This Nordtest engineering method specifies a method for measuring sound pressure levels at prescribed positions surrounding stationary noise sources at industrial plants and calculating the source strength based on the measured sound pressure levels.
The source strength is useful for calculations of sound pressure levels in areas adjacent to industrial plants and for comparing noise emission by equipment from various manufacturers.
For the purpose of this Nordtest method the source strength is a measure of the part of the source sound power which is relevant for the calculation of sound pressure levels at some distance from the source. Sound radiated vertically upwards is neglected in this measure, and the measurement positions are chosen in such a way as to ensure that the sound radiated at angles between 0º and 20º above the horizontal is measured. The sound radiated in this angle interval is most relevant when calculating sound pressure levels in the environment. In general the source strength includes information on source-directional characteristics in the horizontal plane. If a noise source only radiates into nearly horizontal directions and at the same time is nearly omnidirectional in the horizontal plane, the source strength is approximately equal to the sound power level of the source.
Measurements are made in situ outdoors, and the source strength is calculated in octave bands and overall A-weighted. Whenever possible source-directional characteristics are determined.
This Nordtest method is best suited for individual industrial noise sources. In Annex A reference is given to other methods suitable for measuring noise emission from entire industrial plants or from large parts of such plants. Reference is also given to relevant standards for sound power measurements.