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Old 30th August 2006, 12:52 AM   #61
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Hi Zvon,

I think your concern is correct theoritically. working in plastic zone of any material isn't that predictable... There is a way around it.

BTW, please kick me if I'm wrong...

In tech term, what Calvin did was working the film into it's plastic zone just over the yield point (where the film becomes permanently elongated) If you are worried about the longivity of the film/panel, experiment with the force or elongation lenth and you will find the "yield point", then work within the yield point.

When I start on the project. This is the plan: I'll find the weight required at yield point by hanging weight at the stretching ends. This is how i imagine, Take a speciment of say 100 wide 1m length of film, I will use rectangle frame on a table. Double sided tape one end to a table (fix end) and double side tape the other end (free end) on a stick and hang weight on it, then I'll bounce a ping pong ball (like Calvin suggested) on it, then record the weight where the tone of the film stated to stay constant. That should be the yield point.

The next is your choice, one can ease off a few grams to work safely within the elastic zone or do what Calvin did and work in the plastic zone.


Just my two cent worth

Cheers
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Old 30th August 2006, 01:20 PM   #62
Calvin is offline Calvin  Germany
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Hi,

so is that The Hostaphan film I use starts to flow above ~4%.
So with just 2% I stay well away from this border. But as Zvon remarked right, You have to keep such things in mind.
I try to destress the joint spacer-film a bit by using soft materials (even when I use hard spacers I add some soft and damping material at those points) and up till today I had no diaphragm failure so far because of this reason. I have to admit that I have no 10 Years+ experience on this point, but all panels work for several years by now. A bit funny to me that the harder stretched panels all work easier, better and with less flaws than the softly tensioned panels

@AI
You´re right. The panel can be as big as You wish. As long as the rule for the membrane support applies, the panel works unconditionally stable to very high spl-levels, wether it is a very small d/s or a rather big d/s value. When You measure the dimensions of a ML-panel You will easily verify this rule

@WM
aging is a natural problem, especially for certain plastics. UV-Light is the ´destroying´ factor. So You might capsule Your panel to achieve a longer life, and/or You have to use materials which are long lasting by their chemical formulation. Foam surrounds of drivers have been problematic, but so did PVC- and rubber-surrounds too. The foam tapes of 3M are specified as UV-resistant , but I´m convinced, that they won´t hold forever On the other hand I think that a average lifespan of 10-15years is an acceptable value for a speaker.

jauu
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Old 1st September 2006, 01:46 AM   #63
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Hi calvin,

Thanks again for clearing yet another puzzle for me!!

Quote:
so is that The Hostaphan film I use starts to flow above ~4%.
So with just 2% I stay well away from this border. But as Zvon remarked right, You have to keep such things in mind.
I try to destress the joint spacer-film a bit by using soft materials (even when I use hard spacers I add some soft and damping material at those points) and up till today I had no diaphragm failure so far because of this reason. I have to admit that I have no 10 Years+ experience on this point, but all panels work for several years by now. A bit funny to me that the harder stretched panels all work easier, better and with less flaws than the softly tensioned panels
I wouldn't commend on how much tension is desireable but from your experience, I recon it is better would keep at about 3~4% elongation or at exactly the point before the film "flows"..... But I recon it is not as easy to determine this point as it may seem

I think your soft materials really gave that extra elasticity the film need.

Excellent work Calvin!!!
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Old 6th September 2006, 12:45 AM   #64
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Hi guys,
I'd finally ordered my perforated plate.

I will then send for rolling after collection.

I planned to acid-etch the plates at home using battery acid to remove sharp edges/burrs and oil/dirt before applying multiple layers of Polyeutelyne coat.

I recon its a good time to discuss about the film coating. The PVA glue application inspire me into thinking, can we use any other advesive, blend with some graphite powder (or any resistive elements)and apply onto the film?

Is shoe shine wax any bad as film coat?

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Old 6th September 2006, 07:17 AM   #65
Calvin is offline Calvin  Germany
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Hi,

sorry for keeping on repeating
I don´t recommend to stretch the film to the flow point! I stay well off of that point, stretching just ~2% where 4% is possible.

Acid etching might reduce the sharp edges problem a bit, but also reduces the thickness of the metal sheet and rises hole diameter!

I recommend using Polyurethane laquer too and not Polyethylene alone (it just has very high flashover values..all other parameters are less good). A topcoat of PU shows better electrical characteristics for overload conditions (lower surface resistance and higher epsilon).
PU laquer is easily available as a 2-component coating for boats and staircases, so its very rugged, it handles easily and gives very glossy and nice even surfaces.

jauu
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Old 7th September 2006, 07:04 AM   #66
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Default bonding to mylar...

you need to remember that mylar has a surface tension of about 45 dynes per cm Sq which is about the same as polished plate glass in other words very smooth. Not many adhesives will grip on a surface this smooth. Adhesives grip or grab onto and into any small surface irregularity they can find and so have dificulty on very smooth surfaces. Most people think that glues chemically bond materials together but that is no normally the case. Unless you really want to spend your time experimenting and don't mind rebuilding your speakers when they fail you would be best recommended to use one of the several methods that are proven to work and are available. These will cost you some extra money but they will insure that you only have to build your speaker once. You can search to find this information on this forum. Regards Moray James.
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Old 7th September 2006, 08:40 AM   #67
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Hi,

Quote:
I recommend using Polyurethane laquer too
I do not think it's a good idea to cover a high resistivity
protective coating with a lower resistivity coating.

The reason is that you have no electrical path for eliminating
the "playing loud" charge build up in both coatings.

You must use a low resistivity coating from the metal and up,
or You will get a very moody Esl that sometimes will play loud
and sometimes not at all.

I also wonder if Polyurethane has the same low required resistivity as Nylon66 or PVC, shall do some testing.
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Old 7th September 2006, 02:30 PM   #68
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Default Bonding to mylar

The glue to use is Scotchgrip 4693 or 4693H which can be purchased in 5 oz. tube from McMaster-Carr for about $8. A 5 oz tube will be enough glue to make a pair of speakers, if you make a lot of mistakes along the way. If you don't, you'll have plenty left over.

This glue is formulated to bond to low surface energy plastics, such as polyester (mylar). It works. It bonds to the mylar so tightly that the film will tear before the glue lets go.

I_F
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Old 7th September 2006, 05:49 PM   #69
Calvin is offline Calvin  Germany
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Hi,

@silly:
You´re right, the basecoat should have a lower resistivity too. Idon´t recommend PE as insulator.
PU has -at least the infos I´ve got about it- quite similar parameters as PVC and Nylon (Nylon6) with regard to resistance values and epsilon and is easily available as laquer on the market.

jauu
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Old 7th September 2006, 05:52 PM   #70
Calvin is offline Calvin  Germany
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Hi,

@silly:
You´re right, the basecoat should have a lower resistivity too. Idon´t recommend PE as insulator.
PU has -at least the infos I´ve got about it- quite similar parameters as PVC and Nylon (Nylon6) with regard to resistance values and epsilon and is easily available as laquer on the market.

jauu
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