ABSTRACT
If we consider different types of noise emitted from factories, it may be seen that they are numerous. For example, fans may emit a broad band noise but more usually, and more commonly a problem, the noise may be a drone or a whine. Natural draught process furnaces are characterised by the roar at low to mid frequencies. In the case of noise emitted from pipes carrying steam, valves and vents tend to produce a middle to high frequency noise. The wide range of spectra from different sources is illustrated by Fig 1.
