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Old 4th March 2014, 05:15 PM   #1
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Default Extreme Open Baffle Active Speaker inspired by Linkwitz LX521

Recently i visited Siegfried Linkwitz and heard his LX521.
I was positively shocked about the sound quality and the progress he made since my last visit when i heard the final version of the Orion.
I like the Orion, no question. I even build a pair for my friend.
The Orion is neutral balanced and throws a nice soundfield.
What it lacked for my ear is what i call drahma. It is more a polite speaker, never agressive and very clean. The aural attention is more in a wide cut midrange. At the edges of the spectrum, high up and deep down i would wish for more extention and definition. Transients come a bit slow so there could be more resolution and snap. This is more a speaker that does well what it can do well. It is all about avoiding glaring mistakes at the price of ommitting some of the details. Nuff said, the Orion has its time and place.
Nothing prepared me for what Siegfried had in stock.
The LX521 fullfills all my wishes and some...
The sound is now totally free from the speakers. I could not hear sound comming from the baffles, even in close miked pans. That is really unusual and welcome. They totally " disappear ". OK; this has being said many times in reviews, for example in Michael Fremers Review in the 90th of my original Virgos and it is true. I can only tell you that they even " disappear " more then i have heard before in a dynamic speaker. Another feature is also at work here that gives the illusion of the speakers not present : there is absolutely no preasure on the ears.
There is much more to say and i will later.
At the end of the session Siegfried encouraged me to build a pair myself.
I thought long and deep about it. I came to the conclusion that i should design my own version. Not in an attemped to better the LX521 but to have some fun. This thread is about this undertaking.
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Old 4th March 2014, 05:51 PM   #2
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Some more notes about the sound i heard :
The LX gave the impression on being very wideband, subjectively the tweeter is more extended, crisp and fast. Quite an achievement with two inexpensive, small SEAS neodym
drivers. The bass is tighter, deeper, cleaner and has more slam and power.
Transition is seamless.
We could play very loud and dynamic. That gave quite a spectacular presentation.
It was emotional and accurate. Like a camelion the LX could turn from intimate and elegant ( King Singers ) to brutal and snapping ( live solo electric bass ).
We did not find time enough to listen to much classical ( i had too many questions and i can digest only so much from such an opulent meal ) but Mr. Linkwitz is convinced that strings are the LX friend. I have no doubt about it.
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Old 4th March 2014, 05:55 PM   #3
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With extreme material the woofers and the lower mids moved quite a bit but i could not hear any distortion. Siegfried has a very big room so i can not imagine that even a rock and roll addict wants much more. This speaker simply has much more scope and range then the earlier Orion.
Of cause Siegfried told me : " This will be my last speaker ".
Sure, he said that when he made the Orion.
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Old 4th March 2014, 05:56 PM   #4
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How do you like the shelving down FR? Do you think it is correct (the sound and the rationale) ?

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Old 4th March 2014, 06:05 PM   #5
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Some more notes that really challange the way we think in High End :
The speaker cables where 6m long Radio Shack 1.5qmm standart stranded with PVC isolation. Several non precious, magnetic metal connections in the chain.
I usually expect foggy and " dirty " treble that way but the treble was superbly clean, crisp, snappy and shimmering.
The speaker is active. That can not sound homogenius. The amplifiers are not as good as my 20.000,- $ tube, etc. blah, blah, blah.
He used a simple and good OPPO player. No footers, no roomtuning, no nothing...
Well, yes, and i knew it : the speakers are the weakest link in the chain !!!
The room too but with dipols and intelligent placement there is no need for extensive room tuning.

Last edited by Joachim Gerhard; 4th March 2014 at 06:09 PM.
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Old 4th March 2014, 06:08 PM   #6
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Well, i heard the shelving in the Orion and saw the measurements.
I do not think that this made a big diffence to me.
I have no idea how the LX measure or if they are tuned in any way.
Siegfried only told me :
" I made them and no changes since ".
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Old 4th March 2014, 07:24 PM   #7
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So what did i do so far ?
I build the mid-treble baffles. That is really fast and easy.
I copied more or less the shape.
Siegfried told me that the shape is critical to maintain dipole action over a wide range.
He arived at the shape by experiment.
I understand the midrange shape but i had questions about the rather clumsy shape in the treble.
" That is to avoid that the radiation from the back tweeter comes around to the front ".
OK, i dig that.
The shape i use is diffent in that it uses Bezier curves instead of straight lines.
I do not think that is has a lot of consequences to the sound but it is a visual alternative.
In the treble my version has the biggest diffence to the LX521.
I use a dipole AMT donated by Mundorf.
Thanks Raimund.
I decoupled it by springs.
The midrange is the Scan Speak 10cm wideband.
I do not know if it is superiour to the Curve Cone SEAS.
I simply had it in stock.
I wounder if part of the " crispiness " of the LX comes from that Curve material.
When i scratched it with my fingernail it sure gave a crispy sound.
That is very diffent from soft material like Bextrene or unfilled Polypropylen.
Such membranes are known for loss of mircio detail.
The Curve cones obviously do not have that problem.
In the deep mid i use a driver designed by SEAS for me. It has a stiff paper cone, a huge magnet and long throw.
Attached Images
File Type: jpg LGB front.jpg (61.3 KB, 2537 views)
File Type: jpg LGB back.jpg (255.6 KB, 2447 views)

Last edited by Joachim Gerhard; 4th March 2014 at 07:31 PM.
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Old 4th March 2014, 07:30 PM   #8
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I also build a stand from massive spruce.
On this pictures you also see the tweeter decoupling better.
Attached Images
File Type: jpg LGB 3 front.jpg (206.5 KB, 2363 views)
File Type: jpg LGB 4 back.jpg (196.0 KB, 2240 views)
File Type: jpg LGB 5 side.jpg (188.7 KB, 2170 views)
File Type: jpg LGB 6 tweeter back.jpg (549.6 KB, 637 views)
File Type: jpg LGB 7 tweeter front.jpg (747.2 KB, 605 views)
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Old 5th March 2014, 12:31 AM   #9
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Here are the responses of the drivers i measured free field on axis.
The crossover frequencies are supposed to be at 120Hz, 7 Khz, active 4th order and 1kHz
first order passive.
As far i i can tell this will be posible without problems.
I will use the Mini DSP anyway so i can linearize or shape the response more or less at will anyway.
Attached Images
File Type: png Dharma MT 1 MT 2 HT on test panel.PNG (114.8 KB, 620 views)
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Old 5th March 2014, 03:33 AM   #10
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I made some experiments with the passive crossover between the lower and upper midrange.
I ended with an electrical 6dB filter, like in the LX521. Just a coil and a cap.
My next post shows the measurements and adds some commends.
Every child has a name so i will call this speaker from now on Dharma EX.
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