter money would be on the legitimate makers like Voxativ, AER, Cube Audio, GIP etc. Not cheap, but you get what you pay!

3) I think Fertin is long dead, and the current EMS drivers have nothing to do with Fertin, very much like the current PHY-HP has very little to do with the alnico drivers made by late Bernard Salabert, though outwardly they look superficially similar.

With PHY-HP, the situation is more egregeous as I read somewhere that when Salabert died, his family inherited all the tools, and the drivers are now made by completely different tools via completely different process, using completely different albeit similarly looking materials. And, yes, they sound different too. A good testament is- the original Salabert-made drivers never come up for sale, while post-Salabert used drivers are on the ebay at all times...

4) Some among us think that Field-coils do not sound appreciably better per se than their other magnet type counterparts, be it Alnico or ferrite. They do enable more flexibility in adjusting for enclosures by tweaking their Q.

FIY- Even Alnico do not always sound better than ferrite: -IMO, The best sounding Supravox driver is their legendary classic RTF wide-bander and not their Alnico or Field-Coil variant, made into a nice and expensive fodder for the "enthusiasts"...

5) If you are making an OB, instead of going Field-Coil, you may get more mileage and benefits by using spruce plywood instead of the ubiquitous Baltic Birch plywood.

For example, Bernard Salabert (again) hated birch plywood because it is rigid and has a nasty ring to it. Also, the original WE/Bell labs/Altec folks used spruce plywood in their speakers not because it is cheaper (though it is) but because it is softer and does not "ring" and need not be damped- and they understood a thing or two about making their speakers sound great!

Sadly, the majority of current OB builders are not well aware of this, or choose to use Baltic Birch plywood because of its ease due prefinished appearance. If you do decide to go with proper spruce plywood, do make an effort to also make it into a proper sand-filled sandwich, just like both Briggs and Salabert did though they lived forty years apart. Then you may not even need any Field-Coils. (I admit that after twenty-some years at this, being happily married with kids and living in a city apartment, I do prefer proper proper enclosures over OB's...)
Cheers.

 

[Mattes]

Dear all,


I may correct some of the assumptions made by YTob above:


- Michel Fertin is not dead, in fact I hope to meet him in a few weeks.
- EMS drivers are actually build by Michel and Kathy Fertin themselves, more information to be found here: Accueil
- FERTINACOUSTICS builds excellent fieldcoil drivers, more info here: FERTIN ACOUSTICS

- Owner of FERTINACOUSTICS is Marc Amiard.


This looks a little bit strange in combination (and is a little story by itself) but doesn´t change the fact that both gentlemen are friends and believe in peaceful coexistance. Both are building really good fieldcoil drivers, the EMS drivers are better attainable and are, for example, sold by SOLEN in Canada.
The FERTINACOUSTICS drivers are more expensive and are, as only build to order, more difficult to get. In fact, the owners only speak French, but if someone needs help contacting them, I might help out.


All the best


Mattes

 

[jjasniew]

"The differences between rectifiers and filter chains are blatantly audible" - another set of convoluted parameters to sort out.

"They do enable more flexibility in adjusting for enclosures by tweaking their Q". It'd be interesting to see a Qts versus field coil current plot.

I've always wondered what would happen if the field coil was wound in a way that you could modulate it? Vary the speaker Q as a function of loudness or frequency content.

 

[Cagomat]

@Ytob,
everything you wrote are second hand news. You've never heard a Rullit Chassis, and you know he's a fraud. I have already bought 3 pairs of chassis from him and they are the best sounding field coil drivers in the world. Oleg Rullit is an absolutely genius developer and correct businessman.

 

[jtgofish]

The Supravox 215 works well.You can add a ribbon semi super tweeter using say a1 uF capacitor in series. And a cheap15 inch high Qts woofer if you want more bass.

 

[YTob]

@Ytob,
everything you wrote are second hand news. You've never heard a Rullit Chassis, and you know he's a fraud. I have already bought 3 pairs of chassis from him and they are the best sounding field coil drivers in the world. Oleg Rullit is an absolutely genius developer and correct businessman.

I said I do not know Mr. Rullit personally (thank you for correcting me that his name is Oleg and not Alex), never heard his drivers, and did not call him a fraud per se. But, judging by your reply, you seem to be well aware of the sentiments I encountered elsewhere, and of the fact that his reputation is toast as it percolates through various forums. I said that he might be a fraud according to what other enthusiasts say, and advised caution as I encountered multiple references to Mr. Rullit on multiple forums. But If you sir (madam?) are indeed so sattisfied with his drivers- good for you!! I am sincerely glad that it is you who owns these drivers and not poor me! Yet, I still do not understand what you mean by Rullit is "correct businessman", but I see you use other ebullient language like "absolutely genious developer". With such platitudes, Mr. Rullit should be a guest of honor at every panel in Hi-End Munich every year, but perhaps I missed his august appearances throughout the years? I met the poles from Cube Audio, saw Austrians from Aer and Voxativ, have huge respect for the line Nagnetic guys for what they did with Jensen 222 & Iconic, and their experiment mating 755 with Jensen field-coil; but hey, I have not met Rullit. And likely will not. And that's OK. Cheers!

 

[Charcoal]

Rullit IS a fraud. Also still someone could be lucky and got what expected.

 

[paulfk]

Rullit IS a fraud. Also still someone could be lucky and got what expected.

A fraud in what way, I know people that have his field coils and love them, so a) they got what the paid for and b) his work must be good in these instances.

 

[gander]

Rullit lab8 field coil drivers

The Rullit Aero series are some of the best fullrange drivers out there, they do not have the peaky high end exhibit in most fullrange drivers. The high voltage power supply has no correlation with the amplifier being used, it only powers the field coil. I use selenium rectifiers for my power supply.
There are also some vintage German field coil drivers that sound quite good.

I just bought Rullit lab8 Field coil drivers, the best sounding speakers I have heard. they are still breaking in so 100 or 200 more hours to go, but already the low end is impressive, especially in a quasi-open baffle. My power supply now is marginal but I am going to try to build a full wave bridge rectifier with selenium “rectifiers“, which I believe are simply diodes.

I live near Las Vegas and it took a month and a half to get them from Nuremberg Germany. I was getting frustrated but it was worth the wait.

According to Oleg (Rullit) I can use a veriac transformer combined with selenium rectifiers and it should sound great. I would think that a big power capacitor on that and then a DC voltage meter to show what voltage is really coming out would be a good idea.

 

[paulfk]

I just bought Rullit lab8 Field coil drivers, the best sounding speakers I have heard. they are still breaking in so 100 or 200 more hours to go, but already the low end is impressive, especially in a quasi-open baffle. My power supply now is marginal but I am going to try to build a full wave bridge rectifier with selenium “rectifiers“, which I believe are simply diodes.

I live near Las Vegas and it took a month and a half to get them from Nuremberg Germany. I was getting frustrated but it was worth the wait.

According to Oleg (Rullit) I can use a veriac transformer combined with selenium rectifiers and it should sound great. I would think that a big power capacitor on that and then a DC voltage meter to show what voltage is really coming out would be a good idea.

i also just bought silver lab 8, have to collect from our office tomorrow as didn't get back in time on Friday. I would be interested in your power supply, a friend is going to build mine, probably valve rectified, we haven't got started yet. Just to add, Oleg sent the drivers they took a week to get here in uk from Germany