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Measurement microphones and preamplifiers require special voltages for supply and polarisation.
Acoustic measurements also often require special networks such as A-weighting or high-pass filtering; amplification or attenuation of the signal may also be necessary. These facilities are provided by the G.R.A.S. Power Modules.
Standard externally-polarised condenser microphones require a stable polarisation voltage of 200 V DC for proper operation. This may be turned off in the power modules for use with prepolarised microphones.
Low frequency acoustic signals generated, for example, by wind flow may overload the input section of the analyzer etc. This can be avoided by removing frequencies below 20Hz with the high pass filter in the power module.
The A-network is the most frequently used frequency weighting method in acoustics. This approximates the sensitivity of the human ear, and the result is a measurement of the noise as perceived by the human ear.
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Updated 21. december 2006
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