Jig and stretch for curved ESL? - diyAudio
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Old 4th January 2011, 01:22 PM   #1
markusA is offline markusA  Sweden
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Default Jig and stretch for curved ESL?

Let's have a tread dedicated to the jig needed to build curved ESL's?

Me being a n0ob have some thoughts and ideas but I'm sure there are other people out there interested in learning how to actually build a curved panel?

So, please!
If you have any experience in how to practically build curved esl, please share.
How does the jig look like, how do you tension the diaphragm and how do you mount the front and back stator?
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Old 5th January 2011, 11:38 AM   #2
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Mark I will take some photos and post. I followed Sanders "plans" for the form to attach the spacers and impart the curve to the stators. However, for the stretcher part, I did not follow his method, but rather built a large stretcher frame with ends that had the same radius as my panels and used veneer screws to move one of the ends to tension the diaphram. It is important to only stretch lengthwise, and just provide enough tension on the sides to remove wrinkles.
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Old 8th January 2011, 09:58 PM   #3
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I have attached three photos (or at least tried) showing my stretcher, detail around the use of the veneer screws, and stretcher with the "table top" as Sanders calls it. The stretcher is about 50% larger than the stator panels. Curved diaphragms, which are only stretched lengthwise, develop and "hour glass" shape. To minimize this effect, only the center portion of the diaphragm is used. In my case, I used perforated steel that was 40" long, but from end to end my stretcher is nearly 72". I use carpet tape to attach the membrane to the ends of the stretcher, then using the screws in "reverse direction" stretch the membrane over the "table top" about 1.5%. Using very slight pressure, I pull the membrane to the sides with tape to remove any large wrinkles. Once the membrane looks smooth, I lay the outside stator on top of the membrane (which has double sided tape over the spacers) to attach the stator to the diaphragm. Hope this helps, jerry
Attached Images
File Type: jpg Stretcher1.jpg (57.2 KB, 473 views)
File Type: jpg Strecther Detail.jpg (83.2 KB, 445 views)
File Type: jpg Stretcher and Frame.jpg (55.4 KB, 445 views)
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Old 9th January 2011, 01:51 AM   #4
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I like your stretcher Jerry. I've only built flat panels but I've been contemplating building a curved panel this year and considering how I might build the stretcher. Your stretcher is simpler than what I had imagined and that's the way to go, I figure. I had anticipated the diaphragm would need to be quite a bit wider than final panel size because of the deformation that you mentioned. However, it had not occurred to me that the film would also need to be quite a bit longer as well. Thanks for that tip, Jerry!

Are you using 6 micron film?

BTW, I would love to see your speakers!
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Old 9th January 2011, 10:40 AM   #5
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Hi Jerry,

That's a very good stretcher design - good and simple. Thanks for sharing.

Wachara C.
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Old 9th January 2011, 02:29 PM   #6
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Thanks everyone for your very kind comments. Yes I am using 6 micron mylar film. I forgot to mention that my stators are 12" wide, but the stretcher will hold 19" wide film, again to minimize impact of the hour glass effect. I am still constructing the speakers, so do not have any final photos. I have one panel completed (and will use your suggestions for mounting Charlie). At present, I am working mostly on the cabinets for the woofers - it will be a hybrid system. I live in the US-Midwest where temperatures are freezing - so I will either need to wait until it warms, or bring the stretcher inside. Following suggestions of others here, the tape adheres best under warm conditions. I will post pictures as I complete them. I have been a member of this forum for nearly 5 years, and have really appreciated the suggestions and ideas that members have shared. Hopefully I am getting to a point where I can give something in return. Jerry
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Old 12th January 2011, 02:06 PM   #7
markusA is offline markusA  Sweden
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I've been busy with drawing up pcb's (the price I pay for trying to multitask) so my mind's been elsewhere but I do follow the thread and I'm still hoping for more people to post their solutions.

How do you get the right curvature on the stators? I assume you roll them before mounting?
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Old 13th January 2011, 12:40 AM   #8
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I will share what I did, and hope that others will do as well. I started with 40” x 36” perforated steel sheets, which I cut into 40”x 12” pieces for the stators. This evidently relieved some stress within the sheet, which resulted in a slight curve, but not enough (my design was 20 degrees since Sanders indicated this was a “safe” amount). To get the final correct curve, I either taped the stator to the “20 degree table top” for the inner stator, and then glued the acrylic horizontal spacers to the stator to “fix” the final curve to the spacer, or for the outer stators, taped the acrylic spacers to the "table top", and then attached the stator to the spacers (in both cases using epoxy to glue the spacers to the stators). This puts a compression force on the spacers and effectively sets the curvature of the stators (within a degree or two). I pretty much followed Sanders on this and it worked reasonably well. For those thinking of making curved panels, I personally found that there was more work involved in making the “table tops” and stretcher as there was in construction of the stators. Hope this helps, Jerry
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Old 14th January 2011, 10:43 PM   #9
flatman is offline flatman  Australia
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Default My curved panel build

Hi. Story of my curved panel build can be found at

Project History - ESL Array

Being something of a blog it's oddly organized. Start at the bottom of the page and work your way up.

It's worth persevering with; they sound fantastic.
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Old 16th January 2011, 12:56 PM   #10
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Klaatu Audio Elektrostat

I built these speakers to a friend back in -92 who loved the Martin Logan sound, but had no money. I experimented a lot and came up with a design where a special stretching jig wasn't needed. I used flat .8 mm thick steel stators which I had powder coated and then urethane painted. I applied one mm thick double sided foam tape around the stator perimeter and strips of the same material as membrane supports. At the center of the membrane supports, the foam was replaced by 10 mm long plastic pieces for avoiding mechanical compression of the foam strips. The film was mounted with the help of a ordinary stretch frame. After contact stripping, the front stator was laid loosely on top
and the esl package was sunk in a wooden frame as seen on picture and a one meter long 6x50 mm shrink tubed steel bar was mounted from behind, pressing the esl package forward about, if I remember correctly, 30 millimeters or 1,2 inch.

The photo is taken a few months ago when my son discovered my speakers
in an local HiFi equipment shop outside of Malmö.

Remarkably. they still worked as a charm....
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