Electrostatic Actuators

The calibration of microphones using an electrostatic actuator is a widely applied laboratory method for determination of frequency response characteristics of measurement microphones. The actuator produces an electrostatic force which simulates a sound pressure acting on the microphone diaphragm. In comparison with sound based methods, the actuator method has a great advantage -it provides a simpler means of producing a well-defined calibration pressure over a wide frequency range without the special facilities of an acoustics laboratory.

However, the actuator method cannot be used for determination of  microphone sensitivity, as its absolute accuracy is not sufficiently high. Therefore, an actuator frequency response calibration is, in most cases, combined with an absolute sensitivity calibration at a reference frequency. This can be performed  using a pistonphone, a sound level calibrator or other means.