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. 14AA Actuator Supply it complies with IEC 61094-6 “Measurement microphones - Part 6: Electrostatic actuators for determination of frequency responses.”
Typical Applications and use
The RA0014 is used for electrostatic actuator calibration.
With the AC test signal superimposed on the 800V DC polarization voltage, the G.R.A.S. 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.
The RA0014 can be connected directly to the G.R.A.S. 14AA Actuator Supply. 1/2" microphones can be tested directly, adapters for testing of 1/4" and 1/8" microphones are included.
Notice: for the 1/2" microphone 40AU you must use RA0014-S1.
ServiceBefore leaving the factory, all G.R.A.S products are tested. Should a power module become defective, it can be sent to GRAS for repair.
For calibration of condenser microphones under 100 Hz, the G.R.A.S. 42AE low frequency calibrator is recommended.
A maximum test signal output of 300 V peak to peak allows testing at realistic sound pressure levels.
Performance and warranty
The RA0014 is built to high-quality standards which enables G.R.A.S. to offer 3 years warranty against defective materials and workmanship.
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