Section 210.25 - Measurement criteria and proceduresThe parameters and procedures for the measurement of the noise emission levels are prescribed in the Standards.
(a) Quantities measured are defined in § 201.21 of the Standards.(b) Requirements for measurement instrumentation are prescribed in § 201.22 of the Standards. In addition, the following calibration procedures shall be used:(1)(i) The sound level measurement system including the microphone shall be calibrated and appropriately adjusted at one or more nominal frequencies in the range from 250 through 1000 Hz at the beginning of each series of measurements, at intervals not exceeding 1 (one) hour during continual use, and immediately following a measurement indicating a violation.(ii) The sound level measurement system shall be checked not less than once each year by its manufacturer, a representative of its manufacturer, or a person of equivalent special competence to verify that its accuracy meets the manufacturer's design criteria.(2) An acoustical calibrator of the microphone coupler type designed for the sound level measurement system in use shall be used to calibrate the sound level measurement system in accordance with paragraph (b)(1)(i) of this section. The calibration must meet or exceed the accuracy requirements specified in section 5.4.1 of the American National Standard Institute Standards, "Method for Measurement of Sound Pressure Levels," (ANSI S1.13-1971) for field method measurements.(c) Acoustical environment, weather conditions, and background noise requirements are prescribed in § 201.23 of the Standards. In addition, a measurement tolerance of 2 dB(A) for a given measurement will be allowed to take into account the effects of the factors listed below and the interpretations of these effects by enforcement personnel:(1) The common practice of reporting field sound level measurements to the nearest whole decibel;(2) Variations resulting from commercial instrument tolerances;(3) Variations resulting from the topography of the noise measurement site;(4) Variations resulting from atmospheric conditions such as wind, ambient temperature, and atmospheric pressure; and(5) Variations resulting from reflected sound from small objects allowed within the test site.