The signal conditioning requirement for a measurement microphone depends on the type of microphone being used. Externally-polarised condenser microphones require a high-impedance preamplifier to buffer the capsule output impedance down to a level that can drive cable capacitance without frequency response rolloff. IEPE condenser microphones integrate this impedance conversion electronics directly into the capsule housing, so the preamplifier function is inside the microphone body.
Both approaches can provide equivalent acoustic measurement performance, but they have different implications for compatibility, cable length, signal conditioning chain design, and overall system noise floor. Understanding these differences is important for specifying a complete measurement chain.
For accredited testing laboratory work and for applications where uncertainty documentation must meet the most stringent requirements, externally-polarised microphones with separate preamplifiers are the standard choice — IEC 61094 specifies performance in this configuration. For field survey work, industrial noise monitoring, and multi-channel NVH applications where convenience and system simplicity are priorities, IEPE microphones are practical and appropriate.
For externally-polarised condenser microphones, the accredited calibration is performed with the capsule connected to a specified preamplifier type. If the preamplifier is replaced in service, the sensitivity of the new combination must be verified. For IEPE microphones, the calibration is performed with the complete integrated assembly — capsule plus internal electronics — at a defined IEPE supply current. Verify that your DAQ system or signal conditioner provides the specified supply current: under-current operation shifts the bias point of the internal FET and changes the sensitivity.