Free Field Calibration of Microphones

A time-selective technique for free-field reciprocity calibration of condenser microphones.

In normal practice, microphones are calibrated in a closed coupler where the sound pressure is uniformly distributed over the diaphragm. Alternatively, microphones can be placed in a free field, although in that case the distribution of sound pressure over the diaphragm will change as a result of the diffraction of the body of the microphone, and thus, its sensitivity will change. In the two ca...

Free-field calibration of the pressure sensitivity of microphones at frequencies up to 80 kHz

Calibration of the pressure sensitivity of microphones by a free-field method at frequencies up to 80 khz.

A free-field (FF) substitution method for calibrating the pressure sensitivity of microphones at frequencies up to 80 kHz is demonstrated with both grazing and normal-incidence geometries. The substitution-based method, as opposed to a simultaneous method, avoids problems associated with the nonuniformity of the sound field and, as applied here, uses a 1/4-in. air-condenser pressure microphone ...

Far-field ASR on inexpensive microphones

For a connected digits speech recognition task, we have compared the performance of two inexpensive electret microphones with that of a single high quality PZM microphone. Recognition error rates were measured both with and without compensation techniques, where both single-channel and two-channel approaches were used. In all cases the task was recognition at a significant distance (2–6 feet) f...

Energy Distribution of Free Space Field Ionization : Application to Field Strength Calibration

We discuss the method of field strength calibration from energy distributions measurements of free space field ionization. An alternative approach is considered and an improved calibration is suggested. The method of electric field strength calibration from considerations of energy distribution of field ionization in free space above a field ion emitter tip is due to Sakurai and Muller [1,2]. U...