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ESL Diaphragm material, Anyone tried different?
ESL Diaphragm material, Anyone tried different?
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Old 24th December 2017, 12:14 AM   #11
geraldfryjr is offline geraldfryjr  United States
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Originally Posted by MrMagic View Post
@Alastair E
Until someone else that has actually tried different thicknesses for ESLs responds, I can only say that I would take the following into account:

1. The mass of the air that is moved, is usually much heavier than the mass of the film itself.
2. Still, in high frequencies the less mass, the better.
Obviously a thinner film will have a higher frequency response -whether that would be significant or not, I can't say.
3. The resonance will also be higher and weaker.
4. A thinner film will transfer less vibrations to the frame due to less stretching force, more elasticity and resistance.
5. A thinner film will be more vulnerable to sparks that create tiny holes -that depends on the voltage, I haven't seen any holes to the wrap film at 1KV.
This has been discussed, DIY'er Bolserts has shown some graphs of the high end roll off due to various mylar thicknesses.
Sorry I don't have that link handy, as i don't remember the Key words to find it.


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Old 24th December 2017, 08:11 AM   #12
Calvin is offline Calvin  Germany
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Old 24th December 2017, 07:07 PM   #13
golfnut is offline golfnut  New Zealand
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Its complicated

In principle, to understand the overall behaviour of the ESL you should consider the stators, membrane, dustcovers, and grills together.

However, the the membrane thickness does have a fairly simple overall effect very much like a low-pass filter. The cutoff frequency of the low-pass response is about 97 kHz divided by the membrane thickness in microns.


3.5 um mylar has a cutoff frequency of about 28 kHz.

20 um mylar has a cutoff frequency of about 5 kHz.

3.5 um mylar membrane with two 2 um dustcovers on the outside of the ESL gives an overall response much like an ESL with a 7.5 um membrane and a cutoff frequency of about 12 kHz.

To these thicknesses must be added a micron or two for the high resistivity coating - depends what coating you use - Licron is a micron or two.

So you should use

(i) the thinnest practical mylar for the dustcovers.

(ii) < 5 um for high frequency sections

(iii) May use 20 um for bass sections.

When multiple layers of mylar are involved, the response is much more complicated than a low-pass filter due to reflections between the different membranes, but the overall trend is low pass as described.

If the designer has done the job properly, all of these effects and the transformer resonance will have been considered. Pays not to fiddle unless you have an idea of the likely effect of any changes.

“Nothing is more practical than a good theory.”
– Ludwig Boltzmann
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Old 31st December 2017, 09:53 PM   #14
hpeter is offline hpeter  Slovakia
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BLOG. XMOS_U8/PCM5102A > LL1544A > 6H1Pi+µfoll > 2A3_SOV/JJ > LL1660 > STAX SR207 _ SR L300 _ SR007 # LL2748 > 394A > LC 12H/1000µ
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Old 6th January 2018, 06:13 PM   #15
bolserst is offline bolserst  United States
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Originally Posted by geraldfryjr View Post
This has been discussed, DIY'er Bolserts has shown some graphs of the high end roll off due to various mylar thicknesses.
Measurements .vs. theory were posted here for 3 different thicknesses of mylar:
Electrostatic speakers as microphones?

Measurements showing mass added by Licron Crystal coating posted here:
David Lucas ESL

As golfnut already mentioned, once you start adding stators and dustcovers the high frequency behavior gets much more complicated. But, the general trend will always be influenced by the roll-off from diaphragm mass.

Note that the small difference in constant value(93.4kHz .vs. 97kHz) used in my formula and golfnut's(Post#13) is due to the change in speed of sound and air density with temperature. My formula used room temperature values, golfnut's formula uses temp ~ 0degC.

Last edited by bolserst; 6th January 2018 at 06:15 PM.
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Old 16th January 2018, 02:17 PM   #16
esl 63 is offline esl 63
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Warmbier Ecostat is a 2 component polyurethane coating... seems quite interesting.
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