Scope of the new standard

The fundamental requirements for IEC 61672 have not changed. However, practical experience, advances in technology, and current regulations have been taken into account when developing the new standard. The type 0 accuracy category of IEC 651 is almost nonexistent because it is too specialized, while type 3 has been made redundant by the low cost of modern circuitry. Thus the new standard describes only two performance classes corresponding to much improved types 1 and 2 of the previous standard. Important new annexes give detailed procedures for conformance tests and for periodic checks. It is now recognized that the uncertainties of measurement are not negligible and realistic tolerance limits have been specified to include them. Another significant advance for the measurement of impulsive sounds is that a minimum linear operating range of 60 dB is specified for all instruments. Existing and draft European Community Directives call for peak C-weighted measurements and appropriate specifications are given. Requirements for immunity to electrostatic discharges and radio-frequency fields and for radio-frequency emission have been included to cover regulations in Europe and elsewhere. The environmental reference conditions have been changed to 23 °C and 50% relative humidity for consistency with the IEC microphone standards.