Friday, January 11, 2008

DIY Electrostatic Loudspeakers / ESLs - The Diaphragm Conductive Coating

In this step of my build I, make the diaphragms conductive. This is a relatively simple task. But firstly I had to carefully clean the diaphragms with methylated spirit. I did not have any lying around so I used medical grade alcohol swabs. A quick and thorough wipe with the swab followed by a wipe with some dry tissue did the trick. The swabbed, cleaned and dried diaphragms are now ready for the application of the conductive coating. See how clear and reflective they are...All panels swabbed and dried.Here is a picture of the bottle of conductive coating and the utensils for the job, a small plastic cup, a foam applicator and a syringe to measure the amount of fluid to be used.Specific amounts are used to coat each panel. This helps ensures the correct coating density for each panel. No guesswork here.Using the foam applicator, I carefully apply the conductive coating onto the diaphragm. I apply until all the liquid measured for the diaphragm is completely used up. This takes a little practice to get right.Here is a view of the coated treble diaphragm once it has dried. At this stage I started getting the feeling that the coating was a bit thick, more on this later.Here is a view of one of the Full Range Panels. Although it has dried, it would take from a couple of days to a few weeks for the conductive coating to cure. Again looking at the panels, I had a sneaky feeling that the coating was too thick.Next, I put the front and rear halves of the one complete panel together. The front half of the panel is made up of the support structure, the stator and a tensioned conductive diaphragm. The rear half of the panel is made up of the support structure, the stator and a strip of copper foil that will pass high voltage polarising charge to the diaphragm. This foil will come into contact with the conductive side of the diaphragm when they are sandwiched together. I place the 2 completed halves, front and rear together. I do a final check to ensure everything is in order before I marry the halves together. Notice the foil and the diaphragm will come into contact when they are sandwiched together.Carefully, the 2 halves are placed together. I ensure that they are correctly oriented. Then I bring out the plastic channels that will be used to clamp the halves together. A channel is required for each side of the panel. So its 4 channels per panel.Here's a partially clamped panel.Remember that I had this niggling feeling that the conductive coating applied earlier was a little too thick and did not go on as consistently as I would have expected. A quick check revealed that it was indeed too thick. Rob from ER Audio, said that this will lead to a degradation of the Bass. As such I must reapply the conductive coating again. The conductive coating must be diluted with distilled water. It’s my own fault really for not reading the instructions more thoroughly. But before I can apply the correctly diluted coating, I will have to strip the old conductive coating off. I was worried that I may damage the diaphragm and then have to start from scratch. But as it turned out the process of stripping is really very easy. The conductive coating is a water based acrylic, as such I needed an acrylic solvent to strip it off. Acetone was the best choice. All the local hardware stores do not carry Acetone. But I got lucky and found a can at Ace Hardware. I wet some tissue generously with acetone and begin wiping the conductive coating off the diaphragm. The stripping is actually very easy... just be generous with the acetone and tissue. Here is a diaphragm that I have completely stripped. I also clean the diaphragm with the medical grade alcohol swab. Incidentally, after the acetone and isopropyl cleaning, the diaphragm did not look any worse for wear. See for youself...I then mix up a batch of conductive coating, diluted to the correct coating density. Here is a picture of the correctly coated diaphragm.When viewed directly from above, the diaphragm is clear, but when viewed at an angle it has a bluish haze. This is exactly the outcome that I was expecting from my conversations with the designer.The entire process of stripping and re-applying the coating probably took about 2 hours. I am getting really good at this. Well the panel build is finished. I am finally able to clamp all the halves together.Here is a picture of the 6 panels, all finished.And another closer look at the 3 panels that make up one side of the speaker.Next I Install the Electronics and Listen to the panels for the first time.

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