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My DIY electrostatic headphones
Oct 25, 2019 at 3:38 AM Post #3,587 of 4,061
@legopart
I used perforated steel similar to this on my very first test panel.
It is okay, no way near as good as FR4, but worked fine although cutting it to size is not so easy.
Perforated steel is more suited to large ESL speaker panels.
 
Oct 25, 2019 at 5:58 AM Post #3,588 of 4,061
Tachikoma said:
Have you seen this? ("Measuring surface resistance of the coating" at the bottom of the page) https://wireesl.weebly.com/conductive-coating.html

The floor cleaner:
https://imgur.com/exgBEp8
https://imgur.com/kuzE68Q

I have a membrane-based water purifier, but I don't think it can produce proper distilled water.

If my tap water has a conductivity of 800 uS/cm (https://sensorex.com/blog/2017/07/12/conductivity-monitoring-reverse-osmosis/), its resistivity would be 1250 ohm cm, which gives a resistivity of 125 mega ohms/sq for a 0.1 micron layer of water. I have no idea how that would change as the water evaporates, though.
Click to expand...
Yes, I have seen this, but with 9V battery it would give about 9mv with 10Gohm resistance, which is in the lower range of the standard voltmeters and there will be noise and induced EMF. With 500V we are close to the "natural" for the membrane voltage that we use for biasing. The 9V should work fine for lower resistance of less then 1GOhm.
Thanks for the pictures as well, Mr. Muscle is well known. I may try to coat some leftovers of the mylar I use and see what the measurements will show.
Not sure the water purifier can remove the dissolved salts and minerals, although it's reverse osmosis. For sure it's not producing distilled water.
 
Oct 27, 2019 at 12:53 AM Post #3,589 of 4,061
Theoretic question,
Will this schematic work to decrees the bias voltage if needed?
I though about it today
krpKiRQ.png

*something like R of 150Kohm 600v

can it work?
 
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Oct 27, 2019 at 6:36 AM Post #3,590 of 4,061
Yes it should, and by varying R4 and R3 you can regulate the bias But it's not that simple. The total resistance of R4+R3 should be such as not to load the bias which is usually made with voltage multiplier, that can't hold a high load. So 600V/150k = 4mA, which is too much, not talking about that the resistors must be of 2.5W and more. You should make this with at least 2-3MOhm total resistance.
 
Oct 27, 2019 at 6:48 AM Post #3,591 of 4,061
Yesterday I measured different coating resistance. I put some coating and measured with 2 coins separated 5mm from each other and applied 300V to one and measured on the other.
Floor cleaner not diluted - 4.2V - 7GOhm, Floor cleaner diluted about 1:1 - 3.3 - 9GOhm, and Antistatic 100 - 5.8V - 5GOhm.
The results were not consistent, for example Antistatic 100 gave a very high and unstable resistance at one side of the mylar and normal at the other, unlike the floor cleaner which was more or less the same on both sides. Diluted (with tap water) floor cleaner also gave similar results on both sides.
As expected - diluted floor cleaner was with higher resistance. No coating could not be measured at all.
What I liked about the floor cleaner - it was giving pretty stable readings - especially the diluted one - so I may try it next time on my phones - thanks for the hint Tachikoma.
 
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Oct 27, 2019 at 9:11 AM Post #3,594 of 4,061
chinsettawong said:
@lkos98, what brand of floor cleaner do you use?

Thanks guys for your infos. These infos will be very useful for the newbies
Click to expand...

I used what I have at home - Cobra tile cleaner. I guess most of the floor cleaners would give similar results, except maybe for carpet cleaner, which I think has some anti-static components inside. The essence they put (mine got apple) may also affect, but not much I think.
Please note, these measurements are not accurate and should not be used for reference, because:
1. The coated area was not exactly the same for the three coatings.
2. The distance between coins was not exactly the same - I used a simple ruler.
3. The coating might not be evenly applied.
4. The resistance is not only the short line between the coins - it includes all the resistances around coins added in parallel (that's why it's given usually as Ohm/square).

To make a relatively accurate measurement, it should be done I think, on the membrane glued to the spacer and cut, so the coated area is always the same. The voltage should be applied to the spacer ring as we do with the bias and the measurement taken from a coin placed at the center.
The bias resistor is not of a big importance (unless you use low resistance coating - in such case it must be included in the calculations), because it's value is low compared to the membrane resistance. I'm not sure, but the position of the coin exactly in the center should not affect the measurement much (all resistors between the coin circumference and ring are in parallel).
 
Oct 27, 2019 at 4:20 PM Post #3,596 of 4,061
Is it good to store ESH with SILICA GEL ?
silica-gel-500x500.jpg


I heard that it can protect electronics when it storage for long time.
but I heard that too dry area could damage the electrostatic headphones and make them loss the coating on the membrane.

What do you think about that?
 
Oct 29, 2019 at 1:29 PM Post #3,597 of 4,061
lkos98 said:
Yesterday I measured different coating resistance. I put some coating and measured with 2 coins separated 5mm from each other and applied 300V to one and measured on the other.
Floor cleaner not diluted - 4.2V - 7GOhm, Floor cleaner diluted about 1:1 - 3.3 - 9GOhm, and Antistatic 100 - 5.8V - 5GOhm.
The results were not consistent, for example Antistatic 100 gave a very high and unstable resistance at one side of the mylar and normal at the other, unlike the floor cleaner which was more or less the same on both sides. Diluted (with tap water) floor cleaner also gave similar results on both sides.
As expected - diluted floor cleaner was with higher resistance. No coating could not be measured at all.
What I liked about the floor cleaner - it was giving pretty stable readings - especially the diluted one - so I may try it next time on my phones - thanks for the hint Tachikoma.
Click to expand...

Have you opened up a pair of Stax headphones to measure the resistance on their coatings? :p Would not recommend this unless you don't mind the damage.

I just recoated another pair of headphones, this time using a 1:4 dilution (1 part floor cleaner to 4 parts water). The 1:4 coating seems to be a significant improvement over 1:1 - I finally have a balanced pair of headphones. I only recoated the left channel without touching the stock Stax coating on the right channel to make this comparison.
 
Oct 29, 2019 at 2:27 PM Post #3,598 of 4,061
@Tachikoma
Well, if I had one, I might have tried :ksc75smile: . In any case I'm trying to make my own, not to repair a broken one.
So what is your opinion - the coating of your Stax has wiped away or they just use a higher resistance coating? Why don't you measure it, compare with the 1:4 solution and share the results? I'm sure most people in this thread would like to know what would be a "recommended" resistance to use.
 
Oct 29, 2019 at 2:51 PM Post #3,599 of 4,061
honestly, in my experience the resistivity of the diaphragm makes little difference. the requirements are (imho).

the resistance must be low enough to allow the diaphram to charge up in a reasonable time (a few seconds)

it must be low enough such that the diaphragm remains charged (i.e. the resistance must be significantly lower than the leakage resistance to the stators.

finally the resistance must be high enough to prevent the charge migrating across the surface as the diaphragm moves.

this last one is very important, charge migration makes the driver very non-linear, read harmonic distortion.

imagine the diaphragm being driven by 1 hz, it will dome towards one stator and then the other. as the middle of the diaphragm in now nearer the stator the electric field to the stator is higher and the charge will move to the middle of the diaphragm; this would mean the field across the gap would vary based on displacement. only the very low conductivity of the coating stops this happening.

-Steve
 
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