Control of low frequency noise from an environmental test facility

Environmental test chambers are used in the automotive industry to verify the resilience of vehicles. In just a few hours it is possible to take a car from mid-winter in the artic, via a high mountain range, to mid-summer in a desert. Powerful ventilation systems are used to change the temperature, pressure and humidity of the air in the chamber, and the variable speed blowers are a major source of low frequency noise, which can cause significant disturbance at neighbouring properties if there are gaps in silencer performance. This paper details a study to assess the attenuation requirements for a system to meet a standard criterion for low frequency far-field noise levels, and to select a reactive silencer system to achieve that specification under all circumstances. The system used standard silencer components where possible, but needed to take account of long pipe runs through the facility, with tailpipe resonances being a particular issue, and was further constrained by space and loading limits for the building. Design layouts were verified using the Actran FE code, taking account of interactions with existing silencers and transfer functions to the far-field, in order to have very high confidence of a successful outcome.