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CharlieM 21st June 2008 11:26 PM

dots or strips for spacers?
Hello All,

I'm building some 12x48 perf metal esl panels assembled with 3/4 wide 1/16 thick double-sided foam tape. I'm trying to decide whether to use 1/4" width foam strips or 1/2" diameter foam dots for the inner spacers and would like to hear recommendations from the esl builders here. Bear in mind that my stators are less than perfectly flat (tack-weld one together from two pieces) so I will need to be conservative with the distance between spacers in order to keep the diaphram centered.

The attached sketch shows (4) dot layouts on a 12x48 panel-- should I use 1/4 strip spacers or one of these dot layouts? Please let me hear your opinions!


CharlieM 23rd June 2008 02:02 AM

it's a done-deal now
No responses (yet) to the dots versus strip spacer query. Oh well, it's a moot issue for this project now, since I've already assembled one of the esl panels this evening using foam tape strip-spacers. Still, I would like to hear any opinions on sonic differences between dots and strips (resonant modes, resonant frequency, character of the sound).

I was alarmed and astonished to find that the 3-M foam tape didn't stick to the stators very well. I concluded the culprit was the satin clear poly topcoats on the stators rather than the tape. The stators were first spray-coated with about 7 or 8 mils of latex house primer, then black Krylon from an aerosol can, then three sprayed coats of some Minwax clear satin polyurethane left-over from another project. I'm thinking the satin filler in the poly (which dulls the shine) inhibited adhesion to the tape so I advise DON'T USE IT!

Anyway, (due to the poor adhesion) I was afraid the dots were not going to provide enough adhering surface to hold the stators together so I opted for two 3/8" wide vertical strip spacers 3.5" apart and I sanded and solvent cleaned the stator topcoat at those locations; which seemed to improve the adhesion somewhat and the finished panel looks ok.

LESSON LEARNED: Spring for powder coating :-)


moray james 23rd June 2008 04:27 AM

so you know...
high gloss coatings have the most solid content in them so will provide greater dielectric insulatiom. 3M acrylic tapes require a couple of things to work well and to achieve full strength. They are heat and pressure. Get and keep your panels warm and get some weight on the joints. Does not matter how you go about doing either just so you do.

Legis 2nd July 2012 01:25 PM

I went and bought 300 of these things: 3M™ Bumpon™ Protective Products-Shop 3M

Will be trying them on curved stators ("here goes nothing"). Anybody tried dot spacers with curved, is it doable? I planned also to put a M3 nylon screw through each dot so I can compress the stators together (reduce d/s from 3,6mm to 3mm) and make a very nonresonant sandwitch out of them.

Added capacitance should be very small as the area the dots take up is only 10% of the horizontal spacer strips. I also wonder if I get more sensitivity and one very low fundamental frequency as the membrane moves much like one big area.

Legis 2nd July 2012 03:23 PM

First step, making holes (for the nylon screws) to the polyurethane dots with leather hole punch tool:

I might get to membraining tomorrow or the day after that. I will practice first with 12Ám mylar to see if I can make them work in the first place.

tyu 2nd July 2012 03:33 PM

Thanks.. keep the info coming.....goodluck

MJ Dijkstra 2nd July 2012 06:32 PM


The thing I liked very much about silicone dots is:

- you can always add some additional dots if the effect is not enough
- you don't have to worry about the thickness of the dots very much as it settles between the mylar and stator on itself
- you can put them on one side of the mylar only (at the back-side of the esl usually)
-silicone dots have good insulating properties
-they stick well to (clean) mylar
-they can easily be removed (you need to replace the mylar though)

About your curved esl; If the dots are replacing the horizontal curved spacers, than I doubt if these dots are good enough to support the curved shape of the mylar.

Legis 4th July 2012 06:03 PM

Dot system did not work. The membrane got ~1,5mm away from the rear staor between each square. At least I tried:D. Will be going for horizontal spacers, they worked nice, i already made a test hack.

(Aluminum membrane is just for testing, I have it plenty around.)

harry_at 4th July 2012 06:41 PM

Some food for thought regarding vertical acrylic spacers, where the width of each section follows an exponential relationship, in this (long) building thread.

Also with measurements here and here.


Legis 4th July 2012 07:01 PM


Originally Posted by harry_at (
Some food for thought regarding vertical acrylic spacers, where the width of each section follows an exponential relationship, in this (long) building thread.

Also with measurements here and here.


Hi, I actually own those very speakers (is it not obvious from the pictures :D;)).

I will be changin to horizontal spacers because vertical spacing is also problematic due the same reason that the membrane gets closer to back stator in center of each segment. The widest segment is/was 11-12cm wide and the membrane got only ~1-1,5mm away from rear stator. Because of this I got air conduction in that spot when I boosted the bias to >4kV. It would not pay off increasing the number of vertical segments, the radiating area gets smaller, SPL is lost and capacitance increases.

Horizontal spacers keep the distance better equal between the stators and they take less area compared to vertical. I also think that the segment size with horizontal spacers is better regarding the standing waves of the membrane and the fundamental resonance - narrow and long segments resonate longer than more square-like...

I drew this comparison couple of days ago which I ment to post here:

I will be using actually only 10 horizontal strips that reduces their area to ~460cm2, which is still ~41% smaller than the vertical spacing. The layout is also incorrect, I will place the biggest segments on the bottom to get the floor boost to the lowest fundamentals.

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