General Radio 1551C

The 1551C Sound-Level Meter provides a sound level range of 24 dB to 150 dB (re 20 ?N/m2) with ?1 dB accuracy. Completely self-contained and incorporates self-calibration circuitry so you know it's always accurate. Includes ceramic microphone that withstands both temperature and humidity extremes. General Purpose (Type 2) 24 to 150 dB Measurement Range Meets Common Standards: ANSI Standard SI.4-1971; IEC Publication 123, 1961 20Hz to 20kHz Amplifier Response Internal Calibration System