[Muamp]

@Hi-Fi-Apricity
cnc 3020 is very popular. I have one and can highly recommend it.
You can buy one from many suppliers on ebay.
Easy to use, high quality and good value for money.

 

[lkos98]

I started by recoating only one channel (the other channel still had the coating you did for me ), which allowed me to compare the loudness of each coating to a reference. Diluting the coating to increase resistivity is something that has been discussed a fair bit on diyaudio, so I figured that it was worth a try.

Thanks for sharing your experience in coating.
I agree with Chinsetawong though - when you dilute, the resistance increases as you said, because after it dries completely, there is less conduction substance, but the loudness should decrease, because of the charge losses in membrane, cables, etc. Otherwise with no coating at all, you should have highest loudness . If you have higher loudness with diluted coating, it means the coating is not completely dry, as the water has lower resistivity than the floor cleaner.
I also tried floor cleaner and it's working good, but I don't dilute it, the one I use is quite liquid anyway. For me still anti static 100 gives better loudness.

 

[chinsettawong]

I like to think the diaphragm like a battery. When you have high resistance on it, it takes longer time to charge up and also longer time to bleed out. With two different resistances on two different diaphragms, given enough time to charge up, both diaphragms should have the same bias voltage eventually. That’s why I don’t think one can be louder than the other if nothing else is wrong.

 

[statfi]

That’s why I don’t think one can be louder than the other if nothing else is wrong.

Might there be a difference in mass that could lead to a difference?

 

[chinsettawong]

Do you mean the mass from the coating? Wow. That difference should be very, very little and I don’t think it should make the difference.

 

[Tachikoma]

Thanks for sharing your experience in coating.
I agree with Chinsetawong though - when you dilute, the resistance increases as you said, because after it dries completely, there is less conduction substance, but the loudness should decrease, because of the charge losses in membrane, cables, etc. Otherwise with no coating at all, you should have highest loudness . If you have higher loudness with diluted coating, it means the coating is not completely dry, as the water has lower resistivity than the floor cleaner.
I also tried floor cleaner and it's working good, but I don't dilute it, the one I use is quite liquid anyway. For me still anti static 100 gives better loudness.

My personal theory is that if the resistivity is too low, the voltage across the membrane will be significantly less than 580V, since V1/R1 = V2/R2 and the ballast resistor itself is 5 mega ohm. It is also known that most voltmeters won't see 580V (more like ~350V with a typical 10 mega ohm voltmeter) when you measure the bias at the output, since their impedance isn't high enough to see all 580V of the bias.

Obviously if resistivity is too high there won't be any sound either, so there is an ideal value somewhere between infinite resistivity and too little resistivity. I think someone mentioned that Stax membranes have a resistivity around 10^9 ohms per square... meter?

I generally find that recoated membranes are less sensitive than those with the original Stax coating. Case in point, I have a pair of headphones where the right channel has the original coating, and the left channel, my floor cleaner coating. I have to decrease the volume on the right channel by 20% to balance the channels, and the balance does not change over time.

 

[chinsettawong]

We might have different experiences, @Tachikoma.

I have fixed a few pairs of headphones which have imbalanced sound. I only had to recoat one of the diaphragm and the headphones come back to be balanced again.

 

[VandyMan]

I wonder if very small amounts of water are getting trapped between the coating and the membrane throwing everything off. I'm not convinced that all the water would evaporate off.

 

[lkos98]

