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Old 2nd July 2011, 03:23 PM   #1
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Default ESL Pre-construction advice/questions and concerns

Well I have the 4 panels’ powder coated with a primer coated and finished in black powder coated approximately three mils thick, and just contemplating constructing them this weekend. Before I begin I have several concerns I would like to defer to the experts who have constructed these ESL’s first, I constructed the pneumatic stretcher ala Charlie’s construction and wonder if there was any tips on taping the film to the jig?

Secondly, I am using two aluminum angles running parallel to each other which will serve to support the panel vertically however until they are mounted in a frame they will have some horizontal flexibility which may flex the film. Before I begin should I add a horizontal support to the vertical support and weld then together in an “H”or quasi exoskelton frame configuration?

And lastly (for the moment) this is actually 2 questions. Is there any determent in sound quality of spacing distance closer vs. further apart. I am constructing my panels 15 inches wide and with the 2 each ¾” spacers/ edge film support, the functional speaker distance is then reduced to 13 1/2”. If I divide this distance into three, the spacers distance will be under the maximum distance at 4 ½”, or using 2 spacers it will yield a distance of 6 3/4'” I believe this is just over the recommended max distance spacing using 18g. 51% open area, and hole size .1406 hole center .1875. BTW these are going to be use as a hybrid design and therefore using .063 double sided tape.

Any and all suggestions would be greatly appreciated.

Jerry
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Old 2nd July 2011, 04:20 PM   #2
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Quote:
Originally Posted by dochungwell View Post
Well I have the 4 panels’ powder coated with a primer coated and finished in black powder coated approximately three mils thick, and just contemplating constructing them this weekend. Before I begin I have several concerns I would like to defer to the experts who have constructed these ESL’s first, I constructed the pneumatic stretcher ala Charlie’s construction and wonder if there was any tips on taping the film to the jig?

Secondly, I am using two aluminum angles running parallel to each other which will serve to support the panel vertically however until they are mounted in a frame they will have some horizontal flexibility which may flex the film. Before I begin should I add a horizontal support to the vertical support and weld then together in an “H”or quasi exoskelton frame configuration?

And lastly (for the moment) this is actually 2 questions. Is there any determent in sound quality of spacing distance closer vs. further apart. I am constructing my panels 15 inches wide and with the 2 each ¾” spacers/ edge film support, the functional speaker distance is then reduced to 13 1/2”. If I divide this distance into three, the spacers distance will be under the maximum distance at 4 ½”, or using 2 spacers it will yield a distance of 6 3/4'” I believe this is just over the recommended max distance spacing using 18g. 51% open area, and hole size .1406 hole center .1875. BTW these are going to be use as a hybrid design and therefore using .063 double sided tape.

Any and all suggestions would be greatly appreciated.

Jerry
Hi Jerry,
I used double backed tape on the bottom edges of my jig to secure the film.

The 6-micron film is strong but tears very easily if pulled from an edge-- especially if there is a nick in the cut edge. So, I use very sharp scissors to cut nice straight edges with no nicks.

The jig should have smooth radiused edges to prevent the film from grabbing and tearing-- a little car wax on the edges helps the film slide easy.

I would layout a bath towel on the work surface, then layout the film onto it. Then place the jig face down onto the film.

When you wrap the film over the edges, you don't need to pull it tight but you don't want any excess slack either. Wrap the film over the ends, then the sides, and do the corners last. Since the film will bunch up in the corners, you will need more than just the double backed tape along the jig's edge to hold it. You can use one-sided tape to finish securing the film at the corners > pulling the bunched film over and into the corners on the back of the jig, then securing with tape.

If you do happen to get a tear in the film: As long as the tear doesn't extend onto the face of the jig, you can still save it the by patching over the tear with tape.

If you are using 6-micron film, you can use the method below to measure the stretch to 1.5% elongation:

Make two 1/4" wide measuring sticks form strips of wood thin enough to be cut easily with a box knife. Make one stick exactly 12 inches long and the other stick exactly 12 and 3/16 inches long.

