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Old 12th July 2012, 09:51 AM   #31
Calvin is offline Calvin  Germany
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Hi,

the nearfiled response cleared things up, thanks.
As expected the base resonance is still quite high ~+15dB.
The resonance distribution can only be really effective if the dimensions and sizes of the single segments differ considerably.
But if one wants to preserve efficiency within reasonable limits, the allowable differences are way to small to show a significant effect. As such the claims made for this technique are rather marketing blabla.
In the interest of one of the most important parameters -highest efficiency- therefore same sized segments would still be best.
Higher mechanical tension would reduce the Q of the resonance, but also raisen the frequency of Fs.
Mechanical damping with a flow resistance would be much more effective, but typically omits with the clean, proper and good looks of a panel abd would probabely result in acoustic artefacts.

Another Q regarding the measurement setup.
What are the devices used and the parameters of the measurement setup?
As the THD of the measuring devices needs to be taken into account, one has to have an eye especially on the behaviour of the driving amplifier and the microphone. The Plitron toroids will probabely present the amplifier a horric load (electrical phase wise) which will lead to amplifier THD. In addition the impedance minimum will be at the upper end of the frequency range (I assume ~12-15kHz) and of below-1Ohm value. Any amplifier will show an increase in THD with such low impedance values.
Do You happen to know the THD of the mic? It must be a really good device.
I got similar results when Aachen University measured my panels and they used a freshly calibrated, several thousand of Euros costing, B&K capsule.
After B&K one should expect a THD of ~0.1-0.2% at SPLs >100dB.
Our own calibrated Mic, MB550, already costing a couple of hundreds of Euros, gives at least +0.1 to +0.2% higher THD-values than the B&K.
In any case, as Bolserst mentioned, the THD values of a well made panel put every other speaker and many amplifiers to shame. Well done Legis

jauu
Calvin
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Old 12th July 2012, 10:17 AM   #32
Legis is offline Legis  Finland
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Quote:
Originally Posted by Calvin View Post
Hi,

the nearfiled response cleared things up, thanks.
As expected the base resonance is still quite high ~+15dB.
The resonance distribution can only be really effective if the dimensions and sizes of the single segments differ considerably.
But if one wants to preserve efficiency within reasonable limits, the allowable differences are way to small to show a significant effect. As such the claims made for this technique are rather marketing blabla.
In the interest of one of the most important parameters -highest efficiency- therefore same sized segments would still be best.
Higher mechanical tension would reduce the Q of the resonance, but also raisen the frequency of Fs.
Mechanical damping with a flow resistance would be much more effective, but typically omits with the clean, proper and good looks of a panel abd would probabely result in acoustic artefacts.

Another Q regarding the measurement setup.
What are the devices used and the parameters of the measurement setup?
As the THD of the measuring devices needs to be taken into account, one has to have an eye especially on the behaviour of the driving amplifier and the microphone. The Plitron toroids will probabely present the amplifier a horric load (electrical phase wise) which will lead to amplifier THD. In addition the impedance minimum will be at the upper end of the frequency range (I assume ~12-15kHz) and of below-1Ohm value. Any amplifier will show an increase in THD with such low impedance values.
Do You happen to know the THD of the mic? It must be a really good device.
I got similar results when Aachen University measured my panels and they used a freshly calibrated, several thousand of Euros costing, B&K capsule.
After B&K one should expect a THD of ~0.1-0.2% at SPLs >100dB.
Our own calibrated Mic, MB550, already costing a couple of hundreds of Euros, gives at least +0.1 to +0.2% higher THD-values than the B&K.
In any case, as Bolserst mentioned, the THD values of a well made panel put every other speaker and many amplifiers to shame. Well done Legis

jauu
Calvin

Hi, the mic is budget version, uncalibrated Behringer EMC8000. The impedance minimum/resonance is somewhere at ~18kHz according to a simulation with 2700pf panel capacitance and impedance is a good way under 1 ohms with 0,5-0,6R series damping resistor. The reason you assume resonance lower might be that there is phase cancellation at the upper end depending the angle from which I measure the panels. The response goes almost straight to 20kHz from right angle like this: http://i817.photobucket.com/albums/z...o/lhikentt.png Curved panels usually give the smoothest result when measured quite near the edge, at 1/3 - 1/4 of the width of the panel.
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Old 12th July 2012, 04:55 PM   #33
Calvin is offline Calvin  Germany
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Hi,

