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Old 4th July 2012, 07:17 PM   #11
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Quote:
Originally Posted by Legis View Post
Hi, I actually own those very speakers (is it not obvious from the pictures ).
Ahhh, thanks for the info.

What I would change first in this speaker construction, is to change the metallized membrane to one with a high resistance coating. Also in my Esl-63 I got better results (compared with the original graphite coating).

Harry
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Old 4th July 2012, 07:33 PM   #12
tyu is offline tyu  United States
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What MartinLogan did to trun Down the out put Of the panels....Not that i think you wount to do this nor do i....Thay ran more horz bars..
The SL3 panels have the most output an sound the best to me..
The SL3 panels 12"X48" there are 11 hroz bars then the top an bottem so it 13 in all...an the 5 in the middel of the panels are 5" a part....an at the top an the bottem thay are 2"...an the others are 3"...this gives Max output of the panels..An best hi-end....
The more horz bars an closer togather... turns the panels output down....Just my finding..thanks for the input...goodluck

Last edited by tyu; 4th July 2012 at 07:39 PM.
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Old 4th July 2012, 09:49 PM   #13
Legis is offline Legis  Finland
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Quote:
Originally Posted by harry_at View Post
Ahhh, thanks for the info.

What I would change first in this speaker construction, is to change the metallized membrane to one with a high resistance coating. Also in my Esl-63 I got better results (compared with the original graphite coating).

Harry
Hi, already did that. New membrane is 6”m Hostaphan polished with an antistatic vinyl polish spray.

Here are some pictures of the horizontal spacers:

Back stator:

Click the image to open in full size.

Front stator:

Click the image to open in full size.

Close-up:

Click the image to open in full size.


I will be putting five nylon bolts through each spacer (50 bolts per speaker) and squeeze the hell out of the stators and make them very non-resonant. I have already tried it with 16 bolts with acryl spacers, and it made a big difference. The stators were not completely damped with this setup however. With PVC spacers, which are very damped by their nature, and 50 bolts, the stator will be dead as a rock. Lots of work but it does pay off.
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Old 6th July 2012, 07:15 PM   #14
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Now REMEMBER to NOT tension the membrane from side to side at ALL!
Just from top to bottom!!!!!
Or else You will still have a serious problem with the membrane getting closer to the rear stator.

Cheers!
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Old 7th July 2012, 09:03 AM   #15
Calvin is offline Calvin  Germany
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Hi,

the speakers Harry linked to, are really a fine piece of woodwork. For the panel, well, there are several points in the design and building that could be improved.
The metallized membrane beeing one, the way of tensioning the diaphragm another, vertical spacers probabely the worst. The 1:75 Plitron audio tranny will offer the poor amplifiers a tortureous impedance, with close to shortcut values at the upper bandwidth limit and very large phase angles between 2kHz-10kHz. Such a large panel shouldnŽt be matched to the amp with more than 1:50, or You can count the number of amplifiers able-not-only-to-drive-the-thingies-stable-but-still-sounding-well by the five fingers of Your hand.

The distance of the spacers should follow the rule of shortest distance that still allows for the full d/s stroke. The rule of thumb of 1:70-1:100 (under the premise that the HV-bias is optimally high) still applies. Larger distances cost on efficienc and dynamic range (because of lower allowable HV-Bias) as well as shortening the distances (d/s getting larger than required). The spreading of resonances only works with considerable differences in segment area and dimensions. Care should be taken, that the varying dimensions dont cost too much on efficiency. If the panel is of a hybrid-type, the resonance peak probabely wonŽt matter anyway and the spacer distances can be designed for highest efficiency. Only FR-esls might profit from resonance distribution, but then, those are the inferior systems anyway.

The positioning of the smallest segments towards top and bottom of the panel helps to prevent the diaphragm to develop wrinkles at the edges.
To put it the other way round will probabely result in warps and wrinkles in the edges of the panel.

The soft double sided tape used as spacer introduces alot of damping to the stator. But both stator sheets must match precisely in curvature (or the front stator slightly, very slightly less curvature, if the rim is clamped well together), otherwise they will separate slightly in distance over time, with a following decrease in output level. The small soft tape strips are not able to cope with a constant pull over time and will give in. Also the soft strips wonŽt be perfectly flat but follow the hole contour of the stator sheet --> tiny warps. Besides the obviously faster, easier and as such cheaper mounting of the strips, I assume this to be one reason for ML to change from the soft 3M tape spacers to the clear hard spacers.
Since the hard cored spacers also feature thin glue layers the panels are still well dampened if glued together (MLs former panels were just glued at top and bottom, leaving the vast majority pieces of rattling metal). Then thereŽs no need to screw the stators together, which btw, is a true PITA, besides the inferior optics.

jauu
Calvin
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Old 7th July 2012, 09:28 AM   #16
Legis is offline Legis  Finland
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Hi Calvin, thanks for the answer. I agree with aluminum membrane and the vertical spacers. What do you mean with that the way of tensioning the membrane is something one could improve upon?

Here are some pictures I took (pardon for messy room):

Tension tapes:

Click the image to open in full size.

50mm wide tate that locks and secures the membrane from all over (underneath is also the charge ring):

Click the image to open in full size.

Black linen based tape that will define the looks that will show under the acryl side strips of the front stataor (I wanted black looks all the way.)

Click the image to open in full size.

Small pieces of transparent tape is put on the membrane before I made the holes with soldering iron for the nylon screws that go through the spacers. In picrture the holes are already done:

Click the image to open in full size.

