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Old 7th October 2009, 07:15 PM   #11
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Quote:
Originally Posted by Capaciti View Post
a peak up to 20db at resonance indicates a mismatch between membran width and tensioning of the mebran.

I guess you tension the membran mechanically. You should not. imo a heavily streched membran do not sound best. The more important is, that you need months or even years break in time to reach the point , where the tesion reduced itself to a constant and long lasting value. E.g your resonance of 60 Hz wuill decrease to possibly 40 Hz and Q decreases as well.

Better just to make thermal tensioning. glue the membran with lowest tension to the frame. The tension should bejust as high that major wrinkles are reduced.

Take a heat gun, best using one with a temperature indicator and set it to 250C. Move it like a spray gun over the entire area. Keep a distance of about 5cm to the membran. Repeat it 5 times, let the membran cool down for 20 minutes and repeat the treatment 5 times again.

Capaciti
Hello Capaciti,

Thanks for your suggestions. I should have mentioned that the +20dB peak is withought any damping at all. Even adding thin grill cloth to front and back to help keep dust out reduces this by 3-6dB.

I had tried mechanical tensioning, but as you mention the results always seem to change with time. I have been using the thermal tensioning method lately, but use a model airplane film shrink iron which is temperature controlled. It is nice to have a visual LED light indicactor to let you know if you are at the right temperature, or too hot/cold.
http://www.coverite.com/accys/covr2700.html

I usually set it to 325 degF (162 degC) and go over the film several times. Matching of tension from panel to panel is quite good. I'm not sure if this method tensions the film in the same way that a heat gun does or not, but it is easy to do.

Once the diaphragm has been tensioned, is it your experience that adding silicone dots reduces the Q of the resonance along with moving it up in frequency? This is the impression I have gotten from several comments on this forum, but personally I have not noticed the silicone dots providing much, if any damping.

Your comment about there being a mismatch between panel width and tension got me to thinking. Perhaps it is the diaphragm material. I am currently using 1/4mil (6 micron) Hostaphan. Maybe some thinner 3 micron film will provide a better match resulting in improved damping.

bolserst
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Old 7th October 2009, 07:25 PM   #12
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Default QUAD ESL 57 Woofer Panel Damping

Just slightly off topic for this thread, but....

Does anybody know if any damping material was used in the woofer panels of the original Quad ESL 57? The measurements I have seen showing a LF Q of about 2.5 sure makes me think there is, but I have not found any pictures showing the addition of any woven cloth mesh(like the ESL63) or felt(like the tweeter section of the ESL 57).

Perhaps the use of Saran instead of Mylar provided the needed damping.
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Old 7th October 2009, 07:37 PM   #13
SY is offline SY  United States
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Maybe some have better damping properties than others.
Silicone elastomers are pretty poor at damping. High fill helps (it also makes the paste more thixotropic, which will help make the dots more consistent and prevent the "tails"), but you have to be careful about compromising dielectric strength.
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Old 7th October 2009, 09:28 PM   #14
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@ Harry,

no i mean 250 °C since the distance of 5 cm reduces the effective heat to the film surface.

A temperature of 150-160°C would be right for an closed oven, where the heated air molecules are close to the surface.

Check out a heat gun by setting it to 250°C and using a temperature probe, which is included in some affordable multi testers. You will see that a distnace of about 5cm to the probe will show readings about 150°C

@ bolsert,
6µm is fine, smaller like 3µm is not as forgiving wrong tensioning and or heat treatment. The more layers of molecule chains (means thicker film), the more heat and tension will be dissipated. On the other hand the mass of 12µm is causing bandwith limitations at highest frequencies in the audio range.

basically you are right, the silicone dots wont lower Q, since those dots do not add damping, but a strategic distribution of the dots results in a strategic distribution of resonance modes of the membran. If you set them right, you will e.g. create two resonaces 30 and 50 hz with limited Q out of one big 20 Hz resonance with extended Q whithout dots.

As i mentioned before the silicone dot method can optimize a given panel geometrie to best compromise regarding low frequency performance, but bad dots create disturbing sound and to find out the right positions of the dots is a hell of trial and error.

If one is capable of FEM calculations it might assist, but i guess that it is nearly impossible to setup the correct model for the film behaviour. E.g. the polyester film isnt a simple elastic system, but different behaviour depending on conditions for stress and elongation. And Computers are stupid. if you feed them wrong the output is wrong.


OOOOOh, i later on recognized your heat treatment tool, makes a lot of sense to me. The hot surface is in direct contact to the film, thus showing best and reproducible heat transfer to the film. You know, there is always something to learn or at least to think about.....

Capaciti

Last edited by Capaciti; 7th October 2009 at 09:33 PM.
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Old 8th October 2009, 07:07 AM   #15
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Originally Posted by bolserst View Post
Does anybody know if any damping material was used in the woofer panels of the original Quad ESL 57?
Yes there is, it's a some sort of natural fibre cloth on the inside of the back grill.

Some people like to take it out because of poor bass performance, but that is because the speakers are old and the bass gets weaker (lowered sensitivity) and the resonance frequency shifts up in frequency (sometimes over 100Hz!). The cure is to repair the panels and leave the damping mats in, that way it goes all the way down to 40 Hz, and the bass can sound surprisingly well.

