Acoustic Calibrators

The pistonphone produces a nominal sound pressure level of 124 dB at 250 Hz with the aid of two small pistons driven by a motor. To attain a high calibration accuracy with the pistonphone, correction due to the static barometric pressure has to be subtracted or added to the value given on the individual calibration chart for the pistonphone. The correction can be read directly off a barometer supplied with the pistonphone. The acoustical calibrator operates with a miniature loudspeaker and produces a sound pressure level of 94 dB ≈ 1 Pa at 1 kHz using an active feedback loop based on a built-in precision microphone.