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.