Client smartphone recordings before and after fan modification
A high amplitude hum was the cause of noise complaints, both off-site and in the site offices. Short smartphone audio recordings taken in the office and at 10m and 50m from the fan were emailed to us for analysis along with photos of the fan installation.
This analysis showed the hum to be tones at 180Hz and harmonics, matching the blade pass frequency (1800rpm, 6 blades). A silencer had already been fitted to the fan, but this was ineffective due to the low frequency.
We designed an aerodynamic insert to cut the hum at source, simultaneously reducing noise from the intake, the outlet and through the previously fitted enclosure. This was manufactured and installed by local contractor within a few hours downtime (resources required: a fitter for 1 day, materials $70).
This reduced the hum by 25dB, solving the problem with no effect on the fan performance.
