Diaphragm heat treatment

It seems to be a 57 jig re-used for 63.
Strange the neon lights. Is it more for fixing glueing than to heat-set the mylar ?

Looking at this pictures again, these neon are just for...light (imho). The oven is visible on the other side of the jig.
The two weights on the left seem similar to those visible on the onethingaudio site (One Thing Audio/Manufacturers/Quad/Pictures), in background of 1st and 3rd picture.
 
after reading this thread, i decided to get hold of a heat gun and try making a new diaphragm on one of my esl63 treble panels.
just to see if it made any discernible difference as i hadn't heat treated it the last time i refurbed it.

i stretched the mylar on piece of glass using duct tape and a fish weight, tensioning it to around 2,5 kg before going over it with the heat gun.

i adjusted the heat gun by trying it out on a piece of mylar, adjusting the heat to just under the melting point.

it definitely lost a lot of tension after being heat treated, and i had to re-tension it before gluing on the stator.
the mylar does feel slightly different after the heat treatment; its no longer as flexible, and it feels a lot closer to the original mylar.

i haven't tried out the panel yet, as the coating is still drying, but so far it looks promising.

will report back on how it sounds :)
 
after reading this thread, i decided to get hold of a heat gun and try making a new diaphragm on one of my esl63 treble panels.
just to see if it made any discernible difference as i hadn't heat treated it the last time i refurbed it.

i stretched the mylar on piece of glass using duct tape and a fish weight, tensioning it to around 2,5 kg before going over it with the heat gun.

i adjusted the heat gun by trying it out on a piece of mylar, adjusting the heat to just under the melting point.

it definitely lost a lot of tension after being heat treated, and i had to re-tension it before gluing on the stator.
the mylar does feel slightly different after the heat treatment; its no longer as flexible, and it feels a lot closer to the original mylar.

i haven't tried out the panel yet, as the coating is still drying, but so far it looks promising.

will report back on how it sounds :)

Nice to have some feedback on this.
What do you mean by "tensioning it to around 2,5 kg" ? There must be something well known which is insinuated. Like the number of weights and the size of the sheet of mylar.
 
Nice to have some feedback on this.
What do you mean by "tensioning it to around 2,5 kg" ? .

i don't have a tensioning jig, so i use a big piece of glass and duct tape to tension the mylar.
i cut out a piece slightly larger then the stator, reinforce the edges with clear tape to keep it from tearing, and add strips of duct tape along the edges spaced about 2 cm apart.
i then use a fishing weight to individually pull every piece of tape several times, until each pulls at about 2,5 kg.

the reason i chose 2,5 kg, is because someone else using the same tensioning method had measured the resonance frequency of his own panels,
and determined that around 2,5 kg was the suitable amount of pull needed.
since i don't have the necessary equipment to test this myself i decided to just go with that number :eek:
 
i don't have a tensioning jig, so i use a big piece of glass and duct tape to tension the mylar.
i cut out a piece slightly larger then the stator, reinforce the edges with clear tape to keep it from tearing, and add strips of duct tape along the edges spaced about 2 cm apart.
i then use a fishing weight to individually pull every piece of tape several times, until each pulls at about 2,5 kg.

the reason i chose 2,5 kg, is because someone else using the same tensioning method had measured the resonance frequency of his own panels,
and determined that around 2,5 kg was the suitable amount of pull needed.
since i don't have the necessary equipment to test this myself i decided to just go with that number :eek:

All right I understand now. This number 2.5kg is associated with a distance of 2cm. For example this number would become 5kg if the strips were spaced every 4cm to achieve the same tensioning strength.
 
it definitely lost a lot of tension after being heat treated, and i had to re-tension it before gluing on the stator.
the mylar does feel slightly different after the heat treatment; its no longer as flexible, and it feels a lot closer to the original mylar.

i haven't tried out the panel yet, as the coating is still drying, but so far it looks promising.

will report back on how it sounds :)

I thought the mylar shrank after getting the heat-gun treatment, not lost tension?

BTW, since we might not be sure about whether it is mylar, SaranWrap, or cellophane in our panels, what kind of non-destructive testing can we do to determine the right amount of heat (besides Calvin's figure of 150C for mylar)?

(Although it may only be superstitious behaviour on my part, I give my tweeters (and formerly, my loose Dayton-Wright panels) a kind of hair-dryer treatment every year of so. I thought the purpose was to re-shrink and to drive off moisture on the film. I doubt if I let any spot get to 150C, but I suppose i should... if I want to take the risk with a technique with as little control as waving a heat-gun at a speaker panel from a few inches away.)
 
