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Old 6th January 2009, 12:00 PM   #1
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Smile Which spacer thickness to use with ESL?

Dear friends,

I have gathered most of the materials needed to build a pair of ELS. I would like to hear from you regarding the spacer material and its thickness. I am thinking of using double sided tape as a spacer and for attaching the diaphragm to the stators. I have now 1 mm and 1.5 mm tapes. Which one should I use?

I will be making the stators from PCB. I will drill holes on them using my home made CNC machine. The stators will be around 40 cm x 50 cm. What hole size would be good - 2mm, 3mm, 4mm or other?

I would appreciate for all your help.

Wachara C.
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Old 6th January 2009, 02:29 PM   #2
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For the spacers I would use PCB material as well (FR4 is perfect). Tape has trouble keeping the tension and it becomes very difficult if not impossible to disassemble the unit. You can glue the diaphragm to one of the stators and bolt the thing shut (drill some holes through the stator assembly where the spacers are located)

I think the size of 40x50 cm is a bit odd. Do you plan to use electrical segmentation?

The stator spacing depends on what you want to do with the panel. Is it full range or not? A spacing of 1mm should be a good start.

For the hole pattern, holes of 3mm configured like shown in the picture has proven to work rather nicely.
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Old 6th January 2009, 02:57 PM   #3
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Thanks Arend-jan for your quick answer.

I would eventually stack a few of the panels to make a bigger one - something like 4 of 40x50 per side.

So you don't think double sided tape is a good solution. But, I have found mylar to be very difficult to glue with anything. I have a difficult time to find a good epoxy glue here.

When playing loud music on them, would the spacing of only 1mm be a problem? Would the diaphragm ever hit the stator? Or should I put a spacer of 1mm at every 100mm spacing?

Wachara C.
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Old 6th January 2009, 03:03 PM   #4
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Yes you should definitely have multiple spacers otherwise the panel will not be stable. Should be fun to experiment with.

Epoxy glue is crap. You are better of with a contact cement (neoprene or water based) like they use for veneer (wood) glueing.

I know there are people that like to use tape, but with a high tension panel this is likely to slacken over time. Personally, I would not recommend it.
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Old 6th January 2009, 03:18 PM   #5
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Do you mean the yellowish glue that is used for gluing wood?

Wachara C.
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Old 6th January 2009, 03:29 PM   #6
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Yes, but they are not all equal. You will have to test some to find which work for you. Use a very thin layer of glue.

The best glue I was able to find is 3M 4693 but it is troublesome to get outside the US.
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Old 8th January 2009, 10:50 PM   #7
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I would recomment to make a few smaller prototypes before building a larger one. you will find out that there are quite many problems to solve.
For relatively wide panel like yours , I would use slightly higher d/s spacing (probably 1,5 - 2 mm). But it all depends on what lowest frequencies you want to reproduce , what will be drive voltage, etc.


[QUOTE]Originally posted by arend-jan
Epoxy glue is crap. You are better of with a contact cement (neoprene or water based) like they use for veneer (wood) glueing.
[/QUOTE

I have used epoxy glue and found no other to work better. It does not stick to mylar too much , so panels can be easily disassembled, still providing good shear strength. It cures in precisely known time , since no liquids need to evaporate. While curing, it flows and equalizes slowly so the bond will be very flat.
Adding small amount of solvent to expoy (used for diluting nitrocelulose paints) will improve its bonding strength to plastics. Not sure if it works with all epoxy types.
The disadvantage of this glue is that it will not hold stators by itself - they will need to be fixed with screws additionally.
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Old 9th January 2009, 08:37 AM   #8
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Like many, I also started out with epoxy glue many years ago. What I did not like about it is that it gives a relatively thick glue film, it does not really stick to the mylar, and most of all that it is a real mess to remove it from the stators. Perhaps with the solvent that it would work better, but I did not try that (did not even know you can dilute epoxy glue). That's why I went out to search for something different. I must have tried at least a dozen different glues.

What I want from the glue is:

1. a good bond
2. a thin film
3. easy to remove if you have to start over again.
4. no time pressure to attach the film
5. if possible, no health issues

With super glue and primer I did not get a nice fill of the gap and it's nasty stuff to work with (irritates the eyes and respiration). Most other glues that I tried give a thick and uneven glue film, also not good. I tried some proprietary glues for ESLs but they gave me time pressure because the glue had already dried up before I got the whole stator covered.

With the 3M 4693, I get a really thin glue line (almost invisible) and a very good and instant bond. No cure time, just rub over the film once (with my stretcher I have the stator below the film so I can see and manipulate the glue line) and you can cut it loose. I only put the glue on the stator, not on the film.

The instant bond is also an advantage if you want to build as many panels as I do.

The film is not hard to remove if you have to do it all over again, and because the glue line is so thin you only sand it a bit with a piece of paper and you are ready to put on a new diaphragm.

Another glue that works well is LePage Press-Tite Green, a water based contact cement. But the 3M is my favourite.
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Old 9th January 2009, 12:08 PM   #9
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Dear Arend-Jan and Bazukas,

Thanks again for all your advises. May I know what spacer thickness you are using and what is the size of your panel? What is your bias voltage?

I am looking to build a full range ESL. What is the low frequency response I can get if I were to use 1mm, 1.5mm or 2mm spacers? I understand that with a bigger gap between spacers and stators, the diaphragm can vibrate more aggressively and therefore the low frequency would be better. Do I understand it correctly? I have got a 6 micron mylar film which I will be using as diaphragm. Do you think it will be good enough?

I appreciate very much for all your comments.

Wachara C.
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Old 9th January 2009, 01:36 PM   #10
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A full range panel is very hard to do well. There are many factors, too many in fact to explain in a single post. I agree with bazukaz, it is a good idea to build a small panel first and experiment with it so you get to solve the basic problems and get a feeling for diaphragm tension, voltages etc.

If you do a search there have been many posts on the subject. Sorry but there are no single best values, it's all compromises.
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