Hi Kingkorg, its time to present some test results, hope it can help you catching my opinion.
Test Bench: Use a Primo EM21 with adjustable polarization voltage and a capacitively coupled jfet stage, apply a constant tone signal to the capsule, measure the output signal dependant on the externally provided polarization voltage (-30V..+30V).
Test expectations: If your opinion is true, no output signal change should occur whatever pol. voltage is applied. If my opinion is true, there should be a linear relationship between ouput signal and pol. voltage.
Find attached a picture of the test bench, the test circuit and a diagram with the results. For signal measurement and generation REW was used, only the fundamental was measured. SNR was >50 dB, completely sufficient for this little test.
Conclusions:
1. At least for the Primo EM2X capsules my opinion is proven, quod erat demonstrandum.
2. It is unlikely that other electret capsules behave different.
3. Externally applied polarization voltage is always in series with the "internal" pol. voltage (= charge/capacitance).
Best regards Ulli
Test Bench: Use a Primo EM21 with adjustable polarization voltage and a capacitively coupled jfet stage, apply a constant tone signal to the capsule, measure the output signal dependant on the externally provided polarization voltage (-30V..+30V).
Test expectations: If your opinion is true, no output signal change should occur whatever pol. voltage is applied. If my opinion is true, there should be a linear relationship between ouput signal and pol. voltage.
Find attached a picture of the test bench, the test circuit and a diagram with the results. For signal measurement and generation REW was used, only the fundamental was measured. SNR was >50 dB, completely sufficient for this little test.
Conclusions:
1. At least for the Primo EM2X capsules my opinion is proven, quod erat demonstrandum.
2. It is unlikely that other electret capsules behave different.
3. Externally applied polarization voltage is always in series with the "internal" pol. voltage (= charge/capacitance).
Best regards Ulli