Building field coil speakers Rullit Aero

[Lautreamont]

My pleasure, Lautreamont!

Yes, you're correct. The Qts parameter of the driver changes value with voltage, which may allow for use in different applications. Low voltage results in high Qts, which can work for a sealed enclosure, or open baffle design. Conversely, high voltage lowers Qts, which may work well for a ported enclosure. Of course, there are always trade-offs. Lowering voltage for a high Qts comes at the cost of sensitivity.

This is very satisfying and good news - thank you very much. I appreciate all the informative posts on this forum - I learn something new every day.

I will try to investigate the matter more in the coming time and then come with a conclusion. It seems that there's a hope that I can find a cabinet that brings the best out of the Rullit and then match it with a single ended amplifier that produces enough power to tame the "beast" of the field coil while ensuring that there is room enough in my apartment.

 

[Treehaus Audiolab]

Thanks for the shout-out Ken!

Lautremont,
I make complete speakers using the Rullit Aero or Super Aero. In my experience with them, I have found them best suited in more of an open-baffle design. I experimented with open-backed boxes (along with a myriad of other variants) but I did not personally like the color they introduced. I did also find that in an open baffle, the 10" drivers start to roll off perhaps around 90-80hz (its a rather gentle roll-off) and the 8" is probably around 120-130hz (its open baffle, and field coil, so there are a lot of other variables at play) I could enjoy them without any bass augmentation, but they do require a low woofer to complete the sonic picture.

I recommend for our speakers 2ft from the face to the back wall as a minimum, with 3ft+ being preferred.

@TKK has my speakers in his apartment space, he might be able to chime in a bit as well as to how they perform in such environments.

 

[dcathro]

Thanks for the shout-out Ken!

Lautremont,
I make complete speakers using the Rullit Aero or Super Aero. In my experience with them, I have found them best suited in more of an open-baffle design. I experimented with open-backed boxes (along with a myriad of other variants) but I did not personally like the color they introduced. I did also find that in an open baffle, the 10" drivers start to roll off perhaps around 90-80hz (its a rather gentle roll-off) and the 8" is probably around 120-130hz (its open baffle, and field coil, so there are a lot of other variables at play) I could enjoy them without any bass augmentation, but they do require a low woofer to complete the sonic picture.

I recommend for our speakers 2ft from the face to the back wall as a minimum, with 3ft+ being preferred.

@TKK has my speakers in his apartment space, he might be able to chime in a bit as well as to how they perform in such environments.

Hi Rich,

I am curious, at what frequency do your woofer start to roll off in the open baffle?

I know people worry about overloading small rooms, but I have 15" field coils in 130L ported boxes (tuned to 35hz) with open baffle wideband (170 - 6khz) in a small 15 meter sq room. I have the speakers (acoustic center) 3' from the front wall, but the speakers close to the side walls to get bass re-enforcement.

By the way, it is great that you and Ken interact with the DIY guys and give advice. It really does elevate this forum in my opinion!

 

[Lautreamont]

Thanks for the shout-out Ken!

Lautremont,
I make complete speakers using the Rullit Aero or Super Aero. In my experience with them, I have found them best suited in more of an open-baffle design. I experimented with open-backed boxes (along with a myriad of other variants) but I did not personally like the color they introduced. I did also find that in an open baffle, the 10" drivers start to roll off perhaps around 90-80hz (its a rather gentle roll-off) and the 8" is probably around 120-130hz (its open baffle, and field coil, so there are a lot of other variables at play) I could enjoy them without any bass augmentation, but they do require a low woofer to complete the sonic picture.

I recommend for our speakers 2ft from the face to the back wall as a minimum, with 3ft+ being preferred.

@TKK has my speakers in his apartment space, he might be able to chime in a bit as well as to how they perform in such environments.

Thank you very much for sharing your experience. I agree with @dcathro - it is truly amazing that you take your time to visit these forums and share your thoughts. It shows great and genuine character.

I have seen videos of people using the field coil driver as the only single unit but it also makes sense with a woofer. I think the choice of enclosure will probably deduce if I need a bass solution.

I hope TKK will find his way to this thread and share his experiences as well - I hope that a lot of people can learn from this thread.

