BK CAL73 sound calibrator. The CAL73 sound level calibrator is used to calibrate sound level meters and other sound measurement equipment. You can calibrate 1 inch diameter microphones directly and 1/2 inch microphones using 1/2 inch adaptor supplied with the calibrator. Conforms to IEC 60942 (2003) Class 2, ANSI SI.40-1984. 94dB and 114dB Sound calibrator at 1KHz. Accurate and simple to use. Fits 1 inch and ½ inch mic.