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I thought the mylar shrank after getting the heat-gun treatment, not lost tension?
If mylar is mechanically tensioned or stretched before attaching to the frame you can achieve much higher tension than is possible with heat shrinking alone. However the long term stability of the high tension from mechanical tensioning is not the best in my experience. If you heat one of these mechanically tensioned diaphragms to 150C you may relax the diaphragm tension rather than tighten it.

I doubt if I let any spot get to 150C, but I suppose i should... if I want to take the risk with a technique with as little control as waving a heat-gun at a speaker panel from a few inches away.)
You might check out this post for more details on heat shrinking and how to avoid burning holes in your diaphragm.
http://www.diyaudio.com/forums/planars-exotics/177092-teonex-film.html#post2373919
 
Hi,

strong mechanical tension alone will reduce over time. This shows in the lowering of the resonance frequency which may span a range of 20-30Hz over a time of 1/2 a year. After that tension and Fs stabilizes. Heat treatment reduces a strong mechanical tension almost immideately to the final value. The value will still be higher than a heat tensioned membrane alone.

jauu
Calvin
 
Heat treatment reduces a strong mechanical tension almost immideately to the final value. The value will still be higher than a heat tensioned membrane alone.

I hadn't tried this method...mechanical tension followed by heating to relax and stabilize.
This could be very advantageous if you can achieve long term tension stability that is tighter then just heat shrinking.
Thanks for the tip!
 
Let me begin by reminding all how obviously wise it is, when standing on streetcorner in strange city, to ask TWO OR MORE people for the same travel directions. Or for information about stretching ESL membranes using heat.

To this point, I have learned from respected posters that heating (some kinds of film???) will shrink it and make your cells good. Some kinds of film heated to the right temperature (which is wholly impossible to judge except by heating enough to burn holes in the plastic) will shrink 1-3 percent. But nobody has ever indicated whether 1-3 percent is a useful or typical range of shrinking. Or for that matter, how you can take a panel in your hands and tell if the film is too loose or too tight or just right, particularly if your didn't build that cell yourself and/or can't remember and/or never knew the tension, really really, in the first instance.

And I have learned what seems to my simple mind as the opposite, namely, that heating will relax the film like a block of frozen butter until it takes on some kind "correct" tension, presumably closely related to what the builder had in mind, but related, sometimes more and sometimes less, to the original tension on the film.

Footnote: the kind of suggestion made above about testing for resonance, although not simple as with Rice-Kellogg speakers, sounds like the kind of guidance DIYers can use. If somebody would try to give us some advice with that kind of operational/procedural slant.
 
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Hi,

so well then....google for DuPont or Mitsubishi and the type of film You want to use...say Mylar S. Download the Datasheet (2pages) and voila, on the very first page You´ll find a table ´Typical Values for Major Properties´ listing data for various film thicknesses. One of the fields says "Dimensional stability MD/TD,* % Shrinkage at 150°C (302°F) 30min". Man, that was difficult, eyhh? :rolleyes:
And there´s too a general Product information sheet (6 pages) about Mylar, listing even more properties.
I wished all info I need were to find as easy as that.

About mechanical tension. If You just flatten out the film and glue it to the stator frame heating will increase mechanical tension by the shrinking action of the film. The value of mechanical tension remains rather low. Its easy to achieve considerably higher values of tension by mechanical stretching (up to 4% of length elongation with good films). If heat treatment is applied to such a high tensioned membrane stress is reliefed, but remains higher than that of a heat-treated-non-tensioned membrane.

jauu
Calvin
 
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Hi,

so well then....google for DuPont or Mitsubishi and the type of film You want to use...say Mylar S. Download the Datasheet (2pages) and voila, on the very first page You´ll find a table ´Typical Values for Major Properties´ listing data for various film thicknesses. One of the fields says "Dimensional stability MD/TD,* % Shrinkage at 150°C (302°F) 30min". Man, that was difficult, eyhh? :rolleyes:
And there´s too a general Product information sheet (6 pages) about Mylar, listing even more properties.
I wished all info I need were to find as easy as that.
snip

Was my question entirely stupid and was your reply profoundly clever? If so, then I would indeed deserve that kind of ridicule ("Man was that difficult, eyhh? :rolleyes"). Even supposing that my question was stupid, let's have a look at your answer.

(1) how many people have any idea what film is in the old panel they are holding in their hands that needs (maybe?) tightening? Even if they knew EXACTLY which of near-infinite number of generic and proprietary chemical compound names they should plug into Google, as you suggest, how do they know the spec sheet today matches or is helpful for dealing with their old panel and whatever treatments it has already had?

