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In Reply to: RE: Mylar posted by Utley1 on June 09, 2017 at 14:58:38
Temperatures that may occur under extreme conditions but are very unlikely in use nor in shipping nor in a home environment. But there is a cumulative temperature time exposure under stress (the tensioning) that can cause stretching and loosening. Old TIII panels are usually resonating at low 30s hz, while they are tuned at the factory to something like 44hz. Granted that those are now 40 years old, but they do most of the change in the first couple of decades.
However, some have tried to retighten loose mylar with a hair drier the way you do with an Acoustat. ESL panel.
Follow Ups:
Talked to a friend who has cured slackened Mylar on MG-III with the help of a heat gun. The temperature was about 240 degrees Celcius.
Anyone else who has done such a treatment? Earlier reports did not recommend it as the Mylar would not shrink, actually it will increase the slapping of the Mylar against the magnets.
I have tried to get information from Magnepan but they have not yet answered. Is there still a chaos at their service department?
They may have switched among the mylar types over time but I don't know whether they had done so and if so which models and production times had a different mylar.
Found this:
Well the standard bass panel mylar was 23um IIRC and the thinnest they use is in the 20.7 at half that thickness, 0.5 mils. So I am thinking the story matches with Type C
I keep thinking that they should try to use a poly imide film for its better strength at lighter weights and better usability with etched metal, or something like Kaladex that BG use in their Neo drivers.
Wait for it......
Graphene
In a couple decades, maybe sooner.
Too much is never enough
Metal-film laminates use to require a rather thin layer of metal on a thicker plastic film. Magnepan bass drivers use to have thick conductors in order to achieve a high efficiency with weak magnets. I think a bass driver using the concept of BG Neo would be very expensive.
Found this on plastic film:
"Originally Posted by LineSource
Hi Paradise_Ice
Dupont Mylar and Kaladex Polyester films, and Dupont Kapton Polyimide film are probably the most commonly used materials for planar and ribbon speakers.
Dupont Mylar has a Glass Transistion temperature Tg of 80 C
Dupont Kaladex has a Glass Transistion temperature Tg of 122 C
Dupont Kapton has a Glass Transistion temperature Tg of 360 C
Mylar can be found down to 2 microns in thickness, and 2.5, 3.6, and 5.0 micron mylar is pretty easy to find. The low Tg makes it a poor choice for high power metal-film laminates
Kaladex is harder to find below 7.6 micron thickness. Many new planar and ribbon speakers have converted from mylar to Kaladex films for the higher Tg.
Mylar and Kaladex are pretty "quiet" when you vibrate them.
Kapton is easy to get at 7.6 micron. 3.8 micron is also made by Dupont, but you may have to go directly to Dupont for purchase. Kapton's high Tg and melting point of over 400 C make it a very good material for high power planar and ribbon speakers. Kapton is also a good substrate for sputtering metals like Aluminum or copper. Many flexible PC boards use Kapton, as it is safe to solder to without special materials.
Kapton is a little "noisy" when you vibrate it.
There are a wider range of adhesives for Mylar/Kaladex than for Kapton.
mylar 1360 kg/m3
kapton 1535 kg/m3
Aluinum 2700 kg/m3"
The cost in the Neo drivers is in the Neodymium which costs far more than the equivalent magnetic flux from standard strip magnets.
GT audio do their magnets in Neo and use copper on the metalized membrane. I don't know which film they use, but I suspect it is something like Kaladex since it would allow a higher operating temperature for the copper traces and thus a thinner metal foil/metalized layer that would compensate for the heavier copper. With a push pull you get 95 db sensitivity if you wanted to. As they are at 92 db sensitivity for the current model 3 that gives you 6-8 db more sensitivity than the 3.7 so you can get the same output with 1/4 of the current.
I don't know what diaphragm material he chose. He uses aluminum metalized mylar for backing the ribbon which is full length like the maggie ribbon tweeter
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