 

[DasguteOhr]

I've heard Rullit several times, but I liked them best on the horn.
At ebay you find such tractrix horns for 8"and 10" fieldcoils

 

[LanschePlasmaGuy]

I've heard Rullit several times, but I liked them best on the horn.
At ebay you find such tractrix horns for 8"and 10" fieldcoils
View attachment 151532

DasguteOhr,
Thank you for your interesting message.
How would you describe the sound of the Rullit's you have heard in the better front horns? Strengths / weaknesses?
I had my Rullit 8 Aero's in Andy Moore's old Telefunken style open baffle and my Super Aero 9's in a very loosely type of Treehouse Audio open baffle with my Paladin 15 inch field coil bass drivers augmenting the lower end. It will still be a few months until my 1m wide x 1.5 m high x 60 cm front horn is completed (having too much enjoyment with the Klangfilm front horn / Wolf Von Langa field coil compression driver crossed to the Paladin 15 inch field coil bass unit in a vintage Klangfilm style setup.

LPG

 

[DasguteOhr]

DasguteOhr,
Thank you for your interesting message.
How would you describe the sound of the Rullit's you have heard in the better front horns? Strengths / weaknesses?
I had my Rullit 8 Aero's in Andy Moore's old Telefunken style open baffle and my Super Aero 9's in a very loosely type of Treehouse Audio open baffle with my Paladin 15 inch field coil bass drivers augmenting the lower end. It will still be a few months until my 1m wide x 1.5 m high x 60 cm front horn is completed (having too much enjoyment with the Klangfilm front horn / Wolf Von Langa field coil compression driver crossed to the Paladin 15 inch field coil bass unit in a vintage Klangfilm style setup.

LPG

I think the secret is that these horns are made of thin wood and resonate. This creates a bit more fullness in the upper bass and midrange. The music these drivers produce simply sounds more authentic. The Rullits have that detailed sound even without a horn, but with the horn it's even more flesh colorful and explosive. Weakness: I don't think every horn on offer plays linearly and without coloration. But that will mainly bother people who run around with a measuring microphone all day. The fun factor is extremely high. I would keep an eye out for old blueprints for tried-and-tested horns for Telefunken field coils.
Exsample

 

[Treehaus Audiolab]

Hi Rich,

I am curious, at what frequency do your woofer start to roll off in the open baffle?

I know people worry about overloading small rooms, but I have 15" field coils in 130L ported boxes (tuned to 35hz) with open baffle wideband (170 - 6khz) in a small 15 meter sq room. I have the speakers (acoustic center) 3' from the front wall, but the speakers close to the side walls to get bass re-enforcement.

By the way, it is great that you and Ken interact with the DIY guys and give advice. It really does elevate this forum in my opinion!

Im happy to offer a bit of guidance when I can.

As the woofers, I usually cross them over about 95-100hz on the high end, and let them roll off naturally on the bottom end, which is usually in the mid/high 20hz range depending on the room.

 

[Artnet]

At ebay you find such tractrix horns for 8"and 10" fieldcoils

Need some of these for my 8" aero but at Euro 7,355 . I am sure they sound beautiful but will look into getting some made locally

Lautsprechergehäuse/Hörner

www.cjm-audio.de

 

[DasguteOhr]

Need some of these for my 8" aero but at Euro 7,355 . I am sure they sound beautiful but will look into getting some made locally

Lautsprechergehäuse/Hörner

www.cjm-audio.de

Ask at heyder horns for me best hornmanufactor in germany , maybe cheaper.

LMH - Holzhörner (2)

Highend Manufaktur rund um Hornlautsprecher und Komponenten. Hersteller der Hölzhörner r-Trak - sTrak & eTrak. Sonderanfertigungen & Kleinserien.

www.lautsprechermanufaktur-heyder.de

Or joseph crowe diy plan for front horns

Front Horns

Joseph Crowe is a business offering design and built-to-order components and speakers. We specialize in Horn Speakers and Bass Cabinets.

josephcrowe.com

This one looks like a good idea+ ripolsub 15"from 20-90hz

Front Horn No. 1548

In this blog post I feature a recent front horn built. The horn is by far the largest I've built yet. It measures 44.50" x 44.50" at the horn mouth and measures 22" deep. (113cm x 113cm x 56cm) The black oak frame adds another 8” (20cm) to the overall size for a total width of 52.50” (133cm)...

josephcrowe.com

 

[DaveC]

Dear LPG

I must admit that I was reading your initial reply with great joy and satisfaction. It gave me hope that I might was getting into a "life-changing" quest in terms of finding satisfying speakers that could give me years of transcending experiences.

Concluding there are two design options that I proceed with:
1. Front Loaded Horn
Cons: They are large and need space.

2. Open Baffle System
Cons: They are medium sized but needs space behind them.

One of my livings rooms in my apartment (that also functions as my listening room) is 25 square meters with 2,7 meters to the ceilings.

