The National Standard for Sound Pressure in Air: Past, Present and Future

The CSIR-NML has been performing primary calibrations of laboratory standard 1” condenser microphones for the past decade. The semiautomated system was developed by Mr Owen Cramer during 1990. Reciprocity calibration of microphones is a very labor intensive process, relying heavily on the skills of the metrologist. The NML saw the need to expand and improve their capabilities in this area. This requirement lead to the development of a fully automated system. Future developments of the NML’s capability in this area include expanding the new system to facilitate the calibration of 1⁄2” microphones. A pressure chamber is also planned that will enable the NML to perform reciprocity calibrations at various ambient pressure levels.