Hey all, getting ready to make another pair of CLS panels...
Planning on using a Spring Scale to set vertical tension, just need to know value....
From specsheet, the Dupont Mylar C 6 micron should shrink 2% in Machine Direction, and 1.2% in Traverse Direction with 300F heat applied for 30 minutes...but we only want vertical tension, so heat shrink not an option ("barreling" of mylar over spars - yup did it)
Sooooo....Mechanically...
Elongation = F*L/A*E
F= force (what we are looking for)
L= Length
A= Cross sectional area mylar
E= Modulus of elasticity (using Mylar 710kpsi, cannot find Mylar C value)
So plugging numbers, tensioning 36 pounds should get 1% elongation.
I still think this is too high.......anyone know if this is correct, or able to check my calc?
Planning on using a Spring Scale to set vertical tension, just need to know value....
From specsheet, the Dupont Mylar C 6 micron should shrink 2% in Machine Direction, and 1.2% in Traverse Direction with 300F heat applied for 30 minutes...but we only want vertical tension, so heat shrink not an option ("barreling" of mylar over spars - yup did it)
Sooooo....Mechanically...
Elongation = F*L/A*E
F= force (what we are looking for)
L= Length
A= Cross sectional area mylar
E= Modulus of elasticity (using Mylar 710kpsi, cannot find Mylar C value)
So plugging numbers, tensioning 36 pounds should get 1% elongation.
I still think this is too high.......anyone know if this is correct, or able to check my calc?
Attachments
I don't have an answer for you but I have some questions if you don't mind my asking, and some possibly helpful comments.
Questions:
1. I think 1% elongation sounds reasonable but I'm curious: How did you decide that?
2. I prefer 6-micron Mylar but I read somewhere that Martin Logan uses 12-micron Mylar on all their panels. Is that true?
(if so; then 1% elongation would produce much higher tension in 12-micron film, compared to 6-micron film-- which points back to the question of how you settled on 1% elongation. leads me back to the 1% elongation decision came from)
3. If you want 1% elongation, why not just measure it directly, rather than calculating equivalent pulling force?
(measuring it directly by adding some reference marks on the film with a fine-tipped felt pen, and then stretching the film until the span between the marks increase by 1%)
Comments:
I use 6-micron Mylar for my speaker builds and I measure the elongation with reference marks as described above. Mine are flat panels stretched in both directions but I don't see why it wouldn't work to measure the longitudinal elongation on a curved panel.
I have practically no experience rebuilding ML panels but I once replaced the diaphragm on a ML Theater Center Channel panel.
I had no clue how much tension to apply on the diaphragm so, before I removed the old diaphragm, I measured its resonance, then made a shop aid delfection gage and measured it's deflection at center-span of the widest cell, and then tensioned the new diaphragm to the same deflection. The new diaphrgm measured the same resonance so it worked out fine.
Here's a link to a write-up with photos of that Theater panel rebuild: https://jazzman-esl-page.blogspot.com/2011/11/compensating-diplole-phase-cancellation.html
Questions:
1. I think 1% elongation sounds reasonable but I'm curious: How did you decide that?
2. I prefer 6-micron Mylar but I read somewhere that Martin Logan uses 12-micron Mylar on all their panels. Is that true?
(if so; then 1% elongation would produce much higher tension in 12-micron film, compared to 6-micron film-- which points back to the question of how you settled on 1% elongation. leads me back to the 1% elongation decision came from)
3. If you want 1% elongation, why not just measure it directly, rather than calculating equivalent pulling force?
(measuring it directly by adding some reference marks on the film with a fine-tipped felt pen, and then stretching the film until the span between the marks increase by 1%)
Comments:
I use 6-micron Mylar for my speaker builds and I measure the elongation with reference marks as described above. Mine are flat panels stretched in both directions but I don't see why it wouldn't work to measure the longitudinal elongation on a curved panel.
I have practically no experience rebuilding ML panels but I once replaced the diaphragm on a ML Theater Center Channel panel.