Take all slack out of the film, then use the 12" stick and a fine-tip felt pen to place a pair of reference marks 12" apart wide across the width of the film, about midway on the panel. Now place the longer stick next to the reference marks and slowly pump air into the tube to stretch the film.

Stretch the film until the inside edges of the reference marks exactly match the longer stick to achieve the desired 1.5% elongation.

Good luck with it!
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Old 2nd July 2011, 05:24 PM   #3
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Here is how I do it using the bicycle tube stretcher similar to CharlieM's.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

I hope my pictures speak for themselves.

Wachara C.
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Old 2nd July 2011, 05:24 PM   #4
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Thanks Charlie for the tips.

Do you thing that 6 1/2" spacing is too long between spacers, or should I space them closer. If i divide the useable space between the edge support the spacing will be less than 4 1/2" using 2 verticle supports between the 2 edges instead of one?

Thanks as always,
Jerry
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Old 2nd July 2011, 06:47 PM   #5
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Originally Posted by dochungwell View Post
Thanks Charlie for the tips.

Do you thing that 6 1/2" spacing is too long between spacers, or should I space them closer. If i divide the useable space between the edge support the spacing will be less than 4 1/2" using 2 verticle supports between the 2 edges instead of one?

Thanks as always,
Jerry
Jerry,
I would definitely go with two vertical spacers. One reason being that with one spacer you would exceed the 70-100x d/s spacing rule (not by much but it still exceeds it). Another consideration is that it's highly unlikely that your stators are perfectly flat-- in which case there may be areas where the diaphragm is closer to a stator than you might think and thus more prone [there] to the diaphragm slapping the stator at high volume. Not to mention that the pressure waves from any subwoofers in the room will also move the diaphragms more than you might think. For these reasons, I would always opt for the low side of the 70-100x d/s spacing rule.

BTW, Wacara C,
Nice job on that jig!

Last edited by CharlieM; 2nd July 2011 at 06:51 PM.
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Old 2nd July 2011, 08:06 PM   #6
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At this piont since you used Powder coating I would seriuosly consider building your bias supply and test the panels for any leakages before you assemble them.
Powder coating can some times can cause micro pin holes cuased from Gassing.
This is easily remedied from a few generous coats of clear acrylic spray.

You should have absolutely no arcing from any point on the panel and while touching the panel with using a screw driver as a sniffer probe.

A 3 mil coating is abit on the thin side, But it should get you to the 2kv to 3kv bias voltage range which is ample to make them sound very nice.

I used powder coating on my screen stators and a few samples had devolped micro cracks in the coating from excessive bending ( the coater had rolled the first sample into a tube, ).

I had them double coat them and it worked fine but seven years later I had to coat them with some acrylic in order to get to 7.5kv,But,that is an extreme range of course.

It would be a shame to have to tear them apart and a PIA after the fact.
So it would be a good measure to test them first.

Just my 2 cents worth as I have been through this several times,Cheers! jer
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Old 2nd July 2011, 08:11 PM   #7
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Also I would stick to the 100:1 D/S rule as long as you are using a higher crossover frequency.

I have been using 150:1 as I like to dip down into the 200hz range as I can't go much lower than this with out problems due to the resonate frequency's of my panels are in the 65hz to 90hz range.

My 4" wide panels have a D/S of around .070" to .075" and I get stator clipping (slapping) slightly only when driven extremely hard and past their physical and electrical capabilities and at that point they are to loud to stand in the room with them, and, I can't even imagine what a large panel would be like.
I have heard how loud Mavric's panels get when I spoke to him on the phone several times ,and it was incredibly loud as he was shouting and need'nt be .he,he

A slight bending of the panel will not effect its performance until you get your frame built.
My only concern as I had already mentioned is excessive bending can cause micro cracks.
But powder coating is quite durable in this subject of interest, and, I really don't see much for concern as long as much care is taken to keep them from flexing excessively.


Good Luck and Keep us posted !! jer

Last edited by geraldfryjr; 2nd July 2011 at 08:33 PM.
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Old 3rd July 2011, 01:49 PM   #8
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Thank you Kindly, Jer, Charlie and Wachara C.

