Curved Electrostatic Speaker Build

Hello!
A couple months ago I completed my first ESL: A single 12" x 12" panel with 12 micron Mylar and a PVA glue coating. I was pleased enough with the results to make some more! I have started construction on two 12" x 24" curved ESL panels again with 12 micron Mylar, but now with Licron Crystal as the coating. The 12" x 12" panel got pretty loud so nearly 4 times the surface area and better sound dispersion should make these new panels rock!

I hope I'm making making thread right...
Anyway, enjoy!
 
I received the sheet metal about a month ago and I just got to rolling it last weekend. I don't know exactly what the curvature of the metal is but no doubt it will be better than a flat panel in terms of dispersing sound. I've attached some photos of the flat metal and the bent metal.
 

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After soldering the wires onto the stator I hung the panels up for some coats of primer and a just a few coats of black polyurethane spray paint. The black paint is super economic at less than a dollar a can from Home Depot. I just started painting today and should hopefully be finished by the end of the week.
 

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Hi,

You did a nice curvature, though a little too much for my taste.
It'll become difficult to tension the membrane.
Also it looks as if the cuts in vertical direction are not done well.
In the first pic the left edge (top or bottom edge of the panel) looks well cut with no sharp edges.
The side edge though (upper edge in pic) starts quite smooth from the left corner and becoming more rough towards the right corner.
The sharp pin-like structures that appear when less than half of a hole is cut are prone to flashovers and should be avoided as they are also difficult to insulate properly.
Best would be of course a solid rim like the one visible at the lower edge.
Besides insulation issues a solid rim is also advantageous regarding glueing spacers and the membrane to the stator.
Especially the glue joints at the top and bottom rim of the stator must take serious amounts of force from the tensioned membrane.
I hope things will go well, but I'm afraid Your panels required a bit more pre-painting preparation.

jauu
Calvin
 
Hi calvin,
Thanks for the advice. On the edges with the pin-like structures I tried to grind them down so that instead on a sharp edge pointing inwards it was a smoother curve. Aside from grinding the metal itself, do you not think that many layers of paint and electrical tape wrapped around the edges will stop arcing?
Thanks,

Ben
 
Hi,

good to see that You are sensitive to that little but important detail ;)
Many layers of laquer are not neccessarily the way to go, as a thick layer builds up only around the pin structure where it is not only not needed, but may alter the d/s value (with low d/s hybrid panels think in 1/10mm precision range rather than 1mm range).
The buildup at the peak structure itself may still not suffice if its a very sharp pin as the field strength is the strongest here.
Even if the flashover treshold of the insulation is high enough at the beginning, it may age faster and lead to a premature breakdown.
A layer of tape is a good measure to raise the flashover treshold and to protect the edges, but of course should rather be used as an 'add-on' detail, not as a neccessary part of the 'prime' insulation.
Clear singlesided PVC or PP tape (e.g cheap package tape) comes in well tolerated thicknesses around 0.1mm (PP also has self-healing characteristics) and is mechanically quite strong.
Spacers made from 3Ms foam and VHB tapes stick well to PVC tape.
A point that requires Your attention, as the mechanical forces on the glue joints in vertical direction are high and permanent for years.

jauu
Calvin
 
Hi Calvin,
Thanks for your reply. I was thinking of using electrical tape that wraps around the edge of the double stick tape and the stator on each side. Of course on the side with the Mylar I would wrap it over the edge of the Mylar and the stator. If I were to use the PVC tape or packing tape would that go underneath the foam tape and around the edge of the stator to give more surface area for the foam tape to adhere to or over the foam tape and Mylar just like I was planning on doing with the electrical tape?
Thanks,

Ben
 
If anyone could help me it would be greatly appreciated. I'm obviously planning on making a mechanical tensioning jig for the mylar, but I'm worried about the hourglass effect on the mylar. As of right now I'm simply planning on using 1/16" 3M foam tape but I'm worried that A): the 1/16" d/s spacing is not enough and will lead to problems with the diaphragm touching the stator, and B): because the tape will be bonded to the perf metal directly there will not be adequate surface area which will lead to more problems. If that is the case, is there some kind of PVC or acrylic spars which could be epoxied onto the stator and then bond the foam tape to that? If something like that exists that is thin enough it would potentially solve the concerns I have about d/s spacing and the tape slipping.
Building this curved panel is already proving to be way more difficult than my first electrostatic speaker...:scratch:
I hope someone can chime in,