This is one speaker that does not sound better without damping material. In fact it will lose it's wonderful natural midrange if you do.
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Old 8th October 2009, 09:54 AM   #16
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Originally Posted by Capaciti View Post

...no i mean 250 C since the distance of 5 cm reduces the effective heat to the film surface.

A temperature of 150-160C would be right for an closed oven, where the heated air molecules are close to the surface.

Check out a heat gun by setting it to 250C and using a temperature probe, which is included in some affordable multi testers. You will see that a distnace of about 5cm to the probe will show readings about 150C
Thank you.

Yes, with my closed oven a temperature of 150-160 C is right. I have never used a heat gun for tensioning in the past. So I have checked this today with a Leister heat gun set to 250 C. In the first minutes the temperature at 5-6 cm is around 150 C as you have mentioned. After full warm up of the gun I had to increase the distance to 9-10 cm. Only want to mention this if someone has bigger panels where considerably longer working time is needed.

Quote:
Originally Posted by Capaciti View Post

...6m is fine, smaller like 3m is not as forgiving wrong tensioning and or heat treatment. The more layers of molecule chains (means thicker film), the more heat and tension will be dissipated.
I had similar experience with 3m film. This thin one is not forgiving a wrong treatment. The sound is 'hard and edgy' then right from the beginning. And this type of sound will not go away with time. It's ruined forever.


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Originally Posted by Capaciti View Post

...but a strategic distribution of the dots results in a strategic distribution of resonance modes of the membran. If you set them right, you will e.g. create two resonaces 30 and 50 hz with limited Q out of one big 20 Hz resonance with extended Q whithout dots.
As a starting guide, passive resonance tests are very helpful for this. It's easier then to play around with different places for the dots. The exact middle of the panel is not always the best place when you want to split the resonance peak into two smaller ones.

For visualizing the temperature of the film (or hot spots), Arend-Jan mentioned a coating with thermochromic paint. It changes color with temperature. But I have never used it. 'Cool' thing.

Temperature sensitive paint

Harry
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Old 8th October 2009, 02:39 PM   #17
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Quote:
Originally Posted by Capaciti View Post

basically you are right, the silicone dots wont lower Q, since those dots do not add damping, but a strategic distribution of the dots results in a strategic distribution of resonance modes of the membran. If you set them right, you will e.g. create two resonaces 30 and 50 hz with limited Q out of one big 20 Hz resonance with extended Q whithout dots.

As i mentioned before the silicone dot method can optimize a given panel geometrie to best compromise regarding low frequency performance, but bad dots create disturbing sound and to find out the right positions of the dots is a hell of trial and error.

If one is capable of FEM calculations it might assist, but i guess that it is nearly impossible to setup the correct model for the film behaviour. E.g. the polyester film isnt a simple elastic system, but different behaviour depending on conditions for stress and elongation. And Computers are stupid. if you feed them wrong the output is wrong.
I really appreciate you taking the time to answer the many questions my experiments have raised.
My hat is off to you for researching a distribution of silcone dots to optimize low frequency performance. I can only imagine the amount of time and frustration involved in the trial and error process. I may mention this problem to a few guys at work that are fluent in dynamic FEM analysis to see if they would be interested in seeing what solutions NASTRAN might be able to come up with.


Quote:
OOOOOh, i later on recognized your heat treatment tool, makes a lot of sense to me. The hot surface is in direct contact to the film, thus showing best and reproducible heat transfer to the film. You know, there is always something to learn or at least to think about.....
Capaciti
Glad to see that I provided some information in return for you to think about.
Heating the 6m film with a heat gun always made me nervouse. Too far away, and uniform heating did not take place. To close, or hovering in one place too long and you risk burning a hole in the diaphragm. With the Coverite iron, once the temperature is set correctly, I can glide it over the film as needed for uniform treatment without any concern for damaging the film.
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Old 8th October 2009, 02:42 PM   #18
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Originally Posted by arend-jan View Post
Yes there is, it's a some sort of natural fibre cloth on the inside of the back grill.

Some people like to take it out because of poor bass performance, but that is because the speakers are old and the bass gets weaker (lowered sensitivity) and the resonance frequency shifts up in frequency (sometimes over 100Hz!). The cure is to repair the panels and leave the damping mats in, that way it goes all the way down to 40 Hz, and the bass can sound surprisingly well.

This is one speaker that does not sound better without damping material. In fact it will lose it's wonderful natural midrange if you do.
Thanks for the info!
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Old 8th October 2009, 02:54 PM   #19
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Originally Posted by SY View Post
Visual appeal of ESLs was NOT the strong point of mine (rebuilt and modified Acoustats)! I tried them with and without damping mats. I'm not sure that I'd call the effect of the damping bad, just different. It definitely helped to tighten the mid bass and focus the images better, at least in my room. I had about 50% of the active area in thin felt, spaced about a centimeter from the diaphragm.
Hi SY,

The few Acoustat panels I have seen used some fairly thick felt damping pads in the middle 1/3 area of the panel, and nothing on the outter area. Did you remove these pads before applying your thin felt? You mention only applying the damping to 50% of the active area. Can you describe where/why you applied the damping? Any Pics?

I have not experimented yet with partial panel damping...maybe this a better solution to avoiding contamination of the midrange resposne.

bolserst
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Old 9th October 2009, 01:17 PM   #20
Atom666 is offline Atom666  Canada
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I was in an art supply store with my daughter a few months ago and came across some nylon mesh used for silk screening.It looked almost identical to the the damping material used in the ESL63.
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