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Old 17th October 2012, 03:05 PM   #21
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here are a two links that will help you,

Parallel Plate Capacitor Capacitance Calculator

Electronics 2000 | Reactance Calculator

Once you determine your capacitance then you must add that to the transformers capacitance and use that value to find the capacitance reactance (at 20khz) and divide that by the turns ratio squared and then you will have the impedance presented to the amplifier.

jer
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Old 17th October 2012, 03:28 PM   #22
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Hi Gerald,

Thanks - but how do I know how loud it'll play with a given voltage? I'm currently designing the headphone amplifier and it would be feasible to know if I can expect to output 1 mA or 50 mA to reach a moderately high SPL ... I actually don't know ...

BTW, there won't be a transformer on the output of the headphone amplifier. It's a single-ended transistor circuit where one of the stators are grounded.

A smile for you as well

Jesper
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Old 17th October 2012, 03:44 PM   #23
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Here is another great calculator that can help you,

Electrostatic Loudspeaker (ESL) Simulator

50V!?

Have you tried driving your panel with that?

I am thinking that you will need at least 4 times that to get a decent output.

I used a 500v bias an my micro driver and it had about .032" D/S.

jer

Last edited by geraldfryjr; 17th October 2012 at 03:48 PM.
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Old 17th October 2012, 03:53 PM   #24
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Here are some pictures of my micro driver.

jer
Attached Images
File Type: jpg Credit Card ESL 1.JPG (37.7 KB, 109 views)
File Type: jpg Credit Card ESL 2.JPG (38.5 KB, 115 views)
File Type: jpg ripples.jpg (30.6 KB, 82 views)
File Type: jpg sandwhich.jpg (18.0 KB, 82 views)
File Type: jpg stator-closeup1.jpg (29.3 KB, 81 views)
File Type: jpg the set.JPG (65.0 KB, 42 views)
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Old 18th October 2012, 03:51 PM   #25
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Quote:
Originally Posted by gentlevoice View Post
Hi again,

Still in the process of doing the headphones as a question came up which I hope one of you may just know about:

Suppose I design the electrostatic headphone to have spacers of 0.6 mm between the membrane and the stators and a membrane area of about 50 cm2 do you know what the current requirements for the headphone amp will be (I don't play loud and aim at a 50 Vpp maximum output level)?

Regards from autumn Denmark,

Jesper

Hi Gentlevoice,

There is no way that 50Vpp is going to be enough. With a +/-300Vpp on my amp, my headphones with 0.6 mm spacers are just barely loud enough.

How high bias voltage are you aiming at? I use 580V like Stax.

Wachara C.
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Old 18th October 2012, 04:32 PM   #26
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Hey Gerald,

Thanks again - looks very ingenious what you are making ;-) Is it a credit card you use for the membrane frame ....?

I've made some calculations using the simulator you posted a link to and the max SPL with 0.4 mm spacers and 100V RMS is about 92 dBs with some rise in the higher frequencies. I don't listen to music at very high levels so I would say that this is sufficient.

Also, given that I don't listen at high SPLs I reckon it's not necessary to have a thicker spacer than 0.4 mm (?) - that would also help on max SPLs with a somewhat lower output voltage. Maybe the spacer can even be thinner ...?

FYI I've attached the simulation values I've entered. Interestingly, the closer my ear is to the stator, the more linear the headphone seems to become....

Can I ask you what your simulation figures are?

Greetings from Denmark,

Jesper
Attached Images
File Type: jpg diyaudio_ESL_SPL_sim.jpg (165.1 KB, 38 views)
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Old 18th October 2012, 08:11 PM   #27
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Yes I used some Gift Card credit cards for the frame.
The diaphragm size is 59mm X 44mm and the D/S is .0325"
The diaphragm material is some .1 mil mylar that I got from Chemplex Cat.No: 100 .
I also have some .06mil stuff from them as well but i haven't tried it yet, Chemplex Cat.No: 090 .
For the coating I used Licron this was before I had gotten the Crystal formula which is more clear and much much thinner than the regular Licron.

I ran about a 500v bias on it from a tube amp chassis that I had laying around and I used the transformer in it to drive it as well.
I don't know off hand what the turns ratio was but it was a OPT for a pair of EL34's.
I didn't mess with it for very long and I only made the one.
I ended up taking it apart for the pictures But I still have it and it can be reassembled at anytime.

The sound was very good and clean and it got to a nice comfortable volume.
I didn't have a SPL meter at the time.
I was amazed that when there was bass there was bass and was not boomy at all.
At first I thought that it lacked some high end but it was the Youtube video I was listening to that was poor in quality.
I had found other material that was much better and I had not noticed this before until I was listening to this driver.
Getting back into this hobby after 7 years it was the first driver I had running and then I finally got my little ESL panels going about a month later.

Yes when you are right on the diaphragm it will have a flat response.
As you back away from it you will get a rising response at about 6db per octave.
This true for any dipole driver.
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Old 19th October 2012, 07:31 AM   #28
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Hi both :-)

@Wachara: Good to hear from you again, Wachara. Hmmm... 300 Vpp is much higher than I hoped to use - but when entering the difference between 0.6 mm D/S spacing and 0.4 mm spacing in the quadesl simulator it's actually more or less the same as doubling the voltage in terms of the SPL output. So I think I'll try with ~100Vpp and then reducing the D/S distance. If it doesn't play very loud I know what could be the issue .... I also use a 0.9 um membrane so probably that also helps in terms of increasing SPL?

@Gerald: Thanks for elaborating ;-) I don't know what the materials you used are composed of (you might look at my signature ;-)) but in Wachara's thread on ESL headphone design he - or one of the other posters - mentions using normal wood glue (if I remember correctly) for membrane covering. However, I still need to try this out because it seems that the membrane I use already builds up static electricity on its own so maybe it's not needed to cover it .... will have to experiment with that. Back to building ...

Thanks again both of you for replying,

Jesper
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Old 19th October 2012, 10:04 AM   #29
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The diaphragm thickness has no bearing on how loud they will play as this is strictly a function of the operating voltages and the D/S.
Every time you double the D/S you have to increase you voltages by 4 in order to have the same SPL.
The other trade off is How much excursion room you need for the bass frequency's as for every octave lower the excursion increases 4 times for the same SPL.

I have not tried the PVA glue trick yet But I hear it works well and I will be using it on my next build to see how well it works.
I did do some simple test with it a while back but never used it on a Diaphragm as of yet.

Here are some links to that discussion,

ESL Diaphragm coating

ESL Diaphragm coating

ESL Diaphragm coating

The materials I used are just plastics, PCB material,aluminium duct tape, clear acrylic enamel as a stater insulation and Licron from Techspray as the diaphragm coating.
Also, I used double sided transparent tape to mount the Diaphragm to the frame.

jer

Last edited by geraldfryjr; 19th October 2012 at 10:24 AM.
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Old 20th October 2012, 01:46 PM   #30
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Just for you know, I stop using PVA glue as the coating material. The glue is very humidity sensitive. It can attract too much moisture from the air and cause all kinds of problem.

Wachara C.
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