As a result of complaints about noise from 2 large centrifugal fans on a factory roof and the involvement of the Environment Agency, the company had spent £50k on acoustic lagging that had zero effect on noise levels. The result was a prolonged wrangle with the authorities – who eventually suggested that they could try to get a 2nd opinion from us (this is a free analysis and diagnostic service).
They forwarded a video-clip. Analysis of the sound-track proved that the problem was a pair of tones at the blade-pass frequencies of the 2 fans plus 1st harmonics that were interfering and “beating” with each other. We designed the solution (Quiet Fan technology – retro-fit attenuation without silencers) that eliminated the tones as a feature within a few weeks and at a fraction of the cost of conventional alternatives. Only a single site visit was required – the rest of the work was carried out by email.