Uncalibrated Calibrator

Recorded and processed sounds from a broken PISTONPHONE
Nominal: 250Hz-124dB
Brüel & Kjaer
TYPE 4220
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“The calibration frequency, nominally 250Hz, is 251.2Hz ±0.1% as defined by ISO 266. The sound level produced by the pistonphone is nominally 124 ± 0.2 dB re 20 uPa at the reference conditions. Each pistonphone, however, is individually calibrated with an uncertainty of less than 0.09 dB and delivered with a calibration chart. When loaded with a microphone of one of the specified types, the uncertainty is less than 0.12 dB. The high sound level from the pistonphone allows correct calibration to be made in the field, even in very noisy surroundings.”
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en.wikipedia.org/wiki/Measurement_microphone_calibration