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Electrostatic actuators are used to simulate the pressure response of condenser microphones. This is done by exerting an oscillating electrostatic force on the diaphragm of the microphone and measuring the consequent response of the microphone. These electrostatic oscillations must not reverse polarity if frequency doubling is to be avoided. This is over come by applying an electrostatic force comprising a sufficiently high polarisation voltage (800 V) upon which a smaller alternating voltage is superimposed.
By applying such an oscillating electrostatic force which sweeps over a range of frequencies from 100 Hz to 200 kHz, the pressure response of the microphone can be tested. To this must be added corrections to determine the microphone’s response in a free sound field for various angles of incidence as well its response in a diffuse sound field for random angles of incidence.
Care should be taken when calibrating below 200 Hz because of the influence of pressure equalisation in the rear volume of the micropone .
On the other hand, since the frequency response of the microphone is not flat, a small error could be introduced.
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