Externally polarized vs. prepolarized
All GRAS measurement microphones are of the condenser type. This requires a polarization voltage which can either be supplied from an external power supply or the microphone itself can be polarized by injecting a permanent electrical charge into a thin PTFE layer on the microphone backplate.
Externally polarized microphones
These microphones are used with standard preamplifiers such as the GRAS 26AK, which has a 7-pin LEMO connector. The preamplifier must be connected to a power module (for example GRAS 12AK) or an analyzer input which can supply the preamplifier with power as well as 200 V polarization. If you conduct very critical measurements we recommend an externally polarized microphone which is the most accurate and stable.
These microphones are used typically with CCP (Constant Current Power) preamplifiers such as GRAS 26CA. Prepolarized microphones must be connected to an input stage for CCP transducers or be powered by a CCP supply, for example the GRAS 12AL. CCP preamplifiers use standard coaxial cables, which will reduce your costs. The long term and high temperature stability of prepolarized microphones are not as good as for externally polarized microphones.