The battery-powered microphone powering 2221 was model for mobile applications designed and series is on the measurement microphones 25xx and the impedance transformer PRM902, 903 and PRA951 matched. The built-in, low-noise and Wideband precision amplifier with selectable gain (10 dB steps) ensures a precise signal processing. The polarization voltage for condenser microphones is adjusted to 0 (pre-polarized microphones) and?200 ? and tunable for all standard measuring microphones. Error-free operation is substantially guaranteed with the signal. The device automatically stores the last setting when turned off and is immediately ready for use again after the "new start". Low impedance and high-voltage signal outputs provide a correct signal transfer when connecting long lines. The high gain bandwidth product offers an optimum transient response for shock measurements with vibration sensors. For acoustic measurements frequency weightings are implemented A and C (according to IEC, ANSI).