DIY weighted diaphragm stretcher (pic)

[SkySeeker]

Looking at the picture I annexed in the previous post, maybe that would be a good way to tension a curved ESL design!.

I just might try that myself......

[Calvin]

Hi,

way too complicated for a curved design! Use a curved but otherwise standard wooden frame as stretcher.

jauu
Calvin

[arend-jan]

Actually, the weighted stretcher is perfect for a curved stator!

The nice thing is that you can lower the weights on the short sides to keep the wrinkels out and the movable clamps/weights ensure that the tension stays exactly the same when you attach the curved stator to the film from below. I already tried this with a (only slightly) curved stator and it works perfectly. The film just wraps around the curves like a warm blanket in front of the fireplace around your loved one :-)

I started out with a wooden frame stretcher. It is fiddly at best to control the tension properly and make sure it is even across the film. I'm not saying that you can't get good results with it, but I found it hard to get reproducable results. Later I switched to the "ER-audio method": a glass plate and using tape in combination with a tension scale. This works but makes the glueing awkward (because you can't get to it from below) and is also less consistent as I expected. Maybe because the film can get stuck to the glass plate on some places, I don't know. It also takes a lot of time (and tape!) to tension the film this way.

SkySeeker, I like your original ideas for modification, but I doubt they would be actual improvements. Your first idea with the springs would make the tension dependent on the actual position of the film. Intuitivly, I'd say this is a problem. Your second idea with the balancing rods, it might work but I think it will be quite difficult to use it. Envision your device and a formless thin film. How are you going to attach it properly?

But please don't let me stop you from trying! Post pics when you do :-)

[Few]

arend-jan:
Thanks for sharing some of your design. Very nice!

You mentioned that finding clamps that hold the film securely without tearing it was part of the trick. Any advice or suggestions on what sorts of clamps work well? Rubber pads where the clamps contact the film?

Also, you said that low friction pulleys or rollers turned out to be quite important. Did you find that fairly expensive ones were required or did you locate a simple and low cost solution that is adequate? I'm guessing from your photo that you're using pulleys with ball bearings.
Few

[SkySeeker]

I was thinking that for low cost clamps you could use a piece of flat metal/plastic and just tape that to the mylar.

[arend-jan]

Originally posted by Few
Any advice or suggestions on what sorts of clamps work well? Rubber pads where the clamps contact the film?

Sure. I sourced these clamps in a local hardware store. They are no-name el-cheapo "car battery clamps". I mounted rubbers inside the jaws so they have a gentle but good grip.

I'm guessing from your photo that you're using pulleys with ball bearings.

Good guess. Again the pulleys were located in a local hardware shop. They are nylon wheels that originaly have a center hole of 6mm. I drilled out the holes to fit a mini ball bearing. The rods are 8mm C45 steel.

The original quad machine has something similar, where they use large (open) ball bearings with a custom made ring pressed around it. This is probably not something you can do at home.

The most expensive part (you're going to be suprised) where those PVC endcaps for the weights. They charge a staggering 69 euro cents per piece for those! And I needed 112. Go figure.

[diamondsouled]

Nice set up.

Here's a pic of a Beveridge mylar diaphragm being stretched.

http://www.bevaudio.com/Technology.htm

[arend-jan]

Originally posted by diamondsouled
Here's a pic of a Beveridge mylar diaphragm being stretched.

Pfffew, looks like a PITA to set up! I doubt they still do it that way.

The successor of the weighted jig that Quad employed for their ESL63 is a pneumatic driven device, using what looks like piano keys to stretch the film.



The picture is called 'coating' and it is said that this is what is being done by the man with the brush. I doubt it. It is clear to anyone who actually looked at a 63 panel that the coating is sprayed on. Perhaps this is the application of the secret incredient 'X' that was rumoured to be applied to the diaphragm by Quad.

[MJ Dijkstra]

I think the picture shows the quad57 on which the coating was brushed on indeed

[arend-jan]

I'm pretty sure it's not the 57. If you look closely, you can see the stator of a 63 element in a frame vertically on the left of the pic.
As can be deducted from the working of the machine, the stator is glued to the diaphragm from above. The coating on a 63 is on the other side of the diaphragm.

With the 57, the coating was brushed on indeed (on both sides of the diaphragm).