@chinsettawong That is correct, they should sound equally, if we consider there are no losses at all. Unfortunately there is parasitic resistance between membrane and stator/cup/ring (even surrounding air), between cables etc. It's extremely high, that's why we are "allowed" to use very high resistance for coating - Gohms. But once the coating resistance becomes closer to this parasitic resistance, the membrane will charge less. Less charge - lower electrostatic force - lower spl.
@Tachikoma - I'm sorry - I did not fully understand R1 and R2. The voltage on the membrane is a simple voltage divider if you meant this. But membrane itself is not part of this divider, it's not connected to the bias from one side and to the ground at the other. It's in fact a resistor, one end of which is connected to the bias and the other - nowhere - there is no current flowing through it. Yes - if you connect a voltmeter, you actually make a divider 5MOhm - 10Mohm (the voltmeter resistance), but the membrane is connected to the middle point only, so it has no influence at all. Try to connect one side of the membrane to the bias, a voltmeter at the other and ground - you will measure 0V. But if the membrane is aluminium foil and you do the same - then you will measure your 580*10/(10+5) = 386V.
Anyway the most important thing here - we don't care about the voltage on the membrane, but of it's charge. Bias voltage is there to create this charge. And the charge must be constant. "The Electrostatic loudspeaker cookbook" by Roger Sanders explains all this very well. We don't want low resistance coating, because the electrostatic charge is moving fast to the closest point between membrane and stator and creates uneven charge (hence e-force) across the surface, therefor - distortion. For the voltage, it does not matter low or high resistance - it will be one and the same - the bias voltage everywhere on the membrane.
Otherwise low resistance membrane sound louder with my experience. I have tried many types - aluminium foil sounds loudest, ink ribbon (100KOhm) - louder, graphite coating less louder and so on. Anti Static 100 sounds definitely louder than floor cleaner with the same phones and bias. I guess this has something to do with the same charge movement - creates higher force at one spot. This concentrated force moves the whole membrane as is the coil in a dynamic speaker - it moves the whole cone.

 

[Tachikoma]

Erm, voltage is the difference in charge between two points, so yes, we do care about voltage on the membrane. Why would we bother with the exact numerical value of the bias voltage otherwise?

I know the KSE1500 seems to use aluminium foil, but anyway, I will stand by my observation that diluting the coating actually made the driver louder. I doubt that its because of the residual water content, because the sensitivity has been stable over 3 days already.

Also, coating the drivers with multiple layers of undiluted floor cleaner (coat, dry, then coat again) did not make it any louder, despite the addition of conductive substances to the membrane.

It is possible that resistivity has nothing to do with this (perhaps the uniformity of the coating matters more, or there is a chemistry-related reason as to why my floor cleaner works better when diluted), I can live with my hypothesis being wrong. In any case, I don't think the coating is a straightforward issue at all - the ESL diaphragm coating thread on DIYaudio is 120 pages long for a reason.

 

[lkos98]

@Tachikoma Of course bias voltage matters as it's related to the charge. Higher voltage - higher charge and this charge is moving the membrane.
I just wanted to simplify things in ideal world. But membrane resistance is of course also part of the voltage divider mention above, there is some current flowing through it as well, because of the parasitic resistance and capacitance. Membrane itself is part of mechanical resonance and so on - it's quite complicated.
I never wanted to argue about you coating method or your coating material, actually I congratulate you on trying and sharing this with us. I just don't agree with the statement that higher resistance would give a louder sound. For me, your diluted floor cleaner has a lower resistance or for some reason, or may be there is something else involved.
Anyway it doesn't matter much, what is important here is how you like it. If you are happy with the sound - that's great!

 

[chinsettawong]

@Tachikoma, would you kindly share with us the floor cleaner that you use? A picture would be nice.

 

[lkos98]

@Tachikoma, Also I would like to ask you if it's not much of a hustle. Can you try the same solution with a distilled water? May be some salts or minerals in the water are mixed (or react) with the cleaner and stay there even after drying. Do you think this could be a reason?
By the way I'm thinking of a method to measure the resistance with a standard voltmeter. I will connect the membrane in one point (may be with a coin) to a high voltage source for example the bias resistor. At the further side connect the voltmeter and measure. With 10GOhm resistance it should give about 500mV ( 500V*10*1e6/(10*1e^9). I know it's not going to be very accurate, but at least it will give us some numbers to work with.

 

[Tachikoma]

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.

 

[VandyMan]

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

In the US, most supermarkets sell distilled water. I assume that is true elsewhere since people use it for ironing clothes and such.