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NTP - Measurement procedure for non - impulsive noise <br />The following test procedure has been approved by the Executive Director of the MPCA for the measurement <br />of non - impulsive noise. <br />Instrumentation: <br />• a sound level meter and a microphone conforming to type 0, 1, 2, or S specifications under ANSI <br />S1.4-1983 <br />• a calibrator of known frequency and level <br />• a small screwdriver for sensitivity adjustment <br />• microphone windscreen <br />• noise survey form <br />• tripod (optional) <br />Meteorology: <br />• Measurements must not be made in sustained winds or in precipitation which results in a difference of <br />less than 10 decibels between the background noise level and the noise source being measured <br />• Temperature and/or humidity conditions must be within the equipment manufacturer's specifications <br />Location: <br />• Measurements must be made at or within the applicable NAC at the point of human activity nearest <br />the noise source. <br />• Measurements must be made outdoors. <br />• Measurements must be made at least three feet off the ground and away from natural or manmade <br />structures which would prevent an accurate measurement (barriers, houses). <br />Survey Procedure: <br />• Monitoring must be conducted for at least a one hour time period. <br />• Calibration must be performed before and after the monitoring period. Adjustments should be made if <br />necessary. <br />• Sound measuring devices must use the "A" weighting and FAST response characteristics. <br />• Background noise must be at least 10 decibels lower than the noise source being measured. <br />• A survey form must be completed containing date, time, location, noise source, wind speed/direction, <br />temperature, humidity, equipment information (make, model, serial number), site sketch with the <br />location of the noise source and measurement location (including appropriate distances), data and <br />calibration information. A sample survey form is on the following pages. <br />• Follow your manufacturer instructions to obtain the L10 and L50 results. <br />A Guide to Noise Control in <br />Minnesota • October 2008 Minnesota Pollution Control Agency <br />9 <br />