changes are you lower the resonance instead of increasing it. so i would not use heat treatment in any case im afraid. you might ruin them for ever.
I disagree. Today playing test-tones, right speaker developed a big wrinkle to the membrane, frequency was then around 8-9kHz. SO LOOSE the membrane was/is! Only rational solution is the heat treatment with heatgun or replace the mylar totally. Sound is now distorted, so I've nothing to loose (but loosened membrane
)
)I will inform what happened, did I succeed or did I destroy the membrane. As said it's not usable now, so what could go wrong. My speakers are old Audiostatic DCM5, about 20 years of age. I have 40m of 6um thick C-type mylar as backup, if things go wrong. Only need the frame and coating material...
Most polyester films will heat shrink. The degree of shrink is sometimes different, but in the ones I've used I have not seen a huge change from genuine Mylars of various types to Hostaphans.
I would suggest getting a variable, temperature controlled heat gun, if you don't have one. It makes things much easier and more consistent. You don't have to fight an over-hot device, so you can be more thorough and less rushed.
I would suggest getting a variable, temperature controlled heat gun, if you don't have one. It makes things much easier and more consistent. You don't have to fight an over-hot device, so you can be more thorough and less rushed.
Yes, thats the plan. Heat gun with temperature control. But one question, is the control how precise? And about one degree steps.
"When type C (capacitor grade) Mylar film is heated to a temperature in the range of 300 degrees F (149 degrees C) its molecular structure attains a predictable and stable configuration. This is referred to as the “critical” temperature. Heating the film slightly below this temperature will not cause the desired transformation and heating it slightly above this temperature can melt the film. As a result, the temperature window to attain this condition is relatively narrow."
The damage
Horizontal rippling above the damage
"When type C (capacitor grade) Mylar film is heated to a temperature in the range of 300 degrees F (149 degrees C) its molecular structure attains a predictable and stable configuration. This is referred to as the “critical” temperature. Heating the film slightly below this temperature will not cause the desired transformation and heating it slightly above this temperature can melt the film. As a result, the temperature window to attain this condition is relatively narrow."
The damage
Horizontal rippling above the damage
My heat gun is an older Makita HG1100 that has a 1-5 dial on the back, so I can't suggest an exact temperature. It is thermocouple controlled, so pretty good, but in my experience extreme accuracy isn't required. The ability to throttle it consistently is more important.
Since you have some loose Mylar already, I'd do some practice on it to get a feel for your heat gun. If you have some two-sided tape (I like 3M 9485PC), you can do a quick small frame made of whatever you have around and actually shrink a better representation of what you're going to be doing. A six inch by six inch frame is plenty, and it could be ABS plastic, MDF, or whatever you have handy. Apply two-sided tape to the frame. Smooth the Mylar down onto a glass surface, then stick the frame down on it. For the best adhesion, run a wallpaper seem roller over the Mylar/tape. Then you can shrink it.
Mylar does expand until it hits its shrink point, so that's something to be aware of also.
Since you have some loose Mylar already, I'd do some practice on it to get a feel for your heat gun. If you have some two-sided tape (I like 3M 9485PC), you can do a quick small frame made of whatever you have around and actually shrink a better representation of what you're going to be doing. A six inch by six inch frame is plenty, and it could be ABS plastic, MDF, or whatever you have handy. Apply two-sided tape to the frame. Smooth the Mylar down onto a glass surface, then stick the frame down on it. For the best adhesion, run a wallpaper seem roller over the Mylar/tape. Then you can shrink it.
Mylar does expand until it hits its shrink point, so that's something to be aware of also.
Ok, thanks for helpful hints I noticed when checking the speakers, that the stator wires have text "improved heat resisting" on them. That also gives me courage to try. My heat gun have two settings, 300 and 600 degrees of celsius, I 'll try with 300 (500l/min). At first very gentle from further distance while checking does the diaphgrapm react. We shall see how it does work.
I noticed when checking the speakers, that the stator wires have text "improved heat resisting" on them. That also gives me courage to try. My heat gun have two settings, 300 and 600 degrees of celsius, I 'll try with 300 (500l/min). At first very gentle from further distance while checking does the diaphgrapm react. We shall see how it does work.
With only two temperature settings available, you're going to have to be careful. I'd definitely run some experiments on your loose Mylar first before getting near the speaker with that heat gun.
You'll want to keep the heat gun moving. 300 °C is hot. It's going to be a balancing act to get enough temperature in the film to shrink it, but not melt it.
For the best chance of success, I'd get an adjustable temperature heat gun. They've gotten cheaper in the past few years. In the US, you can pick one up for about $30. They aren't the greatest quality, but for occasional use they are fine.
Not that you'll necessarily find the same ones in Finland, but here are a few examples of inexpensive ones with decent reviews:
https://www.homedepot.com/p/TR-Industrial-1500-Watt-Heat-Gun-Kit-TR89200/306210790
1500 Watt Dual-Mode Heat Gun with LCD Display and Variable Temperature
https://www.amazon.com/dp/B07HRBJFTP
https://www.amazon.com/dp/B07CQM8V17
You'll want to keep the heat gun moving. 300 °C is hot. It's going to be a balancing act to get enough temperature in the film to shrink it, but not melt it.
For the best chance of success, I'd get an adjustable temperature heat gun. They've gotten cheaper in the past few years. In the US, you can pick one up for about $30. They aren't the greatest quality, but for occasional use they are fine.