Concluding there are a few considerations before proceeding:
1. Beginners naivety
I have no technical or practical experience putting together a system which means it could be rather risky to proceed.

2. Lack of understanding of field coil
I do not have the necessary understanding of the field coil driver so it would be unwise to strive for an idea without knowing the basic concepts.

I'd recommend the front loaded horn solution. I built a FLH using a 330 Hz LeCleach profile and 4.5" driver, with an 8" you'd want to go larger otherwise it's not going to really be a horn, although it'll help shape directivity.

I post mostly to let you know that while the horn may be large, a wideband horn doesn't need the same kind of space a more conventional 4+ way horn system does. It's much simpler as there's no xo in the midrange, in fact no xo at all is possible, but I find it better to use one to limit excursion and tweeter overlap, just depends on music type and volume. With my horns covering 400-12000 Hz you can listen nearfield with no issues. The horn can produce an excellent polar plot and reduce the contribution of room acoustics, together with a closer distance between speakers and listener it can make for a very immersive, 3D experience that is in some ways superior to a conventional speaker. IMO, FLH + BR bass is superior to OB, the only advantage of OB is you don't have to come up with an enclosure and horn, you bypass some design work but end up with an inferior result.

I use a Acoustic Elegance 15" woofer in a ported box and a Fostex T500, imo once you get this kind of system dialed-in it's really amazing and very rewarding.

 

[DaveC]

Need some of these for my 8" aero but at Euro 7,355 . I am sure they sound beautiful but will look into getting some made locally

Lautsprechergehäuse/Hörner

www.cjm-audio.de

There's some fb groups on building and modifying lowther type drivers, it's not all that difficult or expensive to get into. That's how AER came to be, I think it would not be all that hard to make a similar driver at home. I may try it one day...

 

[Artnet]

Ask at heyder horns for me best hornmanufactor in germany , maybe cheaper.

Thank you for the suggestions. LMH look terrific, Its the Feight to Aus that would concern me but still interesting to find out more.

This one looks like a good idea+ ripolsub 15"from 20-90hz

Have noted this one previously but its a a heavy beast to push around and more intrigued by your previous comment in regards the "...these horns are made of thin wood and resonate."
I also think this would benefit the rullit and then with an optional sub.

 

[DasguteOhr]

Have noted this one previously but its a a heavy beast to push around and more intrigued by your previous comment in regards the "...these horns are made of thin wood and resonate."
I also think this would benefit the rullit and then with an optional sub.

Thats a Oleg Rullit horn thats made for his drivers. A Ripol sub is a fast subwoofer I think that this is a suitable addition to the good response of the rullit.
If you want to build something like this yourself, you'll have to buy Axel Ridtahler's blueprints.

Ridtahler: Soundsysteme - Hifi - Audio - Audiosysteme - Subwoofer ... made in Germany

If you want buy something , I can recommend the Soundkaos Gravitas Sub. 2x 12"or 2x 15"

 

[bonzo75]

Hi Lautreamont.



You mentioned Audio Antiquary, Yamamoto and Shindo. Love the Yamamoto 45 amp and a crazy bargain for the price. The AD1 Yamamoto which I almost bought and was powered by original era AD1's was wonderful but couldn't get rid of the hum and noise it had and the tubes are difficult to find in good nick so I regretfully gave it back. I still have one of the Shindo amps (300b) and I really enjoy it (with qualifications). The Audio Antiquary gear is just incredible (for my listening tastes) but is super revealing of every aspect of your audio setup and is a real microscope into your setup and the recording. When you get everything write though Misho's gear is just bonkers amazing (if your gear is sympathetic to what it needs and if you can get away with only a few watts (even though they may be the ballsiest 4 or so watts on the planet).

Here are some videos of the audioantiquary system

Thread 'Zero Distortion: Altec Assault Redux: orchestra and rock'
https://www.whatsbestforum.com/threads/zero-distortion-altec-assault-redux-orchestra-and-rock.35975/

 

[Lautreamont]

Dear everyone.

I apologize for my absence but I have been working all weekend.

I appreciate all of your comments, reflections and suggestions. The fact that product designers and owners come across these forums and share their experiences without a hidden agenda of branding their own enterprise are truly amazing and admirable. Thank you.

I have corresponded with Oleg and he offers both AlNiCo models and field coil drivers that are either "AERO" or "SUPER AERO" models. I have asked about the differences but I'm contemplating whether investing in field coil now would be a clever decision for the future whilst thinking about, if AlNiCo can suit my modest needs.

