it is used to test the sound levelcalibrate the sound level of environment, mechanic,vehicle,ship and other noise, etc. ... is used to calibrate the sound level meters, test the sound levelcalibrate the sound level of environment, mechanic,vehicle,ship and ... Model: ND9B Standard: GB/T15173, ANSIS1.40 CLASS2,IEC942Output sound level 94dB 114dBAccuracy: 0.3dBFrequency: 1000HzDesign for: 1", 1/2" ...