I had no clue how much tension to apply on the diaphragm so, before I removed the old diaphragm, I measured its resonance, then made a shop aid delfection gage and measured it's deflection at center-span of the widest cell, and then tensioned the new diaphragm to the same deflection. The new diaphrgm measured the same resonance so it worked out fine.
Here's a link to a write-up with photos of that Theater panel rebuild: https://jazzman-esl-page.blogspot.com/2011/11/compensating-diplole-phase-cancellation.html
Hello Charlie!
I remember reading the 1% measurement was the ML norm...don't remember where I saw that tho...
I also read that ML uses 12 micron mylar too...I have quite a bit of 6 micron mylar...
The 1% elongation measurement (and not tension measurement) would be nice, but I would need another person in my rig / method. But that would be best way to measure.
I remember reading the 1% measurement was the ML norm...don't remember where I saw that tho...
I also read that ML uses 12 micron mylar too...I have quite a bit of 6 micron mylar...
The 1% elongation measurement (and not tension measurement) would be nice, but I would need another person in my rig / method. But that would be best way to measure.
On the Theater panel rebuild what I didn't do but wish I had was to measure the elongation--- I only stretched the film until it's deflection at center span measured the same as that of the original diaphragm, so I'm now curious whether it's elongation would have been close to 1%.
In any case, I don't think you can go wrong with 1% elongation but I wouldn't go with any less -- better too tight than loose!
I'm accustomed to flat-panel ESL's, which are perfectly symmetric-- so what amazed me with the curved Theater panel was the degree of asymmetry between spacer-tape thicknesses on the front stator (0.025") versus on the rear stator (0.045"), and how radically asymmetric the diaphragm-to-stator spacing ended up being. The film was very close to the front stator near the spars and dipped very close to the rear stator at center-spans between spars, and yet the panel played perfectlly fine.
In any case, I don't think you can go wrong with 1% elongation but I wouldn't go with any less -- better too tight than loose!
I'm accustomed to flat-panel ESL's, which are perfectly symmetric-- so what amazed me with the curved Theater panel was the degree of asymmetry between spacer-tape thicknesses on the front stator (0.025") versus on the rear stator (0.045"), and how radically asymmetric the diaphragm-to-stator spacing ended up being. The film was very close to the front stator near the spars and dipped very close to the rear stator at center-spans between spars, and yet the panel played perfectlly fine.
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Since it was a Center Channel (thus 250 hz and up?), you can get away with film very close to stator. You would get increased sensitivity with that close too...
Another Idea I had was to use heat, but secure top / bottom only while leave sides loose / unsecured, then secure after heat shrink...
Also, ML using 12 micron (as opposed to 6 micron mylar in my calc) would just increase the cross sectional area by 2, thus reducing the tension I came up with by 2, meaning 18 pounds tension for 12 micron, so thicker mylar would require less tension to get the 1% elongation, not more?
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Hi,
ML certainly used 12µm in the 90s and 20s stretched to 1% or even more.
It was the lowest thickness grade one could get ITO sputtered films at that time.
I think nowadays they use thinner membranes, probabely about 6mm.
In my curved panels with similar dimensions I used 3.8µm and 4.5µm thick films and stretched to almost 1.5% mechanically and heat treated them after.
Still though the thicker film was able to withstand the higher stretch and one could achieve higher Fs values than possible with the thinner films.
Due to the film ML used heat treatment was not feasable though.
jauu
Calvin
ML certainly used 12µm in the 90s and 20s stretched to 1% or even more.
It was the lowest thickness grade one could get ITO sputtered films at that time.
I think nowadays they use thinner membranes, probabely about 6mm.
In my curved panels with similar dimensions I used 3.8µm and 4.5µm thick films and stretched to almost 1.5% mechanically and heat treated them after.
Still though the thicker film was able to withstand the higher stretch and one could achieve higher Fs values than possible with the thinner films.
