Pettersson H.

In a paper making line the number of external noise sources can be up to 80 pcs. On the other hand, external noise level limits in the pulp and paper industry have become increasingly strict over the last 20 years. This means that noise cancellation has become a major cost factor for the pulp and paper mills. Layout aspects and the design of noise abatement measures are therefore very important at the early stages of a project in order to save costs. It is very important to reduce the noise always as near its source as possible. The most important primary noise sources are process and machine room ventilation fans, turbo blowers and vacuum pumps. The exhaust air from these is always blown to the outside and the outlets require silencers both for low and high frequency attenuation. New absorptive (resistive) and reactive silencers recently developed in the acoustics laboratory and their special properties are described. At the planning stage the predicted noise levels in the mill surroundings at predetermined immission points are calculated. These predictions are based on the sound power levels and the coordinates of the noise sources according to ISO standard. The guarantee value for the supplier is the sound power or sound pressure level (at 1m distance) of each noise source. The verification procedure of the attenuation is also discussed, i.e. sound measurements after startup from the discharge according to ISO or DIN standards. The measurements may also be performed in the immission points.