Audiometric earphone calibration using the IEC 303 reference coupler: a cautionary note

The diaphragm of a condenser microphone is exceedingly fragile and, in normal use, is covered by a protective grid. However, when the microphone is incorporated into the IEC 303 reference coupler for the calibration of audiometers or audiometric earphones, the Standard demands that the diaphragm be left exposed. Nevertheless, in order to avoid inadvertent mechanical damage, some users leave a protective grid on the microphone. The effects of two particular grids have been investigated and the magnitude of the resulting errors is indicated.