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30 years ago, Bruel & Kjaer launched the world’s first prepolarized condenser measurement microphones. These microphones combined the high‐performance construction of the normal measurement microphones with a polarized electret layer placed on the back electrode. Since then, prepolarized microphones have gained an increasing share of the measurement microphone market. Prepolarized microphones are flexible in use because they do not need the external polarization, in particular, they can be used with constant current supply preamplifiers (Deltatron, ICP) that are widely used for many purposes in the industry. In order to be used for measurement purposes, the microphones and thereby the electret polarization must be highly stable and reliable. That is indeed achievable, and that is the main emphasis of this paper. A short historical overview of the development of the Bruel & Kjaer prepolarized microphone types is given. The properties of prepolarized microphones are discussed and compared to those of externally polarized microphones. These will include stability with respect to time, temperature, humidity and the chemical environment, as well as distortion and dynamic range. |