Ben
 
Hi,

here´s another pic, showing one of my very first sheet stators.
As You may see the clear tape was attached before glueing the spacers.
You can also see the softly serrated rim of the sheet.
Tensioning jigs have been shown before in other threads.
In basic You need only Tension in the long vertical direction, but You can´t simply use a flat tensioning jig.
There are two constructional ways.
The first is to use two fixed guides, mounted to a frame, one each positioned to the top and low end of the panel with a distance a bit larger than the panel itself.
The guides should have the same curvature as the panel and soft shaped edges so that the membrane can´t be ripped and is able to ´glide´ over the edge of the guides.
The membrane is pulled from the roll and laid over the guides with considerable overhead.
The ends of the membrane may then be fixed/clamped in a single point, of which one may be positioned fixed, while the other shall be moveable.
A weight, or a lever or a screwing mechanism may be attached to the moveable clamp that allows to exert sufficient pulling force on the membrane.
The long vertical parts of the frame may be used to put tape on the membrane and the frame to exert just a tiny amount of horizontal tension to only straighten small wrinkles on the membrane.
The second method is to make the guides thicker and use a material where double sided tape adheres to very well.
One or both guides may be attached to a stiff frame, but moveable by means of screws or weights.
Pull the membrane from the roll and glue it to the guides.
The advantage is that you need much less membrane overhead, but the disadvantage is that it is more difficut to get the membrane glued to the guides without wrinkles and perfectly parallel on both guides.
So I´d rather try method no.1

A last word to the curvature.
Though the curving looks very well and evenly executed the degree of curvature is probabely double the practical value.
Only slight curvature (+-15° max) is practical, as it becomes nearly impossible to shape the membrane wo. the hourglass effect becoming too much (see pic of my panel or from ML).
The curvature is mainly for stability reasons anyway and if You mount the finished panel into a frame a slighter bow is more than sufficient.
The widening of the distribution character as claimed by ML only applies to the highest highs and the effect is much less than the claimed 30°.

1/16" is the upper end of the thickness range I´d recommend.
1.0mm to 1.1mm (~1/24") are values I use and which are ok for hybrid panels working from 200Hz up.
Remember that the most important point in designing a good esl panel is efficiency.
A 50% increase in d/s lowers efficiency considerably and doesn´t gain You anything but almost all parameters will worsen.
To preserve dynamic stability You will have to add horizontal spacers, positioned every 80-90mm distance.
The spacers also help in reducing the hourglass effect and they centre the membrane between the stator sheets.
3M foam and VHB tape (6mm wide) has proven excellent here, as they stick well to the stator and membrane -thereby taking some of the vertical acting tension force from the top and bottom glue joints- and they perform some damping due to heir softness.
When the stators are finally mated such a panel will hardly rattle at all - while the only at the top and bottom glued ML panels rattle like hell, even after beeing mounted to the mounting frame.
When using the 3M foam tapes You should look at one that is designed to stick well to Polyester and the kind of insulation laquer You used.
If You are painting the stators Yourself a ´standard´ PU laquer for boats or staircases is a good choice for the finishing top layers with regard to electrical characteristics and bond strength with 3M tapes.

jauu
Calvin
 

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Hello,

My plan for mechanical tensioning is to cut pieces of MDF to the curvature of the metal and smooth them. The MDF pieces will be placed on either end of a bar clamp that will be able to pull the Mylar to tension. Regarding the sheets, I know that the curvature is too much for your liking and impractical, but will it be too much to make a successful panel? I am planning on using the 3M foam tape as horizontal spacers to reduce the hourglass effect and spread out the tension so that not all of the tension is on one piece of tape. Thanks for the tip on the polyurethane paint, I'll be sure to do that once I'm sure the panels are ready. I'll also use the clear packing tape on the edges of the stators. I notice that on the ends of your panels you use two widths of foam tape. Do you think that that is necessary or is is mostly a safety measure to ensure that there is absolutely no slippage?
Thanks,

Ben
 

neil5m

Member
2013-08-01 12:14 pm
Hi Ben

I re-Mylar'd my ML Clarity panels recently. I put the process up on the Martin Logan Owners website under DIY with pictures of the jig, type of foam tape etc used. I'll send you links to the materials I used.

