What do we know about tension of film? - diyAudio
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Old 30th November 2011, 06:25 PM   #1
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Smile What do we know about tension of film?

I will be using a fish scale pull method... it is quite easy. The scale I have measures to 1000 grams.

Questions...

Is it possible to pull 6 micron mylar too tight to where the bias voltage cannot overcome it without absurd levels or will the mylar break before this level of tension would be a problem?

Heavier Mylar.... higher tension. Lighter Mylar... lower tension.... wrong or right?

I saw that one person was using 800 grams on 3 micron film for the midtweet.
I have found however that 6 micron can be pulled much tighter... what would be a safe or proper range of tension?

3m what tension
6m what tension
12 what tension

Is their an effect on the sound by different tensions that cannot be overcome with higher bias?
One site said tension is probably the least of concerns...?
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Old 30th November 2011, 08:15 PM   #2
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You want to tension your Mylar so that you are stretching it to about ten percent. To answer your question No. You have it the wrong way around, it is almost alway a case of finding enough tension to provide stability and restoring force. Here is an example. In the Acoustat panel Jim used a 65 gage HS Mylar and the panel width was between 8 - 9 inches wide. There was only just enough tension generated when the HS material was shrunk and a felt pad on the back side of the panel was required to help keep the panel stable. Even with the pad in place panels could still collapse under situations of hard drive. This was / is a situation of not enough tension.
The higher the tension the better the stability as the tension is all that you have to provide restorring force. Higher tension will also impact the panel resonance. If you keep to the ten percent stretch you will have your diaphragm tensioned enough to get the job done and provide a safe window of operation. Much more than that and your resonance goes up unnecessarily and you risk damage to the diaphragm. If you find that ten percent stretch does not provide the stabiltity and restorring force necessary then you will have to make your panel narrower. Hope that this helps. Best regards Moray James.
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Old 30th November 2011, 08:33 PM   #3
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Quote:
Originally Posted by moray james View Post
You want to tension your Mylar so that you are stretching it to about ten percent.
Perhaps you meant 2 percent?
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Old 30th November 2011, 08:46 PM   #4
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Forgive a senior moment. I have been trying to remember the exact % amount of stretch that I last used but my brain is on strike. So the easiest way to do this is to stretch to the point of just past plastic, and yes that is probably a percent or two. Thanks for catching this. Best regards Moray James.
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Old 30th November 2011, 08:53 PM   #5
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Thanks Moray. Just the type of answer I was looking for. And thanks bosert for catching the senior moment... which I am starting to have... oh how youth is so wasted on the young... so true, so true and oh how SO TRUE! Thanks guys.
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Old 30th November 2011, 08:53 PM   #6
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No worries

While we are on the subject of tensioning, and Acoustats....
Do you happen to know if Acoustat ever used mechanical tensioning in their production process?
Or did they always use the heat shrink method as shown in the factory tour photos.
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Old 1st December 2011, 05:01 AM   #7
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to the best of my knowledge they used Mylar HS65, never saw anything else but the Aman would know better if they used other films or methods. Best regards Moray James.
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Old 1st December 2011, 11:04 AM   #8
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Quote:
Originally Posted by bolserst View Post
Perhaps you meant 2 percent?
Well, the patents on Magnepan say 1-5 %, it is really less tensioned than an electrostatic. Tensioning is also related to the dimensions of the driver, stator-to-film-distance, distances between diaphragm supports etc. A friend of mine used 85% of the breaking strength for his ESL.

Roger
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Old 1st December 2011, 10:31 PM   #9
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Well I am using a weaker paint foam tape that I can tear apart with out having to scrape the metal... just the standard stuff at home depot you can find. I have pulled them apart and the varnished metal was fine every time... no scraping... and SEEMED to hold the film just fine as far as shearing ... but this is before driving them... it is the 3m stuff. So doing that and a variable PS I should be able to learn a little...
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