Nearby residents complained about the sound generated when a company started to operate a centrifugal fan to extract smoke from a fire test rig. There were also complaints from an adjacent office. The fan is attached to a smoke scrubbing plant and a tall chimney / stack. All this equipment is outside the building. Although the fan and scrubber plant operated during daytime hours only, the company wanted to be able to run it at night in future.
First, the company contacted the equipment supplier who returned and fitted cladding around the fan. Noise complaints continued. The company then tried installing a tall wooden barrier around the fan and chimney / stack. Residents continued to complain about the noise, so this seems to have had little or no effect on the sound. The company wondered if the chimney / stack was acting like an organ pipe and amplifying the fan hum. At this point they contacted us and asked for our help.
Our noise survey showed that at the nearest houses, the fan noise from the smoke extractor, scrubber and chimney / stack exceeded the daytime background noise by 9 dBA. There was also a loud hum sound that was very noticeable and the main cause of the noise complaints. Allowing for the hum, a BS4142 assessment indicated that the corrected noise at the houses exceeded the daytime background by 15 dBA. So a solution needed to reduce noise by at least 15 dBA for daytime operation and substantially more to be able to run at night.
We selected a high performance, low resistance silencer to be installed in a carefully selected location within the chimney / stack. We also designed an engineering modification to reduce the hum sound. The noise reduction modifications were selected / designed to have no noticeable effect on fan extraction performance. Our solution was highly successful, making the fan inaudible at the houses and also at the adjacent office. In fact, the scrubber system could only be heard when standing close to the fan and chimney / stack. There have been no more noise nuisance complaints since our solution was installed.