(2) how many people can make sense of unfamiliar jargon in a chemical spec sheet (to quote you, "Dimensional stability MD/TD") and are willing to proceed to possibly destroy their cherished Quad, Dayton-Wright, Martin Logan or other classic speakers based on these uncertainties? Even when some well-meaning source says something like "up to 4% of length elongation with good films" - does that mean length or width or area or both?

Not to mention, again, the challenges of waving an industrial heat gun at a panel and heating to not (much?) more than 150C. Perhaps the bottom line as you unconsciously demonstrate without humourous intent is that heat shrinking is risky. That might be the intelligent answer even if not an optimistic one.

I think that part of your answer was neither helpful nor funny to me. As I said, ridicule does have its place and when used in skilled hands. But thanks for trying.
 
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Hi,

reg1) is OT, because the whole thread is not about refurbishing, restretching or repairing panels but about the benefits of heat treatment to freshly built panels.
reg2) if one bothers in reading the Datasheet and Product information one would discover that terms like MD/TD are explained in an easy to understand way. If one is not entirely happy with the answers he/she can still ask Qs. But it´d show that he/she at least tried.

Apart from that, I won´t regard a Q ´entirely stupid´ and can comfortably live with ´profoundly clever´ ;-)

jauu
Calvin
 
I know this is an old thread, but i was thinking about this heat threatment. the thing everyone skips is that the whole jig goes into the oven including the weights. this means although the foil relaxes in the oven, it is being stretched by the weights. and is indeed used to stabilize tension, or what now called tensilized mylar ? so i remains at that tension when reaching normal temperatures again.
 
HMM i tried using the quad method. when stretched to deisred res freq. yuou heat it and it drops like 20 hz, re tension then glue. it remained stable. but i wonder about the following thing. in a quad menbrame you ahve to make holes with an solder iron. in my case the foil dropped 9 hz when doing so. i believe mylar can shrink only up to a certain percent, im not sure if this goes for the other direction as well ?? wich would result in the heating in the oven is to get the maximum relax state. after that using a solder iron to cut the holes would maybe not result in the drop in resonance ?
 
ok fixed the solder iron question... hotter element and slimmer. i grinded an old tip of my iron to a verry narrow small point. heated up to MAX witch is...... i dont know nr 10 ? does do the job without any crap left behind. nice and tight.

now the next question is is the heating really needed >?


i left a few tensioned mylars on the frame with different tires. the best tire with the france valve dropped less then 2 hz in 4 hours (the mylar would be glued to the frame by then) then i decided to leave t for the night and my double sided tape gave way... witch got me thinking about double sided tape not being useful for installing membranes , since it creeps. well why would it not creep on my tension RIg?? hmmmmmm well i dont know i hoped it would not.... maybe it did. still i am not sure what is creeping.


1. mylar getting stretched(because its not heat treated , and the molecules did not align perfectly like walker said? (dont know the exact quote)
2. tire/valve leaking?
3. tape creeping

this is while its on the jig, if it can be stable on the jig for like say 24 hours i should be stable on the stator. that brings us to the next step. does the glue hold on the stator, and does making the holes impact the resonance.
 
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Ok i no0ticed my tape was creeping on the JIG, so ur panel gone be as accurate as your jig.

I added adhesive on the place the double sides tape goes. but still the membrane drops in frequency. i did not notice and creep in the tape anymore. this jig thing is getting more complicated then i thought. and i am starting to think everyone ignoring this problems, or dont have a desired resonance frequency in mind (a target within 5 Hz or less) or it has to do with the 3 micron foil. 6 micron is more stable. it might be the foil relaxing and lowering the res. after a while.

problem is that this would happen after the glue dried as well. witch screws up everything. here comes the heat treatment of the quad maybe in action >? or the secret coating wich adds another 4 micron to the 3 micron foil..... the oldest panels i got did not ahve this coating. i gone look up if the res freq of these was lower then the newer panels. maybe that explains something. maybe they added it to achieve stable high tension?
 
Here this is a sipmple jig used by magnepan :)

magnepan_visit_5.jpg



you can see each side has a round bar that has double sided tape applied they layout the mylar onto all bars/rods then just wind them until desired stretch is reached. still in my opinion this leaves allot for error. not sure if they tune it or just have specific amount they turn the rods. since then it would be all relying on how the person pulls the foil onto the rods. that would be weird. measuring would be key here in my opinion. but it could be they dont have that tight tolerances. and all is well.