Due to the film ML used heat treatment was not feasable though.
jauu
Calvin
Calvin
If the film is stretched over a curved stator, glued, and then heat-treated, the film will shrink between the insulators (fish eye effect) and the gap in these places will decrease critically, therefore the film should be stretched with a tensioning device only along the length, and then after gluing, under no circumstances should it be heated with a high-temperature hair dryer.
Hi,
Yes and No!
Yes, as I said, You should only stretch mechanically in one direction if you use a standard PET film like ML does.
No, also as I said, when You use the films I use. 😎
Then mechanical stretch in one direction plus heat treatment is not only possible, but preserves the advantages of a heat treated film without the hour-glassing effect.
jauu
Calvin
Yes and No!
Yes, as I said, You should only stretch mechanically in one direction if you use a standard PET film like ML does.
No, also as I said, when You use the films I use. 😎
Then mechanical stretch in one direction plus heat treatment is not only possible, but preserves the advantages of a heat treated film without the hour-glassing effect.
jauu
Calvin
If your wonderful film doesn't shrink after heat treatment, then what's the point of heat treating it 😀 ?
Hi,
heat treatment reduces and evens out the internal stress, and functions like a preaging or burn-in.
MLs needed to burn in for about 1/2 year till the Fs settled where it was designed for.
Right out of the box a ML didn´t sound right, because the xover points were a bit off.
After heat treatment my panels are ready to play and don´t change for at least the next 10 years and are very consistent in Fs and amplitude response.
And of course does my wonderful film shrink, its just that the shrinkage is very small compared to standard PET films ... just enough to be heat treatable and not enough to show the hour-glass effect. 😊
jauu
Calvin
heat treatment reduces and evens out the internal stress, and functions like a preaging or burn-in.
MLs needed to burn in for about 1/2 year till the Fs settled where it was designed for.
Right out of the box a ML didn´t sound right, because the xover points were a bit off.
After heat treatment my panels are ready to play and don´t change for at least the next 10 years and are very consistent in Fs and amplitude response.
And of course does my wonderful film shrink, its just that the shrinkage is very small compared to standard PET films ... just enough to be heat treatable and not enough to show the hour-glass effect. 😊
jauu
Calvin
I thought that the film needs to be heat-treated (in your words, aged) on a tensioning device and then the finished film needs to be glued to the stator.
Because if you need a very high tension (and a large area requires a very high tension), then heat-treating the film glued to the stator will reduce the tension and that is bad.
Because if you need a very high tension (and a large area requires a very high tension), then heat-treating the film glued to the stator will reduce the tension and that is bad.
Hi,
the heat treatment relaxes the film slightly, but it holds still alot more tension than a heat-alone stretched film.
The reduction of tension could be negative, yes, if You liked or needed the resulting higher Fs of a mechanical stretch.
On the other hand it can be perfect if the resulting Fs settles just where you want it to be in first place.
And we are btw. not talking about a Fs difference of several dozens of Hz, rendering a drum-tight stretched membrane into a flapping sail.
Finally let us not forget that the membrane area and other factors also influence on Fs.
In the end it is a multiple of parameters that need to fall into place for the best compromise.
jauu
Calvin
the heat treatment relaxes the film slightly, but it holds still alot more tension than a heat-alone stretched film.
The reduction of tension could be negative, yes, if You liked or needed the resulting higher Fs of a mechanical stretch.
On the other hand it can be perfect if the resulting Fs settles just where you want it to be in first place.
And we are btw. not talking about a Fs difference of several dozens of Hz, rendering a drum-tight stretched membrane into a flapping sail.
Finally let us not forget that the membrane area and other factors also influence on Fs.
In the end it is a multiple of parameters that need to fall into place for the best compromise.
jauu
Calvin
HI Gents,
If I may, I've watched videos on ML esl panel production, while the mylar film is tensioned vertically, I see that
the production workers are using hands to pull the film laterally to secure film onto the double sided tape.
Question, how does one keeps consistent tension laterally by using hands through out the lenght of the esl panels ?
