ESL Capacitance calculation
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 15th September 2007, 06:52 PM #1 SkySeeker   diyAudio Member   Join Date: Aug 2007 ESL Capacitance calculation The formula for the capacitance of an ESL is given by: C = (8.85E-12 x A) / d Where C is in Farads, A in square meters and d in meters. My question is, what should "d" be? The D/S spacing? but the diaphragm is at constant charge. The audio signal is applied to the stators. Thus should not "d" be the distance between the stators? The books I have seen use D/S, but that seems wrong to me. Is there an explanation why D/S should be used?
 16th September 2007, 07:58 PM #2 ak_47_boy   diyAudio Member   Join Date: Sep 2006 An ESL is a very complex load, i think that formula is just a good approximation. Capacitance increases with area and decreases with spacing. But the spacing is always changing during operation. Edit: There would be stator/stator capacitance also but it would be small and most likely insignificant.
 17th September 2007, 08:22 PM #3 Calvin   diyAudio Member     Join Date: Nov 2004 Location: close to Basel Hi, basically it dosen´t matter which distance You choose! The formula gives an idea about the capacitance value under nosignal conditions. In a symmetrical ESL the distance between stator-stator is twice the distance stator-membrane. The capacitance between stator-stator is one half of that of stator-membrane. This is equal to a series connection of two identical caps....the value is halved. But since the diapgragm is usually coated with a high ohmic value material, it is difficult to measure the stator-diaphragm capacitance. The low-impedance stators You can easily measure. This value is more interesting because it is the one that the amplifier sees (through the transformer). jauu Calvin
 18th September 2007, 08:49 AM #4 SkySeeker   diyAudio Member   Join Date: Aug 2007 > The low-impedance stators You can easily measure. > This value is more interesting because it is the one > that the amplifier sees (through the transformer). Exactly, that is why I was surprised to see the D/S capacitance used in the books. (Sanders, Wagner, Fikier) Have you ever compared the measured and calculated capacitances of your speakers?
 19th September 2007, 03:59 PM #5 Calvin   diyAudio Member     Join Date: Nov 2004 Location: close to Basel Hi, Yes,odf course For the sheet metal stators I use the st-st-capacitance is nearly the same as calculated. jauu Calvin

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