idle tranmission factor

The field- noise transfer factor ( FFT) is a microphone characteristic value. It is the microphone sensitivity determined under defined sound conditions. The "field" represents an anechoic chamber for the FLÜ measurement.

When determining the field-idle transmission factor, the microphones are unloaded, they are "idle" in terms of circuitry. So that there are no repercussions from the termination on the sensitivity or the frequency response, corresponding microphones are terminated with high impedance.

The sound pressure of a 1 kHz signal present at the diaphragm must be 1 Pa, whereby the distance between sound source and microphone is irrelevant. With these boundary conditions, the field-noise transfer factor (FLÜ) is determined. It is given in Decibel Voltage( dBV), is slightly dependent on the microphone type and lies approximately between -30 dBV to -60 dBV.