Quote:
the mic is budget version, uncalibrated Behringer EMC8000.
The results are then really astounding

Quote:
The reason you assume resonance lower might be ...
no, I roughly interpolated the values I know from my panel with a capacitance of 2.2nF and a U of 1:50, giving a imp-minimum at ~19kHz. Since Your panel is considerably bigger I assumed more capacitance. I nearly forgot though that Your d/s is nearly twice the d/s I use. So 18kHz might fit with Your U of 1:75.

jauu
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Old 15th January 2013, 12:52 PM   #34
Legis is offline Legis  Finland
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Has anyone tried mixing silicone dots and strips?

I've been thinking to try out an arrangement (with big curved FR panels) that I would add silicone dots only on the back stator to support the membrane from behind.

Click the image to open in full size.

The dots I have are 3,5mm and the spacers are 3mm so the membrane would be constantly against the dots even when the membrane is moving quite a bit. Curved membranes also tend to flatten ~0,5mm towads the back stators by nature.

My goal is:
1) to be able to use highest possible biases with 3,5m membrane without a fear that the membrane is going to get sucked into the back stator and prevent membrane slapping the stators near it's resonant frequency (which moves the membrane quite much because the Fs is ~35-45HzHz and resonance's Q is quite high due to low-ish tension that 3,5m is capable to support in big panel).
2) Make the membrane's resonant behaviour better/smoother, hoping that silicone dots would smooth out the panel resonances quite a bit. I predict silicone dots would dampen/distribute the main resonance and also smooth the horizontal/vertical standing waves that each segment has..

I'm going to try antistatic spray + acrylic lacguer combo for the membrane coating (now I have graphite boosted Licron Crystal but it's resistance is little on the low side), as it feels good on my sample piece, and I though I could also try out new spacing technique if that would yeald some benefits.

Any thoughts?

Last edited by Legis; 15th January 2013 at 12:58 PM.
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Old 19th January 2013, 03:33 PM   #35
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Seeing your proposed dot layout reminded me of the long-time defunct David Lucas Co. who had plans for a curved ESL using dots (1/2" squares actually of foam tape) in a 2' x 3' panel divided into 6-7 horizontal segments. Each segment, about 5"-6" wide, had seven dots. The Three dots in the center were spaced more closely together than the others. Don't know if this worked very well since I haven't made curved panels, but the idea of altering the spacing of the center dots seems interesting. Good luck.
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Old 20th January 2013, 06:24 AM   #36
Calvin is offline Calvin  Germany
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Hi,

35-45Hz is way too low for a curved panel. Btw. Is there really a 10Hz variation in fs?? +-1Hz should be the aim. Using also a 3.5um in largish panels I always got fs>>120Hz, up to 180Hz, applying the old ratio of 70:1-100:1 of free membrane area length over d/s. Adding dots You might increase the distance of the strips, because going lower than 70:1 compromises on efficiency.
Adding spacers on a single side, the spacers need to stick well to the membrane.
Silicone dots would ditribute resonance but don't damp. They stick quite well to the membrane and they exhibit hydrophobic qualities which helps prevent the buildup of moisture related dirt films that lead to leakage.
As waldtraut suggested, You could position the dots unevenly over the free membrane area. Not only varying in distance to each other, but also not laying in a straight line.

jauu
Calvin
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Old 20th January 2013, 09:31 PM   #37
Bazukaz is offline Bazukaz  Lithuania
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Hi,

Some more comments about silicone dots related to application techniques.
I have found it is really important to gently squeeze each dot just after application so all silicone that is very close to film actually bonds to it. Otherwise buzzing noise can be expected at higher excursions and and low frequencies(<200Hz or so). The dots tend to acquire very shallow angle very close to the film if not pressed. Also they must be round and have no "tails". That means it's easier to apply them after having the film glued, usually.
So, be careful with them!
By the way, different grades of silicone behave very different. They adhere from poor to very excellent to mylar so I suggest testing before use.

Regards,
Lukas.