Oleg recommends both front loaded horn designs, open back cabinets and open baffle solutions. Other types of cabinets negatively influence the music reproduction. He put me in touch with a gentleman from Italy that are building high quality resonance cabinets. The cabinet resembles a cello and should promote the music resonance. I'm proceeding slowly and we'll see if this a solution.

I don't have the parameters and I can't get them since he do not have equipment to measure it. I don't know If this will be a problem.

 

[Lautreamont]

Dear everyone.

My investigating is ongoing and still extremely exciting and I'm learning new things every day. No matter what I'll end up with it has been very educational.

Anyway a few days I ago I was corresponding with a person who didn't agree with the combination of Rullit field coil driver and a front loaded horn. I listed a summary of his main points. I find it rather interesting and perhaps you would too like this information.

1. Waveguide design needs a rising frequency response
• For a linear (flat) response inside a waveguide, the driver itself needs a rising frequency response outside the waveguide.
• This rising response compensates for the waveguide’s natural roll-off.

2. Strong magnets help achieve rising frequency response :
• To get a rising frequency response, you typically need a very strong magnet in the speaker driver.

3. Rullit speakers use weak magnets for dipole use
• Rullit speakers (a specific brand of field-coil drivers) use weaker magnets.
• This is because they are designed to work well in dipole configurations, where a weaker magnet helps produce better bass.

Summary:
• Waveguides need drivers with rising frequency response, which strong magnets help create.
• Rullit drivers are optimized for dipole use, not waveguides, because they use weaker magnets for better bass in open-baffle setups.

 

[LanschePlasmaGuy]

Dear everyone.

My investigating is ongoing and still extremely exciting and I'm learning new things every day. No matter what I'll end up with it has been very educational.

Anyway a few days I ago I was corresponding with a person who didn't agree with the combination of Rullit field coil driver and a front loaded horn. I listed a summary of his main points. I find it rather interesting and perhaps you would too like this information.

1. Waveguide design needs a rising frequency response
• For a linear (flat) response inside a waveguide, the driver itself needs a rising frequency response outside the waveguide.
• This rising response compensates for the waveguide’s natural roll-off.

2. Strong magnets help achieve rising frequency response :
• To get a rising frequency response, you typically need a very strong magnet in the speaker driver.

3. Rullit speakers use weak magnets for dipole use
• Rullit speakers (a specific brand of field-coil drivers) use weaker magnets.
• This is because they are designed to work well in dipole configurations, where a weaker magnet helps produce better bass.

Summary:
• Waveguides need drivers with rising frequency response, which strong magnets help create.
• Rullit drivers are optimized for dipole use, not waveguides, because they use weaker magnets for better bass in open-baffle setups.

Yes,
I mentioned this in the advantages of using a field coil driver (in my case the Rullit's) in a front loaded horn.

You can change the parameters of the driver by changing the voltage to the driver. Think of it as the equivalent of turning the voltage down (equivalent of a smaller magnet) for it to work at it's best in a open baffle.

If you want to put it in a front horn turn the voltage up (like putting on a much bigger magnet) so that as you increase the voltage to the field coil motor (magnet) it will give you a flat frequency response in the front horn but if you kept the driver at the higher field coil voltage and then removed it from the front loaded horn and plced it in a open baffle it would sound very brigh and rolled off at the bottom end (because you have given it a rising frequency response).

So i've just addressed points 1, 2 and 3 above. I have the strongest series of potential magnet (field coil) that Oleg makes which is the Super Aero. The magnetic system is enormous. Please see my photo in an earlier response to you above. It is way bigger than you would find in any conventional driver. No offence but the person you coresponded with and who's information you detailed above when you said that he mentioned in your summary that : "Rullit drivers are optimized for dipole use, not waveguides, because they use weaker magnets for better bass in open-baffle setups." is totally wrong.

Yes you can turn down the voltage on the field coil motor and create a "weak" motor structure and as you turn it up you will find the perfect balance at some point for it working in an open baffle (I think Rich at Treehaus runs his at about 115 volts) but you can also turn the voltage up and create a monster magnetic system that at some stage will make it perfect for a front horn).

Rullit drivers are amongst the best drivers you can buy period and have been designed to be low on compromise (which comes at a financial price and also the requisite power supply etc. to be able to get them working). I happen to think although they are not "cheap" they are incredible value for money. I have no doubt that Songer audio some other brands would be on that list but it's a pretty small one.

There's such a fundamental difference in the sound of a great field coil driver that if your happy to spend the extra money you have a driver for life and your final speaker journey may have stopped. If you buy Oleg's alnico driver you don't have the flexibility to tune it by varying the voltage and although great you won't be getting the magic that the field coil driver will give you.

LPG