G.R.A.S. RA0015 1'' Electrostatic Actuator

Electrostatic actuators are used to simulate the pressure response of condenser microphones. This is done by exerting an oscillating electrostatic force in front of 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 overcome 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 .

With the G.R.A.S. Actuator Supply Type 14AA it complies with IEC 61094 -6 “Measurement microphones - Part 6: Electrostatic actuators for determination of frequency responses.”

Typical Applications and Use

The RA0015 is used for electrostatic actuator calibration.

With the AC test signal superimposed on the 800V DC polarization voltage, the 12AA makes it possible to measure the pressure frequency response of the microphone under test.

Its wide frequency range makes it possible to determine the pressure frequency response of condenser microphones from 100 Hz to 200 kHz. For calibration of condenser microphones under 100 Hz, the low frequency calibrator 42AE is recommended.

A maximum test signal output of 300 V peak to peak allows testing at realistic sound pressure levels.


The RA0015 can be connected directly to the 14AA Actuator Supply. ½-inch microphones can be tested directly, adapters for testing of  1/4-inch and 1/8-inch microphones are included.

Quality and warranty 

The RA0015 is built to high-quality standards which enables G.R.A.S. to offer 3 years warranty against defective materials and workmanship. 


Before leaving the factory, all G.R.A.S products are tested. Should a power module become defective, it can be sent to G.R.A.S. for repair.

Frequency range (±1 dB) Hz TBD
Sound pressure level dB TBD
Power supply, external Vdc TBD
Input signal, max. Vrms TBD
AC output Vrms TBD
Actuator output Vdc TBD
Microphone polarization output Vdc TBD
AC output impedance TBD
Actuator output impedance TBD
Microphone polarization output impedance TBD
Gain dB TBD
ANSI standard S1.10
IEC standard 60318-1 & -2 (former 60318)
Temperature range, operation °C / °F TBD / TBD
Battery type TBD
CE/RoHS compliant/WEEE registered No/
Weight g / oz / TBD