Well, yesterday I took the advice of Charlie and completed my power supply and performed a "probe arc test" to check for arcing through the powder coat. Well as you would expect with the estimated 3mil thick coating there was apparent arcing, mostly in the edges. I sprayed a thick of polyurethane over the entire panel. I will check again later today.

Wachara, Thanks for your pictures, I completed my diaphragm stretcher an it appears to look very similar to both yours and charlies.

Question: Hypothetically; If I would have assembled the panels that arc, and assuming the tension on the film was tensioned to say 1.5 to 2% where the diaphragm would not be easily driven into the panels with high volume, would arcing still occur? (1/16 d/s and 2kv).
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Old 3rd July 2011, 02:18 PM   #9
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I don't think that you will arch your panel with 2KV. Unless you try to play the music extremely loud, I will not worry too much.

Wachara C.
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Old 3rd July 2011, 03:13 PM   #10
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Quote:
Originally Posted by dochungwell View Post
Thank you Kindly, Jer, Charlie and Wachara C.

Well, yesterday I took the advice of Charlie and completed my power supply and performed a "probe arc test" to check for arcing through the powder coat. Well as you would expect with the estimated 3mil thick coating there was apparent arcing, mostly in the edges. I sprayed a thick of polyurethane over the entire panel. I will check again later today.

Wachara, Thanks for your pictures, I completed my diaphragm stretcher an it appears to look very similar to both yours and charlies.

Question: Hypothetically; If I would have assembled the panels that arc, and assuming the tension on the film was tensioned to say 1.5 to 2% where the diaphragm would not be easily driven into the panels with high volume, would arcing still occur? (1/16 d/s and 2kv).
Mmmmm.... I'm hoping Jer will jump in with his thoughts on this-- I'm thinking Jer has done a lot more experimenting with stator coatings and arcing than I.

The stator edges are the areas most prone to arcing so I'm not surprised that you saw arcing there if your probe was actually touching the stator-- and especially if there are any sharp points along the edges you were probing.

The most serious mode of arcing would be stator-to-stator arcing at the panel edges, as this would involve the much higher current output from the amp; which would quickly burn thru stator insulation and get progressively worse very quickly-- and likely even trip the protection circuitry in your amplifier and shut it down.

Now that you've added some polyurethane paint, your insulation will be better. Let me now suggest that you repeat your arcing test in a slightly different way to verify if arcing would occur along the stator edges:

Pick an area on a stator edge that had arced in your earlier test. To this area, apply a layer of the urethane foam tape spacer material and let it overhanging the stator edge about 1/16 inch and tape over the edge as shown in the sketch on my blog page.

Now repeat your arc test, probing along the tape surface near the stator edge. I'm fairly sure you will now see no arcing along the edge, as any arcs would then have to shoot thru the foam tape or take the longer path around the tape overhang to reach the stator and complete the circuit. In reality, the situation is even better, as you would not coat the diaphragm all the way out to the panel edge anyway (see my blog page)-- which makes it very unlikely that you would have any diaphragm-to-stator arcing along the panel edges. Also, any stator-to-stator arcs would then have to shoot thru not one but two layers of foam tape (one layer on each stator)-- so, I'm thinking that if you tape the panel edges as shown in my blog page, it's unlikely you would have any arcing problems along the panel edges, even if your stator coating on the edges isn't so good.

As for arcing in other areas, I will defer to Jer's judgement on how best to test for that before you assemble the panels. You definitely want the side of the stator that has the smoothest hole edges facing the inside of the panel.

If you were to have arcing inside the panel after assembly, you could back off on the bias voltage. The bias supply I use isn't adjustable but you could still back off on the voltage by tapping into the diode/cap ladder at [let's say] the sixth diode rather than the lasts (8th) diode... that would drop your bias voltage from 2.7kv down to about 2kv and substantially reduce any diaphragm/stator arcing -- you would lose a bit of sensitivity but your panel would still play plenty loud (trust me on this, I've tried it).

Jump in here, Jer

Last edited by CharlieM; 3rd July 2011 at 03:21 PM.
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