Compressor Inlet Ducts Noise Reduction
Guidance on the size and velocity of air flow in ducts is given in the chapter on Compressor Installation. A general rule to follow is: avoid coincidence of mechanical noise and acoustic frequencies, otherwise resonance of the pipe system can amplify rather than attenuate the noise.
It sometimes happens that a common intake system may supply more than one compressor. Such an arrangement should be avoided, as there is always the danger of amplified noise when pulsations of two compressors are in phase.
One should always attempt to design the pipework system so as to avoid undesirable frequencies. This is difficult, and it may turn out that when the installation is finished, it is unexpectedly noisy. One may then be faced with having to apply remedial treatment; this can be done by adding acoustic lagging to the outside of the pipes. Lagging should be made of a porous material such as glass fibre attached to the pipe, with an outer layer of dense cladding such as aluminium, steel or leaded plastics.