Could you advice how to connect speaker transformer to single ended ESL made of charged foil (electret)? I'd like check if it can work. As a starting point I use 12V torodial transformer (1:20), FR4 laminate as single stator, spacer and 50micron electret foil.
If you are using an electret you don't need any bias voltage.
With a single ended ESL you would connect one end of the transformer secondary winding directly to the stator and the other end directly to the electret diaphragm.
But we all know a big bias is needed to linearize ordinary ESLs. Not for an electret? Are we talking about electrets with stators on both sides of the film (unlike mics)?
Have there been advances in materials or charging methods for better electrets in recent years?
B.
I've tried ClingZ with 230V->12V transformer, single ended mode, no sound, dead. Could't found any electret foil. Mic manufacturer told me there were some coatings, usually they are pretty thick and he use standard metalized foil.
Why mic and some headphone (Warwick Audio) manufacturers don't use double stator configuration like speakers?
Hi,
The electrical field spanning between the stators acts upon a charge stored on the membrane surface.
Due to leakage one needs a bias supply to ´recharge´ the diaphragm.
The more charge -i.e. the higher the bias voltage- there is on the membrane the higher the SPL ... its not used for ´linearization ... the symmetrical ESL is highly linear wether there´s just low charge or high charge on the membrane.
Electret films are just stored charge, ´frozen´ into the membrane material .... which is why we don´t need a bias supply with those films.
I remember that BASF (yes, the Aspirin guys) had researched for a high-charge film material equivalent to a ~2000V of Bias voltage some years ago.
Seemed they ceased that research though.
The typical PTFE based Electrets only are useable for panels with very small airgaps like Headphones or Mics -proabbabely equivalent to 200-300V of Bias voltage.
jauu
Calvin
I think the key to understanding is not to think in voltage (Bias) terms but in Charge terms.
The electrical field spanning between the stators acts upon a charge stored on the membrane surface.
Due to leakage one needs a bias supply to ´recharge´ the diaphragm.
The more charge -i.e. the higher the bias voltage- there is on the membrane the higher the SPL ... its not used for ´linearization ... the symmetrical ESL is highly linear wether there´s just low charge or high charge on the membrane.
Electret films are just stored charge, ´frozen´ into the membrane material .... which is why we don´t need a bias supply with those films.
I remember that BASF (yes, the Aspirin guys) had researched for a high-charge film material equivalent to a ~2000V of Bias voltage some years ago.
Seemed they ceased that research though.
The typical PTFE based Electrets only are useable for panels with very small airgaps like Headphones or Mics -proabbabely equivalent to 200-300V of Bias voltage.
jauu
Calvin
Electrtet mics still use bias just 10x less. Maybe I haven't learned how to apply graphite coating.
Hi,
that´s not right.
The bias voltage that You apply to a typical electret capsule is only to power the integrated electronics, mostly a JFET Transistor.
The bare electret mic capsule doesn´t require a Bias voltage.
Regarding Your Q from #7: The answer is ease of production and with the tiny excursion of a mic-membrane even a single stator system is low enough in THD.
Also, building asymmetrical yields at least one obstacle in front of the membrane less.
jauu
Calvin
that´s not right.
The bias voltage that You apply to a typical electret capsule is only to power the integrated electronics, mostly a JFET Transistor.
The bare electret mic capsule doesn´t require a Bias voltage.
Regarding Your Q from #7: The answer is ease of production and with the tiny excursion of a mic-membrane even a single stator system is low enough in THD.
Also, building asymmetrical yields at least one obstacle in front of the membrane less.
jauu
Calvin
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+1
I'd like to hear some creative thinking on this challenging issue. Time to charge? Resistance of a small test piece of film? Loudness of panel? Op-amp circuits?
B.
Why graphite if I may ask ? Carbon can get you low res coating if you want. I got some carbon black tattoo ink it's filled with it
But graphite alone won't make an electret 🙁 so I'm not sure why the graphite question is there 🙂
Hi,
in a symmetrical ESL the electrical field developing between the stators exhibits force on any charged object (and if the field is homogenous, the force is the same at any point of the space formed between the two electrodes).
Wether the charge is a 'built-in-feature' of the material used, or applied by a external voltage source to the disphragm coating doesn't matter.
jauu
Calvin
in a symmetrical ESL the electrical field developing between the stators exhibits force on any charged object (and if the field is homogenous, the force is the same at any point of the space formed between the two electrodes).
Wether the charge is a 'built-in-feature' of the material used, or applied by a external voltage source to the disphragm coating doesn't matter.
jauu
Calvin
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