California Code of Regulations
Title 13 - Motor Vehicles
Division 2 - Department of the California Highway Patrol
Chapter 4 - Special Equipment
Article 10 - Vehicle Sound Measurement
Section 1043 - Instrumentation Requirements

(a) Sound Level Meter. Sound level meters used for measurements of vehicles in use shall meet the requirements for Types 1, 2, S 1 A, or S 2 A in the American National Standard Specification for Sound Level Meters S 1.4-1971 or 1983, the requirements for Type 1, 2, 1A, or 2A in the International Electrotechnical Commission Publication 651, "Sound Level Meters," or the requirements in the International Electrotechnical Commission Publication 179, "Precision Sound Level Meters." Sound level meters used for new-vehicle measurements shall meet the Type 1 or S 1 A requirements of the American National Standard Specification for Sound Level Meters, S 1.4-1971 or 1983. As an alternative to making direct measurements using a sound level meter, a microphone or sound level meter may be used with a magnetic tape recorder and/or a graphic level recorder or other indicating instrument provided the system meets the requirements of SAE J184a, July 1978.

(b) Sound Level Calibrator--An acoustic sound level calibrator of the microphone coupler type shall be used to calibrate the entire sound level measurement system. The calibrator shall be calibrated at least annually.

(c) Tachometer--An engine speed tachometer with an accuracy of ± 2% of the meter reading shall be used to determine when maximum rpm is attained in new-vehicle tests.

(d) Anemometer--An anemometer with an accuracy of ± 10% of the reading for wind speeds of 19.3 to 33.2 km/h (12 to 20 mph) shall be used to measure the wind speed at the measurement site at times when there is wind.

(e) Windscreen--A properly installed microphone windscreen recommended by the manufacturer of the sound level meter may be used.