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I am starting to design a DIY speaker that is inspired by a swiss designer named Dominic Stoll. His work was introduced to me by Martina Schöner of Loricraft-Garrard some years ago on the High End in Munich. Dominic designs speakers for PA and Studio Monitoring. His designs are unusual because he uses minimal cabinetry, especially in the midrange and treble where he uses basically only the drivers. It is not an open baffle design because he uses dome midranges and tweeters that come, so to say, with their own cabinet. I had a long discussion with him in the Sushi Bar of the Frankfort Maritim Holtel during the Pro Light and Sound show and was very impressed about the width and depth of his knowlage. Actually this was the first designer i met that designs with dynamic drivers that really talks my language so it was like meeting a long lost relative. Of cause we did not agree on everything and the discussion got fierce for a moment but it was as he was reading my mind.
I will tell you more soon but what i can tell you now is, what the name means.
ZDL stands for Zero Difraction Loudspeaker.
I build a little jig to measure the tweeters "open air". The tweeters i chose are the Vifa OX20SC00-04.


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Hello Joachim,

Unfortunately there is no such thing like zero diffraction :) But you must know that.

I did measurements of tweeter hanging in free air by wires and find multiple around diffractions like in this wavelet graph:


See here for more post #702:

- Elias

ZDL stands for Zero Difraction Loudspeaker.

I build a little jig to measure the tweeters "open air". The tweeters i chose are the Vifa OX20SC00-04.
Yes, i know that. Even if the acoustical sourounding is optimal there is always the behaviour of the membrane. Especially when you use a soft membrane material. There can be out of phase movements that cause comb filtering.
Maybe the titel ZDL is too optimistic but i will do my best to minimise difraction.
In my experience putting the tweeter on a wide baffle can give good results too but the reason i am building this is the rather different aural result. I find the sound that Mr.Stoll gets very attractive in terms of spaciousness and size and precissision of the stage.
I think one of the reasons my classic Audio Physic Virgo 2 sold so well in the 90th was that it used a very slim and rounded baffle that gave a higher measure of off axis treble resulting in a sound that made the speaker "disappear". Mr. Stolls idea is much more radical though but it pulls this magic trick too, even to a higher degree. Nothing is perfect though. So lets see how close i will get.
Today i measured the tweeter on and off axis. This does not look as pretty as your wavelet graph ( i mean in the aestetic sense ) and is presented in the traditional way at 0°, 30° and 60°. The jig and the surrounding material is not optimised in any way. I just used what i could find in the lab but i think from 2.5kHz up it does not look too bad. The on axis response has a slight up tilt and there is a shallow hole from 2.5kHz down and in the deeper regions the sound preasure recovers somewhat. Measured from 30° the balance is nearly flat and well extended and from 60° the sound drops over 15kHz. This is much more offf axis energy then the usual 1" dome on a wide baffle so it fullfills one of my goals. Sensitivity is around 90dB and that fits well to the midranges i elected to use. The well know Scan Speak 10cm wideband that i also use successfully in my Mini MPL but without tweeter there. You can download the specs here :
The impedance curve of the tweeter shows a surprisingly low fundamental resonance at 1.1kHz for something so small. No ferrofluid is used i asume and there must be some impedance control ring or cap fittet because the impedance shows no tendency to rise in the treble.
Tomorrow i will measure distortion and look if those details have any advantage besides extending the response in the higher and deeper ranges. I have a conventional SEAS 19mm tweeter that i will use to compare. That one has ferrofluid, no control ring and a traditional ferrite magnet.


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I went breefly through the link you send me Elias. Interesting interpretation that the sound moves around the tweeter and comes back from behind to interfer. I have not put much thought into that but it inspires me. Many thanks. Was that a conventional tweeter with a rather big frontplate ?
I still do not have a picture of the bigger Midfield Stoll Monitor but there Domink uses a tweeter that as an extended bullet shaped back. I have no idea if that helps to supress the "roundabout effect".
JG , if you want difffuse localization of phantom sources , colored sound , and bad representation/resolution of the recorded sound structure , then this "sToll monitor" kind of "hallsossenwerfer" might be the best of the worst you can find or design by yourself ....

To check phantom sources , use a mono switch on your preamp .

To check the recorded sound structure against speakers , use a good headphone . (Fanfare for the common man > Telarc, is a good recording example, listen to the bouncing echoes of the kettle drums in the concert hall)

For close mic´d recordings with no real info embedded about space , such speakers add some kind of sensation due to a bunch of strong reflections , but certainly this is not "hifi" , it is junk that muddy the sound and keeps you from hearing what the recording really has to offer ...

