Mylar tension on Sequel II

[peregrin288]

Hello all,

I am reconditioning a pair of Martin Logan Sequel IIs. I am at the point where I need to stretch the 6 micron film. Does anybody know what the tension should be for the curved panels? I have seen similar curved stator designs with a tension of 2.5kg. Is this correct?

Thanks for any and all help.
Kris

 

[stokessd]

Have you already removed the original diaphragms? If not, I'd measure the tension on them before disassembly.

With curved panels, you'll want to tension in the non-curved dimension, with only minimal tension in the curved dimension (just to remove any wrinkles).

Sheldon

 

[peregrin288]

Sheldon, thanks for the reply.

The original diaphragms were torn and wrinkled, so there wasn't any way for me to measure without tearing the mylar more. I had heard the same advice about tensioning in the non-curved direction, and only pulling a little in the other direction to get whatever wrinkles out that still happen to be there.

I guess I'll have to try 2.5kg and see what happens.

 

[Bazukaz]

Sheldon, thanks for the reply.

The original diaphragms were torn and wrinkled, so there wasn't any way for me to measure without tearing the mylar more. I had heard the same advice about tensioning in the non-curved direction, and only pulling a little in the other direction to get whatever wrinkles out that still happen to be there.

I guess I'll have to try 2.5kg and see what happens.

Hi,

You can do another trick posted here long time ago. First the diaphragm is stretched just to be free of wrinkles. Then place two dots with a marker lets say 200 mm apart. It needs to be stretched to around 2%(so to 204mm).
I may be wrong but I highly doubt 2.5 kg will be enough(I you are talking about total longitudinal tension). Maybe ten times that... I have had wooden frames(made from 50x50mm material) bending significantly when 2% target is reached, and that with 2 um film.

 

[peregrin288]

Thanks for the info, Bazukaz.

2.5kg was definitely not enough. 4kg worked very well though. I finished the mylar on one panel last night, hoping to do the other today.

I'll post pics of the stretching and mounting jig when I get a chance.

 

[tyu]

Where did you get your mylar?
DId you strip all the back of the dobbel sided tape an put down all new tape?
what did you use at the top an bottem?
what coting well you be using?
I have ML SL3 Like yours panels i need to do the same thing too...Thanks for any info

 

[peregrin288]

Hi tyu,

I stripped everything off the stator and reapplied double-sided foam tape. One strip on the sides, two on the top and bottom.

For supplies and other ideas, see this site:

Jazzman's DIY Electrostatic Loudspeaker Page

There are links to coatings, 3M tape, mylar on eBay, assembly ideas, etc.

This page shows a curved stator like ML, but he attaches the mylar to the back of the front stator. I built a similar tensioning jig and used it upside down. As soon as I find my camera, I'll post pics. He also says he tensions his mylar to 2.5kgs, but I found that I needed 4kgs.

https://sites.google.com/site/eslarray/home/project-history/diaphragmstretchingandgluing

I hope this helps.

 

[tyu]

Bias feeds althe way around would be best!

You may have alredy don this but....I have also here a pr of Acsent an Prodigys...an i have pop the panels apart...lot ezer to do this with the newer ML panels than the older ones like 2001 on...without riping the mylar...an ran a bias strip up the left an right sides of the panels..this give more output to the panels an thay sound much better...ML only runs up the right side ...got too sale panels...it $ 1k for the SL3s now..here some pic you may have seen of the ML guy working on there jig...thanks