Vehicle noise measurement
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DREPARED at the request of the Ministry of Transport, a revised edition of the British Standard BS 3425, Measurement of Noise Emitted by Motor Vehicles, has recently been published that will form the basis of future legislation on vehicle noise. This brings the standard into line with ISO recommendation R 362.
The standard test specified measures the noise a vehicle makes as it accelerates at full throttle past the microphone of a soundlevel meter. Acceleration takes place over a distance of 20 m. (66 ft.), after a rolling start at a speed calculated to produce the maximum noise during the test. It is claimed that this method provides the best combina
tion of simplicity, reproducibility of results and realistic test conditions.
The method of determining the correct approach speed is given for vehicles with either manually operated or automatic gearboxes, vehicles without gearboxes and agricultural machines, including tractors. The nature of the test site is also specified in the standard.
A suitable sound-level meter is specified in part 1 of BS 3539, Sound Level Meters for the Measurement of Noise Emitted by Motor Vehicles.
Copies of BS 3425 may be obtained from the BST Sales Branch, 2 Park Strdet, London WI, price 4s.