You should better talk with someone who knows the flaws of room-speaker interaction , like Andreas Haeger (AH) in Hannover/Germany , he is a physicist and did a lot of research about what makes a good playback system . He was very active in german DIY forums for many years , now absent since a few years , never heard of him?

Really , my impression is you hiend guys have no clue what makes a system bad or good , your subjective is your objective , Woody Allen must be your guru guru :p

best regards - DIY HiFiLeaKZ ;)

ps - why do you think have control rooms angled side walls , in-wall speakers and special room treatment?
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Marvel, this is harsh critique. I have made listening tests with mono as far back as the 70th and i have done research on phanton sources in the 90th with Dipl.Ing. Bernd Theis and Prof.Malkolm Hawksford of the University of Essex. We did a joint AES paper on this research and i presented the paper on the 100th AES convention in Kopenhagen. I will find the paper so that you can download it. My setup method including micro placement even made it into Martin Colloms book together with the Cadas and Wilson method. I teached that method on seminars and presented it to several magazines. Not the least Stereophile that did a 17 page review on the Virgo 2 and my setup method. I have heard the Pluto in Siegfried Linkwitz home and have studied and discussed that design with him in depth.
Speakers like the one i design here work best in the nearfield with the ears not much more then 2m from the speakers ( up 2.4m it works for me ) and the speakers should be far away from room boundaries especially the side walls. I will not go in depth over the content of my paper but under those conditions, phantom images are rather accurate. Still i agree that speakers like that sound different but focus and phantom source imaging are only two requirements for a convincing illusion of musicians playing life in a good room.
During my career i have designed speakers of various builds including conventinal speakers with wide baffles and even a speaker where you listen ONLY to the phantom image that surpresses off axis radiation strongly. Part of that research made it into my patent "Gekreutzte Schallwand".
Please do not make a fool of me. I know about accurate phantom source recreation. Dominics and my designs are in successfull use in a lot of Studios world wide but for monitoring i may build something different.
I play the guitar, sing, compose, record and produce my little band "Die Störung". I have played life and in the studio. My son playes piano and is French Hornist in a youth symphony orchestra. I know how music sounds life. I hear it all day.
The ZDL has no aspiration to be "accurate" ( no speakers is although some "professionals" claim to be able to judge and measure that) in a strict sense, but i will try to make the physical parameters as linear as i can. What i will try to do is to make it sound "beautiful" so that the soul of the music is tranfered and the music reproduced over this speaker evokes emotions in a sence that the reproduction is interesting and satisfying. Marvel, and please do not make jokes about us audiphiles. You are on slippery ground then and may have no idea what it is all about. The High End is what it is and it may or may not have to do with what you "professionals" experience in the studio. It is much about aestetics and emotions but "we" love music as much as "you" do and yes, Woody Allen is cool athough i do not have a guru.
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Sy, i was surpised too but it may be responsible for the "hole" i experience under 2.5kHz.
The wavelength there is around 20cm so the sound travels to the bucket and comes back partly out of phase. Higher frequencies are not affected as much i think. I may put the tweeter in a nylon ball i have and may or may not damp it on the back to avoid the "roundabout problem" ( that was really new information for me ).
The midrange will be eventually put in a wooden ball so the ZDL will look different then the Stoll speakers.
Sy, i was surpised too but it may be responsible for the "hole" i experience under 2.5kHz.

Do you still have the impulse response?

I remember spending an afternoon at Precedent Audio back in the '70s, carving out driver holes in styrofoam balls to mount some SEN-labs domes. It wasn't a new concept even then. Like any other tool on the illusion end of things, the question is always, does the implementation address the design goal and if so, how well?

I don't get the "purity" argument here at all. This isn't electronics, it's loudspeakers. Appreciate you opening this thread and sharing data.
Hi SY ! No, i did not store the impulse response. I measure with a sine sweep and derive the transfer function from that. The transfer finction can of cause be post processed into the impuls response. If you want to know about early reflexions i whould like to present you the Cepstrum. I will do that later. Thanks for your time.
So you played with balls too ?
So you played with balls too ?

Ahem, perhaps we can rephrase that.

Yes, the results were interesting, but Precedent folded before we could really work out the details. It was a remarkable company- transmission line midranges, Sonotube cabinets, modular three ways, Dynaudio drivers, all pretty exotic in 1976. They also sold a zero loop feedback tube-FET hybrid preamp with a switching supply.
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