Not that you'll necessarily find the same ones in Finland, but here are a few examples of inexpensive ones with decent reviews:
https://www.homedepot.com/p/TR-Industrial-1500-Watt-Heat-Gun-Kit-TR89200/306210790
1500 Watt Dual-Mode Heat Gun with LCD Display and Variable Temperature
https://www.amazon.com/dp/B07HRBJFTP
https://www.amazon.com/dp/B07CQM8V17
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well if they used any mechanical force. heating it will drop resonance. you might be able to get a wrinkle out. but it will lower resonance witch lead to other annoying bigger problems like slapping or the foil sticking to one of the stators been there done that
but if ur gone re foil them anyways if it fails then go for it it is allot of work and rather tedious to get right
witch lead to other annoying bigger problems like slapping or the foil sticking to one of the stators been there done that but if ur gone re foil them anyways if it fails
then go for it it is allot of work and rather tedious to get right Ok, maybe I wait until I'll get a proper heat gun with necessary adjustments...I have to check what is available in the market. As said, the speaker is now broken anyway, so I have nothing to loose if I try to fix it.
Edit 10min later: Not fixable, there is a rip in diaghgrapm, about 5cm long. So that's it, new mylar is required. Just wondering what is the right coating material, everybody seems to have a different opinion...
Edit 10min later: Not fixable, there is a rip in diaghgrapm, about 5cm long. So that's it, new mylar is required. Just wondering what is the right coating material, everybody seems to have a different opinion...
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May I revive this thread?
I have a question about heat treatment of Mylar to perform annealing on/for stretched membranes: If e.g. you stretch Mylar, then it's molecular structure gets stressed, like e.g. in a metal after bending it. By a procedure of annealing, the molecular structure then resets to a new arrangement, thus relieving the internal stress. This is why annealing an ESL membrane by thermal processing would seem to be an elegant option.
In general, heating a polymer first leads to an inert (glass) state of the molecules, then, higher up, to the crystallization of the molecules, and finally to a melting. For Mylar/PET, the
See e.g.: https://polymers.netzsch.com/Materials/Details/27
More specifically for annealing, there is a paper from a group who got a 30% cristallization ratio by heating Mylar to only 115°C (instead of 130°C) for 30 minutes for annealing the mylar: I could not read it the whole but only the Abstract
This much for some available data about Mylar and it's structural changes over temperature. Now, I am searching for an elegant and hopefully simple and efficient method to anneal my DIY mylar membranes unter steadily stretching conditions, generally like the old quad method aforementionned in this thread. I think that meanwile it should be easier to do so because of the increased understanding of the molecular processes within the membrane? Has anybody done this at home, and at which conditions, in terms of the heating/chilling profile over temp and time. And if so, then what kind of gear was used?
And another question: Does anybody know wheter it is better to have a membrane with a high (30%), or better a low (Zero = all Glass) ratio of crystallized molecules inside of it? Or does it not matter at all?
I have a question about heat treatment of Mylar to perform annealing on/for stretched membranes: If e.g. you stretch Mylar, then it's molecular structure gets stressed, like e.g. in a metal after bending it. By a procedure of annealing, the molecular structure then resets to a new arrangement, thus relieving the internal stress. This is why annealing an ESL membrane by thermal processing would seem to be an elegant option.
In general, heating a polymer first leads to an inert (glass) state of the molecules, then, higher up, to the crystallization of the molecules, and finally to a melting. For Mylar/PET, the
- Glass transition point Ct is located at 75°C ... 80°C. Heating Mylar to this temperature will result in an amorphous arrangement of it's molecules.
- Crystallization occurs at a max. rate at some 130°C ... 140°C, and up to 150°C or so.
- Melting finally is reached at 250°C.
See e.g.: https://polymers.netzsch.com/Materials/Details/27
More specifically for annealing, there is a paper from a group who got a 30% cristallization ratio by heating Mylar to only 115°C (instead of 130°C) for 30 minutes for annealing the mylar: I could not read it the whole but only the Abstract
This much for some available data about Mylar and it's structural changes over temperature. Now, I am searching for an elegant and hopefully simple and efficient method to anneal my DIY mylar membranes unter steadily stretching conditions, generally like the old quad method aforementionned in this thread. I think that meanwile it should be easier to do so because of the increased understanding of the molecular processes within the membrane? Has anybody done this at home, and at which conditions, in terms of the heating/chilling profile over temp and time. And if so, then what kind of gear was used?
And another question: Does anybody know wheter it is better to have a membrane with a high (30%), or better a low (Zero = all Glass) ratio of crystallized molecules inside of it? Or does it not matter at all?
Mylar is a biaxially oriented in the casting process, it has stresses built in, and that is what contributes to the properties that it has. I'm a mechanical engineer, so I'm going out on a limb here with the chemistry aspects. But the locking in of the stresses by heat setting under tension is key. The heat shrinking is just undoing that heat setting, and it's my assumption that the degree of shrink of each brand and type of boPET is really an indication of the degree of stretching it underwent before heat setting.
https://en.wikipedia.org/wiki/BoPET
Sheldon
https://en.wikipedia.org/wiki/BoPET
Sheldon
It all depends on the purpose of the tension and the size of the membrane. I had huge emitters measuring 2000mm by 400mm and I had to stretch them very long. I used a special tensioner with a pressure gauge, a tension of 20kg was required. But when, after tension, I used a building hair dryer with a temperature of approximately 160 degrees Celsius, the membrane weakened in tension and became less than 10-8 kg. So heat treatment may not always be useful.