Dropping efficiency coating ?

[WrineX]

Hi i have the following problem. i made a small test element to use as tweeter.
but after apllying coating. a transparant glue waterbased from the company HEMA. i dont know if it is exactly the same as the velpon used by so many but it does work. only down side i noticed is this.

after aplying and when its dry i assemble the element en give it a go, pretty high efficiency and after a while it drops. first the membrane only needed half the voltage to be sucked to one stator after an hour i needed the full 4500 volt, and it wont stuck to membrane. and this is a picture of what happens tot the output, first reading (blue) is a reading after 2 hours on full voltage because output dropped to much already. second reading is green and measured after 3.5 hours last but not least, well it is least but ok (red) after 10 hours, its almost to soft to make a decent measurement.

any ideas ?? looks like when its still is a bit wet it works like a charm but fails after it completly dries. or something

[chinsettawong]

Hi WrineX,

Do you keep your diaphragm charged at all the time, or do you charge and measure?

Wachara C.

[WrineX]

its been charged ever since. gone try dif glue today and post results

[Few]

Have you tried inserting a small neon indicator lamp in series with the diaphragm charging circuit so you can monitor the charging rate of the diaphragm? (Faster blinking means a larger charging current.) Perhaps the charge is migrating off your diaphragm via a path that is, for some reason, growing more conductive with time.
Few

[WrineX]

yeha have one, but not blinking verry often, also when the glue alcohol solution is still fresh i works like a charm after it completly dries out its going down the drane. going to get me some real velpon glue and test again maybe more thinner layers willl do the trick. or aybe the glue has diferent mixture of ingredients

[arend-jan]

Calvin suggests adding a couple of drops of black ink to the glue to raise the conductivity (IIRC).

[Capaciti]

Take a breath and aspirate onto the membrane. If efficiency raise up, your coating just works with a certain kind of humidity layer (as most DIY coatings do).

Capaciti

[WrineX]

hmm nice info. by the way wich kind of ink ? suppose the one with carbon black , but i also posted a thread about that where to find stuff with carbon black in it to include in the mix exactly what you say. im really curious if that might do the trick. because just ink is like uh there are 3000 sorts of inks

[Capaciti]

Hi,

i am wondering people telling you about just using some black ink to dope. There is no carbon black in black ink used for writing !! I measured several types of black ink, and never were able to measure some conductivity.

Possibly people dope for having a "good feeling" , but nobody here has proven, means provided measurement readings of black ink.

Folks, before going on suggesting any black ink, tell us about the specific brand, for which you were able to confirm conductivity !

BTW: You can try out different kind of PVA glue. All of them need humidity to work. It depends on the final surface roughness how much water molecules are attracted by the PVA-Layer. Possibly there are types of PVA glue which provide an appropriate layer to attract enough Water, while others dont do. PVA is not conductive.

Capaciti

[WrineX]

yeah thats the question really but i did a little test yesterday with ink from my printer refill kit in combination with the velpon stuff, although i could not measure it the way the mebrane sucked to one stator does say me there is something different with this mix compared to the glue and water only formula. blinking light whas going beserk.