Last edited by Bazukaz; 20th January 2013 at 09:36 PM.
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Old 22nd January 2013, 06:53 PM   #38
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When you add silicon dots within a panel section, you will increase the effective stiffness of the diaphragm so the resonance Frequence, Fs, of that section will increase. To keep the same Fs you will need to make the section wider than if no dots are used. So, for the same Fs, the gain in stability with dots may not be as much as you desire.

As Calvin mentioned, trying to make curved ESLs with Fs < 100Hz is problematic. The best approach is probably to use facets similar to Soundlab. Attachment #1 shows a layout you proposed back in post#10. You had mentioned that with 3mm spacers, the larger 11-12cm wide sections had the diaphragm positioned within 1.5mm of the rear stator. This was because you were using some amount of side-to-side tension which resulted in flat facets rather than curved sections.

Attachment #2 shows that if you kept the same layout, but used 4mm spacers for the rear stator and 2mm spacers for the front stator you would position the diaphragm closer to the middle of the gap even with the side-to-side tension.
Attached Images
File Type: gif curve_facet.gif (7.1 KB, 80 views)
File Type: gif curve_spacer.gif (64.9 KB, 81 views)
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Old 23rd January 2013, 12:09 AM   #39
Legis is offline Legis  Finland
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I have remembraned the first panel, it has worked ok. The difference in Fs of the sections is more pronounced than without the dots when they all seemed to resonate nearly at the same frequency for some reason. Now I get nearfield resonances between 41Hz and 100-120hz and the panel's far field response is more even than without the dots. Because of those high-ish resonances, the bass sound is a tad more drum skin like, but this effect has mitigated in burn in before.

Some time ago I wrote about membrane modulation problem. The membranes got modulated from the woofers output when playing loud because they were at the close proximity of the panels. The dots seem to mitigate this behaviour making the membranes more stable, but I cannot say any conclusive yet. But the first impressions are positive.

They are actually polyurethane dots when I cheked the material, 3M Bumpon.Click the image to open in full size.


I cannot finish the speakers yet because I'm changing the mylar coating. I will be trying Calvin's Tesa glue + water + hi-carbon india ink -recipe this time (india ink is this VERY conductive ink: Dropping efficiency coating ?). For some reason the Licron crystal is not fully satisfactory for me when wiped on. It's not transparent, one layer stays optimally conductive for only 3-4 months and even then I'm not absolute sure about the HF quality compared to some very good HF-coatings like non-hardening antistatic spray (but it has shortcomings elsewhere and cannot be used). I get the ink and the glue in 1-3 weeks.

I also got new 8-8,5kV-capable HV-supplies from Crescendo Systems, powered by Twisted Pear Placid HD shunt regulated power supplies, which I will be installing after I get the transformers. It's interesting to hear how they affect the sound and also to see how high the bias can be set. 4,5kV is not a problem with my current supplies.

Steve, the flattening towards the rear stator is quite minimal, maybe 2,5mm/rear and 3,5mm/front at the worst parts.

Last edited by Legis; 23rd January 2013 at 12:18 AM.
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Old 2nd February 2013, 04:53 PM   #40
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Quote:
Originally Posted by Legis View Post
The difference in Fs of the sections is more pronounced than without the dots when they all seemed to resonate nearly at the same frequency for some reason. Now I get nearfield resonances between 41Hz and 100-120hz
Wow, your diaphragm tension must be extremely light if you are able to get resonance of 41hz with dots added to the sections.

Are you saying that the lowest resonance for some segments is 100Hz and others 41Hz? Or, that you measure resonances between these two extremes across the panel. It is possible that the added dots are accentuating some of the higher diaphragm resonance modes for sections that alos have a lower fundamental resonance.

Quote:
...the flattening towards the rear stator is quite minimal, maybe 2,5mm/rear and 3,5mm/front at the worst parts.
I understand that you have minimal flattening to the rear with your current horizontal sectioning configuration. I was suggesting a way to that you could return to the vertical sectioning your mentioned in post#10 for which you were having the flattening problem.
dots or strips for spacers?

Using vertical sections with flat diaphragm facets allow the use of uniform tension which works better at LF where the diaphragm is moving a large % of the gap.
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