Calibrations of 3 types of sound calibrators by means of 7 different microphone types at 7 standards laboratories have been compared. For a precision type of sound calibrator, the sound pressure levels determined by the laboratories span about 0.09 dB. The corresponding values for ordinary types of sound calibrators are much higher (0.23 dB). The lowest scattering ranges between laboratories were measured with ordinary microphones of type 4134 with a protection grid and type 4144 or 4145 with a coupler ring, but not with the laboratory standard microphones (types 4160, 4134M). At frequencies of 250 Hz and 1000 Hz, the sensitivity levels of nonstandard microphones (types 4176, MK 221) were found to span 0.2 dB.
A sound calibrator is a portable device which produces a known sinusoidal sound pressure of a specified level and frequency. Sound calibrators are used extensively in routine technical measurements for a quick verification or recalibration of microphones used in the field. There are however, in this kind of calibration, sources of errors which are suspected but not well investigated. They originate from the ambient conditions, mainly ambient temperature and pressure. The main errors probably come from the coupling between the calibrators and the microphones. The objective of the project is to investigate how accurately microphones are calibrated by well characterized sound calibrators. Measurements were made with one precision and two ordinary sound calibrators, using seven standard and non-standard microphones.
The range of differences in the measured sound pressure levels was 0.09 dB for the precision sound calibrator and 0.35 dB for the ordinary sound calibrators. It was concluded that some of the discrepancies in the results were due to the coupling between the calibrators and the microphones.
Funding SchemeCSC - Cost-sharing contracts
TW11 0LW Teddington