24.13.232.33
In Reply to: RE: Attn: andy_c re: electrostat impedance curves posted by E-Stat on May 04, 2009 at 14:30:06
Hi
I'm not Andy but i have made many electrostatic speakers back in the old days.
For a one way electrostatic system, one would expect the bell curve you mention.
At the low end, the impedance droops because of the step up transformers parallel inductance (same thing as in a tube amplifier typically).
Up high, the impedance falls because of the parallel C the speaker presents as a load. In the mid of the curve, the resistive component dominates, made from the Rdc of the transformer primary, secondary and other resistances.
Essentially the driver itself is a C with very little else but since you need a large step up ratio to get an acceptable voltage sensitivity, you end up seeing the transformer in line too.
Then, if you make it a two way system with a crossover, then you have two such systems and the effects of the crossover etc.
Basically, it doesn't matter what the impedance is as long as it is higher than than the minimum load the amplifier will tolerate.
This can be more of an issue with ESS speakers because the capacitive reactive load draws the most current up high and the current phase angle leads the voltage, both of which are "different" than electrodynamic speakers and makes it a more difficult load.
An up side however is that the pressure produced is in phase with the voltage (unlike a direct radiator) and so the ESS, like a proper horn, can preserve the input waveshape, that is a square wave in produces a square wave coming out. For the most part, direct radiators do not preserve the input waveshape, they spread the signal out in time too much.
What matters too is that audio systems are a Voltage based reference and not a power based reference. Frequently you see people concerned with the impedance curve.
If the system is flat with a fixed voltage drive, then it is like the recording process where X pressure equals X voltage.
Best,
Tom
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