The thread:
Repanelling ML Clarity's

I still have the Chinese anti-static solution. I could send it across to you to test if you need it. I made a few videos as well.

Regards
Neil
 

neil5m

Member
2013-08-01 12:14 pm
Ben,

I used 3M VHB 5952 tape. It has an acrylic adhesive and will work on both powder coated substrates (the stator) and low surface energy (LSE) substrates (the Mylar membrane). The thickness of the original tape on my ML model was 1mm. I used 1.1mm 3M tape.

For the spars, I bought 0.2mm thickness clear acrylic gel tape with PET backing for some rigidity. There were options of PVC and simply acrylic gel, but they would squish. Rob from ERAudio suggested the PET for rigidity. I made spars from the front clear plastic sheet of bound presentations.

Remember, the rear spars+acrylic tape are thicker than the spars+tape in front. This will also reduce chances of the diaphragm hitting the Stator.

I used Kapton tape on the edges of the stators. They can easily handle high voltages. I suggest not using packing or electric tape as the glue degrades within a year or two and is messy.

Neil
 
Hi,

....but will it be too much to make a successful panel?
Don't know about the chances of success, but just that it becomes more difficult and requires even higher levels of precision and possibly a number of additional test runs, before the proceedings fit.

Packing tape -of decent quality of course- is neither messy nor does it degrade early.
If its PVC tape the 3M tapes -foam and VHB- stick very well to them.

Top and bottom rims need to take considerable amounts of (shear) forces which require a sufficient glue joint area.
The forces are in fact so high, that ML and I also use additional glue area in that we fold the excess membrane back over the rim to glue it on the outside of the stator too.
You have to consider that as Your stator sheets are not solid, but punched up to the top and bottom rim, the glue joint area between stator and spacer is small, i.e. it can take less force.

jauu
Calvin
 

neil5m

Member
2013-08-01 12:14 pm
Yes Calvin, you are right. I didn't realize the stator tops and sides aren't solid. When I rebuilt my panels I did so without any measurements or any real knowledge. Wasn't the right way to do it of course. The forum and reading posts of knowledgable persons like you has been an education for me. I look forward to learning more from your posts. Your website is beautiful too!

On the issue of solid edges for the stators, do you think that using a putty for metal that hardens and becomes rock solid is the way to go?

I remember using this putty for pipe cracks which hardened. I've also used a silicone based putty that hardened like rock and could be worked on later (sanded etc)


Sent from my iPhone using Tapatalk
 
Hi,

never tried Your putty idea, but I don't see a reason it shouldn't work.
It'd be too much effort for my taste, as a slightly larger amount of taped area will do the job also.
The folding back of excess membrane is a very effective trick to increase glue joint area and to handle the shearing forces without reducing the 'active' area of the panel.

Almost all punchers I contacted -even the very large ones- offered to punch Your hole pattern from 4-8 sheets on for reasonable cost, not much more than cutting strips from larger pre-punched sheets.
I'd rather spare the effort and order sheets with solid rims ... which also guarantees that the hole pattern is the same on all sheets, so that the holes of the two mated stators align well, giving best optical transparency.
You can also ask them to use fresh tools, so that the hole edges are less pronounced and less sharp.
Takes less effort to sand them down.
And some can even bend the sheets for You.

jauu
Calvin
 

alexberg

Member
2009-10-01 2:25 pm
In regard to edges. Think a bit and recall how the dents on cars were repaired back then. Use some solder, gentlemen. It's easy to file, you could get round (filleted) edge(s).It's probably will not stand powder coating, however quite a few PbSnAg or tin-silver tin-copper alloys t>300 C will do.