Im also thinking of rebuilding on my ML Odyssey, speaking of which in using a thinner mylar film, would it not cause
the FS to go up say between 6 micron vs original 12 micron ?
Many thks
If I may, I've watched videos on ML esl panel production, while the mylar film is tensioned vertically, I see that
the production workers are using hands to pull the film laterally to secure film onto the double sided tape.
Question, how does one keeps consistent tension laterally by using hands through out the lenght of the esl panels ?
Im also thinking of rebuilding on my ML Odyssey, speaking of which in using a thinner mylar film, would it not cause
the FS to go up say between 6 micron vs original 12 micron ?
Many thks
Hi,
Yeah, I saw that vid also and was astonished about the speed and obvious brute force the operator worked with.
She obviously was very experienced und used to do the procedure that way .... but it also rose the Q of how consistent the process could be .... especially what happens if she had a ´bad´ day or someone else were goin to do it instead?
Contrary to intuition the 12µm thick film allows for soo much higher tensioning force, that the resultant Fs can be considerably higher than with 6µm or thinner films.
I made measurements shwing that phenomen clearly.
jauu
Calvin
Yeah, I saw that vid also and was astonished about the speed and obvious brute force the operator worked with.
She obviously was very experienced und used to do the procedure that way .... but it also rose the Q of how consistent the process could be .... especially what happens if she had a ´bad´ day or someone else were goin to do it instead?
Contrary to intuition the 12µm thick film allows for soo much higher tensioning force, that the resultant Fs can be considerably higher than with 6µm or thinner films.
I made measurements shwing that phenomen clearly.
jauu
Calvin
I think the worker at ML factory just pulls enough to remove wrinkles. My guess is that the vertcal tension is that large that small differences in the weak horizontal tension wont matter.
Of course, they remove the small waviness that occurs with strong longitudinal tension, but no more.
And this is all for one reason, the transverse tension should be several times less than the longitudinal tension to avoid the appearance of an "hourglass", that is, zonal failures of the film between the insulators.
I have such speakers with a height of 2 m of the active part, there is a 6 µm film, now they are used as diffusers😆.
In order to properly stretch and glue the film, I had to make a special tensioning device and I studied well the nature of tension and gluing of such an operation.
And this is all for one reason, the transverse tension should be several times less than the longitudinal tension to avoid the appearance of an "hourglass", that is, zonal failures of the film between the insulators.
I have such speakers with a height of 2 m of the active part, there is a 6 µm film, now they are used as diffusers😆.
In order to properly stretch and glue the film, I had to make a special tensioning device and I studied well the nature of tension and gluing of such an operation.
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Thanks Guys fo the reply, so does this mean that vertical tension is the main focus while lateral tension
is only to remove the wrinkles ??? There was a video in Youtube from a German esl rebuilding shop.
He seems to have a jig where tension is applied both horizontally as well as vertically. To my untrained brains
this seems to be the right way to rebuild the panels. As I recalled he had a tool to measure tension on
the mylar film.
Many thanks again
is only to remove the wrinkles ??? There was a video in Youtube from a German esl rebuilding shop.
He seems to have a jig where tension is applied both horizontally as well as vertically. To my untrained brains
this seems to be the right way to rebuild the panels. As I recalled he had a tool to measure tension on
the mylar film.
Many thanks again
Hi,
exactly. The more curvature the less horizontal stretch.
And a higher vertical tension counters to a small degree a low horizontal stretch.
It also needs to taken into account, that the film mounted in the stretching jig behaves differently to the built-in state, where there are typically additional spacers sectoring the membrane area into smaller segments.
jauu
Calvin
exactly. The more curvature the less horizontal stretch.
And a higher vertical tension counters to a small degree a low horizontal stretch.
It also needs to taken into account, that the film mounted in the stretching jig behaves differently to the built-in state, where there are typically additional spacers sectoring the membrane area into smaller segments.
jauu
Calvin