And here is one ready speaker with all the 50pcs bylon bolts going through the stators squeezing them completely together:

Click the image to open in full size.


The sensitivity increased by 2-3dB compared to the vertical spacers. If I wanted I can also lure in some more sensitivity by squeezing the ylon bolts hard because that will squeeze the PVC spacers a bit to maybe 2,5mm d/s. The stator sandwitch is very sturdy when knocked!

The capacitance dropped by 100pF to ~2700pF.

The speakers will have line level crossover. Maybe 1st order around 200Hz. I have to try different approaches, right now I'm testing them with modded DCX2496 but will go for passive crossover and leave the DCX for bass. Dipole line array woofers from floor to the ceiling with 5pcs of 18" drivers per side will take care of the low registers.
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Old 7th July 2012, 10:46 AM   #17
Calvin is offline Calvin  Germany
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Hi,

the tensioning as done in the thread by hand will hardly give an even distribution of mechanical tension and is prone to panel-2-panel variations, i.e inconsistancies.
With the vertical spacers the diaphragm could probabely be heat treated after mechanical tensioning, but not so with horizontal spacers.
Here a dedicated tensioning frame is required to achieve high precision and consistancy.
Too IŽd suggest to pull the diaphragm around the stator rims to the backside and to fix it there also (at least at top and botttom rim).
This keeps the tension up over a longer period.
Simple taping as shown in the thread will hardly produce longtime stable glue joints.
With apropriate procedures and tooling one could achieve Fs variations < +-1Hz and amplitude variances < +-0.5dB.

2.5mm of d/s for a panel crossed at ~200Hz is like an huge empty airplane Hangar.
Every mil of unused d/s costs on efficiency, since the efficiency drops quadratically with distance.
Even if the HV-Bias is raised to counter the drop, the needed wattage raises.
The loss is so severe that the dynamic range shrinks which even the increased possible excusrsion canŽt completely compensate for.
The THD usually rises sharply below 200Hz, which also speaks against large d/s values.

Regarding the large size of the panel IŽd opt for a lower crossover of maybe 120-150Hz (or even 100Hz if the resonance Fs allows for) to put the d/s to a good use.
If mated with bass drivers as large as 18" the crossover freq needs to be low.
Keep the working range of such large basses possibly below 100Hz.
They donŽt play and integrate well at 200Hz, especially not in a dipole arrangement.
Crossing over at 100Hz or below You might think of using the Basses (and a lower number of them) in CBs.
One driver might already be enough then.
At such a low xover the panels distribution has taken on a dipolar global shape (at >150Hz it transits smoothly into a dipolar cylindrical shape), that may probless be mated with the global distribution shape of the woofer.

jauu
Calvin
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Old 7th July 2012, 12:57 PM   #18
Legis is offline Legis  Finland
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Tensioning tapes are really sturdy s*it, it does not worry me the least. 3M makes very good tapes these days. The glue joints are actually compressed agains the stators/acrylic side strips with 22pcs M6 nylon bolts that can be tightened hard.

I can live with +/- 10Hz differences, although they are not going to be that big (I know from last time I membraned them, that was with the vertical spacers) and they get closer each other in burn in.

That number I said is just electrical crossoverpoint, acoustical crossover point will be totally another story as we all know. I manly make the high pass in order to protect the Plitron from saturation. I usually use only 1st and 2nd order filters, they sound the best.

Here are plots for full range, 100Hz, 150hz, 200hz and 250Hz 1st order filters, measured in the room, mic in the listening postion.

Click the image to open in full size.

I can easily integrate woofers there with every plot because woofers are actively crossed and equalized. I would try an acoustic crossover of ~70-100Hz regardless, I'm not going to fill the room mess at the upper bass with woofers. The excess group delay is always dependant on the actual room response, even sharp parametric EQs don't mess things if the response stays smooth. DCX adds maybe 1-2ms of delay, which is quite annoying but haver to live with it.

I think 150Hz or above that would protect the Plitron with 50Vrms max drive voltage quite good.

Woofers have <1mH inductance and can be used as high as 200Hz with qood guality (first minor THD peak at 350Hz and cone resonance at 1,2khz). No CBs for me with dipoles (been there) . Dipole matches with dipole and dipole bass sounds best to my ears, and I don't mind the huge sizer of the line arrays.

Last edited by Legis; 7th July 2012 at 01:05 PM.
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Old 7th July 2012, 01:42 PM   #19
tyu is offline tyu  United States
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Wow looks like the Real-deal...
thanks for the pic..an info...goodluck
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Old 7th July 2012, 02:35 PM   #20
Legis is offline Legis  Finland
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Quote:
Originally Posted by Calvin View Post
The THD usually rises sharply below 200Hz, which also speaks against large d/s values.
Yes, maybe on some ESL's but not in these with the Plitrons. They make normal cone floorstanders green from the low THD numbers at the bass.

I tightened the nylon bolts and the sensitivity increased like hell. Here's a 105dB sweep with 250Hz 1st order filter, bias 4,7kV and the drive voltage might be ~25Vrms. The THD is 0.2-0.3% @ 105dB (where it peaks so high) and H2 rules with quite a margin (cannot measure higher harmonics, they are at the noise floor of the measuring equipment). Very clean low end also.

Click the image to open in full size.

I have to say that after this sweep I have not stopped smiling. Although my ears ring a bit from 30min sweeping:P. It's time to start on the other one so I get them to equal condition.

Last edited by Legis; 7th July 2012 at 02:38 PM.
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